Activation of central D-1 dopamine receptors stimulates oxytocin release in the lactating rat: evidence for involvement of the hypothalamic paraventricular and supraoptic nuclei.

The stimulatory effect of dopamine (DA) on the release of oxytocin (OT) in lactating rats is exerted at the D-1 DA receptor subtype. Because the neural loci mediating this effect have not been identified, the objective of the present studies was to test whether OT release in the lactating rat would be elevated after central administration of a D-1 DA receptor agonist into the third ventricle (3V) or directly into either the rostral paraventricular/anterior commissural nucleus area (PVN/ACN), the central paraventricular nucleus area, or the supraoptic nucleus (SON), all of which contain OT neurosecretory cells. Lactating rats were implanted with a stainless steel cannula directed into one of the above areas or into the arcuate-ventromedial region of the medial basal hypothalamus (MBH), or sites dorsal to the PVN/ACN or SON, which served as anatomical controls. After 6-7 days of recovery, each animal received an intra-atrial cannula for sequential blood sampling, and was used in experiments 24 h later. Animals were separated from their litters, and following a period of basal blood sampling, received central microinjections of either vehicle, the D-1 DA receptor agonist SKF-38393, or the D-2 DA receptor agonist quinpirole, and blood samples were removed periodically for 60 min. An injection of angiotensin II (Ang II, 100 ng) was made into each site as a positive control for OT release.(ABSTRACT TRUNCATED AT 250 WORDS)