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

Abstract

The central release of both oxytocin and vasopressin within the septum and dorsal hippocampus in response to suckling was studied in conscious, freely-behaving lactating rats. Three consecutive 30-min push-pull perfusions were carried out before, during and after suckling (suckled group) or without suckling (control group). As compared to control levels, suckling resulted in a significantly increased oxytocin release within both limbic brain areas (septum: to 140%, dorsal hippocampus: to 1,600%). After removal of the suckling pups, the oxytocin concentration in the final perfusates remained at the stimulation level (septum) or tended to return to control values (dorsal hippocampus). In contrast to oxytocin, the vasopressin perfusate levels did not differ significantly between unsuckled and suckled ratsThe stimulation of magnocellular oxytocinergic neurons of the hypothalamus during suckling results in a pulsatile and periodic release of oxytocin (OXT) from the posterior pituitary (1, 2). At the mammary gland, the peptide promotes the contraction of myoepithelial cells which surround the alveoli, making milk available for the suckling pups. 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). There is considerable evidence suggesting central effects not only of AVP (14), but also of OXT, including its possible role in influencing behavioural phenomena in the post partum period (15-17). However, little is known whether the peripheral release of OXT, e.g. in response to suckling, is accompanied by central release. Evidence for such release would provide strong support for the idea that OXT may be physiologically involved in central processes related to lactation. Two of the brain areas thought to be involved in milk ejection (18,19) as well as in behavioural regulation (17,20,21) are the septum and dorsal hippocampus. Therefore, in the present study, we investigated the release of endogenous OXT and AVP within both limbic brain areas in the lactating, freely-behaving rat, and the effects of suckling. Res u I tsIn the perfusates sampled from control animals and in the prestimulation perfusates, respectively, both peptides were detectable (septum: OXT 2.50 to 4.60pg/sample, AVP 0.30 to 4.80 pg/sample; dorsal hippocampus: OXT 0.30 to 10.5 pg/ sample, AVP 0.30 to 10.3 pg/sample).Compared to unsuckled controls, in suckled rats there was a significantly increased OXT concentration in perfusates from both the septum (to approximately 140%; P<O.OS) an...

Oxytocin in the Bed Nucleus of the Stria Terminalis and Lateral Septum Facilitates Bursting of Hypothalamic Oxytocin Neurons in Suckled Rats

“…5). However, it is notable suckled rats (32). Microiontophoretic application of OT has been shown to increase both basal and glutamate-induced activity of a high proportion of LS neurons (33), while in vitro a much smaller population of LS neurons are excited by the receptorspecific agonist HO[Thr4,Gly7]0T (34).…”

Release of Oxytocin in the Rat Central Amygdala Modulates Stress-Coping Behavior and the Release of Excitatory Amino Acids

“…In this way, OXT release has been monitored in several in vivo studies mainly focusing on somato-dendritic release within the hypothalamic SON and PVN under physiological or pharmacological conditions (Moos et al, 1989;Neumann et al, 1993a, b;Nishioka et al, 1998;Ludwig et al, 2002;Wigger and Neumann, 2002; for review, see Landgraf and Neumann, 2004). In contrast, only a few reports are available demonstrating fluctuations in the release of OXT within extrahypothalamic brain regions like the septum (Neumann and Landgraf, 1989;Landgraf et al, 1991;Ebner et al, 2000) or the olfactory bulb (Kendrick et al, 1988a, b) under physiologically relevant conditions. Sparse innervation and consequently low concentrations of OXT in the extracellular fluid make quantification of local in vivo release within these limbic brain regions difficult.…”

Maternal aggression in rodents: brain oxytocin and vasopressin mediate pup defence

“…promotion of labour and milk ejection. At the same time, OXT is released within the lactating brain, for example in the PVN and SON themselves but also into other brain regions like the septum, the hippocampus or the olfactory bulb ( [13][14][15][48][49][50][51][52], for review see [44]). There is only one known OXT receptor (OXT-R) and it belongs to the G protein-coupled receptor family [53].…”