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Received: August 27, 2001
Accepted after revision: December 17, 2001
Key Words
Catecholamines * Catecholamine receptors * Catecholamine antagonists * Prolactin * Birds * Vasoactive intestinal peptide * Preoptic area * Arcuate nucleus
Abstract
Avian prolactin (PRL) secretion is regulated by vasoactive intestinal peptide (VIP) neurons residing in the infundibular nuclear complex (INF) of the hypothalamus. This V[Pergic activity is modulated by stimulatory dopaminergic inputs. Dynorphin, serotonin (5-HT), dopamine (DA) and VIP all appear to stimulate PRL secretion along a hypothalamic pathway, expressing K opioid, serotonergic, dopaminergic and VIPergic receptors in succession, with the VIPergic system as the final mediator. Electrical stimulation (ES) within the turkey hypothalamus at the level of the medial preoptic area (POA), the ventromedial hypothalamic nucleus (VMN), the INF or the median eminence (ME) results in the release of PRL. When the selective DI DA receptor antagonist SCH-23390 HCI was infused intraventricularly at the rate of 10 nmol/min, ES in the POA or VMN was unable to increase PRL levels, while ES in the INF and ME did increase PRL to the same level as that of controls. These results were interpreted to suggest that the D^sub 1^ DA receptors involved in PRL release
lie caudally to the VMN and dorsally to the INF. Bilateral microinjections (50 ng) of the D^sub 1^ DA receptor agonist SKF-38393 HCI into the POA or VMN failed to produce any increase in PRL, while similar microinjections in the INF increased PRL significantly within 15 min. Bilateral microinjections of the D^sub 1^ DA antagonist (50 ng) into the INF blocked the rise in PRL associated with ES in the POA. Bilateral microinjections of a D^sub 2^ DA antagonist (50 ng) into the INF failed to block PRL secretion induced by ES in the POA. Tract tracing, using double-label immunocytochemistry, revealed the presence of a monosynaptic dopaminergic pathway projecting from the POA to the INF. These data imply that the only hypothalamic D^sub 1^ DA receptors involved in the regulation of avian PRL secretion are those residing within the INF in the same region as the VIP neurons known to be involved in PRL secretion.
Copyright (c) 2002 S. Karger AG, Basel
Introduction
Dopamine (DA) acts centrally through D^sub 1^ DA receptors to...