GABAergic neurons of rodent brain correspond partially with those staining for glycoconjugate with terminal N-acetylgalactosamine.
Sections of fixed, paraffin-embedded brain from mice and rats were stained with agglutinin from Vicia villosa conjugated to horseradish peroxidase (VVA-HRP) to localize glycoconjugate containing terminal N-acetylgalactosamine (GalNAc). VVA-HRP binding sites were localized in periodic foci at the surface of a selective population of non-pyramidal interneurons in layers II through IV of the rodent cerebral cortex. These multipolar interneurons were shown to utilize gamma-aminobutyric acid (GABA) as a transmitter and thus to be GABAergic by their immunostaining for glutamic acid decarboxylase (GAD) throughout the cytoplasm in serial sections. Pyramidal and other non-pyramidal cortical neurons received GABAergic input as evidenced by punctate immunostaining for GAD on their soma and proximal dendritic arborizations, but these cells failed to show VVA affinity or cytosolic GAD reactivity. Most neurons in the thalamic reticular nucleus stained for the presence of glycoconjugate with terminal GalNAc on their surface and for GAD in the cytosol. In contrast, cerebellar Purkinje cells showed strong cytosolic reactivity with anti-GAD but lacked surface staining with VVA-HRP. These observations show that some but not other populations of GABAergic neurons possess binding capacity for VVA on their surface. The surface of neurons in the deep cerebellar nucleus stained heavily with VVA but failed to show clear cytosolic reactivity for GAD. Some neurons with surface glycoconjugate containing terminal GalNAc are therefore not GABAergic.