Apomorphine injections into the VTA or substantia nigra decreased dopamine (DA) overflow in the n. accumbens and striatum, respectively. Focal infusions of apomorphine into the striatum also decreased striatal DA levels. Chronic treatment with cocaine did not alter the actions of apomorphine, suggesting that neither dendritic nor terminal DA autoreceptor function had been altered. In a separate study it was also found that dendritic release of DA in the VTA was not altered by chronic cocaine. Chronic cocaine did, however, increase the amount of cocaine found in the n. accumbens, striatum and frontal cortex following a subsequent cocaine challenge. Chronic amphetamine did not alter the actions of focally applied amphetamine on DA overflow in the striatum or accumbens. The effects of chronic amphetamine on striatal DA overflow were equivocal following a systemic challenge.
