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Metformin, a first-line anti-diabetic medication, may provide benefits against the pathogenesis of Alzheimer’s disease (AD) or “type 3 diabetes”. However, studies have demonstrated that metformin treatment may increase the risk of AD and aggravate its pathology. At present, no comprehensive investigation of the cognitive impact of chronic metformin treatment has been conducted. To address this issue, we chronically treated transgenic 3xTg-AD and non-transgenic (NT) C57BL/6 mice with metformin (300 mg/kg/day) over 1 and 2 years, respectively. During this period, we assessed behaviours in a number of domains including motivation, attention, memory, visual discrimination, and cognitive flexibility using touchscreen operant chambers. We found that metformin enhanced attention, inhibitory control, and associative learning in younger NT mice (≤16 months). In contrast, the chronic treatment caused impairments in memory retention and discrimination learning at an older age. In AD mice, metformin treatment also caused an impairment in learning and memory as assessed by the object-location paired-associates learning task. Consistent with these results, increased levels of β-amyloid oligomers, plaques, phosphorylated tau, and GSK3β expression were observed in the hippocampus of metformin-treated AD mice. Interestingly, chronic metformin treatment induced an increase in AMPKα1-subunit expression, which has been previously reported in the human AD brain. Potential confounding factors were ruled out since the levels of motivation, locomotion, appetite, body weight, blood glucose, and serum vitamin B12 were not altered by metformin. Our study indicates that the repurposing of metformin should be carefully reconsidered when this drug is used for persons with AD.

Major depressive disorder (MDD) is a stress-related condition hypothesized to involve aberrant reinforcement learning (RL) with positive and negative stimuli. The present study investigated whether repeated early maternal separation (REMS) stress, a procedure widely recognized to cause depression-like behaviour, affects how subjects learn from positive and negative feedback. The REMS procedure was implemented by separating male and female rats from their dam for 6 h each day from post-natal day 5-19. Control rat offspring were left undisturbed during this period. Rats were tested as adults for behavioral flexibility and feedback sensitivity on a probabilistic reversal learning task. A computational approach based on RL theory was used to derive latent behavioral variables related to reward learning and flexibility. To assess underlying brain substrates, a seed-based functional MRI connectivity analysis was applied both before and after an additional adulthood stressor in control and REMS rats. Female but not male rats exposed to REMS stress showed increased response 'stickiness' (repeated responses regardless of reward outcome). Following repeated adulthood stress, reduced functional connectivity from the basolateral amygdala (BLA) to the dorsolateral striatum (DLS), cingulate cortex (Cg), and anterior insula (AI) cortex was observed in females. By contrast, control male rats exposed to the second stressor showed impaired learning from negative feedback (i.e., non-reward) and reduced functional connectivity from the BLA to the DLS and AI compared to maternally separated males. RL in male rats exposed to REMS was unaffected. The fMRI data further revealed that connectivity between the mOFC and other prefrontal cortical and subcortical structures was positively correlated with response 'stickiness'. These findings reveal differences in how females and males respond to early life adversity and subsequent stress. These effects may be mediated by functional divergence in resting-state connectivity between the basolateral amygdala and fronto-striatal brain regions.

Motivation and motivated behaviors are crucial to the survival of living organisms. In the clinical context, inappropriate elevations or decrements in motivation are associated with a variety of adverse indications, ranging from addiction to illicit drugs to a large number of neuropsychiatric and neurodegenerative conditions including schizophrenia, Alzheimer's disease and Huntington's disease where losses of motivation are fundamental to the expression of apathy, a particularly debilitating symptom that is commonly expressed early in pathogenesis. Despite the pervasiveness of pathology-associated changes in motivation, targeted treatment options remain extremely limited, highlighting a need for increased mechanistic understanding and the development of robust motivation assessment platforms with the potential for use in both the preclinical and clinical environments. This chapter provides an overview of the current conceptualization of motivation and the modifiers of this construct and details a range of behavioral assessment paradigms that can be used in preclinical assessment. The importance of enhancing the cross-species translational potential of such paradigms is emphasized, with the development of touchscreen-delivered assessments suggested as a valuable avenue to explore to enable progress in this important area.

Despite considerable advances in both in silico and in vitro approaches, in vivo studies that involve animal model systems remain necessary in many research disciplines. Neuroscience is one such area, with studies often requiring access to a complete nervous system capable of dynamically selecting between and then executing a full range of cognitive and behavioural outputs in response to a given stimulus or other manipulation. The involvement of animals in research studies is an issue of active public debate and concern and is therefore carefully regulated. Such regulations are based on the principles of the 3Rs of Replacement, Reduction and Refinement. In the sub-specialty of behavioural neuroscience, Full/Absolute Replacement remains a major challenge, as the complete ex vivo recapitulation of a system as complex and dynamic as the nervous system has yet to be achieved. However, a number of very positive developments have occurred in this area with respect to Relative Replacement and to both Refinement and Reduction. In this Review, we discuss the Refinement- and Reduction-related benefits yielded by the introduction of touchscreen-based behavioural assessment apparatus. We also discuss how data generated by a specific panel of behavioural tasks developed for this platform might substantially enhance monitoring of laboratory animal welfare and provide robust, quantitative comparisons of husbandry techniques to define and ensure maintenance of best practice.

Impaired behavioral activation and effort-related motivational dysfunctions like fatigue and anergia are debilitating treatment-resistant symptoms of depression. Depressed people show a bias towards the selection of low effort activities. To determine if the broadly used antidepressant fluoxetine can improve behavioral activation and reverse dopamine (DA) depletion-induced anergia, male CD1 mice were evaluated for vigorous escape behaviors in an aversive context (forced swim test, FST), and also with an exercise preference choice task [running wheel (RW)-T-maze choice task]. In the FST, fluoxetine increased active behaviors (swimming, climbing) while reducing passive ones (immobility). However, fluoxetine was not effective at reducing anergia induced by the DA-depleting agent tetrabenazine, further decreasing vigorous climbing and increasing immobility. In the T-maze, fluoxetine alone produced the same pattern of effects as tetrabenazine. Moreover, fluoxetine did not reverse tetrabenazine-induced suppression of RW time but it reduced sucrose intake duration. This pattern of effects produced by fluoxetine in DA-depleted mice was dissimilar from devaluing food reinforcement by pre-feeding or making the food bitter since in both cases sucrose intake time was reduced but animals compensated by increasing time in the RW. Thus, fluoxetine improved escape in an aversive context but decreased relative preference for active reinforcement. Moreover, fluoxetine did not reverse the anergic effects of DA depletion. These results have implications for the use of fluoxetine for treating motivational symptoms such as anergia in depressed patients.

Rationale Dopamine D2-like receptors (D2R) are important drug targets in schizophrenia and Parkinson’s disease, but D2R ligands also cause cognitive inflexibility such as poor reversal learning. The specific role of D2R in reversal learning remains unclear. Objectives We tested the hypotheses that D2R agonism impairs reversal learning by blocking negative feedback and that antagonism of D1-like receptors (D1R) impairs learning from positive feedback. Methods Male Lister Hooded rats were trained on a novel visual reversal learning task. Performance on “probe trials”, during which the correct or incorrect stimulus was presented with a third, probabilistically rewarded (50% of trials) and therefore intermediate stimulus, revealed individual learning curves for the processes of positive and negative feedback. The effects of D2R and D1R agonists and antagonists were evaluated. A separate cohort was tested on a spatial probabilistic reversal learning (PRL) task after D2R agonism. Computational reinforcement learning modelling was applied to choice data from the PRL task to evaluate the contribution of latent factors. Results D2R agonism with quinpirole dose-dependently impaired both visual reversal and PRL. Analysis of the probe trials on the visual task revealed a complete blockade of learning from negative feedback at the 0.25 mg/kg dose, while learning from positive feedback was intact. Estimated parameters from the model that best described the PRL choice data revealed a steep and selective decrease in learning rate from losses. D1R antagonism had a transient effect on the positive probe trials. Conclusions D2R stimulation impairs reversal learning by blocking the impact of negative feedback. Electronic supplementary material The online version of this article (10.1007/s00213-019-05296-y) contains supplementary material, which is available to authorized users.

Drug-associated contexts and discrete cues can trigger motivational states responsible for drug-seeking behavior and relapse. In preclinical research, drug-free conditioned hyperactivity has been used to investigate the expression of memories associated with psychostimulant drug effects. Addictive drugs can produce long-lasting sensitization to their psychomotor actions, a phenomenon known as behavioral sensitization. The neuroplasticity underlying behavioral sensitization appears to be involved in pathological drug pursuit and abuse. In the present study we evaluated drug-free, context-dependent hyperactivity in DBA/2 J mice previously treated with cocaine and we explored whether this conditioned effect was related to behavioral sensitization. Given the role of noradrenergic (NA) neurotransmission in memory retrieval, consolidation and reconsolidation processes, we also investigated whether conditioned hyperactivity in a drug-free state was mediated by NA receptors. Animals underwent a sensitization protocol with six cocaine injections (0, 5, 10 or 20 mg/kg) paired to a particular floor cue. Three days after this sensitization phase, all animals were exposed to the same familiar floor environment without drug treatment. A second test with an unfamiliar floor was conducted 24 h later. Conditioned hyperactivity was also explored after one or three cocaine pairings and was evaluated for its duration (with repeated familiar vs. unfamiliar floor tests). In a series of pharmacological experiments, we evaluated the effects propranolol (a non-selective antagonist of β1- and β2-receptors) and prazosin (α1-receptor antagonist) on conditioned hyperactivity. Cocaine treatment produced both robust sensitization and drug-free conditioned hyperactivity, an effect that lasted up to 17 days (with cocaine 20 mg/kg). A significant correlation between the magnitude of cocaine sensitization and the level of conditioned hyperactivity was found. Propranolol, but not prazosin, blocked context-dependent hyperlocomotion in a drug-free state. Our data, together with a vast body of literature, indicate that the NA system plays a key role in the retrieval and behavioral expression of drug-associated memories.

Physical activities can have intrinsic motivational or reinforcing properties. The choice to engage in voluntary physical activity is undertaken in relation to the selection of other alternatives, such as sedentary behaviors, drugs, or food intake. The mesolimbic dopamine (DA) system plays a critical role in behavioral activation or exertion of effort, and DA antagonism or depletion induces anergia in effort-based decision-making tasks. However, little is known about the neural mechanisms underlying the decisionmaking processes that establish preferences for sedentary vs. activity-based reinforcers. In the present work with male CD1 mice, we evaluated the effect of tetrabenazine (TBZ), a DA-depleting agent, on a three-choice T-maze task developed to assess preference between reinforcers with different behavioral activation requirements and sensory properties [i.e., a running wheel (RW) vs. sweet pellets or a neutral nonsocial odor]. We also studied the effects of TBZ on the forced swim test (FST), which measures climbing and swimming in a stressful setting, and on anxiety tests [dark-light (DL) box and elevated plus maze (EPM)]. In the three-choice task, TBZ reduced time running in the wheel but increased time spent consuming sucrose, thus indicating reduced activation but relatively intact sucrose reinforcement. The effect of TBZ was not mimicked by motivational manipulations that change the value of the reinforcers, such as making the RW aversive or harder to move, food-restricting the animals, inducing a binge-like eating pattern, or introducing social odors. In the FST, TBZ decreased time climbing (most active behavior) and increased immobility but did not affect anxiety in the DL or EPM. These results indicate that the three-choice T-maze task could be useful for assessing DA modulation of preferences for exercise based on activation and effort requirements, differentiating those effects from changes in preference produced by altering physical requirements, food restriction state, and stress during testing.

Perseveration and apathy are two of the most common behavioural and psychological symptoms of dementia (BPSDs) in amyotrophic lateral sclerosis–frontotemporal dementia (ALS–FTD). Availability of a validated and behaviourally characterised animal model is crucial for translational research into BPSD in the FTD context. We behaviourally evaluated the male TDP-43Q331K mouse, an ALS–FTD model with a human-equivalent mutation (TDP-43Q331K) knocked into the endogenous Tardbp gene. We utilised a panel of behavioural tasks delivered using the rodent touchscreen apparatus, including progressive ratio (PR), extinction and visual discrimination/reversal learning (VDR) assays to examine motivation, response inhibition and cognitive flexibility, respectively. Relative to WT littermates, TDP-43Q331K mice exhibited increased responding under a PR schedule. While elevated PR responding is typically an indication of increased motivation for reward, a trial-by-trial response rate analysis revealed that TDP-43Q331K mice exhibited decreased maximal response rate and slower response decay rate, suggestive of reduced motivation and a perseverative behavioural phenotype, respectively. In the extinction assay, TDP-43Q331K mice displayed increased omissions during the early phase of each session, consistent with a deficit in activational motivation. Finally, the VDR task revealed cognitive inflexibility, manifesting as stimulus-bound perseveration. Together, our data indicate that male TDP-43Q331K mice exhibit a perseverative phenotype with some evidence of apathy-like behaviour, similar to BPSDs observed in human ALS–FTD patients. The TDP-43Q331K knock-in mouse therefore has features that recommend it as a useful platform to facilitate translational research into behavioural symptoms in the context of ALS–FTD.

Caffeine is the most consumed psychoactive stimulant and the main active ingredient of energy drinks. Epidemiology studies have shown a positive correlation between the consumption of energy drinks and that of ethanol. The popular belief is that caffeine antagonizes the intoxicating effects of alcohol. Both drugs act on the adenosine system but have opposite effects. Caffeine is a methylxanthine that acts as a nonselective adenosine receptor antagonist, binding to A1 and A2A receptor subtypes. In contrast, ethanol increases extracellular adenosinergic tone. The purpose of this study was to examine the impact of a broad range of doses of caffeine and of selective adenosine A1 and A2A receptor antagonists on voluntary ethanol intake under different ethanol access conditions. C57BL/6 J male mice had access to ethanol (10% w/v) under different conditions: restricted (2 h in the dark), unrestricted (24 h access), or after 4 days of alcohol removal following several periods of unrestricted access. Mice reduced ethanol intake in the restricted access condition after receiving caffeine (20.0 mg/kg), or theophylline (20.0 mg/kg), another methylxanthine. Selective A1 and A2A adenosine receptor antagonists, or their combination, did not have any effect. However, under unrestricted access conditions caffeine and the adenosine A2A receptor antagonist increased ethanol intake. After splitting animals into high, moderate and low ethanol consumers, caffeine (2.5-20.0 mg/kg) significantly increased ethanol consumption in moderate consumers with no effect on low or high consumers. In addition, after reintroducing ethanol access, caffeine (5.0 mg/kg) decreased ethanol consumption among moderate consumers. Thus, caffeine produced different effects on ethanol intake depending on the access condition and the baseline consumption of ethanol.

Motivated behavior is characterized by activation and high work output. Nucleus accumbens (Nacb) modulates behavioral activation and effort-based decision-making. Caffeine is widely consumed because of its energizing properties. This methylxanthine is a non-selective adenosine A1/A2A receptor antagonist. Adenosine receptors are highly concentrated in Nacb. Adenosine agonists injected into Nacb, shift preference towards low effort alternatives. The present studies characterized effort-related effects of caffeine in a concurrent progressive ratio (PROG)/free reinforcer choice procedure that requires high levels of work output, and generates great variability among different animals. Male Sprague-Dawley rats received an acute dose of caffeine (2.5–20.0 mg/kg, IP) and 30 min later were tested in operant boxes. One group was food-restricted and had to lever pressed for high carbohydrate pellets, another group was non-food-restricted and lever pressed for a high sucrose solution. Caffeine (2.5 and 5.0 mg/kg) increased lever pressing in food-restricted animals that were already high responders. However, in non-restricted animals, caffeine (5.0 and 10.0 mg/kg) increased work output only among low responders. In fact, caffeine (10.0 and 20.0 mg/kg) in non-restricted animals, reduced lever pressing among high responders in the PROG task, and also in a different group of animals lever pressing in an easy task (fixed ratio 7 schedule) that uniformly generates high levels of responding. Caffeine did not modify sucrose preference or consumption under free access conditions. Thus, when animals do not have a homeostatic need, caffeine can help those not very intrinsically motivated to work harder for a more palatable reward. However, caffeine can disrupt performance of animals intrinsically motivated to work hard for a better reward.

The impact of caffeine on ethanol consumption and abuse has become a topic of great interest due to the rise in popularity of energy drinks. Energy drinks have many different components, although the main active ingredient is caffeine. These drinks are frequently taken in combination with alcohol, with the belief that caffeine can offset some of the intoxicating effects of ethanol. However, scientific research has not universally supported the idea that caffeine can reduce the effects of ethanol in humans or in rodents, and the mechanisms mediating caffeine–ethanol interactions are not well understood. Caffeine acts as a nonselective adenosine A1 and A2A receptor antagonist, while ethanol has been demonstrated to increase the basal adenosinergic tone via multiple mechanisms. In this chapter, we discuss animal studies that have assessed the impact of ethanol plus caffeine combinations on social processes related to motivation, emotion, and cognition.

© 2018, The Author(s). This review is concerned with methods for assessing the processing of unrewarded responses in experimental animals and the mechanisms underlying performance of these tasks. A number of clinical populations, including Parkinson’s disease, depression, compulsive disorders, and schizophrenia demonstrate either abnormal processing or learning from non-rewarded responses in laboratory-based reinforcement learning tasks. These effects are hypothesized to result from disturbances in modulatory neurotransmitter systems, including dopamine and serotonin. Parallel work in experimental animals has revealed consistent behavioral patterns associated with non-reward and, consistent with the human literature, modulatory roles for specific neurotransmitters. Classical tests involving an important reward omission component include appetitive extinction, ratio schedules of responding, reversal learning, and delay and probability discounting procedures. In addition, innovative behavioral tests have recently been developed leverage probabilistic feedback to specifically assay accommodation of, and learning from, non-rewarded responses. These procedures will be described and reviewed with discussion of the behavioral and neural determinants of performance. A final section focusses specifically on the benefits of trial-by-trial analysis of responding during such tasks, and the implications of such analyses for the translation of findings to clinical studies.

Rationale: Mesolimbic dopamine (DA) regulates behavioral activation and effort-related decision-making in motivated behaviors. Mesolimbic DA D2 receptors are co-localized with adenosine A2A receptors, and they interact in an antagonistic manner. Objectives: A T-maze task was developed to assess dopaminergic involvement in preference between a reinforcer that involves vigorous voluntary activity (running wheel) and a reinforcer that requires minimal behavioral activation (sucrose pellets). Haloperidol (D2 antagonist) was administered to adenosine A2A receptor knockout (A2AKO) and wild-type (WT) littermate controls to assess the involvement of these two receptors in the selection of running wheel activity versus sucrose consumption. Results: Under control conditions, mice spent more time running and less time eating. In WT mice, haloperidol reduced time running but actually increased time-consuming sucrose. However, A2AKO mice did not show the haloperidol-induced shift from running wheel activity to sucrose intake. Prefeeding reduced sucrose consumption in the T-maze in both strains, indicating that this paradigm is sensitive to motivational devaluation. Haloperidol increased c-Fos immunoreactivity in anterior cingulate cortex (ACg) and nucleus accumbens (Acb) core of WT but not KO mice. Conclusions: These results indicate that after DA antagonism, the preference for vigorous physical activity is reduced, while palatable food selection increases. Adenosine A2A receptor deletion provides resistance to these effects of D2 receptor antagonism. These two receptors in Acb core and ACg seem to be involved in the regulation of the intrinsic reinforcing characteristics of voluntary exercise but not in the regulation of the primary reinforcing characteristics of palatable sedentary reinforcers.

Caffeine is a methylxanthine consumed in different context s to potentiate alertness and reduce fatigue. However, caffeine can induce anxiety at hig h doses. Caffeine is also a minor psychostimulant that seems to act as an appetite supp ressant, but there are also reports indicating that it could stimulate appetite. D opamine also is involved in food motivation and in behavioral activation. In the present ser ies of experiments, we evaluated the effects of acute administration of caffeine on food cons umption under different access conditions. CD1 male adult mice had access to highly palatab le food (50% sucrose) in a restricted but habitual context, under continuous or in termittent access as well as under anxiogenic, or effortful conditions. Caffeine (2.5– 20.0 mg/kg) increased intake at the highest dose under familiar continuous and intermitten t access. However, this high dose reduced food intake in the dark-light paradigm. In cont rast, a dopamine-depleting agent, tetrabenazine (TBZ; 1.0–8.0 mg/kg) did not affect fo od intake in any of those experimental conditions. In the T-maze-barrier task that e valuates seeking and taking of food under effortful conditions, caffeine (10.0 mg/kg) d ecreased latency to reach the food, but did not affect selection of the high-food density a rm that required more effort, or the total amount of food consumed. In contrast, TBZ (4.0 mg /kg) reduced selection of the high food density arm with the barrier, thus affecting amount of food consumed. Interestingly, a small dose of caffeine (5.0 mg/kg) was able to reverse the anergia-inducing effects produced by TBZ in the T-maze. These results suggest that caffeine can potentiate or suppress food consumption depending on the context. More over, caffeine did not change appetite, and did not impair orientation toward food under effortful conditions, but it rather helped to achieve the goal by improving speed an d by reversing performance to normal levels when fatigue was induced by dopamine deplet ion.

Major depressive disorder is one of the most common and debilitating psychiatric disorders. Some of the motivational symptoms of depression, such anergia (lack of self-reported energy) and fatigue are relatively resistant to traditional treatments such as serotonin uptake inhibitors. Thus, new pharmacological targets are being investigated. Epidemiological data suggest that caffeine consumption can have an impact on aspects of depressive symptomatology. Caffeine is a non-selective adenosine antagonist for A 1 /A 2A receptors, and has been demonstrated to modulate behavior in classical animal models of depression. Moreover, selective adenosine receptor antagonists are being assessed for their antidepressant effects in animal studies. This review focuses on how caffeine and selective adenosine antagonists can improve different aspects of depression in humans, as well as in animal models. The effects on motivational symptoms of depression such as anergia, fatigue, and psychomotor slowing receive particular attention. Thus, the ability of adenosine receptor antagonists to reverse the anergia induced by dopamine antagonism or depletion is of special interest. In conclusion, although further studies are needed, it appears that caffeine and selective adenosine receptor antagonists could be therapeutic agents for the treatment of motivational dysfunction in depression

The mesolimbic dopamine (DA) system plays a critical role in behavioral activation and effort-based decision-making. DA depletion produces anergia (shifts to low effort options) in animals tested on effort-based decision-making tasks. Caffeine, the most consumed stimulant in the world, acts as an adenosine A1/A2A receptor antagonist, and in striatal areas DA D1 and D2 receptors are co-localized with adenosine A1 and A2A receptors respectively. In the present work, we evaluated the effect of caffeine on anergia induced by the VMAT-2 inhibitor tetrabenazine (TBZ), which depletes DA. Anergia was evaluated in a three-chamber T-maze task in which animals can chose between running on a wheel (RW) vs. sedentary activities such as consuming sucrose or sniffing a neutral odor. TBZ-caffeine interactions in ventral striatum were evaluated using DARPP-32 phosphorylation patterns as an intracellular marker of DA-adenosine receptor interaction. In the T-maze, control mice spent more time running and much less consuming sucrose or sniffing. TBZ (4.0 mg/kg) reduced ventral striatal DA tissue levels as measured by HPLC, and also shifted preferences in the T-maze, reducing selection of the reinforcer that involved vigorous activity (RW), but increasing consumption of a reinforcer that required little effort (sucrose), at doses that had no effect on independent measures of appetite or locomotion in a RW. Caffeine at doses that had no effect on their own reversed the effects of TBZ on T-maze performance, and also suppressed TBZ-induced pDARPP-32(Thr34) expression as measured by western blot, suggesting a role for D2-A2A interactions. These results support the idea that DA depletion produces anergia, but does not affect the primary motivational effects of sucrose. Caffeine, possibly by acting on A2A receptors in ventral striatum, reversed the DA depletion effects. It is possible that caffeine, like selective adenosine A2A antagonists, could have some therapeutic benefit for treating effort-related symptoms.

Introducción: Los organismos continuamente toman decisiones basadas en el valor de los reforzadores y los costes que suponen las respuestas para conseguirlos. La magnitud del esfuerzo que la conducta a ejecutar requiere, influye en esas decisiones. La dopamina (da) en el núcleo accumbens (Nacb), es uno de los neurotransmisores centrales en la regulación de la toma de decisiones basada en el esfuerzo. La adenosina es un neuromodulador cuyos receptores interactúan de manera antagonística con los receptores de da en el Nacb y otras estructuras del circuito motivacional. Métodos: Ratones carentes del receptor a2A (a2Arko) o sus controles recibieron haloperidol, un antagonista de los receptores de da d2, los cuales están co-localizados con los receptores de adenosina a2A, y fueron evaluados en un paradigma de elección entre reforzadores. Se evaluaron dos aspectos fundamentales de la motivación: aspectos activacionales y direccionales. Resultados: En el laberinto en T los animales control eligieron pasar más tiempo corriendo en una rueda de actividad que consumiendo comida dulce. El antagonista de los receptores d2 redujo esta preferencia haciendo que los animales consumieran más dulces. Esto no es un fenómeno de saciedad, ya que cuando a los animales, previamente al test, se les dejaba saciarse de correr y de comer dulce, reducían su contacto con ambos reforzadores. Los animales a2Arko fueron resistentes a los efectos del haloperidol y no redujeron su preferencia por correr en detrimento del consumo de dulces. Discusión: Estos datos pueden contribuir al conocimiento de los mecanismos implicados en síndromes como la anergia que aparece en muchas patologías tales como la depresión. Introduction: Organisms continuously make decisions based on the value of a reward and the costs to get it. The magnitude of the effort required to procure the reward influences those decisions. Dopamine (da) in the motivational circuit, and spcecifically in nucleus accumbens (Nacb), is one of the key neurotransmitters involved in effort-based decision making. da d2 receptors are colocalized with adenosine a2A receptors and they interact in an antagonistic manner. Methods: Wild type (wt) and a2A receptor knockout (a2Arko) mice were used to explore DAergic involvement in the activational and directional components of motivated behaviors when multiple reinforcers are available. Results: A T-maze task was developed for the assessment of preference between physical activity (wheel running) in one arm and a dish with freely available sucrose pellets in the other. Under basal conditions, wt mice spent more time running and less consuming sucrose. After receiving haloperidol wt animals spent less time running, but increased time consuming sucrose and the amount consumed. a2Arko mice did not shift to the less effort-requiring reinforcer, although, like the WT mice, they did reduce sucrose consumption when sucrose was devalued after free sucrose consumption. Discussion: Adenosine a2Arko mice show resistance to the effects of haloperidol. These results indicate that after da antagonism, the preference for vigorous physical activity is reduced, while sucrose reinforcement remains intact. These data may contribute to our knowledge of the mechanisms involved in syndromes such as anergy shown in many pathologies such as depression.

Uno de los síntomas motivacionales característicos de la depresión y que supone un mayor problema para la realización de tareas cotidianas, es la anergia. Este síntoma supone una disminución del vigor y el esfuerzo que el sujeto está dispuesto a realizar para conseguir un objetivo. Las bases neurales de la anergia pueden estudiarse en el laboratorio mediante modelos animales, induciéndose a través de antagonistas dopaminérgicos. En el presente estudio, analizamos los efectos de la manipulación farmacológica del sistema dopaminérgico mediante el antagonismo de los receptores D2 (eticlopride). Como tratamiento que revierta estos síntomas administraremos MSX3, un antagonista de los receptores de adenosina A2a, los cuales están colocalizados con los receptores D2 y tienen efectos opuestos a éstos. Para evaluar los efectos conductuales de estas manipulaciones utilizamos un paradigma operante en el que el animal debe realizar cada vez más esfuerzo (apretando un mayor número de veces una palanca, Programa de Razón Progresiva, PROG) para conseguir una comida más apetecible, o tiene la opción de comer libremente otro tipo de comida menos sabrosa pero de libre acceso (chow). Los resultados demuestran que fármacos que interfieren con la transmisión de DA reducen el nivel de esfuerzo que el animal está dispuesto a realizar cuando tiene opciones menos costosas. Los antagonistas A2a revierten estos efectos y tienen potencial como fármacos para el tratamiento de la anergia en la depresión y en otras patologías como el Parkinson o el síndrome de fatiga crónica. People with depression not only display alterations in mood or affect, but also can show profound motivational impairments such as anergia. Mesolimbic dopamine (DA) is involved in behavioral activation and effort-related processes. Rats with impaired DA transmission reallocate their instrumental behavior away from food-reinforced tasks with high response requirements, and instead select less effortful food-seeking behaviors. DA receptors are colocalized with adenosine receptors but have opposite effects in the intracellular cascade. Thus, adenosine receptors can be a target for therapeutical approaches. In the present study, we used a progressive ratio (PROG)/chow feeding concurrent choice task. With this task, rats can lever press on a pr og schedule reinforced by a preferred high-carbohydrate food pellet, or alternatively approach and consume the less preferred but concurrently available laboratory chow. The DA D2 antagonist eticlopride reduced highest ratio achieved but did not reduce chow intake. In contrast, the A2a antagonist MSX3 coadministrated with eticlopride reversed the effects of the interference with DA transmission.

Blockade of adenosine A2A receptors can potentiate motivation to work for natural reinforcers such as food. Conspecific interaction is a potent natural reinforcer in social animals that can be manifested as preference for social exploration versus other sources of novel stimulation. Deficiencies in this type of motivated behavior (social withdrawal) have been seen in several pathologies such as autism and depression. However, the role of A2A receptors in motivation for social interaction has not been widely explored. Social interaction paradigms evaluate the natural preference of animals for exploring other conspecifics, and the ability to differentiate between familiar versus novel ones. Anxiety is one of the factors that can induce avoidance of social interaction. In the present study, adenosine A2A knockout (A2AKO) and wild-type (WT) mice were assessed for social and anxiety-related behaviors. c-Fos immunoreactivity was evaluated as a measure of neuronal activation in brain areas involved in different aspects of motivation and emotional processes. Although A2AKO mice showed an anxious profile, they displayed higher levels of sociability and were less sensitive to social novelty. WT mice displayed a typical pattern of social recognition 24 h later, but not A2AKO mice, which explored equally both conspecifics. There were no differences between strains in aggressiveness, perseverance or social odor preferences. c-Fos immunoreactivity in A2AKO mice was higher in anterior cingulate and amygdala compared to WT mice. Thus, A2A receptors appear to be potential targets for the improvement of pathologies related to social function.

Ethanol and caffeine are frequently consumed in combination and have opposite effects on the adenosine system: ethanol metabolism leads to an increase in adenosine levels, while caffeine is a non-selective adenosine A1/A2A receptor antagonist. These receptors are highly expressed in striatum and olfactory tubercle, brain areas involved in exploration and social interaction in rodents. Ethanol modulates social interaction processes, but the role of adenosine in social behavior is still poorly understood. The present work was undertaken to study the impact of ethanol, caffeine and their combination on social behavior, and to explore the involvement of A1 and A2A receptors on those actions. Male CD1 mice were evaluated in a social interaction three-chamber paradigm, for preference of conspecific vs. object, and also for long-term recognition memory of familiar vs. novel conspecific. Ethanol showed a biphasic effect, with low doses (0.25 g/kg) increasing social contact and higher doses (1.0–1.5 g/kg) reducing social interaction. However, no dose changed social preference; mice always spent more time sniffing the conspecific than the object, independently of the ethanol dose. Ethanol, even at doses that did not change social exploration, produced amnestic effects on social recognition the following day. Caffeine reduced social contact (15.0–60.0 mg/kg), and even blocked social preference at higher doses (30.0–60.0 mg/kg). The A1 antagonist Cyclopentyltheophylline (CPT; 3–9 mg/kg) did not modify social contact or preference on its own, and the A2A antagonist MSX-3 (1.5–6 mg/kg) increased social interaction at all doses. Ethanol at intermediate doses (0.5–1.0 g/kg) was able to reverse the reduction in social exploration induced by caffeine (15.0–30.0 mg/kg). Although there was no interaction between ethanol and CPT or MSX-3 on social exploration in the first day, MSX-3 blocked the amnestic effects of ethanol observed on the following day. Thus, ethanol impairs the formation of social memories, and A2A adenosine antagonists can prevent the amnestic effects of ethanol, so that animals can recognize familiar conspecifics. On the other hand, ethanol can counteract the social withdrawal induced by caffeine, a non-selective adenosine A1/A2A receptor antagonist. These results show the complex set of interactions between ethanol and caffeine, some of which could be the result of the opposing effects they have in modulating the adenosine system. This work was supported by a grant to MC from Plan Nacional de Drogas (2010/024) Spain. LL-C was supported by a personal grant awarded by FPU (AP2010–3793) Ministerio de Educación, NS-M was supported by a personal grant from UJI (Predoc- UJI/2012/28) and PB was supported by Plan Nacional de Drogas (2010/024)

Ethanol and caffeine are frequently consumed in combination and have opposite effects on the adenosine system: ethanol metabolism leads to an increase in adenosine levels, while caffeine is a non-selective adenosine A1/A2A receptor antagonist. These receptors are highly expressed in striatum and olfactory tubercle, brain areas involved in exploration and social interaction in rodents. Ethanol modulates social interaction processes, but the role of adenosine in social behavior is still poorly understood. The present work was undertaken to study the impact of ethanol, caffeine and their combination on social behavior, and to explore the involvement of A1 and A2A receptors on those actions. Male CD1 mice were evaluated in a social interaction three-chamber paradigm, for preference of conspecific vs. object, and also for long-term recognition memory of familiar vs. novel conspecific. Ethanol showed a biphasic effect, with low doses (0.25 g/kg) increasing social contact and higher doses (1.0–1.5 g/kg) reducing social interaction. However, no dose changed social preference; mice always spent more time sniffing the conspecific than the object, independently of the ethanol dose. Ethanol, even at doses that did not change social exploration, produced amnestic effects on social recognition the following day. Caffeine reduced social contact (15.0–60.0 mg/kg), and even blocked social preference at higher doses (30.0–60.0 mg/kg). The A1 antagonist Cyclopentyltheophylline (CPT; 3–9 mg/kg) did not modify social contact or preference on its own, and the A2A antagonist MSX-3 (1.5–6 mg/kg) increased social interaction at all doses. Ethanol at intermediate doses (0.5–1.0 g/kg) was able to reverse the reduction in social exploration induced by caffeine (15.0–30.0 mg/kg). Although there was no interaction between ethanol and CPT or MSX-3 on social exploration in the first day, MSX-3 blocked the amnestic effects of ethanol observed on the following day. Thus, ethanol impairs the formation of social memories, and A2A adenosine antagonists can prevent the amnestic effects of ethanol, so that animals can recognize familiar conspecifics. On the other hand, ethanol can counteract the social withdrawal induced by caffeine, a non-selective adenosine A1/A2A receptor antagonist. These results show the complex set of interactions between ethanol and caffeine, some of which could be the result of the opposing effects they have in modulating the adenosine system.

Blockade of adenosine A

Psychiatric disorders are often marked by effort-related motivational symptoms such as anergia, fatigue, psychomotor retardation, and alterations in effort-based decision making. Animal studies of effort-related choice behavior are being used to model these symptoms. With these procedures, animals are offered a choice between high effort instrumental actions leading to highly valued reinforcers vs. low effort/low reward options. In the present experiments the motivational effects of a novel dopamine (DA) uptake inhibitor, PRX-14040 (PRX), were assessed using tests of effort-based choice in rats. For the two experiments, rats were tested using the concurrent fixed ratio 5 (FR5)/chow feeding choice task. In the first 2 experiments, the vesicular monoamine transport (VMAT-2) inhibitor tetrabenazine (TBZ), which blocks DA storage and depletes DA, was used to produce a shift in effort-related choice, decreasing lever pressing and increasing chow intake. Co-administration of PRX reversed the effects of TBZ, increasing lever pressing and decreasing chow intake in TBZ-treated rats. In experiment 2, PRX was compared with the catecholamine uptake inhibitor and antidepressant bupropion (Wellbutrin), the stimulant drug methylphenidate, and the wakefulness agent modafinil. All four drugs reversed the effects of TBZ, and PRX compared favorably with these compounds. In the final experiment, PRX was assessed for its ability to increase work output in rats responding on a progressive ratio (PROG)/chow feeding choice task in rats that were otherwise untreated. PRX biased animals towards greater exertion of effort, increasing PROG lever pressing output while decreasing chow intake. In summary, PRX was able to reverse the effects of TBZ, and to increase selection of high effort activities. Taken together, these results suggest that PRX could be useful as a treatment for effort-related motivational dysfunction in humans. This work was supported by a grant to J.S. from Prexa. L. Cruz was supported by a grant from the Valencian Community, Spain. Catechol- amine transporter binding was provided by Euro fi ns, for Prexa Pharma- ceuticals, Inc.

Motivation has been defined as the process that allows organisms to regulate their internal and external environment, and control the probability, proximity and availability of stimuli. As such, motivation is a complex process that is critical for survival, which involves multiple behavioural functions mediated by a number of interacting neural circuits. Classical theories of motivation suggest that there are both directional and activational aspects of motivation, and activational aspects (i.e. speed and vigour of both the instigation and persistence of behaviour) are critical for enabling organisms to overcome work-related obstacles or constraints that separate them from significant stimuli. The present review discusses the role of brain dopamine and related circuits in behavioural activation, exertion of effort in instrumental behaviour, and effort-related decision-making, based upon both animal and human studies. Impairments in behavioural activation and effort-related aspects of motivation are associated with psychiatric symptoms such as anergia, fatigue, lassitude and psychomotor retardation, which cross multiple pathologies, including depression, schizophrenia, and Parkinson’s disease. Therefore, this review also attempts to provide an interdisciplinary approach that integrates findings from basic behavioural neuroscience, behavioural economics, clinical neuropsychology, psychiatry, and neurology, to provide a coherent framework for future research and theory in this critical field. Although dopamine systems are a critical part of the brain circuitry regulating behavioural activation, exertion of effort, and effort-related decision-making, mesolimbic dopamine is only one part of a distributed circuitry that includes multiple neurotransmitters and brain areas. Overall, there is a striking similarity between the brain areas involved in behavioural activation and effort-related processes in rodents and in humans. Animal models of effort-related decision-making are highly translatable to humans, and an emerging body of evidence indicates that alterations in effort-based decision-making are evident in several psychiatric and neurological disorders. People with major depression, schizophrenia, and Parkinson’s disease show evidence of decision-making biases towards a lower exertion of effort. Translational studies linking research with animal models, human volunteers, and clinical populations are greatly expanding our knowledge about the neural basis of effort-related motivational dysfunction, and it is hoped that this research will ultimately lead to improved treatment for motivational and psychomotor symptoms in psychiatry and neurology. This work was supported by a grant to J.S. from the National Institute of Mental Health (MH094966), and to Mercè Correa from U.J.I. P1.1A2013-01.

La adenosina es un neuromodulador del sistema nervioso central involucrado en numerosos procesos y que actúa principalmente en dos tipos de receptores adenosinérgicos (A1 y A2A). La cafeína es una metilxantina que actúa como antagonista no selectivo de estos receptores de adenosina- Recientemente, la cafeína a dosis altas, se ingiere junto a bebidas alcohólicas bajo la creencia popular de que esta metilxantina puede compensar los efectos intoxicantes y sedativos del alcohol. La primera parte de esta tesis, revisa la literatura relacionada con la interacción cafeína-alcohol, y explora el impacto de dosis altas de cafeína, así como de otros antagonistas selectivos de los receptores de adenosina (A1 o A2.A) en interacción con alcohol en diferentes parámetros y como estas sustancias pueden modular la conducta social en modelos animales. Por otra parte, los receptores de A1 A2A se han propuesto como dianas terapéuticas para el tratamiento de alteraciones motivacionales presentes en la depresión. La dopamina (DA) mesolímbica está involucrada en la regulación del componente activacjonal de la motivación. Los receptores de DA (D1 and D2) están colocalizados con los receptores de adef!osina (A1 y A2A_, respectivamente) e interactúan de forma antaica a nivel intracelular y conductual. En la segunda parte de la presente tesis, se estudia el efecto de la cafeína en la revers de la anergia inducida por un depletor dopammergico, tetrabenazma , en modelos animales. Con el objetivo de conocer los mecanismos intracelulares que regulan estos procesos, se estudia también el impacto de estas manipulaciones farmacológicas sobre marcadores de activación de los receptores de adenosina y DA., Adenosine is considered a neuromodulator in the central nervious system (CNS), that interacts with other neurotransmiters and with sorne substances like alcohol, which elevates the adenosinergic tone. Adenosine acts on difierent receptors, being A1 and A2A receptors the most relevant far their presence and action in the brain. Caffeine is a worldwide consume methylxanthine that acts as a non selective adenosine receptors antagonist (A 1/A2A). This drug is generally consumed to reduce fatigue and increase alert. More recently, caffeine al high concetrations is combined with alcoholic beverages under the popular belief that can counteract sorne of the sedative and impairing effects of ethanol. Thus, the first part of the present dissertation, reviews the literature on caffeine-ethanol interaction and adresses the impact of high doses the caffeine on difieren! parameters and how these drugs can modulate social interaction patterns in animal models. On the other hand,A 1 and A2A receptors have been proposed as therapeutical targets far the treatment of motivational impariments. Mesolimbic dopamine (DA) in involved in the regulation of the activational componen! of motivation and DA depletion ar antagonism has shown to impair lhis aspee! of motivation.Adenosine A 1 y A2A receptors are colocatized with DA D1 and D2 receptors respectively in siriatal areas and they interact in antagonistic way al cellular and behavioral level. Several adenosine antagonists have shown to revert the anergia-like effect induced by DA impariments. Thus in the second part of the present dissertation, the impact of caffeine on depression is reviewed and its potential on effort-based decision-making tasks in animal model is studied after te administration of a DA depleting agent. Cellular markers activated alter adenosine and DA receptor interaclons were analyzed in order to elucidate the mechanism of action.

La detección de cambios en los niveles de un neurotransmisor, como la dopamina o de su cascada metabotrópica que se inicia con la activación de sus receptores tras la realización de una conducta o un tratamiento farmacológico en estructuras cerebrales concretas, puede ser realizada con técnicas inmunológicas. Los métodos inmunoquímicos en general se fundamentan en la utilización de anticuerpos específicos para el marcaje de una proteína concreta. En el caso de que se quiera localizar la proteína en áreas o neuronas concretas por inmunohistología, los anticuerpos unidos a enzimas (peroxidasa o fosfatasa) o a fluorocromos aplicados a cortes histológicos de cerebro, se unen a la proteína antigénica de interés permitiendo su marcaje mediante una reacción colorimétrica o emisión de fluorescencia, respectivamente. Esta técnica nos ofrece la oportunidad de realizar un mapeado cerebral y observar en qué regiones la proteína de interés está presente y en qué medida. Por ejemplo, se han utilizado estas técnicas para el marcaje y/o cuantificación de algunos marcadores dopaminérgicos, como el DARPP -32, en el núcleo accumbens. Además, esa proteína puede ser cuantificada mediante la técnica western blot (WB). El WB requiere de la homogeneización del tejido, desnaturalización de proteínas y su separación por peso molecular mediante electroforesis y da como resultado una reacción quimioluminiscente detectable por una película fotográfica. Ambas técnicas son complementarias, pues ofrecen información de localización y permiten cuantificar la proteína. Detecting changes in the levels of a neurotransmitter such as dopamine or changes in the metabotropic cascade initiated by the activation of its receptors in specific brain structures after performing a behavior or receiving a specific drug therapy, can be accomplished with immunological techniques. Immunochemical methods are based onthe affinity of antibodies for a particular protein. The antibodies are bound to a marker that provides color or fluorescence. In the immunohistological methods, after the antibody is applied to a specific brain section where the antigenic protein is localized, neurons containing the targeted protein show the color or fluorescence, and they can be identified and quantified by microscopy and imaging processing techniques. For example, these techniques have been used for the localization and quantification of some dopaminergic markers such as DARPP -32, in the nucleus accumbens. This protein can be quantified also by western blotting (WB). The WB requires tissue homogenization, protein denaturalization and separation of proteins by molecular weight with electrophoresis, and results in a detectable chemiluminescent reaction by an X-ray film. Both techniques complement each other providing information about localization, as well as quantity of protein present in the tissue.

This review paper is focused upon the involvement of mesolimbic dopamine (DA) and related brain systems in effort-based processes. Interference with DA transmission affects instrumental behavior in a manner that interacts with the response requirements of the task, such that rats with impaired DA transmission show a heightened sensitivity to ratio requirements. Impaired DA transmission also affects effort-related choice behavior, which is assessed by tasks that offer a choice between a preferred reinforcer that has a high work requirement vs. less preferred reinforcer that can be obtained with minimal effort. Rats and mice with impaired DA transmission reallocate instrumental behavior away from food-reinforced tasks with high response costs, and show increased selection of low reinforcement/low cost options. Tests of effort-related choice have been developed into models of pathological symptoms of motivation that are seen in disorders such as depression and schizophrenia. These models are being employed to explore the effects of conditions associated with various psychopathologies, and to assess drugs for their potential utility as treatments for effort-related symptoms. Studies of the pharmacology of effort-based choice may contribute to the development of treatments for symptoms such as psychomotor slowing, fatigue or anergia, which are seen in depression and other disorders. US NIH/NIMH MH078023 Shire Fundacio UJI/Bancaixa P1.1B2010-43

Rationale Effort-related motivational symptoms, such as anergia, psychomotor retardation, and fatigue, are an important aspect of depression and other disorders. Motivational symptoms are resistant to some treatments, including serotonin transport (SERT) inhibitors. Objectives Tests of effort-based choice using operant behavior tasks (e.g., concurrent lever pressing/ chow feeding tasks) can be used as animal models of motivational symptoms. Tests of effort-related choice allow animals to choose between high-effort actions that lead to more highly valued rewards vs. low-effort alternatives that lead to less valued rewards (i.e., less preferred or lower magnitude). Rats treated with the vesicular monoamine transport inhibitor tetrabenazine, or the cytokine interleukin-1β (IL-1β), which are associated with depressive symptoms in humans, can alter effort-related choice, reducing selection of the high effort alternative (lever pressing) while increasing intake of freely available chow. Methods The present studies focused upon the ability of lisdexamfetamine (LDX) to increase exertion of effort in rats responding on effort-based choice tasks under several different conditions. Results LDX attenuated the shift from fixed ratio 5 lever pressing to chow intake induced by tetrabenazine and IL-1β. In contrast, the SERT inhibitor s-citalopram failed to reverse the effects of tetrabenazine. When given in combination with tetrabenazine+s-citalopram, LDX significantly increased lever pressing output compared to tetrabenaine+citalopram alone. LDX also increased work output in rats responding on a progressive ratio/chow feeding choice task. Conclusions LDX can increase work output in rats responding on effort-based choice tasks, which may have implications for understanding the neurochemistry of motivational symptoms in humans.

It has been known for some time that nucleus accumbens dopamine (DA) is involved in aspects of motivation , but theoretical approaches to understanding the functions of DA have continued to evolve based upon emerging data and novel concepts. Although it has become traditional to label DA neurons as "reward" neurons, the actual findings are more complicated than that, because they indicate that DA neurons can respond to a variety of motivationally significant stimuli. Moreover, it is important to distinguish between aspects of motivation that are differentially affected by dopaminergic manipulations. Studies that involve nucleus accumbens DA antagonism or depletion indicate that accumbens DA does not mediate primary food motivation or appetite. Nevertheless, DA is involved in appetitive and aversive motivational processes including behavioral activation , exertion of effort, sustained task engagement, and Pavlovian-to-instrumental transfer. Interference with accumbens DA transmission affects instrumental behavior in a manner that interacts with the response requirements of the task and also shifts effort-related choice behavior, biasing animals toward low-effort alternatives. Dysfunctions of mesolimbic DA may contribute to motivational symptoms seen in various psychopathologies, including depression , schizophrenia, parkinsonism, and other disorders.

Mesolimbic dopamine (DA) regulates behavioral activation and effort-related decision-making in motivated behaviors. Mesolimbic DA D2 receptors are co-localized with adenosine A2A receptors, and they interact in an antagonistic manner.A T-maze task was developed to assess dopaminergic involvement in preference between a reinforcer that involves vigorous voluntary activity (running wheel) and a reinforcer that requires minimal behavioral activation (sucrose pellets). Haloperidol (D2 antagonist) was administered to adenosine A2A receptor knockout (A2AKO) and wild-type (WT) littermate controls to assess the involvement of these two receptors in the selection of running wheel activity versus sucrose consumption.Under control conditions, mice spent more time running and less time eating. In WT mice, haloperidol reduced time running but actually increased time-consuming sucrose. However, A2AKO mice did not show the haloperidol-induced shift from running wheel activity to sucrose intake. Prefeeding reduced sucrose consumption in the T-maze in both strains, indicating that this paradigm is sensitive to motivational devaluation. Haloperidol increased c-Fos immunoreactivity in anterior cingulate cortex (ACg) and nucleus accumbens (Acb) core of WT but not KO mice.These results indicate that after DA antagonism, the preference for vigorous physical activity is reduced, while palatable food selection increases. Adenosine A2A receptor deletion provides resistance to these effects of D2 receptor antagonism. These two receptors in Acb core and ACg seem to be involved in the regulation of the intrinsic reinforcing characteristics of voluntary exercise but not in the regulation of the primary reinforcing characteristics of palatable sedentary reinforcers.

Rationale Low doses of dopamine (DA) antagonists and accumbens DA depletions reduce food-reinforced instrumental behavior but do not impair primary food motivation, causing animals to reallocate behavior away from food-reinforced tasks with high response requirements and select less effortful alternatives. However, it is uncertain if this same pattern of effects would occur if sucrose was used as the reinforcer. Objectives These experiments studied the impact of DA depletion and antagonism on performance of an effort-related choice task using sucrose as the reinforcer, as well as sucrose consumption, preference, and taste reactivity tests. Methods The effects of DA manipulations were assessed using a task in which rats chose between lever pressing on a fixed ratio 7 schedule for 5.0 % sucrose versus freely consuming a less concentrated solution (0.3 %). Results The DA depleting agent tetrabenazine shifted effortrelated choice, decreasing lever pressing for 5.0 % sucrose but increasing intake of the concurrently available 0.3 % sucrose. Tetrabenazine did not affect sucrose appetitive taste reactivity, or sucrose consumption or preference, in free consumption tests. The D1 antagonist ecopipam and the D2 antagonist haloperidol also shifted choice behavior at doses that did not alter sucrose consumption or preference. In contrast, sucrose preexposure reduced consumption across all conditions. D3 antagonism had no effects. Conclusions D1 and D2 receptor blockade and DA depletion reduce the tendency to work for sucrose under conditions that leave fundamental aspects of sucrose motivation (intake, preference, hedonic reactivity) intact. These findings have implications for studies employing sucrose intake or preference in animal models of depression. This work was supported by a grant to Mercè Correa from Pla Promoció Investigació UJI (P1.1 A 2013-01) and to John D. Salamone from the National Institute of Mental Health (MH078023). Personal grants were awarded to Marta Pardo (Predoc-UJI/ 2007/43), Noemí San Miguel (Predoc-UJI/ 2012/28), and Laura Lopez-Cruz (FPU AP2010-3793, Ministerio de Educación, Spain)

Disfunciones relacionadas con el esfuerzo como la anergia y la fatiga son síntomas centrales de la depresión y otros trastornos. El sistema dopaminérgico (DA) mesolímbico desempeña un papel crítico en la activación de la conducta. Sin embargo, se ha demostrado que la depleción da no cambia la preferencia cuando no se requiere realizar esfuerzo en la adquisición del reforzador. Aun así, cuando una concentración alta de sucrosa requiere trabajo, los roedores con depleción da reducen el esfuerzo necesario para obtener la concentración preferida pero aún así compensan consumiendo sucrosa menos dulce de libre acceso. En el presente estudio, hemos desarrollado una tarea en un laberinto en T para ratones que nos permita evaluar la preferencia entre tres diferentes tipos de reforzadores situados cada uno en uno de los brazos: actividad física como la condición de refuerzo que requiere un alto esfuerzo, un plato con bolitas de sucrosa de libre acceso, y un agujero en el que se localiza un olor neutro. Los ratones muestran preferencia, de manera innata, por el ejercicio físico y esto es dependiente de las condiciones homeostáticas del animal (si está hambriento o saciado). Por otro lado, observamos un incremento de la preferencia por rodar en la rueda de actividad cuando la comida dulce se devalúa (se le añade un sabor amargo). Los animales que reciben tetrabenazina, un depletor DA que inhibe de manera reversible el transportador vesicular de monoaminas de tipo 2 (VMAT2), demostraron reducir su preferencia por el ejercicio físico, pero aumentaron el consumo de sucrosa de libre acceso. Así pues la reducción de DA produce síntomas de anergia (falta de energía) aunque no de anhedonia (falta de apreciación de las propiedades gustativas apetecibles de la sucrosa). Effort-related dysfunctions such as anergia and fatigue are core symptoms of depression and other disorders. Dopamine (DA) systems play a critical role in behavioral activation. However, previous studies have shown that DA depletion does not change sucrose consumption or preference when no effort is involved in procuring this reinforcer. Nevertheless, when the preferred sucrose concentration requires work, rodents with DA depletions reduce the work output for the preferred highly concentrated sucrose drink but compensate by consuming more of the less sweet but freely available sucrose fluid. In the present studies, we have developed mice T-maze tasks for the assessment of preference between three different type of reinforcers: engagement in physical activity as the high effort reinforcing condition, a dish with freely available sucrose pellets, and a non-social (neutral) odor in the third arm. Mice show an important preference by the physical exercise, and this preference depends on the animal’s homeostatic conditions (satiety or hunger). Moreover, preference for the running wheel increases when the sweet food is devalued. In the present studies, tetrabenozine, a selective and reversible vesicular monoamine transporter-2 (VMAT2) inhibitor reduced preference for physical exercise, but increased sucrose consumption. Thus the reduction of DA produces symptoms of anergy (lack of energy) but not anhedonia (lack of enjoyement of the sucrose taste).

En los últimos años, el consumo de las bebidas energéticas ha incrementado notablemente, así como su concentración de cafeína. Con frecuencia, estas bebidas se consumen junto a grandes cantidades de alcohol con el objetivo de reducir la sedación y la incoordinación producida por esta sustancia. Uno de los mecanismos de acción del alcohol sobre el sistema nervioso central (snc) es el incremento del tono adenosinérgico, el cual puede estar mediando los efectos sedativos e incoordinantes observados tras su consumo. Por otra parte, la cafeína es una metilxantina que actúa como un antagonista no selectivo de los receptores de adenosina a1 y a2A. Con el objetivo de estudiar la interacción entre la cafeína y el alcohol en la incoordinación motora, en el presente estudio con ratones, se administró cafeína de manera aguda y se evaluó su impacto sobre los efectos incoordinantes producidos por el alcohol recibido también de manera aguda, o en animales que han estado pre-expuestos repetidamente a alcohol. Las dosis de ethanol utilizadas en estos experimentos produjeron incoordinación motora, mientras que las dosis de cafeína utilizadas mostraron una tendencia no significativa a mejorar dicha ejecución. La cafeína no revirtió la incoordinación motora inducida por alcohol, independientemente del patrón de administración agudo o repetido. Así pues, dosis medias y altas de cafeína no demuestran un efecto terapéutico sobre el deterioro motor producido por el alcohol. Energy drinks are highly consumed beverages rich in caffeine. In humans, energy drinks are very frequently consumed with alcohol in order to reduce the sedation and incoordination induced by high doses of this drug of abuse. Both drugs have shown to exert that increases the adenosinergic tone, and this effect is thought to mediate the sedative and incoordinating effects observed after alcohol consumption. On the other hand, caffeine is a methylxanthine that acts as a non-selective adenosine antagonist, binding to the two main types of adenosine receptors present in the cns: the A1 and A2A subtypes. The aim of the present study was to fold: to explore the effect of an acute caffeine administration (15 or 30 mg/kg, administered intraperitoneally, IP) on the incoordination effects of ethanol, and to study the acute effect of this methylxanthine in animals that had been repeatedly pre-exposed to ethanol before being tested. The acute administration of ethanol (1.5 g/kg, IP) produced motor impairment in the rotarod when is compared to the control vehicle group. However, caffeine was unable to reverse the impairing effects of an acute dose of ethanol, and did not improved the ataxia produced by a repeated administration of ethanol (1.5 g/kg). Thus, these results show that the non-selective adenosine antagonist caffeine at moderate to high doses (15 and 30 mg/kg) is not efficacious at counteracting the incoordination produced by alcohol in mice, neither after acute, nor after repeated pre-exposure to alcohol.

Background: Depression and related disorders are characterized by deficits in behavioral activation, exertion of effort, and other psychomotor/motivational dysfunctions. Depressed patients show alterations in effort-related decision making and a bias towards selection of low effort activities. It has been suggested that animal tests of effort-related decision making could be useful as models of motivational dysfunctions seen in psychopathology. Methods: Because clinical studies have suggested that inhibition of catecholamine uptake may be a useful strategy for treatment of effort-related motivational symptoms, the present research assessed the ability of bupropion to increase work output in rats responding on a test of effort-related decision-making (ie, a progressive ratio/chow feeding choice task). With this task, rats can choose between working for a preferred food (high-carbohydrate pellets) by lever pressing on a progressive ratio schedule vs obtaining a less preferred laboratory chow that is freely available in the chamber. Results: Bupropion (10.0–40.0 mg/kg intraperitoneal) significantly increased all measures of progressive ratio lever pressing, but decreased chow intake. These effects were greatest in animals with low baseline levels of work output on the progressive ratio schedule. Because accumbens dopamine is implicated in effort-related processes, the effects of bupropion on markers of accumbens dopamine transmission were examined. Bupropion elevated extracellular dopamine levels in accumbens core as measured by microdialysis and increased phosphorylated dopamine and cyclic-AMP related phosphoprotein 32 kDaltons (pDARPP-32) immunoreactivity in a manner consistent with D1 and D2 receptor stimulation. Conclusion: The ability of bupropion to increase exertion of effort in instrumental behavior may have implications for the pathophysiology and treatment of effort-related motivational symptoms in humans. This work was supported by a grant to J.D.S. from the National Institute of Mental Health (MH094966) and to M.C. from U. Jaume I (P1.1 A 2013-01) and UCONN SURF grants to M.R. and M.J.

Rationale\ud Caffeine and theophylline are methylxanthines that are broadly consumed, sometimes at high doses, and act as minor psychostimulants. Both are nonselective adenosine antagonists for A1 and A2A receptors, which are colocalized with dopamine D1 and D2 receptors in striatal areas. Adenosine antagonists generally have opposite actions to those of dopamine antagonists. Although the effects of caffeine are widely known, theophylline has been much less well characterized, especially at high doses.\ud Methods\ud Adult male CD1 mice were used to study the effect of a broad range of doses (25.0, 50.0 or 100.0 mg/kg) of caffeine and theophylline on measures of spontaneous locomotion and coordination, as well as the pattern of c-Fos immunoreactivity in brain areas rich in adenosine and dopamine receptors. In addition, we evaluated possible anxiety and stress effects of these doses.\ud Results\ud Caffeine, at these doses, impaired or suppressed locomotion in several paradigms. However, theophylline was less potent than caffeine at suppressing motor parameters, and even stimulated locomotion. Both drugs induced corticosterone release, however caffeine was more efficacious at intermediate doses. While caffeine showed an anxiogenic profile at all doses, theophylline only did so at the highest dose used (50 mg/kg). Only theophylline increased c-Fos immunoreactivity in cortical areas.\ud Conclusion\ud Theophylline has fewer disruptive effects than caffeine on motor parameters and produces less stress and anxiety effects. These results are relevant for understanding the potential side effects of methylxanthines when consumed at high doses.

Motivated behaviors are often characterized by a high degree of behavioral activation, and work output and organisms frequently make effort-related decisions based upon cost/benefit analyses. Moreover, people with major depression and other disorders often show effort-related motivational symptoms such as anergia, psychomotor retardation, and fatigue. It has been suggested that tasks measuring effort-related choice behavior could be used as animal models of the motivational symptoms of depression, and the present studies characterized the effort-related effects of the vesicular monoamine transport (VMAT) inhibitor tetrabenazine. Tetrabenazine produces depressive symptoms in humans and, because of its selective inhibition of VMAT-2, it preferentially depletes dopamine (DA). Rats were assessed using a concurrent fixed-ratio 5/chow feeding choice task that is known to be sensitive to dopaminergic manipulations. Tetrabenazine shifted response choice in rats, producing a dose-related decrease in lever pressing and a concomitant increase in chow intake. However, it did not alter food intake or preference in parallel free-feeding choice studies. The effects of tetrabenazine on effort-related choice were reversed by the adenosine A2Aantagonist MSX-3 and the antidepressant bupropion. A behaviorally active dose of tetrabenazine decreased extracellular DA in nucleus accumbens and increased expression of DARPP-32 in accumbens medium spiny neurons in a pattern indicative of reduced transmission at both D1and D2DA receptors. These experiments demonstrate that tetrabenazine, which is used in animal models to produce depression-like effects, can alter effort-related choice behavior. These studies have implications for the development of animal models of the motivational symptoms of depression and related disorders.

Considerable evidence indicates that the metabolite of ethanol (EtOH), acetaldehyde, is biologically active. Acetaldehyde can be formed from EtOH peripherally mainly by alcohol dehydrogenase (ADH), and also centrally by catalase. EtOH and acetaldehyde show differences in their behavioral effects depending upon the route of administration. In terms of their effects on motor activity and motivated behaviors, when administered peripherally acetaldehyde tends to be more potent than EtOH but shows very similar potency administered centrally. Since dopamine (DA) rich areas have an important role in regulating both motor activity and motivation, the present studies were undertaken to compare the effects of central (intraventricular, ICV) and peripheral (intraperitoneal, IP) administration of EtOH and acetaldehyde on a cellular marker of brain activity, c-Fos immunoreactivity, in DA innervated areas. Male Sprague-Dawley rats received an IP injection of vehicle, EtOH (0.5 or 2.5 g/kg) or acetaldehyde (0.1 or 0.5 g/kg) or an ICV injection of vehicle, EtOH or acetaldehyde (2.8 or 14.0 μmoles). IP administration of EtOH minimally induced c-Fos in some regions of the prefrontal cortex and basal ganglia, mainly at the low dose (0.5 g/kg), while IP acetaldehyde induced c-Fos in virtually all the structures studied at both doses. Acetaldehyde administered centrally increased c-Fos in all areas studied, a pattern that was very similar to EtOH. Thus, IP administered acetaldehyde was more efficacious than EtOH at inducing c-Fos expression. However, the general pattern of c-Fos induction promoted by ICV EtOH and acetaldehyde was similar. These results are consistent with the pattern observed in behavioral studies in which both substances produced the same magnitude of effect when injected centrally, and produced differences in potency after peripheral administration.

Behavioral activation is regulated by dopamine (DA) in striatal areas. At low doses, while typical antipsychotic drugs produce psychomotor slowing, psychostimulants promote exploration. Minor stimulants such as caffeine, which act as adenosine receptor antagonists, can also potentiate behavioral activation. Striatal areas are rich in adenosine and DA receptors, and adenosine A2A receptors are mainly expressed in the striatum where they are co-localized with DA D2 receptors. Adenosine antagonists with different receptor-selectivity profiles were used to study spontaneous or haloperidol-impaired exploration and c-Fos expression in different striatal areas. Because A2A antagonists were expected to be more selective for reversing the effects of the D2 antagonist haloperidol, A2A receptor knockout (A2ARKO) mice were also assessed. CD1 and A2ARKO male mice were tested in an open field and in a running wheel. Only the A1/A2A receptor antagonist theophylline (5.0–15.0 mg/kg) and the A2A antagonist MSX-3 (2.0 mg/kg) increased spontaneous locomotion and rearing. Co-administration of theophylline (10.0–15.0 mg/kg), and MSX-3 (1.0–3.0 mg/kg) reversed haloperidol-induced suppression of locomotion. The A1 antagonist CPT was only marginally effective in reversing the effects of haloperidol. Although adenosine antagonists did not affect c-Fos expression on their own, theophylline and MSX-3, but not CPT, attenuated haloperidol induction of c-Fos expression. A2ARKO mice were resistant to the behavioral effects of haloperidol at intermediate doses (0.1 mg/kg) in the open field and in the running wheel. A2A receptors are important for regulating behavioral activation, and interact with D2 receptors in striatal areas to regulate neural processes involved in exploratory activity.

The impact of caffeine on the behavioral effects of ethanol, including ethanol consumption and abuse, has become a topic of great interest due to the rise in popularity of the so-called energy drinks. Energy drinks high in caffeine are frequently taken in combination with ethanol under the popular belief that caffeine can offset some of the intoxicating effects of ethanol. However, scientific research has not universally supported the idea that caffeine can reduce the effects of ethanol in humans or in rodents, and the mechanisms mediating the caffeine–ethanol interactions are not well understood. Caffeine and ethanol have a common biological substrate; both act on neurochemical processes related to the neuromodulator adenosine. Caffeine acts as a nonselective adenosine A1 and A2A receptor antagonist, while ethanol has been demonstrated to increase the basal adenosinergic tone via multiple mechanisms. Since adenosine transmission modulates multiple behavioral processes, the interaction of both drugs can regulate a wide range of effects related to alcohol consumption and the development of ethanol addiction. In the present review, we discuss the relatively small number of animal studies that have assessed the interactions between caffeine and ethanol, as well as the interactions between ethanol and subtype-selective adenosine receptor antagonists, to understand the basic findings and determine the possible mechanisms of action underlying the caffeine–ethanol interactions.

IT HAS BEEN POSTULATED THAT A NUMBER OF THE CENTRAL EFFECTS OF ETHANOL ARE MEDIATED VIA ETHANOL METABOLITES: acetaldehyde and acetate. Ethanol is known to produce a large variety of behavioral actions such anxiolysis, narcosis, and modulation of locomotion. Acetaldehyde contributes to some of those effects although the contribution of acetate is less known. In the present studies, rats and mice were used to assess the acute and chronic effects of acetate after central or peripheral administration. Male Sprague-Dawley rats were used for the comparison between central (intraventricular, ICV) and peripheral (intraperitoneal, IP) administration of acute doses of acetate on locomotion. CD1 male mice were used to study acute IP effects of acetate on locomotion, and also the effects of chronic oral consumption of acetate (0, 500, or 1000 mg/l, during 7, 15, 30, or 60 days) on ethanol- (1.0, 2.0, 4.0, or 4.5 g/kg, IP) induced locomotion, anxiolysis, and loss of righting reflex (LORR). In rats, ICV acetate (0.7-2.8 μmoles) reduced spontaneous locomotion at doses that, in the case of ethanol and acetaldehyde, had previously been shown to stimulate locomotion. Peripheral acute administration of acetate also suppressed locomotion in rats (25-100 mg/kg), but not in mice. In addition, although chronic administration of acetate during 15 days did not have an effect on spontaneous locomotion in an open field, it blocked ethanol-induced locomotion. However, ethanol-induced anxiolysis was not affected by chronic administration of acetate. Chronic consumption of acetate (up to 60 days) did not have an effect on latency to, or duration of LORR induced by ethanol, but significantly increased the number of mice that did not achieve LORR. The present work provides new evidence supporting the hypothesis that acetate should be considered a centrally-active metabolite of ethanol that contributes to some behavioral effects of this alcohol, such as motor suppression.

Motivated behavior can be characterized by a high degree of activity, vigor, and persistence. Brain dopamine (DA), particularly in the nucleus accumbens, has been implicated in activational aspects of motivation and effort-related processes. Accumbens DA depletions reduce the tendency of rats to work for food, and alter effort-related decision making, but leave aspects of food motivation such as appetite intact. Recent evidence indicates that the purine neuromodulator adenosine, largely through actions on adenosine A2A receptors, also participates in regulating effort-related processes. Intra-accumbens injections of adenosine A2A agonists produce effects that are similar to those produced by accumbens DA depletion or antagonism. Furthermore, systemic or intra-accumbens injections of adenosine A2A receptor antagonists can reverse the effects of DA D2 antagonists on effort-related choice behavior. In contrast, adenosine A1 receptor antagonists fail to reverse these motivational effects of DA D2 antagonism. These studies have implications for understanding the potential role of adenosine in the development and treatment of energy-related motivational symptoms such as anergia and fatigue in depression and other disorders.

Brain dopamine (DA) and adenosine interact in the regulation of behavioral activation and effort-related processes. In the present studies, a T-maze task was developed in mice for the assessment of effort-related decision making. With this task, the two arms of the maze have different reinforcement densities, and a vertical barrier is positioned in the arm with the higher density (HD), presenting the animal with an effort-related challenge. Under control conditions mice prefer the HD arm, and climb the barrier to obtain the larger amount of food. The DA D2 receptor antagonist haloperidol decreased selection of the HD arm and increased selection of the arm with the low density of reinforcement. However, the HD arm was still the preferred choice in haloperidol-treated mice trained with barriers in both arms. Pre-feeding the mice to reduce food motivation dramatically increased omissions, an effect that was distinct from the actions of haloperidol. Co-administration of theophylline, a nonselective adenosine receptor antagonist, partially reversed the effects of haloperidol. This effect seems to be mediated by the A2A receptor but not the A1 receptor, since the A2A antagonist MSX-3, but not the A1 antagonist CPT, dose dependently reversed the effects of haloperidol on effort-related choice and on c-Fos expression in the dorsal striatum and nucleus accumbens. In addition, adenosine A2A receptor knockout mice were resistant to the effects of haloperidol on effort-related choice in the maze. These results indicate that DA D2 and adenosine A2A receptors interact to regulate effort-related decision making and effort expenditure in mice. This work was supported by a grant to Mercè Correa from Fundació Bancaixa-UJI (P1.1B2010-43), to John D. Salamone from the National Institute of Mental Health (MH078023), to Olga Valverde from MCINN (SAF2010-1593) and ISCIII RTA (RD06/0001/ 1001). Christa E. Müller and Younis Baqi were funded by the BMBF, 01EW0911 in the framework of ERA-NET-NEURON.

The study of the severity of occupational injuries is very important for the establishment of prevention plans. The aim of this paper is to analyze the distribution of occupational injuries by a) individual factors b) work place characteristics and c) working conditions and to analyze the severity of occupational injuries by this characteristics in men and women in Andalusia.Injury data came from the accident registry of the Ministry of Labor and social issues in 2003. Dependent variable: the severity of the injury: slight, serious, very serious and fatal; the independent variables: the characteristics of the worker, company data, and the accident itself. Bivariate and multivariate analysis were done to estimate the probability of serious, very serious and fatal injury, related to other variables, through odds ratio (OR), and using a 95% confidence interval (CI 95%).The 82.4% of the records were men and 17.6% were women, of whom the 78,1% are unskilled manual workers, compared to 44.9% of men. The men belonging to class I have a higher probability of more severe lesions (OR = 1.67, 95% CI = 1.17-2.38).The severity of the injury is associated with sex, age and type of injury. In men it is also related with the professional situation, the place where the accident happened, an unusual job, the size and the characteristics of the company and the social class, and in women with the sector.

Background. The study of the severity of occupational injuries is very important for the establishment of prevention plans. The aim of this paper is to analyze the distribution of occupational injuries by a) individual factors b) work place characteristics and c) working conditions and to analyze the severity of occupational injuries by this characteristics in men and women in Andalusia. Methods. Injury data came from the accident registry of the Ministry of Labor and Social Issues in 2003. Dependent variable: the severity of the injury: slight, serious, very serious and fatal; the independent variables: the characteristics of the worker, company data, and the accident itself. Bivariate and multivariate analysis were done to estimate the probability of serious, very serious and fatal injury, related to other variables, through odds ratio (OR), and using a 95% confidence interval (CI 95%). Results. The 82,4% of the records were men and 17,6% were women, of whom the 78,1% are unskilled manual workers, compared to 44,9% of men. The men belonging to class I have a higher probability of more severe lesions (OR = 1,67, 95% CI = 1,17 – 2,38). Conclusions. The severity of the injury is associated with sex, age and type of injury. In men it is also related with the professional situation, the place where the accident happened, an unusual job, the size and the characteristics of the company and the social class, and in women with the sector Yes Fundamento. El estudio de la gravedad de las lesiones por accidente de trabajo es clave para el establecimiento de planes de prevención. El objetivo de este trabajo es conocer la distribución de las lesiones registradas por accidente de trabajo con baja según: a) las características del trabajador/ora; b) las del centro de trabajo y; c) las condiciones de empleo y del puesto de trabajo; y analizar la gravedad de las lesiones registradas según estas características en hombres y mujeres en Andalucía. Métodos. Se utilizaron los datos del registro de lesiones por accidente de trabajo con incapacidad laboral durante 2003 en Andalucía. Variable dependiente: grado real de la lesión; variables independientes: las características del/a trabajador/a, de la empresa y las del propio accidente. Se realizó un análisis bivariante y multivariante para estimar la probabilidad de lesión grave, muy grave o mortal asociada al resto de variables mediante la razón de odds (OR) y su intervalo de confianza. Resultados. El 82,4% de las lesiones se produjeron en hombres y el 17,6% en mujeres, de las cuales el 78,1% eran trabajadoras manuales no cualificadas, frente al 44,9% de los hombres. En hombres de clase I se encontró una probabilidad mayor de presentar lesiones más graves (OR = 1,67; IC 95% = 1,17-2,38). Conclusiones. La gravedad de las lesiones se relaciona con el sexo, la edad y el tipo de lesión. En los hombres también se asocia con la situación profesional, la clase social, el lugar del accidente, la plantilla del centro y el realizar un trabajo que no es el suyo y en las mujeres con el sector de actividad.

Nucleus accumbens dopamine (DA) plays a critical role in behavioral activation and effort-based decision-making. DA depletions reduce the level of effort that an animal is willing to make to obtain a natural reinforcer, but it does not change preference between freely available reinforcers. On the other hand, drugs whose mechanism …