Motor impairment produced by ethanol and site-selective NMDA receptor antagonists in mice: tolerance and cross-tolerance

Abstract

Current perspectives on clinical use of N-methyl- d-aspartate (NMDA) receptor antagonists infer acute and repeated administration schedules for management of different pathological states. Development of tolerance and cross-tolerance between different antagonists may significantly affect their clinical effectiveness. Since ethanol was repeatedly demonstrated to act as NMDA receptor antagonist, ethanol use may also have its impact on the effects of NMDA receptor ligands. Using the rotarod test in mice, the present study evaluated development of tolerance and cross-tolerance between ethanol (3.2 g/kg, p.o.), competitive NMDA receptor antagonist, d-CPPene (5.6 mg/kg, i.p.), and low-affinity NMDA receptor channel blocker, memantine (30 mg/kg, i.p.), that were administered for seven days once a day after the daily rotarod training session. Acute tests with ethanol (0.3, 1, 1.7, 3.2 g/kg), d-CPPene (0.3, 1, 3, 5.6 mg/kg) and memantine (1, 3, 10, 30 mg/kg) revealed that (a) each of these drugs dose-dependently disrupted rotarod performance in drug-naive mice; (b) in ethanol- and d-CPPene-treated mice, tolerance was observed to ethanol and d-CPPene but not to memantine; moreover, effects of memantine were even more pronounced in d-CPPene-treated subjects; and (c) repeated memantine administration decreased acute motor impairing effects of ethanol, d-CPPene and memantine. Thus, the history of ethanol use or abuse may influence pharmacological activity of NMDA receptor antagonists and this effect is dependent on type of the NMDA receptor antagonist applied.