Histological determination of the microinjection sites
At the end of each experiment, animals were anaesthetized with urethane (1.2 g/kg, i.p.), and Evans blue dye (1%, 100 nL) was microinjected at the site of drug administration in the brain. Then, the animals were perfuse-fixed (intracardiac 0.9% NaCl followed by 10% formalin), and the brains were removed. After fixation in 10% formalin, the brains were sectioned in 40 µm thick frontal cuts for analysis of the injection sites. The actual placement of the microinjection needles was determined upon analysis of serial sections and identified according to the rat brain atlas of Paxinos and Watson (Paxinos & Watson, 1997).