Identification of response properties of ascending axons from dorsal cochlear nucleus.

Electrical stimulation in the dorsal acoustic stria (DAS) and the posterior and dorsal part of the ventral cochlear nucleus (VCN) was used to identify the response properties of efferent axons from the dorsal cochlear nucleus (DCN) in unanesthetized, decerebrate cats. Responses recorded in the DCN of this preparation can be divided into two broad classes, type II/III and type IV. Results of previous studies suggest that one subclass of type II/III units, those without spontaneous activity, are inhibitory interneurons terminating on type IV cells. Most type IV units (34/43) could be antidromically activated from the DAS and most units which could be activated from the DAS were of this type (34/39), suggesting that type IV responses are recorded from the projection cells of the DCN. Few type II/III cells without spontaneous activity could be activated from the DAS (1/30). A few cells of this type (6/32) could be antidromically stimulated from regions of the posterior AVCN or dorsal PVCN through which axon collaterals of some small cell interneurons of the DCN have been reported to pass. No type IV cells could be activated from the VCN (0/22). Thus the results are consistent with some type II/III responses originating in DCN interneurons. Spontaneously active type II/III units had intermediate properties.