Aquaporin-4 (AQP4) is the predominant water channel of brain, which mediates transmembrane water movement at the blood-brain barrier and at the brain-cerebrospinal fluid interface. It has been reported that AQP4 deletion results in an increase of amino acid and monoamine levels in some brain regions of mice, suggesting that AQP4 may participate in region-specific alterations in brain amino acid and monoamine metabolism. In the present study, we examined whether AQP4 affects neurotransmission in acute and chronic cocaine exposure mice. For this purpose, both wild-type and AQP4 knockout mice were used with locomotor activity evaluation and microdialysis methods. The results reveal that AQP4 deletion attenuated locomotor activity in acute and repeated cocaine exposure mice, and induced a decrease of extracellular dopamine and glutamate levels in the nucleus accumbens (NAc), a brain region known to be critically involved in the addictive properties of cocaine. Therefore, AQP4 may play a role in regulating extracellular cocaine-induced dopamine and glutamate release in the brain reward center, and in turn AQP4 deletion may attenuate cocaine reinforcement and dependence.