Assessment of white matter injury following prolonged focal cerebral ischaemia in the rat

The ability of putative neuroprotective compounds to protect against white matter injury remains poorly investigated due to the lack of suitable metho ds for assessing white matter injury. This study was therefore designed to investigate the utility of Tau 1 (oligodendrocytes/axons), myelin basic pro tein (MBP; myelin) and amyloid precursor protein (APP; axons) immunohistoch emistry in assessing white matter injury at various times following middle cerebral artery occlusion (MCAO) in the rat. Focal cerebral ischaemia was i nduced in halothane-anaesthetised rats using an intraluminal thread model. At 24 h, 1 and 2 weeks following MCAO, white matter injury was assessed usi ng Tau 1, APP, MBP and Luxol-fast blue staining and neuronal injury with cr esyl fast violet (CFV). In histologically normal tissue MBP immunoreactivit y was detected in myelinated fibre tracts, while Tau I and APP were axonall y located. At 24 h following permanent MCAO, MBP, and Tau I staining remain ed relatively unchanged within the myelin and axonal compartments of the is chaemic region. In contrast, increased Tau 1 staining was apparent in oligo dendrocytes within ischaemic tissue, while APP accumulated in axons surroun ding the lesion. At I and 2 weeks following transient MCAO, Tau I and APP s taining was markedly decreased within ischaemic tissue. Marked reduction in MBP levels within ischaemic tissue were not detected until 2 weeks followi ng MCAO. The area of axonal injury as assessed by reduced Tau I or APP stai ning correlated with the area of neuronal damage as assessed by CFV stainin g. This study shows that MBP, Tau I and APP immunohistochemistry can be uti lised to assess myelin and axonal integrity following sustained ischaemia u sing standard image analysis techniques.