Cocaine self-administration increases the
incentive motivational properties
of the drug in rats
by
Deroche V, Le Moal M, Piazza PV
Laboratoire de Psychobiologie des Comportements Adaptatifs,
Domaine de
Carreire, Bordeaux, France.
Eur J Neurosci 1999 Aug; 11(8):2731-6
ABSTRACT
A progressive increase in the frequency and intensity of drug use is one of
the major behavioural phenomena characterizing the development of addiction. The
nature of the drug-induced adaptations involved in this escalating drug intake
remains unknown. Some theories propose that this escalation is due to a
progressive decrease (tolerance) in the reinforcing or incentive effects of the
drug. Alternative views posit that with chronic use the reinforcing or incentive
effects of drugs increase, by a sensitization or a learning mechanism. In this
report, we address the question of whether escalating cocaine intake is
paralleled by an increase or a decrease in the reinforcing and incentive effects
of the drug. Using the experimental model of intravenous drug
self-administration with a within-session dose-response paradigm, we first
studied the course of cocaine intake over 14 sessions in rats. After acquisition
of cocaine self-administration, cocaine intake progressively increased at each
dose tested. Then rats, previously allowed to self-administer cocaine during
either six or 29 sessions, were compared in three different tests of the
incentive and reinforcing effects of cocaine: cocaine-induced reinstatement of
self-administration, cocaine-induced runway and cocaine-induced place
conditioning. As compared with rats briefly exposed to cocaine
self-administration (six sessions), rats with the longer experience (29
sessions) exhibited a higher intake of cocaine paralleled by a higher
responsiveness in the cocaine-induced reinstatement and runway tests. Both
groups of rats were similarly sensitive to the rewarding effects of the drug as
evaluated by the threshold dose of cocaine inducing place conditioning. Our
results demonstrate that escalating cocaine intake is paralleled by an increase
in the motivational properties of the drug in the absence of apparent signs of
tolerance to the reinforcing or incentive effects of cocaine.
Cocaine
Drug screening
Rats on speedballs
Heroin and cocaine
Cocaine withdrawal
Addiction and reward
Clinical use of cocaine
The neural basis of addiction