Changes of cytoskeletal protein immunostaining in myelinated fibre tracts after focal cerebral ischaemia in the rat.

Abstract

Breakdown of the cytoskeleton has been proposed to be a central event in the evolution of ischaemic brain damage. Alterations in the immunostaining of cytoskeletal proteins, particularly microtubule-associated protein (MAP) 2, have been suggested to be sensitive markers of ischaemic damage in the somatodendritic compartment. However, axons are also subjected to the adverse conditions created by an ischaemic challenge, but MAP2 is not located in the axonal compartment. The purpose of the present study was to examine immunostaining of beta-tubulin, MAP1a and MAP5, all of which are located in axons as well as perikarya, specifically in myelinated fibre tracts in rats subjected to unilateral middle cerebral artery (MCA) occlusion. In sham-operated control rats immunostaining of all three antibodies in myelinated fibre tracts had a smooth, regular appearance. Two hours after MCA occlusion there were striking changes in the patterns of immunostaining of all three antibodies in myelinated fibre tracts within the MCA territory. These were particularly noticeable in beta-tubulin- and MAP5-stained sections where the pattern in white matter had a rough, globular appearance. This pattern was accentuated at 6 h after MCA occlusion and the presence of "bulb-like" profiles in white matter tracts was notable particularly in the MAP5-stained sections. Thus, the changes in the patterns of staining at 2 h after MCA occlusion may represent the early stages of axonal disconnection, and immunostaining of microtubular proteins may represent a sensitive method to assess ischaemically induced damage to myelinated fibre tracts.