Abstract

After the acute intracisternal administration of 6-hydroxydopamine, a mild reduction of body temperature was observed at room temperature (23°C). Placement of animals in a cold environment after the injection of 6-hydroxydopamine produced a greater reduction of body temperature than that observed at 23°C. Whereas pargyline pretreatment did not alter the response to 6-hydroxydopamine at room temperature, pargyline produced a marked enhancement of the hypothermic response in the cold. With or without pargyline, p-chlorophenylalanine did not alter such liypothermic responses to 6-hydroxydopamine. However, the hypothermie response to acutely administered 6-hydroxydopamine in the cold room was absent in animals treated chronically with 6-hydroxydopamine. These latter results indicate that the release of endogenous catecholamines are essential for the hypothermia caused by the acute injection of this compound. Preferential reduction of norepinephrine significantly reduced the hypothermia of 6-hydroxydopamine but not to the extent observed after the depletion of both catecholamines. Reduction of dopamine did not alter the hypothermic response to 6-hydroxydopamine. Several other phenylethylamines, αmethylnorepinephrine, α-methyloctopamine and metaraminol, were found to produce hypothermia after intracisternal injection. The results with α-methylnorepinephrine after "central sympathectomy" with 6-hydroxydopamine were in marked contrast to those results observed after the acute injection of 6-hydroxydopamine. Instead of being blocked, the hypothermic response to α-methylnorepinephrine was markedly enhanced by "central sympathectomy" suggesting that at least a part of its activity was related to a "direct" action of this amine on central receptors which was enhanced by the neuronal destruction caused by 6-hydroxydopamine.