Meth Self-Administration Procedure

One day after last CUS, rats were placed in sound-attenuating self-administration chambers (MedAssociates, Cat. ENV0008CTT) with a 6 am–6 pm light-on cycle and allowed unrestricted access to food, water and Meth until they reached 400 Meth rewards. The rats were allowed 7 days to reach the 400 rewards criterion. The self-administration chambers were equipped with an active and inactive lever with cue-lights above the lever. The port mounted on the back of the rat was connected to polyethylene (PE) tubing covered by a spring tether attached to a swivel on a counter balance arm. The other end of the swivel was connected via PE tubing to a syringe filled with Meth. The syringe was placed in an infusion pump that delivered 100 μl of 0.1 mg/kg Meth (FR1 schedule) over the course of 5 s when the active lever was pressed. During this period the cue-light above the active lever turned on to indicate a 5 s “time-out”, where additional active lever-presses did not result in a reward. Inactive lever presses were recorded but had no programmed consequences. Upon reaching the 400 rewards criterion, brains were extirpated and capillaries were isolated. The CUS controls remained in the home cage and were killed at time points matching the Meth self-administering groups.