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An electromyographic method for the assessment of naloxone-induced abstinence in morphine-dependent rats
Abstract:
The electromyographic (EMG) activities of suprahyoideal muscle were recorded to measure naloxone-precipitated abstinence signs in morphine-dependent rats anesthetized with urethane (1 g/kg). Rats were rendered dependent on morphine by implanting 2 morphine pellets (75 mg each) and abstinence signs were induced by intravenous injections of various doses of naloxone at different times after pellet implantation. Three precipitated abstinence signs, a) myoclonic twitch activity (MTA), b) mastication, and c) body shakes were observed on EMG recordings after the injection of naloxone. Of these symptoms, only the MTA induced by naloxone (10 microgram/kg) occurred 4h after pellet implantation and its sensitivity to naloxone increased with prolonged pellet implantation. Both mastication and precipitated shakes could be induced at 24h. However, higher doses of naloxone were required to produce the shakes than is required to induce mastication. There appears to be a positive correlation between the intensity of naloxone-induced MTA and the degree of physical dependence on morphine. Since the MTA and mastication can be induced by low doses of naloxone in morphine-dependent rats, we suggest that these two parameters may be used to detect morphine abstinence signs in this species.
Insights
Naloxone-precipitated abstinence signs in morphine-dependent rats were measured using electromyographic (EMG) activity. Myoclonic twitch activity and mastication are sensitive indicators of morphine withdrawal.
Area of Science:
- Neuroscience
- Pharmacology
- Physiology
Background:
- Morphine dependence leads to physical dependence, characterized by withdrawal symptoms upon cessation or antagonist administration.
- Naloxone is a standard opioid antagonist used to precipitate withdrawal in dependent subjects.
- Electromyography (EMG) offers a quantitative method to assess muscle activity associated with withdrawal signs.
Purpose of the Study:
- To investigate and quantify naloxone-precipitated abstinence signs in morphine-dependent rats using EMG.
- To determine the sensitivity of different abstinence signs to naloxone at various time points after morphine pellet implantation.
- To correlate the intensity of specific abstinence signs with the degree of physical dependence.
Main Methods:
- Morphine dependence was established in rats via subcutaneous implantation of morphine pellets.
- Abstinence signs were induced by intravenous naloxone administration at 4 and 24 hours post-implantation.
- Suprahyoideal muscle EMG activity was recorded to measure myoclonic twitch activity (MTA), mastication, and body shakes.
Main Results:
- Myoclonic twitch activity (MTA) was observed as early as 4 hours after morphine pellet implantation and increased in sensitivity with prolonged dependence.
- Mastication and body shakes were induced by naloxone at 24 hours, with mastication requiring lower naloxone doses than shakes.
- A positive correlation was found between the intensity of naloxone-induced MTA and the degree of physical dependence on morphine.
Conclusions:
- Myoclonic twitch activity (MTA) and mastication are sensitive and reliable indicators of morphine abstinence in rats, detectable with low naloxone doses.
- These EMG-measured parameters (MTA and mastication) can serve as valuable tools for assessing physical dependence and withdrawal severity in preclinical models.
- The findings support the use of EMG-based assessments for objective measurement of opioid withdrawal in research settings.