Morphine and propranolol co-administration impair consolidation of Y-maze spatial recognition memory

In the present study, the interaction between morphine and the beta-adrenergic receptor antagonist, propranolol (PROP), in memory consolidation was investigated in a two-trial recognition Y-maze task. Four sets of Y-maze experiments were carried out in mice, with 2 and 4 h inter-trial intervals (ITI) and all drugs administered immediately after the training trials. In the first and second sets of experiments, post-training administration of morphine (0.25 and 2.5 mg/kg) or PROP (2, 10 and 20 mg/kg) alone did not impair memory consolidation after a 2 h ITI. However, in the third and fourth sets of experiments, co-administration of these ineffective doses of morphine (0.25 and 2.5 mg/kg) and PROP (2, 10 and 20 mg/kg) disrupted memory consolidation after a 2 h ITI. Moreover, the relatively higher dose of morphine (2.5 mg/kg) plus the relatively higher doses of PROP (10 and 20 mg/kg) disrupted memory consolidation to a greater extent after a 2 h ITI. Locomotor activity was not affected by any of the drug treatments. Our data shows that morphine and PROP co-administration disrupts the consolidation of spatial recognition memory, suggesting that inactivation of the beta-adrenergic system may contribute to morphine-induced impairment of memory.