(±)-Methylphenidate hydrochloride (Sigma-Aldrich, St. Louis, MO) was dissolved in tap water (1.5 mg/ml) and injected into an oyster cracker to attain a dose of 1.5 mg/kg for oral consumption. Oyster crackers containing tap water (1.0 ml/kg) were used for vehicle control. To mimic a clinical dosing schedule for ADHD treatment (American Academy of Pediatrics Committee on Children With Disabilities and Committee on Drugs, 1996 (link)), groups from each strain were treated Monday-Friday with vehicle or methylphenidate from P28–P55. On days that overlapped with visual discrimination testing (Experiment 1), rats were treated 30-min prior to start of sessions. Amount of time to consume daily oyster crackers averaged < 3 min. A 1.5 mg/kg oral dose of methylphenidate ensured that therapeutically relevant plasma drug levels were achieved and the 30-min pretreatment time ensured that plasma drug levels peaked prior to the start of behavioral sessions (Kuczenski and Segal, 2002 (link)).
Cocaine hydrochloride (NIDA, Bethesda, Maryland, USA) was dissolved in 0.9% sterile saline containing 3 IU heparin/ml. A cocaine unit dose of 0.3 mg/kg (0.8 mg/ml) was used for training. Additionally, cocaine unit doses ranging from 0.003 to 1.0 mg/kg were used to determine dose-response curves. A constant drug delivery time of 1.2 s/100g body weight was maintained by adjusting cocaine concentration for each dose.
For [3H]DA uptake assays, desipramine hydrochloride, paroxetine hydrochloride, nomifensine maleate, ethylenediaminetetraacetic acid (EDTA), sucrose, 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES), 3-hydroxytyramine (DA), sodium chloride and magnesium sulfate were purchased from Sigma-Aldrich Co. (St. Louis, MO). [3H]DA (Dihydroxyphenylethylamine,3,4-[7-3H]; specific activity, 30.3 Ci/mmol) was purchased from PerkinElmer Life and Analytical Sciences Inc. (Boston, MA). α-d-Glucose, l-ascorbic acid, and monobasic potassium phosphate were purchased from Aldrich Chemical Co. (Milwaukee, WI), AnalaR-BHD Ltd. (Poole, UK) and Mallinckrodt (St. Louis, MO), respectively. All other chemicals in the assay buffer were purchased from Fisher Scientific Co. (Pittsburgh, PA).
Cocaine hydrochloride (NIDA, Bethesda, Maryland, USA) was dissolved in 0.9% sterile saline containing 3 IU heparin/ml. A cocaine unit dose of 0.3 mg/kg (0.8 mg/ml) was used for training. Additionally, cocaine unit doses ranging from 0.003 to 1.0 mg/kg were used to determine dose-response curves. A constant drug delivery time of 1.2 s/100g body weight was maintained by adjusting cocaine concentration for each dose.
For [3H]DA uptake assays, desipramine hydrochloride, paroxetine hydrochloride, nomifensine maleate, ethylenediaminetetraacetic acid (EDTA), sucrose, 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES), 3-hydroxytyramine (DA), sodium chloride and magnesium sulfate were purchased from Sigma-Aldrich Co. (St. Louis, MO). [3H]DA (Dihydroxyphenylethylamine,3,4-[7-3H]; specific activity, 30.3 Ci/mmol) was purchased from PerkinElmer Life and Analytical Sciences Inc. (Boston, MA). α-d-Glucose, l-ascorbic acid, and monobasic potassium phosphate were purchased from Aldrich Chemical Co. (Milwaukee, WI), AnalaR-BHD Ltd. (Poole, UK) and Mallinckrodt (St. Louis, MO), respectively. All other chemicals in the assay buffer were purchased from Fisher Scientific Co. (Pittsburgh, PA).
