Methylphenidate alters flash-evoked potentials, body temperature, and behavior in Long-Evans rats

This experiment examined the effects of methylphenidate hydrochloride on flash-evoked potentials (FEPs) recorded from the visual cortex (VC) and superior colliculus (SC) of chronically implanted male Long-Evans rats, as well as on body temperature and open field behavior. FEPs were recorded at 10, 20 and 40 min following intraperitoneal injections of saline, and of doses of 0.7, 2.9, and 11.6 mg/kg methylphenidate on separate days. The 0.7 mg/kg dose did not produce significant effects. In the VC, following administration of the 11.6 mg/kg dose of methylphenidate the amplitude of components P83, N146, and P232 decreased, the amplitude of component N64 briefly increased and components P23, N30, N40, and P48 were unchanged in amplitude. In the SC, component P29 was unaffected, while components P38 and N51 were reduced in amplitude by the 11.6 mg/kg dose of methylphenidate. Peak latencies of components N40, P48, P83, and N146 in the VC and component P38 in the SC were increased by the 11.6 mg/kg dose of methylphenidate. When body temperature was recorded 45 min after drug administration, a mild dose-dependent hypothermia was found with the 2.9 and 11.6 mg/kg methylphenidate doses, suggesting that this may have contributed to the increased latencies. In subsequent open field observations, both line crossings and rearings were significantly increased by the 11.6 mg/kg dose. Increased movement into the center of the testing area was also observed, which could be a sign of increased exploration and reduced anxiety following methylphenidate.