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26
JUL / AUG 2014
I
Healthcare Journal of new orleans
othersmay enjoy the experience but have no
troublewalking away once the bottle’s empty?
Research points to two factors that dis-
tinguish people who become addicted from
people who don’t: genetics and the general
state of stress, quality of life, and mental
health of the person. According to National
Institute on Drug Abuse researchers Chan-
dler, Fletcher, and Volkow, genetic factors
are thought to contribute 40-60% of the
vulnerability to addiction. Extracellular
signal-regulated kinase (ERK), involved in
neuroplasticity and learning as well as stress
and reward circuitry, is one pathway that has
been implicated, with numerous studies
associating altered ERK signaling with opi-
ate dependence. In addition, in April of this
year, a team of American, Israeli, and Chi-
nese researchers, Levan et al., reported a
significant association between two poly-
morphisms of the FKBP5 gene and heroin
addiction. FKBP5 has been shown in animal
and fMRI studies to mediate stress-related
responses and affective disorders. While
these researchers were careful to acknowl-
edge that “drug addictions are caused by
genetic, environmental, and drug-induced
factors,” their results point to a clear and spe-
cific genetic component—that certain people
are born predisposed to becoming addicted
to heroin, and that this predisposition is
rooted in the genetics of the stress response.
If about half of addiction vulnerability is
due to genetic factors, then that leaves the
remaining half due to non-genetic factors.
Chief among these is stress. While stress-
related genes may be a genetic component
of opiate addiction, a stressful or depressing
environment appears to play a fundamental
role in the non-genetic side of addiction. In
the late 1970s, Vancouver biologist Dr. Bruce
Alexander set up an experiment to test the
idea that the environment or state of mind
of the addict formed amore important com-
ponent of addiction than the drug itself. Tra-
ditional animal addiction experiments had
looked at isolated rats in small cages with
essentially nothing to do but press levers to
eat, drink, or receive a drug—these animals
readily became addicted.
Dr. Alexander, reasoning that this is not
a model of a “normal” animal, designed an
experiment to test addiction under more
realistic circumstances. He set up a “Rat
Park”, an enriched environment with 200
times the floor area of a standard labora-
tory cage and an abundance of food, toys,
and wheels for exercise. There were 16–20
Rat
Park
Images copyright
Stuart McMillen
via
ratpark.com
heroin