Sex differences and hormonal influences on acquisition of cocaine self-administration in rats

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.

Exercise Influences the Brain's Metabolic Response to Chronic Cocaine Exposure in Male Rats

Cocaine use is associated with negative health outcomes: cocaine use disorders, speedballing, and overdose deaths. Currently, treatments for cocaine use disorders and overdose are non-existent when compared to opioid use disorders, and current standard cocaine use disorder treatments have high dropout and recidivism rates. Physical exercise has been shown to attenuate addiction behavior as well as modulate brain activity. This study examined the differential effects of chronic cocaine use between exercised and sedentary rats. The effects of exercise on brain glucose metabolism (BGluM) following chronic cocaine exposure were assessed using Positron Emission Tomography (PET) and [18F]-Fluorodeoxyglucose (FDG). Compared to sedentary animals, exercise decreased metabolism in the SIBF primary somatosensory cortex. Activation occurred in the amygdalopiriform and piriform cortex, trigeminothalamic tract, rhinal and perirhinal cortex, and visual cortex. BGluM changes may help ameliorate various aspects of cocaine abuse and reinstatement. Further investigation is needed into the underlying neuronal circuits involved in BGluM changes and their association with addiction behaviors.

Mifepristone decreases nicotine intake in dependent and non-dependent adult rats

BACKGROUND

Addiction to tobacco and nicotine products has adverse health effects and afflicts more than a billion people worldwide. Therefore, there is an urgent need for new treatments to reduce tobacco and nicotine use. Glucocorticoid receptor blockade shows promise as a novel treatment for drug abuse and stress-related disorders.

AIM

These studies aim to investigate whether glucocorticoid receptor blockade with mifepristone diminishes the reinforcing properties of nicotine in rats with intermittent or daily long access to nicotine.

METHODS

The rats self-administered 0.06 mg/kg/inf of nicotine for 6 h per day, with either intermittent or daily access for 4 weeks before treatment with mifepristone. Daily nicotine self-administration models regular smoking, while intermittent nicotine self-administration models occasional smoking. To determine whether the rats were dependent, they were treated with the nicotinic acetylcholine receptor antagonist mecamylamine, and somatic signs were recorded.

RESULTS

The rats with intermittent access to nicotine had a higher level of nicotine intake per session than those with daily access but only the rats with daily access to nicotine showed signs of physical dependence. Furthermore, mecamylamine increased nicotine intake during the first hour of access in rats with daily access but not in those with intermittent access. Mifepristone decreased total nicotine intake in rats with intermittent and daily access to nicotine. Moreover, mifepristone decreased the distance traveled and rearing in the open field test and operant responding for food pellets.

CONCLUSION

These findings indicate that mifepristone decreases nicotine intake but this effect may be partially attributed to the sedative effects of mifepristone.

Cocaine sensitization in male rats requires activation of estrogen receptors

Gonadal steroids play a modulatory role in cocaine use disorders, and are responsible for many sex differences observed in the behavioral response to cocaine. In females, it is well established that estradiol enhances the behavioral response to cocaine. In males, we have recently shown that testosterone enhances sensitization to cocaine but its mechanism of action remains to be elucidated. The current study investigated the contribution of DHT, a non-aromatizable androgen, and of estradiol, in regulating cocaine-induced sensitization in male rats. Gonadectomized (GDX) male rats treated with estradiol sensitized to repeated cocaine administration, while GDX rats treated with DHT did not, implicating estradiol in cocaine sensitization. Furthermore, intact male rats treated with the antiestrogen ICI 182,780 did not show sensitization to repeated cocaine. This study demonstrates the pivotal role of estradiol in cocaine-induced neuroplasticity and neuroadaptations in the rodent brain.

Estradiol reduction through aromatase inhibition impairs cocaine seeking in male rats

Introduction

Clinical and preclinical research on cocaine use disorder (CUD) has shown that sex differences in drug seeking are influenced by hormonal fluctuations. Estradiol (E2), a sex steroid hormone, has been linked to female drug effects, vulnerability to use/abuse, and psychosocial factors. Preclinical studies show that estradiol in females facilitates the extinction of cocaine-seeking behavior indicating a possible role in regulating extinction learning. Similar to females, males' brains contain the aromatase enzyme which converts testosterone to estradiol. However, it is unclear whether estradiol plays a role in male extinction learning as it does in females. Furthermore, how endogenously aromatized estradiol affects drug addiction in males is unknown. Therefore, this study investigated whether endogenous estradiol regulates cocaine seeking in male rats. We hypothesized that decreased aromatase enzyme activity, resulting in decreased estradiol synthesis in male brains, will impair extinction learning leading to increased cocaine-seeking behavior.

Methods

This hypothesis was tested using cocaine-conditioned place preference (CPP), and short access self-administration (SA), followed by extinction and reinstatement. Before each extinction session for CPP or SA, male rats received an injection of either 1 (low dose) or 2.5 mg/kg (high dose) of the aromatase inhibitor Fadrozole (FAD), or vehicle.

Results

FAD groups showed dose-dependent effects on cocaine-seeking behavior compared to the vehicle group during CPP extinction. Specifically, low dose FAD facilitated extinction of cocaine CPP, whereas high dose FAD impaired it. In contrast, neither dose of FAD had any effects on the extinction of cocaine SA. Interestingly, only the low dose FAD group had decreased active lever pressing during cue- and cocaine-primed reinstatement compared to the vehicle group. Neither dose of FAD had an effect on sucrose extinction or reinstatement of sucrose seeking.

Discussion

These results from CPP experiments suggest that estradiol may impact extinction learning, as a low dose of FAD may strengthen the formation of cocaine extinction memory. Additionally, in male rats undergoing cocaine SA, the same low dose of aromatase inhibitor effectively reduced reinstatement of cocaine-seeking behavior. Thus, estradiol impacts cocaine seeking and extinction in both males and females, and it may also influence the development of sex-specific treatment strategies for CUD.

The Role of Estrogen Signaling and Exercise in Drug Abuse: A Review

BACKGROUND

Discovering how sex differences impact the efficacy of exercise regimens used for treating drug addiction is becoming increasingly important. Estrogen is a hormone believed to explain a large portion of sex differences observed during drug addiction, and why certain exercise regimens are not equally effective between sexes in treatment. Addiction is currently a global hindrance to millions, many of whom are suffering under the influence of their brain's intrinsic reward system coupled with external environmental factors. Substance abuse disorders in the U.S. alone cost billions of dollars annually.

REVIEW SUMMARY

Studies involving the manipulation of estrogen levels in female rodents, primarily via ovariectomy, highlight its impact regarding drug addiction. More specifically, female rodents with higher estrogen levels during the estrus phase increase cocaine consumption, whereas those in the non-estrus phase (low estrogen levels) decrease cocaine consumption. If estrogen is reintroduced, self-administration increases once again. Exercise has been proven to decrease relapse tendency, but its effect on estrogen levels is not fully understood.

CONCLUSIONS

Such findings and results discussed in this review suggest that estrogen influences the susceptibility of females to relapse. Therefore, to improve drug-abuse-related treatment, exercise regimens for females should be generated based on key sex differences with respect to males.

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.

Effects of fentanyl self-administration on risk-taking behavior in male rats

RATIONALE

Individuals with opioid use disorder (OUD) exhibit impaired decision making and elevated risk-taking behavior. In contrast to the effects of natural and semi-synthetic opioids, however, the impact of synthetic opioids on decision making is still unknown.

OBJECTIVES

The objective of the current study was to determine how chronic exposure to the synthetic opioid fentanyl alters risk-based decision making in adult male rats.

METHODS

Male rats underwent 14 days of intravenous fentanyl or oral sucrose self-administration. After 3 weeks of abstinence, rats were tested in a decision-making task in which they chose between a small, safe food reward and a large food reward accompanied by variable risk of footshock punishment. Following testing in the decision-making task, rats were tested in control assays that assessed willingness to work for food and shock reactivity. Lastly, rats were tested on a probabilistic reversal learning task to evaluate enduring effects of fentanyl on behavioral flexibility.

RESULTS

Relative to rats in the sucrose group, rats in the fentanyl group displayed greater choice of the large, risky reward (risk taking), an effect that was present as long as 7 weeks into abstinence. This increased risk taking was driven by enhanced sensitivity to the large rewards and diminished sensitivity to punishment. The fentanyl-induced elevation in risk taking was not accompanied by alterations in food motivation or shock reactivity or impairments in behavioral flexibility.

CONCLUSIONS

Results from the current study reveal that the synthetic opioid fentanyl leads to long-lasting increases in risk taking in male rats. Future experiments will extend this work to females and identify neural mechanisms that underlie these drug-induced changes in risk taking.

Delayed estrogen actions diminish food consumption without changing food approach, motor activity, or hypothalamic activation elicited by corticostriatal µ-opioid signaling

Mu-opioid receptor (μ-OR) signaling in forebrain sites including nucleus accumbens (Acb) and ventromedial prefrontal cortex (vmPFC) modulates reward-driven feeding and may play a role in the pathophysiology of disordered eating. In preclinical models, intra-Acb or intra-vmPFC μ-OR stimulation causes overeating and vigorous responding for food rewards. These effects have been studied mainly in male animals, despite demonstrated sex differences and estrogen modulation of central reward systems. Hence, the present study investigated sex differences and estrogen modulation of intra-Acb and intra-vmPFC μ-OR-driven feeding behaviors. First, the dose-related effects of intra-Acb and intra-vmPFC infusions of the μ-OR-selective agonist, DAMGO, were compared among intact female, ovariectomized (OVX) female, and intact male rats. The DAMGO feeding dose-effect function was flattened in intact females relative to the robust, dose-dependent effects observed in OVX females and intact males. Thus, in intact females, intra-Acb DAMGO failed to elevate food intake relative to vehicle, while intra-vmPFC DAMGO elevated food intake, but to a smaller degree compared to males and OVX females. Next, to explore the possible role of estrogen in mediating the diminished DAMGO response observed in intact females, OVX rats were given intra-Acb or intra-vmPFC infusions of DAMGO either immediately after a subcutaneous injection of 17-beta-estradiol 3-benzoate (EB; 5 μg/0.1 mL) or 24 h after EB injection. Intra-Acb DAMGO effects were not changed at the immediate post-EB time point. At the delayed post-EB timepoint, significant lordosis was noted and the duration of intra-Acb DAMGO-driven feeding bouts was significantly reduced, with no change in the number of bouts initiated, locomotor hyperactivity, or Fos immunoreactivity in hypothalamic feeding and arousal systems. Similarly, EB failed to alter the motor-activational effects of intra-vmPFC DAMGO while reducing feeding. These findings indicate that delayed, presumably genomically mediated estrogen actions modulate the μ-OR-generated motivational state by reducing consummatory activity while sparing goal-approach and general arousal/activity. The results additionally suggest that EB regulation of consummatory activity occurs outside of forebrain-μ-OR control of hypothalamic systems.

Methodological approach for an integrated female-specific study of anxiety and smoking comorbidity

Two primary ovarian hormones that fluctuate across the female menstrual cycle-estradiol and progesterone-have been independently linked in separate literatures to nicotine reinforcement and anxiety psychopathology. We identify existing methodological limitations in these literatures, describe an example protocol that was developed to address such limitations, highlight case examples, and offer insights on the resulting advantages and challenges. This protocol was an observational, prospective, within-subjects study of female cigarette smokers who were followed over the course of a complete menstrual cycle. Non-treatment seeking, female cigarette smokers (N = 50), between the ages of 18-40 who have a normal menstrual cycle (25-35 days in length) were recruited from the community. Females with anxiety or mood psychopathology represented 38.0% of the sample. Salivary progesterone and estradiol were assessed each morning via at-home saliva collection methods. Self-reported within-day momentary ratings of anxiety and nicotine reinforcement were collected using ecological momentary assessment (EMA) via a mobile app. Protocol compliance was >85%. Within- and between-subjects heterogeneity was observed in the progesterone and estradiol, anxiety, and nicotine craving measures, especially in the context of anxiety psychopathology. We aimed to integrate the anxiety and nicotine dependence literatures and advance the empirical study of the role of ovarian hormones. This protocol reflects an intensive, yet feasible approach to collecting daily-level naturalistic data related to estradiol, progesterone, anxiety, and nicotine reinforcement.

Interactions between estradiol and ERK, but not mTOR, signaling is necessary for enhanced cocaine-induced conditioned place preference in female rats

Women rapidly progress from recreational cocaine use to dependence, consume greater quantities of cocaine, experience more positive subjective effects of cocaine and have higher incidences of relapse during abstinence. These effects have been replicated in animal models of cocaine addiction and indicate an enhanced sensitivity and therefore, vulnerability of females to cocaine addiction. Furthermore, it has been demonstrated that estradiol (E2) is a key mediator of the aforementioned effects of cocaine in women and female animals. However, studies identifying the influence of E2 on cocaine-associated reward and its underlying neurobiological mechanisms are lacking. Here, we further explored the influence of E2 on cocaine conditioned place preference in female rats. We show that E2 mediates cocaine-conditioned reward by potentiating cocaine-context associations. In addition, the E2-mediated increases in cocaine-induced CPP are associated with increased activation of ERK1/2 and mTOR proteins in the nucleus accumbens, dorsal striatum, and ventral tegmental area. To assess the involvement of ERK1/2 and mTOR in E2-mediated enhanced cocaine-CPP, we inhibited ERK1/2 and/or mTOR activity during cocaine-conditioning and before CPP-test. Inhibition of ERK1/2 during conditioning blocked cocaine-CPP in females, inhibition mTOR was without effect, and inhibiting ERK1/2 and mTOR before CPP-test blocked cocaine-CPP. In conclusion, we have established that E2 enhances cocaine-conditioned reward by potentiating cocaine-context associations formed during conditioning. Additionally, activation of ERK1/2 during cocaine-conditioning is necessary for the potentiation of cocaine-conditioned reward by E2. SIGNIFICANCE STATEMENT: Studies characterizing the molecular substrates underlying the effects of E2 during the formation of cocaine-context associations are virtually unknown. In this study, we established the influence of E2 during the formation of cocaine-CPP and characterized the role of ERK1/2 and mTOR activity on this effect within significant nodes of the reward pathway. The elucidation of the role of E2 in cocaine-induced intracellular signaling fills a significant gap in our knowledge regarding the mechanisms by which E2 affects intracellular signaling pathways to indicate the motivational salience of a stimulus. These data are crucial to our understanding of how fluctuating hormone levels can render females increasing sensitive to the rewarding effects of cocaine.

Estradiol Receptors Inhibit Long-Term Potentiation in the Dorsomedial Striatum

Estradiol, a female sex hormone and the predominant form of estrogen, has diverse effects throughout the brain including in learning and memory. Estradiol modulates several types of learning that depend on the dorsomedial striatum (DMS), a subregion of the basal ganglia involved in goal-directed learning, cued action-selection, and motor skills. A cellular basis of learning is synaptic plasticity, and the presence of extranuclear estradiol receptors ERα, ERβ, and G-protein-coupled estrogen receptor (GPER) throughout the DMS suggests that estradiol may influence rapid cellular actions including those involved in plasticity. To test whether estradiol affects synaptic plasticity in the DMS, corticostriatal long-term potentiation (LTP) was induced using theta-burst stimulation (TBS) in ex vivo brain slices from intact male and female C57BL/6 mice. Extracellular field recordings showed that female mice in the diestrous stage of the estrous cycle exhibited LTP similar to male mice, while female mice in estrus did not exhibit LTP. Furthermore, antagonists of ERα or GPER rescued LTP in estrous females and agonists of ERα or GPER reduced LTP in diestrous females. In males, activating ERα but not GPER reduced LTP. These results uncover an inhibitory action of estradiol receptors on cellular learning in the DMS and suggest a cellular mechanism underlying the impairment in certain types of DMS-based learning observed in the presence of high estradiol. Because of the dorsal striatum's role in substance use disorders, these findings may provide a mechanism underlying an estradiol-mediated progression from goal-directed to habitual drug use.

Sex Chromosome Complement and Estradiol Modify Cocaine Self-Administration Behaviors in Male Mice

INTRODUCTION

Women are more vulnerable to cocaine's reinforcing effects and have a more rapid course to addiction after initial cocaine use as compared to men. Studies in rodents similarly indicate an enhanced sensitivity to the reinforcing effects of cocaine in females versus males. Levels of estradiol (E2) are correlated with vulnerability to the rewarding actions of cocaine. Here, we asked if sex chromosome complement (SCC) influences vulnerability to cocaine use.

METHODS

We used the four-core genotype mouse that produces gonadal males and females with either XX or XY SCC. Mice were gonadectomized and implanted with either an estradiol (E2) or cholesterol-filled pellet. This allowed us to determine the effects of SCC in the absence (cholesterol-treated) and presence of tonic high physiological hormone levels (estradiol). Acquisition of cocaine self-administration was determined over a 12-day period using an escalated dose procedure (0.3 mg/kg/infusion, sessions 1-6; 0.6 mg/kg/infusion, sessions 6-12).

RESULTS

Without estradiol treatment, a greater percentage of castrated XY mice acquired cocaine self-administration and did so at a faster rate than XX castrates and ovariectomized XY females. These same XY males acquired sooner, infused more cocaine, and directed more nose pokes to the rewarded nose-poke hole than XX castrates and XY males receiving E2.

CONCLUSION

Our results suggest that in gonadal male mice, SCC and estradiol can modulate the reinforcing effects of cocaine which may influence the likelihood of cocaine use.

Sex steroid hormone levels associated with dopamine D2/3 receptor availability in people who smoke cigarettes

Introduction

Sex differences exist in tobacco smoking. Women have greater difficulty quitting smoking than men. Tobacco smoking is driven by the reinforcing effects of nicotine, the primary addictive component in cigarettes. Nicotine binds to nicotinic acetylcholine receptors, facilitating dopamine release in striatal and cortical brain regions. Dysregulated dopamine D2/3 receptor signaling in the dorsolateral prefrontal cortex (dlPFC) is associated with cognitive deficits such as impairments in attention, learning, and inhibitory control that impede quit attempts. Sex steroid hormones, such as estradiol and progesterone, influence drug-taking behaviors, through dopaminergic actions, suggesting that their influence may explain sex differences in tobacco smoking. The goal of this study was to relate dlPFC dopamine metrics to sex steroid hormone levels in people who smoke and healthy controls.

Methods

Twenty-four (12 women) people who smoke cigarettes and 25 sex- and age-matched controls participated in two same-day [11C]FLB457 positron emission tomography scans, one before and one after amphetamine administration. D2R availability (BPND) at baseline and after amphetamine administration was calculated. On the same day, plasma samples were collected for the analysis of sex steroid hormone levels: estradiol, progesterone, and free testosterone.

Results

Women who smoke had trending lower levels of estradiol than their sex-matched counterparts. Men who smoke had higher levels of estradiol and trending higher levels of free testosterone than their sex-matched counterparts. Among women only, lower estradiol levels were significantly associated with lower pre-amphetamine dlPFC BPND.

Discussion/conclusion

This study demonstrated that lower estradiol levels are associated with lower dlPFC D2R availability in women which may underlie difficulty resisting smoking.

Lack of sex and estrous stage effects on compulsive behavior assessed using a schedule-induced polydipsia procedure in rats

Preclinical behavior models used for screening pharmacological treatments for mental disorders have generally used only male research subjects, and for studies that have included female subjects, few have utilized sex as a study variable. In fact, many mental disorders vary by prevalence and symptomatology between sexes, creating a need to evaluate established subject models for sex differences. Compulsive behavior is a feature shared across many mental disorders and effective treatments have been examined pre-clinically using the schedule-induced polydipsia procedure in rats. Drugs effective for reducing polydipsia include psychostimulants, such as d -amphetamine. Virtually no studies have examined sex differences using this procedure. For the present study, male and female rats were examined in the schedule-induced polydipsia paradigm. Rats were food-restricted and trained on a fixed-interval food reinforcement schedule and given free access to water during experimental sessions. Estrous stages were assessed during training and test sessions. The psychostimulant d -amphetamine was also tested once stable water consumption occurred. Excessive water intake developed over the course of training. Females required significantly more sessions to reach a stable level of drinking. Treatment with d -amphetamine (1.0 mg/kg, but not 0.25 or 0.5 mg/kg) significantly reduced drinking in both male and female rats. No sex differences were observed across other study variables including comparisons between diestrus and proestrus stages. Overall, these findings suggest that schedule-induced polydipsia procedures that employ similar methods can produce results generalizable across male and female subjects.

A Rat Model of the Brain-Derived Neurotrophic Factor Val66Met Polymorphism Shows Attenuated Motivation for Alcohol Self-Administration and Diminished Propensity for Cue-Induced Relapse in Females

Brain-derived neurotrophic factor (BDNF) has been implicated in alcohol use disorder. The Val66Met polymorphism is a common variant of the BDNF gene (rs6265) which reduces activity-dependent BDNF release, and has been suggested as a risk factor for psychiatric disorders and substance use. Using an operant self-administration paradigm, this study aimed to investigate ethanol preference and ethanol seeking in a novel rat model of the BDNF Val66Met polymorphism, Val68Met rats. Male and female BDNF Val68Met rats of three genotypes (Val/Val, Val/Met and Met/Met) were trained to lever press for a 10% ethanol solution. There was no effect of Val68Met genotype on acquisition of stable response to ethanol or its extinction. Met/Met rats of both sexes had a slight, but significantly lower breakpoint during progressive ratio sessions while female rats with the Met/Met genotype demonstrated a lower propensity for reinstatement of responding to cues. There were no effects of Val68Met genotype on anxiety-like behaviour or locomotor activity. In conclusion, Met/Met rats showed lower motivation to continue to press for a reward, and also a decreased propensity to relapse, suggesting a possible protective effect of the Met/Met genotype against alcohol use disorder, at least in females.

The importance of translationally evaluating steroid hormone contributions to substance use

Clinically, women appear to be more susceptible to certain aspects of substance use disorders (SUDs). The steroid hormones 17β-estradiol (E2) and progesterone (Pg) have been linked to women-specific drug behaviors. Here, we review clinical and preclinical studies investigating how cycling ovarian hormones affect nicotine-, cocaine-, and opioid-related behaviors. We also highlight gaps in the literature regarding how synthetic steroid hormone use may influence drug-related behaviors. In addition, we explore how E2 and Pg are known to interact in brain reward pathways and provide evidence of how these interactions may influence drug-related behaviors. The synthesis of this review demonstrates the critical need to study women-specific factors that may influence aspects of SUDs, which may play important roles in addiction processes in a sex-specific fashion. It is important to understand factors that impact women's health and may be key to moving the field forward toward more efficacious and individualized treatment strategies.

Sex differences in cocaine self-administration by Wistar rats after predator odor exposure

Traumatic stress disorders are defined in part by persistent avoidance of trauma-related contexts. Our lab uses a preclinical model of traumatic stress using predator odor (i.e., bobcat urine) in which some but not all rats exhibit persistent avoidance of odor-paired stimuli, similar to what is seen in humans. Bobcat urine exposure increases alcohol consumption in male Avoider rats, but it has not been tested for its effects on intake of other drugs. Here, we tested the effect of bobcat urine exposure on cocaine self-administration in adult male and female Wistar rats. We did not observe any effect of bobcat urine exposure on cocaine self-administration in male or female rats. We observed that (1) female rats with long access (6 hours) to cocaine self-administer more cocaine than long-access males, (2) long-access males and females exhibit escalation of cocaine intake over time, (3) stressed rats gain less weight than unstressed rats following acute predator odor exposure, (4) baseline cocaine self-administration is predictive of subsequent cocaine self-administration. The results of this study may inform future work on predator odor effects on cocaine self-administration.

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.

Repeated dosing with cocaine produces strain-dependent effects on responding for conditioned reinforcement in Collaborative Cross mice

RATIONALE

Cocaine use disorder (CUD) is a highly heritable form of substance use disorder, with genetic variation accounting for a substantial proportion of the risk for transitioning from recreational use to a clinically impairing addiction. With repeated exposures to cocaine, psychomotor and incentive sensitization are observed in rodents. These phenomena are thought to model behavioral changes elicited by the drug that contribute to the progression into addiction, but little is known about how genetic variation may moderate these consequences.

OBJECTIVES

Here, we describe the use of two Collaborative Cross (CC) recombinant inbred mouse strains that either exhibit high (CC018/UncJ) or no (CC027/GeniUncJ) psychomotor sensitization in response to cocaine to measure phenotypes related to incentive sensitization after repeated cocaine exposures; given the relationship of incentive motivation to nucleus accumbens core (NAc) dopamine release and reuptake, we also assessed these neurochemical mechanisms.

METHODS

Adult male and female CC018/UncJ and CC027/GeniUncJ mice underwent Pavlovian conditioning to associate a visual cue with presentation of a palatable food reward, then received five, every-other-day injections of cocaine or vehicle. Following Pavlovian re-training, they underwent testing acquisition of a new operant response for the visual cue, now serving as a conditioned reinforcer. Subsequently, electrically evoked dopamine release was assessed using fast-scan cyclic voltammetry from acute brain slices containing the NAc.

RESULTS

While both strains acquired the Pavlovian association, only CC018/UncJ mice showed conditioned reinforcement and incentive sensitization in response to cocaine, while CC027/GeniUncJ mice did not. Voltammetry data revealed that CC018/UncJ, compared to CC027/GeniUnc, mice exhibited higher baseline dopamine release and uptake. Moreover, chronic cocaine exposure blunted tonic and phasic dopamine release in CC018/UncJ, but not CC027/GeniUncJ, mice.

CONCLUSIONS

Genetic background is a moderator of cocaine-induced neuroadaptations in mesolimbic dopamine signaling, which may contribute to both psychomotor and incentive sensitization and indicate a shared biological mechanism of variation.

Sex differences in cocaine self-administration by Wistar rats after predator odor exposure

Traumatic stress disorders are defined in part by persistent avoidance of trauma-related contexts. Our lab uses a preclinical model of traumatic stress using predator odor (i.e., bobcat urine) in which some but not all rats exhibit persistent avoidance of odor-paired stimuli, similar to what is seen in humans. Bobcat urine exposure increases alcohol consumption in male Avoider rats, but it has not been tested for its effects on intake of other drugs. Here, we tested the effect of bobcat urine exposure on cocaine self-administration in adult male and female Wistar rats. We did not observe any effect of bobcat urine exposure on cocaine self-administration in male or female rats. We observed that (1) female rats with long access (6 hours) to cocaine self-administer more cocaine than long-access males, (2) long-access males and females exhibit escalation of cocaine intake over time, (3) stressed rats gain less weight than unstressed rats following acute predator odor exposure, (4) baseline cocaine self-administration is predictive of subsequent cocaine self-administration. The results of this study may inform future work on predator odor effects on cocaine self-administration.

The medial preoptic area and acute cocaine's stimulant effects in rats: Potential influences of estradiol and biological sex

The medial preoptic area (mPOA) in the hypothalamus is an important integrator of neuroendocrine signaling and a key regulator of both natural and drug-induced reward. Although the mPOA modulates sex differences in other behaviors, whether it also modulates sex differences in cocaine response remains unclear. To help us better understand the mPOA's role in sex differences associated with cocaine response, we examined cocaine-induced changes in locomotion and neural activity in the mPOA of male and female rats. In addition, neural activity in the striatum, a brain area known to be involved in cocaine response, was examined for comparison purposes. Fos, the protein product of the immediate early gene c-fos, was used as the marker of neural activity. Locomotion chambers were used to measure behavior, radioimmunoassays and vaginal lavages were used to determine hormonal status, and immunohistochemical assays were used to quantify Fos. To account for the effects of gonadal hormones, rats were left gonadally intact and categorized as either 'low-estradiol' or 'high-estradiol' based on their hormonal status on test day. Results indicate that high-estradiol females experienced greater cocaine-induced mPOA Fos-immunoreactivity (Fos-ir) and displayed greater cocaine-induced locomotion than low estradiol females. Conversely, high-estradiol males experienced less cocaine-induced mPOA Fos-ir and displayed less cocaine-induced locomotion than low-estradiol males. Cocaine-induced Fos-ir in the mPOA also correlated with cocaine-induced Fos-ir in areas of the striatum already associated with cocaine response. These findings further support the mPOA's role in the endocrine-mediated response to cocaine. It also identifies the mPOA as a contributor to sex differences in cocaine response and potential differences in vulnerability to developing cocaine use disorders.

Sex differences in the neuroadaptations associated with incubated cocaine-craving: A focus on the dorsomedial prefrontal cortex

Introduction

Women have a shorter course from initial cocaine use to meeting the criteria for cocaine use disorder as compared to men. Preclinical findings similarly indicate that females develop key features of an addiction-like phenotype faster than males, including an enhanced motivation for cocaine and compulsive use, indicating that this phenomenon is biologically based. The goals of this study were to determine whether cocaine-craving, another key feature of addiction, also develops sooner during withdrawal in females than males and to determine whether there are sex differences in the molecular mechanisms associated with its development focusing on markers known to mediate cocaine-craving in males (i.e., dorsomedial prefrontal cortex, dmPFC, expression of brain-derived neurotrophic factor exon-IV, Bdnf-IV, and NMDA receptor subunits, Grin2a, Grin2b, and Grin1).

Methods

Cocaine-craving was assessed following extended-access cocaine self-administration and 2, 7, or 14 days of withdrawal using an extinction/cue-induced reinstatement procedure. Tissue was obtained from the dmPFC immediately after reinstatement testing and gene expression changes were analyzed using real-time qPCR.

Results

In males, cocaine-craving (total extinction and cue-induced reinstatement responding) progressively increased from early to later withdrawal time-points whereas in females, cocaine-craving was already elevated during early withdrawal (after 2 days) and did not further increase at later withdrawal time-points. Levels of cocaine-craving, however, were similar between the sexes. Gene expression changes differed markedly between the sexes such that males showed the expected relapse- and withdrawal-associated changes in Bdnf-IV, Grin2a, Grin2b, and Grin1 expression, but females only showed a modest increase Grin1 expression at the intermediate withdrawal timepoint.

Discussion

These findings indicate that cocaine-craving is similarly expressed in males and females although the time-course for its incubation appears to be accelerated in females; the molecular mechanisms also likely differ in females versus males.

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.

Rapid Eye Movement Sleep Engages Melanin-Concentrating Hormone Neurons to Reduce Cocaine Seeking

BACKGROUND

Persistent sleep disruptions following withdrawal from abused drugs may hold keys to battle drug relapse. It is posited that there may be sleep signatures that predict relapse propensity, identifying which may open new avenues for treating substance use disorders.

METHODS

We trained male rats (approximately postnatal day 56) to self-administer cocaine. After long-term drug withdrawal (approximately postnatal day 100), we examined the correlations between the intensity of cocaine seeking and key sleep features. To test for causal relationships, we then used behavioral, chemogenetic, or optogenetic methods to selectively increase rapid eye movement sleep (REMS) and measured behavioral and electrophysiological outcomes to probe for cellular and circuit mechanisms underlying REMS-mediated regulation of cocaine seeking.

RESULTS

A selective set of REMS features was preferentially associated with the intensity of cue-induced cocaine seeking after drug withdrawal. Moreover, selectively increasing REMS time and continuity by environmental warming attenuated a withdrawal time-dependent intensification of cocaine seeking, or incubation of cocaine craving, suggesting that REMS may benefit withdrawal. Warming increased the activity of lateral hypothalamic melanin-concentrating hormone (MCH) neurons selectively during prolonged REMS episodes and counteracted cocaine-induced synaptic accumulation of calcium-permeable AMPA receptors in the nucleus accumbens-a critical substrate for incubation. Finally, the warming effects were partly mimicked by chemogenetic or optogenetic stimulations of MCH neurons during sleep, or intra-accumbens infusions of MCH peptide during the rat's inactive phase.

CONCLUSIONS

REMS may encode individual vulnerability to relapse, and MCH neuron activities can be selectively targeted during REMS to reduce drug relapse.

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.

Reelin deficiency exacerbates cocaine-induced hyperlocomotion by enhancing neuronal activity in the dorsomedial striatum

The Reln gene encodes for the extracellular glycoprotein Reelin, which regulates several brain functions from development to adulthood, including neuronal migration, dendritic growth and branching and synapse formation and plasticity. Human studies have implicated Reelin signaling in several neurodevelopmental and psychiatric disorders. Mouse studies using the heterozygous Reeler (HR) mice have shown that reduced levels of Reln expression are associated with deficits in learning and memory and increased disinhibition. Although these traits are relevant to substance use disorders, the role of Reelin in cellular and behavioral responses to addictive drugs remains largely unknown. Here, we compared HR mice to wild-type (WT) littermate controls to investigate whether Reelin signaling contributes to the hyperlocomotor and rewarding effects of cocaine. After a single or repeated cocaine injections, HR mice showed enhanced cocaine-induced locomotor activity compared with WT controls. This effect persisted after withdrawal. In contrast, Reelin deficiency did not induce cocaine sensitization, and did not affect the rewarding effects of cocaine measured in the conditioned place preference assay. The elevated cocaine-induced hyperlocomotion in HR mice was associated with increased protein Fos expression in the dorsal medial striatum (DMS) compared with WT. Lastly, we performed an RNA fluorescent in situ hybridization experiment and found that Reln was highly co-expressed with the Drd1 gene, which encodes for the dopamine receptor D1, in the DMS. These findings show that Reelin signaling contributes to the locomotor effects of cocaine and improve our understanding of the neurobiological mechanisms underlying the cellular and behavioral effects of cocaine.

From Molecule to Behavior: Hypocretin/orexin Revisited From a Sex-dependent Perspective

The hypocretin/orexin (Hcrt/Orx) system in the perifornical lateral hypothalamus has been recognized as a critical node in a complex network of neuronal systems controlling both physiology and behavior in vertebrates. Our understanding of the Hcrt/Orx system and its array of functions and actions has grown exponentially in merely 2 decades. This review will examine the latest progress in discerning the roles played by the Hcrt/Orx system in regulating homeostatic functions and in executing instinctive and learned behaviors. Furthermore, the gaps that currently exist in our knowledge of sex-related differences in this field of study are discussed.

Involvement of the ghrelin system in the maintenance and reinstatement of cocaine-motivated behaviors: a role of adrenergic action at peripheral β1 receptors

Cocaine addiction is a significant medical and public concern. Despite decades of research effort, development of pharmacotherapy for cocaine use disorder remains largely unsuccessful. This may be partially due to insufficient understanding of the complex biological mechanisms involved in the pathophysiology of this disorder. In the present study, we show that: (1) elevation of ghrelin by cocaine plays a critical role in maintenance of cocaine self-administration and cocaine-seeking motivated by cocaine-conditioned stimuli; (2) acquisition of cocaine-taking behavior is associated with the acquisition of stimulatory effects of cocaine by cocaine-conditioned stimuli on ghrelin secretion, and with an upregulation of ghrelin receptor mRNA levels in the ventral tegmental area (VTA); (3) blockade of ghrelin signaling by pretreatment with JMV2959, a selective ghrelin receptor antagonist, dose-dependently inhibits reinstatement of cocaine-seeking triggered by either cocaine or yohimbine in behaviorally extinguished animals with a history of cocaine self-administration; (4) JMV2959 pretreatment also inhibits brain stimulation reward (BSR) and cocaine-potentiated BSR maintained by optogenetic stimulation of VTA dopamine neurons in DAT-Cre mice; (5) blockade of peripheral adrenergic β1 receptors by atenolol potently attenuates the elevation in circulating ghrelin induced by cocaine and inhibits cocaine self-administration and cocaine reinstatement triggered by cocaine. These findings demonstrate that the endogenous ghrelin system plays an important role in cocaine-related addictive behaviors and suggest that manipulating and targeting this system may be viable for mitigating cocaine use disorder.

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.

Sex Differences in Psychostimulant Abuse: Implications for Estrogen Receptors and Histone Deacetylases

Substance abuse is a chronic pathological disorder that negatively affects many health and neurological processes. A growing body of literature has revealed gender differences in substance use. Compared to men, women display distinct drug-use phenotypes accompanied by recovery and rehabilitation disparities. These observations have led to the notion that sex-dependent susceptibilities exist along the progression to addiction. Within this scope, neuroadaptations following psychostimulant exposure are thought to be distinct for each sex. This review summarizes clinical findings and animal research reporting sex differences in the subjective and behavioral responses to cocaine, methamphetamine, and nicotine. This discussion is followed by an examination of epigenetic and molecular alterations implicated in the addiction process. Special consideration is given to histone deacetylases and estrogen receptor-mediated gene expression.

Extreme phenotypic diversity in operant response to intravenous cocaine or saline infusion in the hybrid mouse diversity panel

Cocaine self-administration is a complexly determined trait, with a substantial proportion of individual differences being determined by genetic variation. However, the relevant genetic variants that drive heritable differences in cocaine use remain undiscovered. Cocaine intravenous self-administration (IVSA) procedures in laboratory animals provide opportunities to prospectively investigate neurogenetic influences on the acquisition of voluntary cocaine use. Here, we provide information on cocaine (or saline-as a control) IVSA in 84 members of the hybrid mouse diversity panel (HMDP), an array of genetically distinct classical or recombinant inbred strains. We found cocaine IVSA to be substantially heritable in this population, with strain-level intake ranging for near 0 to >25 mg/kg/session. Though saline IVSA was also found to be heritable, a modest genetic correlation between cocaine and saline IVSA indicates that operant responding for the cocaine reinforcer was influenced, at least in part, by unique genetic variants. Genome-wide association studies (GWAS) of infusions earned in cocaine and saline groups revealed significant quantitative trait loci (QTL) on Chromosomes 3 and 14 for cocaine, but not saline, IVSA. Positional candidates were further prioritized through use of bulk RNA sequencing data that revealed genes with cis-eQTL and genetic correlation to number of infusions. Additionally, these data identify reference strains with extreme cocaine IVSA phenotypes, revealing them as polygenic models of risk and resilience to cocaine reinforcement. This work is part of an ongoing effort to characterize genetic variation that moderates cocaine IVSA that may, in turn, provide a more comprehensive understanding of cocaine risk genetics and neurobiology.

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).

A Novel Assay Allowing Drug Self-Administration, Extinction, and Reinstatement Testing in Head-Restrained Mice

Multiphoton microscopy is one of several new technologies providing unprecedented insight into the activity dynamics and function of neural circuits. Unfortunately, some of these technologies require experimentation in head-restrained animals, limiting the behavioral repertoire that can be integrated and studied. This issue is especially evident in drug addiction research, as no laboratories have coupled multiphoton microscopy with simultaneous intravenous drug self-administration, a behavioral paradigm that has predictive validity for treatment outcomes and abuse liability. Here, we describe a new experimental assay wherein head-restrained mice will press an active lever, but not inactive lever, for intravenous delivery of heroin or cocaine. Similar to freely moving animals, we find that lever pressing is suppressed through daily extinction training and subsequently reinstated through the presentation of relapse-provoking triggers (drug-associative cues, the drug itself, and stressors). Finally, we show that head-restrained mice will show similar patterns of behavior for oral delivery of a sucrose reward, a common control used for drug self-administration experiments. Overall, these data demonstrate the feasibility of combining drug self-administration experiments with technologies that require head-restraint, such as multiphoton imaging. The assay described could be replicated by interested labs with readily available materials to aid in identifying the neural underpinnings of substance use disorder.

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.

Sex differences in cocaine-associated memory: The interplay between CB1, mGluR5, and estradiol

We know surprisingly little about the sex differences in the neurobiology of cocaine addiction, except females are more susceptible to the rewarding effects of cocaine than their male counterparts. Only a handful of recent studies have examined the neurobiology of cocaine-induced conditioned place preference (CPP) memory among female rodents. We contribute to this emerging line of research by documenting sex differences in cocaine-associated memory and illustrating the underlying signaling pathways in five experiments. Rimonabant (Rim), a cannabinoid CB₁ antagonist and inverse agonist, exerted a facilitating effect for low-dose cocaine and an impairing effect for high-dose cocaine CPP memory in male mice, as in our previous study, but not in female mice. Nor did we observe the effect exist among CB₁ knockout male mice, which indicated that the CB₁ receptors played a mediating role. We also found that the metabotropic glutamate receptor 5 (mGluR5) was located in the same signaling pathway as CB₁ in male mice. To clarify the mechanisms behind the sex differences, we used ovariectomized (OVX) female mice with estradiol benzoate (EB) replacement. In the OVX female mice, we showed that Rim-alone and EB-alone, but not Rim-and-EB-combined, facilitated the low-dose cocaine CPP memory. Moreover, 4-hydroxytamoxifen (4-OHT), an estrogen receptor (ER) antagonist, blocked Rim's and EB's facilitating effect. Finally, 2-methyl-6-(phenylethynyl)pyridine (MPEP), an mGluR5 antagonist, partially blocked EB's facilitating effect. In sum, we identified sex-specific effects of Rim on cocaine-induced CPP memory and the respective signaling pathways: mGluR5-CB₁ for male mice and ER-mGluR5-CB₁ for female mice. These findings may have merits for the development of sex-specific treatment for cocaine addiction.

Sex Differences and Exogenous Estrogen Influence Learning and Brain Responses to Prediction Errors

Animal studies show marked sex differences as well as effects of estrogen (E2) in the mesocorticolimbic dopaminergic (DA) pathways, which play a critical role in reward processing and reinforcement learning and are also implicated in drug addiction. In this computational pharmacological fMRI study, we investigate the effects of both factors, sex and estrogen, on reinforcement learning and the dopaminergic system in humans; 67 male and 64 naturally cycling female volunteers, the latter in their low-hormone phase, were randomly assigned, double-blind, to take E2 or placebo. They completed a reinforcement learning task in the MRI scanner for which we have previously shown reward prediction error (RPE)-related activity to be dopaminergic. We found RPE-related brain activity to be enhanced in women compared with men and to a greater extent when E2 levels were elevated in both sexes. However, both factors, female sex and E2, slowed adaptation to RPEs (smaller learning rate). This discrepancy of larger RPE-related activity yet smaller learning rates can be explained by organizational sex differences and activational effects of circulating E2, which both affect DA release differently to DA receptor binding capacities.

Sex, menstrual cycle, and hormonal contraceptives influences on global-local processing

The effect of sex hormones on global-local tasks has rarely been studied, offering, when done, conflicting results possibly modulated by the congruency between hierarchical stimuli, and by the attentional demands. Here, we examined the global advantage (GA) effect in men (with high testosterone levels), women in the mid-luteal phase (with high levels of estradiol and progesterone), in the ovulatory phase (with high estradiol but low progesterone levels); and in the early follicular phase and with hormonal contraceptive (HC) use (with low sex hormone levels). The level of processing (global-local), the congruency (congruent vs. incongruent), and attentional demands (divided vs. selective) were manipulated. The divided-incongruent condition was sensible to estradiol and progesterone levels and, in this condition, mid-luteal women performed more locally while men performed more globally. The selective-incongruent condition was sensible to the testosterone level and, in this condition, men were faster. The HC group showed a congruency effect in the GA reaction times (RTs) during both, divided and selective conditions. Finally, the GA RTs of the ovulatory group differed from the early follicular and mid-luteal groups only in the congruent-selective condition, but the performance was not related with sex hormone levels. This result is interpreted in relation with the brain effects of estradiol in the absence but not in the presence of progesterone. Thus, sex, menstrual cycle, HC, task difficulty and sex hormones seem to modulate performance in the global-local task. These factors represent an important source of variability in studies focused on the processing of hierarchical stimuli and allow apparently inconsistent data to be explained.

Individual differences in dopamine uptake in the dorsomedial striatum prior to cocaine exposure predict motivation for cocaine in male rats

A major theme of addiction research has focused on the neural substrates of individual differences in the risk for addiction; however, little is known about how vulnerable populations differ from those that are relatively protected. Here, we prospectively measured dopamine (DA) neurotransmission prior to cocaine exposure to predict the onset and course of cocaine use. Using in vivo voltammetry, we first generated baseline profiles of DA release and uptake in the dorsomedial striatum (DMS) and nucleus accumbens of drug-naïve male rats prior to exposing them to cocaine using conditioned place preference (CPP) or operant self-administration. We found that the innate rate of DA uptake in the DMS strongly predicted motivation for cocaine and drug-primed reinstatement, but not CPP, responding when "price" was low, or extinction. We then assessed the impact of baseline variations in DA uptake on cocaine potency in the DMS using ex vivo voltammetry in naïve rats and in rats with DA transporter (DAT) knockdown. DA uptake in the DMS of naïve rats predicted the neurochemical response to cocaine, such that rats with innately faster rates of DA uptake demonstrated higher cocaine potency at the DAT and rats with DAT knockdown displayed reduced potency compared to controls. Together, these data demonstrate that inherent variability in DA uptake in the DMS predicts the behavioral response to cocaine, potentially by altering the apparent potency of cocaine.

Sex-specific role for prefrontal cortical protein interacting with C kinase 1 in cue-induced cocaine seeking

Disruption of prefrontal glutamate receptor interacting protein (GRIP), which anchors GluA2-containing AMPA receptors (AMPARs) into the synaptic membrane, potentiates cue-induced cocaine seeking in both males and females. Protein interacting with C kinase 1 (PICK1) plays an opposing role to that of GRIP, removing AMPARs from the synapse. Consistent with our hypothesis that disruption of PICK1 in the mPFC would lead to a decrease in addiction-like behaviour, we found that conditional deletion of PICK1 in the mPFC attenuates cue-induced cocaine seeking in male mice. However, prefrontal PICK1 deletion had the opposite effect in females, leading to an increase in cue-induced reinstatement of cocaine seeking. We did not see any effects of PICK1 knockdown on sucrose taking or seeking, suggesting the sex-specific effects do not generalise to natural reinforcers. These findings suggest the role of PICK1 in the prefrontal cortex of females may not be consistent with its accepted role in males. To determine whether these sex differences were influenced by gonadal hormones, we gonadectomised a cohort of males and found that removal of circulating androgens eliminated the effect of prefrontal PICK1 knockdown. As there was no effect of gonadectomy on its own on any of the behavioural measures collected, our results suggest that androgens may be involved in compensatory downstream effects of PICK1 knockdown. Taken together, these results highlight the need for consideration of sex as a biological variable when examining mechanisms underlying all behaviours, as convergent sex differences can reveal different mechanisms where behavioural sex differences do not exist.

Activation of G protein-coupled estradiol receptor 1 in the dorsolateral striatum enhances motivation for cocaine and drug-induced reinstatement in female but not male rats

Background

Estradiol potentiates drug-taking behaviors, including motivation to self-administer cocaine and reinstatement of drug-seeking after extinction in females, but not males. The dorsolateral stratum (DLS) is a region of the brain implicated in mediating drug-seeking behaviors and, more specifically, is a target brain area to study how estradiol regulates these behaviors. The estradiol receptors α, β, and G protein-coupled estradiol receptor 1 (GPER1) are all present in the DLS. In this study, the effects of activating GPER1 in the DLS on drug-seeking are investigated.

Methods

Gonad-intact male and female rats were trained to self-administer cocaine (0.4 mg/kg/inf) on a fixed-ratio 1 schedule of reinforcement. For 4 weeks, animals underwent testing on a progressive ratio schedule of reinforcement to determine their motivation to attain cocaine. Halfway through progressive ratio testing, a selective agonist targeting GPER1 (G1) was administered intra-DLS to determine the contribution of GPER1 activation on motivation for cocaine. The effects of intra-DLS GPER1 activation on drug-induced reinstatement after extinction were subsequently determined.

Results

Activation of GPER1, via intra-DLS G1 administration, potentiated females’ motivation to self-administer cocaine. There was no effect of prior G1 treatment on extinction of cocaine-taking in females; however, G1 treatment resulted in greater drug-induced reinstatement (10 mg/kg cocaine, i.p.). There were no effects of intra-DLS GPER1 activation observed on motivation for cocaine or cocaine-induced reinstatement of responding in males.

Conclusions

These results support the conclusion that activation of GPER1 in the DLS enhances cocaine-seeking behaviors for female, but not male rats.

Escalation and reinstatement of fentanyl self-administration in male and female rats

RATIONALE

Escalation of drug intake and craving are two DSM-5 hallmark symptoms of opioid use disorder (OUD).

OBJECTIVES

This study determined if escalation of intake as modeled by long access (LgA) self-administration (SA) and craving measured by reinstatement are related.

METHODS

Adult male and female Sprague-Dawley rats were trained to self-administer fentanyl across 7 daily 1-h short access (ShA) sessions, followed by 21 SA sessions of either 1- or 6-h duration (ShA or LgA). Following 14 1-h extinction sessions, Experiment 1 assessed reinstatement induced by either fentanyl (10 or 30 µg/kg) or yohimbine (1 or 2 mg/kg), and Experiment 2 assessed reinstatement induced by a drug-associated cue light.

RESULTS

Females acquired fentanyl SA faster than males. When shifted to LgA sessions, LgA rats escalated fentanyl intake, but ShA rats did not; no reliable sex difference in the rate of escalation was observed. In extinction, compared to ShA rats, LgA rats initially responded less and showed less decay of responding across sessions. A priming injection of fentanyl induced reinstatement, with LgA rats reinstating more than ShA rats at the 30 µg/kg dose. Yohimbine (1 mg/kg) also induced reinstatement, but there was no effect of access group or sex. With cue-induced reinstatement, LgA females reinstated less than LgA males and ShA females.

CONCLUSION

Among the different reinstatement tests assessed, escalation of fentanyl SA increased only drug-primed reinstatement, suggesting a limited relationship between escalation of drug intake and craving (reinstatement) for OUD.

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.

Cocaine self-administration induces sex-dependent protein expression in the nucleus accumbens

Substance use disorder (SUD) is a chronic neuropsychiatric condition characterized by long-lasting alterations in the neural circuitry regulating reward and motivation. Substantial work has focused on characterizing the molecular substrates that underlie these persistent changes in neural function and behavior. However, this work has overwhelmingly focused on male subjects, despite mounting clinical and preclinical evidence that females demonstrate dissimilar progression to SUD and responsivity to stimulant drugs of abuse, such as cocaine. Here, we show that sex is a critical biological variable that defines drug-induced plasticity in the nucleus accumbens (NAc). Using quantitative mass spectrometry, we assessed the protein expression patterns induced by cocaine self-administration and demonstrated unique molecular profiles between males and females. We show that 1. Cocaine self-administration induces non-overlapping protein expression patterns in significantly regulated proteins in males and females and 2. Critically, cocaine-induced protein regulation differentially interacts with sex to eliminate basal sexual dimorphisms in the proteome. Finally, eliminating these baseline differences in the proteome is concomitant with the elimination of sex differences in behavior for non-drug rewards. Together, these data suggest that cocaine administration is capable of rewriting basal proteomic function and reward-associated behaviors.

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.

Repeated morphine exposure activates synaptogenesis and other neuroplasticity-related gene networks in the dorsomedial prefrontal cortex of male and female rats

BACKGROUND

Opioid abuse is a chronic disorder likely involving stable neuroplastic modifications. While a number of molecules contributing to these changes have been identified, the broader spectrum of genes and gene networks that are affected by repeated opioid administration remain understudied.

METHODS

We employed Next-Generation RNA-sequencing (RNA-seq) followed by quantitative chromatin immunoprecipitation to investigate changes in gene expression and their regulation in adult male and female rats' dorsomedial prefrontal cortex (dmPFC) after a regimen of daily injection of morphine (5.0 mg/kg; 10 days). Ingenuity Pathway Analysis (IPA) was used to analyze affected molecular pathways, gene networks, and associated regulatory factors. A complementary behavioral study evaluated the effects of the same morphine injection regimen on locomotor activity, pain sensitivity, and somatic withdrawal signs.

RESULTS

Behaviorally, repeated morphine injection induced locomotor hyperactivity and hyperalgesia in both sexes. 90 % of differentially expressed genes (DEGs) in morphine-treated rats were upregulated in both males and females, with a 35 % overlap between sexes. A substantial number of DEGs play roles in synaptic signaling and neuroplasticity. Chromatin immunoprecipitation revealed enrichment of H3 acetylation, a transcriptionally activating chromatin mark. Although broadly similar, some differences were revealed in the gene ontology networks enriched in females and males.

CONCLUSIONS

Our results cohere with findings from previous studies based on a priori gene selection. Our results also reveal novel genes and molecular pathways that are upregulated by repeated morphine exposure, with some common to males and females and others that are sex-specific.