Experiments were terminated by deeply anesthetizing the animals with sodium pentobarbitone (Nembutal). Animals were perfused transcardially with Hartmann’s solution (1.2 L at 36°C), followed by 1 L of 4% paraformaldehyde in phosphate buffer (0.2 M at pH 7.4). In order to reconstruct the recording sites, brains were sectioned coronally at 50 μm, and stained with cresyl violet.