Phospholipase A2 sensitivity of the dorsal root and dorsal root ganglion.

Study Design: This study was designed to characterize the effects of phospholipase A2 on the neural response of dorsal root and dorsal root ganglion in the anesthetized New Zealand White rabbit.

Objectives: To examine the effects of phospholipase A2 on the neural response of somatosensory neurons at the dorsal root ganglion level.

Summary Of Background Data: Phospholipase A2 may be an irritating component of disc tissue that is present in high concentration in painful herniated discs, in synovial fluids, and in sera of rheumatoid arthritis patients. Phospholipase A2 is inflammatory; however, its effects on dorsal roots and dorsal root ganglion response have never been demonstrated.

Methods: Surgically isolated dorsal roots and dorsal root ganglia from New Zealand White rabbits were investigated by electrophysiologic techniques. Phospholipase A2 doses ranging from 100 to 400 U were applied on the mechanically sensitive segments of the dorsal root ganglia, and responses to varying doses were evaluated in relation to elapsed time.

Results: The application of phospholipase A2 on the dorsal root ganglion resulted in possible neurotoxicity at doses more than 375 U, with no significant effect at lower doses except for recruitment of "silent units" at doses ranging from 200 to 340 U.

Conclusions: Phospholipase A2 doses comparable to serum concentrations in human rheumatoid arthritis appeared to be neurotoxic when applied to dorsal root ganglia. At lower doses, silent units become activated that were not active before the phospholipase A2 application. These results suggest that dorsal roots and dorsal root ganglion may be impaired by phospholipase A2, leading to sciatica and low back pain.