Photomicrographs of the caudate nucleus of the macaque monkey. (A) Nissl-stained section showing the density of striatal neurons in this region. (B) Phase-contrast photomicrograph illustrating small (approximately 10 μm in diameter), stellate neurons stained with plasma from a representative AU subject. (C) Section though the caudate nucleus reacted with a monoclonal antibody to GABA. Immunoreactivity is associated with numerous axonal varicosities as well as a variety of neuronal cell types. The small, stellate cell type observed by plasma immunohistochemical staining is also shown in the GABA preparations (black arrow). Other, larger GABAergic neurons (white arrow) can also be observed. Calibration bar, 10/100 μm.