Purkinje cell degeneration and control mice: responses of single units in the dorsal cochlear nucleus and the acoustic startle response

The cartwheel cell is the most numerous inhibitory interneuron of the dorsa l cochlear nucleus (DCN). It is expected to be an important determinant of DCN function. To assess the contribution of the cartwheel cell, we examined the discharge characteristics of DCN neurons and behavioral measures in th e Purkinje cell degeneration (pcd) mice, which lack cartwheel cells, and co mpared them to those of the control mice. Distortion product otoacoustic em issions and auditory brainstem-evoked response thresholds were similar betw een the two groups. Extracellularly recorded DCN single units in ketamine/x ylazine-anesthetized mice were classified according to post-stimulus time h istogram (PSTH) and excitatory-inhibitory response area (EI-area) schemes. PSTHs recorded in mouse DCN included chopper, pauser/buildup, onset, inhibi ted and non-descript types. EI-areas recorded included Types I, II, III, I/ III, IV and V. There were no significant differences in the proportions of various unit types between the pcd and control mice. The pcd units had slig htly lower thresholds to characteristic frequency tones; however, they had spontaneous rates, thresholds to noise, and maximum driven rates to noise t hat were similar to those of the control units. Fed mice had smaller startl e amplitudes, but startle latency, prepulse inhibition/augmentation and fac ilitation by a background tone were comparable between the two groups. From these results, we conclude that DCN function in response to relatively sim ple acoustic stimuli is minimally affected by the absence of the cartwheel cells. Future studies employing more complex and/or multimodal stimuli shou ld help assess the role of the cartwheel cells. (C) 2000 Elsevier Science B .V. All rights reserved.