Search

Compulsive forms of eating displayed by some obese individuals share similarities with compulsive drug taking behaviour, a hallmark feature of substance use disorder. This raises the possibility that drug addiction treatments may show utility in the treatment of compulsive overeating. N-Acetylcysteine (NAC) is a cysteine pro-drug which has experienced some success in clinical trials, reducing cocaine, marijuana and cigarette use, as well as compulsive behaviours such as gambling and trichotillomania. We assessed the impact of NAC on addiction-like behaviour towards highly palatable food in a rat model of diet-induced obesity. Adult male Sprague-Dawley rats were placed on a high-fat high-sugar diet for eight weeks and then assigned to diet-induced obesity-prone (DIO) or diet-induced obesity-resistant (DR) groups based on weight gain. DIO and DR rats were subjected to an operant conditioning paradigm whereby rats could lever press for high-fat high-sugar food pellets. This alternated with periods of signalled reward unavailability. Before treatment DIO rats ate more in their home cage, earned more food pellets in operant sessions, and responded more during periods that signalled reward unavailability (suggestive of compulsive-like food seeking) compared to DR rats. This persistent responding in the absence of reward displayed by DIO rats was ameliorated by daily injections of NAC (100 mg/kg, i.p.) for 14 days. By the end of the treatment period, lever-pressing by NAC-treated DIO rats resembled that of DR rats. These findings suggest that NAC reduces addiction-like behaviour towards food in rats and supports the potential use of this compound in compulsive overeating.

BACKGROUND AND PURPOSE: Muscarinic acetylcholine receptors mediate alcohol consumption and seeking in rats. While M4 and M5 receptors have recently been implicated to mediate these behaviours in the striatum, their role in other brain regions remain unknown. The ventral tegmental area (VTA) and ventral subiculum (vSub) both densely express M4 and M5 receptors and modulate alcohol-seeking, via their projections to the nucleus accumbens shell (AcbSh). EXPERIMENTAL APPROACH: In Indiana alcohol-preferring (iP) male rats, we examined Chrm4 (M4 ) and Chrm5 (M5 ) expression in the VTA and vSub following long-term alcohol consumption and abstinence using RT-qPCR. Using a combination of retrograde tracing and RNAscope, we examined the localisation of Chrm4 and Chrm5 on vSub cells that project to the AcbSh. Using selective allosteric modulators, we examined the functional role of M4 and M5 receptors within the vSub in alcohol consumption, context-induced alcohol-seeking, locomotor activity, and food/water consumption. KEY RESULTS: Long-term alcohol and abstinence dysregulated the expression of genes for muscarinic receptors in the vSub, not in the VTA. Chrm4 was down-regulated following long-term alcohol and abstinence, while Chrm5 was up-regulated following long-term alcohol consumption. Consistent with these data, a positive allosteric modulator (VU0467154) of intra-vSub M4 receptors reduced context-induced alcohol-seeking, but not motivation for alcohol self-administration, while M5 receptor negative allosteric modulator (ML375) reduced initial motivation for alcohol self-administration, but not context-induced alcohol-seeking. CONCLUSION AND IMPLICATIONS: Collectively, our data highlight alcohol-induced cholinergic dysregulation in the vSub and distinct roles for M4 and M5 receptor allosteric modulators to reduce alcohol consumption or seeking.

Alcohol use disorder (AUD) and methamphetamine use disorder (MUD) are prevalent and have high adverse impacts on both the individual and society. Current treatment strategies for these disorders are ineffective at a population level. Lorcaserin, a 5‐HT2C receptor agonist, has shown potential at reducing the symptoms of substance use disorder. This pilot study (initiated prior to market withdrawal) examined feasibility and safety of lorcaserin treatment in people undergoing residential detoxification and treatment for AUD and MUD. This was an open label pilot study of lorcaserin where participants (n = 10 AUD; n = 8 MUD) received 10‐mg lorcaserin daily for 4 days then twice daily for 1 month. Primary outcome measures included recruitment and retention rate, incidence of treatment‐emergent events, incidence of methamphetamine or alcohol withdrawal‐related events, heart rate, and blood pressure. Secondary measures included pharmacokinetic data and self‐reported alcohol or methamphetamine use, craving, and psychological distress. AUD participants were recruited faster and had a greater retention rate compared with MUD participants. Lorcaserin did not alter vital signs, was well tolerated, and had a similar pharmacokinetic profile to individuals with obesity. Lorcaserin reduced self‐reported alcohol and amphetamine‐type substance use and craving in AUD and MUD participants, respectively. Self‐reported psychological health also improved over the treatment period for all participants. Despite the pilot nature of this study, our data support the notion of 5‐HT2C receptors as a therapeutic target for drug and alcohol abuse.

Galanin is a neuropeptide which mediates its effects via three G-protein coupled receptors (GAL1-3 ). Administration of a GAL3 antagonist reduces alcohol self-administration in animal models while allelic variation in the GAL3 gene has been associated with an increased risk of alcohol use disorders in diverse human populations. Based on the association of GAL3 with alcoholism, we sought to characterize drug-seeking behavior in GAL3 -deficient mice for the first time. In the two-bottle free choice paradigm, GAL3 -KO mice consistently showed a significantly increased preference for ethanol over water when compared to wildtype littermates. Furthermore, male GAL3 -KO mice displayed significantly increased responding for ethanol under operant conditions. These differences in alcohol seeking behavior in GAL3 -KO mice did not result from altered ethanol metabolism. In contrast to ethanol, GAL3 -KO mice exhibited similar preference for saccharin and sucrose over water, and a similar preference for a high fat diet over a low fat diet as wildtype littermates. No differences in cognitive and locomotor behaviors were observed in GAL3 -KO mice to account for increased alcohol seeking behavior. Overall, these findings suggest genetic ablation of GAL3 in mice increases alcohol consumption.

This article is part of a themed section on The Importance of Sex Differences in Pharmacology Research. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.21/issuetoc.

Background and Purpose Alcohol use disorders are a leading cause of preventable deaths worldwide, and stress is a major trigger of relapse. The neuropeptide relaxin-3 and its cognate receptor, relaxin family peptide receptor 3 (RXFP3), modulate stress-induced relapse to alcohol seeking in rats, and while the bed nucleus of the stria terminalis has been implicated in this regard, the central nucleus of the amygdala (CeA) also receives a relaxin-3 innervation and CeA neurons densely express RXFP3 mRNA. Moreover, the CeA is consistently implicated in both stress and addictive disorders. Yohimbine precipitates relapse-like behaviour in rodents, although exactly how yohimbine induces relapse is unknown, possibly by increasing stress levels and inducing heightened cue reactivity. Experimental Approach In the current study, we examined the effects of yohimbine (1 mg·kg−1, i.p.) on anxiety-like behaviour in alcohol-experienced rats. Furthermore, we assessed CeA neuronal activation following yohimbine-induced reinstatement of alcohol seeking and the role of the relaxin-3/RXFP3 signalling within the CeA in yohimbine-induced reinstatement to alcohol seeking. Key Results Low-dose yohimbine was anxiogenic in rats with a history of alcohol use. Furthermore, yohimbine-induced reinstatement of alcohol seeking increased Fos activation in CeA corticotrophin-releasing factor, dynorphin and GABA neurons compared with naive and vehicle controls. Bilateral intra-CeA injections of the selective RXFP3 antagonist, R3(B1-22)R, attenuated yohimbine-induced reinstatement of alcohol seeking. Conclusions Collectively, these data suggest that the CeA is a node where yohimbine acts to induce reinstatement of alcohol seeking and implicate the relaxin-3/RXFP3 system within the CeA in this process.

The abuse of volatile solvents such as toluene is a significant public health concern, predominantly affecting adolescents. To date, inhalant abuse research has primarily focused on the central nervous system; however, inhalants also exert effects on other organ systems and processes, including metabolic function and energy balance. Adolescent inhalant abuse is characterized by a negative energy balance phenotype, with the peak period of abuse overlapping with the adolescent growth spurt. There are multiple components within the central and peripheral regulation of energy balance that may be affected by adolescent inhalant abuse, such as impaired metabolic signaling, decreased food intake, altered dietary preferences, disrupted glucose tolerance and insulin release, reduced adiposity and skeletal density, and adrenal hypertrophy. These effects may persist into abstinence and adulthood, and the long‐term consequences of inhalant‐induced metabolic dysfunction are currently unknown. The signs and symptoms resulting from chronic adolescent inhalant abuse may result in a propensity for the development of adult‐onset metabolic disorders such as type 2 diabetes, however, further research investigating the long‐term effects of inhalant abuse upon energy balance and metabolism are needed. This review addresses several aspects of the short‐ and long‐term effects of inhalant abuse relating to energy and metabolic processes, including energy balance, intake and expenditure; dietary preferences and glycemic control; and the dysfunction of metabolic homeostasis through altered adipose tissue, bone, and hypothalamic‐pituitary‐adrenal axis function.

Cerebral small vessel disease (SVD) is an important cause of vascular cognitive impairment. Recent studies have demonstrated that structural connectivity of brain networks in SVD is disrupted. However, little is known about the extent and location of the reduced connectivity in SVD. Here they investigate the rich club organisation-a set of highly connected and interconnected regions-and investigate whether there is preferential rich club disruption in SVD. Diffusion tensor imaging (DTI) and cognitive assessment were performed in a discovery sample of SVD patients (n = 115) and healthy control subjects (n = 50). Results were replicated in an independent dataset (49 SVD with confluent WMH cases and 108 SVD controls) with SVD patients having a similar SVD phenotype to that of the discovery cases. Rich club organisation was examined in structural networks derived from DTI followed by deterministic tractography. Structural networks in SVD patients were less dense with lower network strength and efficiency. Reduced connectivity was found in SVD, which was preferentially located in the connectivity between the rich club nodes rather than in the feeder and peripheral connections, a finding confirmed in both datasets. In discovery dataset, lower rich club connectivity was associated with lower scores on psychomotor speed (beta = 0.29, P < 0.001) and executive functions (beta = 0.20, P = 0.009). These results suggest that SVD is characterized by abnormal connectivity between rich club hubs in SVD and provide evidence that abnormal rich club organisation might contribute to the development of cognitive impairment in SVD. Hum Brain Mapp 38:1751-1766, 2017. (c) 2017 Wiley Periodicals, Inc.

Any type of behavioral change is an effortful process. Thus, the process of behavioral therapy, where clients seek to change maladaptive behavioral patterns, requires high-level cognitive engagement. It is unfortunate, then, that cognitive impairment is a feature of substance use disorders (SUDs), and especially because the domains that tend to be impaired are the very ones involved in the process of therapeutic behavioral change. In this review, we compare the cognitive profile that is frequently observed with chronic SUD with the skills that are required to initiate and sustain behavioral change during rehabilitation. Furthermore, we look to new therapeutic developments that seek to improve cognitive function. We propose that the use of these cognitive enhancing agents as adjuncts to behavioral therapy should help to overcome some of the cognitive barriers imposed by the disorder itself, and hence reduce the chance of relapse.

Alcoholism is a chronic relapsing disorder, and stress is a key precipitant of relapse. The nucleus incertus (NI) is highly responsive to corticotrophin-releasing factor (CRF) and psychological stressors, receives a CRF innervation and expresses CRF1 and CRF2 receptor mRNA. Furthermore, the ascending NI relaxin-3 system is implicated in alcohol seeking in rats. Therefore, in alcohol-preferring rats, we examined the effect of bilateral injections into the NI of the CRF1 receptor antagonist, CP376395 or the CRF2 receptor antagonist, astressin-2B on yohimbine-induced reinstatement of alcohol seeking. Using quantitative PCR analysis of NI micropunches, we assessed the effects of chronic alcohol consumption on gene expression profiles for components of the relaxin-3 and CRF systems. Bilateral intra-NI injections of CP376395 (500 ng/0.25 µl) attenuated yohimbine-induced reinstatement of alcohol seeking. In contrast, intra-NI injections of astressin-2B (200 ng/0.25 µl) had no significant effect. In line with these data, CRF1 , but not CRF2 , receptor mRNA was upregulated in the NI following chronic ethanol intake. Relaxin family peptide 3 receptor mRNA was also increased in the NI following chronic ethanol. Our quantitative PCR analysis also identified CRF mRNA within the rat NI, and the existence of a newly identified population of CRF-containing neurons was subsequently confirmed by detection of CRF immunoreactivity in rat and mouse NI. These data suggest that NI neurons contribute to reinstatement of alcohol seeking, via an involvement of CRF1 signalling. Furthermore, chronic ethanol intake leads to neuroadaptive changes in CRF and relaxin-3 systems within rat NI.

Background and Purpose There is currently no medication approved specifically to treat cocaine addiction. Behavioural interventions such as cue exposure therapy (CET) rely heavily on new learning. Antagonism of the metabotropic glutamate 5 (mGlu5) receptor has emerged as a potential treatment, by reducing the reinforcing properties of cocaine. However, mGlu5 receptor activity is necessary for learning; therefore, such agents could interfere with behavioural treatments. We used a novel rodent model of CET to test the effects of mGlu5 negative and positive allosteric modulators (NAM and PAM) on behavioural therapy. Experimental Approach Rats were trained to press a lever for cocaine in the presence of a discrete cue [conditioned stimulus (CS)] and then extinguished in the absence of the CS. Following lever extinction, half the rats received CS extinction in the same chambers but with the levers withdrawn; the remaining rats received no CS extinction. Before this session, rats received a systemic administration of either vehicle or a mGlu5 NAM (MTEP, experiment 1) or PAM (CDPPB, experiment 2). Cue-induced reinstatement was tested in a drug-free session the following day. Key Results At reinstatement, rats that had received CS extinction showed reduced responding. This effect was attenuated by MTEP treatment before CS extinction. In contrast, administration of CDPPB (PAM) led to decreased reinstatement the following day, regardless of extinction condition. Conclusion and Implications These results suggest that mGlu5 receptor activity is both necessary and sufficient for efficient extinction of a cocaine-associated CS. Therefore, mGlu5 PAMs could enhance the efficacy of CET.

Background and Purpose Abuse of toluene-containing inhalants is an increasing public health problem, especially among adolescents. Abuse during adolescence is associated with emaciation, while industrial exposure leads to altered glycaemic control suggesting metabolic instability. However, the relationship between adolescent inhalant abuse and metabolic dysfunction remains unknown. Experimental Approach To model human abuse patterns, we exposed male adolescent Wistar rats [postnatal day (PND) 27] to chronic intermittent inhaled toluene (CIT, 10 000 ppm) or air (control) for 1 h·day−1, three times a week for 4 weeks. Feeding and body composition were monitored. After 4 weeks, circulating metabolic hormone concentrations and responses to a glucose tolerance test (GTT) were measured. Dietary preference was measured by giving animals access to either a ‘western diet’ plus standard chow (WC + SC) or standard chow alone during 4 weeks of abstinence. Metabolic hormones and GTT were subsequently measured. Key Results Adolescent CIT exposure significantly retarded weight gain, altered body composition, circulating metabolic hormones and responses to a GTT. While reduced body weight persisted, responses to a GTT and circulating hormones appeared to normalize for animals on standard chow following abstinence. In CIT-exposed WC + SC rats, we observed impaired glucose tolerance associated with altered metabolic hormones. Analysis of hypothalamic genes revealed differential expression profiles in CIT-exposed rats following both the exposure period and abstinence, suggesting a central contribution to inhalant-induced metabolic dysfunction. Conclusion and Implications CIT exposure during adolescence has long-term effects on metabolic function, which may increase the risk of disorders related to energy balance and glycaemic control.

The pervasive use of refined sugars in highly accessible, palatable foods and persistent exposure to reinforcing food-associated cues has contributed to overconsumption of sugar-rich diets and the current obesity epidemic in Western society. We have shown previously that brain relaxin-3 mRNA levels positively correlate with sucrose and alcohol intake, and that central antagonism of relaxin-3 receptors (RXFP3) attenuates alcohol self-administration and alcohol-seeking in rats, but food-seeking behaviour and palatable food consumption in mice. To further examine the relationship between motivated appetitive behaviours and relaxin-3/RXFP3 signalling, we investigated the effect of Rxfp3 gene deletion in C57BL/6J mice on sucrose and alcohol self-administration and cue-induced reinstatement (RNST) of sucrose- and alcohol-seeking. Acquisition and maintenance of sucrose and alcohol self-administration was assessed in male wild-type (WT) and Rxfp3 knockout (KO) (C57BL/6J(RXFP3TM1) (/) (DGen) ) littermate mice using fixed ratio (FR) schedules of reinforcement. Mice were subsequently challenged with a progressive ratio (PR) test to measure motivation and, following extinction training, re-exposed to reward-associated cues to evaluate RNST of active lever-responding. Wild-type and Rxfp3 KO mice displayed similar acquisition of FR1 sucrose self-administration, but Rxfp3 KO mice responded less when the instrumental requirement was increased to FR3. These mice also showed a lower breakpoint for sucrose and attenuated cue-induced RNST of sucrose-seeking. Notably, no marked genotype differences in alcohol-responding were observed. In mice, endogenous relaxin-3/RXFP3 signalling promotes self-administration of sucrose under high response requirements and cue-induced RNST of sucrose-seeking, but does not apparently regulate motivation to consume alcohol or alcohol-seeking behaviour.

New Findings What is the central question of this study? Sodium appetite is controlled by conserved neuronal transmitter–receptor systems. Here, we tested the contribution made by relaxin family peptide 3 receptor (RXFP3), the cognate G-protein-coupled receptor for the neuropeptide relaxin-3. What is the main finding and its importance? Intracerebroventricular infusion of an RXFP3 antagonist reduced in a dose-dependent manner the volume of 0.3 m NaCl consumed by sodium-depleted C57Bl/6J (wild-type) mice. This effect was absent in sodium-depleted Rxfp3 knockout mice, and RXFP3 antagonist infusion did not alter water consumption in wild-type mice subjected to multiple thirst tests, indicating both the pharmacological and the physiological specificity of observed effects. Our findings identify endogenous relaxin-3–RXFP3 signalling as a modulator of sodium appetite. Overconsumption of highly salted foods is common in Western diets and contributes significantly to metabolic disorders such as hypertension, renal dysfunction and diabetes. Sodium appetite, or the desire of terrestrial animals to seek and consume sodium-containing salts, is a behaviour mediated by a set of evolutionarily conserved neuronal systems. In these studies, we tested whether this instinctive behavioural drive is influenced by the G-protein-coupled relaxin family peptide 3 receptor (RXFP3), the cognate receptor for the neuropeptide relaxin-3, because relaxin-3–RXFP3 signalling can modulate arousal, motivation and ingestive behaviours. Intracerebroventricular (i.c.v.) infusion of the selective RXFP3 antagonist, R3(B1-22)R, reduced in a dose-dependent manner the volume of 0.3 m NaCl solution consumed when offered to sodium-depleted C57Bl/6J wild-type mice, relative to vehicle-treated control animals. Notably, i.c.v. R3(B1-22)R infusion did not alter 0.3 m NaCl consumption relative to vehicle in sodium-depleted Rxfp3 knockout mice, confirming the pharmacological specificity of this effect. Furthermore, i.c.v. R3(B1-22)R did not alter the volume of water consumed by wild-type mice in three tests where water drinking was the normal physiological response, suggesting that the ability of R3(B1-22)R to reduce activated salt appetite is specific and not due to a generalized reduction in drinking behaviour. These findings identify, for the first time, that endogenous relaxin-3–RXFP3 signalling is a powerful mediator of salt appetite in mice and further elucidate the functional role of the relaxin-3–RXFP3 system in the integrative control of motivated behaviours.

Linked Editorials This Editorial is part of a series. To view the other Editorials in this series, visit: http://onlinelibrary.wiley.com/doi/10.1111/bph.12956/abstract; http://onlinelibrary.wiley.com/doi/10.1111/bph.12954/abstract; http://onlinelibrary.wiley.com/doi/10.1111/bph.12955/abstract and http://onlinelibrary.wiley.com/doi/10.1111/bph.13112/abstract

Orexins (hypocretins) are hypothalamic neuropeptides that innervate the entire neuraxis, including the prelimbic cortex and ventral tegmental area and have been implicated in ethanol-seeking behaviour. The present study aimed to use the orexin-1 (OX1 ) receptor antagonist SB-334867 to examine the role of prelimbic cortex and ventral tegmental area OX1 receptors in cue-induced reinstatement of ethanol-seeking. Ethanol-preferring rats (iP) rats were trained to self-administer ethanol (10 percent v/v, FR3) or sucrose (0.2-1 percent w/v, FR3) in the presence of reward-associated cues before being implanted with indwelling guide cannulae. Rats then underwent extinction training for 11 days. On test days, rats were given a microinjection of vehicle or SB-334867 (3 μg/side) and presented with reward-associated cues to precipitate reinstatement. Results show SB-334867 infused into the prelimbic cortex attenuated cue-induced reinstatement of ethanol-seeking, but not sucrose-seeking. OX1 antagonism in the ventral tegmental area also attenuated cue-induced reinstatement of ethanol-seeking. These findings suggest that OX1 receptors located in the prelimbic cortex and ventral tegmental area are part of a circuit driving cue-mediated ethanol-seeking behaviour.

Addiction to methamphetamine (METH) is a global health problem for which there are no approved pharmacotherapies. The adenosine 2A (A2 A ) receptor presents a potential therapeutic target for METH abuse due to its modulatory effects on striatal dopamine and glutamate transmission. Notably, A2 A receptor signalling has been implicated in the rewarding effects of alcohol, cocaine and opiates; yet, the role of this receptor in METH consumption and seeking is essentially unknown. Therefore, the current study used A2 A knockout (KO) mice to assess the role of A2 A in behaviours relevant to METH addiction. METH conditioned place preference was absent in A2 A KO mice compared with wild-type (WT) littermates. Repeated METH treatment produced locomotor sensitization in both genotypes; however, sensitization was attenuated in A2 A KO mice in a dose-related manner. METH intravenous self-administration was intact in A2 A KO mice over a range of doses and schedules of reinforcement. However, the motivation to self-administer was reduced in A2 A KO mice. Regression analysis further supported the observation that the motivation to self-administer METH was reduced in A2 A KO mice even when self-administration was similar to WT mice. Sucrose self-administration was also reduced in A2 A KO mice but only at higher schedules of reinforcement. Collectively, these data suggest that A2 A signalling is critically required to integrate rewarding and motivational properties of both METH and natural rewards.

Background and Purpose— Cerebral small vessel disease (SVD) is the most common cause of vascular cognitive impairment, with a significant proportion of cases going on to develop dementia. We explor...

Cerebral small vessel disease (SVD) is the primary cause of vascular cognitive impairment and is associated with decline in executive function (EF) and information processing speed (IPS). Imaging biomarkers are needed that can monitor and identify individuals at risk of severe cognitive decline. Recently there has been interest in combining several magnetic resonance imaging (MRI) markers of SVD into a unitary score to describe disease severity. Here we apply a diffusion tensor image (DTI) segmentation technique (DSEG) to describe SVD related changes in a single unitary score across the whole cerebrum, to investigate its relationship with cognitive change over a three-year period. 98 patients (aged 43-89) with SVD underwent annual MRI scanning and cognitive testing for up to three years. DSEG provides a vector of 16 discrete segments describing brain microstructure of healthy and/or damaged tissue. By calculating the scalar product of each DSEG vector in reference to that of a healthy ageing control we generate an angular measure (DSEG θ) describing the patients' brain tissue microstructural similarity to a disease free model of a healthy ageing brain. Conventional MRI markers of SVD brain change were also assessed including white matter hyperintensities, cerebral atrophy, incident lacunes, cerebral-microbleeds, and white matter microstructural damage measured by DTI histogram parameters. The impact of brain change on cognition was explored using linear mixed-effects models. Post-hoc sample size analysis was used to assess the viability of DSEG θ as a tool for clinical trials. Changes in brain structure described by DSEG θ were related to change in EF and IPS (p

Environmental stimuli are powerful mediators of craving and relapse in substance-abuse disorders. This review examined how animal models have been used to investigate the cognitive mechanisms through which cues are able to affect drug-seeking behaviour. We address how animal models can describe the way drug-associated cues come to facilitate the development and persistence of drug taking, as well as how these cues are critical to the tendency to relapse that characterizes substance-abuse disorders. Drug-associated cues acquire properties of conditioned reinforcement, incentive motivation and discriminative control, which allow them to influence drug-seeking behaviour. Using these models, researchers have been able to investigate the pharmacology subserving the behavioural impact of environmental stimuli, some of which we highlight. Subsequently, we examine whether the impact of drug-associated stimuli can be attenuated via a process of extinction, and how this question is addressed in the laboratory. We discuss how preclinical research has been translated into behavioural therapies targeting substance abuse, as well as highlight potential developments to therapies that might produce more enduring changes in behaviour.

Addiction is a devastating disorder that affects 15.3 million people worldwide. While prevalent, few effective treatments exist. Orexin receptors have been proposed as a potential target for anti-craving medications. Orexins, also known as hypocretins, are neuropeptides produced in neurons of the lateral and dorsomedial hypothalamus and perifornical area, which project widely throughout the brain. The absence of orexins in rodents and humans leads to narcolepsy. However, orexins also have an established role in reward seeking. This review will discuss some of the original studies describing the roles of the orexins in reward seeking as well as specific works that were presented at the 2013 International Narcotics Research Conference. Orexin signalling can promote drug-induced plasticity of glutamatergic synapses onto dopamine neurons of the ventral tegmental area (VTA), a brain region implicated in motivated behaviour. Additional evidence suggests that orexin signalling can also promote drug seeking by initiating an endocannabinoid-mediated synaptic depression of GABAergic inputs to the VTA, and thereby disinhibiting dopaminergic neurons. Orexin neurons co-express the inhibitory opioid peptide dynorphin. It has been proposed that orexin in the VTA may not mediate reward per se, but rather occludes the ‘anti-reward’ effects of dynorphin. Finally, orexin signalling in the prefrontal cortex and the central amygdala is implicated in reinstatement of reward seeking. This review will highlight recent work describing the role of orexin signalling in cellular processes underlying addiction-related behaviours and propose novel hypotheses for the mechanisms by which orexin signalling may impart drug seeking. LINKED ARTICLES This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-2

Tobacco smoking is a major cause of death and disease and as such there is a critical need for the development of new therapeutic approaches to treat nicotine addiction. Here, we utilize genetic and pharmacological tools to further investigate the nicotinic acetylcholine receptor (nAChR) subtypes that support intravenous self-administration of nicotine. α4-S248F mice contain a point mutation within the α4 nAChR subunit which confers increased sensitivity to nicotine and resistance to mecamylamine. Here, we show that acute administration of mecamylamine (2 mg/kg, i.p.) reduces established nicotine self-administration (0.05 mg/kg/infusion) in wild-type (WT), but not in α4-S248F heterozygous mice, demonstrating a role for α4* nAChRs in the modulation of ongoing nicotine self-administration. Administration of N,N-decane-1,10-diyl-bis-3-picolinium diiodide (bPiDI), a selective α6β2* nAChR antagonist, dose dependently (5 and 10 mg/kg, i.p.) impairs the acquisition of nicotine self-administration and reduces established nicotine self-administration in WT mice when administered acutely (10 mg/kg, i.p.). This was not due to a general reduction in locomotor activity and the same dose of bPiDI did not affect operant responding for sucrose. bPiDI treatment (10 mg/kg, i.p.) also impaired both the acquisition and maintenance of nicotine self-administration in α4-S248F heterozygous mice. This provides further evidence for the involvement of α6β2* nAChRs in the reinforcing effects of nicotine that underlies its ability to support ongoing self-administration. Taken together, selective targeting of α6β2* or α4α6β2* nAChRs may prove to be an effective strategy for the development of smoking cessation therapies.

We investigated the effects of extinguishing action-reward versus context-reward associations on drug-primed reinstatement, and the potential role of the metabotropic glutamate 5 receptor (mGlu5) in these different types of extinction in rats that self-administer cocaine. We observed that daily context extinction (non-reinforced exposures to the cocaine-taking context with retracted levers) was just as effective as daily lever extinction in reducing cocaine-primed reinstatement compared with passive abstinence. Additionally, systemic injections of the mGlu5 negative allosteric modulator MTEP (3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]-pyridine) following each extinction session significantly impaired the ability of context extinction to reduce cocaine-primed reinstatement, without affecting reinstatement after lever extinction or passive abstinence.

Withdrawal from a chronic period of alcohol consumption is commonly associated with the manifestation of depression, potentially exerting a significant influence on treatment prospects and increasing the likelihood of relapse. Better therapeutic strategies need to be developed to assist with rehabilitation. Here, we report the detection of depression-related behaviours in a mouse model of 6-week free-choice ethanol (10%, v/v) consumption followed by 2-week abstinence. Mice abstinent from alcohol showed increased immobility time on the forced-swim test, reduced saccharin consumption and increased latency to feed in the novelty-suppressed feeding test. By comparison, there was no significant effect on anxiety-related behaviours as determined by testing on the light-dark box and elevated plus maze. We found that the provision of running-wheels through the duration of abstinence attenuated depressive behaviour in the forced-swim and novelty-suppressed feeding tests, and increased saccharin consumption. Given the link between withdrawal from addictive substances and depression, this model will be useful for the study of the pathophysiology underlying alcohol-related depression. The findings of this study establish an interaction between physical activity and the development of behavioural changes following cessation of alcohol consumption that could have implications for the development of rehabilitative therapies.

In the Unicoi Mountains of southwestern North Carolina, USA, a 2 lane scenic byway created a barrier to dispersal for the federally endangered Carolina northern flying squirrel (Glaucomys sabrinus coloratus). Unable to glide across the road, squirrels in the divided subpopulations faced reduced access to mates, den sites, and foraging grounds. We installed 3 pairs of modified wooden utility poles as crossing structures to enable gliding over the road in both directions. Using wildlife cameras, we monitored use of the crossing poles by northern flying squirrels for 15 months. Additionally, we tracked movements of 4 radiocollared northern flying squirrels between habitat patches and checked nest boxes for evidence of squirrels crossing the road. Cameras recorded 5 still images and 25 videos of northern flying squirrels on the crossing poles, with flying squirrels leaping across the road in 56% of videos. Crossings increased from 0 crossings in a previous study to 14 crossings in this study. For the first time since crossing-pole installation, squirrels used dens on the opposite side of the road from where they were initially captured and tagged. We believe that these structure-assisted road crossings in the Unicois are the first observed in a North American gliding mammal. Although northern flying squirrels used crossing poles to glide over a rural, low traffic, 2-lane road, further research should be conducted to determine whether this technique is applicable to different road types and other types of linear barriers in North America. © 2013 The Wildlife Society.

Background Alcohol dependence is a complex psychiatric disorder demanding development of novel pharmacotherapies. Because the cyclic adenosine monophosphate (cAMP) signaling cascade has been implicated in mediating behavioral responses to alcohol, key components in this cascade may serve as potential treatment targets. Phosphodiesterase-4 (PDE4), an enzyme that specifically catalyzes the hydrolysis of cAMP, represents a key point in regulating intracellular cAMP levels. Thus, it was of interest to determine whether PDE4 was involved in the regulation of alcohol use and abuse. Methods Male Fawn-Hooded (FH/Wjd) rats were tested for 5% (v/v) ethanol (EtOH) and 10% (w/v) sucrose operant oral self-administration following treatment with the selective PDE4 inhibitor rolipram (0.0125, 0.025, or 0.05 mg/kg, subcutaneous [s.c.]); rolipram at higher doses (0.05, 0.1, and 0.2 mg/kg, s.c.) was tested to determine its impact on the intake of EtOH, sucrose, or water using the 2-bottle choice drinking paradigm. Subsequent open-field testing was performed to evaluate the influence of higher doses of rolipram on locomotor activity. Results Acute administration of rolipram dose-dependently reduced operant self-administration of 5% EtOH, but had no effect on 10% sucrose responding. Time-course assessment revealed significant decreases in EtOH consumption after rolipram (0.1, 0.2 mg/kg) treatment in continuous- and intermittent access to EtOH at 5% or 10%, respectively. Moreover, chronic rolipram treatment time-dependently decreased 5% EtOH consumption and preference during treatment days and after the termination of rolipram administration. Rolipram at the highest doses (0.1 and 0.2 mg/kg) did decrease locomotor activity, but the effect lasted only 10 and 20 minutes, respectively, which did not likely alter long-term EtOH drinking. Conclusions These results suggest that PDE4 plays a role in alcohol seeking and consumption behavior. Drugs interfering with PDE4 may be a potential pharmacotherapy for alcohol dependence.

Persistent vulnerability to relapse represents a major challenge in the treatment of drug addiction. The brain circuitry that underlies relapse-like behaviour can be investigated using animal models of drug seeking. As yet there have been no comprehensive brain mapping studies that have specifically examined the neuroanatomical substrates of cue-induced opiate seeking following abstinence in a mouse operant paradigm. The aim of this study was to compare the brain regions involved in sucrose vs. morphine seeking following protracted abstinence in mice. Male CD1 mice were trained to respond for either sucrose (10% w/v) or intravenous morphine (0.1 mg kg(-1) per infusion) in an operant paradigm in the presence of a discrete cue. Once stable responding was established, mice were subjected to abstinence in their home cages for 3 weeks and then perfused for tissue collection, or returned to the operant chambers to assess cue-induced reward seeking before being perfused for tissue collection. Brain tissue was processed for Fos immunohistochemistry and Fos expression was quantified in a range of brain nuclei. We identified unique patterns of neuronal activation for sucrose and morphine seeking mice as well as some overlap. Structures activated in both ‘relapse' groups included the anterior cingulate and orbitofrontal cortex, nucleus accumbens shell, bed nucleus of the stria terminalis, substantia nigra pars compacta, ventral tegmental area, hippocampus, periaqueductal grey, locus coeruleus and lateral habenula. Structures that were more activated in morphine seeking mice included the nucleus accumbens core, basolateral amygdala, substantia nigra pars reticulata, and the central nucleus of the amygdala. The dorsal raphe was the only structure examined that was specifically activated in sucrose seeking mice. Overall our findings support a cortico-striatal limbic circuit driving opiate seeking, and we have identified some additional circuitry potentially relevant to reward seeking following abstinence.

Characterizing the neurocircuits and neurotransmitters that underlie arousal and circadian sleep/wake patterns is an important goal of neuroscience research, with potential implications for understanding human mental illnesses, such as major depression. Recent anatomical and functional studies suggest that relaxin-3 neurons and their ascending projections contribute to these functions via actions on key cortical, limbic and hypothalamic circuits. This study reports the behavioral phenotype of C57BL/6J backcrossed relaxin-3 knockout (KO) mice. Cohorts of adult, male and female relaxin-3 KO and wild-type (WT) littermate mice were subjected to a battery of behavioral tests to assess sensorimotor function and complex behavior. No overt deficits were detected in motor-coordination, spatial memory, sensorimotor gating, anxiety-like behavior or locomotor behavior in novel environments; and no marked genotype differences were observed in response to a chronic stress protocol. Notably however, compared to WT mice, relaxin-3 KO mice displayed robust hypoactivity during the dark/active phase when provided with free home-cage access to voluntary running wheels. This circadian hypoactivity was reflected by reduced time spent and distance traveled on running wheels, coupled with an increase in the time spent immobile, possibly reflecting increased sleeping. Overall, these studies support a role for relaxin-3 signaling in the control of arousal and sleep/wakefulness, and identify the relaxin-3 KO mouse as a useful model to study this role further.

BACKGROUND AND PURPOSE The enduring propensity for alcoholics to relapse even following years of abstinence presents a major hurdle for treatment. Here we report a model of relapse following protracted abstinence and investigate the pattern of neuronal activation following cue-induced reinstatement and administration of the orexin1 receptor antagonist SB-334867 in inbred alcohol-preferring rats. EXPERIMENTAL APPROACH Rats were trained to self-administer alcohol under operant conditions and divided into two groups: immediate (reinstated immediately following extinction) and delayed (extinguished and then housed for 5 months before reinstatement). Prior to reinstatement, animals were treated with vehicle (immediate n= 11, delayed n= 11) or SB-334867 (20 mg·kg−1 i.p.; immediate n= 6, delayed n= 11). Fos expression was compared between each group and to animals that underwent extinction only. KEY RESULTS SB-334867 significantly attenuated cue-induced reinstatement in both groups. Immediate reinstatement increased Fos expression in the nucleus accumbens (NAc), infra-limbic (IL), pre-limbic (PrL), orbitofrontal (OFC) and piriform cortices, the lateral and dorsomedial hypothalamus, central amygdala and basolateral amygdala (BLA), and the bed nucleus of the stria terminalis. Following delayed reinstatement, Fos expression was further elevated in cortical structures. Concurrent with preventing reinstatement, SB-334867 decreased Fos in NAc core, PrL and OFC following immediate reinstatement. Following protracted abstinence, SB-334867 treatment decreased reinstatement-induced Fos in the PrL, OFC and piriform cortices. CONCLUSIONS AND IMPLICATIONS Cue-induced alcohol seeking can be triggered following protracted abstinence in rats. The effects of SB-334867 on both behaviour and Fos expression suggest that the orexin system is implicated in cue-induced reinstatement, although some loci may shift following protracted abstinence.

This themed issue of Br J Pharmacol is dedicated to the utility and needs of animal models in psychiatry research. The following articles document strengths and weaknesses, indicate areas where better models are sorely needed and provide examples where pharmacological studies may result in mechanistic breakthrough and aid in drug development. In addition, complicating factors both in disease and treatment strategies are canvassed, such as sex differences, genetic and environmental influences. While not exhaustive, the intention was to use a number of exemplars to stimulate discussion around how animal models can aid in improving our understanding and treatment of many devastating conditions. Linked Articles This article is part of a themed section on Animal Models in Psychiatry Research. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue-20

Aim: Staphylococcus aureus is an important cause of serious illness in children. Antibiotic resistance is an international problem and affects initial antibiotic choice. We aimed to describe susceptibility patterns of S. aureus isolates from Australian children to inform optimal empiric treatment of staphylococcal infections in this population. Methods: We analysed susceptibility data for all S. aureus isolates from children at Australian tertiary paediatric hospitals in 2006. Susceptibility rates were compared between hospitals and states, and with published studies of S. aureus isolates from Australian adults. Results: Overall, the proportion of methicillin- resistant S. aureus (MRSA) in Australian children was low (9.8%), and in each state it was less than for the comparable adult population. There were significant differences in susceptibility patterns between different states. Most MRSA isolates were susceptible to clindamycin (73%) and all isolates were reported as susceptible to vancomycin. Susceptibility patterns for isolates from bacteraemic patients were similar to those for isolates from all patients. Conclusions: These data support current Australian recommendations for the use of flucloxacillin or a first-generation cephalosporin as initial treatment of non-life-threatening staphylococcal infections. However, broad spectrum antibiotic therapy including agents that are effective against MRSA should be considered for more serious infections. Appropriate specimens should be collected for susceptibility testing to enable directed treatment for MRSA and other resistant organisms. This study highlights the importance of using local, age-specific data in planning antibiotic treatment guidelines, as results vary substantially from city to city and between adults and children. © 2010 Paediatrics and Child Health Division (Royal Australasian College of Physicians).

Background and purpose: The current study was designed to: (i) examine whether functional interactions occur between receptors known to regulate alcohol self-administration; and (ii) characterize relapse to alcohol seeking following abstinence. Experimental approach: The selective cannabinoid CB1 receptor antagonist SR141716A (0.03–1.0 mg·kg−1 i.p.) resulted in a dose-dependent reduction in ethanol self-administration in ethanol-preferring Indiana-preferring rats. SR141716A was then co-administered with either the selective glutamate metabotropic glutamate 5 (mGlu5) receptor antagonist 3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine (MTEP) or the selective adenosine A2A receptor antagonist SCH58261. Key results: When administered at individually sub-threshold doses, a combination of SR141716A (0.1 mg·kg−1) and SCH58261 (0.5 mg·kg−1 i.p.) produced a reduction (28%) in ethanol self-administration. Combinations of threshold doses of SR141716A (0.3 mg·kg−1) and SCH58261 (2.0 mg·kg−1, i.p.) caused an essentially additive reduction (68%) in alcohol self-administration. A combination of individually sub-threshold doses of CB1 and mGlu5 receptor antagonists did not affect alcohol self-administration; however, combined threshold doses of SR141716A (0.3 mg·kg−1) and MTEP (1.0 mg·kg−1 i.p.) did reduce ethanol self-administration markedly (80%). Cue-conditioned alcohol seeking was attenuated by pretreatment with MTEP (1.0 mg·kg−1) co-administered with SR141716A (0.3 mg·kg−1 i.p.). In contrast, SCH58261 (2.0 mg·kg−1) co-administered with SR141716A (0.3 mg·kg−1 i.p.) did not reduce cue-conditioned alcohol seeking. Conclusions and implications: Adenosine A2A and cannabinoid CB1 receptors regulated alcohol self-administration additively, but combined low-dose antagonism of these receptors did not prevent cue-conditioned alcohol seeking after abstinence. In contrast, combined low-dose antagonism of mGlu5 and CB1 receptors did prevent relapse-like alcohol seeking after abstinence, suggesting a prominent role for mGlu5 receptors in this paradigm.

BACKGROUND: Epidemiological evidence of co-use of alcohol and areca nuts suggests a potential central interaction between arecoline, a major alkaloid of areca and a muscarinic receptor agonist, and ethanol. Moreover, the central cholinergic system plays an important role in the depressant action of ethanol and barbiturates. The purpose of this study was to investigate the effects of arecoline on pentobarbital- and ethanol-induced hypnosis in mice. METHODS: Male ICR mice were tested for locomotor activity following acute systemic administration of ethanol alone, arecoline alone, or ethanol plus arecoline. For the loss of the righting reflex (LORR) induced by pentobarbital and ethanol, sleep latency and sleeping duration were evaluated in mice treated with arecoline alone or the combination of arecoline and scopolamine or methscopolamine. RESULTS: Ethanol (1.0 to 3.0 g/kg, i.p.) reduced locomotor activity significantly and a declining trend was observed after treatment with arecoline (0.25 to 1.0 mg/kg, i.p.), but there were no synergistic effects of ethanol and arecoline on locomotor activity. The experiments on LORR demonstrated that arecoline (0.125 to 1.0 mg/kg, s.c.) shortened the duration of sleeping induced by ethanol (4.0 g/kg, i.p.), but not pentobarbital (45 mg/kg, i.p.). In addition, alterations of sleep latency were not obvious in both pentobarbital- and ethanol-induced LORR. Statistical analyses revealed that scopolamine (centrally acting), but not methscopolamine (peripherally acting), could antagonize the effect of arecoline on the duration of ethanol-induced LORR in mice. CONCLUSIONS: These results suggest that central muscarinic receptor is a pharmacological target for the action of arecoline to modulate ethanol-induced hypnosis.

Background: Inherited human aldehyde dehydrogenase 2 (ALDH-2) deficiency reduces the risk for alcoholism. Kudzu plants and extracts have been used for 1,000 years in traditional Chinese medicine to treat alcoholism. Kudzu contains daidzin, which inhibits ALDH-2 and suppresses heavy drinking in rodents. Decreased drinking due to ALDH-2 inhibition is attributed to aversive properties of acetaldehyde accumulated during alcohol consumption. However, daidzin can reduce drinking in some rodents without necessarily increasing acetaldehyde. Therefore, a selective ALDH-2 inhibitor might affect other metabolic factors involved in regulating drinking. Methods: Aldehyde dehydrogenase 2 inhibitors were synthesized based on the co-crystal structure of ALDH-2 and daidzin. We tested the efficacy of a highly selective reversible ALDH-2 inhibitor, CVT-10216, in models of moderate and high alcohol drinking rats. We studied 2-bottle choice and deprivation-induced drinking paradigms in Fawn Hooded (FH) rats, operant self-administration in Long Evans (LE), FH, and inbred P (iP) rats and in cue-induced reinstatement in iP rats. We also assayed blood acetaldehyde levels as well as dopamine (DA) release in the nucleus accumbens (NAc) and tested possible rewarding/aversive effects of the inhibitor in a conditioned place preference (CPP) paradigm. Results: CVT-10216 increases acetaldehyde after alcohol gavage and inhibits 2-bottle choice alcohol intake in heavy drinking rodents, including deprivation-induced drinking. Moreover, CVT-10216 also prevents operant self-administration and eliminates cue-induced reinstatement of alcohol seeking even when alcohol is not available (i.e., no acetaldehyde). Alcohol stimulates DA release in the NAc, which is thought to contribute to increased drinking and relapse in alcoholism. CVT-10216 prevents alcohol-induced increases in NAc DA without changing basal levels. CVT-10216 does not show rewarding or aversive properties in the CPP paradigm at therapeutic doses. Conclusion: Our findings suggest that selective reversible ALDH-2 inhibitors may have therapeutic potential to reduce excessive drinking and to suppress relapse in abstinent alcoholics.

Experimental studies in rats have revealed that the neuropeptide relaxin-3 modulates feeding and metabolism, stress responses, arousal, and exploratory behavior. In the present study, two cohorts of mixed background (129S5:B6) relaxin-3 knockout (KO) and wild-type littermate mice were subjected to a series of behavioral tests. Relaxin-3 KO mice appeared healthy and displayed no genotype differences in body weight, motor coordination (as determined via the rotarod), anxiety (light/dark box, elevated plus maze, large open field), spatial memory (Y-maze), or sensorimotor gating (prepulse inhibition). Female KO mice did, however, display hypoactivity, reflected by significantly shorter distances traveled in the automated locomotor cell, large open field, and novel object tests, and had fewer encounters with a novel mouse in a social interaction test. Male KOs, on the other hand, displayed a "hypersensitivity" to stress, spending longer in the Porsolt posture during a repeated forced swim test and losing a significantly greater percentage of their body weight in response to an 8-week chronic stress regimen. These findings support the hypothesis that relaxin-3 signaling contributes to the central control of arousal, exploratory behavior and stress responses.

As a foundation for regulatory and functional studies of central relaxin family peptide receptor systems, we are mapping the distribution of the different receptors in the brain of rat, mouse, and nonhuman primates, attempting to identify the nature of the receptor-positive neurons in key circuits and establish the complementary distribution of the respective ligands in these species. Here we review progress in mapping RXFP1, RXFP2, and RXFP3 (mRNAs and proteins) and their respective ligands and discuss some of the putative functions for these peptides and receptors that are being explored using receptor-selective agonist and antagonist peptides and receptor and peptide gene deletion mouse strains. Comparative studies reveal an association of RXFP1 and RXFP2 with excitatory neurons but a differential regional or cellular distribution, in contrast to the association of RXFP3 with inhibitory neurons. These studies also reveal differences in the distribution of RXFP1 and RXFP2 in rat and mouse brain, whereas the distribution of RXFP3 is more conserved across these species. Enrichment of RXFP1/2/3 in olfactory, cortical, thalamic, limbic, hypothalamic, midbrain, and pontine circuits suggests a diverse range of modulatory actions for these receptors. For example, experimental evidence in the rat reveals that RXFP1 activation in the amygdala inhibits memory consolidation, RXFP2 activation in striatum produces sniffing behavior, and RXFP3 modulation has effects on feeding and metabolism, the activity of the septohippocampal pathway, and spatial memory. Further studies are now required to reveal additional details of these and other functions linked to relaxin family peptide receptor signaling in mammalian brain and the precise mechanisms involved.

Experimentation with volatile substances (inhalants) is common during early adolescence, yet limited work has been conducted examining the neurobiological impact of regular binge use during this key stage of development. Human studies consistently demonstrate that chronic use is associated with significant toxic effects, including neurological and neuropsychological impairment, as well as diffuse and subtle changes in white matter. However, most preclinical research has tended to focus on acute exposure, with limited work examining the neuropharmacological or toxicological mechanisms underpinning these changes or their potential reversibility with abstinence. Nevertheless, there is growing evidence that commonly abused inhalants share common cellular mechanisms, and have similar actions to other drugs of abuse. Indeed, the majority of acute behavioural effects appear to be underpinned by changes in receptor and/or ion channel activity (for example, GABA(A), glycine and 5HT(3) receptor activation, NMDA receptor inhibition), although nonspecific interactions can also arise at high concentrations. Recent studies examining the effects of toluene exposure during the early postnatal period are suggestive of long-term alterations in the function of NMDA and GABA(A) receptors, although limited work has been conducted investigating exposure during adolescence. Given the critical role of neurotransmitter systems in cognitive, emotional and brain development, future studies will need to take account of the substantial neuromaturational changes that are known to occur in the brain during childhood and adolescence, and to specifically investigate the neuropharmacological and toxicological profile of inhalant exposure during this period of development.