Inhibitory zinc-enriched terminals in mouse spinal cord

The ultrastructural localization of zinc transporter-3, glutamate decarboxy lase and zinc ions in zinc-enriched terminals in the mouse spinal cord was studied by zinc transporter-3 and glutamate decarboxylase immunohistochemis try and zinc selenium autometallography, respectively. The distribution of zinc selenium autometallographic, silver grains, and zi nc transporter-3 and glutamate decarboxylase immunohistochemical puncta in both ventral and dorsal horns as seen in the light microscope corresponded to their presence in the synaptic vesicles of zinc-enriched terminals at ul trastructural levels. The densest populations of zinc-enriched terminals we re seen in dorsal horn laminae I, III and IV, whereas the deeper laminae V and VI contained fewer terminals. At ultrastructural levels, zinc-enriched terminals primarily formed symmetrical synapses on perikarya and dendrites. Only relatively few asymmetrical synapses were observed on zinc-enriched t erminals. In general, the biggest zinc-enriched terminals contacted neurona l somata and large dendritic elements, while medium-sized and small termina ls made contacts on small dendrites. The ventral horn was primarily populat ed by big and medium-sized zinc-enriched terminals, whereas the dorsal horn was dominated by medium-sized and small zinc-enriched terminals. The presence of boutons with flat synaptic vesicles with zinc ions and symm etric synaptic contacts suggests the presence of inhibitory zinc-enriched t erminals in the mammalian spinal cord, and this was confirmed by the findin g that zinc ions and glutamate decarboxylase are co-localized in these term inals. The pattern of zinc-enriched boutons in both dorsal and ventral horn s is compatible with evidence suggesting that zinc may be involved in both sensory transmission and motor control. (C) 2001 IBRO. Published by Elsevie r Science Ltd. All rights reserved.