Role of the paraventricular hypothalamic nucleus in the dependence of the pituitary-adrenocortical system reaction on stress factor strength.

The influence of paraventricular hypothalamic nucleus lesion on the stress factor strength, i.e. on the pituitary-adrenocortical system (PACS) reaction dependence, was studied in chronic experiments on rabbits. It was shown that with the electric skin stimulation the increase in current strength from 0.3 to 0.7 mA results in elevation of corticosteroid level in plasma. With further increase of current strength to 0.9-1.1 mA the stress-induced rise in corticosteroids reduces and Wedensky pessimum is observed. Bilateral lesion of the paraventricular hypothalamic nucleus results in reduction of the amplitude of response to all strengths of stimulation, increase in stimulation threshold and decrease in the rate of PACS involvement into the response to stress factor action. However, the pessimal PACS inhibition is preserved after the paraventricular nucleus lesion.