Frequency Selectivity in the Ampullary System of an Elasmobranch Fish (Scyliorhinus Canicula)

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Abstract
Frequency characteristics of the electroreceptive system in Scyliorhinus canicula were determined both by electrophysiological recording of the primary afferent responses and by optical recording of respiratory reflexes after electrical stimulation. The frequency response of the primary afferents shows a maximum gain at about 5 Hz, with slopes of +2.3 and −3.4 dB octave−1 at the low and high frequency side respectively. The phase changes from +60° at 0.03 Hz to −120° at 15 Hz. The sensitivity curve determined by recording the respiratory reflex has a plateau from 0.1 to 1 Hz, with slopes of +2.8 and -;11.4dB octave−1. The highest sensitivity for sinusoidal electrical stimuli was 40nV cm−1 peak-to-peak, in the frequency range 0.1 to 1 Hz. We suggest that the difference between the two curves reflects the convergence of primary afferents on to secondary neurones. We conclude that the low pass filter properties are not imposed by the time constant of the ampulla wall. The low frequency slope found in the behavioural curve presumably represents the slope of the receptor-cell-synapse complex. The Lorenzinian ampullae apparently act as peripheral filters with different tuning curves; these must play a part in frequency discrimination.