Immunocytochemical studies of oedema protein clearance in the rat

Twenty microliters of rat albumin solution was infused into the caudate nucleus of anaesthetized rats and the distribution of the albumin was followed using immunocytochemical methods with LM and EM at 15 min, 24 hr, and 48 hr post-infusion. Fifteen min post-infusion, the albumin was distributed in the extracellular space of the white matter and in the overlying deep cortical layers. At 24 hr post-infusion, the albumin was detected in the extracellular space around the glia limitans. At the surface of the ventricular wall of the 48 hr post-infusion animals, most of the albumin had been cleared from the extracellular space (ECS) of the subependymal white matter and the ependymal clefts, although a large amount of albumin had been observed in these areas at 15 min after infusion. At the temporobasal area of the cortex, there was continuity of the labelled perivascular space of the venous vessel from the deep oedematous area to the cortical surface not only immediately after infusion but also during the chronic phase. In conclusion, oedema fluid and protein migrate not only to the ventricle but upward toward the cortical surfaces to reach the subarachnoid spaces for eventual clearance into CSF. This seemingly occurs in the absence of significant pressure gradients.