Electrophysiological characterization of rat and mouse olfactory receptor neurons from an intact epithelial preparation.

To understand the coding mechanisms underlying olfactory discrimination, it is necessary to characterize odor response properties of olfactory receptor neurons (ORNs). In contrast with rapid progress in molecular biology, there is little physiological data from ORNs in rodent. To facilitate acquisition of such data, we have developed an intact olfactory epithelial preparation from both rat and mouse. We have carried out initial studies of this preparation by monitoring odor responses by patch-clamping directly on the ORN dendritic knobs, a subcellular site very close to the locus of olfactory signal transduction. Our results show that rat and mouse ORNs have similar intrinsic membrane properties. Most cells fired spontaneously at a low frequency (f) and about one half fired repetitively in response to current (I) injection with a linear f/I relation. About one third of rat and mouse ORNs responded to a mixture of four odors in a dose-dependent manner and about 60% of them responded to IBMX, a potent inhibitor of phosphodiesterase. The results suggest that this intact preparation offers the advantage of approximating in vivo physiological conditions, while furnishing an opportunity to map single neuron responses in the epithelium in a spatially-defined manner, using electrophysiological or cell imaging methods.