Agonistic actions of pergolide on firing activity of dopamine neurons in substantia nigra compacta area
Abstract
AIM:
To study the potency of pergolide as a D2 receptor agonist on the firing activity of substantia nigra compacta (SNC) dopamine (DA) neurons compared with that of bromocriptine and to determine whether pergolide has the nature of D1 receptor agonist in vivo.
METHODS:
Extracellular single unit recording techniques.
RESULTS:
Both pergolide and bromocriptine 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 micrograms kg-1) was more potent than bromocriptine (7.8, 95% fiducial limits, 3.3-18.5 mg kg-1). The discharge inhibition of pergolide was attenuated following the injection of selective D2 receptor antagonist spiperone 0.25 mg kg-1 or selective D1 receptor antagonist Sch-23390 1-2 mg kg-1. However, the inhibition caused by bromocriptine was not always attenuated by spiperone.
CONCLUSION:
Pergolide is 650 times more potent than bromocriptine at D2 receptors, and possesses D1 receptor agonist characteristics in vivo.
Keywords:
To study the potency of pergolide as a D2 receptor agonist on the firing activity of substantia nigra compacta (SNC) dopamine (DA) neurons compared with that of bromocriptine and to determine whether pergolide has the nature of D1 receptor agonist in vivo.
METHODS:
Extracellular single unit recording techniques.
RESULTS:
Both pergolide and bromocriptine 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 micrograms kg-1) was more potent than bromocriptine (7.8, 95% fiducial limits, 3.3-18.5 mg kg-1). The discharge inhibition of pergolide was attenuated following the injection of selective D2 receptor antagonist spiperone 0.25 mg kg-1 or selective D1 receptor antagonist Sch-23390 1-2 mg kg-1. However, the inhibition caused by bromocriptine was not always attenuated by spiperone.
CONCLUSION:
Pergolide is 650 times more potent than bromocriptine at D2 receptors, and possesses D1 receptor agonist characteristics in vivo.