produced by applied 5-HT. This suggests that 5-HT may be a normal mediator 

 for excitatory nerves of the heart. - modified author's summary - J.L.M. 



1968 



Welsh, John H. 1954. 



Hydroxy tryptamine: A neurohormone in the invertebrates. Fed. Proc . , Fed. Am. 

 Socs. Exp." Biol. 13: 162-163 (abstract 539). 



5-Hydroxytryptamine (5-HT), also known as serotonin or enteramine, mediates 

 nerve action in certain invertebrates. It excites heart of Venus mercenaria., 

 as does stimulation of visceral ganglion following block of cholinergic 

 inhibitor nerves. Agents that block 5-HT also abolish nervous excitation. 

 Paper chromatography and bioassay have identified and measured quantitatively 

 the acetylcholine (ACh) and 5-HT of pooled cerebro-pleural, visceral, and 

 pedal ganglia of V. mercenaria and Busyoon. In Venus ganglia the ratio of 

 5-HT to ACh is about 4:1, in Busyoon eanalieulatum about 1:1. When the 

 neuromuscular blocking agent mytolon is used to block ACh inhibition of Venus 

 heart, sensitivity to 5-HT is unaltered. When lysergic acid diethylamide or 

 ergot alkaloids are used to block 5-HT they do not affect the response to ACh. 

 Thus, the antagonistic action of these 2 neurohormones on Venus heart is not 

 caused by competition for the same receptor substance. It would appear proper 

 to add 5-HT to the list of chemically known substances produced by nerve cells 

 which act on effectors or other neurons. - J.L.M. 



1969 



Welsh, John H. 1954. 



Marine invertebrate preparations useful in the bioassay of acetylcholine and 

 5-hydroxytryptamine. Nature 173(4411): 955-956. 



It vzas apparent from a brief survey that hearts of several British marine 

 mollusks may be useful in determining and estimating small amounts of 

 acetylcholine (ACh) and 5-hydroxytryptamine (5-HT), as was already known for 

 Venus mercenaria, which is highly sensitive to small amounts of both these 

 substances. More recently it was shown that ganglia of V. mercenaria contain 

 5-HT and ACh, and it is likely that these were the substances present in 

 tissue studied in England. - J.L.M. 



1970 



Welsh, John H. 1955. 



Neurohormones. In The Hormones - Physiology, Chemistry and Applications. 

 Gregory Pincus and Kenneth V. Thimann (eds.) , Vol. 3. Academic Press, Inc., 

 New York: 97-151. 



This chapter reviews the status of knowledge of regulator substances under 

 the headings: diversity of neurohormones and their distribution; production, 

 transport, storage, and release of neurohormones; and recent advances in 

 understanding modes of action. Observations on isolated heart of Venus 

 mercenaria are summarized from the literature. No acetylcholine (ACh) 

 analogue has been found that has a greater physiological activity than ACh 

 itself. The smallest molecular alteration caused a loss of activity, which 

 was not so with other test animals or organs because cholinesterase 

 hydrolysis interfered. Venus heart has a very low level of cholinesterase 

 activity, which confers an advantage related to the precise fit between ACh 

 and receptor, which more than offsets the disadvantage of instability. 

 Depending on concentrations present, ACh may be excitatory or inhibitory on 

 Venus heart. 5-Hydroxytryptamine (5-HT) has a powerful excitor action on 

 Venus heart. At the time of writing few biologists were convinced that 5-HT 

 should be classed as a neurohormone. On Venus heart, LSD (lysergic acid 

 diethylamide) acts as an essentially irreversible analogue of 5-HT. It is 

 suggested that the most characteristic physiological feature of neurons is 

 their production and release of substances of high biological activity that 

 integrate bodily functions. The chapter identifies a number of terms and 

 compounds mentioned frequently in papers on physiology and pharmacology of 

 Mercenaria (Venus) mercenaria. - J.L.M. 



548 



