Bilateral ablation of the vomeronasal organs produces dramatic changes in the EEG of the main olfactory system during paradoxical sleep

Abstract

Background: The vomeronasal organ (VNO) plays an important role in reproductive physiology, behavior, sexual behavior and aggression. Objective: The aim is to report a surprising effect of the removal of the VNO on the cortical electrical activity of the olfactory bulb, piriform lobe and frontal cortex exclusively during paradoxical sleep (PS). Methodology: Seventeen adult armadillos chronically prepared for electrographic recordings were employed. Some animals were subjected to VNO bilateral remove. They were studied during wakefulness and sleep phases. Results: An outstanding phenomenon occurs during PS of armadillos submitted to bilateral ablation of the VNO. There is a dramatic change in the oscillations of the olfactory bulb electrical activity strictly confined to PS. The change consists of the sudden appearance, as soon as PS initiates, of high amplitude gamma oscillations during the whole duration of each PS episode. They disappear as soon as PS comes to an end. The oscillations are also seen in the paleocortex and the frontal neocortex. They disappear after the transverse section of the olfactory peduncles. Conclusions: Our results show the absence of VNO deeply modifies the electrophysiological expression of PS in the olfactory bulb and other extensive brain areas. They are elicited by the centrifugal input to the olfactory bulb. From there they propagate to the piriform and frontal neocortex. These results show a new and subtle role for the organs. Some hypotheses related to the effects of bilateral removal of the VNO are presented.