Adaptive changes in firing rates in goldfish auditory fibers as related to changes in mean amplitude of excitatory postsynaptic potentials.
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.
D000222:Adaptation, Physiological; D000818:Animals; D001307:Auditory Perception / Q000502:physiology*; D003530:Cyprinidae / Q000502:physiology*; D005072:Evoked Potentials, Auditory; D006054:Goldfish / Q000502:physiology*; D008144:Loudness Perception / Q000502:physiology; D013569:Synapses / Q000502:physiology; D009435:Synaptic Transmission; D000159:Vestibulocochlear Nerve / Q000502:physiology*