Sensitivity of peripheral nerve fibres to sodium pentobarbital anaesthesia in rat

The sensitivity of different classes of peripheral nerve fibres to anaesthesia with sodium pentobarbital in rat was tested. The basic approach was to examine changes in compound action potential (CAP) in a rat sural nerve induced by sodium pentobarbital. Rats were either sacrificed by cervical dislocation (control) or anaesthetized with sodium pentobarbital (100 mg/kg, i.p.), and a 30 mm long sural nerve segment excised and placed on electrodes in a thermostatically controlled recording chamber. CAPs were evoked by electrically stimulating the sural nerve segment with supra-threshold stimuli. CAP in control sural nerves consisted of the early component (A axons: 32.73 +/- 2.91 m/s) and the late component (C axons: 0.92 +/- 0.05 m/s) with peak voltage amplitudes 4.9 +/- 1.0 mV and 0.1 +/- 0.03 mV, respectively. Anaesthesia with sodium pentobarbital had no effect on CAP latency. However, the amplitude of CAP of both A and C axons was reduced by approximately 40% and 50%, respectively. The depressant effect of pentobarbital on CAPs was statistically significant for both groups of axons (p<0.01). Non-selective sensitivity of A and C axons to pentobarbital suggests even distribution of receptors for GABA in these two populations of axons in the rat peripheral nerve.