Self-administration chambers
After, at least, one-week of recovery, AMPH self-administration was
performed in standard operant boxes (28 x 26 x 20 cm, Med Associates
Inc., USA). The cannula was connected to a swivel system that allowed
the animal to move freely. Once the animals were connected to the
system, 2 retractable levers were presented. Pressing the active
(correct) lever resulted in i.v. infusion of AMPH (volume: 0.1 ml in 3
s). Furthermore, a light cue above the active lever indicated a timeout
period of 20 s during which no AMPH infusion was available. Pressing the
inactive (incorrect) lever had no programmed consequences.