No evidence that environmental enrichment during rearing protects against cocaine behavioral effects but as an intervention reduces an already established cocaine conditioned place preference

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Abstract

Objectives:

Environmental enrichment (EE) produces differential effects on psychostimulant-related behaviors. Therefore, we investigated whether the timing of EE exposure - during rearing and before cocaine exposure versus in adulthood and after cocaine exposure might be a determining factor.

Methods:

In Experiment 1, rats reared with EE or not (non-EE) were conditioned with cocaine (5, 10 or 20 mg/kg) in one compartment of a CPP apparatus and saline in the other, and later tested for cocaine CPP. In Experiment 2, locomotor activity in response to repeated injections of saline or cocaine was measured in rats raised with EE or non-EE. In Experiment 3 we measured the effects of EE or non-EE during rearing on food-based conditioned approach learning. In Experiment 4, rats were exposed to cocaine CPP conditioning then underwent 60 days of EE or non-EE treatment after which they were tested for cocaine CPP.

Results:

Our results show that rearing in EE did not reduce cocaine CPP or cocaine-induced locomotor activity (Experiments 1 and 2) but significantly facilitated conditioned approach learning (Experiment 3). On the other hand, EE treatment introduced after cocaine conditioning significantly reduced the expression of cocaine CPP (Experiment 4).

Conclusions:

These findings suggest that EE does not protect against cocaine's rewarding and stimulant effects but can reduce already established cocaine effects, suggesting that EE might be an effective treatment for cocaine addiction-related behaviors.

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