Cohabitation with an Ehrlich tumor-bearing cagemate induces immune but not behavioral changes in male mice

Abstract

Cohabitation with Ehrlich ascitic tumor-injected conspecifics induces behavioral, neurochemical, endocrine and immune changes indicative of stress and immune impairment in female mice. The present work analyzed the effects of similar cohabitation in Swiss and Balb/C male mice. At least 12 pairs of male mice were divided into a control group and an experimental group. On experimental day 1 (ED1), one animal within each experimental pair was inoculated with 5 x 10(6) Ehrlich tumor cells intraperitoneally (i.p.); the other animal was kept undisturbed and was referred to as the CSP (companion of a sick partner). One male mouse of each control pair was treated i.p. with 0.9% NaCl (1 mL/kg); the other animal (the CHP, companion of a healthy partner) was kept undisturbed. Cohabitation with a sick partner for 11 days did not induce any behavioral, hypothalamic noradrenergic, corticosterone or adrenal weight changes in the Swiss CSP male mice compared to those of the Swiss CHP group. However, impairments in neutrophil phagocytosis and oxidative burst as well as increased levels of catecholamines were observed in Swiss and Balb/C CSP mice relative to CHP male animals of the same strains on ED11 and ED14, respectively. Moreover, after a challenge with 5 x 106 Ehrlich tumor cells on ED11 of cohabitation, the number and concentration of tumor cells found in the ascitic fluid were higher in the Swiss CSP male mice than in the CHP mice. These data suggest that the immune changes observed in Swiss and Balb/C male CSP mice after cohabitation with a sick cagemate might, ultimately, depend on the changes induced by catecholamines, as previously reported for CSP female mice. However, contrary to that reported in Swiss CSP female mice, changes in behavioral and hypothalamic noradrenaline activity were not found in the Swiss CSP male mice analyzed in this work. This fact suggests that male and female CSP mice might use similar immune but different CNS strategies against the threats posed by the tumor-bearing animals.