A ventral lateral geniculate nucleus projection to the dorsal thalamus and the midbrain in the cat

Retrograde tracing experiments using horseradish peroxidase (HRP) have been utilized for demonstrating the origin of efferent projections of the ventral lateral geniculate nucleus (LGNv) in the cat. HRP-positive cells identifiable as origins of thalamic projections were found in LGNv after injections of HRP into the lateral central intralaminar nucleus. The labeled cells appeared concentrated in the medial part of the internal division of LGNv, consisting of medium-sized multipolar cells. Contralaterally, fewer labeled cells were present in the corresponding part of LGNv. In the case of injections of HRP into the midbrain (pretectum and superior colliculus), labeled cells in LGNv were distributed almost exclusively in its external division, composed of mainly small cells. Little overlap of the distribution of HRP-positive cells was seen in LGNv between the thalamic and midbrain injection cases.