PHOSPHOLIPASE A(2)-INDUCED ELECTROPHYSIOLOGIC AND HISTOLOGIC-CHANGES IN RABBIT DORSAL LUMBAR SPINE TISSUES

Study Design. The present study was designed to characterize the effec t of phospholipase A(2) on the discharge of perispinal sensory nerves in the anesthetized New Zealand white rabbit. Objectives. To examine t he effects of phospholipase A(2) on the neural response of somatosenso ry-neurons innervating the lumbar facet joint and surrounding tissues. Summary of Background Data. An irritating component of disc tissue ma y be phospholipase A(2), which has been found at extraordinarily high levels in herniated and painful discs. Phospholipase A(2) has been sho wn to be inflammatory, but its effect on nerve response has never been shown. Methods. Surgically isolated facet joint capsules from rabbits were investigated by means of electrophysiologic and histologic techn iques. Phospholipase A(2) was injected into the characterized nerve re ceptive field, and responses were evaluated over time with varying dos es. Results. The injection of phospholipase A(2) into the nerve recept ive fields produced neurotoxicity with a 1500-U dose, sensitization of the nerves and recruitment of ''silent units'' with a 750-U dose, and no electrophysiologic effect with a 400-U dose. The tissues injected with phospholipase A(2) and control solutions were examined histologic ally using a hematoxylin and eosin staining technique. In all three do ses, the inflammatory changes were observed as soon as 2 hours after t he injections. In control subjects,no changes were observed.Conclusion s; After phospholipase A(2) injection, the discharge rate of the units showed dose and time dependent patterns. Regardless of the different doses, histologic changes were observed as soon as 2 hours after the p hospholipase A(2) injections.