The morphology and distribution of neurons labeled specifically by the lectin, Vicia villosa (VVA), were examined in striate cortex of adult macaque monkeys. Following incubation with VVA conjugated to histochemical markers, fine punctate reaction product appears to cover the surface of the soma and proximal dendrites of a population of cortical neurons. Although a small number of VVA-labeled cells are located in layers 2, 3A, 5, and 6, approximately 75% are located in a strip of cortex overlying layers 3B through 4Ca. Layers 1 and 4Cβ are virtually devoid of labeled cells. The morphology of labeled cells varies throughout the layers. In the supragranular layers, the labeled cells generally display a round or multipolar soma with a small number of radially disposed dendrites. In deeper layers, labeled cells are multipolar or horizontal, and their proximal dendrites are often more densely labeled. There is no clear correlation between the distribution of labeled cells and the pattern of cytochrome oxidase staining in supragranular layers.

Double labeling of single sections for VVA and for GABA (gamma-aminobutyric acid) immunoreactivity revealed that most VVA-labeled cells are also immunoreactive for GABA. The double-labeled cells comprise approximately 30% of all GABA immunoreactive cells. Soma size analysis of double-labeled cells shows that medium-to-large GABA cells in each layer are labeled by VVA. The soma size, laminar distribution, and morphology of the VVA-labeled GABA cells suggest that they include the large basket cells originally observed in Golgi preparations.