EFFECTS OF NORADRENALINE AND CARBACHOL ON TEMPERATURE REGULATION OF RATS

Noradrenaline (0.2 to 20 ug) and carbachol (0.1 to 1 ug) injected into the preoptic/anterior hypothalamic area, evoked dose‐dependent falls in core temperature at all sites tested, followed in most experiments by delayed increases that were not dose‐related. Muscarine (0.1 to 10 ug) produced effects similar to those evoked by carbachol. These falls in core temperature were associated with increases in tail temperature, locomotor activity and C02 elimination (a measure of metabolic rate). The temperature responses to noradrenaline (10 ug) and to carbachol (1 ug) were antagonized by intrahypothalamic injections of phentolamine (10 ug) and atropine (1 ug), respectively. Analysis of the temperature responses and their respective latencies indicates that carbachol‐induced hypothermia was mediated by cholinoceptors in the anterior hypothalamus, whereas hypothermia after noradrenaline was mediated by adrenoceptors throughout the preoptic/anterior hypothalamic area. Vasodilatation of the tail blood vessels contributed significantly to the hypothermia evoked by carbachol, and to that evoked by injections of noradrenaline into the anterior hypothalamus. Hypothermia induced by noradrenaline injection into the preoptic area, was mediated by effector mechanisms additional to non‐evaporative heat loss. 1979 British Pharmacological Society