Rhinencephalic Involvement in Pituitary Activation by Intraventricular Histamine in the Rabbit Under Nembutal Anesthesia

Abstract

A study of the effects of histamine on activation of the rabbit adenohypophysis reveals the following: Intraventricular histamine in the unanesthetized or etherized female rabbit stimulates electrical arousal and parasympathetic symptoms, but does not activate the relaease of pituitary gonadotropin. Under light Nembutal anesthesia, intraventricular histamine fails to elicit parasympathetic symptoms but evokes "intrinsic olfactory activity" in the rhinencephalon as an essential feature in the process of stimulating the adenohypophysis. Histamine-Nembutal-induced pituitary activation is prevented by olfactory-bulb lesions and by drugs which interfere with the development and transmission of the fast activity of olfactory bulb origin. It is concluded that histamine stimulation of the hypophysis is exerted via rhinencephalic pathways and not by a direct action on the adenohypophysis as a chemical mediator of hypothalamic activity.