Differential inhibition of A, B and C fibres in the rat vagus nerve by lidocaine, eugenol and formaldehyde.
Evoked compound-action potentials (cAP) in all three fibre types of the isolated nerve were reversibly depressed by exposure to the drugs. After 20 min exposure, lidocaine (0.5 mM) depressed the amplitude of the A and B fibre potentials significantly more than the C fibre potential. With eugenol (0.8 mM), there was no significant difference in depression of A, B and C fibre activity. With formaldehyde (4.5 mM), the latency was longer, and the C fibres were initially significantly more depressed than the A and B fibres. As dull pain from a chronically-inflamed pulp is believed to be mediated through C fibres, these results may explain the difficulties in obtaining complete local analgesia with lidocaine. They indicate that application of low concentrations of eugenol and formaldehyde to the pulp-dentine organ may have an analgesic effect on pain mediated through both A and C fibres.
D000200:Action Potentials / Q000187:drug effects; D000698:Analgesia; D000818:Animals; D005054:Eugenol / Q000494:pharmacology*; D005557:Formaldehyde / Q000494:pharmacology*; D008012:Lidocaine / Q000494:pharmacology*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D014630:Vagus Nerve / Q000187:drug effects* / Q000502:physiology
D005557:Formaldehyde; D005054:Eugenol; D008012:Lidocaine