Electrical activity of neurons in the ventrolateral septum and bed nuclei of the stria terminalis in suckled rats: statistical analysis gives evidence for sensitivity to oxytocin and for relation to the milk-ejection reflex.

Our previous results obtained by lesioning or stimulating the ventrolateral part of the lateral septum and the bed nuclei of the stria terminalis suggested that this area is involved in the control of milk ejection pattern in rats. The present study was undertaken with the aim of testing ventrolateral part of the lateral septum-bed nuclei of the stria terminalis neurons as a putative link of the neuronal network controlling the bursting activity of oxytocin neurons in suckled lactating rats (anaesthetized with urethane). Ventrolateral part of the lateral septum-bed nuclei of the stria terminalis neurons were recorded simultaneously with hypothalamic oxytocin neurons in either the paraventricular or supraoptic nucleus in rats with (n = 26) or without (n = 29) periodic milk ejections.

Oxytocin in the bed nucleus of the stria terminalis and lateral septum facilitates bursting of hypothalamic oxytocin neurons in suckled rats.

Abstract Several regions of the forebrain possess high densities of oxytocin (OT)-binding sites including the bed nucleus of the stria terminalis (BST) and lateral septum (LS). In order to examine whether these regions participate in the central facilitation of the milk ejection reflex by OT, microinjections of OT (1 ng in 100 nl containing Janus Green dye) were made into the BST (13 tests) or LS (9 tests) of anaesthetized, suckled rats, while recording the electrical activity of OT neurons in the contralateral supraoptic nucleus. Histological localization of injection sites using Janus Green demonstrated that all BST injections were close to the anterior commissure, and LS injections were all located in the ventral division of the LS.

Release of oxytocin within the supraoptic nucleus during the milk ejection reflex in rats.

To investigate the hypothesis that oxytocin may be released within the magnocellular nuclei in vivo, push-pull cannula perfusions were performed in anaesthetized lactating rats in one supraoptic nucleus of the hypothalamus while recording the intramammary pressure and/or the electrical activity of oxytocin cells in the contralateral supraoptic nucleus. Oxytocin content was measured in samples collected over 15 min, under various conditions: 1) with no stimulation; 2) during suckling and suckling-induced reflex milk ejections; 3) during electrical stimulation of the neuro-hypophysis by trains of pulses that mimicked oxytocin cell bursts; 4) under osmotic stimulation by i.p.

Relationship between oxytocin release and amplitude of oxytocin cell neurosecretory bursts during suckling in the rat.

Plasma concentrations of oxytocin and vasopressin were measured in relationship to oxytocin cell firing during suckling in urethane-anaesthetized rats. Preliminary experiments showed that plasma concentrations of oxytocin and vasopressin, which were increased immediately after anaesthesia, reverted to basal concentrations 3 h later. Moreover, it was found that exogenous oxytocin had entirely disappeared 5 min after i.

[Evaluation of perfusion technics of the magnocellular nucleus of the hypothalamus in vitro and in vivo].

In suckled rats, OT necessary for the occurrence of the neurosecretory bursts on OT cells, is probably released inside the magnocellular nuclei. In order to demonstrate this in vivo release and to precise the mechanism involved, perifusions were realized in vivo on lactating rats and in vitro with isolated magnocellular nuclei. In vivo, the push-pull perifusion of a single supraoptic nucleus (SON) was realized simultaneously with the recording of the electrical activity of OT cells in the contralateral nucleus.

Release of oxytocin and vasopressin by magnocellular nuclei in vitro: specific facilitatory effect of oxytocin on its own release.

The release of endogenous oxytocin and vasopressin by rat paraventricular and supraoptic nuclei in vitro during a 10-min period, 30 min after beginning the incubation, was measured radioimmunologically. Mean basal hormone release per 10 min and per pair of nuclei was: 128.4 +/- 12.