(-)-STEPHOLIDINE VS 12-CHLOROSCOULERINE ENANTIOMERS ON FIRING ACTIVITY OF SUBSTANTIA NIGRAL DOPAMINE NEURONS

To compare the potencies between (-)stepholidine ((-)-SPD) and 12-chlo roscoulerine (CSL) enantiomers on firing of substantia nigra (SN) dopa mine (DAS neurons. METHODS: Extracellular single unit recordings in pa ralyzed rats. RESULTS: In rats, (-)-SPD, (-)-, (+/-)-, and (+)-CSL att neuated iv apomorphine (Apo, 10 mu g . kg(-1)-induced inhibition on fi ring of DA cell, and their ED(50) values were 15.1 (11.9 - 19.4), 7.8 (7.0 - 8.7), 12.6 (2.0 - 17.9) mu g . kg(-1), and 2.9 (2.6 - 3.3) mg . kg(-1)), respectively. Thus, (-)-CSL was 1 time more potent than (-)- SPD and 371 times more potent than (+)-CSL on D-2 receptors. In reserp inized rats, (-)-SPD, (-)-, (+/-)-, and (+)-CSL blocked the inhibition caused by iv 4 mg . kg(-1) SKF-38393, with ED(50) values of 0.53 (0.5 1 - 0.55), 0.51 (0.43-0.60), 1.2 (0.7-2.0), and 5.9 (4.9 - 7.1) mg . k g(-1), respectively. The potency of (-)-CSL was similar to that of (-) -SPD on D-1 receptors and 11 times higher than that of (+)-CSL. CONCLU SION: CSL enantiomers are D-1/D-2 mixed antagonists as (-)-SpD. (-)-CS L is the most, while (+)-CSL is the least, potent one among them.