The three sessions were video-recorded from above, and the times spent in the two corner squares containing the cylinders within the 3- 63-square subdivision were measured with Image J OF4. For the two test sessions, video recording was also done from an obliquely upward position to observe contact between the test mouse and the in-cage mouse. Contact with the in-cage mouse was defined as a forward movement toward the mouse in the cage and subsequent direct contact using the head. The position and posture of the in-cage mouse were observable through the slits of the wires. The contacts were counted on the video records by an observer who was blind to the genotypes. Each in-cage mouse was used once a day; when the habituation session began, the mouse was simultaneously placed in its cylindrical cage on the corners of an OF box that was not being used for the tests. These rules were thought to minimize the difference between the two in-cage mice in the second test sessions in regard to their LY2109761 acclimation to the cylindrical cage and the OF-box environment. After each use, the cylindrical cage was extensively washed with water and rinsed with 90% ethanol, which was then evaporated off, to minimize the effects of remnant materials. For startle response testing, each mouse was put into a small cage and the cage was placed on a sensor block in a soundproof chamber. A dim light was mounted on the ceiling of the soundproof chamber , and 65-dB white noise was presented as background noise. In the auditory startle response test, mice were acclimatized to the experimental conditions for 5 min, and then the experimental session began. In the first session, 120-dB startle stimuli were presented to the mice 10 times, with random inter-trial intervals. In the second session, startle responses to stimuli at various intensities were assessed. Five white noise stimuli at 70 to 120 dB were presented in quasi-random order and with random inter-trial intervals. In the prepulse inhibition session, mice experienced five types of trial: no stimulus; startle stimulus only; prepulse 70 dB and pulse 120 dB; prepulse 75 dB and pulse 120 dB; and prepulse 80 dB and pulse 120 dB. Each trial was performed 10 times in quasi-random order and with random inter-trial intervals. In the final session, a 120-dB startle stimuli was presented to the mice 10 times with random inter-trial intervals. The total duration of an auditory startle response test was about 35 to 40 min. After each trial, the holding chambers were washed with tap water, wiped with a paper towel, and dried. On the first day, after a Y-27632 dihydrochloride 30-min habituation period, the mice were given saline, kept in their home cages for 10 min, and then returned to the OF for a 30-min observation session.