Sex differences in alcohol self-administration and relapse-like behavior in Long-Evans rats

Innate and Acquired Quinine-Resistant Alcohol, but not Saccharin, Drinking in Crossed High-Alcohol-Preferring Mice

BACKGROUND

Alcohol consumption despite aversive consequences is often a key component of an alcoholism diagnosis. Free-choice alcohol consumption despite bitter quinine adulteration in rodents has been seen following several months of free-choice drinking, but there has been little study of whether prolonged access to other palatable substances such as saccharin yields quinine resistance. Selectively bred crossed high-alcohol-preferring (cHAP) mice average blood alcohol levels of over 250 mg/dl during free-choice access, considerably higher than other models. We hypothesized that higher intakes would yield more rapid development of quinine-resistant alcohol (QRA) drinking and quinine-resistant saccharin (QRS) drinking.

METHODS

All experiments used male and female cHAP mice. Experiment 1 compared mice with either 0 or 5 weeks of alcohol drinking history, testing varying (0.032, 0.10, 0.32 g/l) quinine concentrations in ethanol. Experiment 2 examined whether innate QR may exist, comparing animals with a 1 or zero day of drinking history. Experiment 3 examined the effect of varying histories (0, 2, or 5 weeks) of free-choice 10% alcohol drinking on QR alcohol consumption at high quinine concentrations. Finally, Experiment 4 investigated the development of QRS drinking.

RESULTS

We found that we could not detect a history effect in commonly used quinine concentrations, indicating that cHAP mice are innately quinine resistant to 0.10 g/l quinine. However, we were able to determine that a 2-week drinking history was sufficient to induce QRA drinking in cHAP mice at extremely high quinine concentrations (0.74 and 0.32 g/l). However, the history effect was specific to QRA, a saccharin drinking history, did not yield QRS drinking.

CONCLUSIONS

These data suggest that an alcohol drinking history induces maladaptive behaviors, such as drinking in spite of negative consequences, a pattern not seen with saccharin. Furthermore, a strong genetic predisposition to drink may promote an innate aversion resistance compared with commonly used inbred strains.

Operant, oral alcohol self-administration: Sex differences in Sardinian alcohol-preferring rats

Sardinian alcohol-preferring (sP) rats have been selectively bred, over almost 40 years, for high alcohol preference and consumption. sP rats have served as an animal model for more than 120 published studies. With very few exceptions, however, these studies have always employed male sP rats, and little is known about alcohol-related behaviors in female sP rats. The present study was designed to fill, at least in part, this gap. Accordingly, alcohol self-administration under the fixed ratio 4 schedule of reinforcement was compared among male, intact female, and ovariectomized female sP rats. Additionally, it was investigated whether i) estrous cycle influenced alcohol self-administration, and ii) alcohol self-administration in the three sP rat groups differed in sensitivity to pharmacological manipulation. Lever-responding for alcohol was steadily higher in male than intact and ovariectomized female sP rats; conversely, because of large sex differences in rat body weight, estimated amount of self-administered alcohol (in g/kg) did not differ among the three sP rat groups or occasionally was higher in intact female than male and ovariectomized female sP rats. Blood alcohol levels derived from self-administered alcohol i) did not differ among the three sP rat groups and ii) were positively correlated with the number of lever-responses for alcohol and the estimated amount of self-administered alcohol. Treatment with the opioid receptor antagonist, naloxone (0, 0.3, 1, and 3 mg/kg, i.p. [intraperitoneally]), and the positive allosteric modulator of the GABA_B receptor, GS39783 (0, 25, 50, and 100 mg/kg, i.g. [intragastrically]), reduced alcohol self-administration with comparable potency and efficacy in the three sP rat groups. The impact of the estrous cycle on alcohol self-administration was relatively modest, limited to a tendency toward a reduction in the number of lever-responses for alcohol and the estimated amount of self-administered alcohol in estrus and metestrus. Together, these results provide the first characterization of alcohol-seeking and -taking behavior in female sP rats.

Review: Sex-Based Differences in Treatment Outcomes for Persons With Opioid Use Disorder

BACKGROUND AND OBJECTIVES

In order to address the current opioid crisis, research on treatment outcomes for persons with opioid use disorder (OUD) should account for biological factors that could influence individual treatment response. Women and men might have clinically meaningful differences in their experience in OUD treatment and might also have unique challenges in achieving successful, long-term recovery. This review summarizes and synthesizes the current literature on sex-based differences in OUD treatment outcomes.

METHODS

Relevant literature was identified via automated and manual searches using the terms "opioid treatment outcome sex [or gender] differences" and "opiate treatment outcome sex [or gender] differences." Search methodology was consistent with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA), and were conducted within the PubMed electronic database during March and April of 2018.

RESULTS

The initial PubMed search yielded 241 manuscripts and 31 original research articles that met inclusion/exclusion criteria were synthesized in this review. Several important trends emerged, including findings that women are more likely than men to present to treatment with co-occurring mental health conditions such as depression, and that women might respond particularly well to buprenorphine maintenance.

DISCUSSION AND CONCLUSIONS

While much of the literature on this topic is subject to potential cohort effects, interventions that address co-occurring mental health conditions and psychosocial stress might improve treatment outcomes for women with OUD.

SCIENTIFIC SIGNIFICANCE

Funding agencies and researchers should focus attention toward human laboratory studies and clinical trials that are prospectively designed to assess sex-based differences in OUD recovery. (Am J Addict 2019;28:246-261).

Effects of noncontingent ethanol, DHEA, and pregnanolone administration on ethanol self-administration in outbred female rats

Previous research from this laboratory demonstrated that male outbred rats (Long-Evans) can be trained to prefer ethanol (10% v/v) over water during 30-min home-cage sessions and that higher ethanol concentrations (18-32% v/v) can serve as a reinforcer under various operant schedules. Further, we have shown that two neurosteroids, dehydroepiandrosterone (DHEA) and pregnanolone, can readily decrease ethanol self-administration in males. The present study used the same procedures in an attempt to systematically replicate the previous findings in female outbred rats. Rats were first trained to self-administer ethanol in the home cage using a saccharin-fading procedure. Subsequently, a two-bottle preference test was initiated by substituting different ethanol concentrations after subjects reliably consumed 10% ethanol alone. Water was always available during this phase. Next, subjects were transitioned to a fixed-ratio 10 (FR-10) schedule of reinforcement with 0.1 mL of ethanol (18% v/v) serving as the reinforcer so that a concentration-effect curve could be established. Upon completion, subjects were transitioned to an FR-10 FR-20 multiple schedule of ethanol (32% v/v) and food reinforcement to determine whether noncontingent ethanol, DHEA, and pregnanolone could selectively decrease ethanol intake. Not surprisingly, female subjects preferentially consumed ethanol over water at concentrations of 3.2-18% (v/v) during the home-cage procedure, and significantly increased the mean dose of ethanol consumed and blood ethanol concentration (BEC). Similarly, increasing concentrations under an FR-10 schedule significantly increased the dose of ethanol presented and BEC compared to control (water). Finally, under the multiple schedule, noncontingent injections of ethanol (0.32-1.8 g/kg), DHEA (10-100 mg/kg), and pregnanolone (1.8-32 mg/kg) dose-dependently decreased food- and ethanol-maintained responding and the dose of ethanol presented. BEC was significantly decreased by the neurosteroids, but increased by ethanol due to its noncontingent administration. Together, these data replicate only a subset of the data previously obtained in males, suggesting there are sex differences particularly with respect to the effects of DHEA and pregnanolone.

Effects of nicotine conditioning history on alcohol and methamphetamine self-administration in rats

BACKGROUND

Smoking constitutes a significant public health risk. Alcohol and methamphetamine use disorders are also highly co-morbid with smoking, further increasing negative health outcomes. An important question in determining the underlying neurobiology of nicotine poly-drug use is understanding whether having a positive history with nicotine effects alters later drug-taking behavior.

METHODS

The current experiments sought to elucidate whether having an appetitive nicotine conditioning history would affect later alcohol or methamphetamine self-administration. Adult male and female Long-Evans rats were first trained on a discriminated goal-tracking task in which the interoceptive effects of nicotine predicted sucrose reinforcement. As a control, pseudo-conditioned groups were included that had equated nicotine and sucrose experience. Rats were then shifted to either alcohol self-administration or methamphetamine self-administration.

RESULTS

Nicotine conditioning history had no effect on acquisition or maintenance of alcohol self-administration in males or females. In contrast, an appetitive nicotine conditioning history decreased methamphetamine self-administration in female rats, but not males.

CONCLUSIONS

In female, but not male, rats, an appetitive conditioning history with nicotine decreases methamphetamine, but not alcohol, self-administration. This dissociation suggests that the effects may be due to a specific increase in the reinforcing value of methamphetamine. This may have implications for better understanding the progression of drug use from nicotine to methamphetamine.

The Toll-Like Receptor 3 Agonist Poly(I:C) Induces Rapid and Lasting Changes in Gene Expression Related to Glutamatergic Function and Increases Ethanol Self-Administration in Rats

BACKGROUND

Growing evidence suggests that neuroimmune signaling via Toll-like receptors (TLRs) alters brain circuitry related to alcohol use disorders. Both ethanol (EtOH) exposure and the TLR3 agonist, poly(I:C), increase brain TLR3 expression in neurons and glia. Furthermore, previous studies have shown that cortical TLR3 expression is correlated with lifetime EtOH intake in humans.

METHODS

The current experiments investigated the consequences of poly(I:C) treatment on gene expression in 2 brain regions contributing to alcohol reinforcement, the insular cortex (IC) and nucleus accumbens (Acb) and on operant EtOH self-administration, in Long Evans rats.

RESULTS

TLR3 activation increased mRNA levels of neuroimmune genes (TLR3, COX2), glutamatergic genes (mGluR2, mGluR3, GLT1), and the trophic factor BDNF in Acb and IC. Furthermore, increases in each of these genes were correlated with increases in TLR3 mRNA, suggesting that TLR3 induction of these genes may impact excitatory transmission in IC and Acb. TLR3 activation also increased EtOH self-administration 18 days postinjection and enhanced the effects of the mGluR2/3 agonist LY379268 to reduce EtOH self-administration following poly(I:C).

CONCLUSIONS

Together, these findings suggest lasting consequences of TLR3 activation on gene expression including increases in Group II mGluRs in the Acb. Furthermore, we show an important role for TLR3 signaling in EtOH intake, and a functional involvement of Group II mGluRs.

Sexual dimorphism in the neural impact of stress and alcohol

Alcohol use disorder is a widespread mental illness characterized by periods of abstinence followed by recidivism, and stress is the primary trigger of relapse. Despite the higher prevalence of alcohol use disorder in males, the relationship between stress and behavioral features of relapse, such as craving, is stronger in females. Given the greater susceptibility of females to stress-related psychiatric disorders, understanding sexual dimorphism in the relationship between stress and alcohol use is essential to identifying better treatments for both male and female alcoholics. This review addresses sex differences in the impact of stressors on alcohol drinking and seeking in rodents and humans. As these behavioral differences in alcohol use and relapse originate from sexual dimorphism in neuronal function, the impact of stressors and alcohol, and their interaction, on molecular adaptations and neural activity in males and females will also be discussed. Together, the data reviewed herein, arising from a symposium titled "Sex matters in stress-alcohol interactions" presented at the Fourth Volterra Conference on Stress and Alcohol, will highlight the importance of identifying sex differences to improve treatments for comorbid stress and alcohol use disorder in both sexes.

The mineralocorticoid receptor antagonist spironolactone reduces alcohol self-administration in female and male rats

Cortisol/corticosterone and the hypothalamic-pituitary-adrenal (HPA) axis serve an important role in modulating alcohol drinking behaviors. To date most alcohol research has focused on the functional involvement of corticosterone and the glucocorticoid receptor (GR), the primary receptor for corticosterone. Recent studies have indicated that the related mineralocorticoid receptor (MR), which binds both corticosterone and aldosterone, may also play a role in alcohol drinking. Therefore, the purpose of the present study was to test the functional role of MR signaling in alcohol self-administration via pharmacological antagonism of the MR with spironolactone. Male and female Long-Evans rats were trained to self-administer a sweetened alcohol solution (15% (v/v) alcohol +2% (w/v) sucrose). The effects of spironolactone (0, 10, 25, 50 mg/kg; IP) were tested on alcohol self-administration and under "probe extinction" conditions to measure the persistence of responding in the absence of the alcohol reinforcer. Parallel experiments in sucrose self-administration trained rats were used to confirm the specificity of spironolactone effects to an alcohol reinforcer. In female rats spironolactone (50 mg/kg) reduced alcohol self-administration and persistence of alcohol responding. In male rats spironolactone (25 and 50 mg/kg) reduced alcohol self-administration, but not persistence of alcohol responding. Spironolactone reduced sucrose intake in female rats only, and locomotion in male and female rats during sucrose self-administration. There was no effect of spironolactone on persistence of sucrose responding. These studies add to growing evidence that the MR is involved in alcohol drinking, while underscoring the importance of studying both male and female animals.

Studying Sex Differences in Animal Models of Addiction: An Emphasis on Alcohol-Related Behaviors

Animal models are essential for understanding the biological factors that contribute to drug and alcohol addiction and discovering new pharmacotherapies to treat these disorders. Alcohol (ethanol) is the most commonly abused drug in the world, and as the prevalence of alcohol use disorder (AUD) increases, so does the need for effective pharmacotherapies. In particular, treatments with high efficacy in the growing number of female AUD sufferers are needed. Female animals remain underrepresented in biomedical research and sex differences in the brain's response to alcohol are poorly understood. To help bridge the gender gap in addiction research, this Review discusses strategies that researchers can use to examine sex differences in the context of several common animal models of AUD. Self-administration, two-bottle choice, drinking in the dark, and conditioned place preference are discussed, with a focus on the role of estrogen as a mediator of sex differences in alcohol-related behaviors.

Discovery of a Potent, Selective, and Brain-Penetrant Small Molecule that Activates the Orphan Receptor GPR88 and Reduces Alcohol Intake

The orphan G-protein-coupled receptor GPR88 is highly expressed in the striatum. Studies using GPR88 knockout mice have suggested that the receptor is implicated in alcohol seeking and drinking behaviors. To date, the biological effects of GPR88 activation are still unknown due to the lack of a potent and selective agonist appropriate for in vivo investigation. In this study, we report the discovery of the first potent, selective, and brain-penetrant GPR88 agonist RTI-13951-33 (6). RTI-13951-33 exhibited an EC50 of 25 nM in an in vitro cAMP functional assay and had no significant off-target activity at 38 GPCRs, ion channels, and neurotransmitter transporters that were tested. RTI-13951-33 displayed enhanced aqueous solubility compared to (1 R,2 R)-2-PCCA (2) and had favorable pharmacokinetic properties for behavioral assessment. Finally, RTI-13951-33 significantly reduced alcohol self-administration and alcohol intake in a dose-dependent manner without effects on locomotion and sucrose self-administration in rats when administered intraperitoneally.

Functional inactivation of the orbitofrontal cortex disrupts context-induced reinstatement of alcohol seeking in rats

BACKGROUND

The high rate of relapse to drug use remains a central challenge to treating drug addiction. In human and rat models of addiction, environmental stimuli in contexts associated with previous drug use can provoke a relapse of drug seeking. Pre-clinical studies have used the ABA renewal procedure to study context-induced reinstatement of drug seeking. In the current study, we studied the role of the orbitofrontal cortex (OFC) in context-induced reinstatement to alcohol.

METHODS

We trained male and female rats to self-administer alcohol in context A, extinguished drug-reinforced responding in a distinct context B, and assessed context-induced reinstatement in context A or B (control group). Next, we determined the effect of context-induced renewal of alcohol-seeking behavior on the expression of Fos (a neuronal activity marker) in the OFC. Finally, we determined the effect of reversible inactivation by GABAa and GABAb receptor agonists (i.e., muscimol and baclofen, respectively) in the OFC.

RESULTS AND CONCLUSIONS

There were no differences between male and female rats in context-induced reinstatement of alcohol-seeking behavior. Re-exposure to Context A, but not Context B, reinstated alcohol-seeking behavior and increased expression of the neural activity marker Fos in the OFC. Reversible inactivation of the OFC with muscimol and baclofen attenuated context-induced reinstatement. Our data indicated that the OFC mediates context-induced reinstatement of alcohol-seeking behavior.

Role of Exogenous Progesterone in the Treatment of Men and Women with Substance Use Disorders: A Narrative Review

Substance use disorders (SUDs) remain problematic as many individuals are untreated or do not benefit from the currently available interventions. Thus, there is an urgent need to develop novel pharmacological interventions to treat SUDs. Evidence suggests that the female sex hormone, progesterone, attenuates the craving for and the euphoric effects of drugs of abuse. Research to date has demonstrated that progesterone may modulate responses to drugs of abuse and may have utility as a novel treatment for SUDs. A literature search was conducted to identify and examine studies that administered exogenous progesterone. Sixteen publications were identified, exploring the utility of exogenous progesterone or its metabolite, allopregnanolone, among a range of substances, including amphetamines (one study), benzodiazepines (one study), cocaine (nine studies), and tobacco/nicotine (five studies). Results indicated that exogenous progesterone and, its metabolite allopregnanolone, demonstrated preliminary efficacy as a treatment for substance use in both men and women. Notably, progesterone appears to target negative affect and augment cognitive functioning, especially among female substance users. Additional research is needed to explore the potential use of exogenous progesterone and allopregnanolone in the treatment of SUDs, including that associated with alcohol and opioids, but considering the current promising findings, exogenous progesterone and allopregnanolone may have utility as novel pharmacological treatments for SUDs.

Silencing the insular-striatal circuit decreases alcohol self-administration and increases sensitivity to alcohol

Internal drug states/cues can impact drug taking, as pretreatment with a moderate to high alcohol dose (i.e., loading dose) can decrease subsequent alcohol self-administration, alcohol-seeking, and relapse-like drinking. The insular cortex (IC) is implicated in processing information about internal states and findings show that silencing the IC and its projections to the nucleus accumbens core (AcbC) enhance sensitivity to the interoceptive effects of alcohol. Therefore, the goal of the present work was to determine the functional role of IC-AcbC projections in modulating the effects of alcohol pretreatment on operant alcohol self-administration. Long-Evans rats were trained to self-administer a sweetened alcohol solution (15% alcohol (v/v) + 2% sucrose (w/v)) and on test sessions received pretreatment with an alcohol loading dose. A chemogenetic strategy (i.e., hM4D Designer Receptors Exclusively Activated by Designer Drugs [DREADDs]) was implemented to silence the IC-AcbC projections and test the functional role of the insular-striatal circuitry in regulating self-administration following the alcohol loading doses. Alcohol self-administration decreased following pre-session treatment with alcohol, confirming titration of alcohol drinking following a loading dose of alcohol. Chemogenetic silencing of IC-AcbC projections decreased alcohol self-administration under baseline conditions (i.e., water loading dose) and the reduction in self-administration of an alcohol loading dose, implicating a role for this circuit in the maintenance of alcohol self-administration and suggesting increased sensitivity to the alcohol loading dose. These findings provide evidence for the critical nature of insular-striatal circuitry in ongoing alcohol self-administration, and specifically in relation to interoceptive/internal cues that can impact alcohol drinking.

Sex as a biological variable: Drug use and abuse

The study of sex as a biological variable is a necessary emphasis across a wide array of endpoints, including basic neuroscience, medicine, mental health, physiology and behavior. The present review summarizes work from clinical and preclinical populations on sex differences in drug use and abuse, ranging from initiation to escalation/dysregulation and from drug cessation/abstinence to relapse. These differences are analyzed in the context of the addiction cycle conceptualization of Koob and his colleagues and address patterns of drug use (binge/intoxication), motivation underlying its use (withdrawal/negative affect) and likelihood and causes of craving and relapse of drug taking (preoccupation/anticipation). Following this overview, an assessment of the basis for the reported sex differences is discussed in the context of the affective (rewarding and aversive) properties of drugs of abuse and how such properties and their balance vary with sex and contribute to drug intake. Finally, the interaction of sex with several experiential (drug history) and subject (age) factors and how these interactions affect reward and aversion are discussed to highlight the importance of understanding such interactions in predicting drug use and abuse. We note that sex as a biological variable remains one of critical evaluation and that such investigations of sex differences in drug use and abuse continue and be expanded to assess all facets of their mediation, including these affective properties, how their balance may be impacted by the multiple conditions under which drugs are taken and how this overall balance affects drug use and addiction vulnerability.