65.4 Saturday, Jan. 5 Seasonal variation in intracellular glucocorticoid receptor binding in the immune tissues of a wild bird LATTIN, C. R.*; ROMERO, L. M.; Tufts University; Tufts University firstname.lastname@example.org
Glucocorticoids such as corticosterone (CORT) help wild animals regulate their metabolism and cope with environmental stressors, but they can also have immunosuppressive effects. Nelson and others have proposed that animals should have evolved mechanisms to increase immune function to counteract seasonally-recurrent stressors that might otherwise compromise immunocompetence. We hypothesized that this could occur in part by seasonally downregulating immune tissue sensitivity to CORT by reducing concentrations of CORT receptors. We captured wild house sparrows (Passer domesticus) in Massachusetts during 6 different life history stages: molt, early and late winter, pre-egg-laying, breeding and late breeding (n = 12 for each period). Mineralocorticoid receptors (MR) and glucocorticoid receptors (GR) were quantified in spleen and skin using radioligand binding assays, and spleen mass was also assessed. Spleen mass was greater in the late breeding period compared to both winter periods. MR binding in spleen was lower in late breeding compared to pre-laying. There were no seasonal patterns in GR binding in spleen, although overall, female sparrows showed greater GR binding than males. The spleen's increased size and decreased sensitivity to CORT during the late breeding period could be related to the large influx of fledgling birds carrying potential pathogens into the house sparrow population at this time of year, or some other predictable life history event. There were no seasonal changes in MR or GR binding in back or belly skin. There is evidence of local production of glucocorticoids in mammalian skin, so skin receptors could be regulated locally. In any case, these results show that glucocorticoid receptors may be seasonally regulated in a tissue-specific manner.