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Combined use of fentanyl and methamphetamine (FENT + METH) has increased in recent years and has been documented in a growing number overdose deaths each year. The impact of FENT + METH on behavior and neurobiology is not well understood. In this study, male and female Long Evans rats were tested on a limited access, fixed ratio 1 self-administration schedule for increasing doses (1.25-5 μg/kg/infusion; iv) of fentanyl, with and without a single dose (0.1 mg/kg/infusion; iv) of methamphetamine, for 15 days. FENT + METH abolished dose responsiveness to fentanyl in all rats and accelerated intake in males, resulting in patterns of responding that may be more likely to result in adverse effects. Ex vivo slice voltammetry in the nucleus accumbens core showed decreases in dopamine release and reuptake (V max ) following FENT + METH exposure, compared with saline, fentanyl, and methamphetamine alone groups at baseline parameters. Further, significant decreases in dopamine release were observed across a range of stimulation intensities following FENT + METH exposure. Overall, male and female rats displayed sex-specific behavioral and neurobiological responses to FENT + METH exposure, with males displaying increased vulnerability., (© 2024 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

For over four decades, fast-scan cyclic voltammetry (FSCV) has been used to selectively measure neurotransmitters such as dopamine (DA) with high spatial and temporal resolution, providing detailed information about the regulation of DA in the extracellular space. FSCV is an optimal method for determining concentrations of stimulus-evoked DA in brain tissue. When modelling diseases involving disturbances in DA transmission, preclinical rodent models are especially useful because of the availability of specialized tools and techniques that serve as a foundation for translational research. There is known heterogeneity in DA dynamics between and within DA-innervated brain structures and between males and females. However, systematic evaluations of sex- and species-differences across multiple areas are lacking. Therefore, using FSCV, we captured a broad range of DA dynamics across five sub-regions of the dorsal and ventral striatum of males and females of both rats and mice that reflect the functional heterogeneity of DA kinetics and dynamics within these structures. While numerous differences were found, in particular, we documented a strong, consistent pattern of increased DA transporter activity in females in all of the regions surveyed. The data herein are intended to be used as a resource for further investigation of DA terminal function., (© 2024 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

As opposed to those requiring a single action for reward acquisition, tasks necessitating action sequences demand that animals learn action elements and their sequential order and sustain the behaviour until the sequence is completed. With repeated learning, animals not only exhibit precise execution of these sequences but also demonstrate enhanced smoothness and efficiency. Previous research has demonstrated that midbrain dopamine and its major projection target, the striatum, play crucial roles in these processes. Recent studies have shown that dopamine from the substantia nigra pars compacta (SNc) and the ventral tegmental area (VTA) serve distinct functions in action sequence learning. The distinct contributions of dopamine also depend on the striatal subregions, namely the ventral, dorsomedial and dorsolateral striatum. Here, we have reviewed recent findings on the role of striatal dopamine in action sequence learning, with a focus on recent rodent studies., (© 2024 The Author(s). European Journal of Neuroscience published by Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

The anterior cingulate cortex (ACC) has been shown to be critical to many aspects of executive function including filtering irrelevant information, updating response contingencies when reinforcement contingencies change and stabilizing task sets. Nonspecific lesions to this region in rats produce a vulnerability to distractors that have gained salience through prior associations with reinforcement. These lesions also exacerbate cognitive fatigue in tests of sustained attention but do not produce global attentional impairments nor do they produce distractibility to novel distractors that do not have a prior association with reinforcement. To determine the neurochemical basis of these cognitive impairments, dopaminergically selective lesions of the ACC were made in both male and female Long-Evans, hooded rats prior to assessment in two attentional tasks. Dopaminergic lesions of the ACC increase the vulnerability of subjects to previously reinforced distractors and impede formation of an attentional set. Lesioned rats were not more susceptible to the effects of novel, irrelevant stimuli in a test of sustained attention as has been previously shown. Additionally, the effects of dopaminergic lesions were found to differ based on sex. Lesioned female, but not male, rats were more vulnerable than sham-lesioned females to the effects of prolonged testing and the removal of reinforcement during a test of sustained attention. Together, these data support the hypothesis that dopamine in the ACC is critical to filtering distractors whose salience has been gained through reinforcement., (© 2024 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

The maturation of forebrain dopamine circuitry occurs over multiple developmental periods, extending from early postnatal life until adulthood, with the precise timing of maturation defined by the target region. We recently demonstrated in the adult mouse brain that axon terminals arising from midbrain dopamine neurons innervate the anterior corpus callosum and that oligodendrocyte lineage cells in this white matter tract express dopamine receptor transcripts. Whether corpus callosal dopamine circuitry undergoes maturational changes between early adolescence and adulthood is unknown but may be relevant to understanding the dramatic micro- and macro-anatomical changes that occur in the corpus callosum of multiple species during early adolescence, including in the degree of myelination. Using quantitative neuroanatomy, we show that dopamine innervation in the forceps minor, but not the rostral genu, of the corpus callosum, is greater during early adolescence (P21) compared to adulthood (>P90) in wild-type mice. We further demonstrate with RNAscope that, as in the adult, Drd1 and Drd2 transcripts are expressed at higher levels in oligodendrocyte precursor cells (OPCs) and decline as these cells differentiate into oligodendrocytes. In addition, the number of OPCs that express Drd1 transcripts during early adolescence is double the number of those expressing the transcript during early adulthood. These data further implicate dopamine in axon myelination and myelin regulation. Moreover, because developmental (activity-independent) myelination peaks during early adolescence, with experience-dependent (activity-dependent) myelination greatest during early adulthood, our data suggest that potential roles of dopamine on callosal myelination shift between early adolescence and adulthood, from a developmental role to an experience-dependent role., (© 2024 The Authors. European Journal of Neuroscience published by Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

The emergence of compulsive drug-seeking habits, a hallmark feature of substance use disorder, has been shown to be predicated on the engagement of dorsolateral striatal control over behaviour. This process involves the dopamine-dependent functional coupling of the anterior dorsolateral striatum (aDLS) with the nucleus accumbens core, but the mechanisms by which this coupling occurs have not been fully elucidated. The striatum is tiled by a syncytium of astrocytes that express the dopamine transporter (DAT), the level of which is altered in individuals with heroin use disorder. Astrocytes are therefore uniquely placed functionally to bridge dopamine-dependent mechanisms across the striatum. Here we tested the hypothesis that exposure to heroin influences the expression of DAT in striatal astrocytes across the striatum before the development of DLS-dependent incentive heroin seeking habits. Using Western-blot, qPCR, and RNAscope™, we measured DAT protein and mRNA levels in whole tissue, culture and in situ astrocytes from striatal territories of rats with a well-established cue-controlled heroin seeking habit and rats trained to respond for heroin or food under continuous reinforcement. Incentive heroin seeking habits were associated with a reduction in DAT protein levels in the anterior aDLS that was preceded by a heroin-induced reduction in DAT mRNA and protein in astrocytes across the striatum. Striatal astrocytes were also shown to be susceptible to direct dopamine- and opioid-induced downregulation of DAT expression. These results suggest that astrocytes may critically regulate the striatal dopaminergic adaptations that lead to the development of incentive heroin seeking habits., (© 2024 The Authors. European Journal of Neuroscience published by Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

Amphetamine (AMPH) exposure induces behavioural and neurochemical sensitization observed in rodents as hyperlocomotion and increased dopamine release in response to a subsequent dose. Brain Angiotensin II modulates dopaminergic neurotransmission through its AT 1 receptors (AT 1 -R), positively regulating striatal dopamine synthesis and release. This work aims to evaluate the AT 1 -R role in the development and maintenance of AMPH-induced sensitization. Also, the AT 1 -R involvement in striatal dopamine reuptake was analysed. The sensitization protocol consisted of daily AMPH administration for 5 days and tested 21 days after withdrawal. An AT 1 -R antagonist, candesartan, was administered before or after AMPH exposure to evaluate the participation of AT 1 -R in the development and maintenance of sensitization, respectively. Sensitization was evaluated by locomotor activity and c-Fos immunostaining. Changes in dopamine reuptake kinetics were evaluated 1 day after AT 1 -R blockade withdrawal treatment, with or without the addition of AMPH in vitro. The social interaction test was performed as another behavioural output. Repeated AMPH exposure induced behavioural and neurochemical sensitization, which was prevented and reversed by candesartan. The AT 1 -R blockade increased the dopamine reuptake kinetics. Neither the AMPH administration nor the AT 1 -R blockade altered the performance of social interaction. Our results highlight the AT 1 -R's crucial role in AMPH sensitization. The enhancement of dopamine reuptake kinetics induced by the AT 1 -R blockade might attenuate the neuroadaptive changes that lead to AMPH sensitization and its self-perpetuation. Therefore, AT 1 -R is a prominent candidate as a target for pharmacological treatment of pathologies related to dopamine imbalance, including drug addiction and schizophrenia., (© 2024 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

Dopaminergic neurons of the substantia nigra exist in a persistent state of vulnerability resulting from high baseline oxidative stress, high-energy demand, and broad unmyelinated axonal arborisations. Impairments in the storage of dopamine compound this stress because of cytosolic reactions that transform the vital neurotransmitter into an endogenous neurotoxicant, and this toxicity is thought to contribute to the dopamine neuron degeneration that occurs Parkinson's disease. We have previously identified synaptic vesicle glycoprotein 2C (SV2C) as a modifier of vesicular dopamine function, demonstrating that genetic ablation of SV2C in mice results in decreased dopamine content and evoked dopamine release in the striatum. Here, we adapted a previously published in vitro assay utilising false fluorescent neurotransmitter 206 (FFN206) to visualise how SV2C regulates vesicular dopamine dynamics and determined that SV2C promotes the uptake and retention of FFN206 within vesicles. In addition, we present data indicating that SV2C enhances the retention of dopamine in the vesicular compartment with radiolabelled dopamine in vesicles isolated from immortalised cells and from mouse brain. Further, we demonstrate that SV2C enhances the ability of vesicles to store the neurotoxicant 1-methyl-4-phenylpyridinium (MPP + ) and that genetic ablation of SV2C results in enhanced 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced vulnerability in mice. Together, these findings suggest that SV2C functions to enhance vesicular storage of dopamine and neurotoxicants and helps maintain the integrity of dopaminergic neurons., (© 2024 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

The enteric nervous system (ENS) comprises a complex network of neurons whereby a subset appears to be dopaminergic although the characteristics, roles, and implications in disease are less understood. Most investigations relating to enteric dopamine (DA) neurons rely on immunoreactivity to tyrosine hydroxylase (TH)-the rate-limiting enzyme in the production of DA. However, TH immunoreactivity is likely to provide an incomplete picture. This study herein provides a comprehensive characterization of DA neurons in the gut using a reporter mouse line, expressing a fluorescent protein (tdTomato) under control of the DA transporter (DAT) promoter. Our findings confirm a unique localization of DA neurons in the gut and unveil the discrete subtypes of DA neurons in this organ, which we characterized using both immunofluorescence and single-cell transcriptomics, as well as validated using in situ hybridization. We observed distinct subtypes of DAT-tdTomato neurons expressing co-transmitters and modulators across both plexuses; some of them likely co-releasing acetylcholine, while others were positive for a slew of canonical DAergic markers (TH, VMAT2 and GIRK2). Interestingly, we uncovered a seemingly novel population of DA neurons unique to the ENS which was ChAT/DAT-tdTomato-immunoreactive and expressed Grp, Calcb, and Sst. Given the clear heterogeneity of DAergic gut neurons, further investigation is warranted to define their functional signatures and decipher their implication in disease., (© 2024 The Authors. European Journal of Neuroscience published by Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

Psychostimulant use disorders (PSUD) are prevalent; however, no FDA-approved medications have been made available for treatment. Previous studies have shown that dual inhibitors of the dopamine transporter (DAT) and sigma receptors significantly reduce the behavioral/reinforcing effects of cocaine, which have been associated with stimulation of extracellular dopamine (DA) levels resulting from DAT inhibition. Here, we employ microdialysis and fast scan cyclic voltammetry (FSCV) procedures to investigate the effects of dual inhibitors of DAT and sigma receptors in combination with cocaine on nucleus accumbens shell (NAS) DA dynamics in naïve male Sprague Dawley rats. In microdialysis studies, administration of rimcazole (3, 10 mg/kg; i.p.) or its structural analog SH 3-24 (1, 3 mg/kg; i.p.), compounds that are dual inhibitors of DAT and sigma receptors, significantly reduced NAS DA efflux stimulated by increasing doses of cocaine (0.1, 0.3, 1.0 mg/kg; i.v.). Using the same experimental conditions, in FSCV tests, we show that rimcazole pretreatments attenuated cocaine-induced stimulation of evoked NAS DA release but produced no additional effect on DA clearance rate. Under the same conditions, JJC8-091, a modafinil analog and dual inhibitor of DAT and sigma receptors, similarly attenuated cocaine-induced stimulation of evoked NAS DA release but produced no additional effect on DA clearance rate. Our results provide the neurochemical groundwork towards understanding actions of dual inhibitors of DAT and sigma receptors on DA dynamics that likely mediate the behavioral effects of psychostimulants like cocaine., (Published 2024. This article is a U.S. Government work and is in the public domain in the USA.)

Deficits in cost/benefit decision making is a critical risk factor for gambling disorder. Reward-paired cues may play an important role, as these stimuli can enhance risk preference in rats. Despite extensive research implicating the dorsal striatum in the compulsive aspects of addiction, the role of nigrostriatal dopaminergic activity in cue-induced risk preference remains unclear, particularly in females. Accordingly, we examined the effects of manipulating the dopaminergic nigrostriatal pathway on cue-induced risky choice in female rats. TH:Cre rats were trained on the cued version of the rat Gambling Task. This task was designed such that maximal reward is attained by avoiding the high-risk, high-reward options and instead favouring the options associated with lower per-trial gains, as they feature less frequent and shorter time-out penalties. Adding reward-paired audiovisual cues to the task leads to greater risky choice on average. To assess the role of the nigrostriatal pathway, a viral vector carrying either Cre-dependent inhibitory or excitatory DREADD was infused into the substantia nigra. Rats then received clozapine-N-oxide either during task acquisition or after a stable performance baseline was reached. Inhibition of this pathway accelerated the development of risk preference in early sessions and increased risky choice during performance, but long-term inhibition actually improved decision making. Activation of this pathway had minimal effects. These results provide evidence for the involvement of the dopaminergic nigrostriatal pathway in cue-induced risk preference in females, therefore shedding light on its role in cost/benefit decision-making deficits and expanding our knowledge of the female dopaminergic system., (© 2024 The Authors. European Journal of Neuroscience published by Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

The orbitofrontal cortex (OFC) is a key node in the cortico-limbic-striatal circuitry that influences decision-making guided by the relative value of outcomes. Midbrain dopamine from either the ventral tegmental area (VTA) or the dorsal raphe nucleus (DRN) has the potential to modulate OFC neurons; however, it is unknown at what concentrations these terminals release dopamine. Male and female adult dopamine transporter (DAT) IRES-Cre -tdTomato mice were injected with AAV2/8-EF1a-DIO-eYFP into either the DRN or the VTA or the retrograde label cholera toxin B (CTB) 488 in the medial or lateral OFC. We quantified co-expression of CTB 488 or enhanced yellow fluorescent protein (eYFP) with tdTomato fluorescence in VTA or DRN and eYFP fibre density in the medial or lateral OFC. Both VTA and DRN dopamine neurons project to either the medial OFC or the lateral OFC, with greater expression of fibres in the medial OFC. Using fast-scan cyclic voltammetry, we detected optogenetically evoked dopamine from channelrhodopsin 2 (ChR2)-expressing VTA or DRN dopamine terminals in either the medial OFC or the lateral OFC. We assessed if optical stimulation of dopamine from the VTA or the DRN onto the medial OFC could alter layer V pyramidal neuronal firing; however, we did not observe a change in firing at stimulation parameters that evoked dopamine release from either projection even though bath application of dopamine with the monoamine transporter inhibitor, nomifensine, decreased firing. In summary, dopaminergic neurons from the VTA or the DRN project to the OFC and release submicromolar dopamine in the medial and lateral OFC., (© 2023 The Authors. European Journal of Neuroscience published by Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

Parkinson's disease (PD) is characterized by the accumulation of misfolded alpha-synuclein (α-syn) protein, forming intraneuronal Lewy body (LB) inclusions. The α-syn preformed fibril (PFF) model of PD recapitulates α-syn aggregation, progressive nigrostriatal degeneration and motor dysfunction; however, little is known about the time course of PFF-induced alterations in basal and evoked dopamine (DA). In vivo microdialysis is well suited for identifying small changes in neurotransmitter levels over extended periods. In the present study, adult male Fischer 344 rats received unilateral, intrastriatal injections of either α-syn PFFs or phosphate-buffered saline (PBS). At 4 or 8 months post-injection (p.i.), animals underwent in vivo microdialysis to evaluate basal extracellular striatal DA and metabolite levels, local KCl-evoked striatal DA release and the effects of systemic levodopa (l-DOPA). Post-mortem analysis demonstrated equivalent PFF-induced reductions in tyrosine hydroxylase (TH) immunoreactive nigral neurons (~50%) and striatal TH (~20%) at both time points. Compared with reduction in striatal TH, reduction in striatal dopamine transporter (DAT) was more pronounced and progressed between the 4- and 8-month p.i. intervals (36% ➔ 46%). Significant PFF-induced deficits in basal and evoked striatal DA, as well as deficits in motor performance, were not observed until 8 months p.i. Responses to l-DOPA did not differ regardless of PBS or PFF treatment. These results suggest that basal and evoked striatal DA are maintained for several months following PFF injection, with loss of both associated with motor dysfunction. Our studies provide insight into the time course and magnitude of PFF-induced extracellular dopaminergic deficits in the striatum., (© 2024 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

While colloquially recognized for its role in pleasure, reward, and affect, dopamine is also necessary for proficient action control. Many motor studies focus on dopaminergic transmission along the nigrostriatal pathway, using Parkinson's disease as a model of a dorsal striatal lesion. Less attention to the mesolimbic pathway and its role in motor control has led to an important question related to the limbic-motor network. Indeed, secondary targets of the mesolimbic pathway include the hippocampus and amygdala, and these are linked to the motor cortex through the substantia nigra and thalamus. The modulatory impact of dopamine in the hippocampus and amygdala in humans is a focus of current investigations. This review explores dopaminergic activity in the mesial temporal lobe by summarizing dopaminergic networks and transmission in these regions and examining their role in behaviour and disease., (© 2023 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

The dendritic arbour of striatal projection neurons (SPNs) is the primary anatomical site where dopamine and glutamate inputs to the basal ganglia functionally interact to control movement. These dendritic arbourisations undergo atrophic changes in Parkinson's disease. A reduction in the dendritic complexity of SPNs is found also in animal models with severe striatal dopamine denervation. Using 6-hydroxydopamine (6-OHDA) lesions of the medial forebrain bundle as a model, we set out to compare morphological and electrophysiological properties of SPNs at an early versus a chronic stage of dopaminergic degeneration. Ex vivo recordings were performed in transgenic mice where SPNs forming the direct pathway (dSPNs) express a fluorescent reporter protein. At both the time points studied (5 and 28 days following 6-OHDA lesion), there was a complete loss of dopaminergic fibres through the dorsolateral striatum. A reduction in dSPN dendritic complexity and spine density was manifest at 28, but not 5 days post-lesion. At the late time point, dSPN also exhibited a marked increase in intrinsic excitability (reduced rheobase current, increased input resistance, more evoked action potentials in response to depolarising currents), which was not present at 5 days. The increase in neuronal excitability was accompanied by a marked reduction in inward-rectifying potassium (Kir) currents (which dampen the SPN response to depolarising stimuli). Our results show that dSPNs undergo delayed coordinate changes in dendritic morphology, intrinsic excitability and Kir conductance following dopamine denervation. These changes are predicted to interfere with the dSPN capacity to produce a normal movement-related output., (© 2023 The Authors. European Journal of Neuroscience published by Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

Dopamine, a catecholamine neurotransmitter, has historically been associated with the encoding of reward, whereas its role in aversion has received less attention. Here, we systematically gathered the vast evidence of the role of dopamine in the simplest forms of aversive learning: classical fear conditioning and extinction. In the past, crude methods were used to augment or inhibit dopamine to study its relationship with fear conditioning and extinction. More advanced techniques such as conditional genetic, chemogenic and optogenetic approaches now provide causal evidence for dopamine's role in these learning processes. Dopamine neurons encode conditioned stimuli during fear conditioning and extinction and convey the signal via activation of D 1-4 receptor sites particularly in the amygdala, prefrontal cortex and striatum. The coordinated activation of dopamine receptors allows for the continuous formation, consolidation, retrieval and updating of fear and extinction memory in a dynamic and reciprocal manner. Based on the reviewed literature, we conclude that dopamine is crucial for the encoding of classical fear conditioning and extinction and contributes in a way that is comparable to its role in encoding reward., (© 2023 The Authors. European Journal of Neuroscience published by Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

Parkinson's disease (PD) is a neurodegenerative disorder characterized by progressive dysfunction and loss of dopaminergic neurons of the substantia nigra pars compacta (SNc). Several pathways of programmed cell death are likely to play a role in dopaminergic neuron death, such as apoptosis, necrosis, pyroptosis and ferroptosis, as well as cell death associated with proteasomal and mitochondrial dysfunction. A better understanding of the molecular mechanisms underlying dopaminergic neuron death could inform the design of drugs that promote neuron survival. Necroptosis is a recently characterized regulated cell death mechanism that exhibits morphological features common to both apoptosis and necrosis. It requires activation of an intracellular pathway involving receptor-interacting protein 1 kinase (RIP1 kinase, RIPK1), receptor-interacting protein 3 kinase (RIP3 kinase, RIPK3) and mixed lineage kinase domain-like pseudokinase (MLKL). The potential involvement of this programmed cell death pathway in the pathogenesis of PD has been studied by analysing biomarkers for necroptosis, such as the levels and oligomerization of phosphorylated RIPK3 (pRIPK3) and phosphorylated MLKL (pMLKL), in several PD preclinical models and in PD human tissue. Although there is evidence that other types of cell death also have a role in DA neuron death, most studies support the hypothesis that this cell death mechanism is activated in PD tissues. Drugs that prevent or reduce necroptosis may provide neuroprotection for PD. In this review, we summarize the findings from these studies. We also discuss how manipulating necroptosis might open a novel therapeutic approach to reduce neuronal degeneration in PD., (© 2023 The Authors. European Journal of Neuroscience published by Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

Ca 2+ entry into nigrostriatal dopamine (DA) neurons and axons via L-type voltage-gated Ca 2+ channels (LTCCs) contributes, respectively, to pacemaker activity and DA release and has long been thought to contribute to vulnerability to degeneration in Parkinson's disease. LTCC function is greater in DA axons and neurons from substantia nigra pars compacta than from ventral tegmental area, but this is not explained by channel expression level. We tested the hypothesis that LTCC control of DA release is governed rather by local mechanisms, focussing on candidate biological factors known to operate differently between types of DA neurons and/or be associated with their differing vulnerability to parkinsonism, including biological sex, α-synuclein, DA transporters (DATs) and calbindin-D28k (Calb1). We detected evoked DA release ex vivo in mouse striatal slices using fast-scan cyclic voltammetry and assessed LTCC support of DA release by detecting the inhibition of DA release by the LTCC inhibitors isradipine or CP8. Using genetic knockouts or pharmacological manipulations, we identified that striatal LTCC support of DA release depended on multiple intersecting factors, in a regionally and sexually divergent manner. LTCC function was promoted by factors associated with Parkinsonian risk, including male sex, α-synuclein, DAT and a dorsolateral co-ordinate, but limited by factors associated with protection, that is, female sex, glucocerebrosidase activity, Calb1 and ventromedial co-ordinate. Together, these data show that LTCC function in DA axons and isradipine effect are locally governed and suggest they vary in a manner that in turn might impact on, or reflect, the cellular stress that leads to parkinsonian degeneration., (© 2023 The Authors. European Journal of Neuroscience published by Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

Abnormalities in dopamine function might be related to psychiatric disorders such as schizophrenia. Even at the same concentration, dopamine exerts opposite effects on information processing in the prefrontal cortex depending on independent dopamine release modes known as tonic and phasic releases. This duality of dopamine prevents a blanket interpretation of the implications of dopamine abnormalities for diseases on the basis of absolute dopamine levels. Moreover, the mechanisms underlying the mode-specific dopamine abnormalities are not clearly understood. Here, I show that the two modes of dopamine release in the prefrontal cortex of a schizophrenia-like model are disrupted by different mechanisms. In the schizophrenia-like model established by perinatal exposure to inflammatory cytokine, epidermal growth factor, tonic release was enhanced and phasic release was decreased in the prefrontal cortex. I examined the activity of dopamine neurons in the ventral tegmental area (VTA), which sends dopamine projections to the prefrontal cortex, under anaesthesia. The activation of VTA dopamine neurons during excitatory stimulation (local application of glutamate or N-methyl-d-aspartic acid [NMDA]), which is associated with phasic activity, was blunt in this model. Dopaminergic neuronal activity in the resting state related to tonic release was increased by disinhibition of the dopamine neurons due to the impairment of 5HT2 (5HT2A) receptor-regulated GABAergic inputs. Moreover, chronic administration of risperidone ameliorated this disinhibition of dopaminergic neurons. These results provide an idea about the mechanism of dopamine disturbance in schizophrenia and may be informative in explaining the effects of atypical antipsychotics as distinct from those of typical drugs., (© 2023 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

Astrocytes, the most abundant glial cells in the central nervous system, respond to a wide variety of neurotransmitters binding to metabotropic receptors. Here, we investigated the intracellular calcium responses of spinal cord astrocytes to dopamine and noradrenaline, two catecholamines released by specific descending pathways. In a slice preparation from the spinal cord of neonatal mice, puff application of dopamine resulted in intracellular calcium responses that remained in the endfeet. Noradrenaline induced stronger responses that also started in the endfeet but spread to neighbouring compartments. The intracellular calcium responses were unaffected by blocking neuronal activity or inhibiting various neurotransmitter receptors, suggesting a direct effect of dopamine and noradrenaline on astrocytes. The intracellular calcium responses induced by noradrenaline and dopamine were inhibited by the D 1 receptor antagonist SCH 23390. We assessed the functional consequences of these astrocytic responses by examining changes in arteriole diameter. Puff application of dopamine or noradrenaline resulted in vasoconstriction of spinal arterioles. However, blocking D 1 receptors or manipulating astrocytic intracellular calcium levels did not abolish the vasoconstrictions, indicating that the observed intracellular calcium responses in astrocyte endfeet were not responsible for the vascular changes. Our findings demonstrate a compartmentalized response of spinal cord astrocytes to catecholamines and expand our understanding of astrocyte-neurotransmitter interactions and their potential roles in the physiology of the central nervous system., (© 2023 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

Astrocytes, glial cells in the central nervous system, perform a multitude of homeostatic functions and are in constant bidirectional communication with neuronal cells, a concept named the tripartite synapse; however, their role in the dopamine homeostasis remains unexplored. The aim of this study was to clarify the pharmacological and molecular characteristics of dopamine transport in cultured cortical astrocytes of adult rats. In addition, we were interested in the expression of mRNA of dopamine transporters as well as dopamine receptors D1 and D2 and in the effect of dopaminergic drugs on the expression of these transporters and receptors. We have found that astrocytes possess both Na + -dependent and Na + -independent transporters. Uptake of radiolabelled dopamine was time-, temperature- and concentration-dependent and was inhibited by decynium-22, a plasma membrane monoamine transporter inhibitor, tricyclic antidepressants desipramine and nortriptyline, both inhibitors of the norepinephrine transporter. Results of transporter mRNA expression indicate that the main transporters involved in cortical astrocyte dopamine uptake are the norepinephrine transporter and plasma membrane monoamine transporter. Both dopamine receptor subtypes were identified in cortical astrocyte cultures. Twenty-four-hour treatment of astrocyte cultures with apomorphine, a D1/D2 agonist, induced upregulation of D1 receptor, norepinephrine transporter and plasma membrane monoamine transporter, whereas the latter was downregulated by haloperidol and L-DOPA. Astrocytes take up dopamine by multiple transporters and express dopamine receptors, which are sensitive to dopaminergic drugs. The findings of this study could open a promising area of research for the fine-tuning of existing therapeutic strategies., (© 2023 The Authors. European Journal of Neuroscience published by Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

Millions of people suffer from dopamine-related disorders spanning disturbances in movement, cognition and emotion. These changes are often attributed to changes in striatal dopamine function. Thus, understanding how dopamine signalling in the striatum and basal ganglia shapes human behaviour is fundamental to advancing the treatment of affected patients. Dopaminergic neurons innervate large-scale brain networks, and accordingly, many different roles for dopamine signals have been proposed, such as invigoration of movement and tracking of reward contingencies. The canonical circuit architecture of cortico-striatal loops sparks the question, of whether dopamine signals in the basal ganglia serve an overarching computational principle. Such a holistic understanding of dopamine functioning could provide new insights into symptom generation in psychiatry to neurology. Here, we review the perspective that dopamine could bidirectionally control neural population dynamics, increasing or decreasing their strength and likelihood to reoccur in the future, a process previously termed neural reinforcement. We outline how the basal ganglia pathways could drive strengthening and weakening of circuit dynamics and discuss the implication of this hypothesis on the understanding of motor signs of Parkinson's disease (PD), the most frequent dopaminergic disorder. We propose that loss of dopamine in PD may lead to a pathological brain state where repetition of neural activity leads to weakening and instability, possibly explanatory for the fact that movement in PD deteriorates with repetition. Finally, we speculate on how therapeutic interventions such as deep brain stimulation may be able to reinstate reinforcement signals and thereby improve treatment strategies for PD in the future., (© 2023 The Authors. European Journal of Neuroscience published by Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

The existent pre-clinical models of Parkinson's disease do not simultaneously recapitulate severe degeneration of dopamine neurons and the occurrence of alpha-synuclein (aSyn) aggregation in one study system. In this study, we injected aSyn pre-formed fibrils (PFF) and 6-hydroxydopamine (6-OHDA) unilaterally into the striatum of C57BL/6 wild-type male mice at an interval of 2 weeks to induce aggregation of aSyn protein and trigger the loss of dopamine neurons simultaneously in one model and studied the behavioural effects of the combination in these mice. 6-OHDA was tested at three different doses, and 2 μg of 6-OHDA combined with PFF-induced aSyn aggregation was found to produce the most optimal disease phenotype. At 14 weeks timepoint, mice injected with a combination of PFF and 6-OHDA sustained significant damage to the nigrostriatal pathway and exhibited aSyn-positive aggregation. Our data suggest that the neurons that formed large aSyn aggregates were particularly vulnerable to 6-OHDA-induced degeneration. We also demonstrate the manifestation of a relatively aggressive pathology in 2- to 4-month-old mice, as compared to younger 7- to 9-week-old ones. Furthermore, cerebral dopamine neurotrophic factor (CDNF) administered intrastriatally rescued dopamine neurons and motor behaviour of the animals to some extent from 6-OHDA toxicity. However, no such effect could be seen in the novel 6-OHDA + PFFs combination model. For the first time, we demonstrate the combined effect of PFF and 6-OHDA simultaneously in one model. We further discuss the scope for further optimizing this combination model to develop it as a promising pre-clinical platform for drug screening and development., (© 2023 The Authors. European Journal of Neuroscience published by Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

The greater the reward expectations are, the more different the brain's physiological response will be. Although it is well-documented that better-than-expected outcomes are encoded quantitatively via midbrain dopaminergic (DA) activity, it has been less addressed experimentally whether worse-than-expected outcomes are expressed quantitatively as well. We show that larger reward expectations upon unexpected reward omissions are associated with the preceding slower rise and following larger decrease (DA dip) in the DA concentration at the ventral striatum of mice. We set up a lever press task on a fixed ratio (FR) schedule requiring five lever presses as an effort for a food reward (FR5). The mice occasionally checked the food magazine without a reward before completing the task. The percentage of this premature magazine entry (PME) increased as the number of lever presses approached five, showing rising expectations with increasing proximity to task completion, and hence greater reward expectations. Fibre photometry of extracellular DA dynamics in the ventral striatum using a fluorescent protein (genetically encoded GPCR activation-based DA sensor: GRAB DA2m ) revealed that the slow increase and fast decrease in DA levels around PMEs were correlated with the PME percentage, demonstrating a monotonic relationship between the DA dip amplitude and degree of expectations. Computational modelling of the lever press task implementing temporal difference errors and state transitions replicated the observed correlation between the PME frequency and DA dip amplitude in the FR5 task. Taken together, these findings indicate that the DA dip amplitude represents the degree of reward expectations monotonically, which may guide behavioural adjustment., (© 2023 The Authors. European Journal of Neuroscience published by Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

Drug seeking is associated with the ventral tegmental area (VTA) dopaminergic (DA) activity. Previously, we have shown that brief optogenetic inhibition of VTA DA neurons with 1 s pulses delivered every 9 s attenuates cocaine seeking under extinction conditions in rats without producing overt signs of dysphoria or locomotor sedation. Whether recruitment of neuronal pathways inhibiting VTA neuronal activity would suppress drug seeking remains unknown. Here, we asked if optogenetic stimulation of the lateral habenula (LHb) efferents in the rostromedial tegmental nucleus (RMTg) as well as RMTg efferents in VTA would reduce drug seeking. To investigate this, we measured how recruitment of elements of this inhibitory pathway affects cocaine seeking in male rats under extinction conditions. The effectiveness of brief optogenetic manipulations was confirmed electrophysiologically at the level of electrical activity of VTA DA neurons. Real-time conditioned place aversion (RT-CPA) and open field tests were performed to control for potential dysphoric/sedating effects of brief optogenetic stimulation of LHb-RMTg-VTA circuitry. Optogenetic stimulation of either RMTg or LHb inhibited VTA DAergic neuron firing, whereas similar stimulation of RMTg efferents in VTA or LHb efferents in RMTg reduced cocaine seeking under extinction conditions. Moreover, stimulation of LHb-RMTg efferents produced an effect that was maintained 24 h later, during cocaine seeking test without stimulation. This effect was specific, as brief optogenetic stimulation did not affect locomotor activity and was not aversive. Our results indicate that defined inhibitory pathways can be recruited to inhibit cocaine seeking, providing potential new targets for non-pharmacological treatment of drug craving., (© 2022 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

Upon stress exposure, a broad network of structures comes into play in order to provide adequate responses and restore homeostasis. It has been known for decades that the main structures engaged during the stress response are the medial prefrontal cortex, the amygdala, the hippocampus, the hypothalamus, the monoaminergic systems (noradrenaline, dopamine and serotonin) and the periaqueductal gray. The lateral habenula (LHb) is an epithalamic structure directly connected to prefrontal cortical areas and to the amygdala, whereas it functionally interacts with the hippocampus. Also, it is a main modulator of monoaminergic systems. The LHb is activated upon exposure to basically all types of stressors, suggesting it is also involved in the stress response. However, it remains unknown if and how the LHb functionally interacts with the broad stress response network. In the current study we performed in rats a restraint stress procedure followed by immunohistochemical staining of the c-Fos protein throughout the brain. Using graph theory-based functional connectivity analyses, we confirm the principal hubs of the stress network (e.g., prefrontal cortex, amygdala and periventricular hypothalamus) and show that the LHb is engaged during stress exposure in close interaction with the medial prefrontal cortex, the lateral septum and the medial habenula. In addition, we performed DREADD-induced LHb inactivation during the same restraint paradigm in order to explore its consequences on the stress response network. This last experiment gave contrasting results as the DREADD ligand alone, clozapine-N-oxide, was able to modify the network., (© 2022 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

In the glomerular layer of the olfactory bulb, local dopaminergic interneurons play a key role in regulating the flow of sensory information from nose to cortex. These dual dopamine- and GABA-releasing cells are capable of marked experience-dependent changes in the expression of neurotransmitter-synthesising enzymes, including tyrosine hydroxylase (TH). However, such plasticity has most commonly been studied in cell populations identified by their expression of the enzyme being studied and after long periods of sensory deprivation. Here, instead, we used brief 1- or 3-day manipulations of olfactory experience in juvenile mice, coupled with a conditional genetic approach that labelled neurons contingent upon their expression of the dopamine transporter (DAT-tdTomato). This enabled us to evaluate the potential for rapid changes in neurotransmitter-synthesising enzyme expression in an independently identified neuronal population. Our labelling strategy showed good specificity for olfactory bulb dopaminergic neurons, while revealing a minority sub-population of non-dopaminergic DAT-tdTomato cells that expressed the calcium-binding protein calretinin. Crucially, the proportions of these neuronal subtypes were not affected by brief alterations in sensory experience. Short-term olfactory manipulations also produced no significant changes in immunofluorescence or whole-bulb mRNA for the GABA-synthesising enzyme GAD67/Gad1. However, in bulbar DAT-tdTomato neurons, brief sensory deprivation was accompanied by a transient, small drop in immunofluorescence for the dopamine-synthesising enzyme dopa decarboxylase (DDC) and a sustained decrease for TH. Deprivation also produced a sustained decrease in whole-bulb Th mRNA. Careful characterisation of an independently identified, genetically labelled neuronal population therefore enabled us to uncover rapid experience-dependent changes in dopamine-synthesising enzyme expression., (© 2022 The Authors. European Journal of Neuroscience published by Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

Strategies for improving memory are increasingly studied, and exposure to a novel experience can be an efficient neuromodulator. Novelty effects on memory depend on D1-family dopamine receptors (D1Rs) activation. Here, we evaluated the novelty effect on memory persistence of Wistar rats and investigated the contribution of D1Rs and their signalling pathways by protein kinase A (PKA) and C (PKC). Animals with infusion cannulae inserted into the CA1 hippocampus area were trained on the novel object recognition (NOR) task, which involved exploring two different objects. After training, some rats received intrahippocampal infusions of vehicle or D1Rs agonist; others explored a novel environment for 5 min and were infused with a variety of drugs targeting D1Rs and their signalling pathways. We demonstrated that pharmacological stimulation of D1Rs or novelty exposure promoted NOR memory persistence for 14 days and that the novelty effect depended on D1Rs activation. To determine if the D1 and D5 receptor subtypes were necessary for the impact of novelty exposure on memory, we blocked or stimulated PKA or PKC-protein kinases activated mainly by D1 and D5, respectively. Only PKA inhibition impaired the effect of novelty on memory persistence. After novelty and D1Rs blocking, PKA but not PKC stimulation maintained the memory persistence effect. Thus, we concluded that novelty promoted memory persistence by a mechanism-dependent on activating hippocampal D1Rs and PKA pathway., (© 2021 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

The ventral tegmental area (VTA) has three major classes of neurons: dopaminergic (expressing tyrosine hydroxylase; TH), GABAergic (expressing vesicular GABA transporter; VGaT) and glutamatergic (expressing vesicular glutamate transporter 2; VGluT2). While VTA dopaminergic and GABAergic neurons have been further characterized by expression of calcium-binding proteins (calbindin, CB; calretinin, CR or parvalbumin, PV), it is unclear whether these proteins are expressed in rat VTA glutamatergic neurons. Here, by a combination of in situ hybridization (for VGluT2 mRNA detection) and immunohistochemistry (for CB-, CR- or PV-detection), we found that among the total population of VGluT2 neurons, 30% coexpressed CB, 3% coexpressed PV and <1% coexpressed CR. Given that some VGluT2 neurons coexpress TH or VGaT, we examined whether these neurons coexpress CB, and found that about 20% of VGluT2-CB neurons coexpressed TH and about 13% coexpressed VGaT. Because VTA TH-CB neurons are known to target the nucleus accumbens (nAcc), we determined whether VGluT2-CB-TH neurons innervate nAcc, and found that about 80% of VGluT2-CB neurons innervating the nAcc shell coexpressed TH. In summary, (a) CB, PV and CR are detected in subpopulations of VTA-VGluT2 neurons; (b) CB is the main calcium-binding protein present in VTA-VGluT2 neurons; (c) one-third of VTA-VGluT2 neurons coexpress CB; (d) some VTA-VGluT2-CB neurons have the capability to co-release dopamine or GABA, and (e) a subpopulation of VTA glutamatergic-dopaminergic neurons innervates nAcc shell. These findings further provide evidence for molecular diversity among VTA-VGluT2 neurons, neurons that may play a role in specific circuitry and behaviours., (Published 2019. This article is a U.S. Government work and is in the public domain in the USA.)

Gait and postural control deficiencies in Parkinson's disease (PD) involve several specific motor aspects. The aim of this study was to identify and compare the main changes in gait kinematics and postural control with dopaminergic loss in the striatum region. This is a cross-sectional study that included 42 individuals with PD at different motor stages, according to the Hoehn & Yahr scale (H&Y). Motor subsection of the Movement Disorder Society-Unified Parkinson Disease Rating Scale-part III (MDS-UPDRS III) was used to evaluate general motor aspects. Gait kinematics was assessed using a three-dimensional motion capture system. Postural control was assessed by stabilometry using force platforms. Dopamine depletion was verified through 99mTc-TRODAT-1 (SPECT-CT) examination. We included 12, 15 and 15 individuals classified as H&Y I, II and III, respectively. We identified worse values of dopamine transporter uptake, MDS-UPDRS III, gait parameters (velocity, step length and stride length) and center of pressure displacement as the disease progressed. Our results indicate that higher dopaminergic loss and gait and postural control deficits occur between the H&Y levels II and III., (© 2019 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

Nucleus accumbens dopamine plays a key role in reward-directed approach. Past findings suggest that dopamine's role in the expression of learned behavior diminishes with extended training. However, little is known about the central substrates that mediate the shift to dopamine-independent reward approach. In the present study, rats approached and inserted the head into a reward compartment in response to a cue signaling food delivery. On days 4 and 5 of 28-trial-per-day sessions, D1 receptor antagonist R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride (SCH23390) infused to the NAc core reduced the probability and speed of cued approach. The disruptive effect of D1 receptor blockade was specific to the nucleus accumbens core and not seen with drug infusions to nearby dopamine target regions. In rats that received drug infusions after extended training (days 10 or 11), accumbens core D1 receptor blockade produced little effect on the expression of the same behavior. These results could have been due to a continued accumbens mediation of cued approach even after the behavior had become independent of accumbens D1 receptors. However, accumbens core ionotropic glutamate receptor blockade disrupted cued approach during early but not late stages of training, similar to the effects of D1 antagonist infusions. The results suggest that with extended training, a nucleus accumbens D1-dependent behavior becomes less dependent not only on nucleus accumbens D1 transmission but also on excitatory transmission in the nucleus accumbens. These findings fill an important gap in a growing literature on reorganization of striatal function over the course of training., (© 2019 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

The transition from recreational drug use to compulsive drug-seeking habits, the hallmark of addiction, has been shown to depend on a shift in the locus of control over behaviour from the ventral to the dorsolateral striatum. This process has hitherto been considered to depend on the aberrant engagement of dopamine-dependent plasticity processes within neuronal networks. However, exposure to drugs of abuse also triggers cellular and molecular adaptations in astrocytes within the striatum which could potentially contribute to the intrastriatal transitions observed during the development of drug addiction. Pharmacological interventions aiming to restore the astrocytic mechanisms responsible for maintaining homeostatic glutamate concentrations in the nucleus accumbens, that are altered by chronic exposure to addictive drugs, abolish the propensity to relapse in both preclinical and, to a lesser extent, clinical studies. Exposure to drugs of abuse also alters the function of astrocytes in the dorsolateral striatum, wherein dopaminergic mechanisms control drug-seeking habits, associated compulsivity and relapse. This suggests that drug-induced alterations in the glutamatergic homeostasis maintained by astrocytes throughout the entire striatum may interact with dopaminergic mechanisms to promote aberrant plasticity processes that contribute to the maintenance of maladaptive drug-seeking habits. Capitalising on growing evidence that astrocytes play a fundamental regulatory role in glutamate and dopamine transmission in the striatum, we present an innovative model of a quadripartite synaptic microenvironment within which astrocytes channel functional interactions between the dopaminergic and glutamatergic systems that may represent the primary striatal functional unit that undergoes drug-induced adaptations eventually leading to addiction., (© 2019 The Authors. European Journal of Neuroscience published by Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

Chronic neuropathic pain and psychological stress interact to compromise goal-directed control over behaviour following mild psychological stress. The dorsomedial (DMS) and dorsolateral (DLS) striatum in the rat are crucial for the expression of goal-directed and habitual behaviours, respectively. This study investigated whether changes in monoamine levels in the DMS and DLS following nerve injury and psychological stress reflect these behavioural differences. Neuropathic pain was induced by a chronic constriction injury (CCI) of the sciatic nerve in Sprague-Dawley rats. Acute stress was induced using a 15-min restraint. Behavioural flexibility was assessed using the outcome devaluation paradigm. Noradrenaline, serotonin, dopamine and associated metabolites were measured bilaterally from the DLS and DMS. In uninjured rats, restraint increased dopaminergic markers in the left and serotonergic markers in the right of both the DMS and DLS, indicating a possible left hemisphere-mediated dominance. CCI led to a slightly different lateralised effect, with a larger effect in the DMS than in the DLS. Individual differences in behavioural flexibility following CCI negatively correlated with dopaminergic markers in the right DLS, but positively correlated with these markers in the left DMS. A combination of CCI and restraint reduced behavioural flexibility, which was associated with the loss of the left/DMS dominance. These data suggest that behavioural flexibility following psychological stress or pain is associated with a left hemisphere dominance within the dorsal striatum. The loss of behavioural flexibility following the combined stressors is then associated with a transition from left to right, and DMS to DLS dominance., (© 2019 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

Grooming behaviour has different functions on many species during development and can be observed and affected during periods of stress. By selecting male mice with high (HI) and low (LI) immobility traits in the tail suspension test, a screening for antidepressant drugs, we investigate how these phenotypes associated with grooming behaviour may be influenced by the effects of repeated restraint stress. For this we used the sucrose preference test and the splash test in a novel and a familiar cage performed before and after exposure to 2 days of restraint stress. Animals were submitted to an additional day of restraint stress before the hypothalamus, prefrontal cortex and midbrain extraction for dopamine activity analysis. Corticosterone analysis was made in three distinct moments: without stress (prior first restraint session), immediately after the last restrain, and 1 hr after the last restrain episode. Compared to LI group, HI animals exhibited an increased frequency and decreased time of grooming in the familiar cage. In the novel cage, stress increased frequency and time of grooming of HI animals compared to LI. Corticosterone levels were increased in HI animals after 3 days of stress. Lower hypothalamic dopaminergic activity without stress and decreased hypothalamic dopaminergic activity immediately after stress in HI group were observed. The HI group displayed decreased prefrontal cortex dopaminergic activity and increased activity in the mesolimbic area. We proposed that through the influence of stress the two phenotypes manifested as a resilient (LI) and a not resilient (HI) trait in response to restraint stress., (© 2019 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

A large body of data has identified numerous molecular targets through which ethanol (EtOH) acts on brain circuits. Yet how these multiple mechanisms interact to result in dysregulated dopamine (DA) release under the influence of alcohol in vivo remains unclear. In this manuscript, we delineate potential circuit-level mechanisms responsible for EtOH-dependent dysregulation of DA release from the ventral tegmental area (VTA) into its projection areas. For this purpose, we constructed a circuit model of the VTA that integrates realistic Glutamatergic (Glu) inputs and reproduces DA release observed experimentally. We modelled the concentration-dependent effects of EtOH on its principal VTA targets. We calibrated the model to reproduce the inverted U-shape dose dependence of DA neuron activity on EtOH concentration. The model suggests a primary role of EtOH-induced boost in the I h and AMPA currents in the DA firing-rate/bursting increase. This is counteracted by potentiated GABA transmission that decreases DA neuron activity at higher EtOH concentrations. Thus, the model connects well-established in vitro pharmacological EtOH targets with its in vivo influence on neuronal activity. Furthermore, we predict that increases in VTA activity produced by moderate EtOH doses require partial synchrony and relatively low rates of the Glu afferents. We propose that the increased frequency of transient (phasic) DA peaks evoked by EtOH results from synchronous population bursts in VTA DA neurons. Our model predicts that the impact of acute ETOH on dopamine release is critically shaped by the structure of the cortical inputs to the VTA., (© 2018 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

Impulsive-compulsive spectrum disorders are associated with dopamine agonist therapy in some patients. These untoward outcomes occur with direct-acting, full and partial agonists at D2 dopamine family receptors. The disorders typically emerge during chronic treatment, and exhibit common features that are independent of the neurological or psychiatric pathology for which the initial therapy was indicated. It is well-documented that the brain is 'plastic', changing in response to alterations to internal factors (e.g., disease processes), as well as external factors (e.g., therapies). The complexities of these clinical scenarios have eluded a clear depiction of the neurobiology for impulsive-compulsive spectrum disorders and engendered considerable debate regarding the mechanistic underpinnings of the disorders. In this opinion, we use pharmacological concepts related to homeostatic compensation subsequent to chronic receptor activation to provide a unifying construct. This construct helps explain the occurrence of impulsive-compulsive spectrum disorders across disease states, and during therapy with full and partial agonists., (© 2018 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

Mesolimbic dopamine circuits, implicated in incentive motivation, are sensitive to changes in metabolic state such as weight loss and diet-induced obesity. These neurons are important targets for metabolic hormones such as leptin, glucagon-like peptide-1, ghrelin and insulin. Insulin receptors are located on dopamine neurons in the ventral tegmental area (VTA) and we have previously demonstrated that insulin induces long-term depression of excitatory synapses onto VTA dopamine neurons. While insulin can decrease dopamine concentration in somatodendritic regions, it can increase dopamine in striatal slices. Whether insulin directly targets the VTA to alter dopamine release in projection areas, such as the nucleus accumbens (NAc), remains unknown. The main goal of the present experiments was to examine NAc dopamine concentration following VTA administration of insulin. Using in vivo FSCV to detect rapid fluctuations in dopamine concentration, we showed that intra-VTA insulin via action at insulin receptors reduced pedunculopontine nucleus-evoked dopamine release in the NAc. Furthermore, intra-VTA insulin reduced cocaine-potentiated NAc dopamine. Finally, intra-VTA or intranasal insulin decreased locomotor responses to cocaine, an effect blocked by an intra-VTA administered insulin receptor antagonist. Together, these data demonstrate that mesolimbic dopaminergic projections are important targets of the metabolic hormone, insulin., (© 2018 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

Despite decades of research into the neurobiological basis of cocaine abuse, pharmacotherapeutic treatments for cocaine addiction have been largely ineffective. Converging evidence from preclinical research and from outpatient clinical trials suggest that treatment with amphetamine is efficacious in reducing cocaine intake. Although it has been suggested that amphetamine treatment reduces cocaine intake as an agonist replacement therapy, we have shown recently that multiple aspects of dopamine signaling are altered by cocaine self-administration and returned to pre-cocaine function by amphetamine treatment in the nucleus accumbens of male rats. Here, we sought to determine if these effects were also evident in female subjects, and across regions of the striatum. Female rats performed 5 days of cocaine self-administration (1.5 mg kg -1  inj -1 , 40 inj/day) and were treated with a single amphetamine (0.56 mg/kg) or saline infusion 1 hr prior to killing. We then used ex vivo fast-scan cyclic voltammetry in the nucleus accumbens core or dorsolateral caudate-putamen to examine dopamine signaling and cocaine potency. We found that in the nucleus accumbens core, cocaine self-administration decreased dopamine uptake rate and cocaine potency, and both alterations were restored by amphetamine treatment. In the dorsolateral caudate-putamen, neither cocaine self-administration nor amphetamine treatment altered dopamine uptake; however, cocaine potency was decreased by self-administration and returned to control levels by amphetamine. Together, these findings support a role for amphetamine treatment for cocaine addiction outside of agonist replacement therapy, and suggest that the development of cocaine tolerance is similar across sexes., (© 2019 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

The temporal pattern of drug use (pharmacokinetics) has a profound effect on the ability of self-administered cocaine to produce addiction-like behavior in rodents, and to change the brain. To further address this issue, we compared the effects of long access (LgA) cocaine self-administration, which is widely used to model the transition to addiction, with intermittent access (IntA), which is thought to better reflect the pattern of drug use in humans, on the ability of a single, self-administered injection of cocaine to increase dopamine (DA) overflow in the core of the nucleus accumbens (using in vivo microdialysis), and to produce addiction-like behavior. IntA experience was more effective than LgA in producing addiction-like behavior-a drug experience-dependent increase in motivation for cocaine assessed using behavioral economic procedures, and cue-induced reinstatement-despite much less total drug consumption. There were no group differences in basal levels of DA in dialysate [DA], but a single self-administered IV injection of cocaine increased [DA] in the core of the nucleus accumbens to a greater extent in rats with prior IntA experience than those with LgA or limited access experience, and the latter two groups did not differ. Furthermore, high motivation for cocaine was associated with a high [DA] response. Thus, IntA, but not LgA, produced both incentive and DA sensitization. This is consistent with the notion that a hyper-responsive dopaminergic system may contribute to the transition from casual patterns of drug use to the problematic patterns that define addiction., (© 2019 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

For more than three decades it has been known, that striatal neurons become hyperactive after the loss of dopamine input, but the involvement of dopamine (DA) D1- or D2-receptor-expressing neurons has only been demonstrated indirectly. By recording neuronal activity using fluorescent calcium indicators in D1 or D2 eGFP-expressing mice, we showed that following dopamine depletion, both types of striatal output neurons are involved in the large increase in neuronal activity generating a characteristic cell assembly of particular neurons that dominate the pattern. When we expressed channelrhodopsin in all the output neurons, light activation in freely moving animals, caused turning like that following dopamine loss. However, if the light stimulation was patterned in pulses the animals circled in the other direction. To explore the neuronal participation during this stimulation we infected normal mice with channelrhodopsin and calcium indicator in striatal output neurons. In slices made from these animals, continuous light stimulation for 15 s induced many cells to be active together and a particular dominant group of neurons, whereas light in patterned pulses activated fewer cells in more variable groups. These results suggest that the simultaneous activity of a large dominant group of striatal output neurons is intimately associated with parkinsonian symptoms., (© 2019 The Authors. European Journal of Neuroscience published by Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

The striatum, the input structure of the basal ganglia, is a major site of learning and memory for goal-directed actions and habit formation. Spiny projection neurons of the striatum integrate cortical, thalamic, and nigral inputs to learn associations, with cortico-striatal synaptic plasticity as a learning mechanism. Signaling molecules implicated in synaptic plasticity are altered in alcohol withdrawal, which may contribute to overly strong learning and increased alcohol seeking and consumption. To understand how interactions among signaling molecules produce synaptic plasticity, we implemented a mechanistic model of signaling pathways activated by dopamine D1 receptors, acetylcholine receptors, and glutamate. We use our novel, computationally efficient simulator, NeuroRD, to simulate stochastic interactions both within and between dendritic spines. Dopamine release during theta burst and 20-Hz stimulation was extrapolated from fast-scan cyclic voltammetry data collected in mouse striatal slices. Our results show that the combined activity of several key plasticity molecules correctly predicts the occurrence of either LTP, LTD, or no plasticity for numerous experimental protocols. To investigate spatial interactions, we stimulate two spines, either adjacent or separated on a 20-μm dendritic segment. Our results show that molecules underlying LTP exhibit spatial specificity, whereas 2-arachidonoylglycerol exhibits a spatially diffuse elevation. We also implement changes in NMDA receptors, adenylyl cyclase, and G protein signaling that have been measured following chronic alcohol treatment. Simulations under these conditions suggest that the molecular changes can predict changes in synaptic plasticity, thereby accounting for some aspects of alcohol use disorder., (© 2018 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

The widely held view that the pathophysiology of Parkinson's disease arises from an under-activation of the direct pathway striatal spiny neurons (dSPNs) has gained support from a recently described weakening of the glutamatergic projection from the parafascicular nucleus (PfN) to dSPNs in experimental parkinsonism. However, the impact of the remodeling of the thalamostriatal projection cannot be fully appreciated without considering its impact on cholinergic interneurons (ChIs) that themselves preferentially activate indirect pathway spiny neurons (iSPNs). To study this thalamostriatal projection, we virally transfected with Cre-dependent channelrhodopsin-2 (ChR2) the PfN of Vglut2-Cre mice that were dopamine-depleted with 6-hydroxydopamine (6-OHDA). In parallel, we studied the corticostriatal projection to ChIs in 6-OHDA-treated transgenic mice expressing ChR2 under the Thy1 promoter. We found the 6-OHDA lesions failed to affect short-term synaptic plasticity or the size of unitary responses evoked optogenetically in either of these projections. However, we found that NMDA-to-AMPA ratios at PfN synapses-that were significantly larger than NMDA-to-AMPA ratios at cortical synapses-were reduced by 6-OHDA treatment, thereby impairing synaptic integration at PfN synapses onto ChIs. Finally, we found that application of an agonist of the D 5 dopamine receptors on ChIs potentiated NMDA currents without affecting AMPA currents or short-term plasticity selectively at PfN synapses. We propose that dopamine depletion leads to an effective de-potentiation of NMDA currents at PfN synapses onto ChIs which degrades synaptic integration. This selective remodeling of NMDA currents at PfN synapses may counter the selective weakening of PfN synapses onto dSPNs in parkinsonism., (© 2017 The Authors. European Journal of Neuroscience published by Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

Diet influences dopamine transmission in motor- and reward-related basal ganglia circuitry. In part, this reflects diet-dependent regulation of circulating and brain insulin levels. Activation of striatal insulin receptors amplifies axonal dopamine release in brain slices, and regulates food preference in vivo. The effect of insulin on dopamine release is indirect, and requires striatal cholinergic interneurons that express insulin receptors. However, insulin also acts directly on dopamine axons to increase dopamine uptake by promoting dopamine transporter (DAT) surface expression, counteracting enhanced dopamine release. Here, we determined the functional consequences of acute insulin exposure and chronic diet-induced changes in insulin on DAT activity after evoked dopamine release in striatal slices from adult ad-libitum fed (AL) rats and mice, and food-restricted (FR) or high-fat/high-sugar obesogenic (OB) diet rats. Uptake kinetics were assessed by fitting evoked dopamine transients to the Michaelis-Menten equation and extracting C peak and V max . Insulin (30 nm) increased both parameters in the caudate putamen and nucleus accumbens core of AL rats in an insulin receptor- and PI3-kinase-dependent manner. A pure effect of insulin on uptake was unmasked using mice lacking striatal acetylcholine, in which increased V max caused a decrease in C peak . Diet also influenced V max , which was lower in FR vs. AL. The effects of insulin on C peak and V max were amplified by FR but blunted by OB, consistent with opposite consequences of these diets on insulin levels and insulin receptor sensitivity. Overall, these data reveal acute and chronic effects of insulin and diet on dopamine release and uptake that will influence brain reward pathways., (© 2018 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

Dopamine-dependent synaptic plasticity is a candidate mechanism for reinforcement learning. A silent eligibility trace - initiated by synaptic activity and transformed into synaptic strengthening by later action of dopamine - has been hypothesized to explain the retroactive effect of dopamine in reinforcing past behaviour. We tested this hypothesis by measuring time-dependent modulation of synaptic plasticity by dopamine in adult mouse striatum, using whole-cell recordings. Presynaptic activity followed by postsynaptic action potentials (pre-post) caused spike-timing-dependent long-term depression in D1-expressing neurons, but not in D2 neurons, and not if postsynaptic activity followed presynaptic activity. Subsequent experiments focused on D1 neurons. Applying a dopamine D1 receptor agonist during induction of pre-post plasticity caused long-term potentiation. This long-term potentiation was hidden by long-term depression occurring concurrently and was unmasked when long-term depression blocked an L-type calcium channel antagonist. Long-term potentiation was blocked by a Ca 2+ -permeable AMPA receptor antagonist but not by an NMDA antagonist or an L-type calcium channel antagonist. Pre-post stimulation caused transient elevation of rectification - a marker for expression of Ca 2+ -permeable AMPA receptors - for 2-4-s after stimulation. To test for an eligibility trace, dopamine was uncaged at specific time points before and after pre- and postsynaptic conjunction of activity. Dopamine caused potentiation selectively at synapses that were active 2-s before dopamine release, but not at earlier or later times. Our results provide direct evidence for a silent eligibility trace in the synapses of striatal neurons. This dopamine-timing-dependent plasticity may play a central role in reinforcement learning., (© 2018 The Authors. European Journal of Neuroscience published by Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

Previously, we have shown that chemical excitatory drives such as N-methyl-d-aspartate (NMDA) are capable of activating the striatal microcircuit exhibiting neuronal ensembles that alternate their activity producing temporal sequences. One aim of this work was to demonstrate whether similar activity could be evoked by delivering cortical stimulation. Dynamic calcium imaging allowed us to follow the activity of dozens of neurons with single-cell resolution in mus musculus brain slices. A train of electrical stimuli in the cortex evoked network activity similar to the one induced by bath application of NMDA. Previously, we have also shown that the dopamine-depleted striatal microcircuit increases its spontaneous activity generating dominant recurrent ensembles that interrupt the temporal sequences found in control microcircuits. This activity correlates with parkinsonian pathological activity. Several cortical stimulation protocols such as transcranial magnetic stimulation reduce motor signs of Parkinsonism. Here, we show that cortical stimulation in vitro temporarily eliminates the pathological activity from the dopamine-depleted striatal microcircuit by turning off some neurons that sustain this activity and recruiting new ones that allow transitions between network states, similar to the control circuit. When cortical stimulation is given in the presence of L-DOPA, parkinsonian activity is eliminated during the whole recording period. The present experimental evidence suggests that cortical stimulation such as that generated by transcranial magnetic stimulation, or otherwise, may allow reduce L-DOPA dosage., (© 2017 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

Dietary omega-3 fatty acids accumulate and are actively retained in central nervous system membranes, mainly in synapses, dendrites and photoreceptors. Despite this selective enrichment, their impact on synaptic function and plasticity has not been fully determined at the molecular level. In this study, we explored the impact of omega-3 fatty acid deficiency on synaptic function in the hippocampus. Dietary omega-3 fatty acid deficiency for 5 months after weaning led to a 65% reduction in the concentration of docosahexaenoic acid in whole brain synaptosomal phospholipids with no impact on global dopaminergic or serotonergic turnover. We observed reduced concentrations of glutamate receptor subunits, including GluA1, GluA2 and NR2B, and synaptic vesicle proteins synaptophysin and synaptotagmin 1 in hippocampal synaptosomes of omega-3 fatty acid-deficient mice as compared to the omega-3 fatty acid rich group. In contrast, an increased concentration of neuronal inositol 1,4,5-trisphosphate-receptor (IP 3 -R) was observed in the deficient group. Furthermore, omega-3 fatty acid deficiency reduced the long-term potentiation (LTP) in stratum oriens of the hippocampal CA1 area, but not in stratum radiatum. Thus, omega-3 fatty acids seem to have specific effects in distinct subsets of glutamatergic synapses, suggesting specific molecular interactions in addition to altering plasma membrane properties on a more global scale., (© 2018 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

Understanding endogenous neurogenesis and neuronal replacement to mature circuits is a topic of discussion as a therapeutic alternative under acute and chronic neurodegenerative disorders. Adaptive neurogenic response may result as a result of ischemia which could support long-term recovery of behavioral functions. Endogenous sources of neural progenitors may be stimulated by changes in blood flow or neuromodulation. Using a mouse model of unilateral cortical devascularization, we have observed reactive neurogenesis in the perilesional cortex and subventricular zone neurogenic niche. C57BL/6L 4 weeks old male mice were craneotomized at 1 mm caudal from frontal suture and 1 mm lateral from midline to generate a window of 3 mm side. Brain injury was produced by removal of the meninges and superficial vasculature of dorsal parietal cortex. BrdU agent (50 mg/kg, ip) was injected to lesioned and sham animals, during days 0 and 1 after surgery. Sagittal sections were analyzed at 1, 4, 7, and 10 days post-injury. A time-dependent increase in BrdU + cells in the perilesional parietal cortex was accompanied by augmented BrdU + cells in the sub ventricular and rostral migratory stream of ipsilateral and contralateral hemispheres. Neural progenitors and neuroblasts proliferated in the lesioned and non-lesioned subventricular zone and rostral migratory stream on day 4 after injury. Augmented contralateral neurogenesis was associated with an increase in vesicular monoamine transporter 2 protein in the striosomal sub ventricular neurogenic niche of non-lesioned hemisphere., (© 2018 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

Social interaction is known to be the main source of stress in human beings, which explains the translational importance of this research in animals. Evidence reported over the last decade has revealed that, when exposed to social defeat experiences (brief episodes of social confrontations during adolescence and adulthood), the rodent brain undergoes remodeling and functional modifications, which in turn lead to an increase in the rewarding and reinstating effects of different drugs of abuse. The mechanisms by which social stress cause changes in the brain and behavior are unknown, and so the objective of this review is to contemplate how social defeat stress induces long-lasting consequences that modify the reward system. First of all, we will describe the most characteristic results of the short- and long-term consequences of social defeat stress on the rewarding effects of drugs of abuse such as psychostimulants and alcohol. Secondly, and throughout the review, we will carefully assess the neurobiological mechanisms underlying these effects, including changes in the dopaminergic system, corticotrophin releasing factor signaling, epigenetic modifications and the neuroinflammatory response. To conclude, we will consider the advantages and disadvantages and the translational value of the social defeat stress model, and will discuss challenges and future directions., (© 2018 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)