Subcortical auditory and somatosensory afferents to hamster superior colliculus

To determine whether the pattern of superior colliculus (SC) afferents seen in cat is generalizable to other mammalian species, HRP was injected into the SC of twenty hamsters (Mesocricetus auratus). After reaction with TMB, subcortical structures were examined for labeled perikarya. Although most subcortical afferents to SC were similar in cat and hamster, there were differences in auditory and somatosensory SC innervation. In hamster only two putatively auditory structures showed labeled cells, the external nucleus of inferior colliculus and nucleus of the brachium of the inferior colliculus, whereas in cat additional cells are reported in the dorsal cochlear nucleus, trapezoid and superior olivary nuclei, and nucleus of the lateral lemniscus. Again, in hamster the major trigeminal somatosensory input to SC is from spinal trigeminal nucleus caudalis whereas in cat trigeminal input is reported to be from the principalis and oralis portions of the trigeminal nucleus. Thus the hamster possesses a very restricted auditory input to and a different pattern of somatosensory innervation of the SC relative to the cat.