The supraoculomotor cap: a region revealed by NADPH diaphorase histochemistry

The distribution of the enzyme NADPH diaphorase in the region of the periaqueductal gray (PAG) was studied in the rat, rabbit, cat, monkey and human. In each species, the enzyme labelled a small band of neurones located below the level of the aqueduct and directly above the supraoculomotor gray in the middle of the antero-posterior extent of the PAG. The chemical specificity of this region suggests that it is distinct from the lateral PAG above and the supraoculomotor nucleus (Su3) below. We have named it the supraoculomotor cap (Su3C).