The inferior colliculopontine neurons of the cat in relation to other collicular descending neurons.

Cells of origin of the pontine afferents from the inferior colliculus (IC) of cats have been identified by means of retrograde axonal transport of horseradish peroxidase (HRP). Following injections of HRP in the pontine nuclei, many labeled neurons were found ipsilaterally in the caudal parts of the external and pericentral nuclei, while a few cells were found in the central nucleus. Additional neurons occurred in the nuclei of the middle and rostral parts. This organization contrasts with that of other collicular descending systems. Thus, neurons projecting to the superior olivary complex and cochlear nuclei were found predominantly in the central nucleus bilaterally. In the external nucleus labeled cells tended to be distributed in the middle to rostral regions, but they were few in number in the caudal part. Since the locations of IC-pontine neurons are found to be different from those of other IC descending neurons, it may be assumed that the IC-pontine system does not share common functional properties with the other collicular descending neurons. Functional aspects of the IC-pontine neurons are discussed, with a comment on a pathway for the transmission of auditory impulses to the midvermal area of the cerebellum.