Irreverisble differential block of A‐ and C‐fibres following local nerve heating in the cat.

Abstract

SUMMARY1. Local heating of a nerve was used to block conduction in the myelinated or A-fibres while preserving normal function in most of the non-myelinated or Cfibres. Compound action potentials of A-and C-fibres, and impulses in single Cfibres were recorded to measure the block.2. Most experiments were done on the posterior tibial nerve of the cat's hind limb. Conducted heat was applied in successive periods of about 2 min each to 15 mm of the exposed nerve..3. The range of temperatures used was between 45 and 52 'C. Below 46 0C no conduction block was obtained. With increasing temperature the cumulative time of heating required to produce a block in at least 99 % of A-fibres decreased from around 110 min at 46-5 'C to 10 min at 51 'C.4. In the posterior tibial nerve the C-fibre compound action potential was reduced to 0-66 of control (mean of twenty-two experiments) when the A-fibre action potential was less than 1 % of control. The corresponding value of this selectivity coefficient was 0-20 in seven superficial peroneal and sural nerves.5. Once a conduction block of A-fibres was reached the remaining C-fibres showed normal functioning, including conduction of repetitive impulses at up to 30 Hz evoked by electrical nerve and adequate skin stimulation. C-fibre conduction persisted for at least 33 h, but not longer than 3 days. 6. This pure C-fibre nerve might be useful for studying central nervous system effects of C-fibres.

Conduction block of mammalian myelinated nerve by local cooling to 15–30°C after a brief heating

“…3) could reflect different experimental methods. The length of the heated nerve was 15 mm in the previous study (Klumpp and Zimmermann 1980) but was only 9 mm in our study. In addition, a recent study in rats showed that the sciatic nerve could be blocked by increasing local temperature about 9°C from room temperature using very focused (Ͻ0.1 mm) infrared laser (Duke et al 2013).…”

“…7). In addition, these heating durations are only ϳ10% of the durations required to produce a nonreversible nerve block (Klumpp and Zimmermann 1980). However, the safety for repeated application of the short duration heating will still need to be determined.…”

“…It is well known that extreme cold (Ͻ15°C) or heat (Ͼ46°C) can block conduction in mammalian myelinated nerves (Klumpp and Zimmermann 1980;Paintal 1965;Stecker and Baylor 2009). However, long-duration application of these extremely low or high temperatures can result in nerve injury (Jia and Pollock 1999;Vujaskovic et al 1994).…”

“…However, long-duration application of these extremely low or high temperatures can result in nerve injury (Jia and Pollock 1999;Vujaskovic et al 1994). Nonreversible nerve block was produced in cats by locally heating the tibial nerve to 46.5°C for 110 min or to 51°C for 10 min (Klumpp and Zimmermann 1980). Although conduction block was not observed in cat tibial nerves at temperatures Ͻ46°C (Klumpp and Zimmermann 1980), it was reported in dogs that locally heating the sciatic nerve at 45°C for 60 min caused a decrease in nerve conduction velocity and hindlimb dragging for 3-11 mo (Vujaskovic et al 1994).…”

“…Nonreversible nerve block was produced in cats by locally heating the tibial nerve to 46.5°C for 110 min or to 51°C for 10 min (Klumpp and Zimmermann 1980). Although conduction block was not observed in cat tibial nerves at temperatures Ͻ46°C (Klumpp and Zimmermann 1980), it was reported in dogs that locally heating the sciatic nerve at 45°C for 60 min caused a decrease in nerve conduction velocity and hindlimb dragging for 3-11 mo (Vujaskovic et al 1994). Nerve injury was also reported in rats when the sciatic nerve was cooled to 5°C for 120 min (Jia and Pollock 1999).…”