AGONISTIC ACTIONS OF PERGOLIDE ON FIRING ACTIVITY OF DOPAMINE NEURONSIN SUBSTANTIA-NIGRA COMPACTA AREA

AIM: To study the potency of pergolide as a D-2 receptor agonist on th e firing activity of substantia nigra compacta (SNC) dopamine (DA) neu rons compared with that of bromocriptine and to determine whether perg olide has the nature of D-1 receptor agonist in vivo. METHODS: Extrace llular single unit recording techniques. RESULTS: Both pergolide and b romocriptine decreased the spontaneously firing rate of ''sensitive'' and ''insensitive'' DA cells. In regard of ID50 values, pergolide (11. 9, 95 % fiducial limits, 5.7-25.1 mu g kg(-1)) was more potent than br omocriptine (7.8, 95 % fiducial limits, 3.3 -18.5 mg kg(-1)). The disc harge inhibition of pergolide was attenuated following the injection o f selective D-2 receptor antagonist spiperone 0.25 mg kg(-1) or select ive D-1 receptor antagonist Sch-23390 1-2 mg kg(-1). However, the inhi bition caused by bromocriptine was not always attenuated by spiperone. CONCLUSION: Pergolide is 650 times more potent than bromocriptine at D-2 receptors, and possesses D-1 receptor agonist characteristics in v ivo.