Effect of lithium on morphine state-dependent memory of passive avoidance in mice

In the present study, effects of lithium chloride (LiCl) on morphine induced state-dependent memory of passive avoidance task were examined in mice. One-trial step-down paradigm was used for the assessment of memory retention in adult male NMRI mice. Administration of morphine (5 mg/kg) subcutaneously (s.c.) 30 min before training or testing induced impairment of memory performance. Injection of the same dose of the drug 30 min before testing restored memory retention impaired under pre-training morphine effect. Intraperitoneal (i.p.) injection of lithium, 60 min before training or prior to testing also impaired memory performance. Under the pre-training of morphine, the response of the opioid was restored when animals received LiCl (80 and 160 mg/kg) as pre-test injection. Pre-training administration of lower dose of lithium (20 mg/kg), but not the higher doses of the drug (80 and 160 mg/kg) impaired memory retention in passive avoidance test. LiCl-induced impairment of memory retention was restored by pre-test administration of morphine. In the animals receiving pre-training morphine, combined pre-test morphine and LiCl administration increased the restoration of memory by the opioid. It can be concluded that there may be a cross-state dependency between morphine and lithium.