Frequency response characteristics of electroreceptors in the weakly electric fish,Gymnotus carapo

Abstract

Frequency response characteristics of phasic electroreceptors in the weakly electric pulse fish,Gymnotus carapo, were related to the character of a receptor signal (RS) recorded externally over the receptor pore. Receptors that were equally sensitive to a broad range of frequencies produced RS's of a single hump, whereas sharply tuned receptors produced oscillatory RS's (Fig. 4A). Furthermore, the frequency of the recorded oscillation provided a reliable estimate of the receptor's best frequency (Fig. 4B). The two major classes of electroreceptors, burst duration coders and pulse markers, could not be distinguished on the basis of best frequency (BF), Q5, or threshold at BF (Fig. 1A-C). These parameters were widely distributed in both classes. Pulse markers, however, never responded to a pulse stimulus with more than one spike and tended to have shorter latencies than burst duration coders (Fig. 2). Power spectra were calculated for local EOD waveforms recorded with three different electrode configurations (Figs. 6B, 7A-J). The local spectral peak power measured transepidermally in the rostral half of the body was 540±52 Hz, whereas the spectral peak power of the H-T waveform was 1127±90 Hz. Electroreceptors were not sharply tuned to the fish's own EOD, but showed a decrease in median BF from the rostral region where it was 950 Hz to the middle region where it was 350 Hz (Fig. 8A-D).