Alterations in Intracranial Pressure, Blood‐Brain Barrier, and Brain Edema after Sub‐chronic Implantation of a Cannula into the Brain of Conscious Animals

Abstract

Abstract Changes related to the intracranial pressure measured as the ventricular fluid pressure (VFP) accompanying implantation of a small cannula into the brain was studied in conscious rabbits. The cannula (7 mm‐long and 1.3 mm in diameter) was inserted into the left lateral ventricle, the intracerebral part of the cannula occupying 0.0093 cm 3 volume. The ventricular fluid pres sure was continuously recorded on a Grass Polygraph via a cannula and a pressure transducer. Already within 1 hr after insertion of the cannula, VFP started to increase, and within 4–6 hrs it had reached a maximum about 5 times higher than the initial pressure. A slow progressive decrease did not supervene until 30–35 hrs after implantation; at 50 hrs the VFP was only twice the original value. This VFP was maintained during the following 25 hrs after which recording was discontinued. With trypan blue infusion, only an initial, transient, and local damage to the blood‐brain barrier could be demonstrated. Microscopy of stained sections revealed a varying degree of brain edema, anoxic cell damage, and damage to the capillary net work in the region of the track. The variation in extent of these changes corresponded well to the alterations in VFP and hence they see in to be an important reason for these alterations. The findings are discussed in terms of the important error introduced by these pressure alterations when recording various functional parameters from electrodes, needles, cannulas and other small instruments implanted into the brain parenchyma.