Chronic Morphine Exposure in Mice

Morphine sulfate was supplied by NIDA Drug Supply (Research Triangle Park, NC) and dissolved into a 0.2% saccharin solution so that mice would consume morphine via drinking water [31 ]. Saccharin was used in the baseline condition and in the control groups for the duration of the studies. Morphine concentration was gradually increased from 0.3 to 0.5 mg/ml to ensure stable drinking throughout the 11 days of chronic exposure. Dosing stayed at 0.5 mg/ml for the remainder of the experiments [32 (link)]. Body weights and drinking volume were assessed every 2–3 days to confirm morphine ingestion, and adequate body weight was maintained. Clozapine N-Oxide (CNO) (HelloBio, cat. no. 1807) was dissolved in saline and administered i.p. at 1 mg/kg.