Stress-induced sickness behaviors: an alternative hypothesis for responses during maternal separation.

During maternal separation, some primate and nonprimate species show a biphasic (active/passive) response. The second stage is characterized by reduced activity, a hunched body posture, and other behaviors. Traditionally, the second stage has been referred to as "despair" and is considered an animal model for human depression. Recent research in psychoneuroimmunology suggests an alternative hypothesis--that behaviors occurring during the second passive phase represent stress-induced "sickness behaviors." This perspective more readily accounts for findings in widely divergent species, does not require assumptions regarding the ability to express complex emotional states, is empirically testable, and aligns the separation model with recent hypotheses regarding the nature and ontogeny of depressive illness.

Glucocorticoids affect gonadotropin-releasing hormone immunoreactivity in musk shrew brain.

Multiple interactions between the hypothalamic-pituitary-adrenal and the hypothalamic-pituitary-gonadal systems exist. In this study, we asked if glucocorticoid administration affected gonadotropin-releasing hormone (GnRH) immunoreactivity. We found that musk shrews treated with dexamethasone (DEX), a synthetic glucocorticoid, had more GnRH-immunoreactive (ir) cells in the forebrain than did cortisol- or control-treated animals. The effects of DEX were noted rapidly, within 15 min, after administration. These effects were observed in the forebrain as a whole and also in specific subpopulations of GnRH-ir cells located in the medial septum/diagonal band and the hypothalamus.