The main purpose of the present study was to examine the effect of dopamine blockers on memory processes by means of a one-trial passive avoidance (PA) task with ddY mice. Haloperidol (0.025-0.4 mg/kg i.p.) did not affect the PA response when it was given before the training or retention test. Sulpiride (10-80 mg/kg i.p.) had different effects, depending on the doses employed: A lower dose (20 mg/kg) of sulpiride, which is thought to block presynaptic receptors, impaired the PA response but higher doses (40 and 80 mg/kg i.p.) did not affect it when sulpiride was given before the training or retention test. SCH 23390 (0.025-0.1 mg/kg i.p.) impaired the PA response only when it was given before the training. These results suggest that blocking of postsynaptic D-2 receptors does not impair memory processes but blocking of presynaptic D-2 receptors impairs both acquisition and retrieval stages of memory processes following an increase in dopamine release. The involvement of D-1 receptors in memory processes involved in the PA response may be essentially different from that of D-2 receptors, since the blocking of D1 receptors impaired only memory acquisition.
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