RADIAL-ARM MAZE BEHAVIOR IN MICE WHEN A RETURN TO THE HOME CAGE SERVES AS THE REINFORCER

Male ddY mice were housed in a cage with an eight arm radial maze apparatus for 6 h a day. A water bottle was placed at the central platform. The end of each arm ran to the home cage through a guillotine door (G). Food was placed at the home cage. During the housing in the apparatus, one G was raised and the remaining seven G were lowered. The raised G was changed every 45 min in random order. Mice housed in this apparatus learned efficient strategy to return the home cage by trial and error. When they chose the arm in which the G was lowered on their way to the home cage from the platform, they returned to the platform, then chose a different arm until they were able to enter the home cage. The mice housed in this apparatus mastered the radial maze task on the 7th day. When scopolamine (SCO) was injected, SCO buthylbromide had no effect on performance, but SCO hydrobromide (0.2 and 0.4 mg/kg) impaired working memory, dose dependently. These results show that the apparatus is useful for ease in estimating working memory in mice without the use of severe food or water deprivation.