2006-004783-31: A Double-Blind, Randomised, Parallel-Group, Placebo-Controlled, MultiCentre, Phase IIa Study to Assess the Safety, Tolerability, Pharmacokinetics and Pharmacodynamics of Ascending Multiple Oral Doses of AZD3480 in Schizophrenic Patients on Stable Antipsychotic Monotherapy with quetiapine, risperidone or olanzapine