A cuneocochlear pathway in the rat.

Following injections of wheat germ agglutinin-conjugated horseradish peroxidase into the cuneate nucleus of anesthetized rats, retrograde and anterograde label was observed in the cochlear nucleus. Labeled cochlear neurons were found mostly in the ipsilateral dorsal cochlear nucleus and in the contralateral ventral cochlear nucleus. Anterograde label was found primarily ipsilateral to the injection site, and was restricted mainly to the dorsal cochlear nucleus, although label was also observed in the anteroventral cochlear nucleus. Horseradish peroxidase injections were made in the dorsal cochlear nucleus to investigate the source of this pathway. Retrogradely labeled cells in the region of the dorsal column nuclei were located mainly in a shell on the dorsal edge of the cuneate nucleus extending into the white matter of the cuneate fasciculus. The cuneocochlear pathway could provide a direct link between the auditory and somatosensory systems; connections between these two sensory systems may be explained on phylogenetic grounds.