Olfactory deafferentation generates gamma activity in the hippocampus during the wake-sleep cycle in the armadillo (Chaetophractus villosus)

Abstract

Background: There are recent evidence of sleep-dependent changes in olfactory system structure and function which contribute to odor memory and perception. Objective: The aim of the present study is to study the effect of the elimination of the olfactory mucosa on the electrical activity of the hippocampus, olfactory bulb, olfactory tubercle, pyriform cortex and frontal cortex during wakefulness and sleep. Methodology: Fifteen adult armadillos chronically prepared for electrographic recordings were employed in this study. Some animals were subjected to peripheral olfactory deafferentation by removal of the olfactory mucosa. They were studied during wakefulness and sleep phases. Results: The lack of peripheral olfactory input causes invasion in all the structures mentioned by very conspicuous and almost continuous bursts of high amplitude gamma activity (32 Hz) during slow wave sleep and paradoxical sleep. Conclusions: The hippocampus, together with some olfactory structures participates in an outstanding phenomenon produced by the suppression of olfactory receptors. The appearance of continuous bursts of gamma activity is in sharp contrast to other published studies because it is entirely independent from olfactory input. The relevance of this phenomenon is discussed considering the so called non olfactory functions of the olfactory bulb and the participation of the hippocampus in emotion, learning and memory. The importance of studying the effects of peripheral olfactory deafferentation during sleep is emphasized in view of possible derivations of interest for the interpretation of some pathological conditions. The significance of these findings is discussed.