Claustro-neocortical connections in the rat as demonstrated by retrograde tracing with Lucifer yellow.

The retrograde fluorescent tracer Lucifer Yellow (L.Y.) has been used to study claustro-neocortical connections in the rat with respect to their topography. L.Y. was injected in different cortical fields. Labeled cells were found in the ipsilateral claustrum. The distribution of labeled cells reflects the position of the injection sites along the rostro-caudal axis. The results demonstrate that claustro-neocortical projections are arranged in a topographical fashion not only in the cat, rabbit and monkey, but also in the rat. The connections are not as numerous as in the cat and are only ipsilateral. Our study shows in addition that L.Y. can be used as a connectivity tracer in the nervous system.