Diencephalic and mesencephalic afferents of the rat claustrum

The retrograde fluorescent tracers Fast Blue (FB) and Diamidino Yellow (DY) have been used to study subcortical afferents of the claustrum. DY or FB was injected into the claustrum. The greatest amount of labeled cell bodies were observed in the posterior thalamic nuclear complex. They were especially abundant in its caudal part, lying between the medial geniculate body and the pretectal area. In comparison to the numerous labeled cells near the diencephalic-mesencephalic junction, the number of fluorescing neurons in the brain stem was considerably lower. These neurons were mostly concentrated in the monoaminergic cell groups. The results indicate the presence of a substantial projection from the posterior thalamic and anterior pretectal region to the claustrum.