Animals

Male Wistar rats (7–8 weeks old) underwent implantation of guide cannulae, whilst under anesthesia (52 mg/kg sodium pentobarbital via intraperitoneal (i.p.) injection), as described previously (Manahan-Vaughan, 1997). One cannula was implanted into the lateral cerebral ventricle of each hemisphere (0.5 mm posterior to bregma, 1.6 mm lateral to the midline; size: 5.6 mm length, 0.8 mm diameter, 4.5 mm depth).

Animals were allowed 2 weeks to recover, before any behavioral experiment took place. They were housed singly and maintained on a 12 h light/12 h dark cycle with food and water ad libitum.

Two days prior to behavioral training, animal weight was determined and food availability was reduced to achieve 85% of this predetermined body weight. The animal’s weight was subsequently maintained at this level until the end of the experiment. Before beginning the experiment, animals were handled individually for 20 min per day.