Radial glia and cell debris removal during lesion-regeneration of the lizard medial cortex

Intraperitoneal injection of the neurotoxin 3-acetylpyridine (3AP) induces a rapid degeneration of the medial cerebral cortex (lizard fascia dentata) granular layer and of its zinc enriched axonal projection (lizard mossy fib res). After 6-8 weeks post-lesion the cell debris have been removed and the granular layer is repopulated by neurons generated in the subjacent ependy ma. Both processes, neuron incorporation and debris removal, seem to be cru cial for successful regeneration. Scavenging processes in the lesioned mamm alian CNS are usually carried out by microglia and/or astrocytes. In the li zard cerebral cortex there are no free astrocytes and the only glial fibril lary acid (GFAP) immunoreactive cells are radial glia-ependymocytes, simila r to those present during mammalian CNS development. Ependymocytes, in addi tion to their help in vertical migrations of just generated immature neuron s, built the cortical glial scaffold, insulate the blood capillaries, form the outer glial limiting membrane, thus playing an essential role in the li zard cortical blood-brain barrier. In this study, by means of GFAP-immunocy tochemistry and electron microscopy, we have shown that radial glial cells participate actively in the removal/phagocytosis of cellular debris generat ed in the lesion process: mainly degenerated synapses, but interestingly, a lso some neuronal somata. Cell debris taken up by ependymocyte lateral proc esses seem to be progressively transported to either distal (pial) or proxi mal (ventricular) pores of the cell, where they result in lipofuscin accumu lations. The hypothetical subsequent exchange of debris from ependymoglia b y microglia/macrophages and Kolmer cells is discussed.