Odor Response Properties of Rat Olfactory Receptor Neurons

Abstract

Molecular biology studies of olfaction have identified a multigene family of molecular receptors that are likely to be involved in odor transduction mechanisms. However, because previous functional data on peripheral coding were mainly collected from inferior vertebrates, it has been difficult to document the degree of specificity of odor interaction mechanisms. As a matter of fact, studies of the functional expression of olfactory receptors have not demonstrated the low or high specificity of olfactory receptors. In this study, the selectivity of olfactory receptor neurons was investigated in the rat at the cellular level under physiological conditions by unitary extracellular recordings. Individual olfactory receptor neurons were broadly responsive to qualitatively distinct odor compounds. We conclude that peripheral coding is based on activated arrays of olfactory receptor cells with overlapping tuning profiles.

Selective imaging of presynaptic activity in the mouse olfactory bulb shows concentration and structure dependence of odor responses in identified glomeruli

“…Traditionally, dimensions of this odor space have been defined according to psychophysical criteria or the physicochemical nature of odorants (32)(33)(34) or by measuring odorant responses of many individual ORN (13)(14)(15)(35)(36)(37)(38)-no deduction of responses to individual OR has been possible here, however. More recently, glomerular response patterns obtained by intrinsic imaging have been taken to represent odor space coordinates (8,9).…”

“…It is unclear to what extent these features reflect neuronal processing of odors in the OB, and to what extent they embody OR response properties. Odor responses of ORN have been reported as rather unspecific (13)(14)(15), whereas recombinant OR mostly have been reported as narrowly tuned (16)(17)(18). Particular unclear is the representation of odor concentration within the olfactory code.…”

Receptor Heterogeneity and its Effect on Sensitivity and Coding Range in Olfactory Sensory Neurons

“…The only direct evidence we have comes from molecular labeling studies (Malnic et al, 1999), and these suggest that in mice each ORN expresses only one kind of ORP. Duchamp-Viret et al (1999) come to the opposite conclusion using electrophysiological methods to measure the response of individual rat ORNs to stimulation by a suite of structurally dissimilar odorants. Inferring the characteristics of ORP behavior from ORN activity, as in Duchamp-Viret et al (1999) is difficult for several reasons:…”

“…Duchamp-Viret et al (1999) come to the opposite conclusion using electrophysiological methods to measure the response of individual rat ORNs to stimulation by a suite of structurally dissimilar odorants. Inferring the characteristics of ORP behavior from ORN activity, as in Duchamp-Viret et al (1999) is difficult for several reasons:…”

“…Over the past decade, geneticists have become increasingly aware that a surprisingly large number of genes in animals code for ORPs (Buck and Axel, 1991;Buck, 1996;Malnic et al, 1999; see also Mombaerts, 1999): about 1000 or approximately 1% of genes in rats and mice code for ORPs, which appears to be even more diverse than genes coding for ligand receptors associated with the immune system. Recently, Duchamp-Viret et al (1999) argued that responses of individual ORNs to several different classes of compounds (e.g., turpene, camphor, aromatic, and straight-chained ketones) imply that individual frog and rat ORNs express several ORPs. Nonpheromonal insect ORNs are also known to respond individually to a wide array of structurally different odorants [for reviews Masson and Mustaparta (1990), Smith and Getz (1994), Lemon and Getz (1999)] and it is estimated that the fruit fly genome contains on the order of 100 ORP genes [as reviewed in Mombaerts (1999)].…”