Electrophysiological responses from the peripheral olfactory system of the American eel,Anguilla rostrata

Abstract

1. Electrophysiological responses were obtained from the peripheral olfactory system of the American eel,Anguilla rostrata, using three different recording methods: averaged multiunit activity from the olfactory mucosa (MNR), averaged multiunit activity from bundles of olfactory nerve axons (NTR), and the underwater electro-olfactogram (EOG). 2. For each of the three techniques, response magnitude increased exponentially with logarithmic increase in stimulus concentration, denoting a power function (Figs. 2, 3). 3. Thresholds forl-glutamine, determined from NTR, MNR, and EOG recordings, were 10−9.6±0.3mol/l, 10−8.0±0.2mol/l and 10−7.8±0.2 mol/l, respectively. The difference between the NTR and the EOG and MNR thresholds was significant while the difference between EOG and MNR thresholds was not (Table 2). 4. Gamma, the reciprocal of the power function exponent, which is the number of log steps of concentration necessary to produce a tenfold increase in response magnitude, was 10.3±0.4 for the NTR, 6.5±0.4 for the MNR, and 5.3±0.2 for the EOG. The difference between the NTR gamma and the EOG and MNR gammas was significant while the difference between the EOG and MNR gammas was not (Table 2). 5. There was a significant correlation between the relative stimulus effectiveness for 11 amino acids determined with each of the three methods (Fig. 4). 6. An amino acid with 5 or 6 carbon atoms, a linear side chain, and an unsubstituted hydrogen and amino group in the alpha position was generally a highly effective olfactory stimulus. 7. Esterification of the primary carboxyl group ofl-alanine did not result in a loss of stimulatory effectiveness, indicating that a charged carboxyl group may not be necessary for maximal stimulation.