Interaction between anti-Alzheimer and antipsychotic drugs in modulating extrapyramidal motor disorders in mice

Antipsychotics are often used in conjunction with anti-Alzheimer drugs to treat the behavioral and psychological symptoms of dementia (BPSD). Here, we examined the effects of cholinesterase inhibitors (ChEIs), donepezil and galantamine, on antipsychotic-induced extrapyramidal side effects (EPS) in mice. The effects of serotonergic agents on the EPS drug interaction were also evaluated. Donepezil (0.3-3 mg/kg) did not induce EPS signs by itself; however, it significantly potentiated bradykinesia induction with a low dose of haloperidol (0.5 mg/kg) in dose-dependent and synergistic manners. Galantamine (0.3-3 mg/kg) elicited mild bradykinesia at a high dose and dose-dependently augmented haloperidolinduced bradykinesia. The EPS potentiation by galantamine was blocked by trihexyphenidyl (a muscarinic antagonist), but not by mecamylamine (a nicotinic antagonist). In addition, the bradykinesia potentiation by galantamine was significantly reduced by (±)-8-hydroxy-2-(di-n-propylamino)-tetralin (a 5-HT1A agonist), ritanserin (a 5-HT₂ antagonist), and SB-258585 (a 5-HT₆ antagonist). The present results give us a caution for the antipsychotics and ChEIs interaction in inducing EPS in the treatment of BPSD. In addition, second generation antipsychotics, which can stimulate 5-HT_1A receptors or antagonize 5-HT₂ and 5-HT₆ receptors, seem to be favorable as an adjunctive therapy for BPSD.