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

Abstract

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.v. bolus injections of known doses of oxytocin. Suckling did not modify the basal plasma concentration of oxytocin (14.6 +/- 2.9 compared with 14.6 +/- 1.5 pmol/l before suckling) except during a brief period immediately after neurosecretory bursts on oxytocin cells (37.8 +/- 5.2 pmol/l; P less than 0.001, n = 11). The plasma concentration of oxytocin did not differ significantly from the basal concentration 1.5 min later. The plasma concentration of vasopressin never varied. After two neurosecretory bursts of similar amplitude (total number of spikes during the burst) recorded on the same oxytocin cell, the variations in plasma concentration of oxytocin were also similar. When, for a given cell, the amplitude of neurosecretory bursts increased or decreased, the amount of oxytocin released changed in the same way. These data demonstrate (1) that suckling induces pulsatile release of oxytocin without vasopressin, and (2) a direct relationship between the amounts of oxytocin released and the amplitude of oxytocin cell neurosecretory bursts which argue in favour of simultaneous increases or decreases in the neurosecretory burst amplitudes on all oxytocin cells.

Expression of Fos-Related Antigens, Oxytocin, Dynorphin and Galanin in the Paraventricular and Supraoptic Nuclei of Lactating Rats

“…The activity of magnocellular neurons during lactation has been the object of detailed electrophysiological studies. Thus, suck ling elicits a pattern of bursting electrical activity in OXY cells which is parallelled by pulsatile OXY release [3,4], It is known that suckling affects sensory afferent sys tems and results in activation of the magnocellular neu rons in the PVN [28], The induction of nuclear proto oncogene mRNA is one of the first observable conse quences of neuronal activation [5], We have used an anti serum recognizing FRAs generated against the region of c-Fos near the leucine zipper [9], This antiserum recog nizes not only c-Fos protein but also Fos-related antigens [9], but in the present study emphasis is on neuronal acti vation rather than on the visualization of c-Fos specific immunoreactivity. This issue has been discussed by Hoff man et al [8,9], Previous studies have shown that neuronal activity in areas of the brain such as the cortex and hippocampus is influenced by lactation [57][58][59].…”

“…Suckling causes a bursting activity in the para ventricular nucleus (PVN) and a pulsate release of OXY from the posterior pituitary [3,4].…”

Social modulation of stress responses

“…Pharmacological studies in men suggest that OT suppresses HPA axis activity at the levels of the pituitary and adrenal glands [72,90], which may explain why peripheral injections of OT are successful in suppressing the HPA axis [63,88]. The half-life of OT in plasma is very short (1-2 min) and it does not readily cross the blood -brain barrier [91,92]. However, others argue that when relatively large peripheral doses are used the 1-2% of the dose that does cross the blood -brain barrier is functionally significant [93].…”

Septal and Hippocampal Release of Oxytocin, but not Vasopressin, in the Conscious Lactating Rat During Suckling

“…Each OXT release is the result of high frequency bursts of spikes which occur simultaneously in most or all magnocellular OXT cells in the paraventricular and supraoptic nuclei (3-5). In contrast to OXT, arginine vasopressin (AVP) seems not to be involved in this process (6)(7)(8).In addition to the hypothalamo-neurohypophysial projection, immunocytochemical techniques have located OXT-and AVPcontaining fibre terminals in a number of extrahypothalamic brain areas, including the septum and the dorsal hippocampus (9, 10). From these terminals, both OXT and AVP are released in response to appropriate stimulation (1 1 -13).…”

“…Each OXT release is the result of high frequency bursts of spikes which occur simultaneously in most or all magnocellular OXT cells in the paraventricular and supraoptic nuclei (3)(4)(5). In contrast to OXT, arginine vasopressin (AVP) seems not to be involved in this process (6)(7)(8).…”