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Changes in sensitivity to apomorphine during morphine dependence and withdrawal in rats
Summary
Morphine dependence increases rat sensitivity to apomorphine, but this heightened sensitivity reverses during naloxone-precipitated withdrawal. Dopaminergic system changes are implicated in opioid dependence and withdrawal.
Area of Science:
- Neuroscience
- Pharmacology
- Addiction Research
Background:
- Opioid dependence involves complex neurobiological adaptations.
- Central dopaminergic systems play a role in the effects of opioids and withdrawal symptoms.
Purpose of the Study:
- To investigate changes in central dopaminergic system sensitivity during morphine dependence and withdrawal.
- To assess the effects of morphine dependence and naloxone-precipitated withdrawal on apomorphine-induced stereotyped behavior in rats.
Main Methods:
- Apomorphine hydrochloride (ED50 dose) was used to induce stereotyped behavior in control rats, morphine-dependent rats, and rats undergoing naloxone-precipitated withdrawal.
- Morphine dependence was established using subcutaneous pellet implants.
- Naloxone hydrochloride and morphine sulfate were administered to assess their effects on apomorphine-induced behavior.
Main Results:
- Morphine-dependent rats exhibited increased sensitivity to apomorphine compared to controls.
- This increased sensitivity to apomorphine was abolished during naloxone-precipitated withdrawal.
- Naloxone (1.0 mg/kg) antagonized apomorphine-induced stereotyped behavior, an effect also observed with acute morphine administration.
Conclusions:
- Morphine dependence alters central dopaminergic system sensitivity.
- Naloxone-precipitated withdrawal normalizes this altered dopaminergic sensitivity.
- These findings highlight the dynamic changes in dopaminergic neurotransmission during opioid dependence and withdrawal.