Cholinergic transmission in the frog spinal cord.

The effect of acetylcholine and other drugs has been tested on the isolated and sagittally hemisected spinal cord of the frog (Rana temporaria). The release of acetylcholine from this preparation during stimulation of the spinal roots and whole hemicord has also been studied. After inactivation of the tissue cholinesterases acetylcholine was released spontaneously from the preparation at a steady rate of about 5.5 pmole/15 min/preparation. No increase in this release was obtained by stimulating the dorsal roots, but antidromic stimulation of the ventral roots always gave an increase in the rate of acetylcholine release up to 2.3 times the spontaneous level. Direct stimulation of the spinal cord did not alter the rate of acetylcholine release. Acetylcholine (1 mM) and eserine (10 mM) had weak excitatory actions and prolonged the reflex response of the preparation during dorsal root stimulation, but dihydro-beta-erythroidine and atropine had no effect. The response evoked by antidromic ventral root stimulation was potentiated by eserine (10 muM) and depressed by acetylcholine (10 muM) and dihydro-beta-erythroidine (1 muM) as in the toad preparation. The evidence supporting cholinergic transmission at some synapses in the spinal cord is discussed in relation to these results.