Paracellular Pathway for the Resolution of Hydrocephalic Edema

Abstract

Wistar rats weighing 170–200 g were used in this study. To induce hydrocephalus, kaolin suspension was injected into the cisterna magna by the technique previously described [6]. At 1–4 weeks after kaolin injection thin needles were introduced into each lateral ventricle. Either HRP (Sigma type II, 0.5 mg/ml) or lanthanum chloride (LaCl₃; Sigma, 2–3 mM) dissolved in saline was perfused into the ventricle through one of the needles. The duration of lateral ventricle to lateral ventricle perfusion was 0.5–3 h at a pressure of 2–3 cmH₂O. Following the perfusion the brain was fixed by the transcardiac route, first with saline and then with mixture of 4% paraformaldehyde and 0.5% glutaraldehyde in 0.1 M phosphate buffer or sodium cacodylate buffer at pH 7.4 by means of an infusion at 120 cmH₂O. The brain was rapidly removed after transcardiac perfusion and sectioned with a Vibratome (Model 1000, Lancer USA) at a thickness of 50 μm. Some sections were then incubated for peroxidase activity by means of a two-step method [9]. Subsequently, portions of cerebral cortex containing subependymal and subcortical white matter were dissected out. The tissue blocks were rinsed and post-fixed in a buffered solution of 1% OsO₄ for 120 min, followed by dehydration in a graded series of acetone and embedding in Araldite (Merck). Ultrathin sections were examined in a Zeiss EM 10 electron microscope.