Neurohypophyseal Hormones and Memory

Abstract

The posterior pituitary neuropeptides, vasopressin and oxytocin, influence memory processes in an opposite way. While vasopressin facilitates, oxytocin attenuates memory consolidation as well as memory retrieval processes. Vasopressin results in a long-term, time-dependent hypermnesic effect in various active and passive avoidance learning paradigms. Conversely, oxytocin induces long-term, time-dependent amnestic effect in the same behavioral test models. Structure-activity studies reveal that memory consolidation is primarily affected by the N-terminal “ring” structure of the molecules, whereas the C-terminal aminoacids might be responsible for the effects on retrieval. Limbic-midbrain structures (dorsal hippocampus, dorsal septum, dorsal raphe area, etc.) might be neuroanatomical substrates which mediate the influence of these peptides on memory processes. In these structures, vasopressin affects the utilization of catecholamines (mainly that of noradrenaline). Lesioning of the dorsal noradrenergic bundle (coeruleotelencephalic pathway) completely blocks the effect of vasopressin on memory consolidation. It is assumed that the effect of vasopressin on consolidation processes is due to its interaction with limbic-midbrain terminals of the dorsal noradrenergic bundle. The vasopressin-noradrenaline interaction might also be a mode of action of endogenous vasopressin, which exerts a physiological, tonic influence on memory. Recent data on volunteers, elderly or amnestic patients as well as in patients with diabetes insipidus or major affective illness support the view that vasopressin improves, while oxytocin attenuates memory processes in human beings.