Patterns of degeneration in the caudal cochlear nucleus of the cat after cochlear ablation

Abstract

Abstract Study of the caudal cochlear nucleus of the cat confirms the cochlear origin of synaptic terminals, identified in correlated rapid Golgi and electron microscopic preparations of the octopus cell area (OCA) and the dorsal cochlear nucleus (DCN) in normal cats. Type 1 and type 2 endings on octopus cell somas and basal dendrites, as well as type 1 and type 1a endings of the outer DCN, degenerate following complete ipsilateral cochlear ablations and short survival periods (12, 24, 48, 96 hours). Two distinct patterns of synaptic degeneration occur after short survival times; “dense degeneration” occurs in type 1 endings on octopus cells and several endings of the DCN. Dense terminals that contain tightly packed, but intact vesicles, occur most frequently after a 48‐hour survival period. A second type of degeneration, called “flocculent degeneration” occurs in type 1 and type 2 endings of the OCA and in type 1 and type 1a DCN terminals. Between 12 and 48 hours after ablation, the flocculent degeneration involves a continuous breakdown of organelles. Evidence for transneuronal degeneration of octopus cells and DCN granule cells is presented.