Evidence for presynaptic facilitation in primary cochlear afferent neurons.
Evidence for presynaptic facilitation was sought in the discharge patterns of single units in the chinchilla cochlear nerve. Pairs of acoustic clicks, separated by a variable interval, were delivered and spike discharge times stored for offline analysis. By choosing an appropriate binwidth (5 ms) and collecting data only from units with high characteristic frequencies (CF) the response to each click was contained in a single bin. The ratio of spike counts in the bins containing the responses to the two clicks was computed. For units with low spontaneous rates (SR) of discharge (SR less than 8/s), an enhancement of the response to the second click was seen for low stimulus levels. As the stimulus level was raised, the response to the second click became reduced, presumably because of adaptation to the first click. Units with high (SR greater than 15 spikes/s) seldom exhibited enhancement of the response to the second click. The results are explained with a conceptual model in which two processes, depletion and facilitation decay exponentially following a stimulus. Since the two processes have opposite influences on the rate of transmitter release, the magnitudes of both processes may be underestimated by observing their net effect.
D000161:Acoustic Stimulation; D000818:Animals; D002682:Chinchilla; D003056:Cochlear Nerve / Q000502:physiology*; D005072:Evoked Potentials, Auditory; D008959:Models, Neurological; D013569:Synapses / Q000502:physiology*