A TIP TO GET THAT MONKEY OFF YOUR BACK

Macaques With a Low Social Standing Are More Likely to Turn to Cocaine
When Feeling Anxious, Study Shows

Monkeys with a low social standing are more likely to use cocaine when
they are stressed than high-status animals, a study has found.

The results, reported at a conference yesterday in San Diego, offer
clues to the social context of drug use and addiction in humans, said
Michael Nader, a professor in the department of physiology and
pharmacology at Wake Forest University School of Medicine in North
Carolina.

He says that male cynomolgus monkeys, also known as crab-eating or
long-tailed macaques, have a strict social hierarchy. If you put a
bunch of them together, they fight it out to establish who is number
one. The boss gets groomed by its subordinates and the other monkeys
quickly get out of its way as it moves around the pen. The top macaque
has more access to food and will eat all the treats in the pen.

In earlier experiments, Prof. Nader found that the low-status monkeys
were more likely to use cocaine if it was offered to them. They don't
snort it; he fits each monkey with an intravenous catheter, so they
can press a lever and pump the drug into their bloodstream. In the
experiment he reported on yesterday, Prof. Nader increased the
animals' stress level by making them intruders in another social group.

The monkeys aren't actually shoved in with strangers. They stay in a
cage beside them and for 15 minutes listen to their new neighbours
fight.

Afterward, the low-status monkeys indulge in significantly more
cocaine. The high-status monkeys use much less of the drug. Instead,
they tend to treat themselves to banana-flavoured food pellets.

Prof. Nader and his colleagues have already established that being
high or low status physically changes the brains of the monkeys; the
bosses have more of a particular receptor - D2 - for the
neurotransmitter dopamine.

Dopamine is released during nerve-impulse transmission in the brain
and is normally reabsorbed. Cocaine blocks this process, said Prof.
Nader, and the higher levels of dopamine in the synapses, or spaces
between neurons, appears to cause the "high" that cocaine users feel.

Having extra D2 receptors seems to make cocaine less effective, said
Prof. Nader. That's probably why the high-status monkeys use so much
less of it, even when they are stressed.

The next step, he said, is to see if the stressful experience
decreased the number of D2 receptors in the low-status animals. This
could provide a physiological explanation for why it can be difficult
for people to stop using cocaine if they are under a lot of stress.

Prof. Nader also reported yesterday on a new experiment that involved
both high- and low-status macaques. Each monkey got some time on its
own in a larger pen with a chance to explore and learn different ways
to get treats. The enriched environment led to a decreased use of
cocaine in all of the monkeys. The next phase in the research involves
assessing if the three-day vacation increased the number of D2
receptors, especially in the low-status macaques.

In humans, he says, an "enriched environment" would involve having a
steady job and the support of family or friends. It wouldn't be
prison, he says. But studies have shown that people jailed for drug
use who get a job after they are released are less likely to relapse,
he says.

The kind of experiments he does with monkeys wouldn't be possible with
humans, Prof. Nader said. But he is hopeful that his work will lead to
a more effective approach to helping addicts.

As for the monkeys, Prof. Nader says they take such low doses of the
drug and they are so active that he can't see any difference when they
are on it.

"You don't get the impression that they are strung out."