Effects of chronic social stress on neuroendocrine responsiveness to challenge with ethanol, dexamethasone and corticotropin-releasing hormone

Neuroendocrine and behavioral profiles of group-housed rodents differ from those of singly-housed ones. Subordinate rats have elevated plasma corticosterone ( CORT) concentration and impaired activity of the hypothalamic-pituitary-adrenal (HPA) axis compared to dominant cagemates. However, little is known about the effects of social hierarchy on other stress-related hormones. We examined plasma prolactin (PRL) and CORT responses to saline and ethanol ( EtOH) injections, and 1 month later to dexamethasone (DEX) and corticotropin-releasing hormone (CRH) challenges of group- ( triad) and single-housed male rats over a period of 225 days. Social status was determined from behaviors displayed upon initial triad housing. Subordinate rats had lower basal PRL and higher CORT compared to dominant rats. The injection of EtOH (1.25 g/kg) depressed PRL and elevated CORT levels significantly more than the saline injection only in dominant and singly-housed rats. DEX increased PRL levels, most strikingly in dominant rats, and suppressed CORT only in dominant rats. After CRH challenge, plasma CORT increased in all groups, subdominant and subordinate rats displaying blunted responses. Our data demonstrate that social rank and housing conditions affect plasma PRL and CORT concentrations, and modify responses to EtOH, possibly reflecting impairments of HPA axis regulation in socially-housed rats. Copyright (C) 2004 S. Karger AG, Basel.