[Blockade of (+/-) 12-chloroscoulerine on feed-back regulation of dopamine D2 autoreceptors].

AIM

To verify whether (+/-) 12-chloroscoulerine (CSL) is antagonist or agonist effect to D2 autoreceptors.

METHODS

The levodopa content accumulated in the rat striatum was measured by HPLC-ECD, and the DA neuron firing activity in the substantia nigra zona compacta (SNC) was recorded.

RESULTS

The accumulated levodopa content induced by CSL 40 mg.kg-1 was much more than that of 1,4-butyro-lactone (BL) group (P < 0.01). After i.p. injection of apomorphine (Apo) 5 mg.kg-1, the levodopa content was decreased below that of BL group (P < 0.05). The Apo inhibition on levodopa content was completely reversed by CSL (40 mg.kg-1, i.p.) and then increased the levodopa content (2.5 +/- 1.1 micrograms.g-1) over that of Apo group (0.7 +/- 0.3 microgram.g-1, P < 0.01). In the electrophysiologic recording, Apo (15 micrograms.kg-1, i.v.) induced the decrease of SNC DA cell firing rate nearly to zero. At the accumulated dose of CSL up to 80 micrograms.kg-1 (i.v.), the inhibition of Apo was attenuated and the firing activity was restored to predrug level.

CONCLUSION

CSL showed an antagonistic action, an action to D2 autoreceptors.