Circulatory and Behavioural Effects on Electrical Stimulation of the Sympathetic Vasodilator Areas in the Hypothalamus and the Mesencephalon in Un anesthetized Dogs

Blood prrssure, heart rate, blood flow to the hind limb and behaviour wcrv studied in conscious dogs during topical stimulation of the sympathetic vasodilator outflow area in the hypothalamus and the mesencephalon. The responses obtained on stimulation were: a rise in blood pressure, tachycardia and also an increasr in hind limb blood flow which could bc abolished by atropinc. The effects on circulation caused by stimulation were essentially the same in the conscious and the anaesthetized dog. The behavioural changes on stimulation were relatively small and consisted of variations in the degree of alertness. In many experiments marked circulatory responscs were obtained on stimulation without any apparent behavioural reactions. Whether these findings indicate that the cholinergic vasodilator system acts more generally in circulatory homeostabis or is restricted to participation in specific situations as e.g . adjustments preparatory to niuacle effort. is discussed.