Differential effects of prostaglandin F2.ALPHA. on oxytocinergic and non-oxytocinergic neurones in the paraventricular nucleus of the lactating rat.

Abstract

The effects of the prostaglandin F_2α (PGF_2α) given into the third cerebral ventricle on the unit activity of neurosecretory neurones in the paraventricular nucleus (PVN) were studied in urethane-anesthetized rats. The firing activity of PVN neurones was recorded extracellularly and 50 neurones were antidromically identified as neurosecretory neurones. Thirty of them were classified oxytocinergic neurones because they gave a burst of action potential 12-15 sec before reflex milkejection and the remaining twenty PVN neurones which showed no response prior toreflex milk ejections were regarded as non-oxytocinergic ones. Twenty-five (83%) of the 30 oxytocinergic neurones increased in the firing rate following the intraventricular (IVT) injection of PGF_2α (500ng in 1μl of isotonic saline) and the responses lasted for about 20-30min. The remaining 5 (17%) oxytocinergic neurones showed no response in the firing rate to IVT PGF_2α. Fifteen (75%) of the20nonoxytocinergic neurones decreased in the firing activity in response to IVT PGF_2α, and the remaining 5 (25%) of them showed no response. IVT injection of isotonic saline (1μEl) did not affect the firing activityof both the oxytocinergic and nonoxytocinergic cells. The intramammary pressure was slightly increased by the IVT administration of PGF_2α. These findings indicate that IVT PGF_2α has a differential action on oxytocinergic and non-oxytocinergic neurones in rats.