Single unit activity of olfactory neuroreceptors was recorded in frogs. Stimulations with 20 pure chemicals delivered at known concentrations elicited excitatory and/or inhibitory responses in 60 of the 76 recorded units. The responses exhibited various time patterns, partly depending on stimulus intensity. Long lasting after-effects were observed. Out of a total of 1520 odour trials, 317 excited and 33 inhibited the cells, leading to a receptor overall responsiveness of 23%. Various degrees of individual selectivity were encountered in the receptors; the greatest number responded to seven of the 20 odorants. A marked tendency to stimulate the same receptors was observed for several odorants. Three groups could be evidenced: benzene, anisole, dichlorobenzene and bromobenzene; camphor and cineole; tert-butyl alcohol, cyclohexanone and cyclohexanol. Fatty acids tended to be grouped. Sulphurous compounds elicited few responses, except tiophenol. Most of the neuroreceptors responded to odorants belonging to more than one odour group.
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Revial et al. (1978) studied this question.