Membrane properties and conduction velocity in sensory neurones following central or peripheral axotomy.

1. The properties of dorsal root ganglion cells in the lumbosacral segments were examined with intracellular electrodes about 3 weeks after section of the central (dorsal roots) or peripheral processes in the cat.2. Chronic section of the peripheral nerve in the hind limb resulted in a reduction in conduction velocity of both the central and peripheral processes of sensory neurones.3. Sensory neurones arising from the triceps surae and plantaris muscles were subject to ;disuse' conditions for about 3 weeks by section of the ventral roots combined with severance of the Achilles tendon. Under such conditions, the central and peripheral conduction velocities of these sensory neurones tended to decrease, but the decrease was significantly less than that following peripheral nerve section.4. Chronic section of the dorsal roots produced no significant changes in conduction velocity of the central processes of muscle sensory neurones but caused a significant increase in the peripheral conduction velocity.5. The only electrophysiological property of dorsal root ganglion cells which altered following axotomy was the time-dependent membrane rectification in response to hyperpolarizing current pulses. The rectification characteristics were modified by chronic section of the peripheral nerve but not by chronic section of the dorsal root.6. It is concluded that injuries in nerve fibres per se do not necessarily result in a decrease of their conduction velocity and that a decrease in their conduction velocity is associated with changes in the properties of the cell bodies.7. It is suggested that a decrease in conduction velocity following nerve section may require the participation of changes in the neurone cell body.