A novel social fear conditioning procedure alters social behavior and mTOR signaling in differentially housed adolescent rats

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.

Social context modulates active avoidance: Contributions of the anterior cingulate cortex in male and female rats

Actively avoiding danger is necessary for survival. Most research on active avoidance has focused on the behavioral and neurobiological processes when individuals learn to avoid alone, within a solitary context. Therefore, little is known about how social context affects active avoidance. Using a modified version of the platform-mediated avoidance task in rats, we investigated whether the presence of a social partner attenuates conditioned freezing and enhances avoidance compared to avoidance in a solitary context. Rats spent a similar amount of time avoiding during either context; however, rats trained in the social context exhibited greater freezing as well as lower rates of darting and food seeking compared to rats trained in the solitary context. In addition, we observed higher levels of avoidance in females compared to males in the solitary context, but this sex difference was not present in rats trained in the social context. To gain greater mechanistic insight, we optogenetically inactivated glutamatergic projection neurons in the anterior cingulate cortex (ACC) following avoidance training in either context. After avoidance was learned in a social context, photoinactivation of ACC reduced expression of avoidance during a test when the social partner was absent, but not when the partner was present. Our findings suggest a novel contribution of the ACC in avoidance that is learned with a social partner, which has translational implications for understanding ACC dysfunction in those suffering from trauma-related disorders.

Shaping behaviors through social experience and their proposed sensitivity to stress

Mammals have evolved with a range of innate drives, such as thirst and hunger, that promote motivated behaviors to ensure survival. A drive for social engagement promotes social interaction and bond formation. While a stable social environment maintains the opportunity for resource sharing and protection, an additional benefit is provided by the social transmission of information. Social experiences, and information obtained from conspecifics, can be used to learn about threats and opportunities in the environment. This review examines the primary forms of social learning and how they can shape behavior. Additionally, while there is much known about the effects of stress on learning and memory, there is much less known about its effects on social learning and memory. This review will therefore dissect the major factors that contribute to social learning and propose how stress may impact these factors. This may serve as a way to formulate new hypotheses about how stress might impact social learning and the effects of social experiences on behavior.

Active avoidance recruits the anterior cingulate cortex regardless of social context in male and female rats

Actively avoiding danger is necessary for survival. Most research has focused on the behavioral and neurobiological processes when individuals avoid danger alone, under solitary conditions. Therefore, little is known about how social context affects active avoidance. Using a modified version of the platform-mediated avoidance task in rats, we investigated whether the presence of a social partner attenuates conditioned freezing and enhances avoidance learning compared to avoidance learned under solitary conditions. Rats spent a similar percentage of time avoiding during the tone under both conditions; however, rats trained under social conditions exhibited greater freezing during the tone as well as lower rates of darting and food seeking compared to solitary rats. Under solitary conditions, we observed higher levels of avoidance in females compared to males, which was not present in rats trained under social conditions. To gain greater mechanistic insight, we optogenetically inactivated glutamatergic projection neurons in the anterior cingulate cortex (ACC) following avoidance training. Photoinactivation of ACC neurons reduced expression of avoidance under social conditions both in the presence and absence of the partner. Under solitary conditions, photoinactivation of ACC delayed avoidance in males but blocked avoidance in females. Our findings suggest that avoidance is mediated by the ACC, regardless of social context, and may be dysfunctional in those suffering from trauma-related disorders. Furthermore, sex differences in prefrontal circuits mediating active avoidance warrant further investigation, given that females experience a higher risk of developing anxiety disorders.

Social Instability Stress in Adolescence and Social Interaction in Female Rats

Adolescence is a critical time of brain development for regions governing social behaviour and social learning. Social experiences influence the ongoing maturation of the neural structures and ultimately modify the social behaviour of adults in response to social cues. Social instability stress in adolescence (SS; daily 1-hour isolation + change of cage partner in postnatal days [PND] 30-45) leads to a long-lasting reduction in social interaction in SS rats compared with non-stressed (CTL) rats in males; here we investigate females. In a first experiment, we found that female rats exposed to adolescent SS also showed the decrement in social interaction irrespective of age at which tested, and replicated the effects previously found in males. In experiment 2, which involved females only, SS and CTL rats did not differ in anxiety-like behaviour in the elevated plus maze (EPM) and the reduction in social interaction was not significant. Nevertheless, when tested in adolescence at P47 (and not at P71), SS female rats had higher corticosterone release during the social interaction test than did CTL rats, and they exhibited a different pattern of neural activation as measured by immunoreactivity to the protein products of zif268 and c-fos (SS < CTL in medial prefrontal cortex and SS > CTL in hippocampus), and reduced oxytocin immunoreactivity in the paraventricular nucleus of the hypothalamus than did CTL rats. These results extend our previous findings of effects of SS in adolescent female rats on behavioural responses to psychostimulants to social behaviour, and point to directions for investigations of the neural mechanisms involved.

Methods and Challenges in Investigating Sex-Specific Consequences of Social Stressors in Adolescence in Rats: Is It the Stress or the Social or the Stage of Development?

Adolescence is a time of social learning and social restructuring that is accompanied by changes in both the hypothalamic-pituitary-gonadal axis and the hypothalamic-pituitary-adrenal (HPA) axis. The activation of these axes by puberty and stressors, respectively, shapes adolescent development. Models of social stress in rats are used to understand the consequences of perturbations of the social environment for ongoing brain development. This paper reviews the challenges in investigating the sex-specific consequences of social stressors, sex differences in the models of social stress used in rats and the sex-specific effects on behaviour and provides an overview of sex differences in HPA responding to stressors, the variability in pubertal development and in strains of rats that require consideration in conducting such research, and directions for future research.