title: Comparison of the somatosensory evoked potential and the direct cortical response following severe incomplete global ischemia: selective vulnerability of the white matter conduction pathways.
abstract: Eight cats were subjected to graded hemorrhagic hypotension following bilateral carotid ligation to produce incomplete global cerebral ischemia. Three additional cats served as controls. The somatosensory evoked potential (SEP) and direct cortical response (DCR) were monitored in all animals and in each case, the cortical component of the SEP was abolished during progressive ischemia while the morphology of the DCR was well-preserved but with reduced amplitude. Determinations of adenosine triphosphate (ATP), phosphocreatine (PCr), and lactate levels in cerebral cortex and white matter were made in five experimental cats and the three controls. At the time of failure of the cortical SEP, PCr was dramatically reduced and lactate moderately elevated in the white matter while ATP remained unchanged. Cortical lactate was only mildly elevated and PCr and ATP were unchanged accounting for preservation of the DCR. In this model of global ischemia, abolition of the cortical SEP is due to a block of stimulus conduction in white matter projection pathways. A hypothesis to explain the observed metabolic changes is presented and correlation is made to clinical situations.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000378:metabolism; D002545:Brain Ischemia / Q000503:physiopathology*; D002415:Cats; D002540:Cerebral Cortex / Q000503:physiopathology*; D005073:Evoked Potentials, Somatosensory; D007773:Lactates / Q000378:metabolism; D019344:Lactic Acid; D009431:Neural Conduction; D009434:Neural Pathways / Q000503:physiopathology; D010725:Phosphocreatine / Q000378:metabolism
chemical_list: D007773:Lactates; D010725:Phosphocreatine; D019344:Lactic Acid; D000255:Adenosine Triphosphate