Mapping of perineuronal nets in the rat brain stained by colloidal iron hydroxide histochemistry and lectin cytochemistry.

Net-like structures, visualized with the Golgi technique and several histochemical and immunocytochemical methods, have been described to ensheath somata, parts of dendrites and axon initial segments of various types of neurons. The origin and function of these perineuronal nets have been controversially discussed. Recently, it was confirmed that they are glia-associated. In the present study such perineuronal nets were demonstrated by using colloidal iron hydroxide staining for detection of polyanionic components and the plant lectins Vicia villosa agglutinin and Wisteria floribunda agglutinin with affinity for N-acetylgalactosamine. This paper shows their distribution patterns and the occurrence of regional specialization of these nets which might provide a basis to suggest functional implications of these structures. Perineuronal nets were found in more than 100 brain regions, such as neocortex, hippocampus, piriform cortex, basal forebrain complex, dorsal lateral septal nucleus, lateral hypothalamic area, reticular thalamic nucleus, zona incerta, deep parts of superior and inferior colliculus, red nucleus, substantia nigra, some tegmental nuclei, cerebellar nuclei, dorsal raphe and cuneiform nuclei, central gray, trochlear nucleus, pontine and medullar reticular nuclei, superior olivary nucleus and vestibular nuclei. Neurons enwrapped by perineuronal nets not only differ in morphology but also in transmitter content. In neocortical and hippocampal regions there occurs a much higher number of perineuronal nets ensheathing non-pyramidal cells than in paleocortical structures. Most subcortical regions containing perineuronal nets were found to be integrated in motor functions. The findings are discussed with respect to known electrophysiological data of cell types described in our investigation as net-associated. There are some indications that such cells may represent fast firing types.