Intraseptal administration of vasopressin and oxytocin affects hippocampal electroencephalogram in rats

Abstract

Two peptides, arginine 8-vasopressin and oxytocin were tested in rats for their effects on the function of the septum, the pacemaker for hippocampal theta rhythm. The peptides or the placebo were injected in small quantities into the septum or other brain structures. The spectra computed from hippocampal EEGs recorded during paradoxical sleep and slow-wave sleep episodes which followed the injections of peptide, were compared. The peptides in doses of 10 −3 pg or more injected into the septum altered the hippocampal EEG during paradoxical sleep episodes in a similar fashion. The EEG alterations were confined to frequencies of the theta band (4.1 to 12.0 Hz) and consisted of an increase in peak and mean frequencies in this band. The hippocampal EEG during slow-wave sleep was little affected by intraseptal injections of the peptides. Microinjections of AVP in the same or higher (to 10 pg) amounts of the peptide into the frontal cortex or the subicular region of the dorsal hippocampus had little effect on hippocampal activity during either sleep stages. The arginine 8-vasopressin-like effect of intraseptally administered oxytocin on hippocampal synchronization during paradoxical sleep contrasted with the effect found in previous studies in which oxytocin had an effect opposite that of arginine 8-vasopressin. The present study demonstrates that the septal mechanism pacing hippocampal theta rhythm is affected by these peptides. Because the septum receives vasopressinergic innervation, we suggested that the role of this peptidergic innervation includes regulation of processes which are related to generation of the theta rhythm.