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

The effects of the prostaglandin F2 alpha (PGF2 alpha) 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 milk ejection and the remaining twenty PVN neurones which showed no response prior to reflex milk ejections were regarded as non-oxytocinergic ones. Twenty-five (83%) of the30 oxytocinergic neurones increased in the firing rate following the intraventricular (IVT) injection of PGF2 alpha (500ng in 1 microliter of isotonic saline) and the responses lasted for about 20-30 min. The remaining 5 (17%) oxytocinergic neurones showed no response in the firing rate to IVT PGF2 alpha. Fifteen (75%) of the 20 nonoxytocinergic neurones decreased in the firing activity in response to IVT PGF2 alpha, and the remaining 5 (25%) of them showed no response. IVT injection of isotonic saline (1 microliter) did not affect the firing activity of both the oxytocinergic and nonoxytocinergic cells. The intramammary pressure was slightly increased by the IVT administration of PGF2 alpha. These findings indicate that IVT PGF2 alpha has a differential action on oxytocinergic and non-oxytocinergic neurones in rats.