Asymmetrical perfusion fixation in a rodent model of perinatal hypoxia-ischemia may lead to artifactual morphologic asymmetries.

We have observed asymmetries in perfusion between the cerebral hemispheres in immature rats previously subjected to carotid ligation in a model of perinatal hypoxia-ischemia. These asymmetries are associated with marked differences in the number of neurons stained positive by immunoperoxidase protocols for cholinergic neurons utilizing a monoclonal antibody to choline acetyltransferase. These differences are likely to be spurious and due to the asymmetry of perfusion, because fewer stained neurons appear on the unligated side of control animals, in the absence of gliosis or neuron loss. We recommend that quantitative morphologic studies in this model be performed on immersion-fixed specimens.