CHEMISTRY OF THE BRAIN: MOLECULES, MOOD, AND MENTAL ILLNESS - Chemistry: Notable Research and Discoveries - page 77

extracted some of the fluid sur-
rounding this heart and poured
it on another heart, in which the
vagus nerve had been cut away.
he second heart began to beat
faster, as had the first, suggest-
ing that some chemical substance
was in the fluid and was affecting
the heart rate. The experiment in-
dicated that the vagus nerve con-
veys messages from the brain to
the heart by releasing a chemical
or chemicals.
Further research attempted to
identify these chemicals. In 1929,
the British physiologist Sir Henry
Dale (1875-1968) summarized the
research on chemical transmis-
sion and, based on his findings
as well as those of his colleagues,
argued that a chemical known as
acetylcholine was involved. The
German physiologist and physi-
cian Wilhelm Feldberg (1900-93)
and the British researcher Sir John
Gaddum (1900-65) showed in
1934 that certain chemicals such
as acetylcholine are released in the
synapses of nerves, proving that
chemical transmission takes place.
Information processing in the brain, therefore, includes electrochem-
ical processes. Action potentials are electrical impulses, but the messag-
es they carry are generally mediated by chemicals. These chemicals are
known as neurotransmitters since they transmit messages between neu-
rons as well as between neurons and muscles or glands. The following
sidebar discusses neurotransmitters in more detail.
The experiments of Loewi, Dale, Feldberg, Gaddum, and their col-
leagues were conclusive, yet they did not rule out the possibility of other

This colored electron
microscope image depicts
a synapse between the
presynaptic embrane, shown
in pink, and the postsynaptic
membrane, shown in green.
The slightly thickened area
between the pre- and post-
synaptic cells is part of the
synapse. Small circles in the
presynaptic cell are vesicles
containing neurotransmit-
ters. (Dr. Dennis Kunkel/
Visuals Unlimited)