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BACKGROUND: Social behaviour plays a key role in mental health and wellbeing, and developing greater understanding of mechanisms underlying social interaction-particularly social motivation-holds substantial transdiagnostic impact. Common rodent behavioural assays used to assess social behaviour are limited in their assessment of social motivation, whereas the social operant conditioning model can provide unique and valuable insights into social motivation. Further characterisation of common experimental parameters that may influence social motivation within the social operant model, as well as complementary methodological and analytical approaches, are warranted. METHODS: This study investigated the effects of biological sex, housing condition, and time-of-day, on social motivation using the social operant model. This involved training rats to lever press (FR1) for 60-s access to a social reward (same-sex conspecific stimulus). Subjects were male and female Wistar rats, housed under individual or paired conditions, and sessions were conducted either in the mid-late light phase (ZT6-10) or early-mid dark phase (ZT13-17). A behavioural economics approach was implemented to measure social demand and the influence of stimulus partner sex (same- vs. opposite-sex stimulus) on social operant responding. Additionally, video tracking analyses were conducted to assess the degree of convergence between social appetitive and consummatory behaviours. RESULTS: Biological sex, housing conditions, the interaction between sex and housing, and stimulus partner sex potently influenced social motivation, whereas time-of-day did not. Behavioural economics demonstrated that sex, housing, and their interaction influence both the hedonic set-point and elasticity of social demand. Video analysis of social interaction during social operant sessions revealed that social appetitive and consummatory behaviours are not necessarily convergent, and indicate potential social satiety. Lastly, oestrus phase of female experimental and stimulus rats did not impact social motivation within the model. CONCLUSIONS: Social isolation-dependent sex differences exist in social motivation for rats, as assessed by social operant conditioning. The social operant model represents an optimal preclinical assay that comprehensively evaluates social motivation and offers a platform for future investigations of neurobiological mechanisms underlying sex differences in social motivation. These findings highlight the importance of continued consideration and inclusion of sex as a biological variable in future social operant conditioning studies. Humans are social creatures-our everyday interactions with others and the support this provides play a key role in our wellbeing. For those experiencing mental health conditions, people's motivation to engage with others can wane, which can lead them to withdraw from those who support them. Therefore, to develop better treatment strategies for these conditions, we need to gain a deeper understanding of social motivation. Studying social behaviour in animals can facilitate this investigation of social motivation as it allows for a causal understanding of underlying neurobiology that is not possible in human experiments. An optimal way to study social motivation in animals is using the social operant conditioning model, where rats learn to press a lever that opens a door and allows them to interact with another rat for a short time. This study characterised the social operant model by testing whether sex, housing conditions, time-of-day, and the sex of the stimulus partner influence rats' motivation to seek interaction with another rat. We found that female rats were more socially motivated than males, and that rats living alone were more motivated than those living with another rat; interestingly, this effect of housing affected females more than males. Regardless of sex, rats were more motivated to interact with a rat of the opposite sex. These findings provide insights into sex differences in social motivation in rats and new insights into the social operant model which will help guide future research into social motivation and other mental health conditions.

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RATIONALE: Alcopop beverages are generally the first alcoholic beverage that young females drink which contain high levels of sugar and alcohol. The over-consumption of these drinks may encourage alcohol co-administration with methamphetamine (METH) impacting on drinking behaviour and glial function. AIMS: The aims of this study were to evaluate the effect of adolescent binge alcohol exposure on consumption level, anxiety-like behaviour, cross-sensitization with METH and on astrocyte expression in reward related brain regions. METHODS: Adolescent female Sprague-Dawley rats had daily 1-hour oral alcohol consumption of alcopop (ALCP; with sucrose) or ethanol-only (ETOH; without sucrose), transitioned from 5 to 15% (v/v) ethanol content for 34 days. Water and sucrose groups act as controls. During alcohol withdrawal, rats were tested for anxiety on the elevated plus maze (EPM) and locomotor activity following saline or METH (1 mg/kg i.p) treatment. Brains were then collected to assess astrocyte immunofluorescence for glial fibrillary acidic protein (GFAP) in reward-related brain regions. RESULTS: Rats pretreated with 5% ALCP consumed significantly more volume and ethanol intake when compared to 5% EtOH rats. Both ALCP and EtOH groups had a higher preference ratio for 5% than 15% alcohol solutions and ALCP rats had greater ethanol intake at 15% than EtOH rats. Alcohol withdrawal showed no significant differences between groups on anxiety, METH cross-sensitization effects or GFAP intensity in the regions studied. CONCLUSIONS: Overall, the addition of sucrose to alcoholic solutions encouraged female rats to consume larger volumes and greater ethanol intake compared to ethanol-only solutions, yet did not have long lasting effects on behaviour and astrocytes.

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RATIONALE/OBJECTIVES: Targeting cannabinoid receptor type 1 (CB1R) has shown promise for treating opioid withdrawal symptoms. This study aimed to investigate the efficacy of a specific CB1R negative allosteric modulator (NAM), Org27569, in reducing both naloxone-precipitated and protracted withdrawal symptoms in oxycodone-dependent mice. METHODS: Mice received escalating doses of oxycodone (9-33 mg/kg IP) or saline twice daily for 9 days, followed by a final dose of oxycodone (33 mg/kg) or saline in the morning of day 9. In one cohort, the impact of Org27569 (3, 10, and 30 mg/kg) on naloxone (10 mg/kg IP) precipitated withdrawal symptoms was assessed. In another cohort, Org27569 (3 mg/kg) effects on the acquisition of conditioned place aversion to naloxone (0.6 mg/kg) precipitated opioid withdrawal, on behaviour following a 7-9-day abstinence period, and on naloxone (0.6 mg/kg) precipitated withdrawal-induced escape behaviour in a novel assay were assessed. RESULTS: Although Org27569 decreased opioid withdrawal-induced jumping at doses of 10 and 30 mg/kg, these effects were confounded by reduced locomotion. At all doses tested, Org27569 had a modest inhibitory effect on gastrointestinal motility. At the lower dose of 3 mg/kg, which was not confounded by locomotor effects, Org27569 did not impact naloxone-precipitated withdrawal-induced jumping, acquisition of oxycodone withdrawal-induced conditioned place aversion, or naloxone-precipitated withdrawal-induced escape behaviour in a novel assay. A clear protracted opioid withdrawal phenotype was not observed in assays of anxiety-like or social behaviour. CONCLUSIONS: Org27569 effects on negative affective-like symptoms were confounded by locomotor effects and effects on gastrointestinal motility were not opioid withdrawal specific. Further studies are needed in a model that produces a more pronounced protracted withdrawal syndrome.

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Registration of data to a common frame of reference is an essential step in the analysis and integration of diverse neuroscientific data. To this end, volumetric brain atlases enable histological datasets to be spatially registered and analyzed, yet accurate registration remains expertise-dependent and slow. In order to address this limitation, we have trained a neural network, DeepSlice, to register mouse brain histological images to the Allen Brain Common Coordinate Framework, retaining registration accuracy while improving speed by >1000 fold.

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STUDY OBJECTIVES: Exogenous administration of the neuropeptide oxytocin exerts diverse effects on various neurobehavioral processes, including sleep and wakefulness. Since oxytocin can enhance attention to social and fear-related environmental cues, it should promote arousal and wakefulness. However, as oxytocin can attenuate stress, reduce activity, and elicit anxiolysis, oxytocin might also prime the brain for rest, and promote sleep. At present, little research has comprehensively characterized the neuropsychopharmacology of oxytocin-induced effects on sleep-wake behavior and no reconciliation of these two competing hypotheses has been proposed. METHODS: This study explored the effects of oxytocin on sleep-wake outcomes using radiotelemetry-based polysomnography in adult male and female Wistar rats. Oxytocin was administered via intraperitoneal (i.p.; 0.1, 0.3 and 1 mg·kg-1) and intranasal (i.n.; 0.06, 1, 3 mg·kg-1) routes. Caffeine (i.p. and i.n.; 10 mg·kg-1) was administered as a wake-promoting positive control. To ascertain mechanism of action, pretreatment experiments with the oxytocin receptor (OXTR) antagonist L-368,899 (i.p.; 5 mg·kg-1) followed by oxytocin (i.p.; 1 mg·kg-1) were also conducted. RESULTS: In both male and female rats, i.p. oxytocin promoted quiet wakefulness at the cost of suppressing active wakefulness, non-rapid eye movement (NREM) and rapid eye movement (REM) sleep. Several i.p. oxytocin-induced sleep-wake effects were mediated by OXTR binding. In contrast, i.n. oxytocin did not alter most sleep-wake outcomes at any dose tested. Both i.p. and i.n. caffeine demonstrated wake-promoting effects. CONCLUSIONS: These findings help reconcile competing hypotheses of oxytocin-induced effects on sleep-wake behavior: i.p. oxytocin promotes quiet wakefulness-a state of restful environmental awareness compatible with both oxytocin's anxiolytic effects and its enhancement of processing complex stimuli.

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INTRODUCTION: Methamphetamine (METH, "ice") is a potent and addictive psychostimulant. Abuse of METH perturbs neurotransmitter systems and induces neurotoxicity; however, the neurobiological mechanisms which underlie addiction to METH are not fully understood, limiting the efficacy of available treatments. Here we investigate METH-induced changes to neuronal nitric oxide synthase (nNOS), parvalbumin and calretinin-expressing GABAergic interneuron populations within the nucleus accumbens (NAc), prefrontal cortex (PFC) and orbitofrontal cortex (OFC). We hypothesise that dysfunction or loss of these GABAergic interneuron populations may disrupt the excitatory/inhibitory balance within the brain. METHODS: Male Long Evans rats (N = 32) were trained to lever press for intravenous METH or received yoked saline infusions. Following 14 days of behavioural extinction, animals were given a non-contingent injection of saline or METH (1 mg/kg, IP) to examine drug-primed reinstatement to METH-seeking behaviours. Ninety minutes post-IP injection, animals were culled and brain sections were analysed for Fos, nNOS, parvalbumin and calretinin immunoreactivity in eight distinct subregions of the NAc, PFC and OFC. RESULTS: METH exposure differentially affected GABAergic populations, with METH self-administration increasing nNOS immunoreactivity at distinct locations in the prelimbic cortex and decreasing parvalbumin immunoreactivity in the NAc. METH self-administration triggered reduced calretinin immunoreactivity, whilst acute METH administration produced a significant increase in calretinin immunoreactivity. As expected, non-contingent METH-priming treatment increased Fos immunoreactivity in subregions of the NAc and PFC. CONCLUSION: Here we report that METH exposure in this model may alter the function of GABAergic interneurons in more subtle ways, such as alterations in neuronal firing or synaptic connectivity.

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Early life stress (ELS) is associated with perturbed neural development and augmented vulnerability to mental health disorders, including addiction. How ELS changes the brain to increase addiction risk is poorly understood, and there are no therapies which target this ELS-induced vulnerability. ELS disrupts the oxytocin system, which can modulate addiction susceptibility, suggesting that targeting the oxytocin system may be therapeutic in this ELS-addiction comorbidity. Therefore, we determined whether adolescent oxytocin treatment after ELS could: (1) reduce vulnerability to anxiety, social deficits, and methamphetamine-taking and reinstatement; and (2) restore hypothalamic oxytocin and corticotropin-releasing factor expressing neurons and peripheral oxytocin and corticosterone levels. Long Evans pups underwent maternal separation (MS) for either 15 min or 360 min on postnatal days (PND) 1-21. During adolescence (PNDs 28-42), rats received a daily injection of either oxytocin or saline. In Experiment 1, adult rats were assessed using the elevated plus-maze, social interaction procedure, and methamphetamine self-administration procedure, including extinction, and cue-, methamphetamine- and yohimbine-induced reinstatement. In Experiment 2, plasma for enzyme immunoassays and brain tissue for immunofluorescence were collected from adult rats after acute stress exposure. Adolescent oxytocin treatment ameliorated ELS-induced anxiety and reduced methamphetamine- and yohimbine-induced reinstatement in both sexes, and suppressed methamphetamine intake and facilitated extinction in males only. Additionally, adolescent oxytocin treatment after ELS restored oxytocin-immunoreactive cells and stress-induced oxytocin levels in males, and attenuated stress-induced corticosterone levels in both sexes. Adolescent oxytocin treatment reverses some of the ELS effects on later-life psychopathology and vulnerability to addiction.

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RATIONALE: Cannabidiol (CBD) and cannabidiolic acid (CBDA) are non-psychoactive components of the cannabis plant. CBD has been well characterised to have anxiolytic and anticonvulsant activity, whereas the behavioural effects of CBDA are less clear. Preclinical and clinical data suggests that CBD has antipsychotic properties and reduces methamphetamine self-administration in rats. An animal model that is commonly used to mimic the neurochemical changes underlying psychosis and drug dependence is methamphetamine (METH) sensitisation, where repeated administration of the psychostimulant progressively increases the locomotor effects of METH. OBJECTIVE: The aim of this study was to determine whether CBD or CBDA attenuate METH-induced sensitisation of locomotor hyperactivity in rats. METHODS: Eighty-six male Sprague Dawley rats underwent METH sensitisation protocol where they were subjected to daily METH (1 mg/kg on days 2 and 8, 5 mg/kg on days 3-7; i.p.) injections for 7 days. After 21 days of withdrawal, rats were given a prior injection of CBD (0, 40 and 80 mg/kg; i.p.) or CBDA (0, 0.1, 10 and 1000 µg/kg; i.p.) and challenged with acute METH (1 mg/kg; i.p.). Locomotor activity was then measured for 60 min. RESULTS: Rats displayed robust METH sensitisation as evidenced by increased locomotor activity to METH challenge in METH-pretreated versus SAL-pretreated rats. CBD (40 and 80 mg/kg) reduced METH-induced sensitisation. There was no effect of any CBDA doses on METH sensitisation or acute METH-induced hyperactivity. CONCLUSION: These results demonstrate that CBD, but not CBDA, reduces METH sensitisation of locomotor activity in rats at pharmacologically effective doses, thus reinforcing evidence that CBD has anti-addiction and antipsychotic properties.

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RATIONALE: Stress exposure during adolescence contributes to developing a methamphetamine (METH) use disorder. However, most of the studies investigating addiction-related behaviours include only male rodents, despite METH addiction rates being higher in females. Furthermore, animal studies investigating the effects of stress on methamphetamine addiction have used only basic self-administration models which may not be sensitive to the effects of stress. OBJECTIVES: This project explored whether adolescent isolation stress exposure increases the incidence of four key addiction-related behaviours in female rats. METHODS: Thirty-two female rat pups were caged in groups of four or individually during adolescence from postnatal (PND) day 22, with the latter being re-socialised in groups of four on PND 43. In adulthood, rats were tested for addiction-like behaviours in a METH self-administration paradigm modelling motivation to take METH, persistence in drug-seeking behaviour when METH was not available, resistance to extinction, and propensity to reinstate after a period of withdrawal. RESULTS: Adolescent social isolation resulted in lower METH intake during acquisition; however, the paradigm modelling drug-seeking when the drug was unavailable engendered intermittent METH bingeing in all rats, abolishing the group differences in intake during this phase. Adolescent social isolation also accelerated extinction of non-reinforced lever pressing, and increased stress-primed reinstatement, compared to the group-housed rats. CONCLUSIONS: Adolescent social isolation stress alters various methamphetamine addiction-like behaviours in female rats.

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Early life stress (ELS) exposure alters brain development, increasing vulnerability for mental illness in adulthood, including depression. Despite this association, there are no approved pharmacotherapies to protect against the emergence of mental illness resulting from ELS. Recent preclinical work showed that oxytocin (OT) administration in adulthood reduced depressive-like behaviour in male rats with a history of ELS. However, the ability of an OT treatment regime in adolescence, a critical developmental window for the OT system, to prevent the expression of depressive-like behaviours following ELS has not been investigated. Therefore, the present study aimed to determine whether chronic OT administration can ameliorate the enduring effects of ELS on depressive-like behaviours in both male and female rats. Following birth, Long Evans rat pups (N = 107) underwent maternal separation (MS) for either 15 min (MS15) or 6 h (MS360) on postnatal days (PND) 1-21. During adolescence (PND 28-42), rats received a daily injection of either OT (1 mg/kg) or saline. During adulthood (PND 57 onwards), effort-related motivation was measured using a model of effortful choice (EC), while behavioural despair was measured using the forced swim test (FST). Lastly, body and organ weights were measured to examine the physiological impacts of ELS and chronic OT administration. Overall, in both sexes, MS360 increased behavioural despair yet had no impact on effort-related motivation. Importantly, adolescent OT administration prevented the MS360-induced increase in behavioural despair in both males and females. Additionally, MS360 resulted in persistent reductions in body weight in both sexes post-weaning and increased spleen weight in males and adrenal weight in females. OT treatment had no impact on body weight in either sex, but prevented the MS-induced increase in adrenal gland weight in females. Overall, these findings have important implications for using oxytocin as a preventative pharmacotherapy after ELS.

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The neuropeptide oxytocin has emerged as a promising pharmacotherapy for methamphetamine (METH) addiction, and clinical trials of intranasal oxytocin are underway. However, there is debate as to how peripherally administered oxytocin alters brain signalling to modulate addiction processes. Interestingly, there is evidence for functional interactions between peripheral oxytocin administration and the vagus nerve. Therefore, this study investigated whether the effects of peripherally administered oxytocin require vagal signalling to reduce METH self-administration and reinstatement of METH-seeking behaviours. Male and female Sprague-Dawley rats underwent surgery for jugular catheterisation and either subdiaphragmatic vagotomy (SDV) or a sham operation. Rats were trained to self-administer METH, and the effect of peripherally administered oxytocin on METH intake was assessed. Rats then underwent extinction, and effects of oxytocin were assessed on cue- and METH-induced reinstatement of METH-seeking. Oxytocin treatment robustly attenuated METH intake in both sexes, and SDV entirely prevented the suppressant effect of oxytocin (0.3 mg/kg) on METH intake, and partially prevented the effects of 1 mg/kg oxytocin in both sexes. After extinction, SDV decreased the suppressing effects of oxytocin on cue- and METH-primed reinstatement in males, but not females. SDV was functionally confirmed by measuring food intake following administration of the vagal dependent peptide, cholecyostokin-8. Our data suggest that vagus nerve signalling is required for the inhibitory effects of peripherally administered oxytocin on METH self-administration and reinstatement, and that this vagal dependency is partially mediated by sex and drug withdrawal. This study has implications for the use of oxytocin as a therapy for METH use disorder for both sexes.

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BACKGROUND: The incentive sensitisation theory of addiction posits that drug-associated stimuli become imbued with incentive motivational properties, driving pathological drug seeking. However, pre-existing variability in the incentive salience to non-drug reward cues ('sign trackers' (STs); 'goal trackers' (GTs)) is also predictive of the desire for and relapse to cocaine and opioids. Here, we asked whether variation in propensity to attribute incentive salience to a food cue is predictive of reinstatement to the highly addictive psychostimulant methamphetamine (METH), and whether treatment with the promising anti-addiction therapy oxytocin differentially reduces METH behaviour between STs and GTs. METHODS: Rats were trained to associate a Pavlovian cue with delivery of a sucrose pellet over 8 days. They then received jugular vein catheters for intravenous METH self-administration, followed by behavioural extinction, and cue-induced and METH-primed reinstatement to METH-seeking behaviours. Oxytocin was administered prior to self-administration and reinstatement tests. RESULTS: Despite the self-administration of similar amounts of METH, STs reinstated more to METH cues than did GTs, yet METH-priming reinstated STs and GTs similarly. Furthermore, oxytocin attenuated cue-induced reinstatement more so in STs than in GTs, and reduced METH-primed reinstatement to a greater extent in the top quartile of reinstaters, indicating that oxytocin treatment may be most effective for those at highest risk of addiction. CONCLUSIONS: This pre-existing bias towards reward cues presents a possible tool to screen for METH addiction susceptibility and may be useful for understanding the neurobiology of addiction and for pharmacotherapeutic discovery.

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The early postnatal period is a time of tremendous change for the dam and her offspring. During this time, environmental insults such as repeated stress exposure can have detrimental effects. In research that has focused on the effect of postnatal stress exposure on the dams, conflicting changes in maternal care and anxiety-like behaviour have been reported. Additionally, changes to hypothalamic neuropeptides that are crucially involved in the transition to motherhood and stress regulation, namely oxytocin and corticotrophin-releasing factor (CRF), have not been examined. Accordingly, the present study aimed to determine (i) whether repeated postpartum stress increases engagement in maternal care behaviours and anxiety-like behaviour and (ii) whether these behavioural changes correspond with changes to CRF- or oxytocin-immunoreactive (-IR) cells in the paraventricular nucleus (PVN) of the hypothalamus. A non-lactating group was also included to control for the effects of lactation on anxiety and the hypothalamic neuroendocrine system. Following the birth of their litters, Long-Evans dams were separated from their pups from postnatal day (PND) 1 to PND21 for either 15 minutes (maternal separation [MS]15) or 6 hours (MS360). Maternal behaviours were recorded for 30 minutes on select PNDs following the separation. On PND22, dams were exposed to the elevated plus maze, brains were collected, and immunofluorescence analysis of PVN oxytocin- and CRF-IR cells was conducted. Our findings demonstrate that prolonged maternal separation altered typical maternal behaviours and reduced anxiety relative to MS15 dams. At the cellular level, oxytocin-IR cells in the caudal PVN were reduced in MS360 dams to a level similar to that in non-lactating controls, and PVN CRF-IR cells were reduced relative to both MS15 and non-lactating controls. Taken together, these data reveal the behavioural and neuronal changes that occur in the mother dam following repeated postnatal stress exposure.

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Early life trauma is strongly associated with an increased vulnerability to abuse illicit drugs and the impairment of neural development. This includes alterations to the development of the oxytocin system, which plays a pivotal role in the regulation of social behaviours and emotion. Dysregulation of this important system also contributes to increased susceptibility to develop drug addiction. In this review, we provide an overview of the animal models of early life stress that are widely used, and discuss the impact that early life stress has on drug-taking behaviour in adolescence and adulthood in both sexes. We link this to the changes that early life stress has on the endogenous oxytocin system, and how exogenously administered oxytocin may help to re-establish functioning of the system, and in turn, reduce drug-taking behaviour.

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Methamphetamine (METH) abuse is characterised by chronic relapse and anxiety, for which there are no effective pharmacotherapies. Acute treatment with the neuropeptide oxytocin has shown therapeutic potential for METH addiction and has social and anxiolytic effects in METH-naïve rats. However, the effects of chronic oxytocin treatment in METH-experienced rats are unknown. This study investigated the effects of repeated oxytocin treatment during abstinence from METH self-administration on incubation of cue-induced relapse, yohimbine- and METH-induced reinstatement, trait anxiety, and social interaction. Male and female Sprague-Dawley rats self-administered intravenous METH for 2 h/day (12 days) and then on short-access (2 h/day; ShA) or long-access (6 h/day; LgA) sessions (10 days). Rats underwent 30 days of drug abstinence, during which they received 15 days of intraperitoneal oxytocin (1 mg/kg) or saline (days 6-20) injections. Anxiety and social interaction were tested on days 25-28, and incubation was assessed by testing cue-induced relapse on days 2 and 30. Rats underwent extinction after the final cue-relapse test, followed by yohimbine- and METH-primed reinstatement. LgA, but not ShA rats exhibited incubation of METH-craving and enhanced METH-primed reinstatement in both sexes, and enhanced yohimbine-induced reinstatement in females. Importantly, chronic oxytocin attenuated incubation and METH-primed reinstatement in both sexes, and yohimbine-induced reinstatement in females, although only in LgA rats. LgA produced a heightened anxiety phenotype, which was partially rescued by chronic oxytocin treatment. Using a translatable addiction model, these findings demonstrate the therapeutic efficacy of chronic oxytocin after METH self-administration and supports the clinical utility of oxytocin for METH addiction in both sexes.

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BACKGROUND: Methamphetamine is an addictive stimulant that can cause many adverse physical, psychological and psychosocial effects. Preliminary evidence shows cannabidiol, a non-intoxicating constituent of the cannabis plant, may have efficacy in treating opioid and nicotine dependence. However, no study has yet examined whether cannabidiol treatment might impact on methamphetamine addiction. AIMS: The current study investigated whether cannabidiol administration reduces the motivation to self-administer methamphetamine and relapse to methamphetamine-seeking behavior following abstinence. METHODS: Thirty-two male Sprague Dawley rats with implanted jugular vein catheters were initially trained to self-administer methamphetamine via lever press during two-hour sessions on a fixed ratio 1 schedule of reinforcement. Rats in experiment 1 ( n=16) then advanced to a progressive ratio reinforcement schedule to examine the effects of cannabidiol (0, 20, 40, and 80 mg/kg intraperitoneal) on motivation to self-administer methamphetamine. Rats in experiment 2 ( n=16) were tested for cannabidiol effects on methamphetamine-primed reinstatement following extinction. RESULTS: Cannabidiol (80 mg/kg, but not 40 mg/kg, or 20 mg/kg) reduced the motivation to self-administer methamphetamine and attenuated methamphetamine-primed relapse to methamphetamine-seeking behavior after extinction. CONCLUSION: This is the first demonstration that cannabidiol can reduce the motivation to seek and consume methamphetamine, and suggests that cannabidiol might be worth trialing as a novel pharmacotherapy for methamphetamine dependence.

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The neuropeptide oxytocin has shown promise as an effective therapy in pre-clinical models of methamphetamine (METH) addiction. The nucleus accumbens core (NAcc) has been identified as an important site for oxytocin to inhibit METH behaviours, although previous findings suggest that the effects of oxytocin in the NAcc are mediated by receptors other than the oxytocin receptor (OTR). Oxytocin has high affinity for the vasopressin V1A receptor (V1AR) which has been implicated in numerous oxytocin-dependent social behaviours. The aim of this study was to investigate the involvement of the V1AR in mediating the effect of oxytocin treatment to reduce METH-primed reinstatement of METH-seeking behaviour. Male rats were trained to self-administer intravenous infusions of METH by lever press during daily 2-h fixed ratio 1 scheduled sessions for 20 days. Following extinction of lever pressing, rats were tested for the effects of oxytocin alone, oxytocin co-administered with a selective V1AR antagonist, or oxytocin co-administered with a selective OTR antagonist, on METH-primed reinstatement, when administered systemically, or when microinjected into the NAcc. Systemic administration of oxytocin prevented METH-primed reinstatement, an effect which was significantly reduced by systemic pre-treatment with a V1AR but not OTR antagonist. Local administration of oxytocin into the NAcc reduced METH-primed reinstatement, but not when the V1AR was blocked. Our results demonstrate a substantial role for the V1AR in mediating the inhibitory effects of oxytocin on METH-primed reinstatement, and indicate the need for investigations into the differential involvement of V1ARs and OTRs in oxytocin-induced reduction of METH-related behaviours.

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The psychostimulant methamphetamine (METH) is an addictive illicit drug. Systemic administration of the neuropeptide oxytocin modulates METH-related reward and METH-seeking behaviour. Recent findings demonstrated a reduction in METH-induced reward by oxytocin administration into the nucleus accumbens (NAc) core. It is not known, however, if oxytocin acts in this region to reduce relapse to METH-seeking behaviour. Using the drug reinstatement paradigm in rats experienced at METH self-administration, we aimed to determine whether oxytocin pre-treatment within the NAc core would reduce relapse to METH use and if this could be reversed by the co-administration of the oxytocin receptor (OTR) antagonist desGly-NH2,d(CH2)5[D-Tyr2,Thr4]OVT. Male Sprague-Dawley rats underwent surgery to implant an intravenous jugular vein catheter and bilateral microinjection cannulae in the NAc core. Rats were then trained to self-administer intravenous METH (0.1 mg/kg/infusion) by lever press during 2-hour fixed ratio 1 scheduled sessions for 20 days. Following extinction of lever press activity, the effect of microinjecting saline, oxytocin (0.5 pmol, 1.5 pmol, 4.5 pmol) or co-administration of oxytocin (1.5 pmol) and desGly-NH2,d(CH2)5[D-Tyr2,Thr4]OVT (1 nmol, 3 nmol) in the NAc core (500 nl/side) was examined on METH-primed (1 mg/kg, i.p.) reinstatement of drug-seeking behaviour. Our results showed oxytocin directly administered into the NAc core decreased METH-primed reinstatement in a dose-dependent manner. Co-administration of the selective OTR antagonist did not specifically reverse the inhibitory effects of oxytocin on METH priming, suggesting mediation by receptors other than the OTR. These findings highlight an important modulatory effect of oxytocin in the NAc core on relapse to METH seeking.

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