Effect Of Antagonism Of Glutamate Receptors In The PVN Region On Baroreflex In Conscious Rats

The hypothalamic paraventricular nucleus (PVN) is a central site for the integration of the endocrine system and the autonomic nervous system,and a number of studies have shown that the PVN is an important structures for the regulation of body-fluid homeostasis and the central control of cardiovascular function.Though some studies have shown that the PVN enhance the cardiovascular responses induced by direct or indirect stimulation of PVN, but the neurochemical mediators in the PVN responsible for mediating baroreflex are not well understood.Therefore,the objective of this study is to investigate the possible involvement of glutamate (Glu) in the paraventricular nucleus (PVN) in the central regulation of baroreflex.The baroreflex was induced by intravenous injection of phenylephfine in conscious rats,and the extracellular concentration of Glu in the PVN region was measured by microdialysis and high performance liquid chromatography (HPLC) techniques.Next,to determined whether the observed Glu release was involved in the baroreflex,NMDA (N-methyl-D-aspartate) and non-NMDA receptor antagonists,MK-801 (dizocilpine) and CNQX (6-cyano-7-nitroquinoxaline-2,3-dione),were perfused in the PVN region during baroreflex.Our results are as follows:1.The intravenous injection of phenylephrine increased the blood pressure (BP) from 99.5±5.6 mmHg to 149.8±4.3 mmHg,and the heart rate (HR) was reflexly decreased from 400.8＋5.2 beat/min to 273.4±6.7 beat/min,(p<0.05);the Glu concentration in the PVN region immediately increased from basal level 100％to 373.44±47.60% (P<0.01) .2.MK-801 and CNQX (1001.tmol/L) were perfused in the PVN for 20min,and the baroreflex was induced by intravenous injection of phenylephrine.Both glutamate receptors antagonists reduced phenylephrine-induced BP increase (p<0.01),and enhanced the decrease of HR (p<0.01),resulting a significant increase in baroreflex sensitivity (P<0.01) .Conclusion:Glutamate in PVN is involved in central regulation of baroreflex,which may inhibit baroreflex via ionothopic glutamate receptors,and the effect is inhibited.