Distribution of intraventricular horseradish peroxidase in normal and hydrocephalic cat brains.

Abstract

The distribution of intraventricularly injected horseradish peroxidase (HRP) was examined in the ependymal and subependymal tissue of both normal and experimental hydrocephalic cats by light and electron microscopy. At different time intervals after the intracisternal injection of kaolin, the hydrocephalic ventricles were perfused at various intraventricular pressures with mock cerebrospinal fluid (CSF) containing HRP. The uptake and localization of HRP by periventricular brain tissue was studied with respect to transventricular absorption of cerebrospinal fluid. The results of both light and electron microscopic studies have shown that in normal, acute or chronic hydrocephalic cats perfused at either high or low pressure the distribution of HRP is similar. The enzyme was localized mainly to the intercellular spaces, between ependymal cells, glial cells, and in perivascular spaces (in and across the basement membrane of subependymal blood vessels). HRP did not penetrate endothelial tight junctions even in chronic hydrocephalic cats undergoing significant rates of transventricular absorption of CSF. It is concluded that since the distribution of HRP in brain is determined by diffusion, its use as a tracer for the bulk movement of CSF through nervous tissue is limited. It is, however, an excellent extracellular space marker in electron microscopy.