N-Methyl-D-aspartate (NMDA) directly stimulates gonadotropin-releasing hormone (GnRH) neurons to secrete GnRH. It is not known if this stimulatory effect of NMDA is mediated by NO. Northern blot analysis of the immortalized hypothalamic GnRH neuronal cells (GT1-1) mRNA with a neuronal NOS cDNA revealed this clonal cell line expressed neuronal NOS transcripts as a single 10.5-kb band. Immunoblot analysis of GT1-1 proteins with anti-neuronal NOS serum showed that the GT1-1 cells contain neuronal NOS. GT1-1 cells were used to study the effects of NO and NMDA on GnRH release. L-Arginine (10(-2) M), a precursor of NO enhances basal GnRH secretion. Both oxyhemoglobin (Hb)(10(-6)-10(-4) M), a NO scavenger and N omega-nitro-L-arginine (NNA)(10(-3),10(-2) M), a NOS inhibitor and inactivator block basal as well as NMDA-induced GnRH release. Sodium nitroprusside (SNP) (10(-4), 10(-3) M), a NO donor stimulates GnRH release, an effect inhibited by Hb. Incubation of GT1-1 cells in Ca(2+)-free medium abolished the stimulatory effect of NMDA on GnRH release. In contrast, incubation in medium with increasing concentrations of Ca2+ enhances basal GnRH release as well as augments NMDA-mediated GnRH release. The results demonstrate that L-arginine-NO pathway is functional in the GT1-1 cells and an increase in intracellular Ca2+ [Ca2+]i following NMDA receptor activation activates NOS to generate NO. We conclude that endogenous NO mediates, at least in part, basal as well as NMDA-stimulated GnRH release and may play a role as an intercellular messenger in synchronizing pulsatile GnRH release.
[1] A fast approach is developed here to analyze large finite planar periodic arrays of elements in a grounded multilayered medium with relatively arbitrary element truncation boundaries. An array shape matrix is introduced which contains information on the array element truncation boundary, and it can be easily incorporated into preconditioned iterative method of moments matrix solvers without significantly increasing computational resources. The performance of the present approach is illustrated through numerical results.Citation: Mahachoklertwattana, P., P. H. Pathak, and R. J. Burkholder (2008), A fast MoM approach for analyzing large arrays in a grounded multilayered medium, Radio Sci., 43, RS6S05,
A novel approach is developed here to predict electromagnetic radiation/scattering from finite planar periodic arrays of elements in grounded multilayered media with nonrectangular element truncation boundaries. This approach is considered as an extension to a conventional MoM solver developed for analyzing radiation/scattering from finite arrays with rectangular boundaries. An array shape matrix is first introduced which contains the information regarding a nonrectangular array element truncation boundary and it can be easily incorporated into preconditioned iterative MoM matrix solvers without significantly increasing computational resources. Additionally, significant computational acceleration is obtained when the elements of the MoM operator matrix are evalutated in terms of an accurate asymptotic closed form approximation for the multilayered Green's function, which is the kernel of the governing integral equation used in the MoM formulation. Some numerical results are presented to illustrate the performance of this approach.
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