Oxytocin Reduces Cocaine Cued Fos Activation in a Regionally Specific Manner.

Background: Oxytocin may be a possible treatment for multiple neuropsychiatric disorders, including cocaine addiction. Little is known about the site-specific effects of oxytocin on various drug addiction-related brain regions. Furthermore, sexually dimorphic effects of oxytocin on neural function in the addiction circuit have not been established. Here, we studied Fos expression following cocaine-cued reinstatement in both male and female rats. Methods: Male and female rats underwent self-administration, extinction, and reinstatement tests. On test days, rats were given oxytocin or vehicle, and lever pressing was measured in response to conditioned cocaine cues. Rats were perfused and Fos staining measured in the central amygdala, medial prefrontal cortex, nucleus accumbens core, and subthalamic nucleus. Fos/oxytocin double labeling occurred in the paraventricular nucleus of the hypothalamus. Results: Rats reinstated to cocaine cues relative to extinction responding and oxytocin reduced cocaine seeking. Oxytocin combined with contingent cue presentations increased Fos+ oxytocin cell bodies within the paraventricular nucleus of the hypothalamus relative to vehicle. Fos expression robustly increased in the central amygdala following oxytocin administration. Oxytocin reversed cue-induced Fos expression in the medial prefrontal cortex, nucleus accumbens core, and subthalamic nucleus. Central oxytocin infusion also attenuated reinstated cocaine seeking. Conclusions: Oxytocin decreased reinstated cocaine seeking, increased Fos activation in the paraventricular nucleus of the hypothalamus and central amygdala, but normalized cue-induced Fos activation in the medial prefrontal cortex, nucleus accumbens core, and subthalamic nucleus, thereby demonstrating regionally specific activation patterns. No sex differences were seen for the effects of oxytocin on cocaine seeking and Fos activation, indicating that oxytocin acts on similar central neural circuits critical to reinstated cocaine seeking in both males and females.

Oxytocin reduces cocaine seeking and reverses chronic cocaine-induced changes in glutamate receptor function.

BACKGROUND: Oxytocin, a neurohypophyseal neuropeptide, is a potential mediator and regulator of drug addiction. However, the cellular mechanisms of oxytocin in drug seeking remain unknown. METHODS: In the present study, we used a self-administration/reinstatement model to study the effects of oxytocin on cocaine seeking and its potential interaction with glutamate function at the receptor level. RESULTS: Systemic oxytocin dose-dependently reduced cocaine self-administration during various schedules of reinforcement, including fixed ratio 1, fixed ratio 5, and progressive ratio. Oxytocin also attenuated reinstatement to cocaine seeking induced by cocaine prime or conditioned cues. Western-blot analysis indicated that oxytocin increased phosphorylation of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-type glutamate receptor GluA1 subunit at the Ser 845 site with or without accompanying increases in phosphorylation of extracellular signal-regulated kinase, in several brain regions, including the prefrontal cortex, bed nucleus of the stria terminalis, amygdala, and dorsal hippocampus. Immunoprecipitation of oxytocin receptor and GluA1 subunit receptors further demonstrated a physical interaction between these 2 receptors, although the interaction was not influenced by chronic cocaine or oxytocin treatment. Oxytocin also attenuated sucrose seeking in a GluA1- or extracellular-signal-regulated kinase-independent manner. CONCLUSIONS: These findings suggest that oxytocin mediates cocaine seeking through interacting with glutamate receptor systems via second messenger cascades in mesocorticolimbic regions.

Reversing cocaine-induced synaptic potentiation provides enduring protection from relapse.

Cocaine addiction remains without an effective pharmacotherapy and is characterized by an inability of addicts to inhibit relapse to drug use. Vulnerability to relapse arises from an enduring impairment in cognitive control of motivated behavior, manifested in part by dysregulated synaptic potentiation and extracellular glutamate homeostasis in the projection from the prefrontal cortex to the nucleus accumbens. Here we show in rats trained to self-administer cocaine that the enduring cocaine-induced changes in synaptic potentiation and glutamate homeostasis are mechanistically linked through group II metabotropic glutamate receptor signaling. The enduring cocaine-induced changes in measures of cortico-accumbens synaptic and glial transmission were restored to predrug parameters for at least 2 wk after discontinuing chronic treatment with the cystine prodrug, N-acetylcysteine. N-acetylcysteine produced these changes by inducing an enduring restoration of nonsynaptic glutamatergic tone onto metabotropic glutamate receptors. The long-lasting pharmacological restoration of cocaine-induced glutamatergic adaptations by chronic N-acetylcysteine also caused enduring inhibition of cocaine-seeking in an animal model of relapse. These data mechanistically link nonsynaptic glutamate to cocaine-induced adaptations in excitatory transmission and demonstrate a mechanism to chronically restore prefrontal to accumbens transmission and thereby inhibit relapse in an animal model.

Orexin-1 receptor mediation of cocaine seeking in male and female rats.

Previous studies have shown that female rats exhibit enhanced cocaine seeking during multiple phases of cocaine addiction compared with males. The orexin/hypocretin system recently has been implicated in drug addiction in male rats. Based on the known sex differences in cocaine addiction, in the current study we examined orexin-mediated cocaine seeking during self-administration, extinction, and reinstatement in age-matched male (initial weight 250-300 g) and female (initial weight 175-225 g) Sprague-Dawley rats by using the orexin-1 receptor (OX1R) antagonist 1-(2-methylbenzoxazol-6-yl)-3-[1,5]naphthyridin-4-yl urea (SB-334867) (10-30 mg/kg). OX1R blockade had no effect on established cocaine self-administration, but attenuated cocaine seeking during extinction in both male and female rats. It is noteworthy that OX1R blockade potently attenuated cue-induced reinstatement in males but had no effect on females. SB-334867 also reduced cocaine seeking during pharmacological stress-induced (yohimbine, 2.5 mg/kg) and yohimbine + cue-induced reinstatement in both sexes. SB-334867 failed to affect reinstatement induced by cocaine (10 mg/kg) in either male or female rats, but selectively reduced cocaine + cue-induced reinstatement only in males. In separate experiments examining basal and cocaine-induced locomotion, SB-334867 attenuated locomotion in both male and female rats. Finally, assessment of plasma and brain levels of SB-334867 showed that estrus females had slightly higher plasma levels than diestrus females, but no overall sex differences or estrous cycle differences were observed in plasma or brain SB-334867 concentrations. These results show that OX1R signaling plays a role in mediating cocaine seeking, but differs between the sexes for cue-induced reinstatement.

Chronic modafinil effects on drug-seeking following methamphetamine self-administration in rats.

Acute administration of the cognitive enhancing drug, modafinil (Provigil®), reduces methamphetamine (Meth) seeking following withdrawal from daily self-administration. However, the more clinically relevant effects of modafinil on Meth-seeking after chronic treatment have not been explored. Here, we determined the impact of modafinil on Meth-seeking after chronic daily treatment during extinction or abstinence following Meth self-administration. Rats self-administered intravenous Meth during daily 2-h sessions for 14 d, followed by extinction sessions or abstinence. During this period, rats received daily injections of vehicle, 30, or 100 mg/kg modafinil and were then tested for Meth-seeking via cue, Meth-primed, and context-induced reinstatement at early and late withdrawal time-points. We found that chronic modafinil attenuated relapse to a Meth-paired context, decreased conditioned cue-induced and Meth-primed reinstatement, and resulted in enduring reductions in Meth-seeking even after discontinuation of treatment. Additionally, we determined that only a very high dose of modafinil (300 mg/kg) during maintenance of self-administration had an impact on Meth intake. These results validate and extend clinical and preclinical findings that modafinil may be a viable treatment option for Meth addiction.

Chronic N-acetylcysteine during abstinence or extinction after cocaine self-administration produces enduring reductions in drug seeking.

The cysteine prodrug N-acetylcysteine (NAC) has been shown to reduce reinstatement of cocaine seeking by normalization of glutamatergic tone. However, enduring inhibition of cocaine seeking produced by NAC has not been explored under different withdrawal conditions. Thus, the present study determined whether chronic NAC administered during daily extinction training or daily abstinence after withdrawal from cocaine self-administration would reduce cocaine seeking. Rats self-administered intravenous cocaine during daily 2-h sessions for 12 days, followed by daily extinction or abstinence sessions. During this period, rats received daily injections of saline or NAC (60 or 100 mg/kg). Subsequently, rats were tested for cocaine seeking via conditioned cue, cue + cocaine-primed, and context-induced relapse. Chronic NAC administration blunted cocaine seeking under multiple experimental protocols. Specifically, NAC attenuated responding during cue and cue + cocaine-primed reinstatement tests after extinction and context, cue, and cue + cocaine relapse tests after abstinence. Protection from relapse by NAC persisted well after treatment was discontinued, particularly when the high dose was combined with extinction trials. The finding that NAC reduced cocaine seeking after drug treatment was discontinued has important implications for the development of effective antirelapse medications. These results support recent preclinical and clinical findings that NAC may serve as an effective treatment for inhibiting relapse in cocaine addicts.

An acute psychosocial stressor does not potentiate alcohol cue reactivity in non-treatment-seeking alcoholics.

BACKGROUND: Relapse risk factors, such as psychological stress and alcohol cues, are often encountered together. Understanding how they interact has the potential to improve alcoholism treatments. This study was conducted to examine whether an acute psychosocial stressor enhanced alcohol cue reactivity in non-treatment-seeking alcoholics. METHODS: Seventy-nine alcohol-dependent individuals (39 women) randomly received either the Trier Social Stress Test or a no-stress control condition. Stress reactivity was measured with serum adrenocorticotropic hormone and cortisol, mean arterial blood pressure, and subjective distress. Immediately following the stress manipulation, participants held and sniffed a neutral cue then their preferred alcoholic beverage. Cue reactivity was measured by 2 subjective measures of craving following each cue. Additionally, general craving was assessed with the Alcohol Urge Questionnaire at the beginning and end of the laboratory procedure. RESULTS: The stress manipulation showed internal validity on all measures of stress reactivity. There was not a main effect of stress nor a stress × cue interaction on either cue reactivity measure. As expected, there was a main effect of cue (alcohol > neutral cue) on both measures of cue reactivity. General craving increased during the challenge, but not differently by stress group. Magnitude of stress reactivity was not associated with magnitude of cue reactivity, and all results were independent of gender. CONCLUSION: In this well-controlled clinical laboratory study of non-treatment-seeking alcoholics, an acute psychological stressor did not make an alcohol cue a more potent urge-inducing stimulus, and stress had no effect on general alcohol craving.

A comparison of economic demand and conditioned-cued reinstatement of methamphetamine-seeking or food-seeking in rats.

This study examined whether continued access to methamphetamine or food reinforcement changed economic demand for both. The relationship between demand elasticity and cue-induced reinstatement was also determined. Male Long-Evans rats were lever pressed under increasing fixed-ratio requirements for either food pellets or methamphetamine (20 µg/50 µl infusion). For two groups, demand curves were obtained before and after continued access (12 days, 2-h sessions) to the reinforcer under a fixed-ratio 3 schedule. A third group was given continued access to methamphetamine between determinations of food demand and a fourth group abstained from methamphetamine between determinations. All groups underwent extinction sessions, followed by a cue-induced reinstatement test. Although food demand was less elastic than methamphetamine demand, continued access to methamphetamine shifted the methamphetamine demand curve upward and the food demand curve downward. In some rats, methamphetamine demand also became less elastic. Continued access to food had no effect on food demand. Reinstatement was higher after continued access to methamphetamine relative to food. For methamphetamine, elasticity and reinstatement measures were correlated. Continued access to methamphetamine, but not food, alters demand in ways suggestive of methamphetamine accruing reinforcing strength. Demand elasticity thus provides a useful measure of abuse liability that may predict future relapse to renewed drug-seeking and drug use.

Assessment of multiple salivary biomarkers during repetitive transcranial magnetic stimulation (rTMS) treatment for major depression.

Steroid hormones may serve as potential biomarkers of treatment response for major depressive disorder (MDD). Here, we assessed salivary levels of cortisol, dehydroepiandrosterone (DHEA), and DHEA sulfate (DHEA-S), as well as α-amylase activity, across 30 sessions of bilateral repetitive transcranial magnetic stimulation (rTMS) of the dorsolateral prefrontal cortex in MDD patients. While rTMS significantly improved symptoms as measured by three different symptom scales, salivary biomarker levels and their ratios showed no significant changes across sessions. These results do not support the routine clinical use of these biomarkers as reliable indicators of treatment outcome during rTMS administration for MDD.

Neural Substrates and Circuits of Drug Addiction.

Drug addiction is a chronic relapsing disorder, and a significant amount of research has been devoted to understand the factors that contribute to the development, loss of control, and persistence of compulsive addictive behaviors. In this review, we provide an overview of various theories of addiction to drugs of abuse and the neurobiology involved in elements of the addiction cycle. Specific focus is devoted to the role of the mesolimbic pathway in acute drug reinforcement and occasional drug use, the role of the mesocortical pathway and associated areas (e.g., the dorsal striatum) in escalation/dependence, and the contribution of these pathways and associated circuits to conditioned responses, drug craving, and loss of behavioral control that may underlie drug relapse. By enhancing the understanding of the neurobiological factors that mediate drug addiction, continued preclinical and clinical research will aid in the development of novel therapeutic interventions that can serve as effective long-term treatment strategies for drug-dependent individuals.

Reversible inactivation of the basolateral amygdala, but not the dorsolateral caudate putamen, attenuates consolidation of cocaine-cue associative learning in a reinstatement model of drug-seeking.

Previous research has shown that the basolateral amygdala (BLA) mediates stimulus-reward learning, including drug-cue associations, whereas the dorsolateral caudate putamen (dlCPu) primarily mediates stimulus-response (habit) learning. Recent evidence has indicated that the dlCPu may be critical in cocaine-seeking following extended self-administration, but it remains unknown whether the dlCPu plays a role in the early formation of drug-cue associations. The current study used a model of Pavlovian learning to compare the roles of the BLA and dlCPu in the consolidation of cocaine-cue associations that maintain cocaine-seeking during cue-induced reinstatement. Male Sprague-Dawley rats self-administered cocaine (0.2 mg/ 50µL infusion, i.v.) in the absence of cues for 6 days (2 h/day). Immediately following a single 1-h classical conditioning session in which passive cocaine infusions were paired with a light/tone cue, animals received bilateral infusions of the GABA receptor agonists, baclofen/muscimol (1.0/0.1 mm), or vehicle into the BLA or dlCPu. Following additional cocaine self-administration (5 days) and subsequent extinction (no cocaine or cues, 7 days), the ability of the previously cocaine-paired cues to reinstate cocaine-seeking was assessed. Inactivation of the BLA, but not the dlCPu, immediately following the classical conditioning session impaired the consolidation of cocaine-cue associations as seen by decreased cue-induced reinstatement. These results extend previous findings that the BLA mediates the consolidation of learned associations that drive cocaine-seeking during subsequent reinstatement and indicate that the dlCPu does not play a role during initial stimulus-drug associative learning.

Altered dopamine transporter function and phosphorylation following chronic cocaine self-administration and extinction in rats.

Cocaine binds with the dopamine transporter (DAT), an effect that has been extensively implicated in its reinforcing effects. However, persisting adaptations in DAT regulation after cocaine self-administration have not been extensively investigated. Here, we determined the changes in molecular mechanisms of DAT regulation in the caudate-putamen (CPu) and nucleus accumbens (NAcc) of rats with a history of cocaine self-administration, followed by 3weeks of withdrawal under extinction conditions (i.e., no cocaine available). DA uptake was significantly higher in the CPu of cocaine-experienced animals as compared to saline-yoked controls. DAT V(max) was elevated in the CPu without changes in apparent affinity for DA. In spite of elevated CPu DAT activity, total and surface DAT density and DAT-PP2Ac (protein phosphatase 2A catalytic subunit) interaction remained unaltered, although p-Ser- DAT phosphorylation was elevated. In contrast to the CPu, there were no differences between cocaine and saline rats in the levels of DA uptake, DAT V(max) and K(m) values, total and surface DAT, p-Ser-DAT phosphorylation, or DAT-PP2Ac interactions in the NAcc. These results show that chronic cocaine self-administration leads to lasting, regionally specific alterations in striatal DA uptake and DAT-Ser phosphorylation. Such changes may be related to habitual patterns of cocaine-seeking observed during relapse.

P-glycoprotein inhibition potentiates the behavioural and neurochemical actions of risperidone in rats.

Antipsychotic drugs are the mainstay pharmacotherapy for schizophrenia and related psychiatric disorders. While the metabolic pathways of antipsychotic drugs have been well defined, the role of drug transporters in the disposition and effects of antipsychotic drugs has not been systematically explored. P-glycoprotein has ubiquitous expression in brain endothelial cells and plays a protective role by effluxing substrates for elimination and by limiting their accumulation in the central nervous system. Risperidone and several other antipsychotic drugs are substrates of P-glycoprotein. Increased antipsychotic drug entry into the brain via blockade of the P-glycoprotein transporter may facilitate the amount of available drug to its targets, particularly dopamine receptors. By increasing available antipsychotic drug concentrations, P-glycoprotein inhibition offers a novel means of enhanced drug delivery. This study evaluated whether selective P-glycoprotein transporter inhibition would increase the effects of risperidone on relevant indices of behaviour (catalepsy and locomotion) and neurochemistry (dopamine release and metabolism as measured by in-vivo microdialysis). We administered the P-glycoprotein inhibitor, PSC 833 (100 mg/kg p.o.), to rats prior to administration of risperidone at varying doses (0.01-4.0 mg/kg s.c.). P-glycoprotein inhibition significantly increased risperidone-induced cataleptic effects, blockade of amphetamine-induced locomotion, and effects on dopamine turnover as seen by increased striatal dopamine metabolite levels. These results provide functional evidence concordant with prior data for increased brain levels of risperidone following PSC 833 treatment.

Orexin/hypocretin signaling at the orexin 1 receptor regulates cue-elicited cocaine-seeking.

The orexin/hypocretin system has recently been implicated in reward-processing and addiction. We examined the involvement of the orexin system in cue-induced reinstatement of extinguished cocaine-seeking by administering the orexin 1 receptor antagonist SB-334867 (SB) or the orexin 2 receptor antagonist 4-pyridylmethyl (S)-tert-leucyl 6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline (4PT) prior to reinstatement testing. Male Sprague Dawley rats self-administered cocaine in 2-h sessions for 10 days, followed by extinction training. Reinstatement of cocaine-seeking was elicited by presentation of tone + light cues previously paired with cocaine infusions. SB (10, 20 and 30 mg/kg) dose-dependently decreased cue-induced reinstatement of cocaine-seeking without significantly affecting responding during late extinction. 4PT (10 and 30 mg/kg) did not significantly alter cue-induced reinstatement. In separate experiments, the highest doses of SB and 4PT had no significant effect on established cocaine self-administration, and 4PT reduced spontaneous activity in a locomotor test to a greater extent than SB. Finally, SB (30 mg/kg) had no effect on the acquisition of cocaine-paired cues during a Pavlovian cocaine-stimulus conditioning session in the operant chamber. Pretreatment with SB prior to the Pavlovian acquisition session had no effect on subsequent cue-induced reinstatement of cocaine-seeking elicited by those cues. However, pretreatment with SB prior to a second reinstatement session in the same animals significantly attenuated the expression of cue-induced reinstatement. These results show that orexin transmission at the orexin 1 receptor, but not the orexin 2 receptor, is necessary for the reinstatement of cocaine-seeking elicited by drug-paired cues and that orexin signaling is not critical for cocaine reinforcement or cocaine-stimulus conditioning.

Extended methamphetamine self-administration in rats results in a selective reduction of dopamine transporter levels in the prefrontal cortex and dorsal striatum not accompanied by marked monoaminergic depletion.

Chronic abuse of methamphetamine leads to cognitive dysfunction and high rates of relapse, paralleled by significant changes of brain dopamine and serotonin neurotransmission. Previously, we found that rats with extended access to methamphetamine self-administration displayed enhanced methamphetamine-primed reinstatement of drug-seeking and cognitive deficits relative to limited access animals. The present study investigated whether extended access to methamphetamine self-administration produced abnormalities in dopamine and serotonin systems in rat forebrain. Rats self-administered methamphetamine (0.02-mg/i.v. infusion) during daily 1-h sessions for 7 to 10 days, followed by either short- (1-h) or long-access (6-h) self-administration for 12 to 14 days. Lever responding was extinguished for 2 weeks before either reinstatement testing or rapid decapitation and tissue dissection. Tissue levels of monoamine transporters and markers of methamphetamine-induced toxicity were analyzed in several forebrain areas. Long-access methamphetamine self-administration resulted in escalation of daily drug intake ( approximately 7 mg/kg/day) and enhanced drug-primed reinstatement compared with the short-access group. Furthermore, long-, but not short-access to self-administered methamphetamine resulted in persistent decreases in dopamine transporter (DAT) protein levels in the prefrontal cortex and dorsal striatum. In contrast, only minor alterations in the tissue levels of dopamine or its metabolites were found, and no changes in markers specific for dopamine terminals or glial cell activation were detected. Our findings suggest that persistent methamphetamine seeking is associated with region-selective changes in DAT levels without accompanying monoaminergic neurotoxicity. Greater understanding of the neuroadaptations underlying persistent methamphetamine seeking and cognitive deficits could yield targets suitable for future therapeutic interventions.

Attenuation of cocaine-seeking by progesterone treatment in female rats.

Clinical research suggests that gender differences exist in cocaine dependence. Similarly, preclinical studies have shown that female rats exhibit higher response rates during cocaine self-administration, early extinction, and cocaine-primed reinstatement of drug-seeking. These effects are also estrous cycle dependent and inversely related to plasma progesterone, in that proestrus females (high progesterone) exhibit less cocaine-seeking, while estrous females (low progesterone) show the greatest cocaine-seeking. Based on these findings, we hypothesized that progesterone would attenuate cocaine-seeking behavior in intact, freely cycling animals. The role of the estrous cycle on cocaine-seeking behavior during early (first acquisition day) versus late (last maintenance day) cocaine self-administration was also examined. Female, Sprague-Dawley rats self-administered cocaine (0.5 mg/kg/infusion, IV) along a FR1 schedule, followed by daily extinction sessions in the absence of cocaine reinforcement. Once responding was extinguished, rats received an injection of cocaine (10 mg/kg, IP) immediately prior to reinstatement testing. Progesterone (2 mg/kg, SC) or vehicle was administered 20 and 2h prior to the first day of extinction (early cocaine withdrawal) and the reinstatement trials. To determine estrous cycle phase, we assessed vaginal cytology prior to the first acquisition and last maintenance days of cocaine self-administration, the first day of extinction training, and each reinstatement test. During early and late cocaine self-administration, proestrus and estrous females exhibited the greatest levels of active lever responding, respectively. A significant increase in responding also occurred during cocaine-primed reinstatement for estrous versus nonestrous females, an effect that was selectively attenuated by progesterone. However, progesterone was not effective at reducing cocaine-primed reinstatement for females in other phases of the estrous cycle, nor was it effective at reducing cocaine-seeking during early withdrawal. Taken together, these results suggest that progesterone may be a useful therapeutic for preventing relapse in abstinent female cocaine users, especially when the likelihood of relapse is greatest.

Dopamine D1 receptor antagonism in the prelimbic cortex blocks the reinstatement of heroin-seeking in an animal model of relapse.

In brain regions that have been implicated in the reinstatement of drug-seeking, the prelimbic cortex has emerged as a critical regulator of relapse behaviours. Here, the effects of prelimbic cortex dopamine (DA) D(1) receptor antagonism on drug-seeking produced by heroin-paired cues, or by a single priming dose of heroin are examined. Rats lever-pressed daily for i.v. heroin discretely paired with a conditioned stimulus during 3-h sessions for a period of 2 wk, followed by extinction and reinstatement of drug-seeking by previously heroin-paired cues (tone+light) or heroin-priming injections (0.25 mg/kg) in the absence of heroin reinforcement. Intracranial infusion of the DA D(1) receptor antagonist, SCH 23390 (0.02-2.0 microg/side), into the prelimbic cortex potently and dose dependently attenuated heroin-seeking in response to either cue presentations or a priming dose of heroin. These results suggest that DA D1 receptors regulate prefrontal cortex pathways necessary for the reinstatement of heroin-seeking.

Prenatal stress enhances responsiveness to cocaine.

Early environmental events have profound influences on a wide range of adult behavior. In the current study, we assessed the influence of maternal stress during gestation on psychostimulant and neurochemical responsiveness to cocaine, cocaine self-administration, and reinstatement of cocaine-seeking in adult offspring. Pregnant, female Sprague-Dawley rats were subjected to either no treatment or to restraint stress three times per day for the last 7 days of gestation and cocaine-related behavior was assessed in offspring at 10 weeks of age. Relative to controls, a noncontingent cocaine injection elevated locomotor activity as well as nucleus accumbens levels of extracellular dopamine and glutamate to a greater extent in both cocaine-naive and cocaine-experienced prenatal stress (PNS) rats and elevated prefrontal cortex dopamine in cocaine-experienced PNS rats. To assess the impact of PNS on cocaine addiction-related behavior, rats were trained to lever press for intravenous (i.v.) infusions of cocaine (0.25, 0.5, or 1 mg/kg/infusion), with each infusion paired with a light+tone-conditioned stimulus. Lever-pressing was extinguished and cocaine-seeking reinstated by re-exposure to the conditioned cues or by intraperitoneal cocaine-priming injections (5 or 10 mg/kg). PNS elevated active lever responding both during extinction and cocaine-primed reinstatement, but not during self-administration or conditioned-cued reinstatement. PNS also did not alter intake during self-administration. These findings demonstrate that PNS produces enduring nervous system alterations that increase the psychomotor stimulant, motivational, and neurochemical responsiveness to noncontingent cocaine. Thus, early environmental factors contribute to an individual's initial responsiveness to cocaine and propensity to relapse to cocaine-seeking.

Dysregulation of dopamine transporter trafficking and function after abstinence from cocaine self-administration in rats: evidence for differential regulation in caudate putamen and nucleus accumbens.

The profound alterations produced by cocaine on dopamine (DA) neurotransmission raise the possibility that dopamine transporter (DAT)-expressing neurons may modify DA transport in response to repeated cocaine exposure to maintain the appropriate efficiency of DA clearance. In this study, we determined the changes in molecular mechanisms of DAT regulation in rats with a history of repeated cocaine self-administration followed by 3 weeks of abstinence. Using ex vivo caudate putamen (CPu) and nucleus accumbens (NAcc) synaptosomal preparations, we found that DA uptake was significantly higher in the CPu and NAcc of cocaine-experienced animals compared with yoked saline animals. Surface distribution, p-Ser phosphorylation, and protein phosphatase 2A catalytic subunit (PP2Ac) interaction of DAT were all altered in the CPu. Maximal velocity (V(max)) values were elevated both in the CPu and NAcc of cocaine-experienced rats compared with saline controls. Although there was no change in the apparent affinity for DA in the CPu, increased DA affinity was evident in the NAcc. Consistent with elevated DAT activity in cocaine-experienced animals, a higher level of surface DAT, DAT-PP2Ac association, and decreased serine phosphorylation of DAT were observed in the CPu, but not in the NAcc. These results, for the first time, suggest that chronic cocaine self-administration followed by abstinence leads to persisting alterations in normal DAT trafficking and catalytic regulatory cascades in the CPu and NAcc in a brain region-specific manner.

A comparison of the effects of different operant training experiences and dietary restriction on the reinstatement of cocaine-seeking in rats.

Studies on the reinstatement of drug-seeking after withdrawal from chronic drug self-administration have varied in terms of the procedures by which animals are initially trained to self-administer the drug. The current study directly compared whether prior operant training for food pellet reinforcement and/or maintained dietary restriction significantly altered the reinstatement of extinguished cocaine-seeking in the presence of cocaine-paired cues, a priming injection of cocaine (10 mg/kg; i.p.), and the pharmacological stressor, yohimbine (1.25 or 2.5 mg/kg, i.p.). Male Long Evans rats were divided into four groups as follows: a) trained to lever press for food pellets prior to cocaine self-administration and then maintained on a restricted diet, b) trained to lever press for food pellets prior to cocaine self-administration and then placed on an ad libitum diet, c) untrained and maintained on a restricted diet, or d) untrained and placed on ad libitum feeding. All rats readily self-administered cocaine (0.2 mg/50 mul/infusion) and were subsequently extinguished in the absence of cocaine or previously cocaine-paired cues (light+tone). Following extinction, rats experienced cue-, cocaine-, and yohimbine-induced reinstatement testing. No significant differences were seen between groups for lever responding during the maintenance phase and during extinction. Likewise, reinstatement of cocaine-seeking did not vary across groups for cue-, cocaine-, or yohimbine-induced reinstatement. Under these specific parameters, operant training prior to cocaine self-administration and/or dietary restriction do not significantly alter reinstatement of cocaine-seeking. The results arguably support the approach of not using prior lever training with a non-drug reinforcer and to limit the use of dietary restriction only to the acquisition phase of drug self-administration.