Rapid transport of acetylcholine in rat sciatic nerve proximal and distal to a lesion.

Abstract

1. Changes in distribution of acetylcholine (ACh) along the length of the sciatic nerve of the rat have been studied up to 24 hours after axotomy produced usually by crushing but sometimes by cutting or ligating the nerves. The ACh was extracted with trichloracetic acid from 5 mm lengths of nerve cut relative to the lesion and estimated by bio-assay techniques. 2. Axotomy usually produced an increase in the ACh content in the 5 mm on either side of the lesion within 1–2 minutes of operation. Subsequently there was a continued marked increase in ACh content in the 5 mmproximal to the lesion up to nearly three times the control level by 12 hours, with no further increase by 24 hours. In the 5 mmdistal to the lesion there was a further slight increase up to 60% above control by 6 hours with a subsequent decline to about the control level by 24 hours. In the more distal parts of the nerve (i.e. 5–20 mm distal to the lesion) there was a decline in ACh content of about 20% by 6–12 hours after operation. The three types of axotomy produced similar changes. 3. The initial small increase of ACh on both sides of the lesion was probably due to local synthesis of ACh, as previously described by other authors. It is suggested that the marked proximal increase in ACh was due to interruption of a proximo-distal transport of ACh and that the small decline in the more distal parts of the nerve was due to continued transport of ACh out of that segment of the nerve following operation; the size of this decline has been taken as an estimate of the proportion of axonal ACh which is rapidly transportable (20% of the total). The rate of transport of this fraction of the axonal ACh has been estimated as about 5 mm/hour. The rest of the axonal ACh is thought to be either stationary or moving slowly with bulk proximo-distal movement of the axoplasm.