In vitro whole cell recording revealed intrinsic firing properties and single-cell morphology in the cochlear nucleus angularis (NA) of the chick. We classified three major classes of neurons: one-spike, damped, and tonic. A delayed inward rectifying current was observed in all classes during hyperpolarization injections. One-spike neurons responded with a single spike to depolarizing current injection and had small (stubby) radiate dendritic trees. Damped neurons responded with only a few spikes at the onset of positive current injection. More positive current inputs led to a damped response. Damped cell dendrites had a planar orientation parallel to the isofrequency axis in NA. Tonic cells produced trains of action potentials in response to a depolarizing current injection. Three variations of the tonic type had multipolar morphology, with dendrites oriented either radially (I and III) or perpendicular to the tonotopic axis (II; vertical). Tonics I and III differed in the shape of their action potential undershoot. Thus NA is both physiologically and morphologically heterogeneous.
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