In this study, a three-dimensional finite-element model (FEM) of the human middle ear was established, including features of the middle ear which were not considered in the previous model, i.e., the ligaments, tendons, I-S joint, loading of the cochlea, external auditory meatus (EAM), middle-ear cavities, etc. The unknown mechanical properties of these parts and the boundary conditions were determined so that the impedance obtained from the FEM analysis resembled the measurement values. The validity of this model was confirmed by comparing the motion of the tympanic membrane and ossicles obtained by this model with the measurement data, and the effects of the newly considered features on the numerically obtained results were examined. By taking the ligaments and tendons into account and assuming that the cochlea acts as a damper, with this model it was possible to realistically reproduce complex ossicular chain movement. It was found that the middle-ear cavities did not affect the vibration mode of the tympanic membrane. Although the EAM enhanced the sound pressure applied to the tympanic membrane compared with that at the entrance of the EAM, the pressure distribution on the surface of the tympanic membrane was not affected by the EAM.
Detailed information on innervation of the histaminergic system in the brain is essential to an understanding of the physiological roles of this system. In a previous immunocytochemical study with antihistidine decarboxylase (HDC) antibody, we detected extensive networks of histaminergic fibers in many areas of the rat brain (Watanabe et al., '84). In the present study, we improved the immunocytochemical procedure and examined the detailed distribution of histaminergic innervation in the rat brain with anti-HDC antibody. As reported previously, the highest concentrations of fibers were found in the hypothalamic nuclei and medial forebrain bundle. With the modified procedure, we detected more dense networks of HDC-immunoreactive (HDCI) fibers. Furthermore, we demonstrated for the first time the existence of HDCI fibers in other regions, namely, the thalamic nuclei, median eminence, fimbria of the hippocampus, habenular nuclei, superior colliculus, nucleus of the optic tract, parabrachial nuclei, mesencephalic trigeminal nucleus, superior, lateral, and spinal vestibular nuclei, posterior lobe of the hypophysis, and vascular organ of the lamina terminalis. We also found dense transverse fibers in the retrochiasmatic area and supraoptic decussation, which suggests bilateral innervation of the histaminergic system. These results indicate that innervation of the rat brain by the histaminergic system is more extensive than observed previously.
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