RELATIONSHIP BETWEEN ASTROCYTIC PROCESSES AND PERINEURONAL NETS IN RAT NEOCORTEX

''Perineuronal nets'' (PNs) ensheath a subtype of inhibitory neurons i n the mammalian neocortex. In the light of the proposal that PNs consi st of glial processes, we have analyzed the relationship between intra cellularly injected glial cells and PNs in the rat neocortex. Glial ce lls were injected iontophoretically with Lucifer Yellow in lightly fix ed tissue slices and PNs were visualized with the lectin from Vicia vi llosa. Using confocal laser scanning microscopy, glial processes and P Ns were identified as distinct structures. Lectin labeling was consist ently associated with the extracellular space interposed between LY-la beled astrocyte processes and neurons. Of the different types of glial cells injected, only the densely-ramifying protoplasmic astrocytes ex tended processes which could be traced to contact PNs. These protoplas mic astrocytes also sent out processes to adjacent neurons not ensheat hed by PNs, and to capillaries. The present data strongly suggests tha t PNs do not consist of glial processes but rather support the idea th at PNs represent specialized extracellular material interposed between the surface of some inhibitory interneurons and astrocytic processes. (C) 1995 Wiley-Liss, Inc.