Endocrine status and scent attractiveness in male dwarf hamsters Phodopus sungorus injected with thymus-dependent and thymus-independent antigens

We studied the influences of immune activation by thymus-dependent(sheep red blood cells,SRBC)and independent(bacterial lipopolysaccharide,LPS)antigens on odor signals and endocrine status in dwarf hamsters.Administration of SRBS to mature males resulted in a drop of sexual scent attractiveness of soiled bedding collected during 5 days after injection.This effect was accompanied with a decline of fecal testosterone.Reduction of the male scent attractiveness after SRBC treatment had maximum manifestation in males of dwarf hamsters with low humoral immune response to this challenge.Contrary to the effects of SRBC,males injected with LPS showed an increase of scent attractiveness.Differences in the time that mature females spent sniffing olfactory stimuli(LPS vs control),correlated positively with differences in concentration of testosterone in feces collected from LPS and saline treated males.We discuss the adaptive meaning of the opposite olfactory effects,which induced by activation of the nonspecific innate immunity with LPS and by activation of specific acquired immunity with SRBC.

Effect of Shortening Day Length on Immune Function in Siberian Hamsters

In order to understand the effect of gradual changes in photoperiod on immune function, adult female Siberian hamsters (Phodopus sungorus) were randomly divided into the control group (12L:12D, Con, n = 11) and the shortening day length group (SD, n = 11), in which day length was reduced from 12:12 h to 8:16 h light-dark cycle at the pace of half an hour every week. Meanwhile the winter immunoenhancement hypothesis, which holds that animals’ immune function would be enhanced in winter or winter-like conditions, was tested. Gradual shortening day length had no effect on body mass and body composition including wet carcass mass, the subcutaneous, retroperitoneal, mesenteric and total body fat masses in Siberian hamsters. The masses of liver and small intestine with contents were higher in the SD group than in the Con group, however other organ masses such as brain, heart, kidney and so on did not differ between the two groups. Phytohemagglutinin (PHA) response after 24 h of PHA injection was enhanced by the shortening photoperiod, which supported the winter immunoenhancement hypothesis. The masses of spleen and thymus, white blood cells, bacteria killing capacity indicative of innate immunity were not affected, which did not support this hypothesis. In summary, gradually decrease in day length increased cellular immunity, but had no effect on other immunological parameters in Siberian hamsters.