Hypothalamic modulation of the biowarning processes caused by the emotional stress

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To clarify the functional roles of endogenous chemical substances on the behavioral abnormalities caused by the emotional stress, the effects of immobilization stress on food intake and on neural activity in the lateral hypothalamic area(LHA)were investigated. Significant reduction of daily food intake was observed after 2 hr immobilization. Injection of methysergide(5 mg/kg, i. p.)antagonized the immobilization-induced anorexia for 3hr, while injection of naloxane had no effect. To further investigate the activity of serotonin neurons in relation to immobilization stress, the activity of the serotonergic system and single neuron activity changes in the LHA were' investigated in freely behaving rats. A significant increase in the extracellular concentration of 5, HIAA, a metabolic product of serotonin, and concomitant decrease in activity changes of the hypothalamic neurons were observed following the immobilization stress. Brain microdialysis with HPLC/ECD study also clarified the immobilization-induced serotonin release in the hypothalamus. These results suggest that immobilization-induced anorexia is mediated at least in part through serotonergic mechanisms in the hypothalamus.In vivo microdialysis technique was further used for chronic monitoring of the splenic noradrenaline(NA). Immobilization stress caused an increase in the NA release to about 800% of the basal release in conjunction with the suppression of natural killer(NK)cell activity in the spleen. Surgical denervation of the splenic sympathetic nerve significantly attenuated the increased level of NA and it also inhibited the immobilization-induced suppressive effect on the NK activity. These results suggest that NA has an important role in the control of the neuroimmunomodulation in the spleen.