Having found the article in Nature Neuroscience and given it an
initial perusal, I think that its implications are misstated in these
public comments by the senior author:
"Nader said the findings involving these monkeys should not be
interpreted to mean that, in people, those at the top of the social
ladder are the least susceptible to substance abuse.
"`Not so much that every time you get a promotion or you move up in
rank, you're less likely to abuse drugs. I don't think it's the
social subordination versus the CEO that's the main point. It's that
environmental enrichment...can produce rapid and robust changes in
the brain.'"
But the "environmental enrichment"--the shift from individual to
social housing--occurred for all the monkeys, while the neural changes
were detected only in the ones who emerged at the top of the
hierarchy. It seems pretty clear that the findings are about social
dominance, not the more broad idea of "enriched environment."
Presumably that's why the title of the paper is "Social dominance in
monkeys: dopamine D2 receptors and cocaine self-administration."
And let's back up and take another look at this:
"Nader said the findings involving these monkeys should not be
interpreted to mean that, in people, those at the top of the social
ladder are the least susceptible to substance abuse."
Really? Why not? In humans, epidemiological evidence suggests just
such an association: people higher on the social ladder are more
likely to _try_ illegal drugs, yet less likely to become addicted.
(I'll return to that in a moment.) Now, what did Nader's monkeys do?
As far as I can tell, all of them used cocaine. (From the Results
section: "A dose-dependent increase in cocaine intake occurred for the
dominant monkeys, suggesting that these animals were not avoiding
cocaine altogether, but their total intakes were significantly below
those of subordinate monkeys.") But the dominant ones used it in
moderation.
And thanks to the study design, one causal explanation can be ruled
out. The establishment of dominance preceded the availability of
cocaine, so we know that overuse of cocaine didn't cause a loss of
social status. The authors suggest that the chain of causation was:
establishment of dominance --> changes in dopaminergic function -->
changes in propensity to self-administer cocaine. (While still
individually housed, the monkeys that later became dominant were not
distinguishable on any neurochemical or endocrine measure; their only
distinguishing behavior was relatively low locomotor activity.)
Whether or not one accepts that, the monkey data at least demonstrate
that losing a struggle for social dominance can precede a heightened
propensity to use cocaine.
And that may help untangle the knots of causation in the human data I
mentioned. These data are from the National Comorbidity Survey (8098
respondents, age 15-54, 75% Caucasian, 13% African- American), of whom
51% had tried an illicit drug at some point. Look whose drug use
tends to get out of hand:
NCS findings on income and drug use:
1) The likelihood of lifetime *use* of illicit drugs is equal across
income categories;
2) but among people who have tried illicit drugs, the likelihood of
dependence is higher for those whose annual family income is
below $20,000 than for those whose annual family income is
$70,000 or more [OR 2.24, CI 1.43-3.52].
NCS findings on ethnicity and drug use:
1) The likelihood of lifetime *use* of illicit drugs is lower for
African-Americans than for Caucasians [OR .62, CI .51-.74];
2) among people who have tried illicit drugs, the likelihood of
dependence is identical for African-Americans and
Caucasians;
3) but the likelihood of *persistent* dependence (persisting into
the past 12 months) is higher for African-Americans [OR 3.05,
CI 1.05-8.84].
NCS findings on education and drug use:
1) The likelihood of lifetime *use* of illicit drugs is lower for
high-school dropouts [OR 0.53, CI 0.45-0.63] and high-school
graduates [OR 0.81, CI 0.70-0.93] than for college graduates;
2) but among people who have tried illicit drugs, the likelihood of
dependence is higher for high-school dropouts [OR 2.30,
CI 1.60-3.29] and high-school graduates [OR 1.69, CI 1.21-2.37]
than for college graduates.
Frustratingly, the NCS doesn't have the prospective longitudinal
design that would permit us to say what's causing what. My hunch has
always been that much of the variation in vulnerability to addiction
is caused by social status (rather than the reverse). The monkey data
lend credence to that interpretation.
So, Jim Guinee, you asked how much we could generalize from monkeys to
humans. To me, it looks as if the monkeys acted a lot like us.
--David Epstein
[EMAIL PROTECTED]
Sources:
Morgan D, Grant KA, Gage HD, Mach RH, Kaplan JR, Prioleau O, Nader SH,
Buchheimer N, Ehrenkaufer RL, and Nader MA. Social dominance in
monkeys: dopamine D2 receptors and cocaine self-administration.
Nature Neuroscience Advance Online Publication, 2002.
<www.nature.com/cgi-taf/DynaPage.taf?file=/neuro/journal/vaop/ncurrent/full/nn798.html>
[subscriber access only, I'm afraid.]
Warner LA, Kessler RC, Hughes M, Anthony JC, and Nelson CB.
Prevalence and correlates of drug use and dependence in the United
States: Results from the National Comorbidity Survey. Archives of
General Psychiatry 52: 219-229, March 1995.
---
You are currently subscribed to tips as: [EMAIL PROTECTED]
To unsubscribe send a blank email to [EMAIL PROTECTED]
