Influence of Cadmium on glial architecture in Podarcis sicula brain.

The nervous system is built from two broad categories of cells, neurones and glial cells that include the astrocytes, oligodendrocytes, ependymal cells and microglia. Cell bodies of astrocytes are juxtaposed between neurons and the capillary endothelium to form the blood-brain barrier. Given these cytoarchitectural features, they are the first cells of the brain parenchyma to encounter foreign molecules crossing this barrier1. For this they have also a neuroprotective action for the encephalon from cytotoxic action of heavy metals. The cadmium (Cd), a metal highly toxic, can partially pass the blood-brain barrier and it exerts neurotoxic activity2. Numerous studies provide evidence that Cd induces neuronal toxicity and damage to the brain3,4. The influence of the neurotoxic agent Cd on astroglia of Reptile Podarcis sicula was investigated in vivo by means of immunocytochemistry. In this work a group of P. sicula was exposed to an acute treatment by a single i.p. injection (2mg/Kg-BW) of CdCl2 and was sacrificed after 2, 7 and 16 days. Another group of P. sicula was exposed to a chronic treatment for four months with CdCl2 at dose of 1mg/kg-BW in the drinking water and was sacrificed after 10, 30, 60, 90 and 120 days. Serial sections of brains were processed for routine histological and immunodetection of GFAP by ABC technique. GFAP (glial fibrillary acidic protein) is the intermediate filament of glial cells and the most widely accepted marker for glial differentiation. Results: in the brain of P. sicula the general pattern of the GFAP-immunoreactivity was fundamentally represented by long and thick fibers which ran from cell bodies located at the ventricular surface to the meningeal layer. Numerous GFAP-immunopositive structures were observed in the mesencephalon and in the medulla oblongata (fig.1), but thin fibers GFAP(+) were also present in the telencephalon. The most numerous glial cells observed were of radial glia type (fig.2). In the grey matter of the cerebellum an intense immunoreactivity was observed, while round cells with wide marked cytoplasm were localized in the white matter. In the acute treatment: after 2 and 7 days the lizards showed a decrease of the GFAP-immunopositive structures (fig.3). After 16 days this reduction of immunostaining was most considerable (fig.4). The reduction of the presence of the radial glia was most meaningful in the cerebellum and in the optic tectum. In the chronic treatment: after 10 days the encephalon of lizards showed a decrement of GFAP-immunoreactivity only in grey matter of the cerebellum. At 30 days a reduction of expression and distribution of GFAP-immunopositive structures was observed in the telencephalon, mesencephalon and medulla. After 60 days only few GFAP-immunopositive structures were revealed and the absence of the radial glia was observed. Indeed at 90 days the radial glia was observed again in the telencephalon and at 120 days there was a return of occurrence of GFAP structures similar to that of control lizards. These results show that in the lizards an acute and chronic exposure to cadmium provokes decrement of the expression of GFAP marker with possible consequent damage in the function of the glial cells and neurons.