Cholinergic neurons in tunicates: An appraisal of the evidence

Abstract

1. 1. Isolated longitudinal muscles of Ciona intestinalis contract in response to applied cholinesters. Of several esters tried, ACh is the most effective; the threshold concentration is about 10 −7 g/ml. No consistent potentiation of the ACh occurs when eserine is applied. 2. 2. The action of ACh is blocked by banthine, atropine, scopolamine, and by d-tubocurarine. Hexamethonium chloride was found ineffective. 3. 3. ACh was detected in extracts of innervated muscle strips. 4. 4. Stimulated nerve-muscle preparations gave off an ACh-like agent into the perfusion medium; the amount was equivalent to 10 12 molecules of ACh per impulse. 5. 5. d-tubocurarine effectively, and reversibly, blocked the effect of motor nerve stimulation. 6. 6. Applied ACh causes a sharp increase in electrical activity of the muscles. The effect is reversed by d-tubocurarine. 7. 7. In view of the already established presence of ACh in the ganglion from which the motor nerves emerge it is concluded that the longitudinal muscles in the body wall of Ciona are cholinoceptive and that they receive a cholinergic motor innervation.