Tertiary and quaternary local anesthetics protect CNS white matter from anoxic injury at concentrations that do not block excitability.

Abstract

1. Anoxic injury in CNS white matter was studied using the in vitro rat optic nerve preparation. Optic nerves were subjected to 60 min of anoxia, and functional recovery was assessed using the area under the compound action potential (CAP). In normal cerebrospinal fluid, CAP area recovered to 33.5 +/- 9.3% (SD) of control. 2. Lidocaine and procaine (0.1 or 1.0 mM), applied beginning 1 h before anoxia, significantly improved postanoxic recovery of CAP area. However, both agents also depressed the preanoxic CAP. Procaine generally allowed greater recovery with less depression compared with lidocaine. 3. The quaternary derivatives QX-314 (0.1-1.0 mM) and QX-222 (0.3-3.0 mM) resulted in more complete recovery of the CAP area from anoxia, with less depression of preanoxic excitability, compared with the tertiary compounds. At 0.3 mM, QX-314 reduced the preanoxic CAP very little (to 94.4 +/- 14% of control CAP area), yet allowed the postanoxic CAP area to recover to 99.6 +/- 19%. 4. We conclude that quaternary local anesthetics are more effective at protecting CNS white matter tracts from anoxia than tertiary compounds and that these agents can result in markedly improved recovery even at concentrations that do not block conduction. Moreover, given the relative specificity of QX-314 for noninactivating Na+ channels, we hypothesize that this channel subtype plays an important role in mediating anoxic injury in central myelinated axons.