Dopamine infusion into the third ventricle increases gene expression of hypothalamic vasoactive intestinal peptide and pituitary prolactin and luteinizing hormone beta subunit in the turkey.

Turkey prolactin (PRL) secretion is controlled by vasoactive intestinal peptide (VIP) neurons residing in the infundibular nuclear complex (INF) of the hypothalamus. The VIPergic activity is modulated by dopamine (DA) via stimulatory D(1) DA receptors. DA (10 nmol/min for 40 min) was infused into the third ventricle of laying turkey hens to study its effect on circulating PRL, hypothalamic VIP and pituitary PRL and LHbeta subunit mRNA levels. Plasma PRL was significantly elevated after 20 min of DA infusion and remained elevated 30 min after cessation of infusion. Hypothalamic VIP mRNA content was significantly greater in the INF of DA-infused birds than it was in the INF of vehicle-infused control birds. No increase in VIP mRNA due to DA infusion was noted in the preoptic area. Pituitary PRL and LHbeta subunit mRNAs were increased in DA-infused hens as compared to vehicle-infused controls but the rate of increase was more in PRL than LHbeta subunit. This study demonstrates that exogenous DA activates hypothalamic VIP gene expression and this increased expression is limited exclusively to the avian INF. The increased VIP mRNA in the INF is correlated with increased levels of circulating PRL and PRL and LHbeta mRNAs in the anterior pituitary.