Reduced sensitivity to reinforcement in adolescent compared to adult Sprague-Dawley rats of both sexes

Timing of methamphetamine exposure during adolescence differentially influences parvalbumin and perineuronal net immunoreactivity in the medial prefrontal cortex of female, but not male, rats

Adolescence involves significant reorganization within the medial prefrontal cortex (mPFC), including modifications to inhibitory neurotransmission mediated through parvalbumin (PV) interneurons and their surrounding perineuronal nets (PNNs). These developmental changes, which result in increased PV neuron activity in adulthood, may be disrupted by drug use resulting in lasting changes in mPFC function and behavior. Methamphetamine (METH), which is a readily available drug used by some adolescents, increases PV neuron activity and could influence the activity-dependent maturational process of these neurons. In the present study, we used male and female Sprague Dawley rats to test the hypothesis that METH exposure influences PV and PNN expression in a sex- and age-specific manner. Rats were injected daily with saline or 3.0 mg/kg METH from early adolescence (EA; 30-38 days old), late adolescence (LA; 40-48 days old), or young adulthood (60-68 days old). One day following exposure, effects of METH on PV cell and PNN expression were assessed using immunofluorescent labeling within the mPFC. METH exposure did not alter male PV neurons or PNNs. Females exposed in early adolescence or adulthood had more PV expressing neurons while those exposed in later adolescence had fewer, suggesting distinct windows of vulnerability to changes induced by METH exposure. In addition, females exposed to METH had more PNNs and more intense PV neuron staining, further suggesting that METH exposure in adolescence uniquely influences development of inhibitory circuits in the female mPFC. This study indicates that the timing of METH exposure, even within adolescence, influences its neural effects in females.

Modeling methamphetamine use disorder in mammals: Sex differences in behavioral, biochemical, and transcriptional consequences

Methamphetamine (METH) is the most commonly misused amphetamine-type stimulant throughout the globe. METH is very rewarding, and its misuse can lead to a diagnosis of METH use disorder (MUD). Although METH use is observed in both sexes, there are, however, reported differences in the clinical manifestations of METH use and its consequences. These observations indicate the need for more research on the long-term sex-dependent consequences of METH taking in both preclinical and clinical settings. In effect, sex is a biological variable that can impact conclusions drawn from various basic and clinical studies. Thus, the present chapter provides a succinct review of the current state of the research on METH and its sex-associated consequences. In addition to behavioral and cognitive aspects of METH use, we discuss METH-induced changes in neurotransmitter systems and structures in the brain. Thus, the book chapter serves to highlight the significance of sex as a critical element that needs to be considered during discussions of novel therapeutic approaches to MUD.

The role of sex and drug use during adolescence in determining the risk for adverse consequences of amphetamines

Use of amphetamines during adolescence, a critical period of brain development and reorganization, may lead to particularly adverse outcomes that are long-lasting. Similarly, female users may be uniquely vulnerable to certain aspects of drug use. A recognition of the role of use during adolescence and sex on outcomes of amphetamine and methamphetamine exposure are of critical importance in understanding and treating substance use disorders. This chapter highlights what human research, which has been largely epidemiological, suggests about sex and age differences in drug use patterns and outcomes. We also discuss work in laboratory animals that has typically utilized rats or mice exposed to drugs in a non-contingent manner (i.e., involuntarily) or through volitional self-administration. Lastly, we draw attention to the fact that advancing our understanding of the effects of amphetamine and methamphetamine use, the development of problematic drug taking, and the mechanisms that contribute to relapse will require an emphasis on inclusion of age and sex as moderating factors in future studies.

Sex differences in methamphetamine use disorder perused from pre-clinical and clinical studies: Potential therapeutic impacts

Methamphetamine (METH) use, and misuse are associated with severe socioeconomic consequences. METH users develop tolerance, lose control over drug taking behaviors, and suffer frequent relapses even during treatment. The clinical course of METH use disorder is influenced by multifactorial METH-induced effects on the central and peripheral nervous systems. Although these METH-induced consequences are observed in humans of all ages, races, and sexes, sexual dimorphism in these outcomes have been observed in both pre-clinical and clinical settings. In this review, we have provided a detailed presentation of the sex differences reported in human and animal studies. We have therefore presented data that identified the influences of sex on METH pharmacokinetics, METH-induced changes in behaviors, cognitive processes, structural changes in the brain, and the effects of the drug on neurotransmitter systems and molecular mechanisms. Finally, we highlighted the potential significance of sex as a critical variable that should be considered when planning the development of new pharmacotherapeutic approaches against MEH use disorder in humans.

Effects of the GluN2B antagonist, Ro 25-6981, on extinction consolidation following adolescent- or adult-onset methamphetamine self-administration in male and female rats

Previous work suggests adolescent rats have deficient extinction consolidation relative to adults. Although the mechanisms underlying this age difference are currently unknown, studies in adult rats have implicated GluN2B-containing N-methyl-d-aspartate (NMDA) receptor function in extinction consolidation of drug-associated memory. Importantly, GluN2B neurotransmission emerges during adolescent development, and drugs of abuse during adolescence may delay the development of extinction consolidation by disrupting the ontogeny of GluN2B function. Here, we trained Sprague-Dawley rats of both sexes to self-administer methamphetamine [METH, 0.1 mg/kg/infusion intravenous (i.v.)] beginning during adolescence [postnatal (P) day 41] or adulthood (P91). Rats were given short access (2 h) to self-administer METH in seven daily sessions followed by 14 sessions with long access (6 h). Subsequently, rats underwent four daily 30-minute extinction sessions with immediate postsession injections of either a GluN2B antagonist [Ro25-6981; 6 mg/kg, intraperitoneal (i.p.)] or a vehicle solution. After four daily 2-h extinction sessions, a priming injection (1 mg/kg METH, i.p.) was given prior to a final 2-h reinstatement session. During LgA, adolescent-onset rats earn more METH than adult-onset rats and display greater drug-loading behavior. Rats reduced their drug-seeking behavior across the extinction sessions, with no significant group differences. Rats reinstated drug-seeking following the METH-priming injection, with females displaying greater reinstatement than males. These results do not support our a priori hypothesis that adolescent-onset METH use disrupts the ontogeny of GluN2B transmission and contributes to age-of-onset differences in extinction of METH-seeking. However, our findings suggest that age-of-onset contributes to excessive METH-taking, while sex confers vulnerability to relapse to METH-seeking.

Age-specific treatment effects of orexin/hypocretin-receptor antagonism on methamphetamine-seeking behavior

BACKGROUND

Worldwide methamphetamine (METH) use has increased significantly over the last 10 years, and in the US, METH dependence has sky-rocketed among individuals with opioid use disorder. Of significant concern, METH use is gaining popularity among groups with susceptibility to developing severe substance use disorders, such as women and adolescents. Nevertheless, there is no established pharmacotherapy for METH addiction. Emerging evidence has identified the orexin/hypocretin system as an important modulator of reward-driven behavior and a potential target for the treatment of drug addiction and relapse. However, to date, there have been no investigations into the therapeutic efficacy of orexin/hypocretin receptor antagonists for METH-motivated behavior in adolescents or adults. In the present study, we examined the effects of selective antagonists of the orexin-1 (SB-334867, 20 mg/kg) and orexin-2 (TCS-OX2-29, 20 mg/kg) receptors on the reinstatement of METH seeking in both adolescent and adult male and female rats.

METHODS

Rats were trained to self-administer METH (0.05 mg/kg/inf, iv) during two 2-h sessions/day for 5 days. Following 20 sessions of extinction over 10 days, a within-subjects design was used to test for METH seeking precipitated by METH (1 mg/kg, ip) or METH cues after systemic pretreatment with SB-334867 or TCS-OX2-29.

RESULTS

SB-334867 reduced cue-induced reinstatement in males and females, regardless of age. Additionally, METH-induced METH seeking was attenuated by SB-334867 in adolescents and by TCS-OX2-29 in adults.

CONCLUSION

Selective orexin/hypocretin receptor antagonists have significant therapeutic potential for diminishing METH-seeking behavior, although their treatment efficacy may be influenced by age.

AMPed-up adolescents: The role of age in the abuse of amphetamines and its consequences on cognition and prefrontal cortex development

Adolescent use of amphetamine and its closely related, methylated version methamphetamine, is alarmingly high in those who use drugs for nonmedical purposes. This raises serious concerns about the potential for this drug use to have a long-lasting, detrimental impact on the normal development of the brain and behavior that is ongoing during adolescence. In this review, we explore recent findings from both human and laboratory animal studies that investigate the consequences of amphetamine and methamphetamine exposure during this stage of life. We highlight studies that assess sex differences in adolescence, as well as those that are designed specifically to address the potential unique effects of adolescent exposure by including groups at other life stages (typically young adulthood). We consider epidemiological studies on age and sex as vulnerability factors for developing problems with the use of amphetamines, as well as human and animal laboratory studies that tap into age differences in use, its short-term effects on behavior, and the long-lasting consequences of this exposure on cognition. We also focus on studies of drug effects in the prefrontal cortex, which is known to be critically important for cognition and is among the later maturing brain regions. Finally, we discuss important issues that should be addressed in future studies so that the field can further our understanding of the mechanisms underlying adolescent use of amphetamines and its outcomes on the developing brain and behavior.

Extended access self-administration of methamphetamine is associated with age- and sex-dependent differences in drug taking behavior and recognition memory in rats

Individuals who begin drug use during early adolescence experience more adverse consequences compared to those initiating later, especially if they are female. The mechanisms for these age and gender differences remain obscure, but studies in rodents suggest that psychostimulants may disrupt the normal ontogeny of dopamine and glutamate systems in the prefrontal cortex (PFC). Here, we studied Sprague-Dawley rats of both sexes who began methamphetamine (METH, i.v.) self-administration in adolescence (postnatal [P] day 41) or adulthood (P91). Rats received seven daily 2-h self-administration sessions with METH or saccharin as the reinforcer, followed by 14 daily long access (LgA; 6 h) sessions. After 7 and 14 days of abstinence, novel object (NOR) or object-in-place (OiP) recognition was assessed. PFC and nucleus accumbens were collected 7 days after the final cognitive test and NMDA receptor subunits and dopamine D1 receptor expression was measured. We found that during LgA sessions, adolescent-onset rats escalated METH intake more rapidly than adult-onset rats, with adolescent-onset females earning the most infusions. Adolescent-onset rats with a history of METH self-administration exhibited modest deficits in OiP compared to their adult-onset counterparts, but there was no sex difference and self-administration groups did not differ from naïve control rats. All rats displayed intact novel object recognition memory. We found no group differences in D1 and NMDA receptor expression, suggesting no long-lasting alteration of ontogenetic expression profiles. Our findings suggest that adolescent-onset drug use is more likely to lead to compulsive-like patterns of drug-taking and modest dysfunction in PFC-dependent cognition.

Effects of chronic stress on reinstatement of palatable food seeking: Sex differences and relationship to trait anxiety

Previous research in our lab has established a causal role for chronic stress exposure in subsequent increases in relapse-like behaviors in male rats with a history of palatable food self-administration. Given that many of the neurobehavioral consequences of stress are sex dependent, we aimed to determine whether sex differences exist with regard to the effects of chronic stress on relapse. Additionally, because high trait anxiety confers vulnerability to stress-related disorders, we examined whether individual differences in trait anxiety were related to differences in relapse-like behavior after chronic stress exposure. Following elevated plus maze testing for classification into high- or low-anxiety phenotypes, male and female rats responded for highly palatable food pellets. During subsequent extinction training, stress was manipulated (0 or 90 min restraint/day for 7 days). Rats were then tested for cue- and pellet priming-induced reinstatement of palatable food seeking. Results showed that female rats displayed higher levels of responding during cue-induced reinstatement tests compared to males, and that a history of chronic stress caused an attenuation of cue-induced reinstatement in female, but not male, rats. Regarding pellet priming-induced reinstatement, there was a three-way interaction such that neither stress history nor anxiety phenotype was related to reinstatement in females, but a history of stress in males caused increased and decreased responding in low- and high-anxiety rats, respectively. These results suggest that biological sex and trait anxiety level may help to explain differences in vulnerability to relapse among individuals exposed to chronic stress. Such information may be useful in designing more personalized and effective treatments for obesity and eating disorders.

Age- and sex-dependent effects of methamphetamine on cognitive flexibility and 5-HT2C receptor localization in the orbitofrontal cortex of Sprague-Dawley rats

Adolescents and females experience worse outcomes of drug use compared to adults and males. This could result from age- and sex-specific consequences of drug exposure on brain function and cognitive behavior. In the current study, we examined whether a history of intravenous methamphetamine (METH) self-administration impacted cognitive flexibility and 5-HT_2CR localization in the orbitofrontal cortex (OFC) in an age- and sex-dependent manner. Strategy shifting was assessed in male and female Sprague-Dawley rats that had self-administered METH (0.08 mg/kg/inf) or received non-contingent infusions of saline during periadolescence or young adulthood. After all rats reached adulthood, they were tested in an operant strategy shifting task and their brains were subsequently analyzed using immunofluorescence to quantify co-localization of 5-HT_2C receptors with parvalbumin interneurons in the OFC. We found that adolescent-onset females were the only group impaired during discrimination and reversal learning, but they did not exhibit changes in localization of 5-HT_2C receptors. In contrast, adult-onset males exhibited a significant increase in co-localization of 5-HT_2C receptors within parvalbumin interneurons in the left hemisphere of the OFC. These studies reveal that age and sex differences in drug-induced deficits in reversal learning and 5-HT_2CR co-localization with parvalbumin interneurons are dissociable and can manifest independently. In addition, these data highlight the potential for certain treatment approaches to be more suitable in some populations compared to others, such as alleviating drug-induced cognitive deficits as a focus for treatment in adolescent females.

Age and sex differences in behavioral flexibility, sensitivity to reward value, and risky decision-making

Compared with adults, adolescent behavior is often characterized by reduced behavioral flexibility, increased sensitivity to reward, and increased likelihood to take risks. These traits, which have been hypothesized to confer heightened vulnerability to psychopathologies such as substance use disorders (SUDs), have been the focus of studies in laboratory animal models that seek to understand their neural underpinnings. However, rodent studies to date have typically used only males and have adopted standard methodological practices (e.g., weight loss inducing food restriction) that are likely to have a disparate impact on adolescents compared with adults. Here, we used adolescent and adult Sprague-Dawley rats of both sexes to study instrumental behavior tasks that assess behavioral flexibility (strategy shifting and reversal learning; Experiment 1), sensitivity to reward value (outcome devaluation; Experiment 2), and risky decision making (probability discounting; Experiment 3). In Experiment 1, we found that adolescents were faster to acquire reversal learning than adults but there were no differences in strategy shifting. In Experiments 2 and 3, adolescents and adults were equally sensitive to changes in reward value and exhibited similar reductions in preference for a large reward when reinforcement probability was decreased. However, adolescents responded more efficiently and earned reinforcers at a higher rate than their same-sex, adult counterparts. Together, these findings provide only limited support for the existence of an "adolescent-typical" phenotype in Sprague-Dawley rats and instead suggest that age differences in the expression of these behaviors may depend on conditions such as pubertal status and motivational state. (PsycINFO Database Record