| Abstract: | Characteristic increases in neuronal electrical activity associated with the initiation of each LH pulse were recorded from ovariectomized rhesus monkeys bearing multiple chronic electrodes in the medial basal hypothalamus. These electrophysiological manifestations of hypothalamic LHRH pulse generator activity were inhibited by the alpha-adrenergic blocker phentolamine or the alpha 1-adrenoceptor blockers phenoxybenzamine and prazosin. At the dosages used, the effects of single injections of these drugs ranged from a reduction in the frequency of LHRH pulse generator activity to its complete arrest. This was faithfully reflected in the pattern of pulsatile LH discharges. The dopaminergic blocking agent metaclopramide similarly reduced the frequency of the pulse generator or arrested its activity altogether. The alpha 2-adrenoceptor blocker yohimbine had no demonstrable effect on hypothalamic electrical activity at the doses studied. These findings support the view of a central action of alpha 1-adrenergic and dopaminergic blockade on LHRH pulse generator activity and the concept that central adrenergic and dopaminergic inputs can modulate the frequency of the LHRH pulse generator. |
