In vivo electrophysiological recordings of olfactory receptor neuron units and electro-olfactograms in anesthetized rats

Abstract

In vivo recordings of single olfactory receptor neurons and electro-olfactograms (EOG, field potentials from the olfactory mucosa) provide insights into the olfactory processing properties of the olfactory peripheral stage. Because the olfactory receptor neurons are very small electrical generators, it is not easy to unitarily record them in amphibians, reptilians, and fishes. In mammals such recordings are even more difficult to obtain: primarily due to the anatomical configuration in complex turbinates of the olfactory mucosa and its propensity to hemorrhage during surgery; secondarily due to the fact that olfactory receptor neurons are held in closely packed clusters in the olfactory mucosa and are difficult to isolate, from the electrophysiological recording point of view. Here we describe the material and methods we used in vivo, in rats—occasionally, also tested in mice—to get simultaneously receptor neuron single and electro-olfactogram recordings, from septal region or the endoturbinate II, in freely breathing or tracheotomized anesthetized animals. Recording EOG in parallel with receptor neuron units provide, by reflecting the population response to the olfactory stimulus, the continuous assurance of the good physiological state and reactivity of the olfactory epithelium. This configuration will ensure that when a single ORN does not respond to a stimulus it resulted from its qualitative selectivity and not from the olfactory mucosa damaged status.