Differential effects of self-administered cocaine in adolescent and adult rats on stimulus-reward learning.
BACKGROUND
Adult cocaine addicts, abstinent at the time of testing, show a variety of neurocognitive impairments. Less clear is whether there are differences in the degree of impairment if cocaine use is initiated during adolescence rather than adulthood.


OBJECTIVE
Using a preclinical model, we evaluated if stimulus-reward learning was impacted differently in rats exposed to cocaine during adolescence (beginning on postnatal day 37) vs adulthood (beginning on postnatal days 74-79) and then tested after a drug-free period.


METHODS
A yoked-triad design of intravenous cocaine self-administration in adult (n = 8 triads) and adolescent (n = 8 triads) rats was used. Sets of three animals either contingently self-administered cocaine or received cocaine or saline in a noncontingent manner. Rats self-administering 1-mg/kg doses of cocaine responded under a fixed-ratio 5, timeout 20-s schedule of reinforcement. After 18 2-h drug or saline sessions, all rats (now adults) began the drug-free period in their home environments. Testing in a stimulus-reward learning task (conditioned cue preference) began 19 days later.


RESULTS
Self-administration behavior was similar in adolescent and adult rats. Lever responses were not significantly different, and both age groups averaged approximately 20 infusions per session. Rats contingently self-administering cocaine or passively exposed to cocaine during adulthood showed stimulus-reward learning deficits in the conditioned cue preference task. Rats exposed to contingent or noncontingent cocaine during adolescence had normal learning, showing strong preferences for a Froot Loops-paired cue.


CONCLUSIONS
These findings suggest that adolescents are insensitive to cocaine-induced impairment of learning related to amygdala memory system functioning.
Kerstetter
Kerry A
KA
Laboratory of Behavioral Neuroscience, Department of Psychology, Boston University, 64 Cummington St., Boston, MA 02215, USA.
Kantak
Kathleen M
KM
D000367:Age Factors; D000679:Amygdala / Q000187:drug effects / Q000378:metabolism; D000818:Animals; D003042:Cocaine / Q000494:pharmacology*; D019970:Cocaine-Related Disorders / Q000503:physiopathology; D003216:Conditioning, Operant / Q000187:drug effects; D003463:Cues; D018765:Dopamine Uptake Inhibitors / Q000494:pharmacology*; D007262:Infusions, Intravenous; D007858:Learning / Q000187:drug effects*; D008297:Male; D008568:Memory / Q000187:drug effects*; D051381:Rats; D017208:Rats, Wistar; D012055:Reinforcement Schedule; D012201:Reward; D012646:Self Administration
D018765:Dopamine Uptake Inhibitors; D003042:Cocaine