Gamma-aminobutyric acid A receptor and N-methyl-D-aspartate receptor subunit expression in rat spiral ganglion neurons

BACKGROUND： Gamma-aminobutyric acid A （GABAA） and N-methyl-D-aspartate （NMDA） receptors are significant receptors in the central nervous system. An understanding of GABAA and NMDA receptor expression in spiral ganglion neurons （SGN） provides information for the functional role of these receptors in the auditory system. OBJECTIVE： To investigate mRNA expression of GABAA receptor （GABAAR） and NMDA receptor （NMDAR） subunits in the rat SGN. DESIGN, TIME AND SETTING： This in vitro, molecular biological study was performed at the Laboratory of Otolaryngology-Head and Neck Surgery, Guangxi Medical University, China from July 2007 to May 2008. MATERIALS： Reverse Transcriptase Kit and Taq DNA polymerase were purchased from Fermentas Burlington, ON, Canada; GABAAR and NMDAR primers were purchased from Shanghai Sangon, Shanghai, China. METHODS： SGN from 3-5 day postnatal Wistar rats was collected for primary cultures, mRNA expression of GABAAR and NMDAR subunits in the SGN was determined by reverse transcription polymerase chain reaction. MAIN OUTCOME MEASURES： Expression levels of GABAAR and NMDAR subunits were determined by quantitative analysis. RESULTS： GABAAR subunits （αl 6, β1 3, and y1 3） and NMDAR subunits （NR1, NR2A, NR2B, NR2C, NR2D, NR3A, and NR3B） were detected in the SGN. In α subunit genes of GABAAR, α1 and α3 expression was similar （P 〉 0.05） and greater than the other subunits. Of the β subunit genes, β1 subunit mRNA levels were greater than β2 and β3. Of the y subunit genes, y2 subunit mRNA levels were greater than y1 and y3. NR1 mRNA expression was the greatest of NMDAR subunits. CONCLUSION： GABAAR subunits （α1 6, β1-3, and y1-3） and NMDAR subunits （NR1, NR2A, NR2B, NR2C, NR2D, NR3A, and NR3B） were expressed in the rat SGN. Through comparison of GABAAR and NMDAR subunit expression, possible GABAAR combinations, as well as highly expressed subunit combinations, were estimated, which provided information for pharmacological and electrophysiological characteristics of GABAAR in the auditory system.

N-methyl-D-aspartate (NMDA) mediates vascular relaxation via nitric oxide (NO) in rats but not in mice

Amperometric studies have indicated that substance P as well as NMDA stimulates release of NO in rat aortic rings. These data have been confirmed by functional observations of vaso-relaxant action of NMDA within noradrenaline pre-contracted aortic rings, supporting the presence of NMDA receptor in rat aortic rings. It is known that the enzyme endothelial NO synthase (eNOS) mediates vasodilatation not only in rats, but also in C57BL6 mice aortic ring, indicating that in this blood vessel NO is the endogenous endothelium-derived vasodilator. In this work, amperometry together with specifically nitrites insensitive micro-biosensors have been applied to examine the effect of NMDA and substance P upon NO release in rat and in two strains of mice aortic rings. The electrochemical data monitored demonstrate that NMDA mediates vascular relaxation via NO in rats but not in mice. These results are supported by functional data, therefore they suggest that NMDA receptors are “not responding” within these experimental conditions in mice aortic rings.