Relationship between the central hypotensive effect of acupuncture or melatonin and the changes of medullary amino acid neurotransmitter

Abstract

To investigate whether changes of amino acid neurotransmitter releases in the rostral ventrolateral medulla (rVLM) were related to acupuncture and to the antihypertensive effect of melatonin (Mel) microinjected into the anterior hypothalamic area (AHA) of rats with stress-induced hypertension (SIH), as well as to compare and analyze the relationship between the both antihypertensive mechanisms of acupuncture and of Mel in the AHA. Methods: Animal model of SIHR was made by electric foot shocks combined with noises. Electroacupuncture (EA) was used and "Zusanli" acupoint of both side was selected. The technique of drug microinjection into the brain was used to observe the change of blood pressure (BP), and synchronously, brain microdialysis was performed for collecting dialysate samples, and then the concentration of amino acid neurotransmitters in the dialysate samples was determined by high performance liquid chromatography combined with fluorescent detection (HPLC-FD). Results: After the animal received stress treatment, the BP elevated, synchronously, the release of glutamate (Glu) in the rVLM increased, and when EA was performed, the elevated BP of the rats with SIH decreased,simultaneously, the release of Glu in the rVLM decreased also. After Mel was microinjected of into the AHA of the SIHR, the elevated BP attenuated, meanwhile, the release of Glu decreased,and those of γ-aminobutyric acid (GABA) and taurine (Tau) increased in the rVLM.Administration ofbicuculline, an antagonist of GABAA receptor, into the rVLM prior to microinjection of Mel into the AHA could partially block the depressor effect of Mel in the AHA. Conclusion: The decrease in the release of Glu in the rVLM contributes to the antihypertensive effect of both acupuncture and Mel in the AHA in the rats with SIH, and the increase in the release of GABA and Tau in the rVLM is also important to Mel in the AHA.