Zinc-rich synaptic boutons in human temporal cortex biopsies

The distribution of zinc-rich synaptic boutons in biopsies of the temporal cortex from epileptic patients who had undergone surgery is described. Unfi xed cryostat sections were exposed to H2S vapour to precipitate endogenous zinc, which was subsequently shown by silver enhancement. In the temporal c ortex, the stain for zinc was arranged in bands: stain was heavy in layers II and VI, moderate-to-heavy in layers I, III and V, and low in layer IV. T he white matter was virtually devoid of staining. At the electron microscop e level, labelling was found in synaptic boutons that made asymmetric synap tic contacts. Immunohistochemical staining for glutamate receptor subunits GluR2/3 was observed in cell bodies in layers II, III, V and VI, coincident with the layers that showed heavy staining for zinc. Immunostaining for gl utamate receptor subunit GluR1 was prominent in non pyramidal neurons in de ep cortical layers. These results support findings in other mammals and indicate that the human neocortex may contain an extensive system of zinc-rich cortico-cortical co nnections. This system may be altered in pathological conditions. (C) 2000 IBRO. Published by Elsevier Science Ltd. All rights reserved.