Acute and long-term sex-dependent effects of social instability stress on anxiety-like and social behaviours in Wistar rats

The effects of pharmacologic estradiol on anxiety-related behavior in adolescent and adult female mice

Early pubertal onset during adolescence is consistently linked with increased risk of anxiety and depression in girls. Although estradiol tends to have anxiolytic effects on behavior in adulthood, whether estradiol's anxiolytic actions change pre- to post-adolescent development is not clear. Using a rodent model, the current study tested whether anxiety-like responses to estradiol differ before and after adolescence in female mice. Prepubertal and adult C57BL/6 mice were ovariectomized, implanted with vehicle- or estradiol-filled silastic capsules, and behavioral tested 6 days later in the open field and elevated zero maze. A pharmacologic dose of estradiol was administered in silastic capsules (0.72 μg/0.02 mL) to maximize behavioral responses at both ages. In the open field, estradiol implants decreased anxiety-like behavior in adolescent females (relative to vehicle) and had negligible effects on anxiety-related behavior in adult females. These data suggest that adolescence is associated with changes in behavioral responsiveness to estradiol. In the elevated zero maze, adolescent females displayed higher levels of anxiety-like behavior than adults, irrespective of estradiol treatment. These findings demonstrate that substantial changes in anxiety-related behavior occur during adolescence, including an assay-dependent shift in behavioral responsiveness to estradiol.

Juvenile social isolation in Sprague Dawley rats does not have a lasting impact on social behavior in adulthood

Adolescent social interactions are essential for shaping adult behavior in humans. While rodent studies have highlighted the impact of social isolation on behavior, many extend isolation into adulthood, making it challenging to pinpoint the long-term consequences of juvenile isolation. To address these challenges, we examined the effects of social isolation using two independent protocols with male and female Sprague Dawley rats. In both prfotocols, rats were isolated during the juvenile stage; however, in one protocol, rats were re-socialized following isolation and tested in adulthood, while in the other, rats were tested immediately after isolation. This approach allowed us to determine whether social deficits emerged following adolescent isolation and if they could be reversed by re-socialization before adulthood. We found that juvenile isolation had no lasting effects but increased motivation for social interaction immediately after isolation. These findings underscore the need to account for housing conditions and isolation protocols when assessing the effects of social isolation.

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.

A behavioral screening method for predicting PTSD-like phenotypes: Novel application to female rats

BACKGROUND

Only a small percentage of trauma-exposed subjects develop PTSD, with females being twice as likely. Most rodent models focus on males and fail to account for inter-individual variability in females.

NEW METHOD

We tested a behavioral PTSD model in female rats to distinguish between susceptible and resilient individuals. In Experiment 1, female rats underwent footshocks paired with social isolation, a PTSD risk factor. They were re-exposed to the conditioned context to test memory retention, and assessed in the Elevated Plus Maze (EPM) and Social Interaction (SI) tests for anxiety and social behavior.

RESULTS

Footshock-exposed rats showed fear memory retention up to 16 days, indicated by elevated freezing behavior during re-exposure. They also exhibited reduced exploration in the EPM and less SI time compared to controls. In Experiment 2, we classified rats into normal responders, susceptible, and resilient groups based on locomotor activity after trauma, correlating with memory retention and anxiety.

COMPARISON WITH EXISTING METHODS

Unlike existing models focused on males and lacking predictive variables before trauma, our method identifies PTSD-like susceptibility and resilience in female rats by using exploratory behavior as a predictor before trauma exposure.

CONCLUSIONS

Exploratory activity in a novel environment after trauma and before extinction is a reliable predictor of PTSD-like phenotypes and differentiates between susceptible and resilient female rats.

Corticosterone effects induced by stress and immunity and inflammation: mechanisms of communication

The body instinctively responds to external stimuli by increasing energy metabolism and initiating immune responses upon receiving stress signals. Corticosterone (CORT), a glucocorticoid (GC) that regulates secretion along the hypothalamic-pituitary-adrenal (HPA) axis, mediates neurotransmission and humoral regulation. Due to the widespread expression of glucocorticoid receptors (GR), the effects of CORT are almost ubiquitous in various tissue cells. Therefore, on the one hand, CORT is a molecular signal that activates the body's immune system during stress and on the other hand, due to the chemical properties of GCs, the anti-inflammatory properties of CORT act as stabilizers to control the body's response to stress. Inflammation is a manifestation of immune activation. CORT plays dual roles in this process by both promoting inflammation and exerting anti-inflammatory effects in immune regulation. As a stress hormone, CORT levels fluctuate with the degree and duration of stress, determining its effects and the immune changes it induces. The immune system is essential for the body to resist diseases and maintain homeostasis, with immune imbalance being a key factor in the development of various diseases. Therefore, understanding the role of CORT and its mechanisms of action on immunity is crucial. This review addresses this important issue and summarizes the interactions between CORT and the immune system.

Lasting effects of adolescent social instability stress on dendritic morphology in the nucleus accumbens in female and male Long Evans rats

Social instability stress (SS) in adolescence in rats leads to long-lasting changes in social behaviour and reward-related behaviour relative to control rats. Given the role of the nucleus accumbens (NAc) in such behaviours, we investigated the morphology of medium spiny neurons (MSNs), which are most neurons in the NAc, in adult female and male rats exposed to SS in adolescence. Irrespective of sex, SS rats had increased number of dendritic spines in both the core and shell regions of the NAc (2.3 % and 18.1 % increase, respectively). In the core, SS rats had a 16 % reduction in the total dendritic lengths of MSNs, whereas in the shell, SS rats had a greater dendritic length closer to the soma, and particularly in SS female rats, whereas the opposite was found farther from the soma (SS 10.6 % > CTL overall). Although the extent to which such structural changes may underlie the enduring effects of SS in adolescence requires investigation, the results add to evidence that changes to the social environment in adolescence can determine adult neuronal structural.

Pubertal maternal presence reduces anxiety and increases adult neurogenesis in Kunming mice offspring

Puberty is a critical period of emotional development and neuroplasticity. However, most studies have focused on early development, with limited research on puberty, particularly the parental presence. In this study, four groups were established, and pubertal maternal presence (PMP) was assessed until postnatal days 21 (PD21), 28 (PD28), 35 (PD35), and 42 (PD42), respectively. The social interaction and anxiety behaviors, as well as the expression of oxytocin (OT) in the paraventricular nucleus (PVN) and supraoptic nucleus (SON), and the number of new generated neurons and the expression of estrogen receptor alpha (ERα) in the dentate gyrus (DG) were assessed. The results suggest that there is a lot of physical contact between the mother and offspring from 21 to 42 days of age, which reduces anxiety in both female and male offspring in adulthood; for example, the PMP increased the amount of time mice spent in the center area in the open field experiment and in the bright area in the light-dark box experiment. PMP increased OT expression in the PVN and SON and the number of newly generated neurons in the DG. However, there was a sexual difference in ERα, with ERα increasing in females but decreasing in males. In conclusion, PMP reduces the anxiety of offspring in adulthood, increases OT in the PVN and SON, and adult neurogenesis; ERα in the DG may be involved in this process.

Adolescent development of anxiety-related behavior and shifts in behavioral responsiveness to estradiol in female mice

Early pubertal onset during adolescence is consistently linked with increased risk of anxiety and depression in girls. Although estradiol tends to have anxiolytic effects in adulthood, whether sensitivity to estradiol's anxiolytic actions increases during adolescence is not clear. Using a rodent model, the current study tested the hypothesis that a shift in sensitivity to the anxiolytic effects of estradiol occurs during adolescence. To test this hypothesis, prepubertal and adult C57BL/6 female mice were ovariectomized, implanted with vehicle- or estradiol-filled silastic capsules, and behavioral tested one week later in the open field and elevated zero maze. Our hypothesis predicted that estradiol would decrease anxiety-related behavior to a greater extent in adults than in adolescent females, however, our results did not support this hypothesis. In the open field, estradiol implants significantly decreased anxiety-like behavior in adolescent females (relative to vehicle) and had little to no effect on the behavior of adults. These data suggest that adolescence is associated with a downward shift in sensitivity to the anxiolytic effects of estradiol on behavior in the open field. In contrast, although estradiol treatment did not influence anxiety-like responses in the elevated zero maze in early adolescent or adult females, adolescent females displayed significantly higher levels of anxiety-like behavior than adults. These findings demonstrate that substantial changes in anxiety-related behavior occur during adolescence, including a context-dependent shift in behavioral responsiveness to estradiol.

Early life adversities, psychopathologies and novel pharmacological strategies

Exposure to adversities during early life stages (early life adversities - ELA), ranging from pregnancy to adolescence, represents a major risk factor for the vulnerability to mental disorders. Hence, it is important to understand the molecular and functional underpinning of such relationship, in order to develop strategies aimed at reducing the psychopathologic burden associated with ELA, which may eventually lead to a significant improvement in clinical practice. In this review, we will initially recapitulate clinical and preclinical evidence supporting the link between ELA and psychopathology and we will primarily discuss the main biological mechanisms that have been described as potential mediators of the effects of ELA on the psychopathologic risk, including the role for genetic factors as well as sex differences. The knowledge emerging from these studies may be instrumental for the development of novel therapeutic strategies aimed not only at correcting the deficits that emerge from ELA exposure, but also in preventing the manifestation of a full-blown psychopathologic condition. With this respect, we will specifically focus on adolescence as a key time frame for disease onset as well as for early therapeutic intervention. We believe that incorporating clinical and preclinical research data in the context of early life adversities can be instrumental to elucidate the mechanisms contributing to the risk for psychopathology or that may promote resilience. This will ultimately allow the identification of 'at risk' individuals who may benefit from specific forms of interventions that, by interfering with disease trajectories, could result in more benign clinical outcomes.

Synaptic pruning during adolescence shapes adult social behavior in both males and females

Evolutionarily conserved, peer-directed social behaviors are essential to participate in many aspects of human society. These behaviors directly impact psychological, physiological, and behavioral maturation. Adolescence is an evolutionarily conserved period during which reward-related behaviors, including social behaviors, develop via developmental plasticity in the mesolimbic dopaminergic "reward" circuitry of the brain. The nucleus accumbens (NAc) is an intermediate reward relay center that develops during adolescence and mediates both social behaviors and dopaminergic signaling. In several developing brain regions, synaptic pruning mediated by microglia, the resident immune cells of the brain, is important for normal behavioral development. We previously demonstrated that during adolescence, in rats, microglial synaptic pruning shapes the development of NAc and social play behavior in males and females. In this report, we hypothesize that interrupting microglial pruning in NAc during adolescence will have persistent effects on male and female social behavior in adulthood. We found that inhibiting microglial pruning in the NAc during adolescence had different effects on social behavior in males and females. In males, inhibiting pruning increased familiar exploration and increased nonsocial contact. In females, inhibiting pruning did not change familiar exploration behavior but increased active social interaction. This leads us to infer that naturally occurring NAc pruning serves to reduce social behaviors toward a familiar conspecific in both males and females.

Sexual differentiation of neural mechanisms of stress sensitivity during puberty

Anxiety disorders are a major public health concern and current treatments are inadequate for many individuals. Anxiety is more common in women than men and this difference arises during puberty. Sex differences in physiological stress responses may contribute to this variability. During puberty, gonadal hormones shape brain structure and function, but the extent to which these changes affect stress sensitivity is unknown. We examined how pubertal androgens shape behavioral and neural responses to social stress in California mice (Peromyscus californicus), a model species for studying sex differences in stress responses. In adults, social defeat reduces social approach and increases social vigilance in females but not males. We show this sex difference is absent in juveniles, and that prepubertal castration sensitizes adult males to social defeat. Adult gonadectomy does not alter behavioral responses to defeat, indicating that gonadal hormones act during puberty to program behavioral responses to stress in adulthood. Calcium imaging in the medioventral bed nucleus of the stria terminalis (BNST) showed that social threats increased neural activity and that prepubertal castration generalized these responses to less threatening social contexts. These results support recent hypotheses that the BNST responds to immediate threats. Prepubertal treatment with the nonaromatizable androgen dihydrotestosterone acts in males and females to reduce the effects of defeat on social approach and vigilance in adults. These data indicate that activation of androgen receptors during puberty is critical for programming behavioral responses to stress in adulthood.