An immunocytochemical and biochemical study of the microtubule-associated protein Tau during post-lesion afferent reorganization in the hippocampus of adult rats.

A monoclonal antibody against the microtubule-associated protein (MAP) Tau was used to examine the fate of this molecule during post-lesion afferent reorganization in the hippocampus of adult rats. An immunocytochemical analysis was carried out in the dentate gyrus after unilateral destruction of the entorhinal cortex (EC). In the non-denervated hippocampus, Tau immunoreactivity was detected in parallel axons and mossy fibers; no staining was present in neuronal cell bodies and dendrites. A significant decrease in Tau immunoreactivity was detected in the outer 2/3 of the ipsilateral dentate gyrus molecular layer (ML) 2 days after an EC lesion, whereas staining in the inner 1/3 of the same ML increased considerably. This was followed by a very rapid recovery of Tau immunoreactivity in the outer 2/3 of the denervated ML, which by 10 days post-lesion was almost identical to that of the contralateral non-denervated ML. A similar phenomenon was observed in other regions of the hippocampus denervated by the EC lesion. The modifications in Tau immunoreactivity in the denervated hippocampus were also accompanied by changes in the polypeptide composition of this heterogeneous group of MAPs, as revealed by immunoblot analysis of hippocampal extracts obtained at different post-lesion intervals; these changes involved a rapid and significant increase in low molecular weight migrating Tau-immunoreactive polypeptides. The present observations indicate that important modifications in Tau proteins occur in the deafferented hippocampus, a phenomenon that may well be related with the regulation of microtubule polymerization during post-lesion axonal growth.