Lever press training, AMP self-administration and AMP-seeking tests were conducted in standard operant conditioning chambers (ENV-001, Med Associates, St. Albans, VT, USA) enclosed in a sound-attenuating and ventilated cubicle. AMP or SAL infusions were administered via a syringe pump (PHM-100, Med Associates) connected to a 10-ml syringe (Arndt, Garcia, et al., 2015 ;Arndt, Johns, et al., 2015 (link); Garcia et al., 2019 (link); Garcia & Cain, 2020 (link)).