A new method for recording H‐reflexes from the plantar muscles of dogs

Abstract

H‐reflexes were recorded consistently from the plantar muscles of pentobarbitone‐anaesthetised dogs following supramaximal stimulation of the caudal cutaneous sural nerve (CCSN). As the amplitude, shape and latency of successive H‐reflex potentials fluctuated from trial to trial, 16 consecutive sweeps were averaged to quantify the response. The averaged H‐reflex had an amplitude of 1–6 ± 0–9 mV (mean ± SD] and a latency of 20 ± 2 ms. The CCSN‐evoked H‐reflex was recorded together with the CCSN‐evoked compound muscle action potential (SurCMAP), which had a shorter latency (6 ± 1 ms) but comparable size (1–9 ± 1–3 mV). H‐reflex afferents in the CCSN had overlapping but slightly higher electrical thresholds than plantar motoneurone axons. A ‘pure’ H‐reflex could be obtained by injecting local anaesthetic below the site of nerve stimulation. Halothane/nitrous oxide anaesthesia substantially reduced the amplitude of H‐reflex potentials in a reversible fashion.