Sex and ovarian hormones influence vulnerability and motivation for nicotine during adolescence in rats

Impact of SMAASH-C, a novel nutritional supplement, on drug-seeking and toxicity in female and male rats

Relapse to drug use after abstinence is a major challenge in treating substance use disorder. Exposure to drug-associated cues during abstinence can trigger intense craving and precipitate relapse. New and more effective anti-relapse interventions are critically needed, particularly for cocaine use disorder since no effective pharmacological intervention is available. We discovered that a nutritional supplement we developed as part of a nutritional approach for managing patients with substance use disorder reduced patient reports of drug craving and relapse. The goal of this study was to determine the efficacy of this supplement, SMAASH-C, at reducing drug-craving/relapse vulnerability in males and females in rat models with cocaine. Effects were determined following extended-access cocaine self-administration (24-hr/day for 10 days) and a two-week treatment regimen at a moderate and moderate-to-high dose (0.4 and 0.8 g/kg/day) as well as a 6-week regimen at a moderate dose (0.4 g/kg/day; Experiment 2). We also determined its efficacy to offset serum markers of organ toxicity in response to chronic cocaine self-administration and abstinence (aspartate transaminase, alanine transaminase, amylase; urea nitrogen). In females, both the 2- and 6-week SMAASH-C treatment regimens reduced cocaine-seeking (extinction or cue-induced reinstatement), particularly when drug-seeking was heightened (e.g., during estrus). Despite a lack of efficacy to reduce drug-seeking in males, SMAASH-C treatment normalized cocaine/abstinence-induced increases in serum levels of aspartate transaminase and amylase, which are markers of liver and pancreatic toxicity respectively. Thus, the beneficial effects of oral SMAASH-C treatment over abstinence following chronic cocaine self-administration appears to be sex-specific.

Hyperactivity Induced By Vapor Inhalation of Nicotine in Male and Female Rats

Rationale

Preclinical models of electronic nicotine delivery system (ENDS; "e-cigarette") use have been rare, so there is an urgent need to develop experimental approaches to evaluate their effects.

Objective

To contrast the impact of inhaled nicotine across sex.

Methods

Male and female Wistar rats were exposed to vapor from a propylene glycol vehicle (PG), nicotine (NIC; 1-30 mg/mL in PG), or were injected with NIC (0.1-0.8 mg/kg, s.c.), and then assessed for changes in temperature and activity. The antagonist mecamylamine (2 mg/kg) was administered prior to NIC to verify pharmacological specificity. Plasma levels of nicotine and cotinine were determined after inhalation and injection.

Results

Activity increased in females for ~60 minutes after nicotine inhalation, and this was blocked by mecamylamine. A similar magnitude of hyperlocomotion was observed after s.c. administration. Body temperature was reduced after nicotine inhalation by female rats but mecamylamine increased this hypothermia. Increased locomotor activity was observed in male rats if inhalation was extended to 40 minutes or when multiple inhalation epochs were used per session. The temperature of male rats was not altered by nicotine. Plasma nicotine concentrations were slightly lower in male rats than in female rats after 30-minute nicotine vapor inhalation and slightly higher after nicotine injection (1.0 mg/kg, s.c.).

Conclusions

Nicotine inhalation increases locomotor activity in male and female rats to a similar or greater extent than by subcutaneous injection. Sex differences were observed, which may be related to lower nicotine plasma levels, lower baseline activity and/or a higher vehicle response in males.

Nanoassemblies from the aqueous extract of roasted coffee beans modulate the behavioral and molecular effects of smoking withdrawal-induced anxiety in female rats

Antioxidant-rich plant extracts have demonstrated tremendous value as inflammatory modulators and as nanomaterial precursors. Chronic cigarette smoking alters neurotransmitter systems, particularly the glutamatergic system, and produces neuroinflammation. This study aimed to investigate the behavioral and molecular correlates of cigarette smoking withdrawal-induced anxiety-like behavior in rats, and whether these effects could be mitigated by the administration of antioxidant nanoassemblies prepared by spontaneous oxidation of dark-roasted Arabica coffee bean aqueous extracts. Four experimental groups of female Sprague-Dawley rats were randomly assigned to: (i) a control group that was only exposed to room air, (ii) a COF group that was administered 20 mg/kg of the coffee nanoassemblies by oral gavage, (iii) a SMOK group that was exposed to cigarette smoke and was given an oral gavage of distilled water, (iv) and a SMOK + COF group that was exposed to cigarette smoke and administered 20 mg/kg of the coffee nanoassemblies. Animals were exposed to cigarette smoke for 2 h per day, five days per week, with a 2-day withdrawal period each week. At the end of the 4th week, rats began receiving either distilled water or the coffee nanoassemblies before being exposed to cigarette smoke for 21 additional days. Weekly behavioral tests revealed that cigarette smoking withdrawal exacerbated anxiety, while the administration of the coffee nanoassemblies reduced this effect. The effect of cigarette smoking on astroglial glutamate transporters and nuclear factor kappa B (NF-κB) expression in brain subregions was also measured. Smoking reduced the relative mRNA and protein levels of the glutamate transporter 1 (GLT-1) and the cystine/glutamate antiporter (xCT), and increased the levels of NF-κB, but these effects were attenuated by the coffee nanoassemblies. Thus, administration of the antioxidant nanoassemblies decreased the negative effects of cigarette smoke, which included neuroinflammation, changes in glutamate transporters' expression, and a rise in anxiety-like behavior.

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.

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.

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/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.

Acetylsalicylic acid reduces cigarette smoke withdrawal-induced anxiety in rats via modulating the expression of NFĸB, GLT-1, and xCT

Background: Chronic exposure to cigarette smoke produces neuroinflammation and long-term changes in neurotransmitter systems, especially glutamatergic systems. Objective: We examined the effects of cigarette smoke on astroglial glutamate transporters as well as NF-κB expression in mesocorticolimbic brain regions, prefrontal cortex (PFC) and nucleus accumbens (NAc). The behavioral consequences of cigarette smoke exposure were assessed using open field (OF) and light/dark (LD) tests to assess withdrawal-induced anxiety-like behavior. Methods: Sprague-Dawley rats were randomly assigned to five experimental groups: a control group exposed only to standard room air, a cigarette smoke exposed group treated with saline vehicle, two cigarette smoke exposed groups treated with acetylsalicylic acid (ASA) (15 mg/kg and 30 mg/kg, respectively), and a group treated only with ASA (30 mg/kg). Cigarette smoke exposure was performed for 2 h/day, 5 days/week, for 31 days. Behavioral tests were conducted weekly, 24 h after cigarette smoke exposure, during acute withdrawal. At the end of week 4, rats were given either saline or ASA 45 min before cigarette exposure for 11 days. Results: Cigarette smoke increased withdrawal-induced anxiety, and 30 mg/kg ASA attenuated this effect. Cigarette smoke exposure increased the relative mRNA and protein expression of nuclear factor ĸB (NFĸB) in PFC and NAc, and ASA treatment reversed this effect. Also, cigarette smoke decreased the relative mRNA and protein expression of glutamate transporter1 (GLT-1) and the cystine-glutamate transporter (xCT) in the PFC and the NAc, while ASA treatment normalized their expression. Conclusion: Cigarette smoke caused neuroinflammation, alterations in glutamate transporter expression, and increased anxiety-like behavior, and these effects were attenuated by acetylsalicylic acid treatment.

Impact of the natural hormonal milieu on ventral striatal responses to appetitive cigarette smoking cues: A prospective longitudinal study

Background

The female sex hormones estradiol (E) and progesterone (P) galvanize the ventral striatal reward pathway. E elevates ventral striatal dopamine and accelerates drug-cued reinstatement, while P has opposing 'protective' effects on drug-related behavior. We hypothesize that women may exhibit greater ventral striatal responses to smoking cues (SCs) during the late follicular phase of the menstrual cycle (MC) when E is high and unimpeded by P, and reduced responses during the late luteal phase when P is high.

Methods

To test our hypothesis, 24 naturally cycling cigarette-dependent women completed functional magnetic resonance (fMRI) sessions over the course of 3 MCs at select time points to reflect the early follicular (low E and P; LEP, control condition), late follicular (high E, low P; HE) and mid-luteal (high E, high P; HEP) MC phases. During fMRI sessions (counterbalanced by phase), women were exposed to a SC versus nonSC audio-visual clip. Ovulation was verified for each MC, and hormone levels were acquired prior to sessions.

Results

Contrasts within conditions showed that ventral striatal brain responses to SCs versus nonSCs were negligible during LEP and greater during HE (p=0.009) and HP (p=0.016). Contrasts across conditions showed that HE and HEP had greater responses than LEP (p=0.005), and HE had greater responses than HEP (p=0.049).

Conclusions

Results support and extend our retrospective cross-sectional study of the influence of the hormonal milieu on SC reactivity. Results are clinically relevant as they may guide novel, hormonally-informed and immediately translatable treatment strategies that can potentially reduce relapse in naturally cycling women.

Relapse to cotinine seeking in rats: differential effects of sex

Relapse is a defining feature of smoking and a significant challenge in cessation management. Elucidation of novel factors underlying relapse may inform future treatments. Cotinine, the major metabolite of nicotine, has been shown to support intravenous self-administration in rats, implicating it as one potential factor contributing to nicotine reinforcement. However, it remains unknown whether cotinine would induce relapse-like behaviors. The current study investigated relapse to cotinine seeking in two relapse models, the reinstatement of drug seeking and incubation of drug craving models. In the reinstatement model, rats were trained to self-administer cotinine, underwent extinction of cotinine-associated responses, and were tested for cue-, drug-, or stress-induced reinstatement. Conditioned cues associated with cotinine self-administration, cotinine (1-2 mg/kg), or the pharmacological stressor yohimbine (1.25-2.5 mg/kg) induced reinstatement of cotinine seeking. Female rats displayed more pronounced cue-induced, but not drug- or stress-induced reinstatement than male rats. In the incubation of the craving model, rats were trained to self-administer cotinine and underwent forced withdrawal in home cages. Rats were tested for cue-induced cotinine-seeking on both withdrawal day 1 and withdrawal day 18. Rats exhibited greater cue-induced cotinine-seeking on withdrawal day 18 compared to withdrawal day 1, with no difference between male and female rats. These findings indicate that cotinine induces sex-specific relapse to drug seeking in rats, suggesting that cotinine may contribute to relapse.

Dopamine D1-like receptor blockade and stimulation decreases operant responding for nicotine and food in male and female rats

Dopamine has been implicated in the reinforcing effects of smoking. However, there remains a need for a better understanding of the effects of dopamine D1-like receptor agonists on nicotine intake and the role of sex differences in the effects of dopaminergic drugs on behavior. This work studied the effects of D1-like receptor stimulation and blockade on operant responding for nicotine and food and locomotor activity in male and female rats. The effects of the D1-like receptor antagonist SCH 23390 (0.003, 0.01, 0.03 mg/kg) and the D1-like receptor agonist A77636 (0.1, 0.3, 1 mg/kg) on responding for nicotine and food, and locomotor activity were investigated. The effects of SCH 23390 were investigated 15 min and 24 h after treatment, and the effects of the long-acting drug A77636 were investigated 15 min, 24 h, and 48 h after treatment. Operant responding for nicotine and food and locomotor activity were decreased immediately after treatment with SCH 23390. Treatment with SCH 23390 did not have any long-term effects. Operant responding for nicotine was still decreased 48 h after treatment with A77636, and food responding was decreased up to 24 h after treatment. Treatment with A77636 only decreased locomotor activity at the 48 h time point. There were no sex differences in the effects of SCH 23390 or A77636. In conclusion, the D1-like receptor antagonist SCH 23390 reduces nicotine intake and causes sedation in rats. Stimulation of D1-like receptors with A77636 decreases nicotine intake at time points that the drug does not cause sedation.

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.

Unique effects of nicotine across the lifespan

Smoking remains the leading cause of preventable death in the United States. Although combustible cigarettes are largely being replaced by tobacco-free products, nicotine use continues to increase in vulnerable populations, including youth, adolescents, and pregnant women. Nicotine exerts unique effects on specific brain regions during distinct developmental periods due to the dynamic expression of nicotinic acetylcholine receptors (nAChRs) throughout the lifespan. Nicotine exposure is a health concern not only for adults but also has neurotoxic effects on the fetus, newborn, child, and adolescent. In this review, we aim to highlight the dynamic roles of nAChRs throughout gestation, adolescence, and adulthood. We also provide clinical and preclinical evidence of the neurodevelopmental, cognitive, and behavioral consequences of nicotine exposure at different developmental periods. This comprehensive review highlights unique effects of nicotine throughout the lifespan to help elucidate interventions and public health measures to protect sensitive populations from nicotine exposure.

Gender differences in the associations between tobacco smoke exposure and depressive symptoms among U.S. adults: NHANES 2007-2018

BACKGROUND

Findings concerning gender differences in the associations between tobacco smoke exposure (TSE) and depression are inconsistent. This study aimed to investigate the gender-specific associations between active and passive TSE with depressive symptoms in a large, nationally representative sample of U.S. adults.

METHODS

Data were from 27,175 adults aged ≥20 years in the 2007-2018 National Health and Nutrition Examination Survey (NHANES). Depressive symptoms were assessed using the Patient Health Questionnaire-9 (PHQ-9). Multivariable logistic regression was used to adjust for possible confounders. Whether the TSE-depression relationships may differ by age, race/ethnicity, socioeconomic status, body mass index (BMI), and self-reported health status was examined.

RESULTS

After adjustment for lifestyle- and health-related variables, no significant associations between active (OR, 1.16 [95% CI, 0.87-1.55]) and passive TSE (OR, 0.84 [95% CI, 0.59-1.19]) and depressive symptoms were found among men. Among women, active TSE was associated with depressive symptoms (OR, 1.90 [95% CI, 1.51-2.39]), while the association for passive TSE was nonsignificant (OR, 1.11 [95% CI, 0.91-1.34]) after adjusting for lifestyle- and health-related variables. Interaction and subgroup analyses showed that self-reported health status could modify the relationship between passive TSE and depressive symptoms among women. Furthermore, a dose-response relationship between serum cotinine and depressive symptoms was found in women, but not in men.

CONCLUSIONS

This study suggests a stronger TSE-depression association in women than in men. Understanding these gender-specific patterns and identifying the potential moderators of such relationships will enable better targeting of public health interventions.

Sex- and genotype-dependent nicotine plus cue-primed reinstatement is enhanced in adolescent Sprague Dawley rats containing the human CHRNA6 3'-UTR polymorphism (rs2304297)

RATIONALE

Large-scale human candidate gene studies have indicated that a genetic variant (rs2304297) in the alpha(α)6 nicotinic acetylcholine receptor (nAChR) subunit, encoded by the CHRNA6 gene, may play a key role in adolescent nicotine addictive behavior. We hypothesized that the polymorphism selectively enhances nicotine + cue-primed reinstatement, but not nicotine- or cue-reinstatement in α6 ^GG (risk) vs. α6 ^CC (non-risk) allele carriers, without having baseline effects on natural rewards.

METHODS

Using CRISPR-Cas9 genomic engineering, we developed a humanized rat line with the human gene variant of the CHRNA6 3'-UTR ^{C 123 G} polymorphism in Sprague-Dawley rats. Genetically modified adolescent male and female rats were food trained under a fixed-ratio (FR)1 schedule of reinforcement and progressively increased to FR5. Animals were implanted with catheters and began nicotine self-administration (15 μg/kg/infusion) at FR5. Upon reaching stable responding, reinforced behavior was extinguished by removal of drug and cues. Reinstatement testing began for cue only, nicotine only, and nicotine + cue in a Latin Square Design. Animals were returned to extinction conditions for 2 days minimum between testing.

RESULTS

For natural food rewards, nicotine self-administration, progressive ratio, and extinction, adolescent male and female (α6 ^GG and α6 ^CC ) rats exhibited equivalent behaviors. Male α6 ^GG rats show enhanced nicotine + cue-primed reinstatement when compared with male α6 ^CC rats. This genotype effect on reinstatement was not seen in female rats.

CONCLUSION

Our findings support the in vivo functional role of the human CHRNA6 3'-UTR SNP genetic variant in sex-dependently enhancing nicotine seeking behavior in adolescent rats. Overall, the findings support clinical and preclinical data highlighting a role of α6 nAChRs mediating sex heterogeneity in substance use and related phenotypes.

Aerobic exercise as a promising nonpharmacological therapy for the treatment of substance use disorders

Despite the prevalence and public health impact of substance use disorders (SUDs), effective long-term treatments remain elusive. Aerobic exercise is a promising, nonpharmacological treatment currently under investigation as a strategy for preventing drug relapse. Aerobic exercise could be incorporated into the comprehensive treatment regimens for people with substance abuse disorders. Preclinical studies of SUD with animal models have shown that aerobic exercise diminishes drug-seeking behavior, which leads to relapse, in both male and female rats. Nevertheless, little is known regarding the effects of substance abuse-induced cellular and physiological adaptations believed to be responsible for drug-seeking behavior. Accordingly, the overall goal of this review is to provide a summary and an assessment of findings to date, highlighting evidence of the molecular and neurological effects of exercise on adaptations associated with SUD.

Self-administration by female rats of low doses of nicotine alone vs. nicotine in tobacco smoke extract

BACKGROUND

Nicotine has reinforcing effects, but there are thousands of other compounds in tobacco, some of which might interact with nicotine reinforcement.

AIMS

This rat study was conducted to determine if nicotine self-administration is altered by co-administration of the complex mixture of compounds in tobacco smoke extract (TSE).

METHODS

Female Sprague-Dawley rats were tested for self-administration of low doses of nicotine (3 or 10 µg/kg/infusion) at three different rates of reinforcement (FR1, FR3 and FR5) over three weeks either alone or together with the complex mixture of tobacco smoke extract (TSE).

RESULTS

Rats self-administering 3 µg/kg/infusion of nicotine alone showed a rapid initiation on an FR1 schedule, but declined with FR5. Rats self-administering nicotine in TSE acquired self-administration more slowly, but increased responding over the course of the study. With 10 µg/kg/infusion rats self-administered significantly more nicotine alone than rats self-administering the same nicotine dose in TSE. Rats self-administering nicotine alone took significantly more infusions with the 10 than the 3 µg/kg/infusion dose, whereas rats self-administering nicotine in TSE did not. Nicotine in TSE led to a significantly greater locomotor hyperactivity at a dose of 0.1 mg/kg compared to rats that received nicotine alone. Rats self-administering nicotine alone had significantly more responding on the active vs. inactive lever, but rats self-administering the same nicotine doses in TSE did not.

CONCLUSIONS

Self-administration of nicotine in a purer form appears to be more clearly discriminated and dose-related than nicotine self-administered in the complex mixture of TSE.

Sex Differences in the Nicotinic Acetylcholine Receptor System of Rodents: Impacts on Nicotine and Alcohol Reward Behaviors

Alcohol and nicotine are the two most widely used and misused drugs around the world, and co-consumption of both substances is highly prevalent. Multiple lines of evidence show a profound effect of sex in many aspects of alcohol and nicotine reward, with women having more difficulty quitting smoking and showing a faster progression toward developing alcohol use disorder compared with men. Both alcohol and nicotine require neuronal nicotinic acetylcholine receptors (nAChRs) to elicit rewarding effects within the mesolimbic system, representing a shared molecular pathway that likely contributes to the frequent comorbidity of alcohol and nicotine dependence. However, the majority of preclinical studies on the mechanisms of alcohol and nicotine reward behaviors utilize only male rodents, and thus our understanding of alcohol and nicotine neuropharmacology relies heavily on male data. As preclinical research informs the development and refinement of therapies to help patients reduce drug consumption, it is critical to understand the way biological sex and sex hormones influence the rewarding properties of alcohol and nicotine. In this review, we summarize what is known about sex differences in rodent models of alcohol and nicotine reward behaviors with a focus on neuronal nAChRs, highlighting exciting areas for future research. Additionally, we discuss the way circulating sex hormones may interact with neuronal nAChRs to influence reward-related behavior.

Strain and sex matters: Differences in nicotine self-administration between outbred and recombinase-driver transgenic rat lines

Preclinical studies of nicotine self-administration provide important value for the field as they are highly rigorous, controlled, can be conducted quickly, and are generalizable to humans. Given the translational value of the nicotine self-administration model, and the relatively new guidelines of the National Institutes of Health to include sex as a biological variable, strain and sex differences in nicotine acquisition were examined here in two outbred rat strains. Sprague-Dawley (SD) and Long-Evans (LE; wildtype and cholinergic acetyltransferase cre-recombinase transgenic) rats of each sex were implanted with indwelling intravenous jugular catheters. Rats were trained to self-administer nicotine (0.02 mg/kg per infusion, paired with contingent light + tone stimuli). Acquisition criteria were set at a minimum active:inactive response ratio of 2:1 and a minimum of 10 infusions per session, both of which had to be met for a minimum of 10 sessions. Across 10 sessions, male SD rats self-administered significantly more nicotine than female SD rats (p < .05), indicating a sex difference in this strain. LE females self-administered more nicotine than SD females indicative of a strain difference between females (p < .05). SD males increased nicotine infusions across sessions compared to LE males and SD females (p < .05). No strain or sex differences were observed in the number of sessions to reach criteria. No differences between wildtype and transgenic LE rats were observed. These results demonstrate sex and strain differences in nicotine self-administration between SD and LE rats and may lend insight into development of other nicotine self-administration models, where sex and strain may impact acquisition. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Influence of the natural hormonal milieu on brain and behavior in women who smoke cigarettes: Rationale and methodology

Women experience more severe health consequences from smoking, have greater difficulty quitting, and respond less favorably to nicotine replacement therapy than men. The influence of fluctuating ovarian hormones, specifically estradiol (E) and progesterone (P), on brain and behavioral responses during exposure to smoking reminders (i.e., cues) may be a contributing factor. Results from our laboratory suggest that women in the late follicular phase of their menstrual cycle (MC) have enhanced smoking cue (SC) vulnerabilities and reduced functional connectivity in neurocircuitry underlying cognitive control, potentially placing them at greater risk for continued smoking and relapse. The primary aim of this study is to examine and link hormonal status with brain and behavioral responses to SCs over the course of three monthly MCs in naturally cycling women who are chronic cigarette smokers. This longitudinal, counterbalanced study collects brain and behavioral responses to SCs at three time points during a woman's MC. Participants complete psychological and physical examinations, biochemical hormonal verification visits, and at least three laboratory/neuroimaging scan visits. The scan visits include a 10-min SC task during blood oxygen level-dependent (BOLD) data acquisition and are timed to occur during the early follicular phase (low E and P), late follicular phase (high E, unopposed by P), and mid-luteal phase (high P, high E). The primary outcomes include brain responses to SCs (compared to non-SCs), subjective craving, E and P hormone levels, and behavioral responses to SCs. This study addresses a critical gap in our knowledge: namely, the impact of the natural hormonal milieu on brain and behavioral responses to SCs, a powerful relapse trigger. Additionally, this study will provide a roadmap for human sex differences researchers who are obliged to consider the often confounding cyclic hormonal fluctuations of women.

Increases in endogenous progesterone attenuate smoking in a cohort of nontreatment seeking women: An exploratory prospective study

Despite advances in prevention and treatment, cigarette smoking remains a leading cause of preventable death in the United States. Although men and women are equally likely to attempt to quit smoking cigarettes, women are far less likely to achieve abstinence both during and following cessation treatment. Recent evidence suggests that ovarian hormone levels may play a role in successful abstinence attempts in women smokers. The primary goal of this exploratory prospective observational study was to estimate the association between within-participant levels of progesterone and estradiol with associated cigarettes smoked per day in adult women smokers (n = 104). The primary study outcome was self-reported cigarettes smoked per day (CPD) during a 2-week observational period collected using a daily smoking diary. Additionally, participants collected saliva daily, from which hormone levels (progesterone and estradiol) were derived. Higher within-participant progesterone levels were associated with a significant decrease in CPD (p = .008) whereas within-participant estradiol levels were unrelated to CPD (p = .25). Regression models indicated a single change in the trajectory of smoking behavior for both within-participant progesterone and estradiol. When progesterone values were below the change point, there was a significant inverse relationship between within-participant progesterone levels and smoking behavior (p = .025) whereas the relationship was attenuated for higher within-participant progesterone levels (p = .59). The effect of estradiol on smoking behavior was not significant when it was either below (p = .92) or above (p = .16) the change point. Higher within-participant levels of progesterone but not estradiol are associated with reduced CPD in nontreatment seeking women smokers.

Nicotine sensitization (part 1): estradiol or tamoxifen is required during the induction phase and not the expression phase to enable locomotor sensitization to nicotine in female rats

RATIONALE

Nicotine sensitization involves two functionally distinct phases: induction and expression. Estradiol enhances nicotine sensitization in female rats, but it is not known whether this enhancement is specific to one or both phases.

OBJECTIVES

We investigated the effects of estradiol selectively during the induction and the expression of nicotine sensitization.

METHODS

Ovariectomy (OVX) rats were administered E2 during the induction (2 injection days) and/or the expression phase (9 days later) of nicotine sensitization. The selective estrogen receptor modulator tamoxifen (agonist of ERα and ERß, agonist of the g-coupled estradiol receptor GPER1) also was used to elucidate receptor candidates for the effects of E2 on nicotine sensitization.

RESULTS

Gonadally intact female rats exhibited expression of nicotine sensitization after a 9-day delay, whereas OVX females did not. Administration of E2 limited to the induction phase of nicotine sensitization rescued expression of nicotine sensitization in OVX females. Tamoxifen during induction did not alter expression of sensitization in gonadally intact female rats, and, like E2, was sufficient to reverse the dampening effects of OVX on expression of sensitization.

CONCLUSIONS

The enhancing effects of E2 on nicotine sensitization occur during the induction phase of nicotine sensitization, although require a delay to produce the effects on locomotor activity to nicotine, and may involve non-canonical estrogen pathways (e.g., activation of GPER1).

Nicotine sensitization (Part 2): Time spent in the centre of an open field sensitizes to repeated nicotine into the drug-free state in female rats

RATIONALE

Nicotine is initially anxiogenic and becomes anxiolytic after prolonged exposure. The mechanisms that facilitate the shift in anxiety-like behaviour produced by nicotine are unclear.

OBJECTIVE

We investigated the change in time spent in the centre of an open field (as a measure anxiety-like behaviour) produced by three intermittent injections of nicotine as part of experiments of locomotor sensitization to nicotine.

METHODS

Rats were injected with nicotine (0.4 mg/kg) or saline and immediately placed in the open field arena for 1 h on two consecutive days and again 9 days later.

RESULTS

When given saline, time spent in the centre of the arena did not change, whereas repeated nicotine injections increased in time spent in the centre beyond the increase produced by an acute injection of nicotine. Repeated nicotine (and not acute nicotine) also increased time in the centre in a drug-free state when tested 24 h after the last injection.

CONCLUSION

Repeated nicotine sensitized the time spent in the centre of an open field with the long-lasting sensitization of this measure of anxiety-like behaviour evident in a drug-free state, in contrast to locomotor sensitization which does not persist in the drug-free state. The results suggest independence of the mechanisms of sensitization that underlie locomotor and anxiolytic effects.

The reinforcement threshold and elasticity of demand for nicotine in an adolescent rat model of depression

BACKGROUND

The Food and Drug Administration (FDA) is considering setting a nicotine standard for tobacco products to reduce their addictiveness. Such a standard should account for the apparent greater vulnerability to nicotine addiction in some subpopulations, such as adolescents with depression. The present study examined whether the reinforcement threshold and elasticity of demand (i.e., reinforcing efficacy) for nicotine in a genetic inbred rat model of depression (Flinders Sensitive Line [FSL]) differs from an outbred control strain.

METHODS

Acquisition of nicotine self-administration (NSA) across a wide range of nicotine doses was measured in both FSL and Sprague-Dawley (SD) control adolescent rats. At the highest dose, elasticity of demand was also measured. Nicotine pharmacokinetics was examined to determine whether it might modulate NSA, as it does smoking in humans.

RESULTS

FSL rats acquired self-administration quicker and showed more inelastic demand (greater reinforcing efficacy) than SDs at the highest unit dose. However, there was no strain difference in the reinforcement threshold of nicotine. FSL rats exhibited faster nicotine clearance, larger volume of distribution, and lower plasma and brain nicotine concentrations. However, these differences were not consistently related to strain differences in NSA measures.

CONCLUSION

These findings are consistent with studies showing greater dependence and reinforcing efficacy of cigarettes in smokers with depression and those with relatively fast nicotine metabolism. However, these findings also suggest that a nicotine standard to reduce initiation of tobacco use should be similarly effective in both the general adolescent population and those with depression.

A buprenorphine-validated rat model of opioid use disorder optimized to study sex differences in vulnerability to relapse

RATIONALE

Opioid use disorder (OUD) is a major epidemic in the USA. Despite evidence indicating that OUD may be particularly severe for women, preclinical models have yet to establish sex as a major factor in OUD.

OBJECTIVES

Here, we examined sex differences in vulnerability to relapse following intermittent access fentanyl self-administration and protracted abstinence and used buprenorphine, the FDA-approved treatment for OUD, to test the validity of our model.

METHODS

Following acquisition of fentanyl self-administration under one of two training conditions, male and female rats were given extended, 24-h/day access to fentanyl (0.25 μg/kg/infusion, 10 days) using an intermittent access procedure. Vulnerability to relapse was assessed using an extinction/cue-induced reinstatement procedure following 14 days of abstinence; buprenorphine (0 or 3 mg/kg/day) was administered throughout abstinence.

RESULTS

Levels of drug-seeking were high following extended-access fentanyl self-administration and abstinence; buprenorphine markedly decreased drug-seeking supporting the validity of our relapse model. Females self-administered more fentanyl and responded at higher levels during subsequent extinction testing. Buprenorphine was effective in both sexes and eliminated sex and estrous phase differences in drug-seeking. Interestingly, the inclusion of a time-out during training had a major impact on later fentanyl self-administration in females, but not males, indicating that the initial exposure conditions can persistently impact vulnerability in females.

CONCLUSIONS

These findings demonstrate the utility of this rat model for determining sex and hormonal influences on the development and treatment of OUD.

Self-Administration of Cotinine in Wistar Rats: Comparisons to Nicotine

Nicotine is the major addictive component in tobacco. Cotinine is the major metabolite of nicotine and a weak agonist for nicotinic acetylcholine receptors (nAChRs). Nicotine supports self-administration in rodents. However, it remains undetermined whether cotinine can be self-administered. This study aimed to characterize cotinine self-administration in rats, to compare effects of cotinine to those of nicotine, and to determine potential involvement of nAChRs in cotinine's effects. Adult Wistar rats were trained to self-administer cotinine or nicotine (0.0075, 0.015, 0.03, or 0.06 mg/kg per infusion) under fixed-ratio (FR) and progressive-ratio (PR) schedules. Blood nicotine and cotinine levels were determined after the last FR session. Effects of mecamylamine, a nonselective nAChR antagonist, and varenicline, a partial agonist for α4β2* nAChRs, on cotinine and nicotine self-administration were determined. Rats readily acquired cotinine self-administration, responded more on active lever, and increased motivation to self-administer cotinine when the reinforcement requirement increased. Blood cotinine levels ranged from 77 to 792 ng/ml. Nicotine induced more infusions at lower doses during FR schedules and greater breakpoints at higher doses during the PR schedule than cotinine. There was no difference in cotinine self-administration between male and female rats. Mecamylamine and varenicline attenuated nicotine but not cotinine self-administration. These results indicate that cotinine was self-administered by rats. These effects of cotinine were less robust than nicotine and exhibited no sex difference. nAChRs appeared to be differentially involved in self-administration of nicotine and cotinine. These results suggest cotinine may play a role in the development of nicotine use and misuse. SIGNIFICANCE STATEMENT: Nicotine addiction is a serious public health problem. Cotinine is the major metabolite of nicotine, but its involvement in nicotine reinforcement remains elusive. Our findings indicate that cotinine, at doses producing clinically relevant blood cotinine levels, supported intravenous self-administration in rats. Cotinine self-administration was less robust than nicotine. Mecamylamine and varenicline attenuated nicotine but not cotinine self-administration. These results suggest cotinine may play a role in the development of nicotine use and misuse.

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.

Sex chromosome complement influences vulnerability to cocaine in mice

Women acquire cocaine habits faster and are more motivated to obtain drug than men. In general, female rodents acquire intravenous cocaine self-administration (SA) faster and show greater locomotor responses to cocaine than males. Sex differences are attributed to differences in circulating estradiol. We used the four core genotype (FCG) mouse to ask whether sex chromosome complement influences vulnerability to cocaine's reinforcing and/or locomotor-activating effects. The FCG cross produces ovary-bearing mice with XX or XY genotypes (XXF, XYF) and testes-bearing mice with XX or XY genotypes (XXM, XYM). A greater percentage of gonadal females acquired cocaine SA via infusions into jugular catheters as compared with XYM mice, but XXM mice were not significantly different than any other group. Discrimination of the active versus inactive nose poke holes and cocaine intake were in general greater in gonadal females than in gonadal males. Progressive ratio tests for motivation revealed an interaction between sex chromosomes and gonads: XYM mice were more motivated to self-administer cocaine taking more infusions than mice in any other group. Locomotor responses to cocaine exposure revealed effects of sex chromosomes. After acute exposure, activity was greater in XX than in XY mice and the reverse was true for behavioral sensitization. Mice with XY genotypes displayed more activity than XX mice when given cocaine after a 10-day drug-free period. Our data demonstrate that sex chromosome complement alone and/or interacting with gonadal status can modify cocaine's reinforcing and locomotor-activating effects. These data should inform current studies of sex differences in drug use.

Role of Brain Derived Extracellular Vesicles in Decoding Sex Differences Associated with Nicotine Self-Administration

Smoking remains a significant health and economic concern in the United States. Furthermore, the emerging pattern of nicotine intake between sexes further adds a layer of complexity. Nicotine is a potent psychostimulant with a high addiction liability that can significantly alter brain function. However, the neurobiological mechanisms underlying nicotine’s impact on brain function and behavior remain unclear. Elucidation of these mechanisms is of high clinical importance and may lead to improved therapeutics for smoking cessation. To fill in this critical knowledge gap, our current study focused on identifying sex-specific brain-derived extracellular vesicles (BDEV) signatures in male and female rats post nicotine self-administration. Extracellular vesicles (EVs) are comprised of phospholipid nanovesicles such as apoptotic bodies, microvesicles (MVs), and exosomes based on their origin or size. EVs are garnering significant attention as molecules involved in cell–cell communication and thus regulating the pathophysiology of several diseases. Interestingly, females post nicotine self-administration, showed larger BDEV sizes, along with impaired EV biogenesis compared to males. Next, using quantitative mass spectrometry-based proteomics, we identified BDEV signatures, including distinct molecular pathways, impacted between males and females. In summary, this study has identified sex-specific changes in BDEV biogenesis, protein cargo signatures, and molecular pathways associated with long-term nicotine self-administration.

Pre-conception exposure to THC fails to impact nicotine reward in adult offspring

Exposure to environmental stimuli in one generation can produce altered behavioral and neurobiological phenotypes in descendants. Recent work has shown that parental exposure to cannabinoids alters the rewarding properties of other abused drugs in the subsequent generation. However, whether preconception Δ⁹-tetrahydrocannabinol (THC) administration modifies the affective properties of nicotine in offspring is unknown. To address this question, male and female rats (F0) received THC (0 or 1.5 mg/kg) throughout the adolescent window and were bred on PND 65. In Experiment 1, adult F1-THC and F1-Veh progeny (males and females) underwent nicotine locomotor sensitization procedures during which nicotine (0 or 0.4 mg/kg) was administered every other day for five exposures, and locomotor activity was recorded on each exposure followed by a final nicotine challenge. There was no cross-generational effect of THC on nicotine locomotor sensitization, although acute exposure to nicotine produced greater activity in females relative to males independent of THC history. In Experiment 2, adult F1-THC and F1-Veh progeny (males and females) were implanted with jugular catheters and trained to self-administer nicotine (0.03 mg/kg/infusion). Following acquisition, all subjects were allowed to self-administer nicotine on a number of reinforcement schedules, e.g., FR2, FR5 and PR, followed by dose response and extinction procedures. Across all indices, F1-THC and F1-Veh subjects displayed similar IVSA of nicotine with no sex differences. The fact that there was no evidence of cross-generational effects of THC on nicotine suggests that such effects are drug-specific.

Adolescent nicotine and tobacco smoke exposure enhances nicotine self-administration in female rats

Most people start experimenting with tobacco products or e-cigarettes in early adolescence and become habitual smokers in late adolescence or adulthood. These studies investigated if exposure to tobacco smoke or nicotine during early and mid-adolescence affects nicotine intake in late adolescence and early adulthood. Male and female rats were exposed to tobacco smoke from low- and high-nicotine SPECTRUM cigarettes or nicotine (0.3 mg/kg, twice a day) from postnatal day (P) 24-42. The self-administration sessions started at P55. The rats self-administered nicotine for 14-15 days under a fixed-ratio 1 schedule, and on the first day, the maximum number of infusions was twenty. Exposure to smoke from high, but not low, nicotine cigarettes during adolescence increased nicotine self-administration in female but not male rats. Adolescent treatment with nicotine facilitated nicotine self-administration. On the first day of nicotine self-administration, nicotine-treated rats reached the maximum number of infusions before the saline-treated control rats. Nicotine intake was also higher in the nicotine-treated female rats than in the saline-treated females. There was no sex difference in nicotine intake in controls when the data from the studies were combined. Smoke exposure led to a dose-dependent increase in plasma nicotine and cotinine levels in adolescent rats. Exposure to smoke from high-nicotine cigarettes and 0.3 mg/kg of nicotine led to plasma nicotine and cotinine levels that are similar to those in tobacco users. These findings indicate that in females, but not males, exposure to nicotine during adolescence may facilitate smoking and e-cigarette use later in life.

Variability in nicotine conditioned place preference and stress-induced reinstatement in mice: Effects of sex, initial chamber preference, and guanfacine

Relapse to smoking occurs at higher rates in women compared with men, especially when triggered by stress. Studies suggest that sex-specific interactions between nicotine reward and stress contribute to these sex differences. Accordingly, novel treatment options targeting stress pathways, such as guanfacine, an α2-adrenergic receptor agonist, may provide sex-sensitive therapeutic effects. Preclinical studies are critical for elucidating neurobiological mechanisms of stress-induced relapse and potential therapies, but rodent models of nicotine addiction are often hindered by large behavioral variability. In this study, we used nicotine conditioned place preference to investigate stress-induced reinstatement of nicotine preference in male and female mice, and the effects of guanfacine on this behavior. Our results showed that overall, nicotine induced significant place preference acquisition and swim stress-induced reinstatement in both male and female mice, but with different nicotine dose-response patterns. In addition, we explored the variability in nicotine-dependent behaviors with median split analyses and found that initial chamber preference in each sex differentially accounted for variability in stress-induced reinstatement. In groups that showed significant stress-induced reinstatement, pretreatment with guanfacine attenuated this behavior. Finally, we evaluated neuronal activation by Arc immunoreactivity in the infralimbic cortex, prelimbic cortex, anterior insula, basolateral amygdala, lateral central amygdala and nucleus accumbens core and shell. Guanfacine induced sex-dependent changes in Arc immunoreactivity in the infralimbic cortex and anterior insula. This study demonstrates sex-dependent relationships between initial chamber preference and stress-induced reinstatement of nicotine conditioned place preference, and the effects of guanfacine on both behavior and neurobiological mechanisms.

Comparison of the Relative Abuse Liability of Electronic Cigarette Aerosol Extracts and Nicotine Alone in Adolescent Rats: A Behavioral Economic Analysis

Background: Characterizing the determinants of the abuse liability of electronic cigarettes (ECs) in adolescents is needed to inform product regulation by the United States Food and Drug Administration (FDA). We recently reported that Vuse Menthol EC aerosol extract containing nicotine and a range of non-nicotine constituents (e.g., menthol, propylene glycol) had reduced aversive effects compared to nicotine alone in adolescent rats, whereas Aroma E-Juice EC aerosol extract did not. The current study used a behavioral economic approach to compare the relative abuse liability of these EC extracts and nicotine alone in an i.v. self-administration (SA) model in adolescents. Methods: Adolescents were tested for the SA of EC extracts prepared using an ethanol (ETOH) solvent or nicotine and saline, with and without 4% ETOH (i.e., the same concentration in the EC extracts) in 23 h/day sessions. Results. Although acquisition of SA was faster for nicotine + ETOH compared to all other formulations, the elasticity of demand for all nicotine-containing formulations was similar. Conclusions: EC aerosol extracts did not have greater abuse liability than nicotine alone in adolescents. These data suggest that nicotine may be the primary determinant of the abuse liability of these ECs in youth, at least in terms of the primary reinforcing effects of ECs mediated within the central nervous system.

Randomized Clinical Trials Investigating Innovative Interventions for Smoking Cessation in the Last Decade

Every year, billions of dollars are spent treating smoking and related conditions, yet smoking-related morbidity and mortality continue to rise. There are currently only three FDA-approved medications for smoking cessation: nicotine replacement therapy, bupropion, and varenicline. Although these medications increase abstinence rates, most individuals relapse following treatment. This chapter reviews clinical trials published within the past 10 years investigating novel smoking cessation pharmacotherapies. Among these pharmacotherapies, some showed promising results, such as cytisine and endocannabinoid modulators, whereas others failed to produce significant effects. More research is needed to develop drugs that produce higher rates of long-term abstinence and to determine which subgroups of patients benefit from a given treatment.

Adolescent neurodevelopment and substance use: Receptor expression and behavioral consequences

Adolescence is the transitional period between childhood and adulthood, during which extensive brain development occurs. Since this period also overlaps with the initiation of drug use, it is important to consider how substance use during this time might produce long-term neurobiological alterations, especially against the backdrop of developmental changes in neurotransmission. Alcohol, cannabis, nicotine, and opioids all produce marked changes in the expression and function of the neurotransmitter and receptor systems with which they interact. These acute and chronic alterations also contribute to behavioral consequences ranging from increased addiction risk to cognitive or neuropsychiatric behavioral dysfunctions. The current review provides an in-depth overview and update of the developmental changes in neurotransmission during adolescence, as well as the impact of drug exposure during this neurodevelopmental window. While most of these factors have been studied in animal models, which are the focus of this review, future longitudinal studies in humans that assess neural function and behavior will help to confirm pre-clinical findings. Furthermore, the neural changes induced by each drug should also be considered in the context of other contributing factors, such as sex. Further understanding of these consequences can help in the identification of novel approaches for preventing and reversing the neurobiological effects of adolescent substance use.

Menstrual Cycle in Women Who Co-use Marijuana and Tobacco

OBJECTIVE

Marijuana is the most commonly used illicit drug in the United States and co-use with tobacco is increasing. Preliminary studies have indicated that marijuana may suppress luteinizing hormone (LH) or shorten the luteal phase. Although the literature is mixed, these sex hormones may play a role in smoking cessation outcomes. This secondary subgroup analysis aims to explore the menstrual cycle of females who co-use marijuana and tobacco compared with females who only use tobacco in a sample of tobacco treatment-seeking individuals.

METHODS

Female participants, aged 18 to 50 years, who self-reported regular menstrual cycles and co-use of marijuana and tobacco were matched 1:3 by age to participants who only use tobacco. Length of the follicular and luteal phases was determined using First Response Urine LH tests. Wilcoxon 2-sample t tests were used to determine differences in phase lengths between groups.

RESULTS

Thirteen women who co-use marijuana and tobacco, and 39 women who only use tobacco were included in this analysis. Overall, participants were 37.3 ± 8.0 (SD) years of age, mostly Caucasian (67%), and smoked 12.6 ± 5.2 (SD) cigarettes per day. The luteal phase length among participants who co-use marijuana and tobacco (11.4 days ± 2.2 [SD]) was significantly shorter than among participants who only use tobacco (16.8 days ± 11.3 [SD]; P = 0.002). No differences were found in follicular phase length or menstrual cycle length.

CONCLUSIONS

These data suggest that females who co-use marijuana and tobacco may have a shortened luteal phase in comparison with females who only use tobacco. Further studies are needed to better understand how marijuana use may impact the menstrual cycle and affect smoking outcomes.

Smoking-related symptomatology in pregnant smokers during ad libitum smoking and following overnight smoking abstinence

Objective

Current literature suggests there may be a relationship between sex hormones, which dramatically increase during pregnancy, and nicotine use behaviors. We hypothesized that higher progesterone and progesterone:estradiol ratio (P/E₂) would be associated with less smoking-related symptomatology (SRS), better mood and fewer cigarettes smoked per day (CPD) during ad libitum smoking and following overnight abstinence in pregnant women. Associations between SRS, mood, smoking behavior and sex hormones were estimated using multiple linear regression with adjustment for CPD and pregnancy trimester.

Results

There were 35 second trimester and 42 third trimester participants. Participants mean age was 26.2 (SD: 4.1), they smoked 11.3 CPD (SD: 4.4) and the mean nicotine dependence score was 4.94 (SD: 1.98). There were no statistically significant associations between progesterone levels, estradiol levels, or the P/E₂ ratio and SRS or mood measures during ad libitum smoking or following overnight abstinence in this sample of pregnant women. Similarly, there were no associations between sex hormone levels and number of CPD smoked during the ad libitum period. Contrary to our hypothesis, we found no significant associations between sex hormones and SRS, mood or smoking behavior in this sample of pregnant women.

Trial registration ClinicalTrials.gov (NCT01811225), December 6, 2012

Sex differences in nicotine-enhanced Pavlovian conditioned approach in rats

Background

Nicotine exposure enhances Pavlovian conditioned approach (PCA), or the learned approach to reward-predictive cues. While females show elevated approach to conditioned stimuli compared to males, potentially indicating heightened addiction vulnerability, it is unknown how sex may interact with nicotine to influence approach behavior. Additionally, brain-derived neurotrophic factor (BDNF) levels can be altered significantly after repeated nicotine exposure, suggesting a potential mechanism contributing to nicotine-induced behavioral phenotypes. The present study investigated the role of sex on nicotine-induced changes to stimulus-response behavior and associated BDNF protein levels.

Methods

Male and female rats were exposed to nicotine (0.4 mg/kg, subcutaneously) or saline 15 min prior to each PCA session. PCA training consisted of 29 sessions of 15 trials, in which a 30-s cue presentation ended concurrently with a sucrose reward (20% w/v in water, 100 μL), and a 120-s variable intertrial interval occurred between trials. Approach behavior to the cue and reward receptacle was recorded. Preference toward the reward receptacle indicated a goal-tracking phenotype, and preference toward the cue indicated a sign-tracking phenotype, demonstrating that the cue had gained incentive salience. Twenty-four hours after the last PCA session, brain tissue was collected and BDNF levels were measured in the basolateral amygdala, orbitofrontal cortex, and nucleus accumbens using Western blot analysis.

Results

Nicotine exposure enhanced both sign- and goal-tracking conditioned approach, and females showed elevated sign-tracking compared to males. There were no sex-by-drug interactions on conditioned approach. Day-to-day variability in conditioned approach was similar between sexes. In contrast to prior studies, neither repeated exposure to nicotine nor sex significantly affected BDNF expression.

Conclusions

Drug-naïve females exhibited heightened sign-tracking compared to males, and nicotine enhanced conditioned approach similarly in males and females. Further, non-significant changes to BDNF expression in brain regions highly associated with PCA indicate that BDNF is unlikely to drive nicotine-enhanced conditioned behavior.

Longitudinal association between tobacco use and the onset of depressive symptoms among Swedish adolescents: the Kupol cohort study

Tobacco use in adolescence has been linked to the onset of depressive symptoms, but results of previous studies are inconsistent. The aim of this study was to clarify if tobacco use during early adolescence may affect the short-term onset of depressive symptoms. The study is based on Swedish Kupol study (3959 students). Current cigarette smoking, snus use, and tobacco dependence were assessed using questionnaires at baseline and 1-year follow-up. Outcome was the onset of depressive symptoms measured with the CES-DC scale, using a cut-off ≥ 30 as threshold. Adjusted linear and logistic regression models were employed to calculate odds ratios (OR) and corresponding 95% confidence intervals (CI). CES-DC mean score at baseline was 14.3, higher in females than males (17.5 vs 10.9). The incidence of depressive symptoms at follow-up was 8.3%, greater in current than never smokers at baseline (13.7% vs 3.1%). Current cigarette smoking at the age of 13 years was strongly associated with the onset of depressive symptoms 1 year later, particularly in males (OR 12.7, 95% CI: 2.5-63.9), with a significant interaction between tobacco use and sex; feeling dependent on tobacco was also associated with depressive symptoms in males but not in females. Snus and overall tobacco use were not associated with the onset of depressive symptoms. Tobacco use during adolescence appears to influence the onset of depressive symptoms, with a stronger association in males than females. Pubertal maturation and sex-specific response patterns to the scale instrument may explain the moderating effect of sex.

MicroRNA cluster miR199a/214 are differentially expressed in female and male rats following nicotine self-administration

Previous research has established sex differences associated with nicotine intake, however a significant gap in knowledge remains regarding the molecular mechanisms that govern these differences at the transcriptional level. One critical regulator of transcription are microRNAs (miRNAs). miRNAs are a family of non-coding RNAs that regulate an array of important biological functions altered in several disease states, including neuroadaptive changes within the brain associated with drug dependence. We examined the prefrontal cortex (PFC) from male and female Sprague-Dawley rats following self-administration (22 days) of nicotine or yoked saline controls using next generation RNA-Sequencing (RNA-Seq) technology and found an array of miRNAs to be significantly and differentially regulated by nicotine self-administration. Of these, we found the expression of miR-199a and 214, which are expressed on the same cluster of chromosome 1, to be upregulated in the female rats exposed to nicotine; upregulation in this group was further validated by real time polymerase chain reaction (RT-PCR). Bioinformatics analysis to assess common targets of miR-199/214 identified Sirtuin 1 (SIRT1), a nicotinamide adenine dinucleotide (NAD)- dependent deacetylase that plays a role in apoptosis, neuron survival, and stress resistance. Using western-blot, we confirmed downregulation of SIRT1 and increased cleaved caspase 3 expression in the brains of nicotine-exposed female rats and no change in expression levels in the other groups. Collectively, our findings highlight a miR-199/214 regulatory network that, through SIRT1, may be associated with nicotine seeking in females which may serve as a potential therapeutic target for sex-specific treatment approaches.

Status and Future Directions of Preclinical Behavioral Pharmacology in Tobacco Regulatory Science

Behavioral pharmacology is a branch of the experimental analysis of behavior that has had great influence in drug addiction research and policy. This paper provides an overview of recent behavioral pharmacology research in the field of tobacco regulatory science, which provides the scientific foundation for the Food and Drug Administration Center for Tobacco Products (FDA CTP) to set tobacco control policies. The rationale and aims of tobacco regulatory science are provided, including the types of preclinical operant behavioral models it deems important for assessing the abuse liability of tobacco products and their constituents. We then review literature relevant to key regulatory actions being considered by the FDA CTP, including regulations over nicotine and menthol content of cigarettes, and conclude with suggesting some directions for future research. The current era of tobacco regulatory science provides great opportunities for behavioral pharmacologists to address the leading cause of preventable death and disease worldwide.

The influence of smoking and cessation on the human reproductive hormonal balance

Smoking is the most widespread substance dependence in the world. Nicotine and some other components of the cigarette smoke cause various endocrine imbalances, and have negative effects on pituitary, thyroid, adrenal, testicular and ovarian functions. Here, we examined studies that describe the influence of smoking and smoking cessation on the male and female reproductive systems. We also focused on studies providing an account of differences in cessation success rates between men and women. In men, the most common effects associated with smoking are erectile dysfunction and decreasing spermiogram quality. Several groups have studied the effects of cigarette smoking on testosterone levels in men. However, the results have been conflicting. In women, nicotine has an anti-estrogen effect and increases the ratio of androgens to estrogens throughout life. Beside nicotine, other cigarette toxins also cause dysregulation of reproductive and hormonal system, and essentially influence the probability of a successful pregnancy not only in cases of assisted reproduction but also in healthy women. Tobacco addiction is one of the forms of addiction that are generally thought to be different for men and for women. Women are less successful than men in quitting smoking, and nicotine replacement therapy is less effective in female smokers. We also summarize recent studies that have indicated possible reasons.

Animal Research on Nicotine Reduction: Current Evidence and Research Gaps

A mandated reduction in the nicotine content of cigarettes may improve public health by reducing the prevalence of smoking. Animal self-administration research is an important complement to clinical research on nicotine reduction. It can fill research gaps that may be difficult to address with clinical research, guide clinical researchers about variables that are likely to be important in their own research, and provide policy makers with converging evidence between clinical and preclinical studies about the potential impact of a nicotine reduction policy. Convergence between clinical and preclinical research is important, given the ease with which clinical trial participants can access nonstudy tobacco products in the current marketplace. Herein, we review contributions of preclinical animal research, with a focus on rodent self-administration, to the science of nicotine reduction. Throughout this review, we highlight areas where clinical and preclinical research converge and areas where the two differ. Preclinical research has provided data on many important topics such as the threshold for nicotine reinforcement, the likelihood of compensation, moderators of the impact of nicotine reduction, the impact of environmental stimuli on nicotine reduction, the impact of nonnicotine cigarette smoke constituents on nicotine reduction, and the impact of nicotine reduction on vulnerable populations. Special attention is paid to current research gaps including the dramatic rise in alternative tobacco products, including electronic nicotine delivery systems (ie, e-cigarettes). The evidence reviewed here will be critical for policy makers as well as clinical researchers interested in nicotine reduction.

IMPLICATIONS

This review will provide policy makers and clinical researchers interested in nicotine reduction with an overview of the preclinical animal research conducted on nicotine reduction and the regulatory implications of that research. The review also highlights the utility of preclinical research for research questions related to nicotine reduction.

Testing environment shape differentially modulates baseline and nicotine-induced changes in behavior: Sex differences, hypoactivity, and behavioral sensitization

In those who use nicotine, the likelihood of dependence, negative health consequences, and failed treatment outcomes differ as a function of gender. Women may be more sensitive to learning processes driven by repeated nicotine exposure that influence conditioned approach and craving. Sex differences in nicotine's influence over overt behaviors (i.e. hypoactivity or behavioral sensitization) can be examined using passive drug administration models in male and female rats. Following repeated intravenous (IV) nicotine injections, behavioral sensitization is enhanced in female rats compared to males. Nonetheless, characteristics of the testing environment also mediate rodent behavior following drug administration. The current experiment used a within-subjects design to determine if nicotine-induced changes in horizontal activity, center entries, and rearing displayed by male and female rats is detected when behavior was recorded in round vs. square chambers. Behaviors were recorded from each group (males-round: n=19; males-square: n=18; females-square: n=19; and females-round: n=19) immediately following IV injection of saline, acute nicotine, and repeated nicotine (0.05mg/kg/injection). Prior to nicotine treatment, sex differences were apparent only in round chambers. Following nicotine administration, the order of magnitude for the chamber that provided enhanced detection of hypoactivity or sensitization was contingent upon both the dependent measure under examination and the animal's biological sex. As such, round and square testing chambers provide different, and sometimes contradictory, accounts of how male and female rats respond to nicotine treatment. It is possible that a central mechanism such as stress or cue sensitivity is impacted by both drug exposure and environment to drive the sex differences observed in the current experiment. Until these complex relations are better understood, experiments considering sex differences in drug responses should balance characteristics of the testing environment to provide a complete interpretation of drug-induced changes to behavior.

Progesterone for smoking relapse prevention following delivery: A pilot, randomized, double-blind study

INTRODUCTION

Close to half of women who were smokers prior to conception quit smoking in pregnancy, when endogenous progesterone levels are high. However, at least half resume pre-pregnancy smoking levels within weeks after delivery and when progesterone levels drop. The current pilot study tested the feasibility and preliminary efficacy of postpartum progesterone replacement in preventing relapse to smoking in postpartum women with a history of pre-pregnancy smoking.

METHODS

This was an 8-week, double-blind, parallel, randomized, placebo-controlled pilot trial of 41 women with a history of pre-pregnancy smoking who achieved abstinence by 32 weeks of gestation. Immediately following delivery women were randomized to oral micronized progesterone (200mg twice daily) or placebo via computerized urn randomization program. The main outcome measures were descriptions of study feasibility: recruitment and retention. Secondary outcomes were 7-day point prevalence of abstinence at week 8, time to relapse and smoking cravings.

RESULTS

The trial was feasible with adequate randomization, 64% (41/64) of eligible women, and trial retention, 78% (32/41) completed the trial. Women taking progesterone were 1.8 times more likely to be abstinent during week 8 and took longer to relapse (10 vs. 4 weeks) compared to the placebo group, although these differences did not reach statistical significance. After adjusting for age and pre-quit smoking level, the number needed to treat was 7. There was a 10% greater decline per week in craving ratings in the progesterone group compared to placebo (β=-0.10, 95% CI: -0.15, -0.04, p<0.01). No serious adverse events occurred during the trial.

CONCLUSIONS

These preliminary findings support the promise of progesterone treatment in postpartum smokers and could constitute a therapeutic breakthrough.If these preliminary findings can be evaluated and replicated in a larger study with sufficient power, this may constitute an acceptable and safe smoking relapse prevention strategy for use during lactation.

Sex differences in nicotine intravenous self-administration: A meta-analytic review

OBJECTIVE

This report reflects a meta-analysis that systematically reviewed the literature on intravenous self-administration (IVSA) of nicotine in female and male rats. The goal was to determine if sex differences in nicotine IVSA exist, estimate the magnitude of the effect, and identify potential moderators of the relationship between sex differences and nicotine consumption.

METHODS

Extensive search procedures identified 20 studies that met the inclusion criteria of employing both female and male rats in nicotine IVSA procedures. The meta-analysis was conducted on effect size values that were calculated from mean total intake or nicotine deliveries using the Hedges' unbiased g^u statistic.

RESULTS

A random effects analysis revealed that overall females self-administered more nicotine than males (weighted g^u=0.18, 95% CI [0.003, 0.34]). Subsequent moderator variable analyses revealed that certain procedural conditions influenced the magnitude of sex differences in nicotine IVSA. Specifically, higher reinforcement requirements (>FR1) and extended-access sessions (23h) were associated with greater nicotine IVSA in females versus males. Females also displayed higher nicotine intake than males when the experiment included a light cue that signaled nicotine delivery. Sex differences were not influenced by the diurnal phase of testing, dose of nicotine, or prior operant training.

CONCLUSION

Overall, the results revealed that female rats display higher levels of nicotine IVSA than males, suggesting that the strong reinforcing effects of nicotine promote tobacco use in women.

Sex-dependent effects of nicotine on the developing brain

The use of tobacco products represents a major public health concern, especially among women. Epidemiological data have consistently demonstrated that women have less success quitting tobacco use and a higher risk for developing tobacco-related diseases. The deleterious effects of nicotine are not restricted to adulthood, as nicotinic acetylcholine receptors regulate critical aspects of neural development. However, the exact mechanisms underlying the particular sensitivity of women to develop tobacco dependence have not been well elucidated. In this mini-review, we show that gonadal hormone-mediated sexual differentiation of the brain may be an important determinant of sex differences in the effects of nicotine. We highlight direct interactions between sex steroid hormones and ligand-gated ion channels critical for brain maturation, and discuss the extended and profound sexual differentiation of the brain. We emphasize that nicotine exposure during the perinatal and adolescent periods interferes with normal sexual differentiation and can induce long-lasting, sex-dependent alterations in neuronal structure, cognitive and executive function, learning and memory, and reward processing. We stress important age and sex differences in nicotine's effects and emphasize the importance of including these factors in preclinical research that models tobacco dependence. © 2016 Wiley Periodicals, Inc.

Sex differences in nicotine preference

Smoking is the major cause of preventable deaths worldwide, and although there is a decline in overall smoking prevalence in developed countries, the decline in women is less pronounced than in men. Women become dependent faster and experience greater difficulties in quitting. Similar trends have been observed in animal models of nicotine/tobacco addiction. Individual differences in vulnerability to drug abuse are also observed in nicotine/tobacco addiction and point to the importance of sex differences. This Review, summarizes findings from three experimental approaches used to depict nicotine preference in animal models, intravenous and oral nicotine self-administration and nicotine-induced conditioned place preference. Nicotine preference is considered to be reflected in the animal's motivation to administer the drug (intravenously or orally) or to prefer an environment paired with the presence of the drug (conditioned place preference). These approaches all point to the importance of sex and age of the subjects; the preference of females and adolescents appear to be more pronounced than that of males and adults, respectively. A closer look at these factors will help us understand the mechanisms that underlie nicotine addiction and develop strategies to cope. Ignoring sex differences and reaching conclusions based only on studies using male subjects has resulted in erroneous generalizations in the past. Sex differences in nicotine preference have been clearly documented, and awareness on this aspect of nicotine dependence will significantly impact our success in translational research. © 2016 Wiley Periodicals, Inc.

Exercise or saccharin during abstinence block estrus-induced increases in nicotine-seeking

Recent evidence suggests that adolescent and young adult females may be particularly responsive to nicotine use interventions that include exercise or environmental enrichment. This possibility was addressed in the current study by comparing the efficacy of exercise versus non-exercise environmental enrichment (saccharin) during abstinence at reducing subsequent nicotine-seeking/relapse vulnerability in an adolescent-onset rat model. The efficacy of each intervention was examined as a function of estrous cycle phase given findings indicating that hormonal status influences relapse vulnerability and treatment outcome in females. Once adolescent female rats acquired nicotine self-administration, they were given 23-h/day access to nicotine (0.01mg/kg/infusion) for 10days. Following the last self-administration session, rats began a 10-day forced abstinence period with 2-h/day access to an unlocked wheel (exercise, n=15), a bottle containing a saccharin-sweetened solution (0.25%; saccharin, n=19), or without access to a wheel or saccharin (control, n=20). Nicotine-seeking, as assessed under an extinction/cued-induced reinstatement procedure, was examined on day 11 of abstinence. Levels of nicotine-seeking were highest in females tested during estrus as compared to females tested during non-estrus phases. Exercise or saccharin during abstinence reduced nicotine-seeking in females tested during estrus, but neither affected the low levels of nicotine-seeking observed in females tested during non-estrus phases, presumably due to a floor effect. These results demonstrate that exercise or saccharin during abstinence decrease nicotine-seeking, and suggest that either would be effective as an early intervention for nicotine use and addiction in females.

Social learning promotes nicotine self-administration by facilitating the extinction of conditioned aversion in isogenic strains of rats

Both social environment and genetic factors are critical for smoking initiation and nicotine addiction. We reported that rats developed conditioned flavor (i.e., taste and odor) aversion to intravenously self-administered (IVSA) nicotine, and that social learning promoted nicotine IVSA with flavor cues. We thus tested the hypothesis that socially acquired nicotine IVSA is a heritable trait by using female rats of six inbred strains and six F1 hybrids. Each strain was tested for 10 daily IVSA sessions. We found that the intake of nicotine (15 and 30 μg/kg/inf) varied among these strains by 33.7–56.6-fold. The heritability of nicotine intake was estimated to be 0.54–0.65. Further, there was a strong correlation in nicotine intake (R² = 0.85, p < 0.0001) between the two nicotine doses. Another cohort of rats was given three daily IVSA sessions followed by five sessions that tested conditioned flavor aversion. Nicotine intake was highly correlated with the extinction of the conditioned aversion (R² = 0.58, p < 0.005). These data showed that nicotine intake in the socially acquired nicotine self-administration model is controlled by genetic factors and that the role of social learning is likely in facilitating the extinction of conditioned aversive response to nicotine.