Journal of Neurophysiology, Vol 50, Issue 3 573-581, Copyright © 1983 by APS
Adaptive changes in firing rates in goldfish auditory fibers as related to changes in mean amplitude of excitatory postsynaptic potentials
M. Kuno
Relationship between the firing rate in the auditory fibers and the
amplitude of the excitatory postsynaptic potentials (EPSPs) that trigger
afferent impulses was investigated. The unitary EPSPs and spike potentials
were extracellularly recorded from the goldfish large auditory fibers by
means of a microelectrode placed close to the distal terminals. The
relation between the firing rate and the amplitude of the EPSPs was studied
using a variety of stimulus conditions. The firing probability of
phase-locked impulses was linearly related to the mean amplitude of the
EPSPs determined for the same time bins. The same linear relation was
applicable for the firings elicited by different intensities of sound and
observed at various times after onset and also for the firings produced by
applying step increments in intensity. The threshold amplitude of the EPSPs
required for initiation of afferent impulses was unchanged in these
different situations. Random changes in the amplitude of successively
evoked EPSPs were found to underlie the probabilistic nature of the
sequence of afferent firings. The present results indicate that the per
stimulus adaptation and incremental and decremental responses, as observed
in the firing probability of afferent impulses, are largely attributable to
adaptive changes in the mean amplitude of the evoked EPSPs and not to
changes in excitability of the auditory fibers.
