Immunohistochemical localization of quinolinic acid phosphoribosyltransferase in the human neostriatum.

The localization and distribution of quinolinic acid phosphoribosyltransferase, the degradative enzyme of the endogenous excitotoxin quinolinic acid, were studied in the post mortem human neostriatum by immunohistochemistry. In eight neurologically normal human brains, quinolinic acid phosphoribosyltransferase immunoreactivity was detected in both glial cells and neurons. Typically, glial cells containing quinolinic acid phosphoribosyltransferase immunoreactivity had numerous processes radiating from the cell bodies. In Nissl-counterstained sections, most quinolinic acid phosphoribosyltransferase-immunoreactive glial cells showed round, large and pale nuclei. These morphological features indicate that they are probably astrocytes. Neurons containing quinolinic acid phosphoribosyltransferase immunoreactivity had different sizes and shapes and were tentatively classified into three subpopulations. Most were medium-sized cells with ovoid or elongated perikarya. Small quinolinic acid phosphoribosyltransferase-immunoreactive neurons, often spheroid in shape, were particularly noted in a zone of the caudate nucleus adjacent to the lateral ventricle. A few large quinolinic acid phosphoribosyltransferase-positive neurons were also present in both the caudate and putamen. The somatic and dendritic morphology of quinolinic acid phosphoribosyltransferase-immunoreactive neurons closely resembles that of aspiny neurons seen in Golgi preparations. The localization of the specific quinolinic acid-catabolizing enzyme in distinct populations of neostriatal cells suggests specific functional correlates. It remains to be examined how the anatomical organization of quinolinic acid phosphoribosyltransferase immunoreactivity relates to the degradation of quinolinic acid in the striatum, and if the morphological characteristics and distribution of quinolinic acid phosphoribosyltransferase-immunoreactive cells are of relevance for the pathogenesis of neurodegenerative basal ganglia disorders.