Repair of the blood-brain barrier following implantation of polymer capsules.

Past studies of polymer-encapsulated cell lines implanted in the brain indicated their usefulness for transmitter replacement therapy in animal models. Such grafts may have potentially important clinical applications, but their placement into neural parenchyma may cause a traumatic injury resulting in a leaky blood-brain barrier around the implant. This study investigated whether or not injury repair and reformation of the barrier takes place near a polymer capsule implanted in the brain of Sprague-Dawley rats. The two methods used for detection of a leaky barrier were immunocytochemical localization of extravasated serum albumin and circulating Evans blue that binds to serum albumin. Immunocytochemical staining for glial filament protein provided a measure for evaluating injury associated gliosis. Polymer capsules implanted for 10, 16 and 18 days were surrounded by microvessels that leaked detectable quantities of serum albumin into interstitial spaces and, by secondary uptake, into some nearby neurons and reactive astrocytes. Reactive astroglia were observed within the outer regions of the capsule wall and in the near vicinity of the implant after these early survival times. In contrast, at post-implantation times of 46 and 54 days, serum albumin was no longer detected in the neural parenchyma near the macrocapsules and only few reactive astrocytes remained. These findings show that polymer capsules implanted within the cerebrum permit (a) reformation of the blood-brain barrier and (b) occurrence of repair processes that lead to minimal deposition of reactive astroglia near the implanted polymer capsule.