Fig. 2.

Schematic diagram illustrating the DNMTP testing apparatus and procedure. A Plexiglas T-shaped partition was inserted in the water tank (1.8 m in diameter) to create a start section and two choice sections. A sliding panel either remained centered, allowing access to both choice sections, or was moved to one side to block one section. A collapsible escape platform (10 cm²) was located in each one of the two choice sections. In the raised position, the top of the escape platform was 1 cm below the surface of the water, and in the lowered position, the top of the platform was 19 cm below the surface of the water. Only one platform was available (raised position) for the rat for each trial. To train the rat to swim and climb onto the platform, a straight swim procedure (one session, 10 trials) was conducted (for review, see Markowska et al., 1992). A second shaping procedure, using the “T” partition, trains the rat to swim to the platform located in either choice section of the water maze (2 consecutive d, nine trials/d), with starting point at the entrance to the choice section (day 1) or in the start section (day 2). For training, each trial consisted of two parts: an Information Swim (IS) and a Choice Swim (CS). For IS, one choice section was open; the platform was located in the open section in its raised position. The rat was allowed 60 sec to locate the platform. After 10 sec on the platform, the rat was placed in a holding cage for 1 min. For the CS, both choice sections were open, but only the platform in the section that was closed previously was available to the rat. If the rat entered the incorrect section, the sliding door was closed, confining the rat for 30 sec. After punishment, the sliding door was opened, and the rat was allowed to locate the platform in the correct section. One session consisted of nine trials (intertrial interval was ∼10 min).