Cochlear nucleus unit responses to pure tones in the unanesthetized rabbit

Seventy-six units were studied in the cochlear nucleus of unanesthetized, paralyzed rabbits. Most were located in the dorsal cochlear nucleus. Fifty-eight units were characterized according to their response area by the scheme of Evans and Nelson (1973, Exp. Brain Res., 17, 402–427): 22.5% showed purely excitatory response areas (type I/II), 72.5% showed mixed excitatory and inhibitory response areas (types III and IV), and 5% showed purely inhibitory response areas (type V). Ten units had virtually no spontaneous activity so were unclassifiable. When characterized according to the scheme of Pfeiffer (1966, Exp. Brain Res., 1, 220–235), 41% of the units were primary-like, 24% were choppers, 20% were pausers, 3% were buildup, and 1% were on units. There was no overall correlation between the two methods of unit classification, but type I/II units showed a high number of chopper patterns. Dorsal cochlear nucleus units in the unanesthetized rabbit showed response characteristics very similar to those which were reported in the decerebrate cat. However, there was a greater prevalence of primary-like, purely excitatory units in the rabbit dorsal cochlear nucleus. This may have reflected a species difference or have been due to technical considerations. It appears that the rabbit cochlear nucleus has very similar physiologic, as well as anatomic, characteristics as does that of the cat.