Minnesota doctors are again under the microscope of an influential U.S. senator from Iowa — this time because of concerns that expensive medications are being overprescribed at great cost to the publicly funded Medicaid and Medicare programs. U.S. Sen. Charles Grassley, R-Iowa, notified federal authorities Wednesday that he found potential examples of overprescribing after requesting lists from states, including Minnesota, of doctors who issued the most prescriptions for antipsychotic and narcotic medications in 2008 and 2009.