The Impact of Cannabidiol Expectancy on Cortisol Responsivity in the Context of Acute Stress: Associations with Biological Sex.

Background: Cannabidiol (CBD), a nonpsychoactive cannabinoid found in the cannabis plant, has gained interest for its purported stress- and anxiety-reducing effects. However, the mechanisms underlying these effects remain unclear. Our group previously found that CBD expectancy alone resulted in lower state anxiety (vs. CBD-free expectancy) among those who strongly believed it was helpful for such purposes, in addition to influencing physiological measures (i.e., heart rate variability). Aims: Using data collected as part of this previously published larger study, we aimed to explore the extent to which CBD expectancy alone impacts cortisol in the context of a laboratory stressor. Methods: A sample of 43 healthy adults (23 female) participated in one orientation and two experimental laboratory sessions. They received the same oil (CBD-free) during both experimental sessions but were told they received CBD oil in counterbalanced order in one of their sessions. Participants then engaged in a laboratory stressor (the Maastricht Acute Stress Test; MAST) and salivary cortisol samples were collected throughout [T1: baseline; T2: 90-min postabsorption (PA); T3: poststress (0-PS); T4: 10-min poststress (10-PS); T5: 30-min poststress (30-PS)]. Linear marginal models were used for analyses. Results: Findings indicated that a physiological stress response was elicited in the context of the MAST, which is consistent with what has been reported previously. Interestingly, while cortisol levels were significantly lower in the CBD expectancy condition (vs. CBD-free) immediately following the MAST (0-PS) and 10-min later (10-PS), this effect seems to be largely driven by males, evidenced by a three-way interaction. Cortisol levels did not reliably vary across expectancy conditions at any other time point. Conclusion: Overall, these results suggest that CBD expectancy appears to blunt cortisol in anticipation of a stressor, particularly in males. Findings suggest that it is important to consider the impact of drug-related expectations when assessing CBD-related effects on stress-related processes.

A comparative study of Western, high-carbohydrate, and standard lab diet consumption throughout adolescence on metabolic and anxiety-related outcomes in young adult male and female Long-Evans rats.

Anxiety and obesity are prevalent health concerns that are affected by diet in rodents and humans. How diet influences the development and maintenance of anxiety and obesity has been challenging to characterize, in part, due to methodological differences in chosen experimental and control diets. Within the same experiment, anxiety- and obesity-related effects were characterized in rats fed a Western diet (WD) relative to two control diets. Sixty Long-Evans rats split equally by sex were given standard diet (SD), control (i.e., high-carbohydrate) diet (HCD), or WD from weaning until sacrifice in early adulthood. Anxiety-related behavior was characterized in a modified open field test (mOFT) that allowed for the measurement of defensive behaviors (e.g., hiding within a refuge area), in addition to traditional OF measures (e.g., time in center). Both anxiety-related behaviors and hippocampal CA3 BDNF revealed specific sex differences. Neither adolescent weight gain of male and female rats, nor total body weight in early adulthood, were dependent on administration of HCD or WD, although the WD group consumed the most calories. In males only, administration of either WD or HCD resulted in elevated leptin levels relative to administration of the SD. Results indicate that SDs and HCDs are two distinct types of control diets that can affect comparability of studies and that using an SD might reveal more subtle metabolic changes. Control diet choice should be strongly considered during study design and interpretation, depending on specific research goals. Such studies should include both males and females as these effects are sex-specific.

Effect of caffeine on resting-state alpha activity across the human menstrual cycle.

RATIONALE: Caffeine is the most consumed stimulant worldwide, and there is great interest in understanding its neurophysiological effects. Resting-state electroencephalography (EEG) studies suggest that caffeine enhances arousal, which suppresses the spectral power of alpha frequencies associated with reduced alertness. However, it is unclear whether caffeine's neurophysiological effects vary across the human menstrual cycle. OBJECTIVE: The objective of our study was to test whether caffeine's effect on EEG activity differs across the human menstrual cycle. METHODS: Fifty-six female participants were randomly assigned to complete the experiment while in either their menstrual (n = 21), follicular (n = 19), or luteal (n = 16) phase. Each participant completed two study sessions in the same menstrual phase, approximately 1 month apart, during which they were administered either a caffeine pill (200 mg, oral) or a placebo pill in a counterbalanced order using a randomized double-blinded procedure. We measured their eyes-closed resting-state EEG approximately 30 min after pill administration and conducted a spectral power analysis at different frequency bands. RESULTS: Caffeine reduced EEG power in the alpha1 frequency band (8-10 Hz), but only for participants who self-reported higher weekly caffeine consumption. Importantly, caffeine's effects did not differ by menstrual phase. CONCLUSIONS: We conclude that when studying caffeine's effects on resting-state EEG, participants' baseline caffeine consumption is more influential than their menstrual cycle phase. This study has important implications for the inclusion of menstruating individuals in neurophysiological studies of caffeine.

Effects of paternal high-fat diet and maternal rearing environment on the gut microbiota and behavior.

Exposing a male rat to an obesogenic high-fat diet (HFD) influences attractiveness to potential female mates, the subsequent interaction of female mates with infant offspring, and the development of stress-related behavioral and neural responses in offspring. To examine the stomach and fecal microbiome's potential roles, fecal samples from 44 offspring and stomach samples from offspring and their fathers were collected and bacterial community composition was studied by 16 small subunit ribosomal RNA (16S rRNA) gene sequencing. Paternal diet (control, high-fat), maternal housing conditions (standard or semi-naturalistic housing), and maternal care (quality of nursing and other maternal behaviors) affected the within-subjects alpha-diversity of the offspring stomach and fecal microbiomes. We provide evidence from beta-diversity analyses that paternal diet and maternal behavior induced community-wide shifts to the adult offspring gut microbiome. Additionally, we show that paternal HFD significantly altered the adult offspring Firmicutes to Bacteroidetes ratio, an indicator of obesogenic potential in the gut microbiome. Additional machine-learning analyses indicated that microbial species driving these differences converged on Bifidobacterium pseudolongum. These results suggest that differences in early-life care induced by paternal diet and maternal care significantly influence the microbiota composition of offspring through the microbiota-gut-brain axis, having implications for adult stress reactivity.

The impact of depressed mood and coping motives on cannabis use quantity across the menstrual cycle in those with and without pre-menstrual dysphoric disorder.

BACKGROUND AND AIMS: Reported rates of cannabis use among Canadian females are increasing. Female cannabis users progress to cannabis use disorder more rapidly than males (telescoping) and have higher rates of emotional disorder comorbidity. Addictive behaviors may change, along with mood and motivations, across the menstrual cycle (MC), particularly for females with pre-menstrual dysphoric disorder (PMDD). This study aimed to determine whether increases in depressed mood and coping motives would predict increased cannabis use pre-menstrually/menstrually, particularly among females with PMDD. We also assessed positive mood and enhancement motive ratings to establish specificity of predicted depressed mood and coping motive results. DESIGN: Observational study using data collected across 32 days using electronic daily diary methods. SETTING: Nova Scotia, Canada. PARTICIPANTS: Sixty-nine naturally cycling female cannabis users (Mean (M) age = 29.25, Standard Deviation  (SD) = 5.66) with and without retrospectively identified PMDD (via structured clinical interview) and prospectively identified PMDD (via elevated pre-menstrual depressed mood). Self-reported MC phase was validated using salivary progesterone concentrations. MEASUREMENTS: Depressed/positive mood, coping-/enhancement-motivated cannabis use, and cannabis use quantity. FINDINGS: Coping motives explained heightened cannabis use pre-menstrually/menstrually in those with retrospectively identified PMDD. Depressed mood explained increased cannabis use menstrually in those with retrospectively/prospectively identified PMDD. Moreover, prospectively identified PMDD significantly moderated the relationship between depressed mood and cannabis use quantity menstrually. In those with prospectively identified PMDD, positive mood and enhancement motives were associated with decreased cannabis use during the follicular/ovulatory phases. Females with versus without retrospectively identified PMDD also displayed greater overall cannabis use quantity (M [SD] = 3.44[2.84] standard joint equivalents versus 1.85[1.82], respectively; U = 277.50, P = 0.008). CONCLUSIONS: Depressed mood may explain heightened cannabis use menstrually in females with pre-menstrual dysphoric disorder. Coping motives may explain heightened cannabis use pre-menstrually/menstrually in females with retrospectively identified with pre-menstrual dysphoric disorder.

Supplementation with Combined Lactobacillus helveticus R0052 and Bifidobacterium longum R0175 Across Development Reveals Sex Differences in Physiological and Behavioural Effects of Western Diet in Long-Evans Rats.

The gut microbiome affects various physiological and psychological processes in animals and humans, and environmental influences profoundly impact its composition. Disorders such as anxiety, obesity, and inflammation have been associated with certain microbiome compositions, which may be modulated in early life. In 62 Long-Evans rats, we characterised the effects of lifelong Bifidobacterium longum R0175 and Lactobacillus helveticus R0052 administration-along with Western diet exposure-on later anxiety, metabolic consequences, and inflammation. We found that the probiotic formulation altered specific anxiety-like behaviours in adulthood. We further show distinct sex differences in metabolic measures. In females, probiotic treatment increased calorie intake and leptin levels without affecting body weight. In males, the probiotic seemed to mitigate the effects of Western diet on adult weight gain and calorie intake, without altering leptin levels. The greatest inflammatory response was seen in male, Western-diet-exposed, and probiotic-treated rats, which may be related to levels of specific steroid hormones in these groups. These results suggest that early-life probiotic supplementation and diet exposure can have particular implications on adult health in a sex-dependent manner, and highlight the need for further studies to examine the health outcomes of probiotic treatment in both sexes.

Retrospective and prospective assessments of gambling-related behaviors across the female menstrual cycle.

BACKGROUND AND AIMS: Despite increases in female gambling, little research investigates female-specific factors affecting gambling behavior (GB). Although research suggests that some addictive behaviors may fluctuate across menstrual cycle phase (MCP), gambling requires further investigation. In two studies, we examined associations between MCP and three risky GBs: time spent gambling, money spent gambling, and the probability of consuming alcohol while gambling. Associations between MCP and negative affect were also examined in Study 2. We predicted that, consistent with self-medication theory, increases in negative affect (Study 2) and risky GBs (Studies 1 and 2) would occur premenstrually/menstrually relative to other phases. METHODS: Data were obtained from 33 female gamblers using a retrospective timeline followback procedure (Study 1) and from 20 female gamblers using a prospective 32-day, daily diary method (Study 2). In Study 2, salivary progesterone levels verified self-reported MCP validity. RESULTS: Findings revealed significant, but somewhat inconsistent, MCP effects on GBs across studies. The self-medication hypothesis was partially supported. Increases relative to another MCP(s) were found for alcohol consumption while gambling premenstrually, time spent gambling menstrually/premenstrually, money spent gambling menstrually, and negative affect premenstrually. Unexpectedly, findings more consistently indicated that GBs increased during ovulation, suggestive of enhanced reward sensitivity. Progesterone assays validated self-reported MCP (Study 2). DISCUSSION AND CONCLUSIONS: The results suggest a role of ovarian hormones on negative affect and GBs in females. This research could lead to the identification of female-specific factors affecting gambling and the development of more effective interventions for females with, or at risk for, problematic gambling.

Effects of paternal high-fat diet and rearing environment on maternal investment and development of defensive responses in the offspring.

Paternal preconception risk factors (e.g. stress, diet, drug use) correlate with metabolic dysfunction in offspring, which is often comorbid with depressive and anxiety-like phenotypes. Detection of these risk factors or deleterious phenotypes informs a female about prevailing ecological demands, in addition to potential adverse environment-induced phenotypes that may be disseminated to her offspring. We examined whether a F0 male rat's prior exposure to an obesogenic high-fat diet (HFD) influences a female's attraction towards a male, subsequent mother-infant interactions and the development of defensive (emotional) responses in the F1 offspring. Females displayed less interest in the HFD exposed F0 males relative to control diet-exposed F0 males. Dams that reared F1 offspring in larger, semi-naturalistic housing provided more licking and grooming and active arched-back-nursing behavior. However, some of these effects interacted with paternal experience. F0 HFD and maternal rearing environment revealed sex-dependent, between group differences in F1 offspring wean weight, juvenile social interactions and anxiety-like behavior in adolescence. Our results show for the first time in mammals that male exposure to HFD may contribute to stable behavioral variation among females in courtship, maternal care, even when the females are not directly exposed to a HFD, and anxiety-like behavior in F1 offspring. Furthermore, when offspring were exposed to a predatory threat, hypothalamic Crf gene regulation was influenced by early housing. These results, together with our previous findings, suggest that paternal experience and maternal rearing conditions can influence maternal behavior and development of defensive responses of offspring.

Developmental expression of anxiety and depressive behaviours after prenatal predator exposure and early life homecage enhancement.

Stressful events during gestation can have sex-specific effects on brain and behaviour, and may contribute to some of the differences observed in adult stress responding and psychopathology. We investigated the impact of a novel repeated prenatal psychological stress (prenatal predator exposure - PPS) during the last week of gestation in rats on offspring behaviours related to social interaction (play behaviour), open field test (OFT), forced swim test (FST) and sucrose preference test (SP) during the juvenile period and in adulthood. We further examined the role of postnatal environmental, using an enhanced housing condition (EHC), to prevent/rescue any changes. Some effects on anxiety, anhedonia, and stress-related coping behaviours (e.g., OFT, SP and OFT) did not emerge until adulthood. PPS increased OFT anxiety behaviours in adult males, and some OFT and SP behaviours in adult females. Contrary to this, EHC had few independent effects; most were apparent only when combined with PPS. In keeping with age-group differences, juvenile behaviours did not necessarily predict the same adult behaviours although juvenile OFT rearing and freezing, and juvenile FST immobility did predict adult FST immobility and sucrose preference, suggesting that some aspects of depressive behaviours may emerge early and predict adult vulnerability or coping behaviours. Together, these results suggest an important, though complex, role for early life psychological stressors and early life behaviours in creating an adult vulnerability to anxiety or depressive disorders and that environmental factors further modulate the effects of the prenatal stressors.

Analyzing the experiences of adolescent control rats: Effects of the absence of physical or social stimulation on anxiety-like behaviour are dependent on the test.

The present study was designed to systematically assess the control experience routinely used in our laboratory as part of studies on predator odour stress. Specifically, we examined effects of the physical and social components of this control experience on measures of anxiety-like behaviour in adolescent rats. Adolescent animals are at increased susceptibility to environmental perturbations and have been used for such studies much less often. Long-Evans rats of both sexes were subjected to physical stimulation (Exposed or Unexposed) and social stimulation (Single-Housed or Pair-Housed), resulting in four groups. Exposed rats received six 30-min exposures to an enclosed arena containing an unscented piece of cat collar occurring between adolescence and early adulthood, while Unexposed remained in the home cage. Groups of Exposed and Unexposed animals were housed singly (Single-Housed) from early adolescence to early adulthood or Pair-Housed during this time. Experimental procedures began in adolescence and involved repeated assessment of startle amplitude (measure of anxiety-like behaviour) and prepulse inhibition (PPI; a measure of sensorimotor gating) to gauge the short-term impact of social and/or physical stimulation. All animals were re-paired in adulthood prior to a final startle/PPI session to assess if isolation limited to adolescence could impose long-term effects that were not reversible. We also measured anxiety-like behaviour in adulthood using an extended open field test (EOFT; addition of novel objects to the open field on later days), and the elevated plus maze task (EPM), as well as a sucrose preference test (SPT) to measure anhedonia. An absence of social or physical stimulation resulted in increased startle amplitude and some measures of anxiety-like behaviour in the EOFT, but a reduction in such anxiety-like behaviour in the EPM task. These results suggest common neural substrates for the physical and social experiences. Performance in the SPT was unaltered by any experimental treatments. Sensorimotor gating, as measured by PPI, was increased in the absence of physical stimulation with no short-term effect of isolation, or of re-pairing. These results indicate the importance of considering individual components of the rearing environment of rats, while showing the need to use multiple assays of anxiety-like behaviour.

Effects of Paternal Predation Risk and Rearing Environment on Maternal Investment and Development of Defensive Responses in the Offspring.

Detecting past experiences with predators of a potential mate informs a female about prevailing ecological threats, in addition to stress-induced phenotypes that may be disseminated to offspring. We examined whether prior exposure of a male rat to a predator (cat) odor influences the attraction of a female toward a male, subsequent mother-infant interactions and the development of defensive (emotional) responses in the offspring. Females displayed less interest in males that had experienced predator odor. Mothers that reared young in larger, seminaturalistic housing provided more licking and grooming and active arched back-nursing behavior toward their offspring compared with dams housed in standard housing, although some effects interacted with paternal experience. Paternal predation risk and maternal rearing environment revealed sex-dependent differences in offspring wean weight, juvenile social interactions, and anxiety-like behavior in adolescence. Additionally, paternal predator experience and maternal housing independently affected variations in crf gene promoter acetylation and crf gene expression in response to an acute stressor in offspring. Our results show for the first time in mammals that variation among males in their predator encounters may contribute to stable behavioral variation among females in preference for mates and maternal care, even when the females are not directly exposed to predator threat. Furthermore, when offspring were exposed to the same threat experienced by the father, hypothalamic crf gene regulation was influenced by paternal olfactory experience and early housing. These results, together with our previous findings, suggest that paternal stress exposure and maternal rearing conditions can influence maternal behavior and the development of defensive responses in offspring.

An enhanced home cage modulates hypothalamic CRH-ir labeling in juvenile rats, with and without sub-threshold febrile convulsions.

Pre and postnatal environments can have a profound impact on offspring development. This is especially true when considering the origin of neurological diseases, including epilepsy, a relatively common and chronic neurological condition, affecting 1-2% of the population. Previously, we have used maternal stress and an enhanced home cage (EHC) in an effort to identify potential factors in the early environment that may increase the risk for experiencing seizures. First, pregnant Long-Evans rats were exposed to a predator stress (PS). Then, at birth, litters were divided into standard cage (SC) and EHC groups until postnatal Day 14 (PD14) when a model of febrile convulsions was used to determine convulsion susceptibility of the various groups. Twenty-four hours later, pup brains were processed for immunohistochemical detection of corticotrophic releasing hormone (CRH) in the paraventricular nucleus of the hypothalamus. Analysis of CRH immunoreactive (-ir) patterns revealed a buffering of CRH-ir in EHC reared offspring. Further, experiencing convulsions led to decreased CRH-ir. Our results support the concept that postnatal environmental influences affect neonatal programming and neurodevelopment of processes that could underlie seizure susceptibility, and that these effects can be modulated by EHC conditions.

Limbic system activation is affected by prenatal predator exposure and postnatal environmental enrichment and further moderated by dam and sex.

Epilepsy is a relatively common and chronic neurological condition, affecting 1-2% of the population. However, understanding of the underlying pathophysiology remains incomplete. To identify potential factors in the early environment that may increase the risk for experiencing seizures, maternal stress and environmental enrichment (EE) were utilized. Pregnant Long-Evans rats were exposed to an ethologically relevant predator stress (PS) and maternal glucocorticoid (GC) response was assessed across the exposure period. At birth, litters were divided into standard care (SC) and EE groups until postnatal day 14 (PD14) when a model of febrile convulsions was used to determine seizure susceptibility of the various groups. Pup brains were then processed for immunohistochemical detection of FosB from several structures in the limbic system as a measure of neuronal activation. Maternal PS-induced GC levels were elevated early in the exposure period, and pup birth weights, in both sexes, were lower in litters from dams exposed to PS. Seizure scores at PD14 were highly individualized and litter dependent, suggesting a dam-dependent and variable effect of controlled pre- and postnatal environmental factors. Further, analysis of FosB-immunoreactive (-ir) patterns revealed an activity dependent distribution, reflecting individual seizure susceptibility. EE had a varying effect on FosB-ir that was dependent on region. In the hippocampus FosB-ir levels were greater in the EE groups while extra-hippocampal regions showed lower levels of FosB-ir. Our results support the concept that pre- and postnatal environmental influences affect fetal programming and neurodevelopment of processes that could underlie seizure susceptibility, but that the magnitude of these effects appears to be dam- or litter-dependent.

Expression of maternal behavior and activation of the bed nucleus of the stria terminalis during predatory threat exposure: modulatory effects of transport stress.

Past work has established that levels of maternal care provided to rat pups during the postpartum period plays an important role in shaping development of the stress response system, such that high levels of pup licking and grooming and active nursing behaviors are associated with more efficient hypothalamic-pituitary-adrenal responses to stressors in adulthood. Furthermore, a prior study from our laboratory has demonstrated facilitation of maternal care for five days following a one-hour predator odor exposure on the day of giving birth. The present study was an investigation of the effects on maternal care during a one-hour predator odor exposure administered on the day of giving birth, with or without the addition of transport stress immediately prior to the odor exposure. Stress-induced activation of the medial preoptic area (MPOA) and the bed nucleus of the stria terminalis (BNST), two brain regions involved in regulating maternal behaviors, were also quantified using c-Fos immunohistochemistry. Our results show that predator odor exposure soon after birth does not significantly alter expression of maternal behaviors during the hour-long exposure period, unless the dams are also exposed to transport stress, in which case maternal behaviors are reduced during the first 10min of the exposure but not significantly different during the final 10min. Predator odor exposure (with or without additional transport stress) increased c-Fos immunoreactivity in the BNST, but not the MPOA, relative to control odor exposure, suggesting that the BNST may play an important role in integration of threat cues and transduction of their meaning into long-term effects on expression of maternal care. Future experiments should be designed to test the effects of temporary inactivation of the BNST during postpartum predator odor exposure.

Prenatal transport stress, postnatal maternal behavior, and offspring sex differentially affect seizure susceptibility in young rats.

Epilepsy is a heterogeneous and chronic neurological condition of undefined etiology in the majority of cases. Similarly, the pathogenesis of the unprovoked seizures that lead to epilepsy is not known. We are interested in the factors that modify inherent seizure susceptibility, with a particular focus on those occurring during the prenatal and early postnatal periods. Female Sprague-Dawley rats were bred in-house or transported during pregnancy at one of two gestational days (G9 or G16). The effects of transport stress, maternal behavior, and offspring sex were then examined in terms of how they were related to provoked seizure susceptibility to kainic acid (KA) or a model of febrile convulsions (FCs) on postnatal day 14 (P14). We also examined the pattern of neuronal activation in the hippocampus and amygdala as indicated by the density of FosB protein immunoreactivity (FosB-ir). Results demonstrated only a small and inconsistent effect of transport alone, suggesting that the groups differed slightly prior to experimental manipulations. However, the influence of maternal behaviors such as licking and grooming (LG), arched back nursing (ABN), and dam-off time (DO) exerted a much stronger effect on the offspring. Dams designated as high LG gave birth to smaller litters, had pups that weighed less, had greater seizure susceptibility and severity, and had more FosB-ir neurons predominantly in the ventral hippocampus and the medial subnucleus of the amygdala (MeA). We also found a sex-dependent effect such that P14 males were smaller than their female littermates and had a greater seizure susceptibility and severity. Taken together, these results suggest an impact of prenatal and postnatal factors, as well as sex, on seizure susceptibility in young animals.

Stress responses of adolescent male and female rats exposed repeatedly to cat odor stimuli, and long-term enhancement of adult defensive behaviors.

In order to characterize the short- and long-term effects of repeated stressor exposure during adolescence, and to compare the effects of using two sources of cat odor as stressor stimuli, male and female adolescent rats (postnatal day (PND) ∼ 38-46) were exposed on five occasions to either a control stimulus, a cloth stimulus containing cat hair/dander, or a section of cat collar previously worn by a cat. Relative to control stimulus exposure, activity was suppressed and defensive behavior enhanced during exposure to either cat odor stimulus (most pervasively in rats exposed to the collar). Only cloth-exposed rats showed elevated levels of corticosterone (CORT), and only after repeated stressor exposure, but interestingly, rats exposed to the collar stimulus during adolescence continued to show increased behavioral indices of anxiety in adulthood. In this group, the time an individual spent in physical contact with a cagemate during the final adolescent exposure was negatively related to stress-induced CORT output in adulthood, which suggests that greater use of social support during adolescent stress may facilitate adult behavioral coping, without necessitating increased CORT release. These findings demonstrate that adolescent male and female rats respond defensively to cat odor stimuli across repeated exposures and that exposure to such stressors during adolescence can augment adult anxiety-like behavior in similar stressful conditions. These findings also suggest a potential role for social behavior during adolescent stressor exposure in mediating long-term outcomes.

Enhanced stress responses in adolescent versus adult rats exposed to cues of predation threat, and peer interaction as a predictor of adult defensiveness.

Development of the hypothalamic-pituitary-adrenal (HPA) axis is influenced by external factors during early life in mammals, which optimizes adult function for predicted conditions. We have hypothesized that adolescence represents a sensitive period for the development of some aspects of adult stress response regulation. This was based on prior work showing that repeated exposure of rats to a stressor across an adolescent period increases fearfulness in a novel environment in adulthood and results in lower levels of dopamine receptor subtype-2 protein in prefrontal cortex. Here, we further our investigation of both acute and long-term effects of repeated adolescent stressor exposure on physiological (i.e., corticosterone) and behavioral (i.e., defensive behavior) measures of stress responding in male and female rats. Furthermore, we compared outcomes with those following identical manipulations administered in early adulthood and found that animals exposed to cues of predation threat during adolescence showed the most robust defensive responses to a homotypic stressor encountered in adulthood. Peer interaction during control manipulation in adolescence was identified as an important individual characteristic mediating development of adult defensive strategies.