Pre-pubertal gonadectomy and the social consequences of acute ethanol in adolescent male and female rats

From adolescence to late aging: A comprehensive review of social behavior, alcohol, and neuroinflammation across the lifespan

The passage of time dictates the pace at which humans and other organisms age but falls short of providing a complete portrait of how environmental, lifestyle and underlying biological processes contribute to senescence. Two fundamental features of the human experience that change dramatically across the lifespan include social interactions and, for many, patterns of alcohol consumption. Rodent models show great utility for understanding complex interactions among aging, social behavior and alcohol use and abuse, yet little is known about the neural changes in late aging that contribute to the natural decline in social behavior. Here, we posit that aging-related neuroinflammation contributes to the insipid loss of social motivation across the lifespan, an effect that is exacerbated by patterns of repeated alcohol consumption observed in many individuals. We provide a comprehensive review of (i) neural substrates crucial for the expression of social behavior under non-pathological conditions; (ii) unique developmental/lifespan vulnerabilities that may contribute to the divergent effects of low-and high-dose alcohol exposure; and (iii) aging-associated changes in neuroinflammation that may sit at the intersection between social processes and alcohol exposure. In doing so, we provide an overview of correspondence between lifespan/developmental periods between common rodent models and humans, give careful consideration to model systems used to aptly probe social behavior, identify points of coherence between human and animal models, and point toward a multitude of unresolved issues that should be addressed in future studies. Together, the combination of low-dose and high-dose alcohol effects serve to disrupt the normal development and maintenance of social relationships, which are critical for both healthy aging and quality of life across the lifespan. Thus, a more complete understanding of neural systems-including neuroinflammatory processes-which contribute to alcohol-induced changes in social behavior will provide novel opportunities and targets for promoting healthy aging.

Sex-dependent consequences of pre-pubertal gonadectomy: Social behavior, stress and ethanol responsivity

Alcohol consumption can be enhanced or moderated by sensitivity to its aversive and appetitive properties, including positive social outcomes. These differences emerge post-pubertally, suggesting a potential role of gonadal hormones. To determine the role of gonadal hormones in sensitivity to the social impairing and social context-related attenuations in the aversive effects of ethanol, prepubertal male and female rats were gonadectomized (GX) or sham (SH) operated on postnatal day (P) 25, or left non-manipulated (NM). In adulthood (P70), rats were restrained for 90 min prior to challenge with 0.0 or 1.0 g/kg ethanol and social interaction (SI) testing. At P77, groups of 4 same-sex littermates from the same surgical condition were given access to a supersaccharin (SS) solution (3% sucrose, 0.125% saccharin), followed by an intraperitoneal injection of ethanol (0.0, 0.50, 1.0, 1.5 g/kg). Intakes of SS were examined 24h later for expression of conditioned taste aversions. Acute stress prior to SI testing increased frequency of play fighting in both sexes, whereas there were no GX effects on this measure, social investigation nor contact. GX, however, decreased baseline social preference (a social anxiety-like effect) in males, while inducing anxiolytic-like increases in baseline social preference in females. The social drinking test revealed that females developed ethanol conditioned taste aversions at a lower dose relative to males, regardless of surgical condition. These findings suggest a potential role for gonadal hormones in moderating social-anxiety like behaviors but not sensitivity to the social impairing effects of ethanol or ethanol's aversive consequences in a social context.

Peri-pubertal exposure to testicular hormones organizes response to novel environments and social behaviour in adult male rats

Previous research has shown that exposure to testicular hormones during the peri-pubertal period of life has long-term, organizational effects on adult sexual behaviour and underlying neural mechanisms in laboratory rodents. However, the organizational effects of peri-pubertal testicular hormones on other aspects of behaviour and brain function are less well understood. Here, we investigated the effects of manipulating peri-pubertal testicular hormone exposure on later behavioural responses to novel environments and on hormone receptors in various brain regions that are involved in response to novelty. Male rodents generally spend less time in the exposed areas of novel environments than females, and this sex difference emerges during the peri-pubertal period. Male Lister-hooded rats (Rattus norvegicus) were castrated either before puberty or after puberty, then tested in three novel environments (elevated plus-maze, light-dark box, open field) and in an object/social novelty task in adulthood. Androgen receptor (AR), oestrogen receptor (ER1) and corticotropin-releasing factor receptor (CRF-R2) mRNA expression were quantified in the hypothalamus, hippocampus and medial amygdala. The results showed that pre-pubertally castrated males spent more time in the exposed areas of the elevated-plus maze and light-dark box than post-pubertally castrated males, and also confirmed that peri-pubertal hormone exposure influences later response to an opposite-sex conspecific. Hormone receptor gene expression levels did not differ between pre-pubertally and post-pubertally castrated males in any of the brain regions examined. This study therefore demonstrates that testicular hormone exposure during the peri-pubertal period masculinizes later response to novel environments, although the neural mechanisms remain to be fully elucidated.