Effects of risperidone on learning and memory in naive and MK-801-treated rats.

BACKGROUND/AIMS The aim of this study was to investigate the effects of an atypical antipsychotic risperidone (RIS; 0.06, 0.125 or 0.25 mg/kg, intraperitoneal, i.p.) on learning and memory processes, both in naive and MK-801-treated (0.15 mg/kg, i.p.) rats. METHODS Modified elevated plus maze (mEPM), passive avoidance (PA) and Morris water maze (MWM) tasks were used. RESULTS In the mEPM test, RIS (0.125 or 0.25 mg/kg) significantly decreased the transfer latency and reversed MK-801-induced prolongation in the transfer latency of rats on the 2nd day. In the PA test, RIS (0.125 or 0.25 mg/kg) slightly decreased step-through latency (retention latency) but this finding did not reach statistical significance in naive rats. RIS had no effect on MK-801-induced reduction of retention latency. In the MWM test, RIS (0.06, 0.125 or 0.25 mg/kg, i.p.) neither affected the time spent in the escape platform quadrant, nor the distance to the platform in naive rats. It (0.125 mg/kg) tended to increase MK-801-induced reduction of time spent in the escape platform quadrant, but this finding was insignificant. RIS (0.125 mg/kg) significantly shortened MK-801-induced elongation in the distance to the platform. RIS had no effect on the swimming speed of the animals. CONCLUSION RIS might be effective in treating cognitive dysfunctions associated with schizophrenia.