Differential complementary localization of metabolic enzymes for quinolinic acid in olfactory bulb astrocytes

The cellular localizations of the synthetic [3-hydroxyanthranilic acid oxygenase (3HAO)] and degradative [quinolinic acid phosphoribosyltransferase (QPRT)] enzymes of the endogenous excitotoxin quinolinic acid were studied in the adult rat main olfactory bulb by immunohistochemical techniques. 3HAO and QPRT were expressed only in astrocytes. The two enzymes were differentially expressed by astrocytes in a complementary pattern: 3HAO staining was strongest at the glomerular-external plexiform layer junction; QPRT staining was strongest at the glomerular-olfactory nerve layer junction. The complementary distributions of these metabolic enzymes suggests that there could be a gradient of quinolinic acid across the glomerular layer of the main olfactory bulb. Such a gradient could function to restrict the ingrowth of new olfactory axons to the glomeruli and/or to stabilize the formation of new synapses.