Indirect evidence for the importance of axonal transport in maintenance of stores of the mediator of neurogenic oedema.

The importance of axonal transport in maintenance of stores of the mediator of the neurogenic oedema response to electrical stimulation of the saphenous nerve was studied in anaesthetized rats. The neurogenic oedema response was quantified using an Evans blue dye leakage technique. The response was found to be significantly reduced by one 15 min period of electrical stimulation of the nerve at 10Hz with 25 V, 2 ms pulses, and abolished following two 15 min periods of stimulation. There was some recovery of the response over the succeeding 2 h following one 15 min period of stimulation, but there was no recovery up to 48 h after two 15 min periods of stimulation. Bathing the saphenous nerve, in vivo, with colchicine or cutting the nerve, resulted in abolition of the response measured 48 h later. The results suggest that axonal transport from the cell body is essential in the maintenance of stores of the mediator of neurogenic oedema and hence there was no short-term recovery of the response following its abolition by electrical stimulation. The partial recovery observed when the response was reduced but not abolished by previous electrical stimulation, probably occurred by replenishment of mediator from pre-terminal stores.