In vivo electrochemical studies of the effects of cocaine on dopamine nerve terminals in the rat neostriatum

In vivo electrochemical measurements, involving chronoamperometric recordings using monoamine-selective Nafion-coated electrodes, were used to study the effects of locally applied cocaine (50-500 micromolar barrel concentrations) on dopamine (DA) nerve terminals in the neostriatum of the anaesthetized rat. Local application of cocaine did not elicit detectable increases in basal levels of extracellular DA. However, locally applied cocaine significantly augmented the concentration of DA detected following a potassium (K+)-evoked depolarization. Data obtained with a new high-speed chronoamperometric recording technique further support that DA is the predominant species detected electrochemically following potassium-evoked depolarizations both before and after local application of cocaine. Unlike other locally applied uptake inhibitors that we have studied, cocaine failed to augment the time dynamics of released DA. In addition, large doses of the highest concentration of cocaine caused an attenuation of K+-evoked DA release, presumably due to cocaine's local anaesthetic properties. These data suggest that cocaine elevates synaptic levels of DA, but in a manner that is not identical to other potent monoamine uptake inhibitors.