[Self-stimulation reaction in normotensive and hypertensive rats]

The part of noradrenergic mechanisms in self-stimulation (SS) operant behaviour was studied in rats. In all experiments systolic blood pressure (BP) in the tail artery was measured by means of photocells. It was found, that small doses of noradrenaline facilitate the SS, while high doses depress or stop it. The depressive effect is accompanied by a marked increase of BP. Effective blockade of beta-adrenoceptive structures by inderal suppresses SS, and the inhibitory effect is accompanied by a small decrease of BP. Suppressing effect of alpha-adrenoblocking agent, phentolamine, is even more pronounced, but is accompanied by a marked decrease of BP. Beta-agonist isadrin causes a marked facilitation of SS without changes of BP. It is suggested that positive reward in the lateral hypothalamus is due to a direct stimulation of beta-adrenoceptive noradrenergic neuronal elements. Chronic neurogenic hypertension is developed by an overloading of the higher nervous activity. In chronic hypertensive rats there is a pronounced suppression of SS. A transient fail of BP caused by injection of catapresan (hemiton) results in a temporary recovery of normal SS behaviour. It may be concluded that reduction of lever-pressing rate during acute and chronic neurogenic hypertensions is related to baroreceptor mechanisms. The role of the autonomic nervous system in SS behaviour is discussed.