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Journal of Experimental Biology 36,72-91 (1959)
Published by Company of Biologists 1959

The Nerves and Muscles of Medusae : VI. The Rhythm

G. A. HORRIDGE ¹

¹ Gatty Marine Laboratory, University of St Andrews, Scotland

1. Features of the rhythm of isolated ganglia of Aurelia are the high variability of the intervals between beats and their negative first-order serial correlation coefficient.

2. A regular rapid rhythm or a cyclical rhythm is a consequence of stimulation.

3. The effect of stimulation of the primary (diffuse) nerve net is usually a transient acceleration of the rhythm.

4. A rapid, uniform rhythm is usually reset at a similar frequency by an artificially induced beat; a normal rhythm usually shows a slight pause, which is accentuated if several antidromic impulses are initiated.

5. The pause which follows forced beats, the negative serial correlation coefficient and the time course of the return to normal after stimulation indicate a self-regulating mechanism within the ganglion.

6. Stimulation of the ganglion with direct current can stop or accelerate the rhythm but throws no light on the possible mechanism.

7. When the ganglion is inverted the rhythm becomes slower and more variable.

8. Tryptamine accelerates the rhythm. The minimum effective concentration in the bathing sea water was 10^-5 g./ml. Acetylcholine, adrenaline, curare, ephedrine, histamine, 5-hydroxy-tryptamine and physostigmine have no effect.

9. The theoretical relation between the rhythm of one ganglion and of eight connected ganglia shows that the apparent redundancy of ganglia gives a more regular rhythm.

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