Stimulation by Dopamine of Luteinizing Hormone-Releasing Hormone (LHRH) Release from the Mediobasal Hypothalamus in Male Rats1

Abstract

Effects of neurotransmitters on in vitro release of LHRH from fragments of mediobasal hypothalamus were investigated. Incubations were carried out for 10 min in a Locke-HEPES medium in the presence of dithioerythritol (10−5M) and bacitracin (2 x 10−5M) to prevent catecholamine oxidation and peptide degradation, respectively. Addition of 3 x 10−9M to 10−7M concentrations of dopamine (DA) to the incubation medium released doserelated amounts of LHRH from hypothalamic fragments, including the medial and lateral palisadic zones of the median eminence, which contain most of the tubero-infundibular DA terminals. LHRH release did not occur when norepinephrine (10−7M) was added instead of DA or was it obtained when DA was incubated with the caudal portion of the mediobasal hypothalamus or the organum vasculosum of the lamina terminalis, which also contain LHRH but are poorly innervated by DA neurons. The effect of DA on palisadic structures was blocked by the addition of pimozide. Moreover, it seemed to be steroi...