Neither amphetamine nor sub-anesthetic ketamine treatment during adolescence impairs devaluation in rats tested during adulthood

TL;DR

This study finds that adolescent exposure to amphetamine or ketamine in rats does not impair their goal-directed behavior in adulthood.

Contribution

The study is among the first to examine the effects of adolescent drug exposure on devaluation behavior in adulthood in rats.

Findings

Adolescent amphetamine or ketamine exposure did not impair goal-directed action in adulthood.

Compensation between strategies did not overcome potential impairments.

Results suggest discrepancies with prior literature may stem from testing conditions or training methods.

Abstract

Much of the existing animal literature on the devaluation task suggests that prior repeated exposure to drugs of abuse during adulthood can impair goal-directed action, but the literature on human drug users is mixed. Also, the initiation of drug use often occurs during adolescence, but examinations of the effects of drug exposure during adolescence on behavior in the devaluation task are lacking.

We examined whether repeated exposure during adolescence to amphetamine (3 mg/kg injections every-other day from post-natal day 27–45) or ketamine (twice daily 30 mg/kg injections from post-natal day 35–44) would impair behavior in a devaluation test when tested drug-free in adulthood. Rats were trained to press a left lever with a steady cue-light above it for one reinforcer and a right lever with a flashing cue-light above it for a different reinforcer. We tested whether any impairments in goal-directed action could be overcome by compensation between strategies by giving rats information based on lever-location and cue-lights during the test that was either congruent (allowing compensation) or incongruent (preventing compensation between strategies) with the configurations during training.

Our results provided no evidence for impairment of goal-directed action during adulthood after adolescent amphetamine or ketamine exposure.

We discuss possible reasons for this discrepancy with the prior literature, including 1) the age of exposure and 2) the pattern in the previous literature that most previous demonstrations of drug exposure impairing devaluation in laboratory animals may be attributed to either drug-associated cues present in the testing environment and/or accelerated habit learning in tasks that predispose laboratory animals towards habit formation with extended training (with training procedures that should resist the formation of habits in the current experiment). However, additional research is needed to examine the effects of these factors, as well a potential role for the particular doses and washout periods to determine the cause of our finding of no devaluation impairment after drug exposure.

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