Opposite environmental regulation of heroin and amphetamine self-administration in the rat.
BACKGROUND
The circumstances of drug taking are thought to play a role in drug abuse but the evidence of it is anecdotal. Previous studies have shown that the intravenous self-administration of cocaine is facilitated in rats non-residing in the test chambers relative to rats that live in the test chambers at all times. We investigated here whether environmental context could exert its modulatory influence on heroin and amphetamine self-administration as well.


METHODS
Independent groups of rats were given the possibility to self-administer different doses of heroin or amphetamine (12.5, 25.0, or 50.0 microg/kg). Some animals were housed in the self-administration chambers (resident groups) whereas other rats were transported to the self-administration chambers only for the test sessions (non-resident groups).


RESULTS
Amphetamine-reinforcing effects were more pronounced in non-resident rats than in resident rats, as previously reported for cocaine. Quite unexpectedly, the opposite was found for heroin. Because of this surprising dissociation, some of the rats trained to self-administer amphetamine were later given the opportunity to self-administer heroin. Also in this case, resident rats took more heroin than non-resident rats.


CONCLUSIONS
These findings suggest an unforeseen dissociation between opioid and psychostimulant reward and demonstrate that even in the laboratory rat some contexts are associated with the propensity to self-administer more opioid than psychostimulant drugs and vice versa, thus indicating that drug taking is influenced not only by economical or cultural factors but also can be modulated at a much more basic level by the setting in which drugs are experienced.
Caprioli
Daniele
D
Department of Human Physiology and Pharmacology, University of Rome Sapienza, Rome, Italy.
Celentano
Michele
M
Paolone
Giovanna
G
Lucantonio
Federica
F
Bari
Andrea
A
Nencini
Paolo
P
Badiani
Aldo
A
D000661:Amphetamine / Q000494:pharmacology; D019969:Amphetamine-Related Disorders / Q000523:psychology*; D000818:Animals; D000697:Central Nervous System Stimulants / Q000494:pharmacology; D003216:Conditioning, Operant / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004777:Environment; D003932:Heroin / Q000494:pharmacology; D006556:Heroin Dependence / Q000523:psychology*; D008297:Male; D009294:Narcotics / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012055:Reinforcement Schedule; D012646:Self Administration
D000697:Central Nervous System Stimulants; D009294:Narcotics; D003932:Heroin; D000661:Amphetamine