Perinatal narcotic addiction in mice: sensitization to morphine stimulation.

The injection of morphine sulfate into baby mice twice daily for 5 days increased their running reaponse to morphine when they were tested as adults. If treatment was completed before the mice were )5 days old there was no effect. Sensitization to morphine running was longer-lasting than either analgesic tolerance or tolerance to morphine running may be a form of denervation hypersensitivity that has several features in common with noise-induced sensitization to audiogenic seizures.