Social isolation induces behavioral and neuroendocrine disturbances relevant to depression in female and male prairie voles

Abstract

Supportive social interactions may be protective against stressors and certain mental and physical illness, while social isolation may be a powerful stressor. Prairie voles are socialty monogamous rodents that model some of the behavioral and physiological traits displayed by humans, including sensitivity to social. isolation. Neuroendocrine and behavioral parameters, selected for their relevance to stress and depression, were measured in adult female and mate prairie voles following 4 weeks of social. isolation versus paired housing. In Experiment 1, oxytocin-immunoreactive cell. density was higher in the hypothalamic paraventricular nucleus (PVN) and plasma oxytocin was elevated in isolated females, but not in mates. In Experiment 2, sucrose intake, used as an operational. definition of hedonia, was reduced in both sexes following 4 weeks of isolation. Animals then received a resident-intruder test, and were sacrificed either 10min later for the analysis of circulating hormones and peptides, or 2h later to examine neural activation, indexed by c-Fos expression in PVN cells immunoreactive for oxytocin or corticotropin-releasing factor (CRF). Compared to paired animals, plasma oxytocin, ACTH and corticosterone were elevated in isolated females and plasma oxytocin was elevated in isolated mates, following the resident-intruder test. The proportion of cells double-labeled for c-Fos and oxytocin or c-Fos and CRF was elevated in isolated females, and the proportion of cells double-labeled for c-Fos and oxytocin was elevated in isolated mates following this test. These findings suggest that social isolation induces behavioral and neuroendocrine responses relevant to depression in mate and female prairie voles, although neuroendocrine responses in females may be especially sensitive to isolation. (C) 2007 Elsevier Ltd. All rights reserved