Beta-Adrenergic Receptors in the Premammillary Nucleus Mediate the Inhibition of LH Release Evoked by Locus ceruleus Stimulation

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Abstract
The neurotransmitter and adrenoceptors involved in the inhibition of luteinizing hormone (LH) release induced by stimulating the locus ceruleus nucleus (LC) were characterized in ovariectomized, estrogen-primed rats in which the release of LH was triggered by electrical stimulation of the medial preoptic area. Blockade of norepinephrine [NE] synthesis by the injecton of the dopamine .beta.-hydroxylase inhibitors, diethyldithiocarbamate or fusaric acid, prevented the inhibition of LH release; blockade of epinephrine synthesis by injecting the phenylethanolamine N-methyltransferase inhibitor, 2,3-dichloro-methylbenzylamine, had no effect. The inhibition of LH release was prevented by systemic injection of propranolol but not of phenoxybenzamine. This inhibition was also suppressed in rats in which the ventral premammillary (PM) nucleus ipsilateral to the stimulated LC was lesioned, or in animals with a transverse cut placed just in front of the PM. A similar response was seen in rats in which propranolol but not phenoxybenzamine was applied to the PM ipsilateral to the stimulated LC. NE, acting through .beta.-adrenoceptors mediates the transmission of impulses which, orginating in the LC, inhibit the release of LH. The LC adrenergic fibers synapse in the PM before the neural information they convey is transferred to the gonadotropin-releasing hormone containing neurons.