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

Summary

• 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.