Plasma progesterone levels and cocaine-seeking in freely cycling female rats across the estrous cycle

The positive reinforcing effects of cocaine and opposite-sex social contact: roles of biological sex and estrus

RATIONALE

Preclinical studies report that drug use and social contact mutually influence the reinforcing effects of one another. Most of these studies have used same-sex dyads exclusively, and the role of factors related to biological sex and hormonal fluctuations are not well understood.

OBJECTIVES

The purpose of this study was to examine the reinforcing effects of cocaine and social contact with an opposite-sex partner in male and female rats, and how these effects are modulated by ovarian hormones.

METHODS

Male and female rats were trained in a nonexclusive choice procedure in which cocaine and social contact with an opposite-sex partner were simultaneously available on concurrent progressive ratio schedules of reinforcement. To examine the effects of ovarian hormones related to estrous cycling, Experiment 1 used naturally cycling, gonadally intact females, whereas Experiment 2 used ovariectomized females, and estrus was artificially induced with exogenous hormones.

RESULTS

In both experiments, cocaine and social contact functioned as robust reinforcers, and there were no significant effects of biological sex or estrus status of the females. The positive reinforcing effects of both cocaine and social contact increased as a function of cocaine dose, indicating that contingent cocaine administration increases the reinforcing effects of social contact.

CONCLUSIONS

These data suggest that cocaine use among opposite-sex partners may enhance factors that contribute to social bonding.

Exploring ketamine's reinforcement, cue-induced reinstatement, and nucleus accumbens cFos activation in male and female long evans rats

Ketamine (KET), a non-competitive N-methyl-d-aspartate (NMDA) receptor antagonist, has rapid onset of antidepressant effects in Treatment-Resistant Depression patients and repeated infusions are required to sustain its antidepressant properties. However, KET is an addictive drug, and so more preclinical and clinical research is needed to assess the safety of recurring treatments in both sexes. Thus, the aim of this study was to investigate the reinforcing properties of various doses of KET (0-, 0.125-, 0.25-, 0.5 mg/kg/infusion) and assess KET's cue-induced reinstatement and neuronal activation in both sexes of Long Evans rats. Neuronal activation was assessed using the protein expression of the immediate early gene cFos in the nucleus accumbens (Nac), an important brain area implicated in reward, reinforcement and reinstatement to most drug-related cues. Our findings show that KET has reinforcing effects in both male and female rats, albeit exclusively at the highest two doses (0.25 and 0.5 mg/kg/infusion). Furthermore, we noted sex differences, particularly at the highest dose of ketamine, with female rats displaying a higher rate of self-administration. Interestingly, all groups that self-administered KET reinstated to drug-cues. Following drug cue-induced reinstatement test in rats exposed to KET (0.25 mg/kg/infusion) or saline, there was higher cFos protein expression in KET-treated animals compared to saline controls, and higher cFos expression in the core compared to the shell subregions of the Nac. As for reinstatement, there were no notable sex differences reported for cFos expression in the Nac. These findings reveal some sex and dose dependent effects in KET's reinforcing properties and that KET at all doses induced similar reinstatement in both sexes. This study also demonstrated that cues associated with ketamine induce comparable neuronal activation in the Nac of both male and female rats. This work warrants further research into the potential addictive properties of KET, especially when administered at lower doses which are now being used in the clinic for treating various psychopathologies.

Differential effects of deep brain stimulation on reinstatement of cocaine seeking in male and female rats

There are currently no FDA-approved treatments for cocaine use disorder. Recent preclinical and clinical studies showed that deep brain stimulation (DBS) in limbic regions reduced drug seeking behavior. Our previous work indicated that DBS of the nucleus accumbens shell attenuated reinstatement of cocaine seeking, a model of relapse, in male rats. The current experiments were designed to evaluate the effect of electrical DBS on cocaine reinstatement in female rats across the estrous cycle. Rats were allowed to self-administer cocaine and lever responding was subsequently extinguished. Cocaine seeking was reinstated by an acute injection of experimenter-delivered cocaine. The effect of nucleus accumbens shell DBS vs. sham stimulation on cocaine-primed reinstatement was evaluated in female and male rats using a within-subjects counterbalanced design. Consistent with previous work, accumbens shell DBS suppressed cocaine seeking in male rats. In sharp contrast, accumbens shell DBS had no effect on cocaine reinstatement in female rats evaluated in either the estrus or non-estrus phases. These results suggest that changes across the estrous cycle are not responsible for the differences in the effect of DBS on cocaine reinstatement between female and male rats.

The estrous cycle has no effect on incubation of methamphetamine craving and associated Fos expression in dorsomedial striatum and anterior intralaminar nucleus of thalamus

Relapse is a major challenge in treating drug addiction, and drug seeking progressively increases after abstinence, a phenomenon termed "incubation of drug craving". Previous studies demonstrated both sex differences and an effect of estrous cycle in female rats in incubation of cocaine craving. In contrast, while incubation of methamphetamine craving is similar across sexes, whether estrous cycle plays a role in this incubation has yet to be fully addressed. Moreover, whether neural mechanisms underlying incubation of methamphetamine craving differ across estrous cycles is largely unknown. To address these gaps, we first compared methamphetamine self-administration, and methamphetamine seeking on both abstinence days 1 and 28 between male rats and female rats across the estrous cycle. Next, we examined neuronal activation associated with incubated methamphetamine seeking in dorsomedial striatum (DMS) and lateral portion of the anterior intralaminar nucleus of thalamus (AIT-L), two brain areas previously implicated in incubation of methamphetamine craving. We found no effect of sex or estrous cycle on methamphetamine self-administration and methamphetamine seeking on abstinence days 1 and 28. We also found no effect of sex or estrous cycle on the number of Fos-expressing cells in DMS or AIT-L following methamphetamine seeking test. Taken together, our results showed that methamphetamine self-administration and incubation of methamphetamine craving was not dependent on sex or estrous cycles under our experimental condition, and the role of DMS and AIT-L in incubation of methamphetamine craving may be similar across sexes and across estrous cycles in female rats.

Serotonin Signaling in Hippocampus during Initial Cocaine Abstinence Drives Persistent Drug Seeking

The initiation of abstinence after chronic drug self-administration is stressful. Cocaine-seeking behavior on the first day of the absence of the expected drug (Extinction Day 1, ED1) is reduced by blocking 5-HT signaling in dorsal hippocampal cornu ammonis 1 (CA1) in both male and female rats. We hypothesized that the experience of ED1 can substantially influence later relapse behavior and that dorsal raphe (DR) serotonin (5-HT) input to CA1 may be involved. We inhibited 5-HT1A/1B receptors (WAY-100635 plus GR-127935), or DR input (chemogenetics), in CA1 on ED1 to test the role of this pathway on cocaine-seeking persistence 2 weeks later. We also inhibited 5-HT1A or 5-HT1B receptors in CA1 during conditioned place preference (CPP) for cocaine, to examine mechanisms involved in the persistent effects of ED1 manipulations. Inhibition of DR inputs, or 5-HT1A/1B signaling, in CA1 decreased drug seeking on ED1 and decreased cocaine seeking 2 weeks later revealing that 5-HT signaling in CA1 during ED1 contributes to persistent drug seeking during abstinence. In addition, 5-HT1B antagonism alone transiently decreased drug-associated memory performance when given prior to a CPP test, whereas similar antagonism of 5-HT1A alone had no such effect but blocked CPP retrieval on a test 24 h later. These CPP findings are consistent with prior work showing that DR inputs to CA1 augment recall of the drug-associated context and drug seeking via 5-HT1B receptors and prevent consolidation of the updated nondrug context via 5-HT1A receptors. Thus, treatments that modulate 5-HT-dependent memory mechanisms in CA1 during initial abstinence may facilitate later maintenance of abstinence.

The effects of gonadal hormones on heroin Self-Administration in male gonadectomized rats

RATIONALE

Previous studies have shown that gonadal hormones influence opioid self-administration in female rodents, but very few studies have examined these effects in male rodents.

OBJECTIVES

The purpose of this study was to examine the effects of chronic hormone treatment on intravenous heroin self-administration in gonadectomized male rats using both physiological and supraphysiological doses of testosterone, estradiol, or progesterone.

METHODS

Gonadectomized male rats were surgically implanted with intravenous catheters and trained to self-administer heroin on a fixed ratio (FR1) schedule of reinforcement. Using a between-subjects design, rats were treated daily with testosterone (0.175 or 1.75 mg, sc), estradiol (0.0005 or 0.005 mg, sc), progesterone, (0.0125 or 0.125 mg, sc), or their vehicles. After 14 days of chronic treatment, a dose-effect curve was determined for heroin (0.0003-0.03 mg/kg/infusion) over the course of one week.

RESULTS

Neither testosterone nor estradiol altered responding maintained by heroin. In contrast, the high dose of progesterone (0.125 mg) reduced responding maintained by all doses of heroin to saline-control levels. This dose of progesterone did not reduce responding maintained by food on a progressive ratio schedule in either food-restricted or food-sated rats.

CONCLUSIONS

These data indicate that exogenous progesterone or a pharmacologically active metabolite selectively decreases heroin intake in male rodents, which may have therapeutic implications for men with opioid use disorder.

Estradiol and Mu opioid-mediated reward: The role of estrogen receptors in opioid use

Opioid use and opioid use disorder are characterized by sex and gender differences, and some of these differences may be mediated by differences in the hormonal milieu within and across individuals. This review focuses on the role of ovarian hormones, and particularly estradiol, on the endogenous mu opioid receptor system. There is an abundance of data indicating that estradiol influences the activity of endogenous mu opioid peptides, the activation of mu opioid receptors, and the internalization and desensitization of mu opioid receptors. These effects have functional consequences on behaviors mediated by endogenous mu opioid receptor activity and on sensitivity to mu opioid agonists and antagonists. Recent behavioral data suggest these consequences extend to mu opioid reward, and preclinical studies report that estradiol decreases self-administration of mu opioid receptor agonists across a range of experimental conditions. Data collected in human laboratory studies suggest that estradiol may have functionally similar effects in clinical populations, and thus estrogen receptors may be a potential target in the development of novel therapeutics. This review summarizes data from cellular assays to clinical trials to explore how estradiol influences mu opioid receptor activity, as well as potential ways in which estrogen receptors may be targeted to address the problems of opioid use.

Role of oestrous cycle and orbitofrontal cortex in oxycodone seeking after 15-day abstinence in female rats

Relapse to oxycodone seeking progressively increases after abstinence in rats, a phenomenon termed incubation of oxycodone craving. We have previously shown that the orbitofrontal cortex (OFC) plays a critical role in incubation of oxycodone craving in male rats. Here, we examined the effect of oestrous cycle on incubated oxycodone seeking in female rats, and whether the critical role of OFC in incubated oxycodone seeking generalizes to female rats. We first assessed oxycodone self-administration and incubated oxycodone seeking on abstinence day 15 across the oestrous cycle. Next, we determined the effect of chemogenetic inactivation of OFC by JHU37160 (J60), a novel agonist for Designer Receptors Exclusively Activated by Designer Drugs (DREADDs), on incubated oxycodone seeking on abstinence day 15. Finally, we determined the effect of J60 alone on incubated oxycodone seeking on abstinence day 15. We found no difference in oxycodone intake across oestrus, pro-oestrus, and metoestrus stages during oxycodone self-administration training. Incubated oxycodone seeking was also similar between nonoestrus and oestrus female rats. Moreover, chemogenetic inactivation of OFC by J60 decreased incubated oxycodone seeking on abstinence day 15, while J60 alone had no effect on incubated oxycodone seeking in no-DREADD control rats. Taken together, results here show that the oestrous cycle has no effect on oxycodone intake and incubated oxycodone seeking in female rats under our experimental conditions. Furthermore, consistent with our previous findings in male rats, results here show that OFC also plays a critical role in incubated oxycodone seeking in female rats.

Effect of Sex and Cross-Sex Hormone Treatment on Renal Monocarboxylate-Transporter Expression in Rats

Proton- and sodium-dependent monocarboxylate transporters (MCTs/SMCTs) are determinants of renal clearance through the renal reabsorption of monocarboxylate substrates. Prior studies with intact females and males, ovariectomized females and castrated males have revealed the hormonal regulation of renal monocarboxylate-transporter expression, prompting investigation into the regulatory role of individual hormones. The aim of the present study is to evaluate the effect of exogenous sex and cross-sex hormones on renal MCT1, MCT4, CD147 and SMCT1 mRNA and membrane-bound protein expression. Ovariectomized (OVX) females and castrated (CST) male Sprague Dawley rats received estrogen and/or progesterone, testosterone, or a corresponding placebo treatment for 21 days prior to kidney collection. The quantitative measurement of mRNA and membrane-protein levels were conducted using qPCR and Western blot. Quantitative analysis revealed the combination estrogen/progesterone treatment reduced membrane MCT1 and 4 expression and increased SMCT1 expression, while testosterone administration increased MCT1 membrane-protein expression. Correlation analysis indicated that plasma 17β-estradiol was negatively correlated with MCT1 and MCT4 membrane expression, while testosterone was positively correlated. In contrast, SMCT1 membrane expression was positively correlated with 17β-estradiol and progesterone concentrations. MCT1, MCT4, CD147 and SMCT1 renal expression are significantly altered in response to female and male sex hormones following sex and cross-sex hormone treatment in OVX and CST rats. Further studies are needed to understand the complex role of sex hormones, sex hormone receptors and the impact of puberty on MCT/SMCT regulation.

Intermittent cocaine self-administration has sex-specific effects on addiction-like behaviors in rats

Intermittent access (IntA) models of cocaine self-administration were developed to better model in rodents how cocaine is used by human drug users. Compared to traditional continuous access (ContA) models, IntA has been shown to enhance several pharmacological and behavioral effects of cocaine, but few studies have examined sex differences in IntA. Moreover, no one has examined the efficacy of cue extinction to reduce cocaine seeking in the IntA model, which has previously shown to be ineffective in other models that promote habit-like cocaine seeking. Therefore, rats were implanted with jugular vein catheters and dorsolateral striatum (DLS) cannulae and trained to self-administer cocaine paired with an audiovisual cue with ContA or IntA. In subsets of rats, we evaluated: the ability of Pavlovian cue extinction to reduce cue-induced drug seeking; motivation for cocaine using a progressive ratio procedure; punishment-resistant cocaine taking by pairing cocaine infusions with footshocks; and dependence of drug-seeking on DLS dopamine (a measure of habit-like behavior) with the dopamine antagonist cis-flupenthixol. Overall, cue extinction reduced cue-induced drug seeking after ContA or IntA. Compared to ContA, IntA resulted in increased motivation for cocaine exclusively in females, but IntA facilitated punished cocaine self-administration exclusively in males. After 10 days of IntA training, but not fewer, drug-seeking was dependent on DLS dopamine most notably in males. Our results suggest that IntA may be valuable for identifying sex differences in the early stages of drug use and provide a foundation for the investigation of the mechanisms involved.

Sex/Gender Differences in the Time-Course for the Development of Substance Use Disorder: A Focus on the Telescoping Effect

Sex/gender effects have been demonstrated for multiple aspects of addiction, with one of the most commonly cited examples being the "telescoping effect" where women meet criteria and/or seek treatment of substance use disorder (SUD) after fewer years of drug use as compared with men. This phenomenon has been reported for multiple drug classes including opioids, psychostimulants, alcohol, and cannabis, as well as nonpharmacological addictions, such as gambling. However, there are some inconsistent reports that show either no difference between men and women or opposite effects and a faster course to addiction in men than women. Thus, the goals of this review are to evaluate evidence for and against the telescoping effect in women and to determine the conditions/populations for which the telescoping effect is most relevant. We also discuss evidence from preclinical studies, which strongly support the validity of the telescoping effect and show that female animals develop addiction-like features (e.g., compulsive drug use, an enhanced motivation for the drug, and enhanced drug-craving/vulnerability to relapse) more readily than male animals. We also discuss biologic factors that may contribute to the telescoping effect, such as ovarian hormones, and its neurobiological basis focusing on the mesolimbic dopamine reward pathway and the corticomesolimbic glutamatergic pathway considering the critical roles these pathways play in the rewarding/reinforcing effects of addictive drugs and SUD. We conclude with future research directions, including intervention strategies to prevent the development of SUD in women. SIGNIFICANCE STATEMENT: One of the most widely cited gender/sex differences in substance use disorder (SUD) is the "telescoping effect," which reflects an accelerated course in women versus men for the development and/or seeking treatment for SUD. This review evaluates evidence for and against a telescoping effect drawing upon data from both clinical and preclinical studies. We also discuss the contribution of biological factors and underlying neurobiological mechanisms and highlight potential targets to prevent the development of SUD in women.

The interaction of membrane estradiol receptors and metabotropic glutamate receptors in adaptive and maladaptive estradiol-mediated motivated behaviors in females

Estrogen receptors were initially identified as intracellular, ligand-regulated transcription factors that result in genomic change upon ligand binding. However, rapid estrogen receptor signaling initiated outside of the nucleus was also known to occur via mechanisms that were less clear. Recent studies indicate that these traditional receptors, estrogen receptor α and estrogen receptor β, can also be trafficked to act at the surface membrane. Signaling cascades from these membrane-bound estrogen receptors (mERs) can rapidly alter cellular excitability and gene expression, particularly through the phosphorylation of CREB. A principal mechanism of neuronal mER action has been shown to occur through glutamate-independent transactivation of metabotropic glutamate receptors (mGlu), which elicits multiple signaling outcomes. The interaction of mERs with mGlu has been shown to be important in many diverse functions in females, including driving motivated behaviors. Experimental evidence suggests that a large part of estradiol-induced neuroplasticity and motivated behaviors, both adaptive and maladaptive, occurs through estradiol-dependent mER activation of mGlu. Herein we will review signaling through estrogen receptors, both "classical" nuclear receptors and membrane-bound receptors, as well as estradiol signaling through mGlu. We will focus on how the interactions of these receptors and their downstream signaling cascades are involved in driving motivated behaviors in females, discussing a representative adaptive motivated behavior (reproduction) and maladaptive motivated behavior (addiction).

Estradiol and progesterone in female reward-learning, addiction, and therapeutic interventions

Sex steroid hormones like estradiol (E2) and progesterone (P4) guide the sexual organization and activation of the developing brain and control female reproductive behavior throughout the lifecycle; importantly, these hormones modulate functional activity of not just the endocrine system, but most of the nervous system including the brain reward system. The effects of E2 and P4 can be seen in the processing of and memory for rewarding stimuli and in the development of compulsive reward-seeking behaviors like those seen in substance use disorders. Women are at increased risk of developing substance use disorders; however, the origins of this sex difference are not well understood and therapeutic interventions targeting ovarian hormones have produced conflicting results. This article reviews the contribution of the E2 and P4 in females to functional modulation of the brain reward system, their possible roles in origins of addiction vulnerability, and the development and treatment of compulsive reward-seeking behaviors.

Estrous cycle and hormone regulation of stress-induced reinstatement of reward seeking in female mice

Women are more vulnerable to stress-induced craving, which may be associated with increased vulnerability to relapse. Susceptibility to stress-induced craving also appears to be modulated by the menstrual cycle and is negatively correlated with circulating progesterone levels in women. However, the factors that contribute to relapse vulnerability are poorly characterized in female animals. In this study, we assessed whether chronic ethanol exposure, estrous cycle, or exogenous progesterone administration modulated vulnerability to stress-induced reinstatement. To model ethanol dependence, adult female C57Bl/6J mice underwent chronic intermittent ethanol (CIE) exposure via vapor inhalation. Seventy-two hours after the final ethanol exposure, food-restricted mice began training in a conditioned place preference paradigm (CPP) for a food reward, followed by extinction training. Mice were then subjected to forced swim stress and assessed for reinstatement of their preference for the reward-paired chamber. CIE did not affect stress-induced reinstatement. However, stress-induced reinstatement was attenuated during the diestrus phase, when endogenous levels of progesterone peak in female mice. Further, administration of exogenous progesterone mimicked the attenuated reinstatement observed in diestrus. These findings indicate that circulating hormone levels modulate susceptibility to relapse-like behaviors and implicate progesterone as a potential target for treating stress-induced relapse in women.

Sex differences and hormonal regulation of metabotropic glutamate receptor synaptic plasticity

Striking sex differences exist in presentation and incidence of several psychiatric disorders. For example, major depressive disorder is more prevalent in women than men, and women who develop alcohol use disorder progress through drinking milestones more rapidly than men. With regards to psychiatric treatment responses, women respond more favorably to selective serotonin reuptake inhibitors than men, whereas men have better outcomes when prescribed tricyclic antidepressants. Despite such well-documented biases in incidence, presentation, and treatment response, sex as a biological variable has long been neglected in preclinical and clinical research. An emerging family of druggable targets for psychiatric diseases, metabotropic glutamate (mGlu) receptors are G-protein coupled receptors broadly distributed throughout the central nervous system. mGlu receptors confer diverse neuromodulatory actions of glutamate at the levels of synaptic plasticity, neuronal excitability, and gene transcription. In this chapter, we summarize the current preclinical and clinical evidence for sex differences in mGlu receptor function. We first highlight basal sex differences in mGlu receptor expression and function and proceed to describe how gonadal hormones, notably estradiol, regulate mGlu receptor signaling. We then describe sex-specific mechanisms by which mGlu receptors differentially modulate synaptic plasticity and behavior in basal states and models relevant for disease. Finally, we discuss human research findings and highlight areas in need of further research. Taken together, this review emphasizes how mGlu receptor function and expression can differ across sex. Gaining a more complete understanding of how sex differences in mGlu receptor function contribute to psychiatric diseases will be critical in the development of novel therapeutics that are effective in all individuals.

5-HT1B receptor agonist enhances breakpoint for cocaine on a progressive ratio (PR) schedule during maintenance of self-administration in female rats but reduces breakpoint for sucrose

Background: Previous research showed that the 5-HT_1B receptor agonist CP94253 enhanced cocaine reinforcement rate during maintenance of daily self-administration (SA), but inhibited reinforcement rate after 21 days of abstinence in male rats. Here we examined whether female rats show similar effects of CP94253 during maintenance as males across estrous cycle phases.

Methods: Female rats trained on a fixed ratio 5 (FR5) cocaine reinforcement schedule were tested for the effects of CP94253 (5.6 mg/kg, s.c.) on cocaine reinforcement rate during each phase of the estrous cycle, with access to either low (0.075 and 0.1875) or high (0.375 and 0.75) cocaine doses available for 1 h sequentially in descending dose order. Other female and male rats trained on a progressive ratio (PR) schedule of cocaine or sucrose reinforcement were tested for CP94253 (0, 3.2, 5.6, and 10 mg/kg, s.c.) effects on reinforcement rate in 3-h sessions. CP94253 effects on responding during sucrose cue-reactivity were also examined post-abstinence.

Results: Regardless of sex, CP94253 enhanced breakpoints on the PR schedule during maintenance of cocaine SA but attenuated breakpoints for sucrose reinforcement and decreased responding during sucrose cue-reactivity. FR results showed that CP94253 attenuated cocaine reinforcement rate during all estrous cycle phases except metestrus.

Conclusions: Overall, we suggest that CP94253 increased incentive motivation for cocaine during maintenance of SA in female and male rats, yet decreased motivation for sucrose. We also suggest that 5-HT_1BRs modulate motivation similarly across sexes except when females are in metestrus.

The influence of sex and reproductive cycle on cocaine-induced behavioral and neurobiological alterations: a review

This systematic review (SR) was aimed at answering two questions: (1) how sex and ovarian hormones alter behavior associated with cocaine use; (2) which possible neurobiological mechanisms explain behavioral differences. Three different researchers conducted a search in PUBMED for all kinds of articles published between the years of 1991 to 2021 on the theme "reproductive cycle and cocaine", "estrous cycle and cocaine", "menstrual cycle and cocaine", "fluctuation of ovarian hormones and cocaine", "estrogen and cocaine" and "progesterone and cocaine". Sixty original studies were identified and subdivided into experimental rodent studies and clinical trials. Experimental studies were characterized by author/year, species/strain, sex/number, age/weight, dose/route/time of administration, hormonal assessment, or administration. Clinical trials were characterized by author/year, sex/number, age, exclusion criterion, dose/route of administration/time of cocaine, and hormonal assessment. Results gathered showed that rodent females develop increased consumption, seeking behavior, craving, relapse, locomotion, increases in stress and anxiety, among other behavioral alterations during peaks of estrogen. These observations are related to the direct effects played by ovarian hormones (in particularly estradiol), in dopamine, but also in serotonin neurons, and in brain regions such as the tegmental area, the nucleus accumbens, the hypothalamus, the amygdala and the prefrontal cortex. Increased sensitization to cocaine presented by high estradiol females was linked to the activation of a CBR1-mediated mechanism and GABA-A-dependent suppression of inhibitory synaptic activity of the prelimbic prefrontal cortex. Estradiol facilitation of cocaine-increased locomotion and self-administration was shown to require the release of glutamate and the activation of metabotropic glutamate receptors subtype 5. Clinical studies also tend to point to a stimulatory effect of estradiol on cocaine sensitization and a neuroprotective effect of progesterone. In conclusion, the results of the present review indicate a need for further preclinical and clinical trials and neurobiological studies to better understand the relationship between sex and ovarian hormones on cocaine sensitization.

Get to grips with motivation: Slipping and gripping movements are biased by approach-avoidance context

People are better at approaching appetitive cues signaling reward and avoiding aversive cues signaling punishment than vice versa. This action bias has previously been shown in approach-avoidance tasks involving arm movements in response to appetitive or aversive cues. It is not known whether appetitive or aversive stimuli also bias more distal dexterous actions, such as gripping and slipping, in a similar manner. To test this hypothesis, we designed a novel task involving grip force control (gripping and slipping) to probe gripping-related approach and avoidance behavior. 32 male volunteers, aged 18–40 years, were instructed to either grip (“approach”) or slip (”avoid”) a grip-force device with their right thumb and index finger at the sight of positive or negative images. In one version of this pincer grip task, participants were responding to graspable objects and in another version of the task they were responding to happy or angry faces. Bayesian repeated measures Analysis of variance revealed extreme evidence for an interaction between response type and cue valence (Bayes factor = 296). Participants were faster to respond in affect-congruent conditions (“approach appetitive,” “avoid aversive”) than in affect-incongruent conditions (“approach aversive,” “avoid appetitive”). This bias toward faster response times for affect-congruent conditions was present regardless of whether it was a graspable object or a face signaling valence. Since our results mirror the approach and avoidance effects previously observed for arm movements, we conclude that a tendency favoring affectively congruent cue-response mappings is an inherent feature of motor control and thus also includes precision grip.

Hormonal milieu drives economic demand for cocaine in female rats

There are substantial sex differences in drug abuse, and a key feature of cocaine addiction is pathologically high motivation for drug. We investigated the role of ovarian hormones on cocaine demand in female rats using a within-session threshold behavioral economics (BE) procedure, which allows us to compare motivation for drug across hormonal states and sex while controlling for differences in dose and intake. This approach quantifies demand elasticity (α) and free consumption (Q₀, consumption at null effort) to determine motivation for cocaine. Overall, female rats showed greater motivation for cocaine compared to males. However, this difference was cycle phase-dependent - motivation for cocaine when females were in proestrus was lower compared to the same animals across cycle phases, and overall similar to that of males. Hormonal cycle phase accounted for 70% of the within-subject variance in demand elasticity, obscuring other individual differences in female demand. High serum progesterone (P4; e.g., in proestrus) predicted decreased cocaine motivation (high demand elasticity), whereas serum estradiol (E2) correlated to greater intake at null effort (Q₀). However, individual differences were revealed across OVX females, who displayed a range of demand elasticity, as seen in males. E2 replacement in OVX females increased motivation for cocaine, whereas P4 replacement decreased motivation. We also found that as few as 4 weeks of cocaine self-administration accelerated estropause in female rats as young as 12 weeks old. By 13 weeks of self-administration, proestrus epochs were no longer observed, and cocaine demand was potentiated by persistent estrus in all females. Thus, P4 signaling is a key modulator of cocaine demand in females that may underlie previously observed sex differences in addiction phenotypes.

Is Illicit Substance Use Gender-Specific? The Basic Points of Mental and Health Disorders

Among the groups of users of illicit substances, a high percentage are persons deprived of their liberty; at the same time, each social and age group is also affected, to one degree or another. The purpose of this study is to provide general data on the relationship between different psychostimulants, clinical and socio-demographic studies, and gender, both among the general population and in one of the most at-risk groups. This review identifies the use of illicit substances as gender-specific in the general population. A detailed study of the causal relationship between the use of illicit substances and gender was carried out. Electronic databases Academic Search Complete, PubMed, HealthCare, Web of Science, and Google Scholar were searched for relevant studies up to 2022 associated with drug abuse and mental and health disorders. The analysis indicated that the human population showed significant differences between the sex of the consumer as to the type of drug consumers, development of addiction, and relapse. We focus on the pathological changes caused by drug use, the personal and physiological individual traits that influence drug choice, and the extent of use in one of the most affected groups of individuals. The study may provide some guidance in developing gender-specific treatment and prevention, including response to some pharmacological and behavioral therapies. The review is intended for a wide audience of social workers, toxicologists, and pharmacologists.

Nuclear factor kappa B signaling within the rat nucleus accumbens core sex-dependently regulates cue-induced cocaine seeking and matrix metalloproteinase-9 expression

Chronic drug self-administration and withdrawal are associated with distinct neuroimmune adaptations that may increase drug craving and relapse vulnerability in humans. The nuclear factor kappa-B (NF-κB) pathway is a critical regulator of many immune- and addiction-related genes such as the extracellular matrix enzyme matrix metalloproteinase-9 (MMP-9), which is a known modulator of learning, memory, and synaptic plasticity. While some studies suggest striatal NF-κB signaling may regulate drug-conditioned behavior, no studies to date have examined whether NF-κB signaling within the nucleus accumbens core (NAc core) alters downstream neuroimmune function and cue-motivated cocaine seeking following a period of forced abstinence, whether any effects are specific to cocaine over other reinforcers, or whether sex differences exist. Here, we examined whether viral-mediated knockdown of the p65 subunit of NF-κB within the NAc core would alter MMP-9 expression and cue-induced cocaine- and sucrose-seeking behavior following a period of forced abstinence in male and female rats. We demonstrate that NAc core p65 knockdown results in a significant decrease in cue-induced cocaine seeking in males but not females. This effect was specific to cocaine, as p65 knockdown did not significantly affect cue-induced sucrose seeking in either males or females. Moreover, we demonstrate that males express higher levels of MMP-9 within the NAc core and nucleus accumbens shell (NAcSh) compared to females, and that p65 knockdown significantly decreases MMP-9 in the NAc core of males but not females among cocaine cue-exposed animals. Altogether, these results suggest that NAc core NF-κB signaling exerts modulatory control over cue-motivated drug-seeking behavior and downstream neuroimmune function in a sex-specific manner. These findings highlight the need to consider sex as an important biological variable when examining immunomodulatory mechanisms of cocaine seeking.

The effects of artificially induced proestrus on heroin intake: A critical role for estradiol

Heroin intake decreases markedly during proestrus in normally cycling female rats; however, it is not known whether estradiol, progesterone, or both hormones are responsible for these decreases in heroin intake. The purpose of the present study was to examine the roles of estradiol and progesterone in heroin intake by artificially inducing a proestrus state in ovariectomized rats. To this end, ovariectomized female rats were implanted with intravenous catheters and trained to self-administer heroin (0.0075 mg/kg/infusion) on a fixed ratio (FR1) schedule of reinforcement. After 1 week of training, rats were tested at weekly intervals with estradiol (0.005 mg, sc) or vehicle 22 hr before a test session and progesterone (0.125 mg, sc) or vehicle 0.5 hr before a test session to artificially mimic the naturally occurring hormone concentrations characteristic of late proestrus. Administration of estradiol 22 hr prior to testing and progesterone 0.5 hr prior to testing significantly reduced heroin intake relative to the previous training day and vehicle control. It is interesting that this same effect was observed when only estradiol, but not progesterone, was administered. These data suggest that estradiol but not progesterone is responsible for the proestrus-induced decreases in heroin intake previously reported in normally cycling female rats. These findings differ from those reported previously with stimulants and suggest that estrogen-based pharmacotherapies may be of value to women with opioid use disorder. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Sex Differences in Opioid and Psychostimulant Craving and Relapse: A Critical Review

A widely held dogma in the preclinical addiction field is that females are more vulnerable than males to drug craving and relapse. Here, we first review clinical studies on sex differences in psychostimulant and opioid craving and relapse. Next, we review preclinical studies on sex differences in psychostimulant and opioid reinstatement of drug seeking after extinction of drug self-administration, and incubation of drug craving (time-dependent increase in drug seeking during abstinence). We also discuss ovarian hormones' role in relapse and craving in humans and animal models and speculate on brain mechanisms underlying their role in cocaine craving and relapse in rodent models. Finally, we discuss imaging studies on brain responses to cocaine cues and stress in men and women.The results of the clinical studies reviewed do not appear to support the notion that women are more vulnerable to psychostimulant and opioid craving and relapse. However, this conclusion is tentative because most of the studies reviewed were correlational, not sufficiently powered, and not a priori designed to detect sex differences. Additionally, imaging studies suggest sex differences in brain responses to cocaine cues and stress. The results of the preclinical studies reviewed provide evidence for sex differences in stress-induced reinstatement and incubation of cocaine craving but not cue- or cocaine-induced reinstatement of cocaine seeking. These sex differences are modulated in part by ovarian hormones. In contrast, the available data do not support the notion of sex differences in craving and relapse/reinstatement for methamphetamine or opioids in rodent models. SIGNIFICANCE STATEMENT: This systematic review summarizes clinical and preclinical studies on sex differences in psychostimulant and opioid craving and relapse. Results of the clinical studies reviewed do not appear to support the notion that women are more vulnerable to psychostimulant and opioid craving and relapse. Results of preclinical studies reviewed provide evidence for sex differences in reinstatement and incubation of cocaine seeking but not for reinstatement or incubation of methamphetamine or opioid seeking.

Factors modulating the incubation of drug and non-drug craving and their clinical implications

It was suggested in 1986 that cue-induced cocaine craving increases progressively during early abstinence and remains high during extended periods of time. Clinical evidence now supports this hypothesis and that this increase is not specific to cocaine but rather generalize across several drugs of abuse. Investigators have identified an analogous incubation phenomenon in rodents, in which time-dependent increases in cue-induced drug seeking are observed after abstinence from intravenous drug or palatable food self-administration. Incubation of craving is susceptible to variation in magnitude as a function of biological and/or the environmental circumstances surrounding the individual. During the last decade, the neurobiological correlates of the modulatory role of biological (sex, age, genetic factors) and environmental factors (environmental enrichment and physical exercise, sleep architecture, acute and chronic stress, abstinence reinforcement procedures) on incubation of drug craving has been investigated. In this review, we summarized the behavioral procedures adopted, the key underlying neurobiological correlates and clinical implications of these studies.

A systematic review of the effect of ovarian sex hormones on stimulant use in females

Stimulant use disorder is associated with significant global health burden. Despite evidence for sex differences in the development and maintenance of stimulant use disorder, few studies have focused on mechanisms underpinning distinct trajectories in females versus males, including the effect of the ovarian sex hormones estrogen and progesterone. This review aimed to identify and synthesise the existing preclinical and clinical literature on the effect of ovarian sex hormones on stimulant consumption in females. A systematic search of peer-reviewed literature identified 1593 articles, screened using the following inclusion criteria: (1) adult female humans or animals, (2) using stimulant drugs, (3) ovarian sex hormones were administered exogenously OR were measured in a validated manner and (4) with stimulant consumption as an outcome measure. A total of 50 studies (3 clinical and 47 preclinical) met inclusion criteria. High-estrogen (low progesterone) phases of the menstrual/estrus cycle were associated with increased stimulant use in preclinical studies, while there were no clinical studies examining estrogen and stimulant consumption. Consistent preclinical evidence supported progesterone use reducing stimulant consumption, which was also identified in one clinical study. The review was limited by inconsistent data reporting across studies and different protocols across preclinical laboratory paradigms. Importantly, almost all studies examined cocaine use, with impact on methamphetamine use a significant gap in the existing evidence. Given the safety and tolerability profile of progesterone, further research is urgently needed to address this gap, to explore the potential therapeutic utility of progesterone as a treatment for stimulant use disorder.

Environmental enrichment reduces heroin seeking following incubation of craving in both male and female rats

BACKGROUND

Contemporary treatments for heroin use disorder demonstrate only limited efficacy when the goals are long term abstinence and prevention of relapse. We have demonstrated that environmental enrichment (EE) reduces cue-induced heroin reinstatement in male rats. The present study is an attempt to extend the "anti-relapse" effects of EE to female rats and to periods where incubation of craving is hypothesized to occur.

METHODS

This experiment implemented a 3-phase procedure. In Phase 1, male and female rats were trained to self-administer heroin for 15 days. Phase 2 consisted of a 3- or 15-day forced abstinence (FA) period. In Phase 3 half of the rats were placed into EE and the other half in non-EE housing and subsequently tested for responding in extinction (no heroin or cues) for 15 days followed by a cue-induced reinstatement test.

RESULTS

We found that rats in the 15 days FA condition showed significantly enhanced drug seeking during extinction, irrespective of sex. We also found that EE significantly reduced this effect. During reinstatement, EE significantly reduced drug seeking in male and female rats and in both 3- and 15-day FA groups.

CONCLUSIONS

EE, with or without prolonged FA, effectively reduced heroin seeking in male and female rats. These findings indicate that EE can reduce drug-seeking in males and females and when putative incubation of craving (i.e., prolonged abstinence period) has occurred and suggest that it may aid in the development of future long-term behavioral treatments for individuals at risk for heroin relapse.

Effects of Sex and Estrous Cycle on the Time Course of Incubation of Cue-Induced Craving following Extended-Access Cocaine Self-Administration

Cocaine addiction is a devastating public health epidemic that continues to grow. Studies focused on identifying biological factors influencing cocaine craving and relapse vulnerability are necessary to promote abstinence in recovering drug users. Sex and ovarian hormones are known to influence cocaine addiction liability and relapse vulnerability in both humans and rodents. Previous studies have investigated sex differences in the time-dependent intensification or "incubation" of cue-induced cocaine craving that occurs during withdrawal from extended-access cocaine self-administration and have identified changes across the rat reproductive cycle (estrous cycle). Female rats in the estrus stage of the cycle (Estrus Females), the phase during which ovulation occurs, show an increase in the magnitude of incubated cue-induced cocaine craving compared with females in all other phases of the estrous cycle (Non-Estrus Females). Here we extend these findings by assessing incubated craving across the estrous cycle during earlier withdrawal periods (withdrawal day 1 and 15) and later withdrawal periods (withdrawal day 48). We found that this increase in the magnitude of incubated craving during estrus (Estrus Females) is present on withdrawal day 15, but not on withdrawal day 1, and further increases by withdrawal day 48. No difference in the magnitude of incubated craving was observed between Males and Non-Estrus Females. Our data indicate that the effects of hormonal fluctuations on cue-induced cocaine craving intensify during the first month and a half of withdrawal, showing an interaction among abstinence length, estrous cycle fluctuations, and cocaine craving.

The effects of chronic estradiol treatment on opioid self-administration in intact female rats

Heroin intake decreases significantly during proestrus in normally cycling female rats, and this effect is mediated by endogenous estradiol but not endogenous progesterone. The purpose of this study was to determine whether chronic administration of exogenous estradiol decreases intake of the semi-synthetic opioid, heroin, and the fully synthetic opioid, remifentanil, in intact female rats. Normally cycling female rats were implanted with intravenous catheters and trained to self-administer heroin on a fixed ratio (FR1) schedule of reinforcement. Rats were treated chronically with daily administration of either a low dose of estradiol (0.5 mcg, sc), a high dose of estradiol (5.0 mcg, sc), or vehicle (peanut oil, sc). After two weeks of heroin self-administration training, dose-effect curves were determined for both heroin and remifentanil. Chronic administration of estradiol non-significantly decreased heroin intake and significantly decreased remifentanil intake. Estradiol-induced decreases in remifentanil intake were dose-dependent, characterized by large effect sizes, and greatest in rats treated with the high dose of estradiol. These data indicate that chronic estradiol administration decreases opioid intake in intact female rats with medium to large effect sizes across opioids. These findings suggest that estrogen-based pharmacotherapies may represent a novel treatment approach for women with opioid use disorder.

Addiction among women and sexual minority groups

Gender-related alcohol and drug abuse problems are related not only to biologic differences but also to social and environment factors, all of which can influence the clinical presentation, consequences of use, and treatment approaches. The number of women becoming addicted to alcohol or drugs of abuse has significantly increased with women becoming the fastest-growing group of substance abusers in the United States. Given that women experience a more rapid progression of their addiction than men, it is important that we understand and address the differences to help develop prevention and treatment programs that are tailored for women, incorporating trauma assessment and management, comorbidities, financial independence, pregnancy, and child care.

Consideration of sex as a biological variable in the translation of pharmacotherapy for stress-associated drug seeking

Stress is a frequent precipitant of relapse to drug use. Pharmacotherapies targeting a diverse array of neural systems have been assayed for efficacy in attenuating stress-induced drug-seeking in both rodents and in humans, but none have shown enough evidence of utility to warrant routine use in the clinic. We posit that a critical barrier in effective translation is inattention to sex as a biological variable at all phases of the research process. In this review, we detail the neurobiological systems implicated in stress-induced relapse to cocaine, opioids, methamphetamine, and cannabis, as well as the pharmacotherapies that have been used to target these systems in rodent models, the human laboratory, and in clinical trials. In each of these areas we additionally describe the potential influences of biological sex on outcomes, and how inattention to fundamental sex differences can lead to biases during drug development that contribute to the limited success of large clinical trials. Based on these observations, we determine that of the pharmacotherapies discussed only α₂-adrenergic receptor agonists and oxytocin have a body of research with sufficient consideration of biological sex to warrant further clinical evaluation. Pharmacotherapies that target β-adrenergic receptors, other neuroactive peptides, the hypothalamic-pituitary-adrenal axis, neuroactive steroids, and the endogenous opioid and cannabinoid systems require further assessment in females at the preclinical and human laboratory levels before progression to clinical trials can be recommended.

Behavioral sex differences in cocaine and opioid use disorders: The role of gonadal hormones

Females are more vulnerable than males to many aspects of cocaine use disorder. This vulnerability also translates to opioid use disorder, with females exhibiting stronger behavioral responses than males to drugs such as heroin and morphine. While there is evidence for many overlapping neural mechanisms underlying cocaine and opioid abuse, there is also a breadth of evidence indicating divergent effects of the drugs on synaptic plasticity. This makes it unclear whether the behavioral sex differences seen in substance use disorder across different drugs of abuse rely on the same mechanisms. Ovarian hormones have consistently been implicated as drivers of the behavioral sex differences in cocaine taking and seeking. While there are far fewer studies on the role of ovarian hormones in opioid use disorder, the existing data suggest that ovarian hormones may not drive these behavioral effects in the same manner as in cocaine use disorder. This review highlights evidence that behavioral sex differences in substance use disorder might be driven by different mechanisms depending on drug class.

Estradiol Regulation of the Prelimbic Cortex and the Reinstatement of Cocaine Seeking in Female Rats

Relapse susceptibility in women with substance use disorders (SUDs) has been linked to the estrogen, 17β-estradiol (E2). Our previous findings in female rats suggest that the influence of E2 on cocaine seeking can be localized to the prelimbic prefrontal cortex (PrL-PFC). Here, we investigated the receptor mechanisms through which E2 regulates the reinstatement of extinguished cocaine seeking. Sexually mature female rats underwent intravenous cocaine self-administration (0.5 mg/inf; 14 × 2 h daily) and extinction, and then were ovariectomized before reinstatement testing. E2 (10 µg/kg, i.p.) alone did not reinstate cocaine seeking, but it potentiated reinstatement when combined with an otherwise subthreshold priming dose of cocaine. A similar effect was observed following intra-PrL-PFC microinfusions of E2 and by systemic or intra-PrL-PFC administration of the estrogen receptor (ER)β agonist, DPN, but not agonists at ERα or the G-protein-coupled ER1 (GPER1). By contrast, E2-potentiated reinstatement was prevented by intra-PrL-PFC microinfusions of the ERβ antagonist, MPP, or the GPER1 antagonist, G15, but not an ERα antagonist. Whole-cell recordings in PrL-PFC layer (L)5/6 pyramidal neurons revealed that E2 decreases the frequency, but not amplitude, of GABAA-dependent miniature IPSCs (mIPSC). As was the case with E2-potentiated reinstatement, E2 reductions in mIPSC frequency were prevented by ERβ and GPER1, but not ERα, antagonists and mimicked by ERβ, but not GPER1, agonists. Altogether, the findings suggest that E2 activates ERβ and GPER1 in the PrL-PFC to attenuate the GABA-mediated constraint of key outputs that mediate cocaine seeking.

Modulation of heroin intake by ovarian hormones in gonadectomized and intact female rats

RATIONALE

Heroin intake decreases during the proestrus phase of the estrous cycle in female rats. Circulating concentrations of both estradiol and progesterone peak during proestrus, and it is not known which of these hormones, or their combination, are responsible for these effects.

OBJECTIVES

The purpose of this study was to determine the effects of estradiol, progesterone, and their combination on heroin self-administration in female rats.

METHODS

In Experiment 1, the estrous cycle of intact female rats was tracked daily. If a rat was in proestrus, either the estrogen receptor antagonist, raloxifene, the progesterone receptor antagonist, mifepristone, or their combination was administered 30 min prior to a heroin self-administration session. In Experiment 2, separate groups of ovariectomized female rats were treated chronically with exogenous estradiol, progesterone, estradiol + progesterone, or vehicle, and heroin intake was examined over a 100-fold dose range.

RESULTS

In Experiment 1, raloxifene, but not mifepristone, significantly blocked proestrus-associated decreases in heroin intake. In Experiment 2, estrogentreated rats self-administered less heroin than any other group and significantly less heroin than rats treated with progesterone.

CONCLUSIONS

These data suggest that (1) estradiol but not progesterone is responsible for proestrus-associated decreases in heroin intake and (2) estradiol decreases heroin intake relative to progesterone. These data differ from those reported previously with stimulants and suggest that estrogen-based pharmacotherapies may be of value to women with opioid use disorder.

Behavioral Alterations and Decreased Number of Parvalbumin-Positive Interneurons in Wistar Rats after Maternal Immune Activation by Lipopolysaccharide: Sex Matters

Maternal immune activation (MIA) during pregnancy represents an important environmental factor in the etiology of schizophrenia and autism spectrum disorders (ASD). Our goal was to investigate the impacts of MIA on the brain and behavior of adolescent and adult offspring, as a rat model of these neurodevelopmental disorders. We injected bacterial lipopolysaccharide (LPS, 1 mg/kg) to pregnant Wistar dams from gestational day 7, every other day, up to delivery. Behavior of the offspring was examined in a comprehensive battery of tasks at postnatal days P45 and P90. Several brain parameters were analyzed at P28. The results showed that prenatal immune activation caused social and communication impairments in the adult offspring of both sexes; males were affected already in adolescence. MIA also caused prepulse inhibition deficit in females and increased the startle reaction in males. Anxiety and hypolocomotion were apparent in LPS-affected males and females. In the 28-day-old LPS offspring, we found enlargement of the brain and decreased numbers of parvalbumin-positive interneurons in the frontal cortex in both sexes. To conclude, our data indicate that sex of the offspring plays a crucial role in the development of the MIA-induced behavioral alterations, whereas changes in the brain apparent in young animals are sex-independent.

Influence of ovarian hormones on value-based decision-making systems: Contribution to sexual dimorphisms in mental disorders

Women and men exhibit differences in behavior when making value-based decisions. Various hypotheses have been proposed to explain these findings, stressing differences in functional lateralization of the brain, functional activation, neurotransmitter involvement and more recently, sex hormones. While a significant interaction of neurotransmitter systems and sex hormones has been shown for both sexes, decision-making in women might be particularly affected by variations of ovarian hormones. In this review we have gathered information from animal and human studies on how ovarian hormones affect decision-making processes in females by interacting with neurotransmitter systems at functionally relevant brain locations and thus modify the computation of decision aspects. We also review previous findings on impaired decision-making in animals and clinical populations with substance use disorder and depression, emphasizing how little we know about the role of ovarian hormones in aberrant decision-making.

Sex, stress, and prefrontal cortex: influence of biological sex on stress-promoted cocaine seeking

Clinical reports suggest that females diagnosed with substance use disorder experience enhanced relapse vulnerability compared with males, particularly during stress. We previously demonstrated that a stressor (footshock) can potentiate cocaine seeking in male rats via glucocorticoid-dependent cannabinoid type-1 receptor (CB1R)-mediated actions in the prelimbic prefrontal cortex (PrL-PFC). Here, we investigated the influence of biological sex on stress-potentiated cocaine seeking. Despite comparable self-administration and extinction, females displayed a lower threshold for cocaine-primed reinstatement than males. Unlike males, footshock, tested across a range of intensities, failed to potentiate cocaine-primed reinstatement in females. However, restraint potentiated reinstatement in both sexes. While sex differences in stressor-induced plasma corticosterone (CORT) elevations and defensive behaviors were not observed, differences were evident in footshock-elicited ultrasonic vocalizations. CORT administration, at a dose which recapitulates stressor-induced plasma levels, reproduced stress-potentiated cocaine-primed reinstatement in both sexes. In females, CORT effects varied across the estrous cycle; CORT-potentiated reinstatement was only observed during diestrus and proestrus. As in males, CORT-potentiated cocaine seeking in females was localized to the PrL-PFC and both CORT- and restraint-potentiated cocaine seeking required PrL-PFC CB1R activation. In addition, ex vivo whole-cell electrophysiological recordings from female layer V PrL-PFC pyramidal neurons revealed CB1R-dependent CORT-induced suppression of inhibitory synaptic activity, as previously observed in males. These findings demonstrate that, while stress potentiates cocaine seeking via PrL-PFC CB1R in both sexes, sensitivity to cocaine priming injections is greater in females, CORT-potentiating effects vary with the estrous cycle, and whether reactivity to specific stressors may manifest as drug seeking depends on biological sex.

Sex differences in oral oxycodone self-administration and stress-primed reinstatement in rats

The opioid epidemic has become a severe public health problem, with approximately 130 opioid-induced deaths occurring each day in the United States. Prescription opioids are responsible for approximately 40% of these deaths. Oxycodone is one of the most commonly abused prescription opioids, but despite its prevalent misuse, the number of preclinical studies investigating oxycodone-seeking behaviors is relatively limited. Furthermore, preclinical oxycodone studies that include female subjects are even more scarce, and it is critical that future work includes both sexes. Additionally, the oral route of administration is one of the most common routes for recreational users, especially in the early stages of drug experimentation. However, currently, only two studies have been published investigating operant oral oxycodone self-administration in rodents. Therefore, the primary goal of the present study was to establish an oral oxycodone operant self-administration model in adult male and female rats, as well as to examine a potential mechanism of stress-primed reinstatement. We found that females consumed significantly more oral oxycodone than males in operant self-administration sessions. We also found that active oxycodone self-administration was reduced by mu opioid receptor antagonism and by substitution of water for oxycodone solution. Lastly, we induced stress-primed reinstatement and found that this behavior was significantly attenuated by antagonism of the neurokinin-1 receptor, consistent with our prior work examining stress-induced reinstatement of alcohol- and cocaine-seeking.

Acquisition of remifentanil self-administration: Enhanced in female rats but no effect of adolescent stress exposure

Animal models of acquisition have been vital in shaping our understanding of vulnerability factors that influence susceptibility to drugs of abuse. Decades of research substantiates a number of biological, environmental, and behavioral factors that predict vulnerability - many of which have been important in the development of early intervention efforts in humans. The goal of the present study was to examine the acquisition of a synthetic opioid derivative in 66 adult male and female Long-Evans rats following histories of stress exposure during adolescence. Stress-exposed rats were subjected to a mild stress paradigm, which included alternating exposure to synthetic fox feces and physical restraint for eight days. Following stress induction and assessment, all rats were implanted with intravenous catheters in order to self-administer remifentanil (1 μm/kg/infusion) with no prior operant training. Acquisition of remifentanil self-administration was measured over 15 days. Findings indicate that regardless of stress condition, female rats acquired remifentanil self-administration sooner and emitted more active lever presses than males. Stress exposed animals exhibited increased anxiety-like response compared to the control group following exposure to stress, operationalized as decreased exploratory behavior on an Elevated Plus Maze. However, these effects were not expressed as significant differences in self-administration by stress. Together, these findings indicate that sex differences are evident in remifentanil self-administration.

The therapeutic potential of exercise for neuropsychiatric diseases: A review

Exercise is known to have a myriad of health benefits. There is much to be learned from the effects of exercise and its potential for prevention, attenuation and treatment of multiple neuropsychiatric diseases and behavioral disorders. Furthermore, recent data and research on exercise benefits with respect to major health crises, such as, that of opioid and general substance use disorders, make it very important to better understand and review the mechanisms of exercise and how it could be utilized for effective treatments or adjunct treatments for these diseases. In addition, mechanisms, epigenetics and sex differences are examined and discussed in terms of future research implications.

Sex and the dopaminergic system: Insights from addiction studies

Sex differences are present in psychiatric disorders associated with disrupted dopamine function, and thus, sex differences in dopamine neurobiology may underlie these clinical disparities. In this chapter, we review sex differences in the dopaminergic system with a focus on substance use disorders, especially tobacco smoking, as our exemplar disorder. This chapter is organized into five sections describing sex differences in the dopaminergic system: (1) neurobiology, (2) role of sex hormones, (3) genetic underpinnings, (4) cognitive function, and (5) influence on addiction. In each section, we provide an overview of the topic area, summarize sex differences identified to date, highlight addiction research, especially clinical neuroimaging studies, and suggest avenues for future research.

Acute ovarian hormone treatment in freely cycling female rats regulates distinct aspects of heroin seeking

Females are at higher risk for certain opioid addictive behaviors, but the influence of ovarian hormones is unknown. In our rat model of heroin self-administration, females exhibited higher relapse rates that correlated with rates of heroin seeking on the first extinction session. We administered estradiol alone, or in combination with progesterone, 30 min prior to the first extinction session in freely cycling, heroin-seeking female rats. Although neither treatment produced long-term effects on relapse, each treatment regulated distinct aspects of heroin seeking. Estradiol treatment enhanced extinction memory retention, whereas the combination treatment acutely reduced expression of heroin seeking.

Tamoxifen Blocks the Development of Motivational Features of an Addiction-Like Phenotype in Female Rats

Women become addicted sooner after initiating cocaine use as compared to men. Preclinical studies reveal a similar vulnerability in females, with findings from ovariectomized rats suggesting that estradiol mediates the enhanced vulnerability. However, since ovariectomy depletes not only estradiol, but all ovarian hormones, its role in a physiological context is not clear. Thus, the goal of this study was to determine the role of estradiol in the development of an addiction-like phenotype in ovary-intact females treated chronically with the selective estrogen receptor (ER) modulator tamoxifen. We hypothesized that tamoxifen, by antagonizing ERs, would block the development of an addiction-like phenotype as defined by an enhanced motivation for cocaine (assessed under a progressive-ratio schedule), and a heightened vulnerability to relapse (assessed under an extinction/cue-induced reinstatement procedure). Effects were examined following extended access cocaine self-administration (24-h/day; 4-discrete trials/h; 1.5 mg/kg/infusion) and 14-days of abstinence, conditions optimized for inducing an addiction-like phenotype. As predicted, motivation for cocaine was increased following extended-access self-administration and protracted abstinence in the vehicle (sesame oil) and no-injection control groups, but not in the tamoxifen group indicating that ER signaling is critical for the development of this feature of an addiction-like phenotype. Surprisingly, the increase in motivation for cocaine following abstinence was also attenuated in the vehicle group as compared to no-injection controls suggesting that oil/injections also affected its development. Contrary to our hypothesis, tamoxifen did not decrease vulnerability to relapse as this group responded at similar levels during initial extinction sessions and cue-induced reinstatement testing as compared to controls. Tamoxifen did, however, impair extinction learning as this group took longer to extinguish as compared to controls. Taken together, these findings indicate that estradiol is critical for the extinction of drug-associated cues and the development of motivational features of addiction.

Sigma-1 receptor antagonist, PD144418, selectively reduces female motivation for food during negative energy balance

Sigma-1 (σ1) receptors have been investigated for their involvement in learning, rewarding and motivational processes. PD144418, a σ1 receptor antagonist, has been found to produce a dose-dependent attenuation of locomotor activity induced by cocaine, and by itself, does not suppress basal locomotor activity in mice. Moreover, PD144418 decreases the motivational effort of a food-reinforced behavior in male rats, without altering appetite or food palatability. It remains unknown whether the PD144418 can alter the motivational effort of a food-reinforced behavior in response to altered energy homeostasis, as is the case under 24 -h food deprivation. Additionally, while the previous experiments indicate effects in male rats, there has been no research examining the effects of PD144418, or any other σ1 receptor antagonist, on motivational aspects of feeding in females. The present study examined the effects of PD144418 on motivational aspects of feeding in male and female rats using an operant task under sated or food deprived conditions. Results indicated that when animals are sated, at the highest dose (10 μmol/kg), under a progressive ratio (PR) reinforcement schedule, PD144418 significantly attenuated the breakpoint and the number of active lever responses for sucrose pellets in both males and females. When animals are in a state of energy deficit, as is the case following 24-hr food deprivation, PD144418 does not alter motivationally driven operant responding as measured by the breakpoint in either sex but does alter the number of earned reinforcers responses in females.

Sex differences in the reward deficit and somatic signs associated with precipitated nicotine withdrawal in rats

Female smokers are more likely to relapse than male smokers, but little is known about sex differences in nicotine withdrawal. Therefore, male and female rats were prepared with minipumps that contained nicotine or saline and sex differences in precipitated and spontaneous nicotine withdrawal were investigated. The intracranial self-stimulation (ICSS) procedure was used to assess mood states. Elevations in brain reward thresholds reflect a deficit in reward function. Anxiety-like behavior was investigated after the acute nicotine withdrawal phase in a large open field and the elevated plus maze test. The nicotinic receptor antagonist mecamylamine elevated the brain reward thresholds of the nicotine-treated rats but did not affect those of the saline-treated control rats. A low dose of mecamylamine elevated the brain reward thresholds of the nicotine-treated male rats but not those of the females. Mecamylamine also precipitated more somatic withdrawal signs in the nicotine-treated male than female rats. Minipump removal elevated the brain reward thresholds of the nicotine-treated rats for about 36 h but did not affect those of the saline-treated rats. There was no sex difference in the reward deficit during spontaneous nicotine withdrawal. In addition, the nicotine-treated male and female rats did not display increased anxiety-like behavior three to four days after minipump removal. In conclusion, these studies suggest that relatively low doses of a nicotinic receptor antagonist induce a greater reward deficit and more somatic withdrawal signs in male than female rats, but there is no sex difference in the reward deficit during spontaneous withdrawal.

Incubation of Cocaine Craving After Intermittent-Access Self-administration: Sex Differences and Estrous Cycle

BACKGROUND

Studies using continuous-access drug self-administration showed that cocaine seeking increases during abstinence (incubation of cocaine craving). Recently, studies using intermittent-access self-administration showed increased motivation to self-administer and seek cocaine. We examined whether intermittent cocaine self-administration would potentiate incubation of craving in male and female rats and examined the estrous cycle's role in this incubation.

METHODS

In experiment 1, male and female rats self-administered cocaine either continuously (8 hours/day) or intermittently (5 minutes ON, 25 minutes OFF × 16) for 12 days, followed by relapse tests after 2 or 29 days. In experiments 2 and 3, female rats self-administered cocaine intermittently for six, 12, or 18 sessions. In experiment 4, female rats self-administered cocaine continuously followed by relapse tests after 2 or 29 days. In experiments 3 and 4, the estrous cycle was measured using a vaginal smear test.

RESULTS

Incubation of cocaine craving was observed in both sexes after either intermittent or continuous drug self-administration. Independent of access condition and abstinence day, cocaine seeking was higher in female rats than in male rats. In both sexes, cocaine seeking on both abstinence days was higher after intermittent drug access than after continuous drug access. In female rats, incubation of craving after either intermittent or continuous drug access was significantly higher during estrus than during non-estrus; for intermittent drug access, this effect was independent of the training duration.

CONCLUSIONS

In both sexes, intermittent cocaine access caused time-independent increases in drug seeking during abstinence. In female rats, the time-dependent increase in drug seeking (incubation) is critically dependent on the estrous cycle phase.

Exogenous progesterone for cannabis withdrawal in women: Feasibility trial of a novel multimodal methodology

BACKGROUND

Sex differences in cannabis use disorder (CUD) and its treatment have been identified. Women report more severe withdrawal and have shown worse treatment outcomes. Ovarian hormones are implicated in these differences and research suggests that exogenous progesterone may be an effective pharmacotherapy.

METHODS

The current randomized, placebo-controlled, feasibility trial tested a novel multimodal methodology for administering exogenous progesterone during acute cannabis withdrawal. Eight heavy cannabis using women received micronized progesterone (200 mg bid) (n = 3) or matching placebo (n = 5) during the early follicular phase of their menstrual cycle over a 5-day study period while abstaining from cannabis. Laboratory visits (days 1 and 5) included biological and self-report assessments, while home-based procedures (days 2-4) included ambulatory assessments, video data capture and tele-drug testing, and biological assessments. Primary outcomes were medication adherence and salivary hormone levels, and the exploratory outcome was cannabis withdrawal severity.

RESULTS

Medication adherence rates were high as assessed via self-report (100.0%) and video data capture (98.0%). Salivary progesterone levels differed between groups over time (p < 0.027) and the progesterone group achieved levels within the normal range during the luteal phase in healthy adults. All tele-drug tests were negative confirming cannabis abstinence and there was an indication (p = 0.07) of reduced cannabis craving among participants receiving progesterone.

CONCLUSION

More effective and sex-based treatments for cannabis use disorder are needed. The current study provides a novel multimodal methodology with low participant burden for investigating new medications for cannabis withdrawal. Clinical trials of progesterone for cannabis withdrawal may be warranted.

Extinction to amphetamine-associated context in female rats is dependent upon conditioned orienting

RATIONALE

Females are considered more susceptible to the reinforcing effects of drugs and subsequently at increased risk for drug abuse and relapse after treatment. Estrogen is known to facilitate drug effects in females. However, other factors which contribute to the incidence of drug abuse are important to identify in order to recognize early risk factors and develop effective prevention and treatment schemes. Cue-directed behavior (aka sign tracking) has been implicated as a behavioral phenotype which identifies populations susceptible to drug abuse, partly due to its association with impulsivity and heightened dopamine function.

OBJECTIVES AND METHODS

In this study, we investigate the viability of conditioned orienting (a form of cue-directed behavior) as a potential phenotype which predicts drug proclivity in female rats. In addition, we examine any influence endogenous female hormones across the estrous cycle may have on conditioned orienting and drug proclivity.

RESULTS AND CONCLUSIONS

Utilizing an amphetamine-conditioned place preference task, results suggest that the orienting phenotype is an effective predictor of drug proclivity in females. Rats exhibiting enhanced orienting behavior show more robust preference for an amphetamine-associated context and are more resistant to extinction of this preference than nonorienting counterparts. Furthermore, both conditioned orienting behavior and conditioned place preference are minimally influenced by the estrous cycle.

Sex differences in neural mechanisms mediating reward and addiction

There is increasing evidence in humans and laboratory animals for biologically based sex differences in every phase of drug addiction: acute reinforcing effects, transition from occasional to compulsive use, withdrawal-associated negative affective states, craving, and relapse. There is also evidence that many qualitative aspects of the addiction phases do not differ significantly between males and females, but one sex may be more likely to exhibit a trait than the other, resulting in population differences. The conceptual framework of this review is to focus on hormonal, chromosomal, and epigenetic organizational and contingent, sex-dependent mechanisms of four neural systems that are known-primarily in males-to be key players in addiction: dopamine, mu-opioid receptors (MOR), kappa opioid receptors (KOR), and brain-derived neurotrophic factor (BDNF). We highlight data demonstrating sex differences in development, expression, and function of these neural systems as they relate-directly or indirectly-to processes of reward and addictive behavior, with a focus on psychostimulants and opioids. We identify gaps in knowledge about how these neural systems interact with sex to influence addictive behavior, emphasizing throughout that the impact of sex can be highly nuanced and male/female data should be reported regardless of the outcome.

The Modulating Role of Sex and Anabolic-Androgenic Steroid Hormones in Cannabinoid Sensitivity

Cannabis is the most commonly used illicit drug worldwide. Although its use is associated with multiple adverse health effects, including the risk of developing addiction, recreational and medical cannabis use is being increasing legalized. In addition, use of synthetic cannabinoid drugs is gaining considerable popularity and is associated with mass poisonings and occasional deaths. Delineating factors involved in cannabis use and addiction therefore becomes increasingly important. Similarly to other drugs of abuse, the prevalence of cannabis use and addiction differs remarkably between males and females, suggesting that sex plays a role in regulating cannabinoid sensitivity. Although it remains unclear how sex may affect the initiation and maintenance of cannabis use in humans, animal studies strongly suggest that endogenous sex hormones modulate cannabinoid sensitivity. In addition, synthetic anabolic-androgenic steroids alter substance use and further support the importance of sex steroids in controlling drug sensitivity. The recent discovery that pregnenolone, the precursor of all steroid hormones, controls cannabinoid receptor activation corroborates the link between steroid hormones and the endocannabinoid system. This article reviews the literature regarding the influence of endogenous and synthetic steroid hormones on the endocannabinoid system and cannabinoid action.