Neuronal localization of tyrosine hydroxylase gene products in human neocortex

Tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis, has been reported to be present in interneurons in human cerebral cortex. In this study, immunocytochemical analysis using monoclonal anti-TH antibodies was employed to demonstrate the specific expression of tyrosine hydroxylase protein by a distinct subpopulation of nonpyramidal neurons in human neocortex. These neurons were present in greatest density in layer VI of limbic and higher order association regions. The presence of TH gene products in human neocortex was confirmed by the demonstration, using both in situ hybridization histochemistry and polymerase chain reaction methodology, that the mRNA for human TH is expressed in human neocortex. These findings raise important questions regarding the role played by these TH-containing neurons in human neocortical function.