Neuroendocrine effects of cytokines in the rat

The necessity ot maintain and/or restore homeostasis is an essential feature of mammals. This requires complex interactions between body cells, such as those from the immune and neuroendocrine systems, and in particular implies that the occurrence of immune activation be conveyed to the brain. It is now widely recognized that following infection, injury or inflammation, some immune cells (particularly macrophages) produce polypeptides called cytokines, interleukins or lymphokines /48/. These proteins provide the basis for intercellular communication between leukocytes (hence the name "interleukins") and mediate the immunoinflammatory responses (in particular T and B lymphocyte proliferation) /4,177/. In addition, interleukins (IL) can enter the general circulation and reach cells of the neuroendocrine axes, a phenomenon which represents one arm of the bidirectional communication links between the immune and the endocrine systems /25/. The early events which take place after presentation of an antigen (the so-called "acute-phase response" /89/) include metabolic and endocrine changes, such as changes in the circulating levels of insulin, TSH, GH, LH and ACTH, as well as adrenal and gonadal steroids /7,14/. This article reviews our present state of knowledge with regard to the hypothalamic-pituitary-adrenal (HPA) and hypothalamic-pituitary-gonadal (HPG) axes of the rodent in response to interleukins.