NERVOUS ACTION 



niechanisin of muscle function, il is dillicult to conceive that a great 

 variety of chemical mechanisms are required for the transmission of 

 the nervous impulse. 



There is another aspect which requires some comment. Fol- 

 lowing the discovery of Loewi that an active compound, the Vagusstojjf, 

 is released if the vagus is stimulated, it was necessary to identify this 

 compound. Once its identity with acetylcholine had been established 

 and its release following nerve stimulation repeatedly demonstrated, 

 the question arose as to what information could be expected from the 

 determination of the ester itself and of its concentration in different 

 nerves or tissues. Acetylcholine is found in almost all tissues, but the 

 amounts are small, a few micrograms per gram or even a fraction of a 

 microgram per gram. As previously discussed, acetylcholine is, in 

 living tissue, a very unstable ester. We do not know what fraction 

 of the total amount present in the living tissue may be extracted with 

 our crude chemical methods, especially in nerve tissue, where acetyl- 

 choline may be so rapidly destroyed. Although the same values will 

 be obtained using the same conditions, the meaning appears obscure. 

 A concentration of 0.2 or 0.4 micrograms of acetylcholine per gram of 

 brain is difficult to interpret, if the same amounts are found in liver, 

 pancreas, or lung. In the spleen of ox and horse are found amounts 

 of 4 to 30 micrograms per gram, although there is no indication at 

 all that the ester has any function in this organ. No acetylcholine has 

 been found in the spleen of other animals. Chemical compounds may 

 occur in small amounts everywhere. Acetylcholine has been found 

 in the potato. The presence or absence of traces of it thus appears 

 less significant and not comparable to the finding of a mechanism such 

 as a powerful and specific enzymic system. 



The enzyme systems specifically responsible for the formation, 

 and destruction of acetylcholine are, on the other hand, found mainly 

 in the nerve cell. Most other tissues do not contain them. But, 

 besides this localization, the data obtained on the concentration of 

 choline esterase do make possible the correlation with function. The 

 amounts of acetylcholine which may be split per gram of brain per 

 hour vary usually between 50 and 500 milligrams according to species 

 and center, although they are very constant for each species and each 

 center. This means that the amount of acetylcholine which may be 

 split per gram of brain in one millisecond is of the order of magnitude 



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