Sex differences in the long-lasting consequences of adolescent ethanol exposure for the rewarding effects of cocaine in mice

Cannabidiol or ketamine for preventing the impact of adolescent early drug initiation on voluntary ethanol consumption in adulthood

Background

Few studies have previously evaluated the long-term impact of initiating the combined use of alcohol and cocaine early-in-life during adolescence. Our preclinical study characterized changes in affective-like behavior and/or voluntary ethanol consumption emerging later on in adulthood induced by a prior adolescent drug exposure, as well as tested therapeutical interventions (i.e., cannabidiol or ketamine) to prevent the observed effects.

Methods

We performed three independent studies with male and female Sprague-Dawley rats, treated in adolescence (postnatal days, PND 29-38) with non-contingent paradigms of ethanol, cocaine, their combination or vehicle. Later on, adult rats were (1) scored for their affective-like state (forced-swim, elevated-plus maze, novelty-suppressed feeding, sucrose preference), (2) allowed to freely drink ethanol for 6 weeks (two-bottle choice), or (3) treated with cannabidiol or ketamine before given access to ethanol in adulthood.

Results

No signs of increased negative affect were observed in adulthood following the adolescent treatments. However, adolescent ethanol exposure was a risk-factor for later developing an increased voluntary ethanol consumption in adulthood, both for male and female rats. This risk was similar when ethanol was combined with adolescent cocaine exposure, since cocaine alone showed no effects on later ethanol intake. Finally, rats exposed to adolescent ethanol and pretreated in adulthood with cannabidiol (and/or ketamine, but just for females) reduced their ethanol voluntary consumption.

Conclusion

Our data provided two therapeutical options capable of preventing the impact of an early drug initiation during adolescence by decreasing voluntary ethanol consumption in adult rats.

Effects of adolescent ethanol exposure on adult nondrug reward seeking behavior in male and female mice

BACKGROUND

Adolescent alcohol use is associated with an increased likelihood of developing an alcohol use disorder in adulthood, potentially due to the effects of alcohol exposure on reward-seeking behavior. However, it remains unclear whether adolescent drinking is sufficient to alter nondrug reward seeking in adulthood. As adolescence is a period of both brain and sexual maturation, which occur in a sex-dependent manner, males and females may be differentially sensitive to the consequences of adolescent alcohol exposure. The present study investigated whether adolescent ethanol exposure affected food reward taking and seeking in male and female adult mice.

METHODS

Male and female C57BL/6J mice underwent intermittent ethanol exposure (AIE) via vapor inhalation during early adolescence (28-42 days of age). At 10 weeks of age, the mice were trained in a conditioned place preference paradigm (CPP) for a food reward. We measured food consumption, CPP, and cFos expression in multiple brain regions following CPP testing. Data were analyzed using repeated measures analysis of variance with exposure (air vs. AIE), sex, and time as factors.

RESULTS

AIE exposure increased food consumption during CPP training in adult male mice, but reduced pellet consumption in adult female mice. AIE exposure impaired CPP expression only in female mice. Despite these behavioral differences, exposure to the reward-paired chamber did not induce differential cFos expression following CPP testing in the prelimbic and infralimbic cortices or the nucleus accumbens core and shell.

CONCLUSION

These findings indicate that adolescent ethanol exposure disrupted nondrug reward taking and seeking in adulthood in female mice and altered consumption in adult male mice.

Prepulse inhibition can predict the motivational effects of cocaine in female mice exposed to maternal separation

The prepulse inhibition (PPI) of the startle response can identify the rodents that are more sensitive to the effects of cocaine. Mice with a lower PPI presented a higher vulnerability to the effects of cocaine and a higher susceptibility to developing a substance use disorder (SUD). Maternal separation with early weaning (MSEW) is a relevant animal model to induce motivational alterations throughout life. Nevertheless, only a few studies on females exist, even though they are more vulnerable to stress- and cocaine-related problems. Hence, the aim of the present study was to evaluate the ability of PPI to identify females with a greater vulnerability to the long-term consequences of early stress on the motivational effects of cocaine. Female mice underwent MSEW and were classified according to their high or low PPI. They were then assessed in the cocaine-induced locomotor sensitization test, the conditioned place preference paradigm or the operant self-administration paradigm. Additionally, they were also evaluated in the passive avoidance task, the tail-suspension and the splash tests. The results revealed that the females with lower PPI presented higher consequences of MSEW on the effects of cocaine and showed an increase in anhedonia-like behaviours. Our findings support that a PPI deficit could represent a biomarker of vulnerability to the effects of cocaine induced by MSEW.

Ethanol pre-exposure differentially impacts the rewarding and aversive effects of α-pyrrolidinopentiophenone (α-PVP): Implications for drug use and abuse

RATIONALE

Exposure to a drug can subsequently impact its own reactivity as well as that of other drugs. Given that users of synthetic cathinones, i.e., "bath salts", typically have extensive and varied drug histories, an understanding of the effects of drug history on the behavioral and physiological consequences of synthetic cathiones may be important to their abuse liability.

OBJECTIVES

The goal of the current work was to assess the effects of an ethanol pre-exposure on the rewarding and aversive effects of α-PVP.

METHODS

Adult male Sprague Dawley rats were exposed to ethanol prior to combined conditioned taste avoidance/conditioned place preference training in which rats were injected with 1.5, 3 or 5 mg/kg of racemic α-PVP or vehicle. Following a 7-day washout period, rats were then tested for thermoregulatory effects of α-PVP using subcutaneous probes to measure body temperature changes over the course of 8 h. This was followed 10 days later by assessments for α-PVP-induced locomotor activity and stereotypies over a 1-h session.

RESULTS

α-PVP induced significant dose- and trial-dependent taste avoidance that was significantly attenuated by ethanol history and dose- and time-dependent increases in locomotor activity that were significantly increased by ethanol. α-PVP also induced place preferences and dose- and time-dependent increases in body temperature, but these measures were unaffected by ethanol history.

CONCLUSIONS

α-PVP's aversive effects (as measured by taste avoidance) were attenuated, while its rewarding effects (as indexed by place preference conditioning) were unaffected, by ethanol pre-exposure. Such a pattern may indicate increased α-PVP abuse liability, as changes in the balance of aversion and reward may impact overall drug effects and likelihood of drug intake. Future self-administration studies will be necessary to explore this possibility.

The persistent impact of adolescent binge alcohol on adult brain structural, cellular, and behavioral pathology: A role for the neuroimmune system and epigenetics

Adolescence is a critical neurodevelopmental window for maturation of brain structure, neurocircuitry, and glia. This development is sculpted by an individual's unique experiences and genetic background to establish adult level cognitive function and behavioral makeup. Alcohol abuse during adolescence is associated with an increased lifetime risk for developing an alcohol use disorder (AUD). Adolescents participate in heavy, episodic binge drinking that causes persistent changes in neurocircuitry and behavior. These changes may underlie the increased risk for AUD and might also promote cognitive deficits later in life. In this chapter, we have examined research on the persistent effects of adolescent binge-drinking both in humans and in rodent models. These studies implicate roles for neuroimmune signaling as well as epigenetic reprogramming of neurons and glia, which create a vulnerable neuroenvironment. Some of these changes are reversible, giving hope for future treatments to prevent many of the long-term consequences of adolescent alcohol abuse.

Effect of chronic binge-like ethanol consumption on subsequent cocaine reinforcement in rhesus monkeys

BACKGROUND

Although most individuals with cocaine use disorder also abuse alcohol, little is known about the behavioral and pharmacological mechanisms that promote co-abuse. For example, it is unclear whether prior experience with alcohol renders individuals more sensitive to cocaine when it is subsequently experienced.

METHODS

This study examined the effects of chronic ethanol consumption on subsequent cocaine reinforcement in rhesus monkeys. Six monkeys consumed 2.0 g/kg ethanol in a binge-drinking paradigm and 6 monkeys drank a non-alcoholic solution 5 days per week. After 9 months, each monkey's sensitivity to acquiring cocaine self-administration was determined. Monkeys performed an operant response resulting in food pellet delivery under a fixed-ratio 30 schedule of reinforcement. Saline, then ascending doses of cocaine, were substituted for food pellets until a cocaine dose was reached at which the number of cocaine injections delivered differed significantly from saline injections delivered. Following acquisition, a complete cocaine dose-effect curve was generated to determine whether ethanol consumption altered the reinforcing potency of cocaine determined by calculating the ED₅₀ of the ascending limb of each subject's curve.

RESULTS

Although individual variability was observed, the cocaine dose which initially served as a reinforcer did not differ between ethanol-drinking and control groups and, within the ethanol-drinking group, was not related to the amount of ethanol consumed. Moreover, the reinforcing potency of cocaine did not differ between groups.

CONCLUSION

Taken together, the data suggest that a history of binge-like alcohol consumption does not affect sensitivity to cocaine when it is subsequently first experienced.

Drug addiction co-morbidity with alcohol: Neurobiological insights

Addiction is a chronic disorder that consists of a three-stage cycle of binge/intoxication, withdrawal/negative affect, and preoccupation/anticipation. These stages involve, respectively, neuroadaptations in brain circuits involved in incentive salience and habit formation, stress surfeit and reward deficit, and executive function. Much research on addiction focuses on the neurobiology underlying single drug use. However, alcohol use disorder (AUD) can be co-morbid with substance use disorder (SUD), called dual dependence. The limited epidemiological data on dual dependence indicates that there is a large population of individuals suffering from addiction who are dependent on more than one drug and/or alcohol, yet dual dependence remains understudied in addiction research. Here, we review neurobiological data on neurotransmitter and neuropeptide systems that are known to contribute to addiction pathology and how the involvement of these systems is consistent or divergent across drug classes. In particular, we highlight the dopamine, opioid, corticotropin-releasing factor, norepinephrine, hypocretin/orexin, glucocorticoid, neuroimmune signaling, endocannabinoid, glutamate, and GABA systems. We also discuss the limited research on these systems in dual dependence. Collectively, these studies demonstrate that the use of multiple drugs can produce neuroadaptations that are distinct from single drug use. Further investigation into the neurobiology of dual dependence is necessary to develop effective treatments for addiction to multiple drugs.

Adolescent binge-ethanol accelerates cognitive impairment and β-amyloid production and dysregulates endocannabinoid signaling in the hippocampus of APP/PSE mice

Previous research in rodents suggests that the long-term neurobehavioral disturbances induced by chronic ethanol (EtOH) exposure could be due to endocannabinoid system (ECS) alterations. Moreover, ECS failure has been proposed to mediate the cognitive impairment and β-amyloid production in Alzheimer disease (AD). Thus, in the present study, we evaluated the effects of adolescent EtOH binge drinking on the cognitive disturbances, hippocampal β-amyloid levels, and in the ECS expression on a transgenic mouse model (APP/PSEN, AZ) of AD. We exposed AZ and wild-type mice to a binge-drinking treatment during adolescence. At 6 and 12 months of age, we evaluated hippocampal-dependent learning and memory: β-amyloid concentrations and RNA and protein levels of cannabinoid type-2 receptors (CB2), diacylglycerol lipase-α (DAGLα), and monoacylglycerol lipase (MAGL) in the hippocampus. The results showed that binge-EtOH treatment worsens cognitive function and increases β-amyloid levels in AZ. At 6 months, EtOH heightens CB2 (RNA and protein) and DAGLα (RNA) expression in wild type but not in AZ. On the contrary, EtOH enhances MAGL RNA expression only in AZ. At 12 months, AZ displays increased levels of CB2 (RNA and protein) and DAGLα (protein) compared with control. Similar to what happens at 6 months, EtOH induces an increase in CB2 gene expression in wild type but not in AZ; however, it augments CB2 and DAGLα protein levels in both genotypes. Therefore, we propose that adolescent binge drinking accelerates cognitive deficits associated with aging and AD. It also accelerates hippocampal β-amyloid accumulation in AZ and affects differently the ECS response in wild type and AZ.

One Is Not Enough: Understanding and Modeling Polysubstance Use

Substance use disorder (SUD) is a chronic, relapsing disease with a highly multifaceted pathology that includes (but is not limited to) sensitivity to drug-associated cues, negative affect, and motivation to maintain drug consumption. SUDs are highly prevalent, with 35 million people meeting criteria for SUD. While drug use and addiction are highly studied, most investigations of SUDs examine drug use in isolation, rather than in the more prevalent context of comorbid substance histories. Indeed, 11.3% of individuals diagnosed with a SUD have concurrent alcohol and illicit drug use disorders. Furthermore, having a SUD with one substance increases susceptibility to developing dependence on additional substances. For example, the increased risk of developing heroin dependence is twofold for alcohol misusers, threefold for cannabis users, 15-fold for cocaine users, and 40-fold for prescription misusers. Given the prevalence and risk associated with polysubstance use and current public health crises, examining these disorders through the lens of co-use is essential for translatability and improved treatment efficacy. The escalating economic and social costs and continued rise in drug use has spurred interest in developing preclinical models that effectively model this phenomenon. Here, we review the current state of the field in understanding the behavioral and neural circuitry in the context of co-use with common pairings of alcohol, nicotine, cannabis, and other addictive substances. Moreover, we outline key considerations when developing polysubstance models, including challenges to developing preclinical models to provide insights and improve treatment outcomes.

Cocaine-induced behavioral sensitization is greater in adolescent than in adult mice and heightens cocaine-induced conditioned place preference in adolescents

Adolescents are more sensitive than adults to the neural and behavioral effects of psychostimulants, and exhibit greater vulnerability to drug abuse, dependence or relapse into these conditions. We have reported that cocaine pretreatment during adolescence promotes the expression of behavioral sensitization to a greater extent than when the pretreatment occurs at adulthood. Behavioral sensitization has been associated to the transition from drug use to addiction and is postulated to indicate heightened sensitivity to the appetitive motivational effects of drugs. The relationship between behavioral sensitization and conventional measures of drug reward, such as conditioned place preference (CPP), has yet to be thoroughly investigated, and little is known about age-related differences in this phenomenon. The present study tested cocaine-induced CPP in adolescent and adult mice exposed to cocaine (or vehicle) pretreatment, either in an intermittent or "binge" (i.e., heavy cocaine use on a single occasion, which increases the likelihood of experiencing cocaine-related problems) fashion. Cocaine administration induced behavioral sensitization to a greater extent in adolescent than in adult mice. Cocaine-induced CPP was fairly similar in vehicle pretreated adolescent and adult mice, yet greater in adolescent vs. adults after cocaine-induced sensitization. The results confirmed the higher sensitivity of adolescent mice to cocaine-induced behavioral sensitization and suggest its association with greater sensitivity to cocaine's rewarding effects.

Adolescent fluoxetine history impairs spatial memory in adult male, but not female, C57BL/6 mice

BACKGROUND

Epidemiological reports indicate that mood-related disorders are common in the adolescent population. The prevalence of juvenile major depressive disorder has resulted in a parallel increase in the prescription rates of fluoxetine (FLX) within this age group. Although such treatment can last for years, little is known about the enduring consequences of adolescent antidepressant exposure on memory-related performance.

METHODS

We exposed separate groups of adolescent (postnatal day [PD] 35) male and female C57BL/6 mice to FLX (20 mg/kg) for 15 consecutive days (PD35-49). Three weeks after FLX exposure (PD70), we assessed learning and memory performance on a single-day training object novelty recognition test, or a spatial memory task on the Morris water maze (MWM).

RESULTS

We found that FLX pretreatment did not influence performance on either the object novelty recognition task or the MWM, 24 h after training. Conversely, 48 h post spatial-training on the MWM, FLX pretreated male mice spent significantly less time on the quadrant of the missing platform during a standard probe trial. No differences in MWM performance were observed in the adult female mice pretreated with FLX.

LIMITATIONS

A limitation of this study is that normal adolescent mice (i.e., non-stressed) were evaluated for memory-related behavior three weeks after antidepressant exposure. Thus, it is possible that FLX pre-exposure in combination with animal models for the study of depression may yield different results.

CONCLUSION

Together, these results demonstrate enduring spatial memory-related deficiencies after pre-exposure to FLX during adolescence in male, but not female, C57BL/6 mice.

Sugar Addiction: From Evolution to Revolution

The obesity epidemic has been widely publicized in the media worldwide. Investigators at all levels have been looking for factors that have contributed to the development of this epidemic. Two major theories have been proposed: (1) sedentary lifestyle and (2) variety and ease of inexpensive palatable foods. In the present review, we analyze how nutrients like sugar that are often used to make foods more appealing could also lead to habituation and even in some cases addiction thereby uniquely contributing to the obesity epidemic. We review the evolutionary aspects of feeding and how they have shaped the human brain to function in "survival mode" signaling to "eat as much as you can while you can." This leads to our present understanding of how the dopaminergic system is involved in reward and its functions in hedonistic rewards, like eating of highly palatable foods, and drug addiction. We also review how other neurotransmitters, like acetylcholine, interact in the satiation processes to counteract the dopamine system. Lastly, we analyze the important question of whether there is sufficient empirical evidence of sugar addiction, discussed within the broader context of food addiction.

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.

Effects of environmental enrichment upon ethanol-induced conditioned place preference and pre-frontal BDNF levels in adolescent and adult mice

Environmental enrichment (EE) provides a non-pharmacological tool to alter drug-induced reward, yet its effects on ethanol-induced reward remain controversial. We analyzed adolescent vs. adult (mice) differences in the influence of EE on ethanol-induced conditioned place preference (CPP). The effects of these treatments on brain-derived neurotrophic factor (BDNF) levels in the prefrontal cortex were examined in a separate group of animals. Ethanol-induced CPP was found in adults, and it was similar in EE and in animals reared under standard housing conditions (SC). Adolescents kept under EE, but not those in SC, exhibited CPP. Among SC, but not among EE, adolescents, BDNF levels were significantly lower in those treated with ethanol than in those given vehicle. These results indicate that, compared to adults, adolescent exhibited reduced sensitivity to ethanol’s rewarding effects, yet the youth but not the adults exhibited sensitivity to the promoting effect of EE upon CPP by ethanol. Ethanol significantly reduced BDNF levels in adolescents reared under standard housing conditions, but not in adult mice nor in adolescents given EE housing conditions. The present results add to the plethora of adolescent-specific responses to ethanol or to environmental stimuli that may put the youth at risk for escalation of ethanol intake.

Prior Exposure to Alcohol Has No Effect on Cocaine Self-Administration and Relapse in Rats: Evidence from a Rat Model that Does Not Support the Gateway Hypothesis

The gateway hypothesis posits that initial exposure to legal drugs promotes subsequent addiction to illicit drugs. However, epidemiological studies are correlational and cannot rule out the alternative hypothesis of shared addiction vulnerability to legal and illegal drugs. We tested the gateway hypothesis using established rat alcohol exposure procedures and cocaine self-administration and reinstatement (relapse) procedures. We gave Wistar or alcohol-preferring (P) rats intermittent access to water or 20% alcohol in their homecage for 7 weeks (three 24-h sessions/week). We also exposed Wistar rats to air or intoxicating alcohol levels in vapor chambers for 14-h/day for 7 weeks. We then tested the groups of rats for acquisition of cocaine self-administration using ascending cocaine doses (0.125, 0.25, 0.5, 1.0 mg/kg/infusion) followed by a dose-response curve after acquisition of cocaine self-administration. We then extinguished lever pressing and tested the rats for reinstatement of drug seeking induced by cocaine-paired cues and cocaine priming (0, 2.5, 5, 10 mg/kg, i.p.). Wistar rats consumed moderate amounts of alcohol (4.6 g/kg/24 h), P rats consumed higher amounts of alcohol (7.6 g/kg/24 h), and Wistar rats exposed to alcohol vapor had a mean blood alcohol concentration of 176.2 mg/dl during the last week of alcohol exposure. Alcohol pre-exposure had no effect on cocaine self-administration, extinction responding, and reinstatement of drug seeking. Pre-exposure to moderate, high, or intoxicating levels of alcohol had no effect on cocaine self-administration and relapse to cocaine seeking. Our data do not support the notion that alcohol is a gateway drug to cocaine.

Binge ethanol drinking during adolescence modifies cocaine responses in mice

Binge ethanol drinking is an emerging pattern of excessive consumption among adolescents and young adults. Repeated ethanol intoxication has negative consequences during critical periods of brain development. Therefore, binge ethanol intake represents a vulnerability factor that promotes subsequent manifestations of neuropsychiatric disorders. In this study, we investigated the effects of oral binge ethanol intake during adolescence on the subsequent effects of cocaine in C57BL/6 mice. Firstly, we evaluated the oral ethanol intake of two binge ethanol procedures with different ethanol concentrations (20% v/v versus 30%, v/v). The highest ethanol intake was found in mice exposed to the lower ethanol concentration (20% v/v). In a second experiment, mice exposed to binge ethanol procedure were evaluated to study the effects of cocaine on locomotor activity, behavioural sensitization, and the reinforcing effects of cocaine in the self-administration paradigm. Mice exposed to ethanol binging showed discrete detrimental effects in responses to cocaine in the different experiments evaluated. Our findings revealed that the pattern of binge ethanol consumption in adolescent mice here evaluated produced a weak facilitation of cocaine responses. The present study highlights the importance of interventions to limit the deleterious effects of binge ethanol drinking during adolescence.

Sex differences in subjective and objective responses to a stimulant medication (methylphenidate): Comparisons between overweight/obese adults with and without binge-eating disorder

OBJECTIVE

The purpose of this study was to examine sex differences in response to a single dose of a psychomotor-stimulant medication (methylphenidate: MP) and to assess whether expected differences were moderated by binge-eating disorder (BED) status. It is anticipated that findings will shed light on factors that contribute to response variation in the use of stimulant pharmacotherapy to treat BED.

METHOD

The study employed a double-blind, drug-placebo, cross-over design in overweight/obese adults with BED (n = 90) and without BED (n = 108). Emotional/mood ratings were assessed every 15 minutes after oral administration of the drug/placebo, and appetite, cravings, and consumption were assessed during a laboratory-based snack-food challenge.

RESULTS

Women reported earlier and more sustained "overall" effects of the drug-including "feeling high"-than the men. There was also a significantly greater suppression in appetite ratings, food cravings, and food consumption from the placebo to the drug condition among the women. Indeed, among men there were no significant differences between the two conditions on any of the food-related variables. BED status also did not moderate any of the drug-placebo differences.

DISCUSSION

These findings are relevant to the use of stimulant pharmacotherapy for BED, and raise the possibility that overweight/obese men may be relatively less responsive to this form of treatment. © 2015 Wiley Periodicals, Inc. (Int J Eat Disord 2016; 49:473-481).