TETRODOTOXIN-RESISTANT IMPULSES IN SINGLE NOCICEPTOR NERVE-TERMINALS IN GUINEA-PIG CORNEA

1. Extracellular recording techniques have been used to study nerve im pulses in single sensory nerve terminals in guinea-pig cornea isolated in vitro. 2. Nerve impulses occurred spontaneously and were evoked by electrical stimulation of the ciliary nerves. 3. The nerve impulses w ere identified as originating in polymodal receptors, mechanoreceptors or 'cold' receptors. All three types are believed to be nociceptors. 4. Tetrodotoxin (TTX, 1 mu M) blocked nerve impulses evoked by electri cal stimulation of the ciliary nerves. However, ongoing and/or natural ly evoked nerve impulses persisted in the presence of TTX in all three types of receptors. Lignocaine (lidocaine; I mM) blocked all electric al activity. 5. TTX-resistant sodium channels therefore play a major r ole in generating the action potentials that signal pain to the brain.