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Stress is known to affect the intensity of the immune response. The involvement of central regulatory structures in mediating these changes was addressed by analyzing the extent of activation of neurons in the hypothalamus (in terms of the number of c-Fos-positive cells) in rats 2 h after i.v. administration of lipopolysaccharide alone and on the background of electrical pain stimulation. Studies were performed using 52 male Wistar rats weighing 200-250 g. c-Fos protein expression was studied by immunohistochemical analysis. Increases in the quantity of c-Fos-positive cells 2 h after administration of lipopolysaccharide were seen in the following hypothalamic structures: AHN, PVH, LHA, VMH, DMH, and PH. After electrical pain stimulation, the number of c-Fos-positive cells increased in these same hypothalamic structures (AHN, PVH, LHA, VMH, DMH, and PH). The combination of electrical pain stimulation and lipopolysaccharide administration led to a decrease in the extent of activation in hypothalamic structures AHN, PVH, LHA, and VMH as compared with the characteristic reaction to lipopolysaccharide without electrical pain stimulation. Electrical pain stimulation suppressed the intensity of the immune response induced by lipopolysaccharide (as assessed by local hemolysis and counts of the numbers of spleen antibody-forming cells). Thus, changes in the extent of activation of hypothalamic structures (AHN, PVH, LHA, VMH) correlated with the development of stress-induced immunosuppression, i.e., morphofunctional mapping of the extent of activation of hypothalamic structures allowed identification of which changes in hypothalamic cell activity occurred with stress-induced changes in immune system responses to antigen administration.

The influences of different treatments on the expression of the c-fos gene in the spinal cord and brain (hypothalamus) was studied in rats using various types of anesthesia. Synthesis of c-Fos-like proteins occurred only in the spinal cord in conditions of constant 1.5% halothane anesthesia. Use of induction anesthesia with 1.5% halothane allowed detection of c-Fos-like protein expression in cells of the rat spinal cord (lumbar segments) and brain, both when animals were placed in a hammock and when mechanical pain stimulation or electromagnetic irradiation of the skin with UHF currents were applied. The pattern of brain structures reacting to mechanical pain stimulation with expression of c-Fos-like protein was identified. This type of stimulation was shown to induce increases in the quantity of c-Fos-positive cells in the lateral hypothalamic area (LHA), the ventromedial (VMH) and dorsomedial (DMH) hypothalamic nuclei, and in the ventral hypothalamic area (AHA) by 116%, 167%, 101%, and 157% respectively as compared with controls. Skin irradiation with UHF currents decreased the intensity of mechanical pain stimulation-induced synthesis of c-Fos-like protein in most structures (LHA, VMH, DMN, and AHA by 32.8%, 29%, 15%, and 33% respectively). Only induction halothane anesthesia allowed identification of hypothalamic structures reacting to mechanical pain stimulation and the modifying effects of irradiating the skin with UHF currents on the intensity of these reactions.

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