Figure 1.

Elevated plus maze behaviour in male and female mice at different ages. ICR mice were purchased from Harlan, Madison, WI, and were divided in three age groups of each sex (5–7 mice/group) as shown. Prior to use, mice were group housed on a 12 h light/dark cycle with lights on at 6:00 AM. All studies were carried out in accordance with the Declaration of Helsinki and with the Guide for the Care and Use of Laboratory Animals and were approved by the Institutional Animal Care and Use Committee of the Medical College of Wisconsin. The EPM consists of four arms 30 cm long and 5 cm wide, two open without walls and two closed by 30 cm high walls; the apparatus is elevated 40 cm above the floor (San Diego Instruments). Experiments began by placing a single mouse on the central platform facing an open arm: behaviors were recorded for 5 min as they explored the maze. Data were analyzed using video-based EthoVision System data analysis software (EthoVision 3.1; Noldus Information Technology). A: Percent entries into the open arms were calculated as the number of open arm entries/(open + closed arm entries) ×100. B: Total entries into open and closed arms. C: Total time spent in the closed arms. * p<0.05; ** p<0.01 and *** p<0.005 compared to the 4–6 week old group.