Identification of cell types in brain slices of the inferior colliculus.

Different type neurons in the inferior colliculus may have different functions. Recent intracellular studies of the inferior colliculus suggest that intrinsic electrical properties contribute to discharge patterns, but the intrinsic discharge patterns have not been fully characterized in the central nucleus, the main part of the inferior colliculus. Whether different types of neurons are related to different discharge patterns is unclear. We have used intracellular and whole-cell patch clamp-recording techniques in a brain slice preparation to better characterize discharge patterns and cell types in the central nucleus. Several types of discharge pattern were found in the inferior colliculus in response to long pulses of intracellular depolarizations. Rebound and buildup-pauser discharges, together, comprise neurons with a sustained response and are the majority of the neurons in the inferior colliculus. Both of these types of discharge pattern could be adapting or regular. Onset discharges distinguished another group of neurons. Onset neurons can also entrain to higher frequency stimuli than sustained neurons. Discharge patterns are correlated with distinctive current-voltage relationships and with some aspects of dendritic morphology. However, the morphological data demonstrates that the discharge patterns do not correspond simply to disc-shaped (flat) or stellate (less-flat) categories. This is the first extensive analysis of electrophysiological properties of the central nucleus of the inferior colliculus in vitro. We suggest that there may be at least three functional classes of neurons and have implications for signal processing in the inferior colliculus.