Co-localization of tyrosine hydroxylase and GABA immunoreactivities in human cortical neurons

Samples of human cerebral cortex were stained immunocytochemically for tyrosine hydroxylase (TH) and gamma-aminobutyric acid (GABA). TH-positive neurons were in small number and predominated in the deep infragranular layers V-VI contrasting with numerous GABA-positive neurons scattered in all layers. Co-localization of TH- and GABA-like immunoreactivities in a single cell was studied by the double immunolabeling technique with the elution-restaining procedure. Only 50% of the TH-positive neurons also expressed GABA-like immunoreactivities. The two markers were detectable in the somata and not in the processes of the cells. The double-labeled cells were mainly fusiform and medium-sized and were observed in layer VI. These observations suggest that the TH-positive cells form a mixed neuronal population, only a part of which corresponds to the GABAergic class of intrinsic interneurons.