The Discovery of Chemical Neurotransmission
Already in 1903, Loewi, in a discussion with Walter M. Fletscher from Cambridge
(at that time an associate in Marburg), raised the idea that nerve endings could contain
chemical substances which would be released by the nerve terminals upon stimulation so that
these substance in their turn would stimulate the effective organ.
At that time, however, Loewi did not see a way to prove this hypothesis. Only in 1920
the idea for the crucial experiment occurred to him in a dream:
- "The night before Easter Sunday of that year I awoke, turned on the light, and jotted down a few notes
on a tiny slip of thin paper. Then I felt asleep again. It occurred to me at six o'clock in the morning
that I had written down something most importnat, but I was unable to decipher the scrawl.
The next night, at three o'clock, the idea returned. It was the design of an experiment to determine
whether or not the hypothesis of chemical transmission that I had uttered seventeen years ago was correct.
I got up immediately, went to the laboratory, and performed a simple experiment on a frog heart
according to the nocturnal design." [...]
- "These results unequivocally proved that the nerves do not influence the heart directly but liberate
from their terminals specific chemical substances which, in their turn, cause the well-known
modifications of the function of the heart characteristic of the stimulation of the heart."
- (Otto Loewi: An Autobiographic Sketch, Univ. of Chicago Press, 1960)
Drawing and Description of Humoral Transmission
by Otto Loewi for his son Guido, about 1950.
"If a nerve by a stimulus gets an impulse this impulse is
propagated within the nerve and is transmitted to the respec
tive effective organs (heart, muscle, gland) innervated by
the nerve. The question arose by which means the impulse
coming from the nerve is transmitted to the effector organ.
I was able to solve this question by proving that the
impulse running down within the nerve liberates from
its endings chemical substances (Acetylcholine or Adre-
naline respectively) which in their turn influence the
effector organ exactly like the stimulation of the nerve.
With other words: the influence of nervous stimulation
on an organ is not a direct one but an indirect one
mediated to the organ by chemical substances
released by the nerve stimulation in its endings."
Thomas Griesbacher.
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