No abstract

We previously reported that GnRH gene expression was enhanced by progesterone (P) in the hypothalamus from ovariectomized and estrogen (OVX+E) treated immature rats. Recent studies indicate that excitatory amino acids may play an important role in the regulation of GnRH secretion and gene expression by steroids. Therefore the present study attempts to examine whether excitatory amino acids are involved in the P-induced GnRH gene expression and release in vitro. MK-801, an NMDA receptor antagonist or CNQX, a non-NMDA receptor antagonist, was administered to OVX+E+P-treated prepubertal female rats. GnRH mRNA was determined by Northern blot hybridization using ³²P-labeled antisense RNA, and GnRH release in vitro from the hypothalamic fragments was monitored by GnRH radioimmu-noassay. The administration of MK-801 (0.2 mg/kg) for 2h significantly reduced the P-induced GnRH gene expression and release, whereas CNQX (0.4 mg/kg) had no effect. These results clearly indicate that excitatory amino acids by way of NMDA receptor are involved in the transsynaptic regulation of GnRH gene expression.

We investigate the drying process of monodisperse colloidal film over a wide range of Péclet numbers (Pe) by using the Brownian dynamics simulation. We analyze the detailed process in three aspects; accumulation front, normal stress, and microstructure. The evolution of particle distribution is quantified by tracking the accumulation front. The accumulated particles contribute to the continuous increase of the normal stress at the interface. At the substrate, the normal stress first stays constant and then increases as the accumulation front touches the substrate. We quantitatively analyze the stress development by a scaled normal stress difference between the two boundaries. At all tested Pe, the stress difference increases to the maximum, followed by a decrease during drying. Interestingly, a mismatch is observed between the stress difference maximum and the initial stress increase at the substrate. The microstructural analysis reveals that this mismatch is related to the microstructural development at the substrate.

The local shear stress of non-Brownian suspensions was investigated using the lattice Boltzmann method coupled with the smoothed profile method. Previous studies have only focused on the bulk rheology of complex fluids because the local rheology of complex fluids was not accessible due to technical limitations. In this study, the local shear stress of two-dimensional solid particle suspensions in Couette flow was investigated with the method of planes to correlate non-Newtonian fluid behavior with the structural evolution of concentrated particle suspensions. Shear thickening was successfully captured for highly concentrated suspensions at high particle Reynolds number, and both the local rheology and local structure of the suspensions were analyzed. It was also found that the linear correlation between the local particle stress and local particle volume fraction was dramatically reduced during shear thickening. These results clearly show how the change in local structure of suspensions influences the local and bulk rheology of the suspensions.

Concentrated hard-sphere suspensions in the liquid and crystal coexistence region show a unique nonlinear behavior under a large amplitude oscillatory shear flow, the so-called strain stiffening, in which the viscosity or modulus suddenly starts to increase near a critical strain amplitude. Even though this phenomenon has been widely reported in experiments, its key mechanism has never been investigated in a systematic way. To have a good understanding of this behavior, a numerical simulation was performed using the lattice Boltzmann method (LBM). Strain stiffening was clearly observed at large strain amplitudes, and the critical strain amplitude showed an angular frequency dependency. The distortion of the shear stress appeared near the critical strain amplitude, and the nonlinear behavior was quantified by the Fourier transformation (FT) and the stress decomposition methods. Above the critical strain amplitude, an increase in the global bond order parameter Ψ(6) was observed at the flow reversal. The maximum of Ψ(6) and the maximum shear stress occurred at the same strain. These results show how strongly the ordered structure of the particles is related to the stress distortion. The ordered particles maintained a bond number of "two" with alignment with the compressive axis, and they were distributed over a narrow range of angular distribution (110°-130°). In addition, the ordered structure was formed near the lowest shear rate region (the flow reversal). The characteristics of the ordered structure were remarkably different from those of the hydroclusters which are regarded as the origin of shear thickening. It is clear that strain stiffening and shear thickening originate from different mechanisms. Our results clearly demonstrate how the ordering of the particles induces strain stiffening in the liquid and crystal coexistence region.