Pathways and terminal fields of the cochlearofugal somatostatin tracts of very young rats.

The cochlearofugal somatostatin (SRIF) neuron system of very young rats (between newborn and 1 week old) was investigated by means of the indirect immunofluorescence technique of Coons. Cochlear nuclei (both dorsal and ventral cochlear nuclei) of this stage contain numerous SRIF-positive cells which are scarcely found in adult rats. Based upon the experimental findings obtained by this study, the majority of SRIF-positive fibers originating from these nuclei reach the contralateral inferior colliculus via well-established cochlearo-inferior collicular tracts such as dorsal acoustic striae, intermediate acoustic striae and trapezoid body, respectively. The possible significance of SRIF in the development of the auditory system is briefly discussed.