CHEMISTRY OF THE BRAIN: MOLECULES, MOOD, AND MENTAL ILLNESS - Chemistry: Notable Research and Discoveries - page 85

these proteins or to molecules that manufacture or bind them, research-
ers can locate and identify specific neurotransmitters and the neurons
that use them. These methods will be described shortly.
Observant researchers can also find clues by noticing the effects of
certain drugs. Reserpine is a drug that has been used to treat high blood
pressure, among other disorders, but in the 1950s, a few years after it
was isolated and marketed, physicians noticed that about 15 percent
of the patients who took it became depressed. Subsequent research
showed a side effect—an unintended consequence—of the drug was
to make certain synaptic vesicles porous. Neurotransmitter molecules
leak out, reducing the effectiveness of the transmission. This happened
for the neurotransmitter group known as the monoamines—dopamine,
norepinephrine, and serotonin. The finding was one of the first links
between neurotransmitter function and mood disorders.
nEuroTrAnSMITTErSAnd
dEPrESSIon
Diagnosing depression is not a simple matter. Everyone experiences
sadness once in a while, and in certain situations, such as the loss of
a loved one, it is expected. The American Psychiatric Association, a
group of professional psychiatrists, publishes the Diagnostic and Statis-
tic Manual of Mental Disorders, a manual that outlines the criteria for
diagnosing psychiatric disorders. This widely followed manual is peri-
odically updated, and it is currently in its fourth edition. DSM-IV, as it
is often abbreviated, defines a major depressive episode to be when the
patient shows a depressed mood or the absence of pleasure for a certain
period of time, as well as exhibiting some other symptoms such as loss
of sleep, appetite, or recurrent thoughts of suicide. Depression is one
of the most common disorders, with millions of cases diagnosed every
year in the United States alone.
About the same time as the reserpine finding, physicians noticed
that some of the drugs used to treat other diseases appeared to have a
beneficial side effect—raising the patient's mood. Upon further testing,
a chemically modified version of one of these drugs effectively reduced
the symptoms of depressed patients. This drug, iproniazid, inhibits
MAO, the enzyme that destroys the monoamine neurotransmitters—
dopamine, norepinephrine, and serotonin. As a result, more of these