Percentage incidence of gamma-aminobutyric acid neurons in the claustrum of the rabbit and comparison with the cortex and putamen.

We describe the incidence of gamma-aminobutyric acid (GABA)ergic neurons after post-embedding immunocytochemistry on semithin sections of the claustrum, putamen and lateral, dorsal and medial cortical areas. Twelve percent of the neurons counted in the claustrum of 11 rabbits were GABAergic. This incidence was significantly higher in the dorsal halves of both the insular and endopiriform claustra than in the ventral (13 vs. 10%). The incidence of GABAergic cells was 4% in the putamen, 14% in the insular cortex, 15% in areas 17 and 18 and 13% in area 29d. Thus, our results indicate that in contrast to the putamen the incidence of GABAergic cells was similar in the claustrum and cortical areas. We interpret this in the light of the pallial origin of the claustrum, which has recently been substantiated.