ORIGINS OF AXONS IN CATS ACOUSTIC STRIAE DETERMINED BY INJECTION OF HORSERADISH-PEROXIDASE INTO SEVERED TRACTS

Origins and terminations of fibers of the dorsal and intermediate acoustic striae were studied by surgically severing these tracts and injecting HRP [horseradish peroxidase] into the incision. This procedure resulted in filling the severed axons with HRP. Filled axons were traced to cell groups of origin and to some terminations of the acoustic striae. HRP-labeled terminals were found in the cochlear nuclei and in periolivary cell groups. Filling of cells with HRP ranged from being complete, resulting in Golgi-like images, to being barely detectable. Labeled cells were abundant in the dorsal and posteroventral cochlear nucleus adjacent to the injection and scattered throughout the periolivary cell groups of both sides, being highest in concentration around the ipsilateral lateral superior olive. On the side contralateral to the injection, labeled cells were found along the medial border of the dorsal cochlear nucleus, in the interstitial nucleus of the stria of Held and sparsely throughout the ventral cochlear nucleus. The distribution of labeled cells was similar following HRP injections of the dorsal cochlear nucleus, except that these injections revealed additional descending projections from the inferior colliculi and from the ventral nucleus of the trapezoid body of both sides. These additional projections were interpreted as entering the CN [cochlear nucleus] by a ventral route. These findings agree with physiological recordings made from fibers of the acoustic striae.