Related Experiment Video
Updated: Aug 15, 2026
Assessment of Morphine-induced Hyperalgesia and Analgesic Tolerance in Mice Using Thermal and Mechanical Nociceptive Modalities
Published on: July 29, 2014
Effects of morphine on spontaneous activity of 18-day rat fetus
The effects of morphine on spontaneous activity of 18-day fetal rats have been observed in utero. Morphine injected subcutaneously in the dam caused a decrease in fetal spontaneous activity which was dose-dependent. The maximum depression of activity occurred after 20 mg/kg was administered to the dam. Activity returned to control levels following naloxone administration to the dam. Fetuses which had been chronically exposed to morphine from days 7 through 17 and observed on day 18 of gestation became hyperactive following administration of naloxone to the dam. This is thought to represent fetal withdrawal.
The effects of morphine on spontaneous activity of 18-day fetal rats have been observed in utero. Morphine injected subcutaneously in the dam caused a decrease in fetal spontaneous activity which was dose-dependent. The maximum depression of activity occurred after 20 mg/kg was administered to the dam. Activity returned to control levels following naloxone administration to the dam. Fetuses which had been chronically exposed to morphine from days 7 through 17 and observed on day 18 of gestation became hyperactive following administration of naloxone to the dam. This is thought to represent fetal withdrawal.
