Claustro-neocortical connections in the cat and rat demonstrated by HRP tracing technique.

1. Following HRP injections (Sigma VI) into the sensorimotor, association and auditory cortex of the cat HRP positive neurons were found in the dorsal claustrum (claustrum dorsale, cl. insulare) on the side of the injection and contralaterally. The finding of HRP positive neurons in the ipsilateral and contralateral claustrum is considered an evidence of uncrossed as well as of crossed claustro-neocortical projections. 2) HRP positive neurons in the ipsilateral claustrum multipolar in number the labeled neurons of the contralateral claustrum. 3) The uncrossed and crossed claustro-neocortical projections in the cat are arranged anteroposteriorly. 4) The neurons of the claustrum containing retrogradely transported HRP possess middle size and large perikarya of multiply, pyramidal, triangular and spindle shape. 5) Between the neocortical formation and the dorsal claustrum of the cat there is a cortico-claustral and claustro-cortical interconnection. 6) Following an HRP injection into the frontal parietal cortex of the rat we observed in the ipsilateral claustrum a small number of HRP positive mulipolarr and triangular perikarya.