MICROGLIAL CELLS IN THE BRAIN OF PLEURODELES WALTL (URODELA, SALAMANDRIDAE) AFTER WALLERIAN DEGENERATION IN THE PRIMARY VISUAL-SYSTEM USINGBANDEIRAEA-SIMPLICIFOLIA ISOLECTIN B-4-CYTOCHEMISTRY

In the brain of the salamander Pleurodeles waltl, microglial cells wer e investigated cytochemically with isolectin B-4 (IB4) of Bandeiraea s implicifolia after optic nerve transection and during subsequent regen eration. Double-labeling with an antibody directed against the glial f ibrillary acidic protein of astrocytes revealed no immunoreactivity in microglial cells and confirmed the absence of non-radial, free astrog lial cells in the tectum. After two days, IB4-labeled microglial cells began to populate the rostral parts of the primary visual system. The origin of these early vimentin-immunoreactive microglial cells seemed to be mainly IB4-labeled cells in a perivascular position and meninge al macrophages. After 12 days, microglial cells infiltrated the tectum in four layers: one in the ependyma, one in the outermost periventric ular grey, and two in the degenerating visual neuropil where activated microglial cells displayed a ramified morphology. After 3 weeks, micr oglial cells accumulated within the degenerating neuropil while reduci ng their processes. After 7 weeks, the number of microglial cells was still increased on the affected side. The subarachnoid space above the neuropil where regenerating retinal afferents arrived was filled with IB4-labeled macrophages. Only very few microglial cells were seen in co-existence with Muller cells in the lesioned and intact retinae, whe reas microglial cells and macrophages were IB4-labeled in the optic ne rve head and at the era serrata. (C) 1994 Wiley-Liss, Inc.