Transitory disappearance of microglia during the regeneration of the lizard medial cortex

Abstract

In normal lizards, microglial cells populate the medial cortex (a zone homologous to the hippocampal fascia dentata), with a preferential distribution along the border between the granular cell layer and the plexiform layers. Intraperitoneal injection of the neurotoxin 3-acetylpyridine (3AP) induces a selective lesion in the medial cortex with a rapid degeneration of the granular layer and its zinc-enriched axonal projection. Within 6-8 weeks, the granular layer is, however, repopulated by a new set of neurons generated in the subjacent ependyma and the cell debris is removed. The aim of this study was to determine to what extent microglia were involved in the scavenging processes during the regeneration process. To this end we studied the brains of regenerating lizards at different times after 3AP lesion, visualising microglial cells by the nucleoside diphosphatase (NDPase) histochemical reaction. Surprisingly, we found that stained microglial cells disappeared 6-8 hours after 3AP injection and remained absent until 10-15 days after injection. One month postlesion an increased population of microglial cells was found scattered throughout all plexiform layers of the cortex. Thorough examination of semithin and ultrathin sections confirmed the absence of microglia in the medial cortex of recent lesioned animals but the presence of an exuberant population after 1 month postlesion. In the tissue, phagocytotic scavenging was carried out by radial ependymocytes, not by microglia.

Naturally occurring cell death and migration of microglial precursors in the quail retina during normal development

“…We found that microglial cells traverse the INL only after cell death has ceased in this layer. This sequence is similar to that reported in the lizard medial cortex in which massive neuronal death has been induced experimentally (López-García et al, 1994). Our results suggest that radial migration of microglial precursors in the quail retina occurs in two phases: migration across the NFL and GCL to the vitreal border of the IPL and migration across the IPL and INL to gain access to the OPL.…”

3‐acetylpyridine‐induced degeneration in the adult ascidian neural complex: Reactive and regenerative changes in glia and blood cells

“…In lizards, removal of the degenerating axonal and cellular debris occurred through the combined action of microglia, radial glial cells, and astrocytes (Font et al, ). Further, 3AP lesion in lizards resulted in the loss of microglia and astrocytes from the lesioned area, followed by an increase in microglia and astrocytes in the overall cortex (López‐García et al, ).…”

Absence of post‐lesion reactive gliosis in elasmobranchs and turtles and its bearing on the evolution of astroglia

“…On the other hand, some types of glial reactions have been reported in teleost fishes (goldfish, C. auratus : Bernstein and Bernstein, , ; Bignami et al, ; Wolburg and Kastner, ; Stafford et al, ; Nona and Stafford, ; gymnotiform fish, Stenarchus latifrons : Anderson et al, ) and amphibians (frogs, Xenopus laevis : Reier, ; R. pipiens : Scott and Foote, ; newt, Triturus pyrrhogaster : Stensaas and Feringa, ), and even in a reptile (lizard, Gallotia galloti : Romero‐Alemán et al, ; Lang et al, ), although, for example, Lopez‐Garcia et al () and Molowny et al () mentioned no astroglial reaction following cortical lesions in another lizard species ( Podarcis sicula ).…”