Hypothermia following intraventricular injection of hemicholinium-3 in rats.

1. In unanaesthetized rats, a dose of 50 mug of hemicholinium-3 injected into the cerebral ventricles produced a prolonged hypothermia which was unaffected by the simultaneous administration of choline. This suggests that it was not due to inhibition of acetylcholine synthesis.2. An intraperitoneal injection of 50 mug of hemicholinium-3 also produced hypothermia which, however, was blocked by choline which suggests that it is due to inhibition of acetylcholine synthesis.3. Hyoscine and hexamethonium did not block the hypothermia produced by intraventricular hemicholinium-3, but some antagonism was obtained with phentolamine, imipramine and amphetamine.4. When hemicholinium-3 was administered intraventricularly to rats pretreated with desmethylimipramine, a lethal hyperthermia developed.5. It is concluded that no central cholinergic mechanism is involved in the hypothermia of the rat resulting from an intraventricular injection of hemicholinium-3.