Interactions between caffeine and cocaine in tests of motor activity: role of the adenosine A2 receptor

Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to digital@library.tamu.edu, referencing the URI of the item.Includes bibliographical references.The interaction between cocaine and caffeine as well as the role of adenosine A2 receptors in this interaction were assessed in three experiments. In the first experiment horizontal activity was measured in rats that were treated with an acute injection of caffeine (0.0, 10.0, 20.0, or 40.0 mg/kg), cocaine (0.0, 5.0,10.0, 20.0 mg/kg) or their combination. Both drugs increased horizontal activity in a dose-dependent fashion. The combination of drugs produced an additive effect, with combinations of low doses of each drug producing greater effects than when either drug was administered alone. A second experiment indicated that an increase in motor activity was also produced by administration of the specific adenosine A2 antagonist, DMPX. However, this drug failed to alter the acute motor activating effects of cocaine. In a final experiment, caffeine-induced increase in activity was not antagonized by the adenosine A2 agonist, DPMA. Therefore, it appears that although caffeine and cocaine both produce horizontal activity, and that these effects of the two drugs interact, the interaction does not involve caffeine's antagonism of A2 receptors. A possible mechanism involves dopamine uptake inhibition produced by cocaine and noradrenergic mechanism facilitated by caffeine