Statistically, people who exercise are much less likely than inactive
people to abuse drugs or alcohol. But can exercise help curb
addictions? Some research shows that exercise may stimulate reward
centres inthe brain, helping to ease cravings for drugs or other
substances. But according to an eye-opening new study of
cocaine-addicted mice, dedicated exercise may in some cases make it
even harder to break an addiction.
The study, conducted by researchers at the BeckmanInstitute for
Advanced Science and Technology at the University of Illinois in
Urbana-Champaign, began by dividing male mice into those that had or
did not have running wheels in their cages. All of the mice were
injected with a chemical that marks newly created brain cells.
The animals then sat in their cages or ran at will for 30 days.
Afterward, the mice were placed in small multi-roomchambers in the lab
and introduced to liquid cocaine. They liked it.
Researchers frequently use a model known as "conditioned place
preference" to study addiction in animals. If a rodent returns to and
stubbornly plants itself in aparticular place where it has received a
drug or other pleasurable experience, then the researchers conclude
that the animal has become habituated. It badly wants to repeat the
experience that it associates with that place.
All of the mice displayed a decided place preference for the spot
within their chamber where they received cocaine. They had learned to
associate that location with the pleasuresof the drug. All of the mice
had, essentially, become addicts.
Some of the sedentary animals were then given running wheels and
allowed to start exercising.Meanwhile, those mice thathad always had
wheels continued to use them.
Then the researchers cut off the animals' drug supply and watched how
long it took them to stop scuttling to their preferred place. This
process, known as "extinction of the conditioned place preference," is
thought to indicate that an animal hasovercome its addiction.
The researchers noted two distinct patterns among the addicted
exercisers. The formerly sedentary mice that had begun running only
after they became addicted lost their conditioned place preference
quickly and with apparent ease. For them, it appeared relatively easy
to break thehabit.
Those that had been runners when they first tried cocaine, however,
losttheir preference slowly, if at all. Many, in fact, never stopped
hanging out in thedrug-associated locale, a rather poignant reminder
of the power of addiction.
"There is good news and maybe not-so-good news about our findings,"
says Justin S. Rhodes, a professor of psychology at the University of
Illinois and an author, with Martina L. Mustroph and others, of the
study, published in The European Journal of Neuroscience.
It does indicate that shedding an addiction acquired when a person has
been exercising could be extra challenging, he says.
"But, really, what the studyshows," he continues, "is how profoundly
exercise affects learning."
When the brains of the mice were examined, he points out, the runners
hadabout twice as many new brain cells as the animals that had
remained sedentary, a finding confirmed by earlier studies. These
cells were centered in each animal's hippocampus, a portion of the
brain critical for associative learning, or the ability to associate a
new thought with its context.
So, the researchers propose, the animals that had been running before
they were introduced to cocaine had a plentiful supply of new brain
cells primed to learn. And what they learned was to crave the drug.
Consequently, they had much more difficulty forgetting what they'd
learned and movingon from their addiction.
That same mechanism appeared to benefit animals that had started
running after becoming addicted. Their new brain cells helped them to
rapidly learn to stop associating drug and place,once the cocaine was
takenaway, and start adjusting to sobriety.
"Fundamentally, the resultsare encouraging," Rhodes says. They show
that by doubling the production ofrobust, young neurons, "exercise
improves associative learning."
But the findings also underscore that these new cells are
indiscriminate anddon't care what you learn. They will amplify the
process, whether you're memorizing Shakespeare or growing dependent on
nicotine.
None of which, Rhodes says, should discourage people from exercising
or from using exercise to combat addictions. "We looked at one narrow
aspect" of exercise and addiction, he says, related to learned
behaviors and drug seeking.::
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