Voluntary morphine ingestion, morphine dependence, and recovery from withdrawal signs.

We are reporting on conditions (without forced drinking or premedications) where rats voluntarily drink high quantities of sucrose-morphine solutions in preference to water. The volume ingested is inversely related to the morphine concentration in the liquid. The morphine antagonist, nalorphine, produced a clear set of opiate withdrawal signs in these (voluntarily) morphine-drinking rats. The severity of withdrawal signs was a function of the amount of ingested morphine. The present finding is the first report to show that rats ingest high quantities of sucrose-morphine without premedication or forced hydration procedures.