Perineuronal nets in the rat medial nucleus of the trapezoid body surroundneurons immunoreactive for various amino acids, calcium-binding proteins and the potassium channel subunit Kv3.1b

Perineuronal nets (PNs) are known as chondroitin sulfate-rich, lattice-like coatings of the extracellular matrix ensheathing mainly GABAergic, parvalb umin-containing neurons especially in the cerebral cortex. PNs have also be en detected around GABA-immunonegative cells which were shown to be not ami nergic, cholinergic, nitrinergic or peptidergic in various brain regions of some mammalian species. To find out whether glycine and aspartate may occu r in net-bearing neurons the present study was focused on the rat medial nu cleus of the trapezoid body (MNTB) which contains a large portion of cells immunoreactive for these amino acids, but appears to be devoid of GABA-immu noreactive cell bodies. PNs were detected around many glycine- and aspartat e-immunopositive neurons in the MNTB by carbocyanine double labeling and co nfocal laser scanning microscopy. An additional finding was that the lectin -cytochemically stained extracellular matrix surrounds the calretinin-immun oreactive calyces of Held known as giant glutamatergic endbulbs which cover glycinergic principal cells in the MNTB. As elucidated by triple fluoresce nce labeling. the vast majority of somata co-expressed the calcium-binding proteins parvalbumin and calbindin, but not calretinin. The observed co-loc alization of PNs and immunoreactivity for the voltage-dependent potassium c hannel Kv3.lb - as an established marker of fast-firing parvalbumin-contain ing neurons - supports the assumed function of PNs as a cation exchanger en suring rapid ion transport as required by highly active nerve cells. (C) 20 01 Elsevier Science B.V. All rights reserved.