294 John H. Welsh 



that the heart of the horse clam, Schizothaerus nuttaUii, was highly suitable for deter- 

 mining the action of crude extracts of Metridium and Cyanea tentacle extracts. Using 

 the isolated ventricle of Schizothaerus, as we had previously used the Venus ventricle, 

 it was apparent that whole sea-water extracts of tentacles of both Metridium and 

 Cyanea contained a mixture of heart excitor and inhibitor substances. However, a 

 powerful excitor material usually was dominant and tended to obscure the action of 

 the inhibitor material. The results will not be reported in detail, since later experi- 

 ments done elsewhere are more readily interpreted. However, a sample set of records, 

 comparing the action of extracts with histamine, deserve to be shown. Fig. 1 shows the 

 marked excitor actions of Metridium and Cyanea extracts on the Schizothaerus heart. 

 The former extract caused an increase in amplitude and frequency and a tonic shorten- 

 ing of the heart (= rise in base line), while the Cyanea extract caused an increase in 

 frequency and more marked tonic shortening of the heart. Such differences could be 

 due to relatively greater amounts of the excitor substance in Cyanea tentacles. 



When histamine was tested on the same heart, it was found to have a weak excitor 

 action when added in an amount to give 0-5 mg histamine dihydrochloride per 

 milhlitre of fluid bathing the heart. It is most unlikely that histamine could be the 

 constituent of tentacle extract producing the marked excitation, and we shall see from 

 later experiments that, in fact, it is not. These experiments done at Friday Harbor 

 did, however, prompt further pursuit of the identity of the material with the marked 

 excitor action, and this work will now be reported. 



III. OBSERVATIONS MADE AT THE BIOLOGICAL LABORATORIES, HARVARD 

 UNIVERSITY AND THE LABORATORY, PLYMOUTH, ENGLAND 



(a) Evidence for the presence of 5-hydroxytryptamine in tentacle extracts 



In the course of a study of cardio-excitor substances acting on the Venus heart, a 

 recently-available indole amine, 5-hydroxytryptamine (5-HT), was tested. It was 

 found to be far more active than other common biological amines such as adrenaline, 

 nor-adrenaline, histamine and tyramine (Welsh, 1953 a). By means of paper chroma- 

 tography and bioassay, 5-HT was found to occur in the nervous systems of several 

 molluscs, including Venus mercenaria (Welsh, 1953 b; 1954). The excitor action of 

 extracts of tentacles of Metridium dianthus tested on the Venus heart, and of the sea 

 anemone, Calliactis parasitica, when tested on the Buccinum heart (Fig. 2), so closely 

 paralleled that of 5-HT that an attempt to identify the unknown substance by chroma- 

 tography was suggested. This was done for extracts of Metridium and Physalia 

 tentacles, and clear evidence for the occurrence of 5-HT in these extracts was obtained. 

 This study will be reported in some detail elsewhere. When equal weights of body 

 wall and tentacles o{ Metridium were extracted, much more 5-HT was found in tentacles 

 than in body wall. This suggests, but does not prove, that the 5-HT is contained in 

 nematocysts, which are far more numerous on the tentacles than they are in the body 

 wall tissues, even though pieces of acontia were doubtless included with the latter. 



5-HT produces pain at a low concentration (10"* g/ml) when applied to a blister 

 area on the forearm (Armstrong, Dry, Keele and Markham, 1953). 5-HT is also a 

 very effective releaser of histamine (Feldberg and Smith, 1953). Thus, through direct 

 action or through the release of histamine, 5-HT in nematocyst toxin could be respon- 

 sible for the itching and burning, as well as the weals and haemorrhagic condition, 

 that may follow contact with certain coelenterates. Recently, Jaques and Schachter 



