Immunocytochemical and physiological evidence of a synapse between dopamine- and Luteinizing Hormone Releasing Hormone-containing neurons in the ewe median eminence.

Publisher Website
Google Scholar
Abstract
Immunocytochemical labeling revealed that the arcuate nucleus (ARN) of the ewe''s hypothalamus contains numerous tyrosine hydroxylase (TH)-positive neurons, that appear to lack dopamine-.beta.-hydroxylase (DBH)-like immunoreactivity. Axons of these presumed dopaminergic neurons coverage in the median eminence (ME) with LHRH-containing axons originating mostly from neurons situated in the medial preoptic area. Electron microscopic double labeling revealed synaptic contacts between TH-positive presynaptic profiles and LHRH-containing postsynaptic elements. Samples of ME, ARN, paraarcuate and lateral hypothalamus were dissected and incubated to assess LHRH release and tissue content. Only ME-LHRH release was significantly reduced in the presence of dopamine (DA). All other regions released equal amounts with and without DA. Thus, a presynaptic dopaminergic inhibition of LHRH-containing axons at the level of the ME might contribute to the regulation of LHRH release into the portal vessels.