Selective distribution of N-acetylaspartylglutamate immunoreactivity in the extrapyramidal system of the rat.

N-Acetylaspartylglutamate (NAAG), a neuron-specific dipeptide, was found by immunocytochemistry to be localized in specific compartments of the extrapyramidal system of the rat. Cellular and neuropil NAAG-like immunoreactivity (NAAG-IR) was evident throughout the pallidum, entopeduncular nucleus, subthalamic nucleus, and all subdivisions of the substantia nigra. By contrast, only a minority of cells of the caudate-putamen and those of the accumbens nucleus stained positively for NAAG. In general, neuronal NAAG-IR was widespread in all ventroposterior output zones of the extrapyramidal system, while cellular immunostaining was greatly reduced in the corticostriate receptive zones. These data suggest that NAAG may serve some neuronal communication function in the extrapyramidal processing circuits and output projections to the thalamus and midbrain. Additionally, neuronal NAAG immunolabeling differentiates corticostriate receptive zones from pallidal and nigral subdivisions of the extrapyramidal system in the rat.