An unexpected incidence of convulsive attack in male mice after long-term isolated condition

Unexpected convulsive attacks were observed in male dd-D mice which were reared for a long-term experiment. After three months from the onset of rearing, some of mice showed convulsive attacks when they were handled in such routine laboratory procedures as weighing, clearing of cage and feeding. The convulsive attack was observed only among the mice being reared individually in each of sections of cage and did not occur in the mice which had been reared as a colony. The incidence rate of convulsive attack increased as the rearing period was prolonged. Our finding was similar to King and coworkers' report (1955) in which convulsions were observed in the singly housed C3H mice. The one thing particular in our observation was the difference of incidence rate according to the extent of isolation, i.e., the higher rate was observed on the condition of mice without other mice in the neighbouring sections than those with neighbouring mate. The neighbouring mate acted some roles to change susceptibility to convulsive attack, even though separated by a sheet of wire-netting.