Supply of a nondrug substitute reduces escalated heroin consumption.
Neuropsychopharmacol. 2007-10-31; 33(9): 2272-2282
DOI: 10.1038/sj.npp.1301602
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Escalation of drug consumption-a hallmark of addiction-has been hypothesized to
be associated with a relative devaluation of alternative nondrug rewards and thus
with a decrease in their ability to compete with or to substitute for the drug.
In a behavioral economic framework, decreased substitutability of nondrug rewards
for drug would explain why drug consumption is behaviorally dominant and
relatively resistant to change (eg price-inelastic) in drug-addicted individuals.
The goal of the present study was to test this hypothesis using a validated rat
model of heroin intake escalation. Escalation was precipitated by long (6 h, long
access (LgA)), but not short (1 h, short access (ShA)), daily access to i.v.
heroin self-administration. After escalation, the effects of price (ie
fixed-ratio value) on heroin consumption were assessed under two alternative
reward conditions: in the presence or absence of a nondrug substitute for heroin
(ie four freely available chow pellets). As expected, escalated heroin
consumption by LgA rats was less sensitive to price than heroin consumption by
ShA rats, showing that heroin had acquired greater reinforcing strength during
escalation. However, supplying a substitute during access to heroin was
sufficient to reverse this post-escalation increase in the reinforcing
effectiveness of heroin. Thus, escalated heroin consumption is not associated
with a decreased sensitivity to competing nondrug rewards. Escalated drug use may
therefore persist, not so much because of a relative devaluation of nondrug
substitutes, but because of a loss or reduction of their availability.