Papers of the Week

The purpose of this study was to examine the changes in cold block of unmyelinated C-fibers in the tibial nerve by pre-conditioning with heating and to develop a safe method for thermal block of C-fiber conduction. In 7 cats under α-chloralose anesthesia, C-fiber evoked potentials elicited by electrical stimulation were recorded on the tibial nerve during block of axonal conduction induced by exposing a small segment (9 mm) of the nerve to cooling (from 35 °C to ≤5 °C) or heating (45 °C). Before heating partial, reproducible, and reversible cold block was first detected at a threshold cold block temperature of 15 °C and complete cold block occurred at a temperature of ≤5 °C. After heating the nerve at 45 °C for 5-35 minutes the threshold cold block temperature significantly (p<0.05) increased from 15° C to 25 °C and the complete cold block temperature significantly (p<0.05) increased from ≤5 °C to 15°C on average. The increased cold block temperatures persisted for the duration of the experiments (30-100 minutes) while the amplitude of the C-fiber evoked potential measured at 35 °C recovered significantly (p<0.05) to about 80% of control. This study discovered a novel thermal method to block mammalian C-fibers at an elevated temperature (15-25 °C), providing the opportunity to develop a thermal nerve block technology to suppress chronic pain of peripheral origin. The interaction between heating and cooling effects on C-fiber conduction indicates a possible interaction between different temperature sensitive channels known to be present in the mammalian C-fibers.