The release of acetylcholine from the spinal cord of the cat by antidromic stimulation of motor nerves

Abstract

ACh [acetylcholine] was measured in the effluent from the perfused lumbosacral cord of the cat with or without stimulation of the central ends of the cut left dorsal roots. In about 30% of the preparations ACh was obtained in the samples collected at rest (average 3.3 ng/min); the amount of ACh release was increased 1.3-9 times by stimulation of the peripheral nerves. The average amount of ACh collected during stimulation of the peripheral nerves at 5/sec was 6.9 ng/min. Antidromic motor nerve impulses responsible for the ACh release were likely to be only those in alpha motor fibres. There was a depression in ACh release/stimulus as the stimulus frequency was increased more than 10/sec. Such changes in ACh release with various stimulus frequencies were correlated with depression in the response of Renshaw cells to excitation through motor-axon collaterals. Amounts of ACh release during stimulation of the peripheral nerves at 5/sec. were significantly increased for 1 or 2 min. after a short tetanic stimulation of the nerves. Intravenous injection of dihydro-[BETA] -erythroidine did not reduce the amount of ACh release produced by stimulation of the peripheral nerves. It is concluded that antidromic impulses in alpha motor fibres liberate ACh from the presynaptic terminals at the central synapses on Renshaw cells.