Effect of the anesthetic tricaine (MS-222) on nerve activity in the anterior lateral line of the oyster toadfish, Opsanus tau

Inductive neural telemetry was used to record from microwire electrodes chronically implanted into the anterior lateral line nerve of the toadfish, Opsanus tau. Spontaneous neural activity and the response of lateral line fibers to water current were continually monitored from 17 primary afferent fibers before, during, and after the administration of the anesthetic tricaine (MS-222). Significant decrease in spontaneous and evoked activity and increase in interspike interval was noted when anesthetic concentrations were ≥0.010%. Neural activity returned to control levels within ∼90 min of anesthetic withdrawal. Decreasing the pH of the solution without the anesthetic caused transient heightened sensitivity, indicating that tricaine and not the concurrent drop in pH was responsible for the decrease in sensitivity during anesthesia. During a secondary challenge with the anesthetic 24 h after the first, fibers initially showed faster recovery however overall recovery kinetics were similar. Although high tricaine concentration was correlated with decreased neural sensitivity, the concentrations normally used to maintain anesthesia in the toadfish did not have significant effect on the evoked firing rate. Thus given sufficient time to recover from the induction of surgical anesthesia, it may be possible to maintain the animal under light anesthesia while minimizing the physiological effects of tricaine.