Possible involvement of stress hormones and hyperglycaemia in chronic mild stress-induced impairment of immune functions in diabetic mice.

Stress, an important aspect of modern life, has long been associated with an altered homeostatic state. Little is known about the effect of the life stress on the outcome of diabetes mellitus, especially related to the higher risk of infections. Here, we evaluate the effects of chronic mild stress (CMS) exposure on the evolution of type I diabetes induced by streptozotocin administration in BALB/c mice. Exposure of diabetic mice to CMS resulted in a significant reduction of survival and a sustained increase in blood glucose values. Concerning the immune response, chronic stress had a differential effect in mice with diabetes with respect to controls, showing a marked decrease in both T- and B-cell proliferation. No correlation was found between splenic catecholamine or circulating corticosterone levels and the proliferative response. However, a significant negative correlation was found between glucose levels and concanavalin A- and lipopolysaccharide-stimulated proliferative responses of T and B cells. A positive correlation between blood glucose and splenic catecholamine concentrations was found in diabetic mice but not in controls subjected to CMS. Hence, the present report shows that diabetic mice show a worse performance in immune function after stress exposure, pointing to the importance of considering life stress as a risk factor for patients with diabetes.

Retreat site selection and social organization in captive electric fish, Apteronotus leptorhynchus.

Gymnotiform fish use their electric organ discharge for electrolocation and communication. They are active nocturnally and seek retreat sites during the day. We examined retreat site selection in Apteronotus leptorhynchus by assessing their preference for retreat tubes that differed in opacity and dimension. Isolated fish preferred opaque to clear tubes, long and narrow diameter tubes to short, wide diameter tubes, and open-ended to closed tubes. We also assessed how groups of fish distributed themselves in tubes according to sex and electric organ discharge frequency under four conditions: (1) unlimited tube availability, (2) limited tube availability, (3) variation in tube opacity, and (4) variation in tube dimension. When tube availability was unlimited, fish generally preferred to occupy tubes alone. However, females, but not males, often cohabited tubes with consexuals. When tube availability was limited, females were more often than males found outside of tubes. When tubes varied by opacity and dimension, fish clustered most commonly in preferred tube types (opaque and long tubes). Males with the highest electric organ discharge frequencies usually occupied the most preferred tube type. Thus, fish have clear preferences in selecting retreat sites and groups of fish reveal their dominance relationships when presented with variation in retreat sites.