The cluster of arachnoid diverticula in the occipital bone: report of two cases with literature review.

The authors report two cases of multicentric osteolytic lesions in the occipital bone without any history of head trauma. The excisional biopsy of the first case revealed that the lesion was multicentric but a continuous cavity with the subarachnoid space through various sizes of dural defect, and the cavities were covered by arachnoid lining. Together with the previously reported similar 5 cases, the characteristic common feature is multicentric osteolytic lesions in the occipital bone at advanced age without marginal sclerosis. "The cluster of arachnoid diverticula in the occipital bone (CADOB)" is probably the most appropriate term for these non-traumatic lesions with the following characteristics: elderly patients, occipital bone, midline, multiple, intact outer table, nonsclerotic margin and without history of trauma. Operation may not be indicated because of its non-progressive and benign nature.

Modal behavior in single-mode slab waveguides consisting of inhomogeneous cores.

We present an analytical method for TE and TM modes in weakly guiding inhomogeneous single-mode slab waveguides. Based on our results, the modal behavior or propagation constants depend on index profiles of the waveguides. It is important to know how the modal behavior depends on the index profile in single-mode waveguides, because it determines wave-front characteristics of propagating modes.

Simple measuring technique for the diffraction efficiency of slanted volume gratings at various wavelengths.

To measure diffraction efficiencies of gratings as a function of wavelength, it is necessary to have quasi-monochromatic light sources of various wavelengths. We propose a method to measure the wavelength dependence of the grating diffraction efficiency by using a quasi-monochromatic light source. This method of estimating the real diffraction characteristics of the gratings for various wavelengths is very useful and simple. First the diffraction efficiency of the grating as a function of various incident-beam angles of monochromatic light is measured, then, using these data, we can obtain the diffraction efficiencies for various wavelengths of the same incident angle of light by virtue of a mathematical-conversion method. The mathematical-conversion results for two laminated differently slanted angle gratings of the same volume grating period are in good agreement with the experimental ones.

Prostaglandin D synthase (beta-trace) in human arachnoid and meningioma cells: roles as a cell marker or in cerebrospinal fluid absorption, tumorigenesis, and calcification process.

Glutathione-independent prostaglandin D synthase (PGDS) is an enzyme responsible for biosynthesis of prostaglandin D2 in the CNS and is identical to a major cerebrospinal fluid protein, beta-trace. Although PGDS has been identified recently in rat leptomeninges, little information is available about human meninges or meningiomas. Here, we report PGDS to be expressed consistently in 10 human arachnoid and arachnoid villi and in 21 meningiomas by immunohistochemistry, Western blot, and reverse transcription (RT)-PCR analyses. In arachnoid, PGDS immunoreactivity was seen in arachnoid barrier cells but was negligible in arachnoid trabecula and pia mater. In contrast, in arachnoid villi, PGDS was seen in core arachnoid cells rather than in the cap cell cluster or arachnoid cell layer. Meningioma cells also showed intense immunoreactivity in the perinuclear region, and it was often concentrated within meningocytic whorls and around calcifying psammoma bodies. Immunoelectron microscopic data, when compared with the ultrastructure, showed that PGDS was localized at rough endoplasmatic reticulum of arachnoid and meningioma cells. Western blot showed a 29 kDa immunoreactive band indicating PGDS, but the extent of expression was variable from case to case, which was compatible with immunohistochemical data. RT-PCR revealed PGDS gene expression in all meningiomas studied, regardless of histological subtypes, and also in human arachnoid villi. Because human arachnoid and meningioma cells exclusively express PGDS, it can be considered their specific cell marker. These results show functional differences in various types of meningeal cells attributable to differences in PGDS expression.

Expression of NF2 gene product merlin in arachnoid villi and meningiomas.

Neurofibromatosis type 2 (NF2) gene encodes a novel 595 amino acid protein named merlin. Recently, Ruttledge et al demonstrated inactivation of NF2 gene in approximately 60% of sporadically occurring meningiomas. Merlin is thought to physiologically exist beneath the cell membrane, and to form a part of modulation in signal transduction, for example, information concerning contact inhibition. In NF2-related tumors, it is supposed that the mutation of merlin results in loss of this signal transduction leading to tumorigenesis. In this paper, we investigated the expression of NF2 gene product merlin in arachnoid villi and meningiomas. The immunohistochemical staining of merlin showed a striking contrast between arachnoid villi and meningiomas. In arachnoid cells, merlin was labeled in the whole cytoplasm, but not within the nuclei. In contrast, in meningiomas, immunoreactivity of merlin was mainly seen in the nuclei. These results suggest that arachnoid cells with normal merlin are capable of normal signal transduction, whereas meningioma cells with mutated merlin show impairment of signal transduction which may lead to tumorigenesis.

Dynamic changes of cathepsins B and L expression in the monkey hippocampus after transient ischemia.

Enzymatic activities, expressions, and the immunohistochemical localization of lysosomal cystein proteases, cathepsins B and L, were analyzed in the monkey hippocampus after transient ischemia to clarify the mechanism of delayed cornu Ammonis (CA)-1 neuronal death. By enzymatic assay, the activity of cathepsin B increased in CA-1, 24 h after the ischemic insult, while that of cathepsin L decreased. On Western blotting, the protein contents of both cathepsins B and L increased immediately after ischemia. By immunohistochemistry, cathepsins B and L were stained as coarse granules in the perikarya of control CA-1 neurons, but in postischemic CA-1 neurons they were released from lysosome granules. In contrast, in CA-2 and the remaining sectors, enzymatic activities increased after ischemia, and immunoreactivities of cathepsins B and L increased only within lysosome granules. These results suggest that cathepsins B and L may play an important role in the breakdown of certain cell proteins in the postischemic CA-1 neurons.

Computer-generated holograms: application to intensity variable and wavelength demultiplexing holograms.

We report two kinds of Fresnel-type computer-generated hologram, namely, an intensity variable hologram and a wavelength demultiplexing hologram. The former shows that diffraction intensity can be controlled almost independently by the spatial frequencies of the holograms. The latter shows wavelength demultiplexing holograms. Combining the former intensity-controlled holograms, uniform diffraction intensity of different wavelengths can be realized.

Comparison of numerical simulation on active rectangular waveguide couplers by vector, scalar finite element, and effective refractive index methods.

We compare the vector finite element, scalar finite element, and effective refractive index methods for the calculation of the modal properties of active rectangular waveguide couplers. We find that the scalar finite element method is highly reliable when the refractive index difference between the core and the cladding is <15% and/or for large aspect ratios. We also find that the effective refractive index method is particularly difficult to use in treating active waveguides.

Numerical analyses of optically coupled active and passive dielectric slab waveguides for TM modes.

Propagation characteristics of optically coupled dielectric waveguides including active and passive waveguides are studied in terms of scalar and vector field finite element methods. First, characteristics of couplings for asymmetric passive waveguides, i.e., modal dispersions and field distributions, are obtained using a vector field finite element method. Second, a scalar field finite element method is applied to active coupled slab waveguides, and modal propagation characteristics, i.e., dispersion relationships, modal gains, phase characteristics, and electromagnetic field distributions, are investigated in detail. Characteristics depending on parameters such as gain, symmetrical conditions of waveguides, and numbers of waveguides are obtained. As a result, weak coupling phenomena due to unequal gains are observed and it is found that a modal gain depends on optical power confinement factors. In this paper only TM modes are treated, but our method can be used to obtain TE modes.

Analysis of almost-periodic distributed feedback slab waveguides via a fundamental matrix approach.

A unified approach to obtain the characteristics of almost-periodic grating slab waveguides including gain in the waveguide is reported. In this approach the waveguides are divided into short segments, and in each segment the gratings are assumed to be periodic, that is, parameters such as coupling coefficient, grating phase, deviations from the Bragg frequency, and gain in the waveguide are independent of a propagation direction z. Then characteristics of almost-periodic grating slab waveguides can be obtained by multiplying each F matrix of a short segment with the proper grating phase conditions at the interface between two adjacent segments. The appropriateness of this approach is shown for typical aperiodic grating waveguides such as tapered, chirped, and phase-shifted gratings. The results obtained by this method are compared with others and prove to be in good agreement with the results obtained by other methods. In addition to these characteristics, it is shown that the F matrix can be used to obtain the threshold conditions for distributed feedback laser oscillations including reflections from cleaved edges.