Vesicular γ-aminobutyric acid transporter expression in rat periaqueductal gray matter.

Vesicular γ-aminobutyric acid transporter, an integral membrane protein, mediates γ-aminobutyric acid uptake into synaptic vesicles. Investigation of its expression in the rat periaqueductal gray matter using light and electron microscopic immunocytochemical techniques documents immunoreactivity in numerous puncta in all periaqueductal gray columns, with slightly denser labeling on the outer edge of the dorsolateral portion and least dense labeling in the rostral-dorsomedial portion. Electron microscopic observations show immunoreactivity over synaptic vesicles of terminals exhibiting the standard features of inhibitory synapses. Unlabeled axon terminals making symmetric synapses are also commonly observed. These data suggest the following: (i) the γ-aminobutyric acid uptake is slightly greater in the dorsolateral and less intense in the rostral-dorsomedial portion and (ii) the possible existence of an additional inhibitory amino acid transporter.