Behavioral Sensitization to Apomorphine in Pigeons (Columba livia ): Blockade by the D1 Dopamine Antagonist SCH-23390

Repeated administration of apomorphine leads to a context-dependent pecking response sensitization. Previously sensitized pigeons ( Columba livia ) challenged with saline in the same context show a conditioned response (CR). The authors studied the effects of intrastriatal injections of the dopamine (D 1 ) antagonist SCH-23390 on both the sensitized response and the CR. When coadministered with apomorphine, SCH-23390 inhibited the initial response to apomorphine, prevented the development of sensitization, and impaired the maintenance of an already developed sensitization. However, SCH-23390 had no effect on the retrieval of a previously established CR. It is concluded that the activation of D 1 receptors in the caudal avian striatum is necessary for the acquisition and maintenance of the sensitization, but not for the expression, of the CR.