Role of Dopamine Receptors and the Changes of the Tyrosine Hydroxylase Mrna in Acupuncture Analgesia in Rats

Abstract

Previous studies have shown that dopamine (DA) is involved in electroacupuncture analgesia (EAA). L-tetrahydropalmatine (l-THP), a DA receptor antagonist was proved to potentiate EAA in both laboratory research and clinical practice. In the present study SK&F-38393 and quinpirole (Qui), selective agonists of D₁ or D₂ receptors respectively were injected into nucleus (N.) accumbens of rats to investigate the roles of D₁ and D₂ receptors in the potentiation of EAA induced by l-THP. The injection of D₁ agonist SK&F-38393 (5μg or 20μg) attenuated the potentiation of EAA induced by l-THP, 10 μg SK&F-38393 attenuated EAA as well, while the injection of D₂ agonist Qui (10 μg or 20 μg) had no effect on EAA and the potentiation of EAA induced by l-THP. DA release was shown to increase in EAA in previous work, however, whether the synthesis of DA was influenced is still unknown. In the present study, dot blot technique was applied to observe the effect of noxious stimulation or electroacupuncture on the level of tyrosine hydroxylase (TH) mRNA in rat brain. Noxious electric stimulation was found to elevate the TH mRNA level in substantia nigra (SN) and hypothalamus, while electro-acupunture attenuated the effect of noxious stimulation on TH mRNA. The results indicate that D₁ but not D₂ receptor in N. accumbens plays an important role in EAA. EA might regulate the biosynthesis of DA by altering the TH gene transcription.