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Neurochemical predisposition to self-administer morphine in rats
S D Glick1, C Merski, S Steindorf
1Department of Pharmacology and Toxicology, Albany Medical College, NY 12208.
Brain Research
|April 24, 1992
Summary
Individual differences in brain dopamine systems influence morphine self-administration. Dopamine metabolite levels in the striatum and medial prefrontal cortex predict drug-seeking behavior initiation and maintenance.
Area of Science:
- Neuroscience
- Neurochemistry
- Behavioral Pharmacology
Background:
- Individual variability in drug self-administration suggests underlying neurochemical differences.
- Dopamine systems are implicated in reward and motivation, key factors in drug seeking.
Purpose of the Study:
- To identify neurochemical predispositions for morphine self-administration in rats.
- To investigate the role of dopamine and its metabolites in the mesocorticolimbic and nigrostriatal systems during morphine intake.
Main Methods:
- In vivo microdialysis was used to measure extracellular dopamine and its metabolites (DOPAC, HVA) in rat brain regions.
- Rats were trained to intravenously self-administer morphine or press a lever for water.
Main Results:
- Striatal DOPAC/HVA levels inversely correlated with morphine self-administration during the maintenance phase.
- Hemispheric asymmetries in striatal metabolites correlated with acquisition of self-administration.
- Medial prefrontal cortex DOPAC/HVA levels (especially on the right) positively correlated with acquisition, predicting initiation.
Conclusions:
- Individual differences in dopamine system organization and activity contribute to variability in drug-seeking behavior.
- Distinct dopamine mechanisms underlie the initiation and maintenance of morphine intake, involving the nucleus accumbens, striatum, and medial prefrontal cortex.