ATLANTA — A social studies teacher barricaded himself inside a classroom at a Georgia high school on Wednesday and fired a handgun in what may have been a warning shot, authorities said.No students were in the classroom at the time, and the only injury was a student who hurt her ankle running when Dalton High School was evacuated. It wasn't immediately clear why the teacher had the gun and school and fired it.The shooting happened with a nation on edge two weeks after a Florida school shooting left 17 students and faculty dead and ignited a new debate over gun control in America. Within minutes of the shooting, students hunkered down at Dalton High took to social media to call for restricting gun rights.The teacher, 53-year-old Jesse Randal Davidson, was taken into custody without incident after a 30- to 45-minute standoff with officers, Dalton police spokesman Bruce Frazier said.