Positive Feedback of Vasopressin on its Own Release in the Central Nervous System: in vitro Studies

Abstract

In this paper evidence is shown that synthetic arginine vasopressin (AVP) can evoke marked in vitro release of endogenous immunoreactive AVP (I-AVP) from male rat septal and hypothalamic tissue superfused in vitro. The stirnulatory action was dosedependent with a maximal amplification factor of 2.3 when using 14 pg of synthetic AVP as the stimulus. It was highly specific since only AVP was effective and not three closely related substances such as lysine vasopressin, oxytocin and a 4-9 C fragment of AVP.This reproducible effect of AVP required, however, effective concentrations of bacitracin M) in the superfusion medium to inhibit aminopeptidase(s) capable of inactivating AVP. Lastly, the stimulatory action of AVP on its own release was not blocked by a V,-receptor antagonist of AVP but was blocked by a V,-antagonist. It is proposed that this novel and robust positive feedback of AVP on its own release may be involved in the mechanism of memory consolidation of certain behavioral tasks known to be affected by AVP. toThe role of arginine vasopressin (AVP) as a neurotransmitter or neuromodulator in the CNS is supported by an array of experimental evidence ranging from neuroanatomical (l), biochemical (2-4), electrophysiological (5, 6) and behavioral findings (7). The release of this neuropeptide from extrahypothalamic regions in the CNS such as the lateral dorsal septum (DS) and dorsal hippocam-PUS (DH) in freely behaving male rats (8) as well as from in vitro preparations (9) of these tissues has contributed to strengthen such a concept.In the preceding paper (8) we demonstrated that synthetic AVP infused directly into the DS of freely behaving rats by way of a push-pull cannula (PPC) had a robust and reliable stimulatory action on its own release. In this paper, we study in vitro the charxteristics of this novel positive feedback action of AVP in the septum by means of an in vitro superfusion system (10). Resu itsIn the previous paper (8) it was shown that to measure detectable levels of immunoreactive AVP (I-AVP) from the septum of freely behaving male rats the superfusion medium had to contain effective concentrations of bacitracin, an aminopeptidase inhibitor. Therefore, in these in vitro experiments we first studied the spontaneous release of I-AVP from septal fragments in the Presence of different concentrations of bacitracin in the perfusion medium as well as the response of the tissue to a pulse of synthetic AVP infused for 5 min. Interestingly, though an infusion of 15 pg for 5 min at interval 6 in chambers superfused with Krebs-Ringer phosphate medium (KRP) containing 5 x lo-', 5 x or 1 0-4 M bacitracin induced similar stimulatory responses of 46.4, 37.2, 35.4 and 41.3 pg/40 min, basal release was clearly affected since 1 of 6, 2 of 6, 5 of 6 and 5 of 6 samples had detectable levels, respectively. Since M bacitracin did not interfere in the assay this dose was used thereafter. Fig. 1 shows individual examples of the pattern of I-AVP release from septal fragments superfused in vitro with KRP with...

Differential modulation of lateral septal vasopressin receptor blockade in spatial learning, social recognition, and anxiety-related behaviors in rats

“…The V 2 receptor has only recently been demonstrated in the brain [20,23]. Although a functional V 2 -type receptor has been suggested to exist in the septum as well [13,26,37], its presence there seems too low to be detected. The use of a combined V 2 /V 1 antagonist in the present experiment ensured blockade of both types of VP receptors in the LS.…”

“…This VP originates from neurons in the medial amygdala and the bed nucleus of the stria terminalis (BNST) [5,9,10,47]. The VP-containing fibers have synaptic endings in the LS, where VP exerts an excitatory action [36], This action is presumably mediated through the postsynaptically located V 1a receptor subtype [32,35,39,40,44], although an additional involvement of the V 2 receptor subtype cannot be excluded [13,26,37]. The presence of this VP network suggests a modulatory role of VP in lateral septal functioning.…”

Vasopressin released within the septal brain area during swim stress modulates the behavioural stress response in rats

“…So far, the release of AVP within the septum has been studied almost exclusively after pharmacological stimulation either in vitro in superfusion media (Buijs & Van Heerikhuize 1982;Ramirez et al . 1990b;Landgraf et al .…”

“…So far, the release of AVP within the septum has been studied almost exclusively after pharmacological stimulation either in vitro in superfusion media (Buijs & Van Heerikhuize, 1982;Ramirez et al, 1990b;Landgraf et al, 1991a) or in vivo by means of the very effective (i.e. relatively high recovery), but also often unbalanced, push-pull perfusion technique (Demotes-Mainard et al, 1986;Landgraf et al, 1988;Ramirez et al, 1990a).…”

In vivo and in vitro Effects of Arginine-Vasopressin Receptor Antagonists on the Hypothalamic-Pituitary-Adrenal Axis in the Rat

“…Interestingly, whereas CRH has been demonstrated to inhibit its own secretion in an ultrashort negative feed back loop fashion [7], AVP has been reported to stimulate its own secretion in the central nervous system via Vi receptors [30].…”