Anatomical re-evaluation of the corticostriatal projections to the caudate nucleus: a retrograde labeling study in the cat.

Abstract

The distribution of cortical neurons projecting to the cat caudate nucleus (CN) was examined using retrograde labeling methods. Single injections of either horseradish peroxidase conjugated with wheat germ agglutinin (HRP-WGA), or the fluorescent tracers Fast Blue (FB) or Diamidino Yellow (DY) were made into different regions of the CN. This study confirms the following previous findings. (1) Labeled neurons were observed in the frontal and parieto-temporal cortices. (2) The corticocaudate cells were mainly located in layer V, although some cells were also observed in layer III and occasionally in layers II and VI. (3) Dorsal injections into the rostral CN yielded more dorsal labeling in the cerebral cortex. However, ventral cortical areas such as the ventral part of the prelimbic (PL) cortical area and the insular cortex (sylvian anterior (SA), agranular and disgranular insular areas) presented retrograde labeling after both dorsal and ventral injections into the CN. (4) Dorsal injections into the CN labeled all subdivisions of areas 4 and 6 whereas the ventral ones labeled only the areas 4delta, 6alphabeta, 6aalpha, 6iffu. The novel findings of this study are as follows. (1) The cortical area 6betabeta and the dorsolateral prefrontal area (PfDl) were labeled in all our cases. In addition, PL, anterior limbic, SA and rostral part of cingulate (Cg) cortical areas were also labeled in most of our cases. (2) Ventral injections into the CN elicited a higher number of retrogradely labeled neurons in the ventral prefrontal area than dorsal injections. (3) A topographical relationship was found between the caudal CN and the dorsomedial prefrontal area so that dorsal injections in the caudal CN elicited retrograde labeling in the rostral PfDl, whereas ventral injections labeled the caudal PfDl. (4) A topography from dorsal to rostral and ventral to caudal was also observed between injections into the CN and PL and Cg. (5) A mediolateral topography was observed in the presylvian, cruciate and splenial sulci.