Temperature effects of reserpine injected into the cerebral ventricles of rabbits and cats

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Abstract
In unanesthetized rabbits and cats reserpine was injected through a chronically implanted cannula in the left lateral cerebral ventricle, and rectal temperature was recorded. In rabbits the reserpine (0.5-0.6 mg) caused a rise in temperature, frequency defecation and sedation. On repeating the intra-ventricular injections at 24 hr. intervals the rise in temperature was not obtained with the 2nd or 3rd injection, but defecation and sedation still occurred. When the hyperthermic response to intraventricular reserpine had disappeared the anterior hypothalamus still responded to intraventricular noradrenaline [norepinephrine] which produced a rise in temperatuture. In cats the reserpine (0.5-0.75 mg) caused a biphasic change in temperature, i.e. an initial fall followed by a rise, frequent defecation, and catalepsy. On repeating the intraventricular injections at 24 hr. intervals the initial hypothermic phase of the temperature response was not obtained with the 2nd or 3rd injection, but the late rise, defecation and catalepsy were still produced. When the hypothermic phase had disappeared the hypothalamus still responded to intraventricular noradrenaline or adrenaline [epinephrine] which produced a fall, and to intraventricular 5-hydroxytryptaroine (5-HT) which produced a rise in temperature. The rise in temperature in rabbits and the intial fall produced in cats is not due to a direct action of reserpine on the cells of the anterior hypothalamus but to noradrenaline released from adrenergic fibers ending at these cells. When these fibers are depleted of their noradrenaline by 1 or 2 injections of resperine, these effects are not obtained because noradrenaline is no longer available to be released in sufficient amounts to raise temperature in rabbits and to lower it in cats.