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Journal of Experimental Biology 49,387-400 (1968)
Published by Company of Biologists 1968

Electrical Activity in the Hydroid Cordylophora

G. O. MACKIE ¹

¹ Department of Zoology, University of Alberta, Edmonton, Canada

1. Cordylophora has two major hydranth pacemaker systems, one producing slow,, biphasic pulses at 2.0-4.0 sec. intervals (slow pulse or SP system) and one exhibiting sharp, predominantly negative potentials singly or in bursts with a normal interval of 1.5-2.0 sec. between pulses (fast pulses, FPs).

2. Both SPs and FPs are recorded throughout the hydranth, but do not spread to and are not co-ordinated in adjacent hydranths.

3. SPs could not consistently be evoked artificially and showed no clear behavioural correlates. FPs occur during feeding and following electrical stimulation, where they may accompany a muscle response.

4. FPs appear superimposed on SPs when both systems are active. Such a composite event advances the SP rhythm by an amount close to the normal FP inter-pulse time, but compensatory adjustment of the SP rhythm then occurs.

5. Treatment with 10^-5 g./ml. tetrodotoxin has no apparent effect on Cordylophora.

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