Environmental enrichment decreases the rewarding but not the activating effects of heroin.
BACKGROUND
Environmental conditions during adolescence, a critical period of brain maturation, can have important consequences on subsequent vulnerability to drugs of abuse. We have recently found that the behavioral effects of cocaine as well as its ability to increase expression of zif-268 are reduced in mice reared in enriched environments (EE).


OBJECTIVE
The present experiments examined whether environmental enrichment has protective influences on the effects of heroin, a drug of addiction whose mechanism of action differs from that of cocaine.


METHODS
Mice were housed either in standard environments (SE) or in EE from weaning to adulthood before any drug exposure. EE were constituted by big housing cages and contained constantly a running wheel and a small house and four to five toys that were changed once a week with new toys of different shapes and colors. We assessed the influence of EE on the ability of heroin to (1) induce conditioned place preferences, (2) induce behavioral sensitization, (3) increase dopamine levels in the nucleus accumbens (NAc), and (4) increase expression of the immediate early gene zif-268 in the striatum.


RESULTS
Conditioned place preference but not behavioral sensitization was reduced in EE mice compared to SE mice. Heroin induced similar increases in dopamine levels and in the expression of zif-268 in the NAc of EE and SE mice.


CONCLUSIONS
The rewarding effects of heroin are blunted by EE and appear to be, at least in part, independent from activation of the mesolimbic system.
El Rawas
Rana
R
Institut de Physiologie et Biologie Cellulaires, University of Poitiers, CNRS, 40 avenue du recteur Pineau, Poitiers 86022, France.
Thiriet
Nathalie
N
Lardeux
Virginie
V
Jaber
Mohamed
M
Solinas
Marcello
M
D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D003213:Conditioning, Psychological / Q000187:drug effects*; D004777:Environment; D003932:Heroin / Q000009:adverse effects*; D006556:Heroin Dependence / Q000523:psychology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D012201:Reward
D003932:Heroin