This study analyzed in Balb/C mice the effects of individual housing on behavior, serum
corticosterone and resistance to Ehrlich
tumor growth. Mice (60 days old) were individually (IH) or grouped housed (G) (10-12 animals/cage) for 14-21 days. The 1st day of the housing condition was considered experimental day 1 (ED1). Results showed that on ED21, IH mice, when compared to G mice, presented no differences on
corticosterone serum levels when kept undisturbed; however, an increased level of this
hormone was observed in IH mice after an immobilization stress challenge. An increased time spent in the plus-maze closed arms and a decreased time in the open arms were also observed in IH mice. When compared to G animals, after inoculation with 10(5) Ehrlich
tumor cells on ED1, IH mice presented an increase in volume of ascitic fluid and number of
tumor cells. The survival time of IH mice was also shorter than that measured in G animals. Furthermore, IH mice injected with a different number of
tumor cells on ED1 always presented increased Ehrlich
tumor cells than G group. Interestingly, these effects were not observed when the
tumor cells injection was done on ED4. These results suggest that individual-housing conditions induce an altered immune-endocrine response and, at the same time, decrease animals' resistance to Ehrlich
tumor growth. It is proposed that the neural link between the behavioral and immunological changes observed after the stress of individual housing might involve the activation of the HPA axis.