INHIBITION OF NEMATOCYST DISCHARGE IN HYDRA FED TO REPLETION

¹ Department of Developmental and Cell Biology, School of Biological Sciences, University of California, Irvine, California 92664

1) The pattern of nematocyst discharge was observed in hydra fed shrimp until repletion. Some time after cessation of ingestion stenotele discharge ceases, and at a later time desmoneme discharge is greatly diminished. Lack of capture of shrimp is not due to a rapid release of desmonemes in animals fed to repletion.

2) Stenotele discharge remains severely inhibited until regurgitation of the remainder of the previous meal. Thereafter, stenotele discharge becomes progressively less inhibited and is normal 4-5 hours later.

3) Discharge of stenotele mounted on the body column is partially inhibited in animals fed to repletion, but far less inhibited than for the stenoteles in the tentacles.

4) Cessation of stenotele discharge after feeding to repletion is not due to the absence of mature stenoteles, as there are at least twice as many mature stenoteles present in the tentacles as are needed to feed to repletion.

5) Inhibition of stenotele discharge is correlated with a gastral cavity filled with shrimp, but is not correlated with the absolute number of shrimp ingested.

6) Physical distention of the gastral cavity due to the ingested shrimp is not the cause of inhbition of stenotele discharge.

7) The changes in inhibition of stenotele discharge are gradual. Stenoteles in heads severed from animals fed to repletion recover from inhibition of discharge in thirty minutes. The lag time between cessation of ingestion and inhibition of discharge is ten-twenty minutes.

8) A concentrated homogenate of Artemia injected into the gastral cavity inhibits stenotele discharge to a greater extent than does a dilute homogenate.

9) The results indicate that hydra can inhibit stenotele and desmoneme discharge, and that a metabolite(s), obtained from the Artemia is involved in the inhibition.

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