EFFECT OF PERIPHERAL INFLAMMATORY PAIN ON THE BLOOD-BRAIN BARRIER

Abstract

Currently, there is a growing body of research characterizing the blood-brain barrier (BBB) under normal physiological conditions; however, little is known about BBB regulation under pathophysiological conditions, such as inflammatory pain. This dissertation elucidates peripheral inflammatory pain effects on the BBB both functionally in terms of permeability and structurally via tight junction (TJ) protein expression and regulation.Inflammation was produced by subcutaneous injection of formalin, lambda-carrageenan, or complete Freund's adjuvant (CFA) into the right hind paw of rats. In situ perfusion and Western blot analyses were performed to assess BBB integrity after inflammatory insult. In situ brain perfusion determined that peripheral inflammation significantly increased the uptake of a membrane impermeant marker, sucrose into the cerebral hemispheres in all inflammatory models. Subsequently, a 0-168h time course study of lambda-carrageenan-induced inflammatory pain elicited a biphasic increase in BBB permeability of sucrose with the first phase occurring from 1-6h and the second phase occuring at 48h. Lambda-carrageenan-induced inflammatory pain also increased brain uptake of a commonly used analgesic, codeine at the same time-points. This is the first known observation that peripheral inflammation results in greater analgesic drug uptake to the brain. This uptake also correlated with its antinociceptive profile over a 168h time course. This suggests the presence of inflammatory pain may be an important consideration in therapeutic drug dosing, potential adverse effects and/or neurotoxicity.Western blot analyses showed altered TJ protein expression during peripheral inflammation. Occludin significantly decreased in the lambda-carrageenan- and CFA-treated groups. ZO-1 expression was significantly increased in all pain models. Claudin-1 protein expression was present at the BBB and remained unchanged during inflammation. Actin expression was significantly increased in the lambda-carrageenan- and CFA-treated groups. Over a 72h time period with lambda-carrageenan-induced inflammatory pain, altered TJ protein expression of occludin and ZO-1 correlated with permeability changes in BBB function. This is the first report of peripheral inflammation inducing alterations in TJs and increasing permeability of the BBB. This dissertation demonstrates that changes in the structure of TJs leading to alterations in the BBB may have important clinical ramifications concerning central nervous system homeostasis and therapeutic drug delivery.