Intracellularly Labeled Fusiform Cells in Dorsal Cochlear Nucleus of the Gerbil. I. Physiological Response Properties

Abstract

Fusiform cells in the dorsal cochlear nucleus (DCN) of barbiturate-anesthetized Mongolian gerbils were characterized physiologically and labeled with neurobiotin. This report is based on 17 fusiform cells for which there was reasonable confidence in the association between physiological data and recovered anatomy. The qualitative morphology of these cells was no different from that reported in previous studies. The acoustic response properties were generally consistent with those described in the barbiturate-anesthetized cat. Most responses were of the pauser or buildup type, but a dependence on stimulus frequency and intensity was observed. Stimulus-evoked sustained depolarizations and large, long-lasting afterhyperpolarizations were common membrane potential features. The cells in this study showed a greater tendency to discharge regularly than did those of the cat, likely as a result of the longer interstimulus interval used. Barbiturate anesthesia appears to mask an interspecies difference in DCN physiology that is apparent in unanesthetized, decerebrate preparations. The response of these fusiform cells to a depolarizing current pulse could be altered by the presence of a hyperpolarizing prepulse. Buildup, pauser, and chopper patterns could each be created using appropriate combinations of hyperpolarizing and depolarizing pulse amplitudes. Thus the adult gerbil appears to express the inactivating potassium conductance previously shown to affect fusiform cell firing patterns in vitro. The results further demonstrate that the effects of these potassium currents are readily observed in vivo. Finally, the fusiform cells in this study were quite variable with respect to a number of response properties, including the resting potential, input resistance, spontaneous activity, relative noise index, normalized tone slope, and regularity histogram shape. This diversity likely results from cell-to-cell variations in the balance of activity within the relatively complex network to which the fusiform cells belong, although effects of impalement may contribute to the extent of the diversity.