Effect of atropine and oxotremorine on the release of acetylcholine from the frog spinal cord.

The in vitro frog spinal cord has been used to study acetylcholine (ACh) release and spinal root potentials. The preparation bathed in an eserine-containing medium spontaneously released ACh into the bathing fluid. This release was enhanced by atropine in a dose-related and long-lasting manner and transiently by oxotremorine. The release rate of ACh was increased by low frequency ventral root stimulation; this increase was found to be proportionally the same after application of atropine. Oxotremorine did not modify the elctrically-evoked ACh release but blocked or reduced the effect of atropine. It is concluded that the stimulatory action of atropine on ACh output cannot be entirely explained by an interaction of atropine with presynaptic cholinergic receptors and that other indirect mechanisms (via interneurones) may play a role in this effect.