Cobaltous chloride-induced hypothermia. II: Pretreatment with sympathoplegics, antihistamines, and narcotic antagonists.

Body temperature depression was noted in rats, mice, and hamsters following intraperitoneal cobaltous chloride administration (25 mg/kg). Intracerebral cobalt injection elicited hypotermia in rats and mice but not in hamsters. Body temperature depression appeared to be centrally mediated in rats and mice and peripherally mediated in hamsters. The effect of intraperitoneal and intracerebral pretreatment with phentolamine, diphenhydramine, propranolol, cimetidine, and naloxone on the mouse rectal temperature response to cobalt (25 mg/kg ip) was noted. Systemic phentolamine injection (intraperitoneal) did not alter the cobalt response, whereas intracerebral administration partially antagonized cobalt-induced hypothermia, indicating that antagonism was mediated centrally. Pretreatment with propranolol and cimetidine failed to modify the temperature response. Intracerebral diphenhydramine did not influence cobalt hypothermia. However, this agent reduced the cobalt response when given intraperitoneally, presumably through a peripheral inhibitory mechanism. The intracerebral injection of naloxone 30 min prior to cobalt slightly enhanced hypothermia, apparently through a central action. Intracerebral 6-hydroxydopamine injection depleted brain norepinephrine and dopamine but exhibited no apparent influence on cobalt-induced hypothermia.