[Changes in the level of cortisol in the blood of rabbits during self stimulation]

The time-course of changes in the blood plasma cortisol level during activation of the positive reinforcement system was studied in experiments on adult chinchilla male rabbits. The self-stimulation status of the brain lateral hypothalamus was utilized as a model for positive reinforcement. The basal cortisol level in intact rabbits, determined by means of radioimmunoassay, was equal to 5.31 +/- 0.87 micrograms% over a period of 10 to 2 hours p.m. The blood collection procedure, using the method of the ear marginal vein dissection, increases the cortisol concentration 30 minutes after blood collection by 19.4%, i.e. augments its level up to 6.37 +/- 0.90 micrograms%. A significant rise (P less than 0.01) of hormone release into the blood (two-fold) is seen 5 to 15 minutes following the self-stimulation test. Cortisol level remains heightened 1 hour after the self-stimulation experiment. The intensity of the corticotropic activity was not dependent on the hypothalamus, stimulated by force or by animals themselves. On the basis of the data obtained it is concluded that the hormonal response is directly dependent both on hypothalamic electric stimulation and on the motivative mechanism activation. The very positive reinforcement, timing to the post-stimulating period and being of full value only during the adaptive behavioral act, is not stress-inducing.