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Methadone induced physical dependence in the rat
Abstract:
Although the morphine withdrawal syndrome has been well described in the rat, a syndrome having similar characteristics has not been demonstrated following chronic methadone treatment. In this study we describe the behavioral effects produced by naloxone (4 mg/kg sc) following 72 hours of continuous iv infusion of methadone, (12.2 micrograms/kg/min), morphine (12.2 to 97.9 micrograms/kg/min) or saline. The cessation of methadone or morphine but not saline treatment followed by naloxone resulted in graded signs including wet dog shakes, escape attempts, self-stimulation and body weight loss and quantal signs including diarrhea, ear blanching, exophthalmos, ptosis, tachypnea and teeth chattering. These results indicate that this mode of methadone administration produces physical dependence characterized by a morphine-like withdrawal syndrome in the rat.
Insights
Chronic methadone infusion in rats induced physical dependence, manifesting a withdrawal syndrome similar to morphine. Naloxone administration precipitated these distinct behavioral and physiological signs in dependent rats.
Area of Science:
- Pharmacology
- Neuroscience
- Addiction Research
Background:
- The morphine withdrawal syndrome is well-documented in rats.
- However, a comparable syndrome following chronic methadone treatment has not been clearly demonstrated.
- Understanding opioid withdrawal is crucial for addiction treatment and management.
Purpose of the Study:
- To investigate the development of physical dependence and withdrawal signs following chronic intravenous methadone administration in rats.
- To compare the withdrawal syndrome induced by methadone with that of morphine.
- To characterize the behavioral and physiological effects of naloxone-precipitated withdrawal after methadone or morphine treatment.
Main Methods:
- Rats received continuous intravenous infusions of methadone, morphine, or saline for 72 hours.
- Naloxone (4 mg/kg) was administered subcutaneously after the infusion period to precipitate withdrawal.
- Behavioral signs (e.g., wet dog shakes, escape attempts) and physiological signs (e.g., diarrhea, tachypnea) were recorded and quantified.
Main Results:
- Cessation of methadone or morphine treatment, followed by naloxone, resulted in a graded series of withdrawal signs.
- Observed signs included wet dog shakes, escape attempts, self-stimulation, body weight loss, diarrhea, ear blanching, exophthalmos, ptosis, tachypnea, and teeth chattering.
- Saline-treated rats did not exhibit these withdrawal phenomena.
Conclusions:
- Continuous intravenous methadone administration in rats produces physical dependence.
- The precipitated withdrawal syndrome is characterized by signs similar to those observed in morphine withdrawal.
- These findings demonstrate a morphine-like withdrawal syndrome following chronic methadone administration in rats, highlighting its potential for inducing physical dependence.