The perforating vessels in the brainstem of the Mongolian gerbil were ex-amined by India ink injection and the brainstem microvascular architecture was examined by Mercox injection.
1. Three types of perforating vessels were identified. Type 1 perforators branched into capillaries soon after penetrating the brainstem, type 2 perfora-tors changed into capillaries in the middle of the brainstem, and type 3 perfo-rators penetrated the dorsal part of the brainstem and changed into capillaries. The diameter of type 1 perforators was 10-15μm, that of type 2 was 20-25μm, and that of type 3 was 35-55μm.
2. The capillary blood vessels generally showed T-shaped or Y-shaped branching but occasional atypical configurations were observed. The blood flow may be regulated by these different configurations.
3. We observed no difference between the capillary blood vessels of the vestibular nucleus and those of the cochlear nucleus.
4. We observed that the brainstem contains a dense capillary network, and that blood flow in the perforators was regulated by the site of entry into the brainstem and by the diameter of the perforating vessel.
