Effects of repeated apomorphine administrations on lithium state-dependent memory of inhibitory avoidance performance were examined in mice. Post-training administrations of lithium (10 and 20 m/kg) decreased memory of a single-trial inhibitory avoidance task. Pre-test administration of lithium (10 and 20 mg/kg) reversed amnesia induced by the drug given after training, with maximum response at 10 mg/kg. Moreover, repeated administration of apomorphine (once daily injections of 0.5 μg/mouse, for three consecutive days followed by five days of no drug treatment) increased memory retrieval by lower doses (1.25, 2.5 and 5 mg/kg, i.p.) of pre-test lithium. On the other hand, repeated administrations of SCH 23390 (0.5 and 1 μg/mouse) or sulpiride (0.3 and 1 μg/mouse) prevented improving effect of pre-test lithium (10 mg/kg). The results suggest that repeated administration of dopamine receptor agents possibly induced sensitization which affects the lithium response in an inhibitory avoidance task.
