Stress in adolescence and drugs of abuse in rodent models: role of dopamine, CRF, and HPA axis

Effects of Adolescent Social Isolation on PFC's β-Catenin Levels and Anxiety-Like Behaviors in Male and Female Rats: Study of the Role of Dopaminergic D2 Receptors

Adolescence is a key period of development when major cognitive and neurobiological changes occur. Results from our lab showed that 5 days of social isolation in adolescent rats led to molecular changes in the Wnt/β-catenin pathway and to higher cocaine responses during adulthood. We assessed whether 5 days of social isolation (SI) during adolescence would impact on β-catenin levels in the prefrontal cortex (PFC) and nucleus accumbens (NAcc) as well as on anxiety-like behaviors in a sex- and time-dependent manner. We also investigated the role of dopaminergic neurotransmission on that impact, by using repeated administration of a D2 antagonist. Male and female Wistar rats were socially isolated between postnatal day (PND)30 to 35 or kept in their home cages (non-isolated), while they were treated with sulpiride (100 mg/kg, ip) or vehicle. Anxiety-like behaviors and exploratory activity were estimated by the open field test at 24 h (PND36) or 9 days (PND44) after isolation. Then, they were euthanized at PND36 or PND45, and β-catenin levels were analyzed by Western blot in PFC and NAcc. Our findings show that a brief SI during adolescence leads to a long-term impact on both β-catenin levels (10 days, PND45) and anxiety-like behaviors (9 days, PND44) with a significant increase and decrease, respectively, in female rats. In contrast, male rats show a rapid decrease in β-catenin levels in the PFC with no changes in anxiety-like behaviors (24 h, PND36). These suggest that adolescent SI induces mostly long-term changes in female while short term changes in male rats. Moreover, these changes seem to be modulated by dopaminergic neurotransmission since a sulpiride treatment during isolation prevented them.

The double-edged sword of stress: A systematic meta-analysis on how stress impacts creativity

The present study provides up-to-date meta-analytical estimates of the impact of experimentally induced stress on individuals' creative performance. Using a three-level meta-analytic model, we observed an overall negative effect of stress on creativity (d = -0.20). Our analysis reveals that this relationship is nuanced, and influenced by a variety of factors. Social-evaluative threats (SETs) did not significantly affect creativity overall (d = -0.08). Specifically, tests significantly reduced creativity, while competition showed a non-significant positive trend and (expected) performance evaluation showed a non-significant negative trend. Furthermore, results showed that mild SETs (one element) slightly but not significantly increased creativity, whereas severe SETs (three elements) significantly decreased it, indicating a curvilinear relationship. Non-social stressors, including time pressure and physical stress, significantly hindered creative performance (d = -0.45), with challenging tasks also showing a negative but non-significant effect. Additionally, the impact of stress on creativity varied by age group. Children's creativity was notably reduced by competition, physical stress, and challenging tasks, whereas adults and adolescents' creativity appeared to benefit from competition. Adults' creative performance was most negatively impacted by time pressure and remained relatively stable across other stressors. These findings underscore the complex and multifaceted nature of the effects of stress on creativity. The theoretical and practical implications are discussed.

Adolescent social isolation increases social behavior in Wistar rats: Role of post-weaning isolation housing on Social Familiarity-induced Anxiolysis (SoFiA) and social memory in adulthood

Social connectedness is a critical part of adolescent development. Social support provides a robust facilitator for managing anxiety disorders that afflict nearly 1⁄3 of the U.S. adult population at some point in life. Consequently, it is important to understand the neurobiological mechanisms underlying the impact of social affiliation, or lack thereof, on treating or causing maladaptive anxiety states. In the current experiment, we manipulated the housing conditions in Wistar rats beginning on postnatal day (P) 21, rearing them in pairs (RP), in isolation (RI), or purchased adults rats reared at the facility (RF). We tested adult rats in the open field test, the social interaction habituation test (SI-Hab), which is a social safety learning animal model, and in the social recognition test (SRT), which is an animal model of sociability and social memory. Rats RI showed generalized increases in SI time compared to rats RP. However, there was no effect of rearing on acquisition of social safety during SI-Hab. During the SRT, rats RI exhibited a preference for a novel rat indicating robust social memory, whereas rats RP did not. Rats RF exhibited higher thigmotaxis relative to RP and RI and lower movement compared to RP in the novel open field. Numerous social and non-social behaviors were correlated with each other, and some depended on rearing condition. Based on correlation differences between RI and RP rats, RI history may be more conducive to the anxiolytic aspects of the SI-Hab protocol, which may improve the ability to deal with a perceived threat.

Acute Restraint Stress Enhances Prosocial Behavior in Rats via Oxytocin and Fear-Related Circuits

BACKGROUND

Stress is a critical determinant of social behavior, with oxytocin playing a key role in buffering stress effects and facilitating social bonding. However, the relationship between stress-induced fear and oxytocin-associated sociability remains unclear, particularly in contexts reminiscent of prior stress. This study investigates whether acute restraint stress (ARS) alters anxiety-related behaviors and prosocial choices, and whether these effects can be modulated by pharmacological intervention targeting the oxytocin and corticotropin-releasing hormone (CRH) systems.

METHODS

Sprague-Dawley rats were subjected to ARS and assessed for anxiety-like behavior using the elevated T-maze (ETM) and for prosocial behavior using the social choice test (SCT). The effects of the oxytocin receptor antagonist L-368899 and CRH receptor antagonist antalarmin were evaluated in this paradigm. Plasma corticosterone was checked peripherally and the tissue concentrations of serotonin (5-HT), dopamine (DA), and norepinephrine (NE) were measured in the hippocampus, medial prefrontal cortex (mPFC), and amygdala to assess stress-related neurochemical changes in the fear circuit.

RESULTS

(i) ARS rats showed a significant increase in prosocial preference compared to control, an effect blocked by L-368899 or antalarmin. (ii) ARS rats exhibited reduced corticosterone levels, together with shorter avoidance latency, and longer escape latency in the ETM. (iii) Neurochemically, ARS rats had decreased DA and increased NE levels in the mPFC, both of which were normalized by L-368899 treatment.

CONCLUSIONS

Oxytocin modulates stress-induced alterations in monoaminergic activity within the mPFC, influencing social choice behavior. These findings provide new insights into the neurobiological mechanisms underlying stress-related sociability and the context-dependent role of oxytocin in fear memory and social behavior.

Reduced sensitivity to cocaine effects and changes in mesocorticolimbic dopamine receptors in adolescent sexually active female rats

RATIONALE

The sexual behavior of the female rat is highly motivated, and the mesocorticolimbic dopaminergic system -involved in psychostimulants effects- has been implicated in its regulation. Female rats begin to express sexual behavior during adolescence, a period during which this system is not yet mature.

OBJECTIVE

To examine the impact of cocaine on sexual motivation and behavior of adolescent and adult female rats, and to determine the dopamine receptors binding in mesocorticolimbic areas of these females.

METHODS

The effect of acute administration of cocaine (0.0, 10.0, and 20.0 mg/kg, intraperitoneally) on the male´s incentive value for females and on their sexual behavior in late adolescent (45-55 days old) and adult (100-120 days old) rats was assessed during late proestrus. The binding of D1-like and D2-like receptors in the striatum and medial prefrontal cortex (mPFC) of adolescent and adult rats were determined by autoradiography.

RESULTS

Cocaine did not affect females´ preference for the male. However, 10 mg/kg of cocaine reduced the expression of sexual motivated responses and 20 mg/kg also diminished sexual receptivity exclusively in adult subjects. Moreover, cocaine-induced a more pronounced hyper-locomotion in adult than in late adolescent rats. Late adolescent females exhibited higher dopamine receptors binding in the mPFC and reduced D2-like receptors binding in the Nucleus Accumbens shell when compared to adults.

CONCLUSIONS

Late adolescent females are less sensitive than adults to the detrimental effects of cocaine on sexual behavior and locomotion. This phenomenon is accompanied by variation in dopamine receptors in mesocorticolimbic areas affected by this psychostimulant.

Dopamine D1 receptor agonist alleviates post-weaning isolation-induced neuroinflammation and depression-like behaviors in female mice

BACKGROUND

Major depressive disorder is a significant global cause of disability, particularly among adolescents. The dopamine system and nearby neuroinflammation, crucial for regulating mood and processing rewards, are central to the frontostriatal circuit, which is linked to depression. This study aimed to investigate the effect of post-weaning isolation (PWI) on depression in adolescent mice, with a focus on exploring the involvement of microglia and dopamine D1 receptor (D1R) in the frontostriatal circuit due to their known links with mood disorders.

RESULTS

Adolescent mice underwent 8 weeks of PWI before evaluating their depression-like behaviors and the activation status of microglia in the frontostriatal regions. Selective D1-like dopamine receptor agonist SKF-81,297 was administered into the medial prefrontal cortex (mPFC) of PWI mice to assess its antidepressant and anti-microglial activation properties. The effects of SKF-81,297 on inflammatory signaling pathways were examined in BV2 microglial cells. After 8 weeks of PWI, female mice exhibited more severe depression-like behaviors than males, with greater microglial activation in the frontostriatal regions. Microglial activation in mPFC was the most prominent among the three frontostriatal regions examined, and it was positively correlated with the severity of depression-like behaviors. Female PWI mice exhibited increased expression of dopamine D2 receptors (D2R). SKF-81,297 treatment alleviated depression-like behaviors and local microglial activation induced by PWI; however, SKF-81,297 induced these alterations in naïve mice. In vitro, SKF-81,297 decreased pro-inflammatory cytokine release and phosphorylations of JNK and ERK induced by lipopolysaccharide, while in untreated BV2 cells, SKF-81,297 elicited inflammation.

CONCLUSIONS

This study highlights a sex-specific susceptibility to PWI-induced neuroinflammation and depression. While targeting the D1R shows potential in alleviating PWI-induced changes, further investigation is required to evaluate potential adverse effects under normal conditions.

ERK2 Signaling in the Nucleus Accumbens Facilitates Stress Susceptibility and Cocaine Reinstatement

Background

Second-messenger signaling within the mesolimbic reward circuit plays a key role in the negative effects of stress and the underlying mechanisms that promote drug abuse. Because the nucleus accumbens (NAc) integrates reward valence, we investigated how ERK2 (extracellular signal-regulated protein kinase-2) signaling affects the development of stress-related comorbidities, including negative affect and drug sensitivity.

Methods

We assessed how chronic unpredictable stress influenced the phosphorylation of ERK2-signaling proteins within the NAc of male Sprague Dawley rats. Using a herpes simplex virus, we either upregulated or downregulated NAc ERK2 activation and evaluated behavioral responses to stress-eliciting stimuli (elevated plus maze, open field, forced swim test) and cocaine-seeking behavior (conditioned place preference, self-administration). We also examined ERK2-mediated modifications in spine morphology of medium spiny neurons within the NAc.

Results

Chronic unpredictable stress increased the phosphorylation of ERK2-signaling proteins within the NAc. Viral-mediated activation of NAc ERK2 enhanced susceptibility to both depression- and anxiety-related stimuli and increased cocaine-seeking behavior (conditioned place preference and reinstatement). These behavioral changes were associated with an increase in stubby and mushroom spines of NAc medium spiny neurons. Conversely, downregulation of ERK2 activation attenuated affect-related behavioral responses in the forced swim test and blunted cocaine's rewarding effects without influencing NAc spine morphology.

Conclusions

NAc ERK2 contributes to stress-induced behavioral deficits, including anxiety- and depression-like phenotypes, while promoting cocaine-seeking behavior. These findings suggest that ERK2 signaling in the NAc plays a role in the comorbidity of these related syndromes.

How childhood adversity affects components of decision making

Extreme and chronic adverse experiences in childhood are linked to disruptions in a wide range of behavioral processes, including self-regulation, increased risk taking, and impulsivity. One proposed mechanism for these effects is alterations in how children learn and use information about rewards and risk in their environment. This type of decision making is a complex and multifaceted process consisting of distinct subcomponents, each of which may have varying effects on behavior. Here, we conducted a systematic review of the literature examining how reward and risk related decision making is influenced by childhood adversity. We aimed to identify whether childhood adversity is associated with alterations in how children learn about value information and how they subsequently use that information to inform decisions. Results suggest adverse experiences in childhood primarily impacts how individuals prioritize avoidance of risk and leads to devaluation of rewards.

Region-specific neuroadaptations of CRF1 and CRF2 expression following heroin exposure in female rats

While stress increases vulnerability to development of addiction, the recruitment of corticotropin releasing factor (CRF) with excessive drug use heightens the risk of stress-induced relapse. CRF signaling is transmitted via CRF1 and CRF2 receptors, but the roles of these receptors in heroin self-administration and related neuroadaptations of the CRF system within mesolimbic brain loci are not well understood. In this study, we first investigated the causal role of CRF1 and CRF2 receptors in heroin self-administration. Intracerebroventricular (ICV) microinjections of antalarmin (a CRF1 antagonist) or astressin-2B (a CRF2 antagonist) caused brief, dose-dependent reductions in heroin self-administration in female rats, suggesting that these receptors play a critical role in heroin-motivated behaviors. We then used western blotting to examine neuroadaptive changes to CRF1 and CRF2 receptor expression in key forebrain and midbrain regions associated with opioid addiction. Female Long Evans rats treated with escalating doses of heroin for 16 days demonstrated significantly higher naloxone-precipitated withdrawal symptoms than saline-treated rats. Heroin-treated rats showed a significant decrease in CRF1 receptor protein expression in the ventral tegmental area (VTA) and an increase in the nucleus accumbens (NAc) but no changes in the prefrontal cortex (PFC), insula, dorsal striatum (dSTR), dorsal hippocampus (dHippo), anterior hypothalamus (HYPTH), amygdala, or substantia nigra (SN) as compared to saline-treated rats. After chronic heroin exposure, CRF2 receptor expression was significantly downregulated in the dHippo, VTA and HYPTH but not in the other brain regions we investigated. The results of this study suggest that: (1) CRF1 and CRF2 receptors play an important role in self-administration and (2) heroin exposure may lead to region-specific neuroadaptation of CRF1 and CRF2 receptors. Such neuroadaptations might in part contribute to the continuation of drug use and stress-induced relapse.

Adolescent stress differentially modifies dopamine and norepinephrine release in the medial prefrontal cortex of adult rats

Adolescent stress (AS) has been associated with higher vulnerability to psychiatric disorders such as schizophrenia, depression, or drug dependence. Moreover, the alteration of brain catecholamine (CAT) transmission in the medial prefrontal cortex (mPFC) has been found to play a major role in the etiology of psychiatric disturbances. We investigated the effect of adolescent stress on CAT transmission in the mPFC of freely moving adult rats because of the importance of this area in the etiology of psychiatric disorders, and because CAT transmission is the target of a relevant group of drugs used in the therapy of depression and psychosis. We assessed basal dopamine (DA) and norepinephrine (NE) extracellular concentrations (output) by brain microdialysis in in the mPFC of adult rats that were exposed to chronic mild stress in adolescence. To ascertain the role of an altered release or reuptake, we stimulated DA and NE output by administering either different doses of amphetamine (0.5 and 1.0 mg / kg s.c.), which by a complex mechanism determines a dose dependent increase in the CAT output, or reboxetine (10 mg/kg i.p.), a selective NE reuptake inhibitor. The results showed the following: (i) basal DA output in AS rats was lower than in controls, while no difference in basal NE output was observed; (ii) amphetamine, dose dependently, stimulated DA and NE output to a greater extent in AS rats than in controls; (iii) reboxetine stimulated NE output to a greater extent in AS rats than in controls, while no difference in stimulated DA output was observed between the two groups. These results show that AS determines enduring effects on DA and NE transmission in the mPFC and might lead to the occurrence of psychiatric disorders or increase the vulnerability to drug addiction.

Comprehensive Review of Chronic Stress Pathways and the Efficacy of Behavioral Stress Reduction Programs (BSRPs) in Managing Diseases

The connection between chronic psychological stress and the onset of various diseases, including diabetes, HIV, cancer, and cardiovascular conditions, is well documented. This review synthesizes current research on the neurological, immune, hormonal, and genetic pathways through which stress influences disease progression, affecting multiple body systems: nervous, immune, cardiovascular, respiratory, reproductive, musculoskeletal, and integumentary. Central to this review is an evaluation of 16 Behavioral Stress Reduction Programs (BSRPs) across over 200 studies, assessing their effectiveness in mitigating stress-related health outcomes. While our findings suggest that BSRPs have the potential to enhance the effectiveness of medical therapies and reverse disease progression, the variability in study designs, sample sizes, and methodologies raises questions about the generalizability and robustness of these results. Future research should focus on long-term, large-scale studies with rigorous methodologies to validate the effectiveness of BSRPs.

Sex-dependent effects of acute stress in adolescence or adulthood on appetitive motivation

RATIONALE

Intensely stressful experiences can lead to long-lasting changes in appetitive and aversive behaviors. In humans, post-traumatic stress disorder increases the risk of comorbid appetitive disorders including addiction and obesity. We have previously shown that an acute stressful experience in adult male rats suppresses motivation for natural reward.

OBJECTIVES

We examine the impact of sex and age on the effects of intense stress on action-based (instrumental) and stimulus-based (Pavlovian) motivation for natural reward (food).

METHODS

Rats received 15 unsignaled footshocks (stress) in a single session followed by appetitive training and testing in a distinct context. In Experiment 1, stress occurred in either adolescence (PN28) or adulthood (PN70) with appetitive training and testing beginning on PN71 for all rats. In Experiment 2, stress and appetitive training/testing occurred in adolescence.

RESULTS

Acute stress in adolescent females suppressed instrumental motivation assessed with progressive ratio testing when testing occurred in late adolescence or in adulthood, whereas in males stress in adolescence did not suppress instrumental motivation. Acute stress in adulthood did not alter instrumental motivation. In contrast, Pavlovian motivation assessed with single-outcome Pavlovian-to-instrumental transfer (SO-PIT) was consistently enhanced in females following adolescent or adult stress. In males, however, stress in adolescence had no effect, whereas stress in adulthood attenuated SO-PIT.

CONCLUSIONS

Acute stress in adolescence or adulthood altered instrumental motivation and stimulus-triggered Pavlovian motivation in a sex and developmentally specific manner. These findings suggest that the persistent effects of acute stress on Pavlovian and instrumental motivational processes differ in females and males, and that males may be less vulnerable to the deleterious effects of intense stress during adolescence on appetitive motivation.

A gut (microbiome) feeling about addiction: Interactions with stress and social systems

In recent years, an increasing attention has given to the intricate and diverse connection of microorganisms residing in our gut and their impact on brain health and central nervous system disease. There has been a shift in mindset to understand that drug addiction is not merely a condition that affects the brain, it is now being recognized as a disorder that also involves external factors such as the intestinal microbiota, which could influence vulnerability and the development of addictive behaviors. Furthermore, stress and social interactions, which are closely linked to the intestinal microbiota, are powerful modulators of addiction. This review delves into the mechanisms through which the microbiota-stress-immune axis may shape drug addiction and social behaviors. This work integrates preclinical and clinical evidence that demonstrate the bidirectional communication between stress, social behaviors, substance use disorders and the gut microbiota, suggesting that gut microbes might modulate social stress having a significance in drug addiction.

Characterization of the Neurochemical and Behavioral Effects of the Phenethylamine 2-Cl-4,5-MDMA in Adolescent and Adult Male Rats

BACKGROUND

The proliferation of novel psychoactive substances (NPS) in the drug market raises concerns about uncertainty on their pharmacological profile and the health hazard linked to their use. Within the category of synthetic stimulant NPS, the phenethylamine 2-Cl-4,5-methylenedioxymethamphetamine (2-Cl-4,5-MDMA) has been linked to severe intoxication requiring hospitalization. Thereby, the characterization of its pharmacological profile is urgently warranted.

METHODS

By in vivo brain microdialysis in adolescent and adult male rats we investigated the effects of 2-Cl-4,5-MDMA on dopamine (DA) and serotonin (5-HT) neurotransmission in two brain areas critical for the motivational and rewarding properties of drugs, the nucleus accumbens (NAc) shell and the medial prefrontal cortex (mPFC). Moreover, we evaluated the locomotor and stereotyped activity induced by 2-Cl-4,5-MDMA and the emission of 50-kHz ultrasonic vocalizations (USVs) to characterize its affective properties.

RESULTS

2-Cl-4,5-MDMA increased dialysate DA and 5-HT in a dose-, brain area-, and age-dependent manner. Notably, 2-Cl-4,5-MDMA more markedly increased dialysate DA in the NAc shell and mPFC of adult than adolescent rats, while the opposite was observed on dialysate 5-HT in the NAc shell, with adolescent rats being more responsive. Furthermore, 2-Cl-4,5-MDMA stimulated locomotion and stereotyped activity in both adolescent and adult rats, although to a greater extent in adolescents. Finally, 2-Cl-4,5-MDMA did not stimulate the emission of 50-kHz USVs.

CONCLUSIONS

This is the first pharmacological characterization of 2-Cl-4,5-MDMA demonstrating that its neurochemical and behavioral effects may differ between adolescence and adulthood. These preclinical data could help understanding the central effects of 2-Cl-4,5-MDMA by increasing awareness on possible health damage in users.

Alcohol and stress exposure across the lifespan are key risk factors for Alzheimer's Disease and cognitive decline

Alzheimer's Disease and related dementias (ADRD) are an increasing threat to global health initiatives. Efforts to prevent the development of ADRD require understanding behaviors that increase and decrease risk of neurodegeneration and cognitive decline, in addition to uncovering the underlying biological mechanisms behind these effects. Stress exposure and alcohol consumption have both been associated with increased risk for ADRD in human populations. However, our ability to understand causal mechanisms of ADRD requires substantial preclinical research. In this review, we summarize existing human and animal research investigating the connections between lifetime stress and alcohol exposures and ADRD.

Adolescent restraint stress enhances adult nicotine reinforcement in male and female rats

Adolescent stress is a risk factor for the initiation of nicotine use, but whether adolescent stress can enhance nicotine reinforcement when it is initiated later in adulthood is unknown, and it is unclear whether males and females are equally impacted. Therefore, this study assessed physiological responses (body weight and blood serum corticosterone - CORT) to restraint stress (RS) during adolescence (P28-55) or during adulthood (P70-96) in male and female Sprague-Dawley rats. When all subjects reached adulthood (P69 or 110; 2 weeks after termination of stress exposure), they were tested on sucrose preference and intravenous single-dose nicotine (0.03 mg/kg/infusion) self-administration. It was found that all rats displayed a significant CORT response to RS. Importantly, stress during adolescence, but not during adulthood, enhanced subsequent acquisition of nicotine intake tested in adulthood. Although this effect was observed in both sexes, only males displayed reduced body weight gain and adult sucrose preference. Moreover, regardless of stress exposure, females were more stimulated by nicotine, consumed more nicotine overall, and displayed enhanced nicotine seeking. These results suggest that adolescence is a period of heightened sensitivity to the enhancing effect of repeated stress on the susceptibility to develop nicotine dependence later in life in both sexes.

Associations between cannabis use, opioid misuse and severe psychological distress in adolescents: A cross-sectional school-based study

BACKGROUND

Cannabis use and nonmedical use of prescription opioids are consumed by a small to moderate number of adolescents. However, little is known about their combined influence on mental health in this age group. This study examined the association between cannabis use, nonmedical use of prescription opioids, or both with serious psychological distress among adolescents and tested if sex could moderate these associations.

METHODS

We based our analyses on cross-sectional data from the 2019 Ontario Student Drug Use and Health Survey, a provincially representative sample of students in grades 7 through 12 (aged 11-20 years or older) across Ontario, Canada (n= 7097; mean age: 15.2 ± 1.2 years). Logistic regression analyses were adjusted for important covariates.

RESULTS

We found that 20.5% reported cannabis use only, 5.8% reported opioid use only, and 5% reported both cannabis and opioid use. Cannabis use only (odds ratio [OR]:1.91; 95% confidence interval [CI]:1.53-2.37), opioid use only (OR: 2.21; 95% CI: 1.63-3.00), and both cannabis and opioid use (OR: 3.24; 95% CI: 2.25-4.66) were associated with greater odds of serious psychological distress after adjustment for covariates. Associations were similar for males and females.

CONCLUSION

The use of both cannabis and opioids is significantly associated with serious psychological distress among adolescents. Adolescents who use both cannabis and opioids represent a small and vulnerable group that should be targeted in future interventions against mental health problems. Health professionals should consider screening for polysubstance use, especially when working with adolescents who use cannabis.

Repeated toluene and cyclohexane inhalation produces differential effects on HPA and HPT axes in adolescent male rats

Misused volatile solvents typically contain toluene (TOL) as the main psychoactive ingredient. Cyclohexane (CHX) can also be present and is considered a safer alternative. Solvent misuse often occurs at early stages of life, leading to permanent neurobehavioral impairment and growth retardation. However, a comprehensive examination of the effects of TOL and CHX on stress regulation and energy balance is lacking. Here, we compared the effect of a binge-pattern exposure to TOL or CHX (4,000 or 8,000 ppm) on body weight, food intake, the hypothalamus-pituitary-adrenal (HPA) and hypothalamus-pituitary-thyroid (HPT) axes in male adolescent Wistar rats. At 8,000 ppm, TOL decreased body weight gain without affecting food intake. In addition, TOL and CHX altered the HPA and HPT axes' function in a solvent- and concentration-dependent manner. The highest TOL concentration produced HPA axis hyperactivation in animals not subjected to stress, which was evidenced by increased corticotropin-releasing-factor (CRF) release from the median eminence (ME), elevated adrenocorticotropin hormone (ACTH) and corticosterone serum levels, and decreased CRF mRNA levels in the hypothalamic paraventricular nucleus (PVN). TOL (8,000 ppm) also increased triiodothyronine (T3) serum levels, decreased pro-thyrotropin-releasing-hormone (pro-TRH) mRNA transcription in the PVN, pro-TRH content in the ME, and serum thyroid stimulating hormone (TSH) levels. CHX did not affect the HPA axis. We propose that the increased HPT axis activity induced by TOL can be related to the impaired body weight gain associated with inhalant misuse. These findings may contribute to a better understanding of the effects of the misused solvents TOL and CHX.

Sex and age differences in mice models of effort-based decision-making and anergia in depression: the role of dopamine, and cerebral-dopamine-neurotrophic-factor

Mesolimbic dopamine (DA) regulates vigor in motivated behavior. While previous results have mainly been performed in male rodents, the present studies compared CD1 male and female mice in effort-based decision-making tests of motivation. These tests offered choices between several reinforcers that require different levels of effort (progressive ratio/choice task and 3-choice-T-maze task). Sweet reinforcers were used in both tasks. In the operant tasks, females worked harder as the task required more effort to access a 10% sucrose solution. Although males and females did not differ in preference for 10% vs 3% solutions under free concurrent presentation, females consumed more of the 10% solution when tested alone. The operant task requires a long period of training and changes in the DA system due to age can be mediating long-term changes in effort. Thus, age and sex factors were evaluated in the T-maze task, which requires only a short training period. Both sexes and ages were equally active when habituated to the running wheel (RW), but females consumed more sweet pellets than males, especially at an older age. Both sexes had a strong preference for the RW compared to more sedentary reinforcers in the 3-choice-T-maze test, but older animals spent less time running and ate more than the young ones. The DA-depleting agent tetrabenazine reduced time running in older mice but not in adolescents. Cerebral-dopamine-neurotrophic-factor was reduced in older mice of both sexes compared to adolescent mice. These results emphasize the importance of taking into account differences in sex and age when evaluating willingness to exert effort for specific reinforcers.

Viral-mediated expression of Erk2 in the nucleus accumbens regulates responses to rewarding and aversive stimuli

Second-messenger signaling within the mesolimbic reward circuit is involved in both the long-lived effects of stress and in the underlying mechanisms that promote drug abuse liability. To determine the direct role of kinase signaling within the nucleus accumbens, specifically mitogen-activated protein kinase 1 (ERK2), in mood- and drug-related behavior, we used a herpes-simplex virus to up- or down-regulate ERK2 in adult male rats. We then exposed rats to a battery of behavioral tasks including the elevated plus-maze, open field test, forced-swim test, conditioned place preference, and finally cocaine self-administration. Herein, we show that viral overexpression or knockdown of ERK2 in the nucleus accumbens induces distinct behavioral phenotypes. Specifically, over expression of ERK2 facilitated depression- and anxiety-like behavior while also increasing sensitivity to cocaine. Conversely, down-regulation of ERK2 attenuated behavioral deficits, while blunting sensitivity to cocaine. Taken together, these data implicate ERK2 signaling, within the nucleus accumbens, in the regulation of affective behaviors and modulating sensitivity to the rewarding properties of cocaine.

Social stress under binge-like alcohol withdrawal in adolescence: evidence of cannabidiol effect on maladaptive plasticity in rats

BACKGROUND

Alcohol binge drinking may compromise the functioning of the nucleus accumbens (NAc), i.e. the neural hub for processing reward and aversive responses.

METHODS

As socially stressful events pose particular challenges at developmental stages, this research applied the resident-intruder paradigm as a model of social stress, to highlight behavioural neuroendocrine and molecular maladaptive plasticity in rats at withdrawal from binge-like alcohol exposure in adolescence. In search of a rescue agent, cannabidiol (CBD) was selected due to its favourable effects on alcohol- and stress-related harms.

RESULTS

Binge-like alcohol exposed intruder rats displayed a compromised defensive behaviour against the resident and a blunted response of the stress system, in addition to indexes of abnormal dopamine (DA)/glutamate plasticity and dysfunctional spine dynamics in the NAc. CBD administration (60 mg/kg) was able to: (1) increase social exploration in the binge-like alcohol exposed intruder rats, at the expenses of freezing time, and in control rats, which received less aggressive attacks from the resident; (2) reduce corticosterone levels independently on alcohol previous exposure; (3) restore DA transmission and (4) facilitate excitatory postsynaptic strength and remodelling.

CONCLUSIONS

Overall, the maladaptive behavioural and synaptic plasticity promoted by the intersection between binge-like alcohol withdrawal and exposure to adverse social stress can be rescued by a CBD détente effect that results in a successful defensive strategy, supported by a functional endocrine and synaptic plasticity. The current data highlight CBD's relevant therapeutic potential in alcohol- and stress-related harms, and prompt further investigation on its molecular targets.

Effect of the glucocorticoid receptor antagonist PT150 on acquisition and escalation of fentanyl self-administration following early-life stress

There is comorbidity between posttraumatic stress disorder (PTSD) and opioid use disorder (OUD), perhaps because PTSD-like stressful experiences early in life alter the hypothalamic-pituitary-adrenal stress axis to increase the risk for OUD. The present study determined if the glucocorticoid receptor antagonist PT150 reduces the escalation of fentanyl intake in rats exposed to a "two-hit" model of early-life stress (isolation rearing and acute stress). Male and female rats were raised during adolescence in either isolated or social housing and then were given either a single acute stress (restraint and cold-water swim) or control treatment in young adulthood. Rats were then treated daily with PT150 (50 mg/kg, oral) or placebo and were tested for acquisition of fentanyl self-administration in 1-hr sessions, followed by escalation across 6-hr sessions. Regardless of PT150 treatment or sex, acquisition of fentanyl self-administration in 1-hr sessions was greater in isolate-housed rats compared to social-housed rats; the acute stress manipulation did not have an effect on self-administration even though it transiently increased plasma corticosterone levels. During the 6-hr sessions, escalation of fentanyl was observed across all treatment groups; however, there was a significant PT150 Treatment × Sex interaction. While males self-administered more than females overall, PT150 decreased intake in males and increased intake in females, thus negating the sex difference. Although PT150 may serve as an effective treatment for reducing the risk of OUD following early-life stress in males, further work is needed to determine the mechanism underlying the differential effects of PT150 in males and females. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Age-dependent effects of tobacco smoke and nicotine on cognition and the brain: A systematic review of the human and animal literature comparing adolescents and adults

Cigarette smoking is often initiated during adolescence and an earlier age of onset is associated with worse health outcomes later in life. Paradoxically, the transition towards adulthood also marks the potential for recovery, as the majority of adolescents are able to quit smoking when adulthood emerges. This systematic review aimed to evaluate the evidence from both human and animal studies for the differential impact of adolescent versus adult repeated and long-term tobacco and nicotine exposure on cognitive and brain outcomes. The limited human studies and more extensive yet heterogeneous animal studies, provide preliminary evidence of heightened fear learning, anxiety-related behaviour, reward processing, nicotinic acetylcholinergic receptors expression, dopamine expression and serotonin functioning after adolescent compared to adult exposure. Effects of nicotine or tobacco use on impulsivity were comparable across age groups. These findings provide novel insights into the mechanisms underlying adolescents' vulnerability to tobacco and nicotine. Future research is needed to translate animal to human findings, with a focus on directly linking a broader spectrum of brain and behavioural outcomes.

Mood and behavior regulation: interaction of lithium and dopaminergic system

Lithium is one of the most effect mood-stabilizing drugs prescribed especially for bipolar disorder. Lithium has wide range effects on different molecular factors and neural transmission including dopaminergic signaling. On the other hand, mesolimbic and mesocortical dopaminergic signaling is significantly involved in the pathophysiology of neuropsychiatric disorders. This review article aims to study lithium therapeutic mechanisms, dopaminergic signaling, and the interaction of lithium and dopamine. We concluded that acute and chronic lithium treatments often reduce dopamine synthesis and level in the brain. However, some studies have reported conflicting results following lithium treatment, especially chronic treatment. The dosage, duration, and type of lithium administration, and the brain region selected for measuring dopamine level were not significant differences in different chronic treatments used in previous studies. It was suggested that lithium has various mechanisms affecting dopaminergic signaling and mood, and that many molecular factors can be involved, including brain-derived neurotrophic factor (BDNF), cAMP response element-binding protein (CREB), β-catenin, protein kinase B (Akt), and glycogen synthase kinase-3 beta (GSK-3β). Thus, molecular effects of lithium can be the most important mechanisms of lithium that also alter neural transmissions including dopaminergic signaling in mesolimbic and mesocortical pathways.

Sleep Deprivation Induces Dopamine System Maladaptation and Escalated Corticotrophin-Releasing Factor Signaling in Adolescent Mice

Sleep disruption is highly associated with the pathogenesis and progression of a wild range of psychiatric disorders. Furthermore, appreciable evidence shows that experimental sleep deprivation (SD) on humans and rodents evokes anomalies in the dopaminergic (DA) signaling, which are also implicated in the development of psychiatric illnesses such as schizophrenia or substance abuse. Since adolescence is a vital period for the maturation of the DA system as well as the occurrence of mental disorders, the present studies aimed to investigate the impacts of SD on the DA system of adolescent mice. We found that 72 h SD elicited a hyperdopaminergic status, with increased sensitivity to the novel environment and amphetamine (Amph) challenge. Also, altered neuronal activity and expression of striatal DA receptors were noticed in the SD mice. Moreover, 72 h SD influenced the immune status in the striatum, with reduced microglial phagocytic capacity, primed microglial activation, and neuroinflammation. The abnormal neuronal and microglial activity were putatively provoked by the enhanced corticotrophin-releasing factor (CRF) signaling and sensitivity during the SD period. Together, our findings demonstrated the consequences of SD in adolescents including aberrant neuroendocrine, DA system, and inflammatory status. Sleep insufficiency is a risk factor for the aberration and neuropathology of psychiatric disorders.

Binge eating promotes ethanol self-administration in female rats with a history of intermittent ethanol exposure at adolescence

BACKGROUND

Ethanol drinking begins during adolescence and, particularly when occurs in a binge-like pattern, exerts lingering adverse consequences. Pre-clinical studies indicate that intermittent ethanol exposure (IEA, a model of repeated ethanol intoxication), or binge eating (BE) can increase subsequent ethanol consumption. It is unknown if the promoting effects of BE upon ethanol drinking are found in female rats and are modulated by IEA at adolescence. This study assessed interactive effects between IEA and BE, upon ethanol drinking.

METHODS

Female Wistar rats were given 4.0 g/kg ethanol, every other day from postnatal day 25-45. At adulthood, they were exposed to sessions in which a brief offering of a sizeable portion of highly palatable sugary pills was followed by a 120-min exposure to an ethanol bottle.

RESULTS

Exploratory activity and recognition memory was not affected by the IEA. Glutathione peroxidase and catalase activity, and lipid peroxidation (measured in blood and brain at the end of the procedure) were not significantly affected by IEA or BE exposure. BE alone had a mild promoting effect on ethanol ingestion. Those rats that underwent IEA and BE, however, exhibited heightened and sustained ethanol self-administration (average of 2.12 g/kg/120 min, vs 1.15 g/kg/120 min of the other groups), that persisted throughout the BE sessions. IEA and a history of BE also promoted ethanol intake or preference in a two-bottle endpoint test.

CONCLUSION

The study suggests that exposure to IEA exerts, when followed by BE at adulthood, promoting effects upon ethanol intake, particularly at concentrations ≥ 6%.

Impact of Mephedrone on Fear Memory in Adolescent Rats: Involvement of Matrix Metalloproteinase-9 (MMP-9) and N-Methyl-D-aspartate (NMDA) Receptor

Treatment of Post-Traumatic Stress Disorder (PTSD) is complicated by the presence of drug use disorder comorbidity. Here, we examine whether conditioned fear (PTSD model) modifies the rewarding effect of mephedrone and if repeated mephedrone injections have impact on trauma-related behaviors (fear sensitization, extinction, and recall of the fear reaction). We also analyzed whether these trauma-induced changes were associated with exacerbation in metalloproteinase-9 (MMP-9) and the GluN2A and GluN2B subunits of N-methyl-D-aspartate (NMDA) glutamate receptor expression in such brain structures as the hippocampus and basolateral amygdala. Male adolescent rats underwent trauma exposure (1.5 mA footshock), followed 7 days later by a conditioned place preference training with mephedrone. Next, the post-conditioning test was performed. Fear sensitization, conditioned fear, anxiety-like behavior, extinction acquisition and relapse were then assessed to evaluate behavioral changes. MMP-9, GluN2A and GluN2B were subsequently measured. Trauma-exposed rats subjected to mephedrone treatment acquired a strong place preference and exhibited impairment in fear extinction and reinstatement. Mephedrone had no effect on trauma-induced MMP-9 level in the basolateral amygdala, but decreased it in the hippocampus. GluN2B expression was decreased in the hippocampus, but increased in the basolateral amygdala of mephedrone-treated stressed rats. These data suggest that the modification of the hippocampus and basolateral amygdala due to mephedrone use can induce fear memory impairment and drug seeking behavior in adolescent male rats.

Neonatal bilateral whisker trimming in male mice age-dependently alters brain neurotransmitter levels and causes adolescent onsets of social behavior abnormalities

Tactile perception via whiskers is important in rodent behavior. Whisker trimming during the neonatal period affects mouse behaviors related to both whisker-based tactile cognition and social performance. However, the molecular basis of these phenomena is not completely understood. To solve this issue, we investigated developmental changes in transmitters and metabolites in various brain regions of male mice subjected to bilateral whisker trimming during the neonatal period (10 days after birth [BWT10 mice]). We discovered significantly lower levels of 3-methoxy-4-hydroxyphenyl glycol (MHPG), the major noradrenaline metabolite, in various brain regions of male BWT10 mice at both early/late adolescent stages (at P4W and P8W). However, reduced levels of dopamine (DA) and their metabolites were more significantly identified at P8W in the nuclear origins of monoamine (midbrain and medulla oblongata) and the limbic system (frontal cortex, amygdala, and hippocampus) than at P4W. Furthermore, the onset of social behavior deficits (P6W) was observed later to the impairment of whisker-based tactile cognitive behaviors (P4W). Taken together, these findings suggest that whisker-mediated tactile cognition may contribute toprogressive abnormalities in social behaviors in BWT10 mice accompanied by impaired development of dopaminergic systems.

Resilience to social defeat stress in adolescent male mice

Adverse social experiences during adolescence are associated with the appearance of mental illness in adulthood. Social defeat (SD) is an ethologically valid murine model to study the consequences of social stress. In adolescent mice, SD induces depressive-like behaviors, increased anxiety and potentiates the reinforcing effects of cocaine and alcohol. However, not all mice exposed to SD will be susceptible to these effects. Adult mice resilient to the effects of SD show a consistent phenotype being resilient to depressive-like behaviors and to the increase in cocaine and alcohol consumption. The aim of the present study was to characterize the resilient phenotype to depressive-like behaviors and increase cocaine and ethanol rewarding effects of mice socially defeated during adolescence. To that end, adolescent mice were exposed to repeated SD, and 24 h after the last encounter, they underwent a social interaction test (SIT) in order to evaluate depressive-like behaviors. Cocaine-induced reward conditioning and ethanol intake was evaluated in two different sets of mice 3 weeks after the last SD using cocaine-induced conditioned place preference (CPP) and oral ethanol self-administration (SA). The neuroinflammation response was measured at the end of the experimental procedure by measuring striatal and cortical levels of IL-6 and CX3CL1. The results confirmed that a comparable percentage of adolescent mice develop resilience to depressive-like behaviors to that observed in adult mice. However, increased anxiety was more severe in resilient mice. Likewise, an increased preference for an ineffective dose of cocaine and an increased ethanol consumption was observed in resilient mice compared to controls. The increase in IL-6 and CX3CL1 was mainly observed in the striatum of susceptible mice compared to that of control mice. Our results confirm that, contrary to prior assumptions in adults, responses to SD stress are more complex and singular in adolescents, and caution should be taken for the correct interpretation and translation of those phenotypes.

Methylation pattern and mRNA expression of synapse-relevant genes in the MAM model of schizophrenia in the time-course of adolescence

Schizophrenia is highly heritable and aggregating in families, but genetics alone does not exclusively explain the pathogenesis. Many risk factors, including childhood trauma, viral infections, migration, and the use of cannabis, are associated with schizophrenia. Adolescence seems to be the critical period where symptoms of the disease manifest. This work focuses on studying an epigenetic regulatory mechanism (the role of DNA methylation) and its interaction with mRNA expression during development, with a particular emphasis on adolescence. The presumptions regarding the role of aberrant neurodevelopment in schizophrenia were tested in the Methyl-Azoxy-Methanol (MAM) animal model. MAM treatment induces neurodevelopmental disruptions and behavioral deficits in off-springs of the treated animals reminiscent of those observed in schizophrenia and is thus considered a promising model for studying this pathology. On a gestational day-17, adult pregnant rats were treated with the antimitotic agent MAM. Experimental animals were divided into groups and subgroups according to substance treatment (MAM and vehicle agent [Sham]) and age of analysis (pre-adolescent and post-adolescent). Methylation and mRNA expression analysis of four candidate genes, which are often implicated in schizophrenia, with special emphasis on the Dopamine hypothesis i.e., Dopamine receptor D₂ (Drd2), and the "co-factors" Disrupted in schizophrenia 1 (DISC1), Synaptophysin (Syp), and Dystrobrevin-binding protein 1 (Dtnbp1), was performed in the Gyrus cingulum (CING) and prefrontal cortex (PFC). Data were analyzed to observe the effect of substance treatment between groups and the impact of adolescence within-group. We found reduced pre-adolescent expression levels of Drd2 in both brain areas under the application of MAM. The "co-factor genes" did not show high deviations in mRNA expression levels but high alterations of methylation rates under the application of MAM (up to ~20%), which diminished in the further time course, reaching a comparable level like in Sham control animals after adolescence. The pre-adolescent reduction in DRD2 expression might be interpreted as downregulation of the receptor due to hyperdopaminergic signaling from the ventral tegmental area (VTA), eventually even to both investigated brain regions. The notable alterations of methylation rates in the three analyzed co-factor genes might be interpreted as attempt to compensate for the altered dopaminergic neurotransmission.

Age-dependent effects of social isolation on mesolimbic dopamine release

In humans, social isolation is a known risk factor for disorders such as substance use disorder and depression. In rodents, social isolation is a commonly used environmental manipulation that increases the occurrence of behaviors related to these disorders. Age is thought to influence the effects of social isolation, but this predictive relationship is not well-understood. The present study aimed to determine the effects of social isolation on mesolimbic dopamine release at different developmental age points in mice. The experimental ages and their corresponding comparison to human age stages are as follows: 1 month = adolescence, 4 months = mature adulthood, 12 months = middle adulthood, and 18 months = older adult. Mice were socially isolated for 6 weeks during these developmental stages, then in vivo fixed potential amperometry with recording electrodes in the nucleus accumbens was used to measure stimulation-evoked dopamine release, the synaptic half-life of dopamine, dopamine autoreceptor functioning, and the dopaminergic response to cocaine. Isolation altered dopamine functioning in an age-dependent manner. Specifically, isolation increased dopamine release in the adult ages, but not adolescence, potentially due to increased inhibitory effects of dopamine autoreceptors following adolescent social isolation. Regarding the cocaine challenge, isolation increased dopaminergic responses to cocaine in adolescent mice, but not the adult mice. These findings have implications for clinical and experimental settings. Elucidating the relationship between age, social isolation, and neurochemical changes associated with substance use disorder and depression may lead to improvements in preventing and treating these disorders.

Age-related differences in the effect of chronic alcohol on cognition and the brain: a systematic review

Adolescence is an important developmental period associated with increased risk for excessive alcohol use, but also high rates of recovery from alcohol use-related problems, suggesting potential resilience to long-term effects compared to adults. The aim of this systematic review is to evaluate the current evidence for a moderating role of age on the impact of chronic alcohol exposure on the brain and cognition. We searched Medline, PsycInfo, and Cochrane Library databases up to February 3, 2021. All human and animal studies that directly tested whether the relationship between chronic alcohol exposure and neurocognitive outcomes differs between adolescents and adults were included. Study characteristics and results of age-related analyses were extracted into reference tables and results were separately narratively synthesized for each cognitive and brain-related outcome. The evidence strength for age-related differences varies across outcomes. Human evidence is largely missing, but animal research provides limited but consistent evidence of heightened adolescent sensitivity to chronic alcohol's effects on several outcomes, including conditioned aversion, dopaminergic transmission in reward-related regions, neurodegeneration, and neurogenesis. At the same time, there is limited evidence for adolescent resilience to chronic alcohol-induced impairments in the domain of cognitive flexibility, warranting future studies investigating the potential mechanisms underlying adolescent risk and resilience to the effects of alcohol. The available evidence from mostly animal studies indicates adolescents are both more vulnerable and potentially more resilient to chronic alcohol effects on specific brain and cognitive outcomes. More human research directly comparing adolescents and adults is needed despite the methodological constraints. Parallel translational animal models can aid in the causal interpretation of observed effects. To improve their translational value, future animal studies should aim to use voluntary self-administration paradigms and incorporate individual differences and environmental context to better model human drinking behavior.

The impulsive horse: comparing genetic, physiological and behavioral indicators to that of human addiction

Stress and genotype elicit changes in impulse control in a range of species that are attributable to adaptations in both the central and peripheral nervous system. We examined aspects of this mechanism in the horse by assessing the effect of a dopamine receptor genotype (DRD4) and central dopaminergic tone (measured via spontaneous blink rate [SBR] and behavioral initiation rate [BIR]), on measures of impulsivity, compulsivity (3-choice serial reaction time task) and sympathetic/ parasympathetic system balance (heart rate variability [HRV]). Genotype did not have a significant effect on any of the parameters measured. SBR but not BIR correlated significantly with levels of impulsivity. There was no clear association of HRV parameters with either measures of central dopaminergic activity or impulsivity/compulsivity. Overall, some elements of the data suggest that the horse may be a useful animal model for assessing the genetic and environmental factors that lead to the physiological and behavioral phenotype of human addiction, particularly when considering the relationship between central dopaminergic tone and impulsivity.

The Influence of Social Isolation on Social Orientation, Sociability, Social Novelty Preference, and Hippocampal Parvalbumin-Expressing Interneurons in Peripubertal Rats - Understanding the Importance of Meeting Social Needs in Adolescence

The fulfillment of belonging needs underlies a variety of behaviors. In order to understand how social needs unmet during maturation shape everyday life, we examined social motivation and cognition in peripubertal rats, as a rodent model of adolescence, subjected to social isolation (SI) during early and early-to-mid adolescence. The behavioral correlates of social orientation (social space preference), sociability (preference for social over non-social novelty), and social novelty preference (SNP) were examined in group-housed (GH) and single-housed (SH) rats in a 3-chamber test. The response to social odors was examined to gain insights into the developmental role of social odors in motivated social behavior. Differentiation between appetitive (number of visits/approaches) and consummatory (exploratory time) aspects of motivated social behavior was done to determine which facet of social motivation characterizes maturation when social needs are met and which aspect dominates when social needs are unsatisfied. The SI-sensitive parvalbumin-expressing interneurons (PVI) in the hippocampus were examined using immunohistochemistry. The main findings are the following: (1) in GH rats, the preference for social space is not evident regardless of animals' age, while sociability becomes apparent in mid-adolescence strictly through consummatory behavior, along with complete SNP (appetitive, consummatory); (2) SH promotes staying in a social chamber/space regardless of animals' age and produces an appetitive preference for it only in early-adolescent animals; (3) SH promotes sociability (appetitive, consummatory) regardless of the animals' age and prevents the SNP; (4) the preference for a social odor is displayed in all the groups through consummatory behavior, while appetitive behavior is evident only in SH rats; (5) the response to social odors does not commensurate directly to the response to conspecifics; (6) SH does not influence PVI in the hippocampus, except in the case of early-adolescence when a transient decrease in the dentate gyrus is observed. These results accentuate the developmental complexity of social motivation and cognition, and the power of SI in adolescence to infringe social maturation at different functional levels, promoting appetitive behavior toward peers overall but harming the interest for social novelty. The findings emphasize the importance of the fulfillment of basic social needs in the navigation through the social world.

Effects of regular cannabis and nicotine use on acute stress responses: chronic nicotine, but not cannabis use, is associated with blunted adrenocortical and cardiovascular responses to stress

RATIONALE

Cannabis is one of the most prevalent substances used by tobacco smokers and, in light of the growing list of states and territories legalizing cannabis, it is expected that co-use of cannabis and nicotine will escalate significantly and will lead to continuing challenges with tobacco use.

OBJECTIVES

This study was conducted to examine the interactive effects of chronic cannabis and nicotine use on adrenocortical, cardiovascular, and psychological responses to stress and to explore sex differences in these effects.

METHODS

Participants (N = 231) included cannabis-only users, nicotine-only users, co-users of both substances, and a non/light-user comparison group. After attending a medical screening session, participants completed a laboratory stress session during which they completed measures of subjective states, cardiovascular responses, and salivary cortisol during baseline (rest) and after exposure to acute stress challenges.

RESULTS

Nicotine use, but not cannabis use, was associated with blunted cortisol and cardiovascular responses to stress across both men and women. Men exhibited larger cortisol responses to stress than women. Co-users had significantly larger stress-related increases in cannabis craving than cannabis-only users. Cannabis users reported smaller increases in anxiety during stress than cannabis non/light-users, and both male nicotine-only users and male cannabis-only users experienced significantly smaller increases in stress than their non/light-user control counterparts.

CONCLUSIONS

This study replicates and extends earlier research on the impacts of sex and nicotine use on stress responses, and it provides novel findings suggesting that when co-used with nicotine, cannabis use may not confer additional alterations to physiological nor subjective responses to stress. Co-use, however, was associated with enhanced stress-related craving for cannabis.

Early Life Social Stress Causes Sex- and Region-Dependent Dopaminergic Changes that Are Prevented by Minocycline

Early life stress (ELS) is known to modify trajectories of brain dopaminergic development, but the mechanisms underlying have not been determined. ELS perturbs immune system and microglia reactivity, and inflammation and microglia influence dopaminergic transmission and development. Whether microglia mediate the effects of ELS on dopamine (DA) system development is still unknown. We explored the effects of repeated early social stress on development of the dopaminergic system in male and female mice through histological, electrophysiological, and transcriptomic analyses. Furthermore, we tested whether these effects could be mediated by ELS-induced altered microglia/immune activity through a pharmacological approach. We found that social stress in early life altered DA neurons morphology, reduced dopamine transporter (DAT) and tyrosine hydroxylase expression, and lowered DAT-mediated currents in the ventral tegmental area but not substantia nigra of male mice only. Notably, stress-induced DA alterations were prevented by minocycline, an inhibitor of microglia activation. Transcriptome analysis in the developing male ventral tegmental area revealed that ELS caused downregulation of dopaminergic transmission and alteration in hormonal and peptide signaling pathways. Results from this study offer new insight into the mechanisms of stress response and altered brain dopaminergic maturation after ELS, providing evidence of neuroimmune interaction, sex differences, and regional specificity.

Peer presence and familiarity as key factors to reduce cocaine intake in both rats and humans: an effect mediated by the subthalamic nucleus

RATIONALE

Stimulant use, including cocaine, often occurs in a social context whose influence is important to understand to decrease intake and reduce associated harms. Although the importance of social influence in the context of drug addiction is known, there is a need for studies assessing its neurobiological substrate and for translational research.

OBJECTIVES

Here, we explored the influence of peer presence and familiarity on cocaine intake and its neurobiological basis. Given the regulatory role of the subthalamic nucleus (STN) on cocaine intake and emotions, we investigated its role on such influence of social context on cocaine intake.

METHODS

We first compared cocaine consumption in various conditions (with no peer present or with peers with different characteristics: abstinent peer or drug-taking peer, familiar or not, cocaine-naive or not, dominant or subordinate) in rats (n = 90). Then, with a translational approach, we assessed the influence of the social context (alone, in the group, in a dyad with familiar or non-familiar peers) on drug intake in human drug users (n = 77).

RESULTS

The drug consumption was reduced when a peer was present, abstinent, or drug-taking as well, and further diminished when the peer was non-familiar. The presence of a non-familiar and drug-naive peer represents key conditions to diminish cocaine intake. The STN lesion by itself reduced cocaine intake to the level reached in presence of a non-familiar naive peer and affected social cognition, positioning the STN as one neurobiological substrate of social influence on drug intake. Then, the human study confirmed the beneficial effect of social presence, especially of non-familiar peers.

CONCLUSION

Our results indirectly support the use of social interventions and harm reduction strategies and position the STN as a key cerebral structure to mediate these effects.

The enduring behavioral and neurobiological effects of a flavor cue paired with alcohol drinking during adolescence on the incentive properties of the flavor cue in adulthood in female alcohol-preferring (P) rats

BACKGROUND

Alcohol use disorders (AUDs) affect 15 million people nationwide, 4% of which are adolescents (ages 12-17) and adolescents who binge drink significantly increase their likelihood of suffering from an AUD in adulthood. Research shows that cues (i.e. flavors) paired with alcohol (EtOH) produce significant cue-induced alcohol craving and contribute to relapse in adolescent and adult populations. However, there is a lack of research focused on how cues that accompany EtOH drinking during adolescence, affect EtOH craving later in life. The current study sought to examine the sex- and developmental-dependent effects of adolescent exposure to flavor cues associated with EtOH on operant-lick behavior and cue-induced dopamine (DA) levels within the nucleus accumbens shell (AcbSh; reward structure) in adulthood.

METHODS

Adolescent alcohol-preferring (P) rats were randomly assigned to one of 4 groups and received 24 hr. access to three bottles on their home cage: Paired: 0.1% blueberry flavor extract (BB) + 15% v/v EtOH and 2 water bottles; Unpaired: 0.1% BB, 15% v/v EtOH, and water; 15% EtOH alone, and 2 water bottles; BB alone and 2 water bottles. Home cage fluid consumption was measured for 2-weeks. On the third week bottles were removed and all animals underwent 9 days of operant training using an operant sipper paradigm. This consisted of two sipper spouts connected to the computer by a lickometer, which registered tongue contacts with the sipper tube (Paired: BB+EtOH or water; Unpaired BB or EtOH; EtOH alone: EtOH or water; BB alone: BB or water). When the fixed ratio (FR) requirement for number of licks/tongue contacts was met, a liquid delivery solenoid dispensed 0.05 ml of fluid into the sipper tube. Following the final operant session all rats remained in their home-cage for approximately 40 days until adulthood at which point they were returned to the operant chambers and tested for appetitive and consummatory behavior in response to the flavor cue (all rats: BB or water; NO EtOH). Two weeks after the final operant session all rats underwent microdialysis testing to examine cue-induced DA levels in the AcbSh.

RESULTS

Data indicated that animals in the paired group exhibited a significantly greater level of licking at the BB sipper and a significantly greater level of DA release in response to the flavor cue compared to the other groups.

CONCLUSIONS

Overall, the data suggest that cues paired with EtOH during adolescence may produce persistent changes to the behavioral and neurobiological mechanisms that contribute to an increased risk of developing an AUD later in life.

Associations of cannabis use, opioid use, and their combination with serious psychological distress among Ontario adults

Considering the widespread use of cannabis and opioids, examining the use of cannabis, opioids and their combination with serious psychological distress (SPD) is important. A total of N = 12,358 adults participating in the Monitor surveillance study between 2014 and 2019 were included. Cannabis and opioid use reflected any use of the substances in the past 12 months. SPD was defined as having a score of 13 or more on the Kessler-6 questionnaire, a 6-item scale that includes feeling nervous, hopeless, restless or fidgety, sad or depressed. Odds ratios (ORs) were estimated from logistic regression models accounting for complex survey design and sociodemographic factors. Overall, 12.8% of the sample reported cannabis use only, 18% reported opioid use only, and 4.9% reported both cannabis and opioid use. Use of both cannabis and opioids was significantly associated with SPD in both women (OR = 4.24; 95% CI, 2.34 to 7.69), and in men (OR = 2.99; 95% CI, 1.56 to 5.73) compared to use of neither. The joint association of cannabis and opioids with SPD was additive. Addressing those who use both cannabis and opioids may help reduce the burden of SPD among adults in Ontario.

Ayahuasca, a psychedelic beverage, modulates neuroplasticity induced by ethanol in mice

Alcohol use disorder needs more effective treatments because relapse rates remain high. Psychedelics, such as ayahuasca, have been used to treat substance use disorders. Our study aimed to evaluate the effects of ayahuasca on ethanol-induced behavioral sensitization (EIBS). Swiss mice received 2.2 g/kg ethanol or saline IP injections every other day across nine days (D1, D3, D5, D7, and D9), and locomotor activity was evaluated 10 min after each injection. Then, animals were treated daily with ayahuasca (corresponding to 1.76 mg/kg of N,N-dimethyltryptamine, DMT) or water by oral gavage for eight consecutive days. On the seventh day, mice were evaluated in the elevated plus maze. Then, mice were challenged with a single dose of ethanol to measure their locomotor activity. Dopamine receptors, serotonin receptors, dynorphin, and prodynorphin levels were quantified in the striatum and hippocampus by blot analysis. Repeated ethanol administration resulted in EIBS. However, those animals treated with ayahuasca had an attenuated EIBS. Moreover, ayahuasca reduced the anxiogenic response to ethanol withdrawal and prevented the ethanol-induced changes on 5-HT1a receptor and prodynorphin levels in the hippocampus and reduced ethanol effects in the dynorphin/prodynorphin ratio levels in the striatum. These results suggest a potential application of ayahuasca to modulate the neuroplastic changes induced by ethanol.

Neurobiological Bases of Alcohol Consumption After Social Stress

The urge to seek and consume excessive alcohol is intensified by prior experiences with social stress, and this cascade can be modeled under systematically controlled laboratory conditions in rodents and non-human primates. Adaptive coping with intermittent episodes of social defeat stress often transitions to maladaptive responses to traumatic continuous stress, and alcohol consumption may become part of coping responses. At the circuit level, the neural pathways subserving stress coping intersect with those for alcohol consumption. Increasingly discrete regions and connections within the prefrontal cortex, the ventral and dorsal striatum, thalamic and hypothalamic nuclei, tegmental areas as well as brain stem structures begin to be identified as critical for reacting to and coping with social stress while seeking and consuming alcohol. Several candidate molecules that modulate signals within these neural connections have been targeted in order to reduce excessive drinking and relapse. In spite of some early clinical failures, neuropeptides such as CRF, opioids, or oxytocin continue to be examined for their role in attenuating stress-escalated drinking. Recent work has focused on neural sites of action for peptides and steroids, most likely in neuroinflammatory processes as a result of interactive effects of episodic social stress and excessive alcohol seeking and drinking.

The impact of adolescent nicotine exposure on alcohol use during adulthood: The role of neuropeptides

Nicotine and alcohol abuse and co-dependence represent major public health crises. Indeed, previous research has shown that the prevalence of alcoholism is higher in smokers than in non-smokers. Adolescence is a susceptible period of life for the initiation of nicotine and alcohol use and the development of nicotine-alcohol codependence. However, there is a limited number of pharmacotherapeutic agents to treat addiction to nicotine or alcohol alone. Notably, there is no effective medication to treat this comorbid disorder. This chapter aims to review the early nicotine use and its impact on subsequent alcohol abuse during adolescence and adulthood as well as the role of neuropeptides in this comorbid disorder. The preclinical and clinical findings discussed in this chapter will advance our understanding of this comorbid disorder's neurobiology and lay a foundation for developing novel pharmacotherapies to treat nicotine and alcohol codependence.

The impact of social variables in preclinical models of cocaine abuse

At present, there are no US Food and Drug Administration–approved treatments for cocaine use disorders. One consideration for this lack of treatment efficacy stems from the appropriate use of animal models. The premise of this commentary is that social behavior needs to be incorporated in animal models of cocaine use disorder. The goal of this commentary is to describe some of the strengths and limitations of recent preclinical animal models of cocaine abuse which have incorporated social behavior. There are many ways to include social variables into preclinical research, and the study design will depend on the questions asked. Four general types of studies incorporating social factors are described: those involving aggression (that is, maternal neglect and social defeat), modeling, social reward, and social housing, including social isolation. The inclusion of social variables into preclinical research will help identify biobehavioral markers that may lead to an individualized treatment approach that more effectively decreases cocaine use. These studies will aid in the development of novel pharmacotherapies as well as non-pharmacological interventions (for example, punishment, alternative reinforcers, and environmental enrichment) that would be critical for informing policy decisions.

Impact of Early Life Stress on Reward Circuit Function and Regulation

Early life stress - including experience of child maltreatment, neglect, separation from or loss of a parent, and other forms of adversity - increases lifetime risk of mood, anxiety, and substance use disorders. A major component of this risk may be early life stress-induced alterations in motivation and reward processing, mediated by changes in the nucleus accumbens (NAc) and ventral tegmental area (VTA). Here, we review evidence of the impact of early life stress on reward circuit structure and function from human and animal models, with a focus on the NAc. We then connect these results to emerging theoretical models about the indirect and direct impacts of early life stress on reward circuit development. Through this review and synthesis, we aim to highlight open research questions and suggest avenues of future study in service of basic science, as well as applied insights. Understanding how early life stress alters reward circuit development, function, and motivated behaviors is a critical first step toward developing the ability to predict, prevent, and treat stress-related psychopathology spanning mood, anxiety, and substance use disorders.

Mesocorticolimbic Dopamine Pathways Across Adolescence: Diversity in Development

Mesocorticolimbic dopamine circuity undergoes a protracted maturation during adolescent life. Stable adult levels of behavioral functioning in reward, motivational, and cognitive domains are established as these pathways are refined, however, their extended developmental window also leaves them vulnerable to perturbation by environmental factors. In this review, we highlight recent advances in understanding the mechanisms underlying dopamine pathway development in the adolescent brain, and how the environment influences these processes to establish or disrupt neurocircuit diversity. We further integrate these recent studies into the larger historical framework of anatomical and neurochemical changes occurring during adolescence in the mesocorticolimbic dopamine system. While dopamine neuron heterogeneity is increasingly appreciated at molecular, physiological, and anatomical levels, we suggest that a developmental facet may play a key role in establishing vulnerability or resilience to environmental stimuli and experience in distinct dopamine circuits, shifting the balance between healthy brain development and susceptibility to psychiatric disease.

NLRP3 Inflammasome Is Involved in Cocaine-Mediated Potentiation on Behavioral Changes in CX3CR1-Deficient Mice

Microglia, the primary immunocompetent cells of the brain, are suggested to play a role in the development of drug addiction. Previous studies have identified the microglia-derived pro-inflammatory factor IL1β can promote the progression of cocaine addiction. Additionally, the activation status of microglia and “two-hit hypothesis” have been proposed in the field of drug addiction to explain how early life stress (ELS) could significantly increase the incidence of drug addiction in later life. However, the mechanisms underlying microglia prime and full activation and their roles in drug addiction remain greatly unexplored. Here, we employed CX3CR1-GFP mice (CX3CR1 functional deficiency, CX3CR1−/−) to explore whether primed microglia could potentiate cocaine-mediated behavioral changes and the possible underlying mechanisms. CX3CR1−/− mice revealed higher hyperlocomotion activity and conditional place preference than wild-type (WT) mice did under cocaine administration. In parallel, CX3CR1−/− mice showed higher activity of NLR family pyrin domain-containing 3 (NLRP3) inflammasome than WT mice. Interestingly, CX3CR1 deficiency itself could prime NLRP3 signaling by increasing the expression of NLPR3 and affect lysosome biogenesis under basal conditions. Taken together, our findings demonstrated that the functional status of microglia could have an impact on cocaine-mediated reward effects, and NLRP3 inflammasome activity was associated with this phenomenon. This study was consistent with the two-hit hypothesis and provided solid evidence to support the involvement of microglia in drug addiction. Targeting the NLRP3 inflammasome may represent a novel therapeutic approach for ameliorating or blocking the development of drug addiction.

Social Stress and Aggression in Murine Models

Throughout life, animals engage in a variety of social interactions ranging from the affiliative mother-offspring interaction and juvenile play to aggressive conflict. Deprivation of the appropriate social interaction during early development is stressful and disrupts the development of appropriate social behaviors and emotional responses later in life. Additionally, agonistic encounters can induce stress responses in both dominant and subordinate individuals. This review focuses on the social stress that escalates aggressive behavior of animals and discusses the known neurobiological and physiological mechanisms underlying the link between social stress and aggression. Social instigation, a brief exposure to a rival without physical contact, induces aggressive arousal in dominant animals and escalates aggressive behaviors in the following agonistic encounter. Furthermore, the experience of winning an aggressive encounter is known to be as rewarding as addictive drugs, and the experience of repeatedly winning induces addiction-like behavioral and neurobiological changes and leads to abnormal aggressive behaviors. Social isolation stress in early development from neonatal to juvenile and adolescent periods also affects aggressive behavior, but these effects largely depend on the strain, sex, and species as well as the stage of development in which isolation stress is experienced. In conclusion, understanding neurobiological mechanisms underlying the link between social stress and aggression will provide an important insight for the development of more effective and tolerable treatments for maladaptive aggression in humans.

Drugs and bugs: Negative affect, psychostimulant use and withdrawal, and the microbiome

BACKGROUND AND OBJECTIVES

A growing body of literature demonstrates that the human microbiota plays a crucial role in health and disease states, as well as in the body's response to stress. In addition, the microbiome plays a role in psychological well-being and regulating negative affect. Regulation of negative affect is a factor in psychostimulant abuse disorders. We propose a risk chain in which stress leads to negative affect that places an individual at risk to develop or relapse to psychostimulant abuse disorder. Stress, negative affect, and psychostimulant use all alter the gut microbiome.

METHODS

This review brings together the literature on affective disorders, stress, and psychostimulant abuse disorders to assess possible modulatory actions of the gut-brain axis to regulate these conditions.

RESULTS

Studies reviewed across the various disciplines suggest that the dysbiosis resulting from drug use, drug withdrawal, or stress may cause an individual to be more susceptible to addiction and relapse. Probiotics and prebiotics reduce stress and negative affect.

SCIENTIFIC SIGNIFICANCE

Treatment during the withdrawal phase of psychostimulant abuse disorder, when the microbiome is altered, may ameliorate the symptoms of stress and negative affect leading to a reduced risk of relapse to psychostimulant use.

Peri-adolescent exposure to (meth)amphetamine in animal models

Experimentation with psychoactive drugs is often initiated in the peri-adolescent period, but knowledge of differences in the outcomes of peri-adolescent- vs adult-initiated exposure is incomplete. We consider the existing animal research in this area for (meth)amphetamines. Established for a number of phenotypes, is lower sensitivity of peri-adolescents than adults to acute effects of (meth)amphetamines, including neurotoxic effects of binge-level exposure. More variable are data for long-term consequences of peri-adolescent exposure on motivational and cognitive traits. Moreover, investigations often exclude an adult-initiated exposure group critical for answering questions about outcomes unique to peri-adolescent initiation. Despite this, it is clear from the animal research that (meth)amphetamine exposure during the peri-adolescent period, whether self- or other-administered, impacts brain motivational circuitry and cognitive function, and alters adult sensitivity to other drugs and natural rewards. Such consequences occurring in humans have the potential to predispose toward unfortunate and potentially disastrous family, social and livelihood outcomes.