Midazolam hydrochloride

In general, all drugs were prepared fresh on the morning of the test session or the night before. Ethanol (95%) was diluted to 20% w/v in water for doses ≤ 1.0 g/kg, and to 25% and 30% for 1.5g/kg and 2.0g/kg tests respectively, leading to gavage volumes between 30–50ml for all doses tested. Pentobarbital was purchased in prepared form (Nembutal, 50 mg/ml), and midazolam hydrochloride (Sigma Aldrich) was diluted in saline to 3 mg/ml. Both drugs were administered through the nasogastric gavage, followed by a gavage of water up to the training dose volume (30–45ml). (+)-MK-801 hydrogen maleate (Sigma Aldrich) was diluted in saline to 0.2–0.5 mg/ml, morphine maleate salt (Sigma Aldrich) was diluted in saline to 5 mg/ml, and muscimol (Tocris) was diluted in saline to 7 mg/ml. Drug concentrations were based on the salt form of the drug. All i.m. drug preparations were less than 3ml, and if the injection volume exceeded 1ml, it was given across two injection sites. Vehicle injections matched the maximum drug volume given. All drugs administered i.m. (pentobarbital, MK-801, morphine, muscimol) were filtered through a 20μm millipore filter into a sterile vial prior to administration.

Racemic MDMA [(±)-3,4-methylenedioxymethamphetamine hydrochloride] and M100907 were kindly provided by the National Institute of Drug Abuse (Baltimore, MD, USA). Ketanserin tartrate and methyllycaconitine citrate were purchased from TOCRIS (Ellisville, MO, USA). Hexamethonium bromide, midazolam hydrochloride, and WAY100,635 maleate were purchased from Sigma (St. Louis, MO, USA). Drug dosages (mg/kg) were expressed as the weight of the salt and injected at a constant volume of 1 mL/kg (dissolved in 0.9% NaCl). MDMA and ketanserin were injected intraperitoneally, and other drugs were administered subcutaneously.

Diazepam (Sigma-Aldrich, St. Louis MO) was dissolved in a 10% ethanol solution which was used as the vehicle control solution for experiments in which Diazepam was studied. midazolam hydrochloride (Sigma-Aldrich, St. Louis, MO) was dissolved in normal saline which served as the control solution for experiments in which midazolam was studied. Flumazenil was commercial grade (Romazicon™; Genetech, Inc., San Francisco, CA).