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Opposing tonically active endogenous opioid systems modulate the mesolimbic dopaminergic pathway
R Spanagel1, A Herz, T S Shippenberg
1Department of Neuropharmacology, Max Planck Institute for Psychiatry, Martinsried, Federal Republic of Germany.
Summary
The mesolimbic dopamine system involves opposing mu and kappa opioid systems. These systems tonically regulate dopamine release in the nucleus accumbens, impacting mood and addiction treatment.
Area of Science:
- Neuroscience
- Neuropharmacology
Background:
- The mesolimbic dopaminergic system is key to the motivational effects of drugs of abuse.
- The precise opioid action sites and endogenous opioid peptide roles in dopamine modulation are unclear.
Purpose of the Study:
- To investigate the role of mu and kappa opioid systems in regulating dopamine release within the mesolimbic pathway.
- To identify the specific brain regions involved in opioid-mediated dopamine modulation.
Main Methods:
- In vivo microdialysis was used to measure dopamine release.
- Highly selective mu and kappa opioid receptor ligands were administered to assess their effects.
Main Results:
- Mu-opioid receptor stimulation in the ventral tegmental area increased dopamine release; blockade decreased it.
- Kappa-opioid receptor stimulation in the nucleus accumbens decreased dopamine release; blockade increased it.
- Both mu and kappa receptor activation are essential for maintaining basal dopamine release in the nucleus accumbens.
Conclusions:
- Functionally opposing mu and kappa opioid systems tonically regulate dopamine release in the nucleus accumbens.
- These findings suggest implications for treating opiate dependence and affective disorders by targeting these opioid systems.