Codeine phosphate

Citric acid monohydrate, acetyl-β-methylcholine chloride, salbutamol sulfate, atropine, cinnamaldehyde, codeine phosphate, chlorpheniramine maleate (Sigma-Aldrich, Poole, UK), and levodropropizine, (Eurodrug, The Hague, Netherlands), were all dissolved in sterile saline (0.9%; Baxter Healthcare Ltd., Thetford, UK). Tiotropium bromide (Chiesi Farmaceutici, Parma, Italy) was prepared as a stock solution of 6 mM and diluted with sterile saline. All drugs were prepared fresh on the day of use. Roflumilast (CAS162401-32-3; Kemprotec, Carnforth, UK) is poorly soluble in saline and was therefore prepared in neat solutol (2%, Kolliphor HS15, 42966; Sigma-Aldrich) and diluted to the final concentration on the day of use. Capsaicin (Sigma-Aldrich) was prepared as a stock solution of 25 mg/ml (8:1:1 saline:ethanol:Tween 20; Fisher Scientific, Loughborough, UK). HC-030031 (2-(1,3-dimethyl-2,6-dioxo-1,2,3,6-tetrahydro-7H-purin-7-yl)-N-(4-isopropylphenyl)acetamide; Chiesi Farmaceutici) was prepared as a stock solution of 300 mg/ml in sterile saline and 1% solutol.

Compounds used in this study include atropine sulfate (Sigma Chemical Co., St. Louis, MO, United States), artificial Cerebral Spinal Fluid (CSF) (Harvard Apparatus, Holliston, MA, United States), codeine phosphate (Sigma Chemical Co., St. Louis, MO, United States), and baclofen (Research Biochemicals, Natick, MA, United States). Baclofen (i.a.), codeine (i.a.), and atropine were dissolved in physiological saline. Artificial CSF was employed as the vehicle for i.t. administration of baclofen and codeine.