Odor discrimination by frog olfactory receptors - 2nd study

Abstract. Single unit activity of olfactory receptors was recorded in the frog. Seventy per cent of the receptors displayed a resting frequency lower than 20 spikes min"1. A 20 ways olfactometer was designed to automatically stimulate the olfactory epithelium with 20 highly purified, simple odorants belonging to several chemical series, each at a single supraliminal concentration. Twenty three cells failed to respond to any of the 20 stimuli. Following a total of 1160 stimulations delivered to 58 receptor cells, 241 activating and 59 inhibitory responses were recorded, leading to an overall selectivity of 25.8%. Twelve units were excited by only one of the 20 chemicals. The activating and inhibitory responses were submitted to mathematical procedures (calculation of the Pearson's V correlation coefficient, Benzecri's analysis of correspondences) in order to determine similarities or proximities between odorants according to the response profiles of the receptors. The odour space built from these data was clearly multidimensional. The five primary aliphatic alcohols of the sample failed to exhibit any special inter-relationship, except the propanol-butanol pair. Camphor was quite unrelated to the other chemicals. Six odorants which possess in common the aromatic nucleus were found to be related by high correlation coefficients; they grouped themselves in a cluster in factor analysis diagrams. They are: benzene, naphthalene, anisole, aceto-phenone and the almond pair nitrobenzene-benzaldehyde. 1