and were approved by the Ethics Committee for Animal Experiments, Institute of Pharmacology. Habituation (day 1) Psychopharmacology (2011) 214:911–921 Table 1 Pairs of different stim- uli used in the mouse version of the ASST Dimension Odor Medium Animals The studies were performed on male C57Bl/6J mice (Institute of Pharmacology breeding facility, originating from the Jackson Laboratories and purchased from Charles- River, Germany) weighing approximately 24 g and being approximately 7 to 8 weeks old at the start of the experiment. The mice were housed in standard laboratory cages under standard colony A/C-controlled conditions: room temperature of 21±2°C, humidity of 40% to 50%, and a 12-h light/dark cycle (lights on at 06:00). The mice were individually housed and mildly food deprived (2.9 g of food pellets per day), with ad libitum access to water for 1 week prior to testing. Mice were food restricted throughout the experiment to maintain approximately 85% of their initially body weight. Behavioral testing was performed during the light phase of the light/dark cycle. Different groups of animals were used in different drug experiments. Attentional set-shifting task procedure The experiments were performed according to the proce- dure for mice described by Garner et al. (2006) and Papaleo et al. (2008) with some modifications. The mice were tested in a black acrylic U-shaped maze apparatus (W× L, 39× 39 cm) with a wire grid floor. The starting compartment provided an entrance via guillotine doors into two identical testing compartments. A bowl with water was placed in the starting compartment to allow mice free access to water throughout the whole training procedure. The food reward (1/8 of Honey Nut Cheerio, Nestle®) was presented in containers (glass dishes, 5 cm in diameter, 3 cm in depth). The containers were defined by a pair of cues with two stimulus dimensions: different kinds of digging media and distinct odors (2 μl of a flavoring essence, Dr. Oetker®, Poland, on a piece of the blotting paper fixed to the external wall of a glass dish prior to use). Different containers were used for each combination of the digging medium and odor. Stimulus dimensions are shown in Table 1. The entire study consisted of several experiments. Each experiment was performed on three consecutive days with training sessions 1 and 2 on the 2nd and 3rd days (Table 2). Exemplar pairs Orange Arrack Fine gravel Beads Lemon Almond Crumpled tissue Aluminum balls Spicy Vanilla Cardboard Plastic 913 Cream Rum Bamboo sticks Polystyrene On the first day of testing, mice were habituated to the apparatus, containers, and food reward for 5 min. The four phases of shaping were then initiated; the first three phases with two trials each and the fourth phase with three trials were performed sequentially. During each trial, the mouse was placed in the starting compartment, and the guillotine door was raised to allow entry to the test compartment with the containers filled with the food reward. During the first phase, the food reward was placed at the bottom of an empty container. For the next phase, the containers were filled with 0.5 cm of wood shavings, and the food reward was placed on top of the filling. In the third phase, the reward was placed under a thin layer of wood shavings. In the final phase, the food reward was buried under 2 cm of wood shavings. Once the mice retrieved the food reward, they were allowed to consume it before being returned to the starting compartment. Session 1 (2nd day) and session 2 (3rd day) Each mouse was trained to discriminate between pairs of containers that differed in odor and/or the media covering the food reward. This training was performed during two sessions, which consisted of several phases with several trials. During each trial, the animal was placed in the starting compartment, and the guillotine door was raised to give the mouse access to two containers, only one of which contained the food reward. The food reward was buried under the surface of distinct digging media. The first three trials of each session were “free”, meaning that even after an incorrect choice, the door remained open, and the mouse was allowed to investigate and collect the food reward from the opposite container. On subsequent trials, the door was closed upon the animal’s entry to the compartment. If the mouse started to dig in the un-baited container (i.e., the container without the food reward), an error was recorded, the trial was terminated, and the mouse was returned to the starting compartment. Each mouse had to reach a criterion of eight correct discriminations out of ten consecutive trials to complete each phase. The inter-trial interval was approximately 5 s, and the interval between consecutive phases in a given session was approximately 45 s. We followed the protocol of Papaleo et al. (2008) by inserting additional phases (IDS2 and IDSR2). However, in