Effects of central or peripheral axotomy on membrane properties of sensory neurones in the petrosal ganglion of the cat.

1. The properties of sensory neurones in the petrosal ganglion of the cat were examined in vitro with intracellular electrodes 8 days after section of the central (bulbar roots) or peripheral process. Two types of cells, both with conduction velocities faster than 2 m/s and with humps on the falling phases of their action potentials (H-neurones), were studied: glossopharyngeal neurones arising from the tongue and pharynx, and carotid neurones originating in the carotid body and carotid sinus. 2. Peripheral axotomy produced an increase in action potential duration and a marked decrease in the amplitude and duration of the spike after-hyperpolarization in both glossopharyngeal and carotid neurones. 3. The maximum rate of depolarization of the action potential increased after peripheral axotomy in glossopharyngeal cells but did not change in carotid neurones. 4. The time-dependent inward rectification in response to hyperpolarizing pulses was markedly reduced in both types of cells after peripheral axotomy. 5. Section of the peripheral process produced a decrease of the rheobase of glossopharyngeal cells, but not of carotid neurones. After axotomy the proportion of cells giving tonic discharges in response to long depolarizing pulses increased from 13 to 54% among carotid neurones but did not change in glossopharyngeal cells. 6. No significant changes in membrane potential or input resistance of either group of cells were found after peripheral axotomy. 7. Central axotomy did not produce any changes in the electrophysiological properties of glossopharyngeal or carotid neurones. 8. Peripheral conduction velocity was decreased in both types of cells after peripheral axotomy, but did not change after section of the bulbar roots. 9. It is concluded that the electrical properties of sensory neurones are modified after peripheral axotomy but not after central axotomy. Furthermore, the changes produced by peripheral axotomy are different in neurones innervating different peripheral targets. 10. The possibility that some electrical properties of sensory neurones are maintained by their peripheral targets is discussed.