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  • Author or Editor: Norihito Shimamura x
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Norihito Shimamura, Tetsuji Sekiya, Akinori Yagihashi and Shigeharu Suzuki

Object. It has been empirically recognized that the cochlear nerve is highly vulnerable to traumatic stress resulting from surgical procedures; therefore, careful manipulation of the cochlear nerve is mandatory in preventing trauma-induced hearing loss during cerebellopontine angle (CPA) surgery. There is, however, no precise knowledge about the temporal pattern of cochlear nerve degeneration following trauma. This study was performed to determine the temporal pattern of injury that occurs after cochlear nerve trauma, knowledge of which is indispensable not only to neurosurgeons but also to all those who manage lesions involving the cochlear nerve.

Methods. Right suboccipital craniectomies were performed in groups of rats with the aid of a surgical microscope, and the seventh and eighth cranial nerve trunks were identified at the internal auditory meatus. The cochlear nerve was quantifiably compressed while compound action potentials of the cochlear nerve were monitored and recorded. Following injury, one group of rats was killed for histological examination at the end of each week for 4 weeks. Data from this study disclosed that the degeneration of the compressed cochlear nerve progressed in a relatively rapid manner and was complete within 1 week after the insult. The main pathophysiological mechanisms responsible for cochlear neuronal death in this experimental setting appeared to be necrosis, and an apoptotic mechanism seemed to play a subsidiary role.

Conclusions. Accurate knowledge about the temporal profile of trauma-induced cochlear nerve degeneration is closely linked with the problem of the therapeutic time window. The results of the present study indicated that any measures to ameliorate cochlear nerve degeneration following trauma should be started as early as possible (within 1 week) after an injury.

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Tetsuji Sekiya, Norihito Shimamura, Toru Hatayama and Shigeharu Suzuki

Object. Cochlear neurons are inevitably exposed to traumatic stress during surgical removal of an acoustic neuroma; that event is an important cause of postoperative cochlear neuronal degeneration, with subsequent loss of spiral ganglion cells (SGCs). The object of this study was to investigate whether preoperative pharmacological treatment can enhance the resistance of cochlear neurons to the traumatic stress of surgery.

Methods. Cochlear neuronal degeneration was induced in 17 rats by controlled compression of the cerebellopontine angle portion of the cochlear nerve. Dizocilpine maleate (MK-801; 10 mg/kg), an N-methyl-d-aspartate (NMDA) antagonist, was administered intraperitoneally to six of the 17 rats 30 minutes before compression occurred. Two weeks after compression, each rat was killed, and the numbers of SGCs in histological preparations of temporal bones were counted.

Conclusions. Spiral ganglion cells were more numerous in rats administered dizocilpine maleate (p < 0.03) than in rats that did not receive treatment, indicating that receptor-mediated glutamate neurotoxicity may participate in the pathogenesis of trauma-induced cochlear neuron death and that administration of an NMDA antagonist before surgery may protect the nerve from injury leading to hearing loss.

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Naoya Matsuda, Hiroki Ohkuma, Masato Naraoka, Akira Munakata, Norihito Shimamura and Kenichiro Asano

Object

Cerebral vasospasm after subarachnoid hemorrhage (SAH) is a serious complication. Free radicals derived from subarachnoid clotting are recognized to play an important role. Oxidized low-density lipoprotein (ox-LDL) and lectin-like oxidized LDL receptor-1 (LOX-1) have been shown to be related to the pathogenesis of atherosclerosis and may increase in cerebral arteries after SAH, due to the action of free radicals derived from a subarachnoid clot. These molecules may also affect the pathogenesis of vasospasm, generating intracellular reactive oxygen species and downregulating the expression of endothelial NO synthase (eNOS). If so, apple polyphenol might be effective in the prevention of vasospasm due to an abundant content of procyanidins, which exhibit strong radical scavenging effects, and the ability to suppress ox-LDL and LOX-1. The purposes of this study were to investigate changes in levels of ox-LDL and LOX-1 after SAH and whether administering apple polyphenol can modify cerebral vasospasm.

Methods

Forty Japanese white rabbits were assigned randomly to 4 groups: an SAH group (n = 10); a shamoperation group (n = 10), which underwent intracisternal saline injection; a low-dose polyphenol group (n = 10) with SAH and oral administration of apple polyphenol at 10 mg/kg per day from Day 0 to Day 3; and a high-dose polyphenol group (n = 10) with SAH and oral administration of apple polyphenol at 50 mg/kg per day. At Day 4, the basilar artery and brain was excised from each rabbit. The degree of cerebral vasospasm was evaluated by measuring the cross-sectional area of each basilar artery, and the expression of ox-LDL, LOX-1, and eNOS was examined for each basilar artery by immunohistochemical staining and reverse transcriptase polymerase chain reaction. In addition, neuronal apoptosis in the cerebral cortex was evaluated by TUNEL.

Results

Compared with the sham group, the expression of ox-LDL and LOX-1 in the basilar arterial wall was significantly increased in the SAH group, the expression of eNOS was significantly decreased, and the cross-sectional area of basilar artery was significantly decreased. Compared with the SAH group, the cross-sectional area of basilar artery was increased in the polyphenol groups, together with the decreased expression of ox-LDL and LOX-1 and the increased expression of eNOS. In the high-dose polyphenol group, those changes were statistically significant compared with the SAH group. In the low-dose polyphenol group, those changes were smaller than in the high-dose polyphenol group. No apoptosis and no changes were seen in the cerebral cortex in all groups.

Conclusions

This is the first study suggesting that ox-LDL and LOX-1 increase due to SAH and that they may play a role in the pathogenesis of vasospasm. It is assumed that procyanidins in apple polyphenol may inhibit a vicious cycle of ox-LDL, LOX-1, and ROS in a dose-dependent manner. Apple polyphenol is a candidate for preventive treatment of cerebral vasospasm.