Electroreceptors of a weakly electric fish
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The hypothesis of an active electroreceptor filter, characterized by an underdamped, oscillatory impulse response, was tested indirectly by investigating the pattern of afferent discharges resulting from receptor excitation with electric field pulses. When stimulated with a single, high amplitude, short duration pulse the majority of afferents responded with bursts of two or three spikes having interspike intervals, in individual fish, correlated to the individual's electric organ discharge period, and, more importantly, with the best frequency of the corresponding receptor. Pulses causing current to flow into the receptor from the bath resulted in shorter response latencies and more spikes per burst than pulses of the opposite polarity. The polarity dependent latency shift was also correlated with the best frequency of the receptor and the electric organ discharge repetition rate of an individual, but it was much shorter than expected based on the prediction of a generator potential in the form of a classical underdamped oscillation. Because of this it is concluded that the generator potential oscillations increase in period for successive cycles. This was essentially confirmed by the form of the receptor organ excitability cycle which was measured by using a two pulse stimulus paradigm.
Further confirmation of the existence of an oscillatory generator potential was obtained by recording compound action potentials from the afferent nerve and comparing the single peaked potentials obtained by direct nerve shock with the multipeaked potentials evoked by receptor activity in response to electric field pulses in the water.
The physiological properties of tuberous electroreceptors are nearly the same as the properties of receptors in the phylogenetically related vertebrate auditory system. This leads to the suggestion that the two systems have in common similar physiological mechanisms, and that the oscillatory receptor properties observed for electroreceptors may serve, in the auditory system, as the basis for a proposed second filter.
KeywordsElectric Field Pulse Interspike Interval Compound Action Potential Good Frequency Electric Organ Discharge
electric organ discharge
mean of the distribution
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