708 



Greenberg, M. J., and T. C. Jegla. 1963. 



The action of 5-hydroxytryptamine and acetylcholine on the rectum of the 

 Venus clam, Mercenaria me re en aria. Comp. Biochem. Physiol. 9(4): 275-290. 



Experiments were done on isolated rectum of large quahogs suspended under 

 500 mg tension in an aerated, water- jacketed bath of artificial seawater 

 at 15°C. Movements are assumed to be caused by longitudinal muscle fibers. 

 Circular muscle is also present, but contractions of this muscle could not 

 account entirely for the effects observed. Drugs were added directly to the 

 bath and expressed as molar concentration in the bath. Movements were recorded 

 by kymograph. 5-Hydroxytryptamine (5HT) excites the rectum. Low doses often 

 induce rhythmical activity; higher concentrations inhibit beat and increase 

 tone. 5HT is mimicked by tryptamine and lysergic acid diethylamide and 

 antagonized by methylsergide. Benzoquinonium chloride, d-tubocurarine, and 

 morphine (the latter slightly) antagonize tone increase and augment beat 

 induced by 5HT. Atropine potentiates tone increase; its effect on beat is 

 related to its tonotropic effect. Acetylcholine (ACh) produces phasic and 

 tonic responses. The first is a transient tension increase. The tonic effect 

 is bimodal; low concentrations diminish and high concentrations augment rectal 

 tone. Tone, amplitude, and frequency of recta stimulated to beat by 5HT are 

 decreased by low concentrations of ACh, large doses increase tone and 

 obliterate beat. Low doses of benzoquinonium (10~5 M) augment ACh tone 

 increase; higher doses usually are antagonistic, depending also on ACh 

 concentration. Atropine (5xl0~5 m) is a more effective antagonist than an 

 equimolar dose of benzoquinonium. The effect of ACh apparently depends on 

 rectal tension prior to dose. 5HT appears to stimulate cholinergic nerves as 

 well as exciting rectal musculature directly. Multiple sites of action of 

 ACh are suggested. The paper describes some of the pharmacology of hard clam 

 rectum, shows how data obtained can elucidate the nature of components of the 

 organ, and suggests some interactions. - expanded authors' abstract - J.L.M. 



709 



Greenberg, Michael J., and Donald A. Windsor. 1962. 



Action of acetylcholine on bivalve hearts. Science 137: 534-535. 



The effect of acetylcholine (ACh) on isolated ventricles of 3 9 bivalve 

 species from 2 families most frequently excites and depresses the heart. 

 Responses do not appear to be distributed phylogenetically , but there is 

 some uniformity of response within families. Venerids for the most part 

 show no excitation; Mercenaria mercenaria shows only depression. Bivalve 

 heart muscle conforms closely to other molluscan muscle in its pharmacological 

 reactions to ACh. - W.J.B. and J.L.M. 



710 



Greenberg, M. J., R. A. Agarwal , L. A. Wilkens, and P. J. B. Ligon. 1973. 



Chemical regulation of rhythmical activity in molluscan muscle. In J. 

 Salanki (ed.) Neurobiology of Invertebrates. Mechanisms of rhythm 

 regulation. Akademiai Kiado, Budapest, Hungary: 123-142. 



Discovery of chemical transmission of nerve impulses across neuro-neural and 

 myo-neural synapses in vertebrates led to at least 2 lines of investigation 

 in molluscs and other animals. Attempts were made to identify vertebrate 

 neurohumors, acetylcholine (ACh), and catecholamines, in molluscan ganglion 

 extracts; and molluscan pharmacology developed as these substances were 

 tested on molluscan muscle preparations, and as e'ffective antagonists were 

 found. Some preparations, particularly hearts, were extremely sensitive to 

 known transmitter substances and ganglion extracts, and they soon supplanted 

 such standard objects as frog heart as bioassays in neurochemical studies of 

 mollusks. 5-Hydroxytryptamine (5HT) was identified at about the same time in 

 molluscan and vertebrate tissues, and the role of 5HT as a neurotransmitter 

 was first proposed for a molluscan system. Recently, excitatory and 

 inhibitory substances other than the compounds named above were reported in 

 molluscan ganglia and other tissues. In M. meroenaria such chemically 



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