1854 



Twarog, Betty M. 1974. 



"Immunity" to paralytic shellfish toxin in bivalve molluscs. In A. M. 

 Cameron et al. (eds.), Proc . 2nd Internat. Symp. on Coral Reefs. Vol. 1. 

 Illus. Map. Great Barrier Reef Committee, Brisbane, Australia: 505-512. 



Nerves of Mytilus edulis and certain bivalves, including Meroenaria 

 mercenaria, are resistant to blocking effects of saxitoxin (STX) , an active 

 principle of paralytic shellfish toxin, and tetrodotoxin (TTX) , derived from 

 puffers. Resistance to STX and TTX is a property of individual nerve 

 fibers, and is not caused by a protective sheath around fibers. Na 

 deficiency reduces and blocks the action potential, so resistance does not 

 depend on development of a non-sodium spike-generating mechanism. Species 

 resistant to STX can and do accumulate levels of paralytic shellfish toxin 

 dangerous to man. M. meroenaria, among other bivalves, was relatively 

 insensitive, although not fully resistant, to STX. The blocking effect was 

 reversed after washing off STX or TTX. M. meroenaria was most resistant to 

 STX of 4 species tested, but relatively less resistant to TTX. In September 

 1972, during a red tide along the northeast coast of Mass., quahogs and 

 oysters accumulated no toxin at Eastham, Mass., whereas other species 

 contained amounts as great as over 10,000 yg/100 g. Meroenaria, although 

 resistant, possibly did not accumulate toxin because it may have escaped 

 exposure to Gonyaulax, although Mytilus and My a in the same area had high 

 levels of toxin. Reasons should be explored. - J.L.M. 



1855 



Twarog, Betty M., and Irvine H. Page. 1953. 



Serotonin content of some mammalian tissues and urine and a method for its 

 determination. Am. J. Physiol. 175(1): 157-161. 



Most extracts were assayed on isolated heart of Venus mercenaria supplied 

 within 24 hrs of digging. Clams could be maintained for weeks at about 5°C 

 in tanks of shallow aerated seawater. Inhibitory effects of acetylcholine 



(ACh) and analogous quaternary ammonium compounds on isolated hearts was 

 eliminated by maintaining in the bath a concentration of 10~5m (6ug/cc) of 

 mytolon chloride. Threshold of Venus heart to serotonin lay between 10~^M 

 and 10 _ 8 (0.00018 and 0.0018 yg/cc) bath concentration. Sensitivity 

 appeared to increase with decreasing temp, as has been reported with ACh. 

 When serotonin was added, to yield concentrations 0.0018 and 0.018 yg/cc 

 in the 'bath, amplitude of beat was regularly increased by from 10% to 50%. 

 In this range, excitation by serotonin varied linearly with logarithm of 

 concentration. Excitation was complete within 2 minutes. Immediate 

 recovery followed washing with fresh sea water, and within 10 minutes the 

 test could be repeated with no change in magnitude of response. No after- 

 effects were seen unless concentrations above 10~^M (0.18 yg/cc) were 

 applied. Venus heart was insensitive to Pitressin and angiotonin in all 

 concentrations. It was excited by adrenaline and tyramine only at con- 

 centrations near 10~5m and showed no response to histamine at this 

 concentration. Responses to adrenaline and tyramine differed quantitatively 

 from response to serotonin. Sensitivity to tryptamine and to cinobufotenine 



(N, N-dimethyl-5-hydroxytryptamine) was high. Threshold for these last 

 substances lay at a concentration between 20 and 100 times greater (sic) 

 than serotonin threshold. After experiments with tissues of dogs, and 

 brains of rats and rabbits, it was concluded that isolated Venus heart 

 provides a sensitive and selective measure of serotonin activity. Serotonin 

 occurs in acetone extracts of dog, rat, and rabbit brain in amounts ranging 

 from 0.1 to 0.3 yg/g tissue, and it is normally excreted in human and dog 

 urine in amounts varying between 0.1 and 1.0 yg/cc. - J.L.M. 



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