Regulation of Prolactin Secretion by Dopamine at the Level of the Hypothalamus in the Turkey

Abstract

Avian prolactin (PRL) secretion is regulated by vasoactive intestinal peptide (VIP) neurons residing in the infundibular nuclear complex (INF) of the hypothalamus. This VIPergic 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 ĸ 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 D₁ DA receptor antagonist SCH-23390 HCl 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 D₁ DA receptors involved in PRL release lie caudally to the VMN and dorsally to the INF. Bilateral microinjections (50 ng) of the D₁ DA receptor agonist SKF-38393 HCl 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 D₁ DA antagonist (50 ng) into the INF blocked the rise in PRL associated with ES in the POA. Bilateral microinjections of a D₂ 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 D₁ 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.

Expression of D₁ and D₂ Dopamine Receptors in the Hypothalamus and Pituitary during the Turkey Reproductive Cycle: Colocalization with Vasoactive Intestinal Peptide

“…The present results agree with immunohistochemical studies indicating the distribution of DA neurons throughout the avian hypothalamus [28, 54, 55]. DA neurons project from the preoptic area to the INF [55].…”

“…The number and size of VIP-ir neurons within the mediobasal hypothalamus of the turkey increases when plasma PRL is high, as it does in the domesticated pigeon and ring dove during the initiation of crop milk secretion and feeding of offspring [58, 59]and in the incubating bantam hen [60]. The current findings clearly indicate that the differential expression of stimulatory D 1D DA receptor mRNA in the hypothalamus relates to the degree of prolactinemia in turkey hens, and that the central site for DA mediation of VIP is located within the INF, in the same region as the VIP neurons known to be involved in PRL secretion [55]. …”

“…DA neurons project from the preoptic area to the INF [55]. The number of VIP-immunoreactive (VIP-ir) cells [56, 57]and VIP mRNA [34]dramatically increases in the INF of the incubating turkey hen.…”

A direct neuronal connection between the subparafascicular and ventrolateral arcuate nuclei in non-lactating female rats. Could this pathway play a role in the suckling-induced prolactin release?

“…The VMN has been suggested to play a role in the regulation of PRL in the turkey [17]; it is unlikely that this nucleus relays suckling stimulus to TIDA neurons in mammals. However, the PPN is a very important nucleus in the process of lactation, especially since it has been shown to be activated by the suckling stimulus [12, 18] as well as by exteroceptive stimuli from pups such as visual, olfactory, and auditory in the absence of suckling.…”

Prolactin, dopamine receptor D1 and Spot14α polymorphisms affect production traits of Hungarian Yellow hens

“…For example, prolactin (a hormone from the pituitary) has crucial roles in regulation of egg production, since broodiness is induced by elevated prolactin concentrations, which causes temporary suppression of the ovary, and interruption of laying (Sharp et al, 1984). Prolactin secretion can be stimulated by dopamine, a neurotransmitter that operates by activating hypothalamic dopamine D1 receptors (Youngren et al, 2002). Prolactin and dopamine receptors are involved in a wide spectrum of biological activities; however, only limited genotype-growth associations have been reported in chickens (Bhattacharya et al, 2011).…”