Short-access and long-access amphetamine self-administration
After training, rats were divided into 2 groups with an equal number of AMPH injections during the last 3 training session. One group continued to self-administer AMPH (0.03 mg/kg/infusion) for 1 hour/day (the short (ShA) access group: SERT+/+ n= 14, SERT-/- n=13), and the other group self-administered the same dose for 6 hours/day (the long (LgA) access group: SERT+/+ n= 14, SERT-/- n=13) [see also: (Gipson & Bardo, 2009)]. Protein expression data of these groups were compared to a new group of animals that was subjected to surgery, but were not exposed to AMPH (the AMPH-naive group: SERT+/+ n= 6, SERT-/- n=6; Fig 1b). The animals were tested daily between 8 am and 6 pm, for 18 consecutive days [see also: (Verheij et al., 2018)] and the order of testing ShA and LgA groups was changed every day. Due to a limited number of self-administration chambers, self-administration was performed in 2 cohorts of SERT+/+ and SERT-/-animals, of which the intake did not differ.