Retrograde axonal transport of different fluorescent tracers from the neocortex to the suprageniculate nucleus in the rat.

The retrograde fluorescent tracers in a combination of two different dyes (Fluoro gold/Nuclear yellow or Fast blue/Fluoro gold) were used for the study of the projections from the medial geniculate body to the frontal and temporal cortices in rats. There were only single-labeled cells, no double-labeled ones in the medial geniculate body (MGB). The suprageniculate nucleus (SG) was considered to be the origin of the rat direct pathway to the frontal cortex. The present results suggest that projections from the suprageniculate nucleus to the frontal cortex and the temporal cortex consist of separate neuronal groups in the rat MGB and SG. The inputs to the SG from the auditory and oculomotor system may be processed in different ways.