Journal of Neurophysiology, Vol 55, Issue 2 244-255, Copyright © 1986 by APS
Generator potentials and spike initiation in auditory fibers of goldfish
I. Kyogoku, S. Matsuura and M. Kuno
Responses were recorded extra- or intracellularly from single, small
afferent fibers of the goldfish saccule, that is, S2 fibers, to clarify how
the spontaneous and sound-evoked firings in these fibers are initiated from
generator potentials. Spontaneously active units randomly selected from the
saccular nerve of five goldfish (total 78 units) were classified by the
coefficient of variation (CV) of interspike intervals into irregular (59
units; CV greater than 0.3), intermediate (10 units), and regular types (9
units; CV less than 0.23). The irregular type showed a burst (38 units) or
random (21 units) pattern of firing in spontaneous activity. In cases where
a clear generator potential could be recorded in response to each sound
wave, spontaneous generator potentials could also be observed in the
absence of stimulus sound. These spontaneous potentials were irregular in
amplitude and time course, and often contained components much slower than
the sound-evoked generator potentials. The sound-evoked generator
potentials in S2 fibers were produced with a delay of 0.4-0.85 ms following
each sound wave, and had a time course comparable to the sound-evoked
excitatory postsynaptic potentials (EPSPs) of large S1 fibers. They also
shared other properties such as adaptive decline in amplitude, incremental
and decremental responses, and off-suppression. The mean amplitude of the
sound-evoked generator potentials in S2 fibers was linearly related to the
rate of afferent firing. There was no apparent difference in the action
potential threshold amplitude for spontaneous and sound-evoked generator
potentials. It may be concluded that the generator potentials that underlie
the spontaneous and sound-evoked firing of S2 fibers are produced by the
release of transmitter by hair cells.
