Projections of the nuclei of the lateral lemniscus in the cat: an autoradiographic study

Abstract

Following injections of [ staggered 3 H] leucine into the dorsal (DLL) and the ventral (VLL) nucleus of the lateral lemniscus in the cat, the efferent projections were studied with the autoradiographic method. Injections into DLL result in heavy labelling in the bilateral inferior colliculus (IC) and the contralateral DLL. Within IC, labeling is dense in the ventrolateral part of the central nucleus (CNv) and moderate in the external nucleus (EN). Labeling in the dorsomedial part of the central nucleus of IC (CNd) is very sparse. All labeled fibers bound for the contralateral side cross in the dorsal part of the midbrain tegmentum at the intercollicular levels via the so-called commissure of Probst. The distribution pattern of labeling in the contralateral IC is almost the same as that in the ipsilateral. In contrast to the cases of injections into DLL, injections into VLL produce labeling in the ipsilateral CNv and EN without labeling in the contralateral IC. A precise comparison of the distribution pattern of labeling within CNv between DLL and VLL injection cases reveals that DLL contributes fibers densely to the dorsal portion of CNv in the proximity of CNd and sparsely to the ventral portion; by contrast, VLL sends many fibers to the ventral portion close to the lateral lemniscus and a few to the dorsal portion. Thus it is suggested that CNv is further divided into dorsal and ventral subdivisions in terms of the terminal zones of afferentsfrom DLL and VLL to CNv. In addition, labeling is found in the medial geniculate body, the nucleus of the trapezoid body and the marginal regions of the superior olivary nuclear complex in both DLL and VLL injection cases, while labelings in the superior colliculus and the pretectum are observed in DLL injection cases only.