Temperature insensitivity of short-term adaptation in single-units of the chick cochlear nerve.

Short-term adaptation in acoustically stimulated chick cochlear nerve fibers has recently been shown to have similar kinetics as the readily-releasable vesicle pool in patch-clamped chick hair cells, suggesting that short-term adaptation depends on the dynamics of hair cell exocytosis. Our understanding of the relationship between these two phenomena has been hampered by differences in the temperatures at which the two types of data have been collected. In this report, the effect of temperature on short-term adaptation was studied in single-units of the chick cochlear nerve. Compared to units recorded at 38-41 degrees C, spontaneous and evoked firing rates were markedly decreased when the temperature was lowered to 28-32 degrees C, but the rate of short-term adaptation during 100 ms tone bursts was relatively unchanged, with a temperature Q(10), of approximately 1.2. The continued similarity of the adaptation time-constant of cooled units to vesicle depletion kinetics in chick hair cells measured at room temperature suggests that comparison of in vitro hair cell exocytosis and in vivo cochlear nerve firing properties may not be confounded by temperature differences between the two approaches.