U50488 hydrochloride

Cocaine hydrochloride, d-amphetamine sulfate, and MDPV were obtained through NIDA Drug Supply. Tetrodotoxin (TTX) was obtained from Alamone Labs (Jerusalem, Israel). U50488 hydrochloride and nor-BNI were obtained from Tocris. All other reagents and chemicals were obtained from Sigma-Aldrich. Drugs were prepared as stock solutions in water and dissolved freshly before use in aCSF.

planarians (Dugesia dorotocephala) were purchased from Carolina Biological Supply (Burlington, NC, USA). Upon arrival in the laboratory, planarians were maintained in the aqueous solution provided by Carolina Biological Supply, acclimated to room temperature (21 °C), and tested within 3 days of receipt. DAMGO and the kappa agonist U50,488 hydrochloride was purchased from Tocris Biosciences (St. Louis, MO, USA). Naltrexone hydrochloride (NTX) and the kappa opioid receptor antagonist, nor-Binaltorphimine dihydrochloride (nBNI), were purchased from Sigma-Aldrich (St. Louis, MO, USA). Morphine sulfate was provided by NIDA Drug Supply (Bethesda, MD, USA). All drugs were dissolved in spring water, with stock and working solutions prepared daily, and concentrations were based on prior planarian work and Kd values of DAMGO (Tallarida et al., 2014 (link); Zhao et al., 2003 (link)). Behavioral experiments were conducted between 10 AM and 4 PM. Behavioral responses were quantified by a trained observer with a stopwatch who was blinded to drug treatment. planarians are large enough (average length about 3–15 mm) so that behavior can be observed and quantified with the naked eye, so behavioral responses were quantified without the aid of a microscope. Experiments and behavioral observations were conducted in ‘real time’, and no videotaping was used.