Environmental enrichment decreases intravenous self-administration of amphetamine in female and male rats.
BACKGROUND
Previous work has shown that environmental enrichment alters amphetamine-induced locomotor activity and conditioned place preference.


OBJECTIVE
The present study examined the effect of environmental enrichment on amphetamine self-administration.


METHODS
Female and male rats were raised from 21 days of age in one of three different conditions: an enriched condition (EC) containing novel objects and social partners, a social condition (SC) containing social partners only, or an isolated conditioned (IC) without objects or social partners. Beginning at 51 days of age, rats were then tested for operant responding for a sucrose reinforcer using an incremental fixed ratio (FR) requirement across four sessions. Rats were then implanted with a chronic indwelling intravenous catheter and were allowed to self-administer amphetamine (0.03 or 0.1 mg/kg per infusion) for five FR1 sessions, followed by a progressive ratio (PR) session.


RESULTS
EC rats initially showed an increase in sucrose-reinforced responding relative to IC rats and this environment-induced difference was greater in females than in males. However, in both sexes, the environment-induced difference in sucrose-reinforced responding dissipated completely across repeated sessions. With amphetamine self-administration, both EC and SC rats earned fewer infusions than IC rats across repeated FRI sessions using the low dose of amphetamine (0.03 mg/kg per infusion), but not using the higher dose of amphetamine (0.1 mg/kg per infusion). EC rats also earned fewer self-infusions of the low amphetamine dose on the PR session relative to IC rats. The effects of environmental enrichment on amphetamine self-administration were similar in both females and males.


CONCLUSIONS
These results suggest that environmental enrichment may serve as a protective factor for reducing amphetamine self-administration.
Bardo
M T
MT
Department of Psychology, University of Kentucky, Lexington 40506, USA. mbardo@pop.uky.edu
Klebaur
J E
JE
Valone
J M
JM
Deaton
C
C
D000661:Amphetamine / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D003216:Conditioning, Operant / Q000187:drug effects; D018765:Dopamine Uptake Inhibitors / Q000008:administration & dosage / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004777:Environment; D005260:Female; D007275:Injections, Intravenous; D008297:Male; D009043:Motor Activity / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D012646:Self Administration; D012727:Sex Characteristics; D012931:Social Environment; D013395:Sucrose / Q000494:pharmacology
D018765:Dopamine Uptake Inhibitors; D013395:Sucrose; D000661:Amphetamine