Sex differences in non-reinforced responding for cocaine

Sex-biased effects of outcome devaluation by sensory-specific satiety on Pavlovian-conditioned behavior

Goal-directed behavior relies on accurate mental representations of the value of expected outcomes. Disruptions to this process are a central feature of several neuropsychiatric disorders, including addiction. Goal-directed behavior is most frequently studied using instrumental paradigms paired with outcome devaluation, but cue-evoked behaviors in Pavlovian settings can also be goal-directed and therefore sensitive to changes in outcome value. Emerging literature suggests that male and female rats may differ in the degree to which their Pavlovian-conditioned responses are goal-directed, but interpretation of these findings is complicated by the tendency of female and male rats to engage in distinct types of Pavlovian responses when trained with localizable cues. Here, we used outcome devaluation via sensory-specific satiety to assess the behavioral responses in male and female Long Evans rats trained to respond to an auditory CS (conditioned stimulus) in a Pavlovian-conditioning paradigm. We found that satiety-induced devaluation led to a decrease in behavioral responding to the reward-predictive CS, with males showing an effect on both port entry latency and probability and females showing an effect only on port entry probability. Overall, our results suggest that outcome devaluation affects Pavlovian-conditioned responses in both male and female rats, but that females may be less sensitive to outcome devaluation.

Paternal alcohol exposure attenuates maintenance and reinstated operant responding for alcohol in the offspring of rats

BACKGROUND

The heritability of alcohol use disorder is close to 50%, yet common genetic variants account for less than 5% of risk. The missing heritability may reflect environmental exposure in the parents prior to conception. Indeed, paternal alcohol exposure has many behavioral and biological consequences for rodent offspring. We recently found that paternal alcohol exposure attenuated the acquisition of operant alcohol self-administration in offspring of rats of both sexes. Here we test whether this effect extends to other phases of operant self-administration thought to model motivation, craving, and relapse.

METHODS

Wistar male rats exposed to alcohol vapors or air for 6 weeks were mated with alcohol-naïve females 8 weeks later. The adult offspring were trained to lever press for alcohol and tested under several conditions: (1) maintenance responding under a progressive ratio schedule, (2) extinction responding due to removal of the alcohol delivery contingency, (3) reinstatement of extinguished responding in the presence of alcohol-associated cues, and (4) reinitiation of lever press responding for alcohol delivery under fixed and progressive ratio schedules.

RESULTS

Alcohol-sired offspring showed reduced responding under the progressive ratio schedule and blunted cue-induced reinstatement of extinguished responding. Alcohol-sired offspring also emitted fewer responses during extinction sessions and did not reinitiate responding to the same extent as control-sired rats after alcohol delivery was restored.

CONCLUSIONS

Across all conditions, paternal alcohol exposure led to a reduction in the reinforcing effects of alcohol in offspring. These results are consistent with studies conducted with paternal cocaine exposure except that here we find effects in rats of both sexes.

Outcome devaluation by sensory-specific satiety alters Pavlovian-conditioned behavior in male and female rats

Goal-directed behavior relies on accurate mental representations of the value of expected outcomes. Disruptions to this process are a central feature of several neuropsychiatric disorders, including addiction. Goal-directed behavior is most frequently studied using instrumental paradigms paired with outcome devaluation, but cue-evoked behaviors in Pavlovian settings can also be goal-directed and therefore sensitive to changes in outcome value. Emerging literature suggests that male and female rats may differ in the degree to which their Pavlovian-conditioned responses are goal-directed, but interpretation of these findings is complicated by the tendency of female and male rats to engage in distinct types of Pavlovian responses when trained with localizable cues. Here, we used outcome devaluation via sensory-specific satiety to assess the behavioral responses in male and female Long Evans rats trained to respond to an auditory CS (conditioned stimulus) in a Pavlovian-conditioning paradigm. We found that satiety-induced devaluation led to a decrease in behavioral responding to the reward-predictive CS, with males showing an effect on both port entry latency and probability and females showing an effect only on port entry probability. Overall, our results suggest that outcome devaluation affects Pavlovian-conditioned responses in both male and female rats, but that females may be less sensitive to outcome devaluation.

Chronicity of repeated blast traumatic brain injury associated increase in oxycodone seeking in rats

Numerous epidemiological studies have found co-morbidity between non-severe traumatic brain injury (TBI) and substance misuse in both civilian and military populations. Preclinical studies have also identified this relationship for some misused substances. We have previously demonstrated that repeated blast traumatic brain injury (rbTBI) increased oxycodone seeking without increasing oxycodone self-administration, suggesting that the neurological sequelae of traumatic brain injury can elevate opioid misuse liability. Here, we determined the chronicity of this effect by testing different durations of time between injury and oxycodone self-administration and durations of abstinence. We found that the subchronic (four weeks), but not the acute (three days) or chronic (four months) duration between injury and oxycodone self-administration was associated with increased drug seeking and re-acquisition of self-administration following a 10-day abstinence. Examination of other abstinence durations (two days, four weeks, or four months) revealed no effect of rbTBI on drug seeking at any of the abstinence durations tested. Together, these data indicate that there is a window of vulnerability after TBI when oxycodone self-administration is associated with elevated drug seeking and relapse-related behaviors.

Sex and Age Effects on Neurobehavioral Toxicity Induced by Binge Alcohol

Historically, most alcohol neurotoxicity studies were conducted in young adult males and focused on chronic intake. There has been a shift towards studying the effects of alcohol on the adolescent brain, due to alcohol consumption during this formative period disrupting the brain's developmental trajectory. Because the most typical pattern of adolescent alcohol intake is heavy episodic (binge) drinking, there has also been a shift towards the study of binge alcohol-induced neurobehavioral toxicity. It has thus become apparent that binge alcohol damages the adolescent brain and there is increasing attention to sex-dependent effects. Significant knowledge gaps remain in our understanding of the effects of binge alcohol on the female brain, however. Moreover, it is unsettling that population-level studies indicate that the prevalence of binge drinking is increasing among American women, particularly those in older age groups. Although study of adolescents has made it apparent that binge alcohol disrupts ongoing brain maturational processes, we know almost nothing about how it impacts the aging brain, as studies of its effects on the aged brain are relatively scarce, and the study of sex-dependent effects is just beginning. Given the rapidly increasing population of older Americans, it is crucial that studies address age-dependent effects of binge alcohol, and given the increase in binge drinking in older women who are at higher risk for cognitive decline relative to men, studies must encompass both sexes. Because adolescence and older age are both characterized by age-typical brain changes, and because binge drinking is the most common pattern of alcohol intake in both age groups, the knowledge that we have amassed on binge alcohol effects on the adolescent brain can inform our study of its effects on the aging brain. In this review, we therefore cover the current state of knowledge of sex and age-dependent effects of binge alcohol, as well as statistical and methodological considerations for studies aimed at addressing them.

Sex Differences and the Role of Estradiol in Mesolimbic Reward Circuits and Vulnerability to Cocaine and Opiate Addiction

Although both men and women become addicted to drugs of abuse, women transition to addiction faster, experience greater difficulties remaining abstinent, and relapse more often than men. In both humans and rodents, hormonal cycles are associated with females' faster progression to addiction. Higher concentrations and fluctuating levels of ovarian hormones in females modulate the mesolimbic reward system and influence reward-directed behavior. For example, in female rodents, estradiol (E2) influences dopamine activity within the mesolimbic reward system such that drug-directed behaviors that are normally rewarding and reinforcing become enhanced when circulating levels of E2 are high. Therefore, neuroendocrine interactions, in part, explain sex differences in behaviors motivated by drug reward. Here, we review sex differences in the physiology and function of the mesolimbic reward system in order to explore the notion that sex differences in response to drugs of abuse, specifically cocaine and opiates, are the result of molecular neuroadaptations that differentially develop depending upon the hormonal state of the animal. We also reconsider the notion that ovarian hormones, specifically estrogen/estradiol, sensitize target neurons thereby increasing responsivity when under the influence of either cocaine or opiates or in response to exposure to drug-associated cues. These adaptations may ultimately serve to guide the motivational behaviors that underlie the factors that cause women to be more vulnerable to cocaine and opiate addiction than men.

Early life stress and the propensity to develop addictive behaviors

There is a vast literature on effects of early life manipulations in rodents much of which is aimed at investigating the long-term consequences related to emotion and cognition in adulthood. Less is known about how these manipulations affect responses reflective of alcohol (AUD) and substance (SUD) use disorders. The purpose of this paper is to review the literature of studies that employed early life manipulations and assessed behavioral responses to psychoactive substances, specifically alcohol, opiates, and stimulants, in rodents. While the findings with alcohol are more limited and mixed, studies with opiates and stimulants show strong support for the ability of these manipulations to enhance behavioral responsivity to these substances in line with epidemiological data. Some outcomes show sex differences. The mechanisms that influence these enduring changes may reflect epigenetic alterations. Several studies support a role for altered DNA methylation (and other epigenetic mechanisms) as biological responses to early environmental insults. The chemical changes induced by DNA methylation affect transcriptional activity of DNA and thus can have a long-term impact on the individual's phenotype. Such effects are particularly robust when they occur during sensitive periods of brain development (e.g., first postnatal weeks in rodents). We review this emerging literature as it relates to the known neurobiology of AUDs and SUDs and suggest new avenues of research. Such findings will have implications for the treatment and prevention of AUDs and SUDs and could provide insight into factors that support resiliency.

Contributions of prolonged contingent and non-contingent cocaine exposure to escalation of cocaine intake and glutamatergic gene expression

Similar to the pattern observed in people with substance abuse disorders, laboratory animals will exhibit escalation of cocaine intake when the drug is available over prolonged periods of time. Here, we investigated the contribution of behavioral contingency of cocaine administration on escalation of cocaine intake and gene expression in the dorsal medial prefrontal cortex (dmPFC) in adult male rats. Rats were allowed to self-administer intravenous cocaine (0.25 mg/infusion) under either limited cocaine-(1 h/day), prolonged cocaine-(6 h/day), or limited cocaine-(1 h/day) plus yoked cocaine-access (5 h/day); a control group received access to saline (1 h/day). One day after the final self-administration session, the rats were euthanized and the dmPFC was removed for quantification of mRNA expression of critical glutamatergic signaling genes, Homer2, Grin1, and Dlg4, as these genes and brain region have been previously implicated in addiction, learning, and memory. All groups with cocaine-access showed escalated cocaine intake during the first 10 min of each daily session, and within the first 1 h of cocaine administration. Additionally, the limited-access + yoked group exhibited more non-reinforced lever responses during self-administration sessions than the other groups tested. Lastly, Homer2, Grin1, and Dlg4 mRNA were impacted by both duration and mode of cocaine exposure. Only prolonged-access rats exhibited increases in mRNA expression for Homer2, Grin1, and Dlg4 mRNA. Taken together, these findings indicate that both contingent and non-contingent "excessive" cocaine exposure supports escalation behavior, but the behavioral contingency of cocaine-access has distinct effects on the patterning of operant responsiveness and changes in mRNA expression.

Sex-specific attenuation of impulsive action by progesterone in a go/no-go task for cocaine in rats

RATIONALE

Previous work indicated that progesterone (PRO) reduced impulsive choice for cocaine in female but not male rats (Smethells et al. Psychopharmacology 233:2999-3008, 2016). Impulsive action, typically measured by responding for a reinforcer during a signaled period of nonavailability of natural reinforcers, predicts initiation and escalation of drug use in animals and humans. The present study examined impulsive action for cocaine using PRO in male and female rats trained on a go/no-go task.

OBJECTIVE

Rats were trained on a go/no-go task to respond for cocaine infusions (0.4 mg/kg/inf). During the "go" component, responding was reinforced on a VI 30-s schedule, whereas during the "no-go" component, withholding a response was reinforced on a differential reinforcement of other behavior (DRO) 30-s schedule. A response during the no-go component resets the DRO timer and served as a measure of impulsive action. After baseline responding was established, rats were pretreated with vehicle (VEH) or PRO (0.5 mg/kg), and DRO resets and responding during the go component for cocaine were compared in males vs. females.

RESULTS

DRO resets were significantly lower following PRO treatment compared to VEH in female, but not male, rats. Response rates and overall infusions during the go component were not significantly altered by PRO in either females or males.

CONCLUSION

Treatment with PRO resulted in a sex-specific reduction in impulsive action for cocaine, while not affecting cocaine self-administration.

Sex Differences in Animal Models: Focus on Addiction

The purpose of this review is to discuss ways to think about and study sex differences in preclinical animal models. We use the framework of addiction, in which animal models have excellent face and construct validity, to illustrate the importance of considering sex differences. There are four types of sex differences: qualitative, quantitative, population, and mechanistic. A better understanding of the ways males and females can differ will help scientists design experiments to characterize better the presence or absence of sex differences in new phenomena that they are investigating. We have outlined major quantitative, population, and mechanistic sex differences in the addiction domain using a heuristic framework of the three established stages of the addiction cycle: binge/intoxication, withdrawal/negative affect, and preoccupation/anticipation. Female rats, in general, acquire the self-administration of drugs and alcohol more rapidly, escalate their drug taking with extended access more rapidly, show more motivational withdrawal, and (where tested in animal models of "craving") show greater reinstatement. The one exception is that female rats show less motivational withdrawal to alcohol. The bases for these quantitative sex differences appear to be both organizational, in that estradiol-treated neonatal animals show the male phenotype, and activational, in that the female phenotype depends on the effects of gonadal hormones. In animals, differences within the estrous cycle can be observed but are relatively minor. Such hormonal effects seem to be most prevalent during the acquisition of drug taking and less influential once compulsive drug taking is established and are linked largely to progesterone and estradiol. This review emphasizes not only significant differences in the phenotypes of females and males in the domain of addiction but emphasizes the paucity of data to date in our understanding of those differences.

Toll-like Receptors in the Vascular System: Sensing the Dangers Within

Toll-like receptors (TLRs) are components of the innate immune system that respond to exogenous infectious ligands (pathogen-associated molecular patterns, PAMPs) and endogenous molecules that are released during host tissue injury/death (damage-associated molecular patterns, DAMPs). Interaction of TLRs with their ligands leads to activation of downstream signaling pathways that induce an immune response by producing inflammatory cytokines, type I interferons (IFN), and other inflammatory mediators. TLR activation affects vascular function and remodeling, and these molecular events prime antigen-specific adaptive immune responses. Despite the presence of TLRs in vascular cells, the exact mechanisms whereby TLR signaling affects the function of vascular tissues are largely unknown. Cardiovascular diseases are considered chronic inflammatory conditions, and accumulating data show that TLRs and the innate immune system play a determinant role in the initiation and development of cardiovascular diseases. This evidence unfolds a possibility that targeting TLRs and the innate immune system may be a novel therapeutic goal for these conditions. TLR inhibitors and agonists are already in clinical trials for inflammatory conditions such as asthma, cancer, and autoimmune diseases, but their study in the context of cardiovascular diseases is in its infancy. In this article, we review the current knowledge of TLR signaling in the cardiovascular system with an emphasis on atherosclerosis, hypertension, and cerebrovascular injury. Furthermore, we address the therapeutic potential of TLR as pharmacological targets in cardiovascular disease and consider intriguing research questions for future study.

Role of Corticotropin Releasing Factor 1 Signaling in Cocaine Seeking during Early Extinction in Female and Male Rats

Locus coeruleus norepinephrine (LC-NE) and corticotropin releasing factor (CRF) neurons are involved in stress responses, including stress’s ability to drive drug relapse. Previous animal studies indicate that female rats exhibit greater drug seeking than male rats during initial drug abstinence. Moreover, females are more sensitive to the effect of stress to drive drug seeking than males. Finally, LC-NE neurons are more sensitive to CRF in females compared to males. We hypothesized that increased drug seeking in females on extinction day one (ED1) is due to increased response to the stress of early withdrawal and is dependent upon the increased response of LC in females to CRF. We predicted that LC-NE neurons would exhibit Fos activation on ED1, and that blocking CRF1 signaling would decrease drug seeking on ED1 measured by responding on an active lever previously associated with cocaine self- administration. After chronic cocaine self-administration, female and male rats underwent a test for initial extinction responding by measuring lever pressing in the absence of cocaine. Prior to this Extinction Day 1 (ED1) session, rats were injected with vehicle or the selective CRF1 antagonist (CP) to measure effects of CRF antagonism on drug seeking during early abstinence. ED1 increased corticosterone in female rats, in proportion to lever responding in male and female, indicating that ED1 was stressful. Pretreatment with CP decreased cocaine seeking on ED1 more effectively in female compared to male rats. This increase in responding was associated with an increase in activation of LC NE neurons. Together, these findings indicate that stress, and signaling at CRF receptors in LC, may be involved in the increased drug seeking during initial abstinence.

Sex differences in reinstatement of cocaine-seeking with combination treatments of progesterone and atomoxetine

Two repurposed medications have been proposed to treat cocaine abuse. Progesterone, a gonadal hormone, and atomoxetine, a medication commonly used to treat attention deficit/hyperactivity disorder, have both been separately shown to reduce cocaine self-administration and reinstatement (i.e., relapse). The goal of the present study was to examine sex differences in the individual effects of PRO and ATO as well as the combination PRO+ATO treatment on cocaine (COC), caffeine (CAF), and/or cue-primed reinstatement of cocaine-seeking. Adult male and female Wistar rats lever-pressed under a FR 1 schedule for cocaine infusions (0.4mg/kg/inf). After 14 sessions of stable responding in daily 2-h sessions, rats underwent a 21-day extinction period when no drug or drug-related stimuli were present. Rats were then separated into four groups that received PRO (0.5mg/kg) alone (PRO+SAL), ATO (1.5mg/kg) alone (VEH+ATO), control (VEH+SAL) or combination (PRO+ATO) treatments prior to the reinstatement condition. Reinstatement of cocaine-seeking to cues and/or drug injections of cocaine or caffeine was tested after extinction. During maintenance, females self-administered more cocaine than males, but no sex differences were seen during extinction. Females showed greater cocaine-seeking than males after a CAF priming injection. Individual treatment with ATO did not decrease reinstatement under any priming condition; however, the combination treatment decreased cocaine-seeking under the COC+CUES priming condition in males, and both PRO alone and the combination treatment decreased cocaine-seeking in the CAF+CUES condition in females. Overall, PRO alone was only effective in reducing reinstatement in females, while the combination treatment was consistently effective in reducing reinstatement in both sexes.

Sex differences in the acquisition and maintenance of cocaine and nicotine self-administration in rats

RATIONALE

Consistent sex differences are observed in human drug addiction, with females often exceeding males on drug intake. However, there is still a need for animal models for some aspects of addiction such as acquisition of drug self-administration and the subsequent development of drug-seeking.

OBJECTIVES

The present study examined sex differences in the acquisition and maintenance of self-administration of two widely used stimulants, cocaine and nicotine.

METHODS

Male and female rats self-administered cocaine (0.4 mg/kg/infusion) or nicotine (0.03 mg/kg/infusion) daily under a fixed-ratio 1 (FR 1) schedule until acquisition criteria were met (maximum of 30 sessions). The self-administration criterion for cocaine was ≥20 infusions in a 2-h session and ≥5 infusions in a 1-h session for nicotine. Sex differences were assessed by examining the percentage of rats that met acquisition criteria, the number of sessions to meet criteria, and the number of infusions earned during the maintenance phase.

RESULTS

A significantly higher percentage of male rats acquired both cocaine and nicotine self-administration than females, and males met acquisition criteria in fewer sessions. However, after criteria were met, females self-administered more cocaine than males during the first 5 days of maintenance. There were no sex differences in nicotine infusions post-acquisition.

CONCLUSIONS

Differences in acquisition amongst sexes can reveal factors that are integral to initiation of drug use, an often overlooked phase of drug addiction.

Brain-derived neurotrophic factor and addiction: Pathological versus therapeutic effects on drug seeking

Many abused drugs lead to changes in endogenous brain-derived neurotrophic factor (BDNF) expression in neural circuits responsible for addictive behaviors. BDNF is a known molecular mediator of memory consolidation processes, evident at both behavioral and neurophysiological levels. Specific neural circuits are responsible for storing and executing drug-procuring motor programs, whereas other neural circuits are responsible for the active suppression of these "seeking" systems. These seeking-circuits are established as associations are formed between drug-associated cues and the conditioned responses they elicit. Such conditioned responses (e.g. drug seeking) can be diminished either through a passive weakening of seeking- circuits or an active suppression of those circuits through extinction. Extinction learning occurs when the association between cues and drug are violated, for example, by cue exposure without the drug present. Cue exposure therapy has been proposed as a therapeutic avenue for the treatment of addictions. Here we explore the role of BDNF in extinction circuits, compared to seeking-circuits that "incubate" over prolonged withdrawal periods. We begin by discussing the role of BDNF in extinction memory for fear and cocaine-seeking behaviors, where extinction circuits overlap in infralimbic prefrontal cortex (PFC). We highlight the ability of estrogen to promote BDNF-like effects in hippocampal-prefrontal circuits and consider the role of sex differences in extinction and incubation of drug-seeking behaviors. Finally, we examine how opiates and alcohol "break the mold" in terms of BDNF function in extinction circuits.

Individual variation in the propensity to attribute incentive salience to a food cue: influence of sex

There is considerable individual variation in the propensity of animals to attribute incentive salience to discrete reward cues, but to date most of this research has been conducted in male rats. The purpose of this study was to determine whether sex influences the propensity to attribute incentive salience to a food cue, using rats from two different outbred strains (Sprague-Dawley [SD] and Heterogeneous Stock [HS]). The motivational value of a food cue was assessed in two ways: (i) by the ability of the cue to elicit approach toward it and (ii) by its ability to act as a conditioned reinforcer. We found that female SD rats acquired Pavlovian conditioned approach behavior slightly faster than males, but no sex difference was detected in HS rats, and neither strain showed a sex difference in asymptotic performance of approach behavior. Moreover, female approach behavior did not differ across estrous cycle. Compared to males, females made more active responses during the test for conditioned reinforcement, although they made more inactive responses as well. We conclude that although there are small sex differences in performance on these tasks, these are probably not due to a notable sex difference in the propensity to attribute incentive salience to a food cue.

Age and sex differences in reward behavior in adolescent and adult rats

Compared to adults, adolescents are at heightened risk for drug abuse and dependence. One of the factors contributing to this vulnerability may be age-dependent differences in reward processing, with adolescents approaching reward through stimulus-directed, rather than goal-directed, processes. However, the empirical evidence for this in rodent models of adolescence, particularly those that investigate both sexes, is limited. To address this, male and female rats that were adolescents (P30) or adults (P98) at the start of the experiment were trained in a Pavlovian approach (PA) task and were subsequently tested for the effects of reward devaluation, extinction, and re-acquisition. We found significant interactions between age and sex: females had enhanced acquisition of PA and poorer extinction, relative to males, while adolescents and females were less sensitive to reward devaluation than male adults. These results suggest that females and adolescents exhibit reward behavior that is more stimulus-directed, rather than goal-directed.

Sex and estrous cycle differences in cocaine-induced approach-avoidance conflict

Human and animal research indicates that females may have a higher biological propensity for cocaine abuse than do males. Furthermore, reproductive status modulates the subjective effects of cocaine in women and self-administration rates in rats. Despite the attention that has been given to the modulation of appetitive responses by reproductive status and the well-known mixed positive and negative subjective effects of cocaine, it is unknown if similar effects are observed on aversive responses to cocaine. The present study examines the impact of sex and estrous cycle on approach-avoidance behavior for cocaine as measured in the runway self-administration model. Male and freely cycling female Sprague Dawley rats were trained to traverse a straight alley for single daily injections of 1.0 mg/kg intravenous cocaine over 21 trials. Relative to males, females had significantly longer start latencies but significantly faster approach and shorter run times during the first week of training. Further, estrus females displayed significantly fewer approach-avoidance retreats across all sessions relative to non-estrus females. These results suggest that females initially exhibit greater motivation for cocaine (faster approach) than do males and that the drug's anxiogenic properties have a reduced impact on the motivation to seek cocaine (fewer retreats) in females during the estrus phase relative to other reproductive phases. These findings indicate that both sex and reproductive status contribute to the motivation for cocaine and that sex differences in addiction vulnerability may be attributable in part to differences in the motivational impact of both the appetitive and aversive properties of cocaine.

Influence of sex on reinstatement of cocaine-conditioned place preference

To explore sex differences in reinstatement of conditioned place preference, we subjected intact male and female Long Evans rats to an extended conditioned place preference (CPP) paradigm, which included observations of acquisition, extinction, and reinstatement of a preference to cocaine-paired stimuli. In a series of experiments, separate groups of animals were given six 30-min pairings of one chamber with cocaine (3, 5, 10, 15, 20, 25mg/kg) and six of the other with saline on alternate days. Overall, there were no sex differences in acquisition of cocaine CPP at any of the six doses tested (p>0.05). All animals established cocaine CPP at each of the six doses tested during the acquisition test, with the exception of the group of females conditioned with 5mg/kg. Preferences for the cocaine-paired chamber were successfully extinguished for both males and females after an extinction-training period. CPP reinstatement was achieved by the groups of males and females given training and priming doses of 10, 15, 20, and 25mg/kg (p<0.05). Overall, our reinstatement data demonstrate that reinstatement of cocaine CPP is greater for female versus male animals. Females showed a greater magnitude of reinstatement of cocaine CPP when trained and primed with 15 and 25mg/kg as compared to males (p<0.05). Further, at the three highest doses tested (15, 20, and 25mg/kg), females showed a greater magnitude of CPP in the reinstatement phase of CPP compared to that of the initial acquisition phase (p<0.05). The reinstatement data for the males show that the 20mg/kg dose resulted in the highest levels of reinstatement preference for male rats. These results indicate that sex differences in reinstatement to conditioned behavior maybe due, in part, to females forming a stronger association for the salience of the drug and the environment in which it was administered.

Low doses of cocaine decrease, and high doses increase, anxiety-like behavior and brain progestogen levels among intact rats

There are sex and hormonal differences in response to cocaine that have been demonstrated in people and animal models. Cocaine can alter secretion of progestogens, such as progesterone (P), and its neuroactive metabolite, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP). However, little research has been done on the neuroendocrine effects in the initiation phase of cocaine use. We hypothesize that some sex/hormonal differences in initiation phase responses to cocaine may be related to formation of progestogens. To investigate the role of progestogens in sex differences in response to acute cocaine, male and female rats in the high (proestrous) or low (diestrous) progestogen phase of the estrous cycle were administered cocaine (0, 5, 10, or 20mg/kg, IP). We examined cocaine's acute neuroendocrine effects on P and 3alpha,5alpha-THP levels, as well as its effects on acute psychomotor stimulation, anxiety, and sexual behaviors. Among rats that had P and/or 3alpha,5alpha-THP levels increased in response to cocaine, enhanced acute psychomotor stimulation was observed. Results suggest that cocaine produces U-shaped curves for progestogens, and anxiety-like behaviors. Male rats were less susceptible to these effects of cocaine than were proestrous or diestrous female rats. However, cocaine's disruption of sexual behaviors was similar among males and proestrous females. These data suggest a complex interaction between hormonal milieu and the neuroendocrine and behavioral effects of cocaine.

Sex differences in the effects of allopregnanolone on yohimbine-induced reinstatement of cocaine seeking in rats

Sex differences exist in several aspects of cocaine abuse, and recent research suggests that this may be due, in part, to differential sensitivity to stress. Women, compared to men, exhibit greater stress-induced cocaine craving and responses to both cocaine and stress fluctuate during phases of the hormonal cycle. The goal of the present study was to compare male and female rats on the maintenance and extinction of cocaine seeking and on an animal model of stress-induced relapse by administering the pharmacological stressor yohimbine. An additional goal was to examine possible sex-specific treatment effects of the progesterone metabolite, allopregnanolone, on yohimbine-induced reinstatement. Male and female rats were trained to lever press for i.v. infusions of cocaine (0.4 mg/kg). Following a 14-day maintenance period, cocaine solutions were replaced with saline, and rats were allowed to extinguish lever pressing. Subsequently, rats were administered saline, yohimbine (2.5mg/kg), or allopregnanolone (15 mg/kg)+yohimbine (2.5mg/kg) priming injections on separate days using a within-subjects reinstatement procedure. The results indicated that females were more resistant to extinction than male rats and that both groups reinstated cocaine seeking following injections of yohimbine; however, female rats responded more than males to yohimbine-priming injections. Additionally, allopregnanolone blocked yohimbine's potentiating effect on responding in females but not males. These results suggest that females may be more sensitive than males to stress-induced reinstatement of cocaine-seeking behavior, and the progesterone metabolite, allopregnanolone, offers protection against this vulnerability.