Ethoxylated castor oil

The specific adenosine A_2AR antagonist KW6002 (5 mg/kg, Sundia, USA) for male C57B6/J mice was suspended in vehicle [15% DMSO (Sigma, St Louis, MO, USA), 15% ethoxylated castor oil (Sigma) and 75% saline] and was administered by intraperitoneal injection. The KW6002 and vehicle groups had six male C57B6/J mice each. CNO (Sigma) for A_2A‐rM3Ds mice was dissolved in DMSO and then administered by intraperitoneal injection (1 mg/kg). The CNO and vehicle groups had six male A_2A‐rM3Ds mice each.

The following drugs were used in the present study: KW-6002 ((E)-1,3-diethyl-8-(3,4-dimethoxystyryl)-7-methyl-3,7-dihydro-1H-purine-2,6-dione, a selective adenosine A_2AR antagonist) and DPCPX (8-cyclopentyl-1,3-dipropylxanthine, a selective adenosine A₁R antagonist). KW-6002 (1 mg/kg, 5 mg/kg, Sundia, United States) was suspended in dimethyl sulfoxide (DMSO, sigma), ethoxylated castor oil (Sigma) and water with a proportion of 15%:15%:70%. DPCPX (6 mg/kg, Abcam) was dissolved in 0.9% NaCl with 5% DMSO. The control mice were treated with corresponding vehicles. All the solutions were prepared immediately before administration. The administered doses of KW-6002 and DPCPX referred to previous researches (Chen et al., 2001 ; Prediger et al., 2004 (link); Nguyen et al., 2014 (link)). Drugs were injected intraperitoneally (i.p.) routinely in a volume of 0.1 ml/10 g of body weight. The specific drug administration time course depended on experimental designs: prior to (30 min before) and post (10 min after) everyday RI training for learning and consolidation periods of instrumental learning, respectively (Figure 2A), while treated 30 min before devaluation test/omission test, but not available in the RI training sessions for expression of instrumental behavior (Figure 3A).

KW6002 ((E)-1,3-diethyl-8-(3,4-dimethoxystyryl)-7-methyl-3,7-dihydro-1H-purine-2,6-dioe), a selective adenosine A_2AR antagonist, 5 mg/kg (Sundia, Walnut, CA, USA), was fully dissolved in a 1:1 mixture of dimethylsulfoxide (DMSO, Sigma, Burlington, MA, USA) and ethoxylated castor oil (Sigma). This mixture (30%) was then further diluted in water (70%) to obtain a KW6002 suspension. The control mice were treated with vehicle. Drugs were injected intraperitoneally (i.p.) routinely in a volume of 0.1 mL/10 g of body weight. In the single-pellet reaching task, drugs were administrated only during the testing phase (5 consecutive days) 30 min before testing. The drug was given every 6 h in the sunflower seed opening test.