Influence of daily social stimulation on behavioral and physiological outcomes in an animal model of PTSD

Abstract

IntroductionWe have shown in previous work that acute episodes of predator exposure occurring in the context of chronic social instability produced PTSD‐like sequelae in rats. Our animal model of PTSD contained two components: (1) acute trauma, immobilization of rats in close proximity to a cat twice in 10 days, and (2) chronic social instability, 31 days of randomized housing of cage cohorts. Here we tested the hypothesis that daily social stimulation would block the development of the PTSD‐like sequelae.MethodsBeginning 24 h after the first cat exposure, adult male rats were given our established PTSD model, alone or in conjunction with daily social stimulation, in which all rats within a group interacted in a large apparatus for 2 h each day for the final 30 days of the PTSD regimen. All behavioral, for example, anxiety, memory, startle testing, and physiological assessments, for example, body growth, organ weights, and corticosterone levels, took place following completion of the psychosocial stress period.ResultsDaily social stimulation blocked the expression of a subset of PTSD‐like effects, including predator‐based cued fear conditioning, enhanced startle response, heightened anxiety on the elevated plus maze and the stress‐induced suppression of growth rate. We also found that social stimulation and psychosocial stress produced equivalent outcomes in some measures, including adrenal and heart hypertrophy, thymus atrophy, and a reduction in poststress corticosterone levels.ConclusionsDaily exposure of rats to a highly social environment blocked the development of a subset of trauma‐induced sequelae, particularly fear‐related outcomes. It is notable that daily social stimulation normalized a subset, but not all, of the PTSD‐like effects. We discuss our findings in the context of the literature demonstrating that social stimulation can counteract the adverse effects of traumatic stress on behavioral and physiological measures, as well as to produce its own stress‐like outcomes.

Social housing and social isolation: Impact on stress indices and energy balance in male and female Syrian hamsters ( Mesocricetus auratus )

“…Thymus involution is a well-accepted hallmark of stress, and we obtained a modest reduction in thymus mass in group housed animals. This finding is consistent with previously reported reductions in thymus mass in hamsters repeatedly exposed to a predator odor [39] and in rats subjected to cat odor or chronic, unstable group housing [40]. Our results are obviously just a single measure obtained after four weeks of stable housing conditions, and additional research would be necessary to determine a time course for the effect of housing or the effect of changing group composition in grouped animals on the thymus gland.…”

Microbial lysate upregulates host oxytocin

“…By contrast, stimulation of social behavior or improving sense of well-being by enrichment of caging decreased corticosterone levels while counteracting thymus shrinkage in both mice and rats (Abou-Ismail and Mahboub, 2011; Seetharaman et al, 2016; Van Loo et al, 2004). A study in genetically engineered mice has provided direct evidence linking thymus gland size and function with corticosterone (Youn et al, 2011).…”

Behavioral and Neurobiological Assessments of Predator-Based Fear Conditioning and Extinction

“…We reported that rats exposed to a cat on two occasions, occurring within a 31-day period of chronic social instability, exhibited numerous behavioral and physiological outcomes which resemble the clinical symptoms of PTSD (for reviews see [67] & [68]). The most relevant observation from this work with regard to the current study is our finding that rats exhibit a long-term fear conditioned memory of the context and cue associated with the cat exposure component of chronic psychosocial stress [69]- [71] which persisted for at least 4 months [72].…”