10 



All 3 species were found to contain isoprenoid, iso, anteiso, and normal 

 odd-numbered fatty acids qualitatively similar to those in higher forms of 

 aquatic life. Branched-chain and normal odd-numbered fatty acids tended to 

 be associated quantitatively with trends in neighboring normal even-numbered 

 fatty acids, specifically with myristic, palmitic, and stearic acids. 

 - modified authors' abstract - J.L.M. 



Agarwal, R. A., and Michael J. Greenberg. 1968. 



Some properties of cardioexcitors from the ganglia of freshwater clams. Proc. 

 24th Internatl. Congr. Physiol. Sci. 7:4 (abstract 10). 



Aqueous extracts of ganglia of 3 freshwater clam species were tested for their 

 effects on isolated hearts of the same species and of Meraenaria meraenaria. 

 Some fractions had excitatory effects on all hearts, others had quite 

 different effects on freshwater clam and Meraenaria hearts. The observations 

 suggested that neural secretions, other than the usual transmitters, may have 

 a role in long-term maintenance of rhythmical muscular activity. - J.L.M. 



11 



12 



Agarwal, R. A., and Michael J. Greenberg. 1969. 



A comparative study of cardioactive agents from bivalve tissue. Comp. 

 Biochem. Physiol. 31(6) : 835-850. 



Bivalve ganglia and heart tissues contain substances that affect cardiac 

 rhythmicity. These substances can be separated from common molluscan 

 neurohumors (5-HT, ACh, and catecholamines) by gel filtration, and can be 

 distinguished from these transmitters by their pharmacological properties. 

 Of unidentified substances, only Peak C had a consistent and strong effect 

 on isolated hearts of bivalves. Peak C can be recognized by the difference 

 in characteristic responses elicited from hearts of Meraenaria and Amblema. 

 M. meraenaria, as a kind of standard mollusk, was used for ganglion extracts 

 to compare with freshwater bivalves, and Meraenaria hearts were used for 

 bioassay. Peak C was present in all tissues examined, but its concentration 

 was highest in ganglia. It was concluded that Peak C is a substance of 

 nervous origin, and that its role in the animal is, at least in part, to 

 maintain long-term rhythmicity in active hearts. - J.L.M. 



Agarwal, R. A., P. J. B. Ligon, and Michael J. Greenberg. 1972. 



The distribution of cardioactive agents among molluscan species and tissues. 

 Comp. Gen. Pharmacol. 3(11): 249-260. 



Five cardioactive substances, in addition to acetylcholine (ACh) and 

 5-hydroxytryptamine (5HT) , have been separated from ganglion and non-nervous 

 tissue extracts of members of the 4 major molluscan classes, including 

 Meraenaria meraenaria. The as yet unidentified active substances were named 

 peaks A, B, B°, C, and D. Nervous tissues always had more of the active 

 substances than non-nervous tissues. All ganglion extracts contained peaks A, 

 B°, ACh, and C. Peaks B and D, and 5HT were missing from only one species 

 each. No catecholamine peak resembling that of Meraenaria was found in any 

 extract tested. Each active fraction was identified mainly by its elution 

 volume and by its effects on M. meraenaria heart and other assay hearts. 

 Responses of isolated Meraenaria hearts to peaks A, B, C, D, and 5HT were 

 similar, in that amplitude, frequency, and at high doses, tone were increased. 

 Peak D response became distinct only after 5HT excitation of Meraenaria heart 

 was blocked by UML. Responses of Meraenaria ventricles to dopamine and B° 

 were similar in their effects on tone, amplitude, and frequency of heartbeat. 

 All substances had highest activities in ganglion extracts. Degree of 

 localization varied: peak C was strongly restricted to nervous tissue; 

 activity of peak A was most evenly distributed. The powerful pharmacological 

 agents peaks C and B° were widely distributed in molluscan ganglia. Peak B° 

 activity was noted for the first time in these studies. Peaks C and B° were 

 partially purified. Peak C activity is produced by a small, positively 



