2.3.2. Experiment 2
The subjects were first intraperitoneally administered either naloxone
(Nal group: n = 8) or saline (Sal group: n = 8).
Twenty-five minutes after administration, each subject was gently placed
in the center of a polypropylene box (44 × 66 × 39.8 cm) located in a
dark room illuminated by dim red light. Behaviors were recorded for 15
min using a video camera (HDR-HC9, Sony) and an HDD-BD recorder
(DMR-BW770; Panasonic).