Microglial activation in facial motoneuron degeneration following facial nerve axotomy

의학과/석사[한글] 외상이나 종양 혹은 수술 등에 의해 발생할 수 있는 얼굴신경의 손상은 얼굴신경운동핵 내 신경세포의 퇴행성 변화를 일으킬 수 있다. 신경 손상에 따른 얼굴운동신경세포의 퇴행성 변화와 그 기전을 연구함에 있어서 얼굴신경절단 모델은 유용하게 사용된다. 특히 두개외 얼굴신경 절단을 시행할 경우 뇌-혈관 장벽의 손상 없이 신경아교세포의 반응을 연구할 수 있다는 장점이 있다. 본 실험의 목적은 두개골 밖에서 얼굴신경을 절단한 다음 얼굴운동신경세포의 퇴행성 변화와 그에 수반되는 activating transcription factor 3 (ATF3)와 phospho-c-Jun (pc-Jun)의 발현을 조사하여 이들 immediate early gene의 발현이 내포하는 기능적 의의를 추론하며, 신경세포사에 반응하여 활성화되는 미세아교세포의 기능적 역할을 면역조직화학적 방법으로 규명하는 것이다. 얼굴신경운동핵 내 신경세포의 수와 크기는 두개외 얼굴신경 절단 후 시간이 경과함에 따라 반대쪽에 비해 점진적으로 감소하였다. 얼굴운동신경세포의 수는 얼굴신경 절단 후 지속적으로 감소하여 16주와 24주에서는 반대쪽에 비해 각각 21.9%와 34.8%가 유의하게 감소하였다. 축삭 절단 후 초기에는 대다수의 얼굴운동신경세포 핵에서 ATF3와 pc-Jun이 발현되었지만, 흥미롭게도 얼굴신경 절단 8주 이후에는 매우 위축된 형태를 보이는 퇴행성 신경세포에서만 지속적으로 ATF3와 pc-Jun이 발현되었다. 신경 절단 후 2주 까지는 포식 활성의 표지자로 알려진 ED1의 면역 활성이 주로 미세아교세포의 세포체와 세포질돌기에 미세한 입자상으로 산재하였으며, 나중에는 phagosome으로 보이는 비교적 큰 구형의 입자들이 강한 ED1 면역반응성을 나타내었다. 신경 절단 후 초기에 ED1 면역반응세포의 수가 OX-6 면역반응세포 보다 훨씬 많은 것으로 보아 미세아교세포의 포식활성이 major histocompatibility complex II의 발현에 선행하는 것으로 생각되었다. 시간이 경과함에 따라 많은 활성 미세아교세포가 ED1과 OX-6에 모두 면역반응성을 나타내었고, 이들은 모두 굵은 세포질돌기를 가진 분지형 미세아교세포의 형태를 보였다. 이 분지형 활성 미세아교세포들은 얼굴운동신경세포를 밀접하게 둘러싸고 있었으며, 이들이 강한 ED1 면역반응성을 나타내는 것으로 보아 활발한 포식작용을 수행하고 있는 것으로 판단되었다. 그러나 아메바형 미세아교세포는 거의 관찰할 수 없었다. 이상의 결과는 두개골 밖에서 얼굴신경을 절단할 경우 일부 얼굴운동신경세포의 퇴행성 변화가 일어나고 ATF3와 pc-Jun의 지속적인 발현이 신경손상으로 유도된 퇴행성 변화 기전에 중요한 인자로 작용함을 나타내는 것이며, 아울러 이에 반응하여 활성화된 분지형 미세아교세포가 퇴행성 신경세포를 둘러싸서 포식작용을 수행함을 증명하는 것이다. [영문]Facial nerve injury caused by trauma, cancer, and surgery may exert degenerative effects on neurons of the facial motor nucleus. For studying nerve injury-induced changes and the underlying mechanisms in the facial motor nucleus, facial nerve axotomy model was found to be useful. One particular advantage of employing extracranial facial nerve axotomy is that one can study glial responses without damaging the blood-brain barrier. The purposes of this study were to investigate whether the extracranial axotomy produces any degenerative changes in the facial motor nucleus, and what mechanisms underlie the changes with focuses on functional roles of the immediate early genes such as activating transcriptional factor 3 (ATF3) and phospho c-Jun (pc-Jun), and microglial responses using immunohistochemical techniques. The extracranial facial nerve axotomy gradually decreased the number and size of neurons in the ipsilateral side of facial motor nucleus. 21.9% and 34.8% of the ipsilateral neuronal profiles were down-regulated at 16 and 24 weeks following the axotomy, respectively. At the early degenerative stage, most ipsilateral facial motoneurons expressed ATF3 and pc-Jun in the nuclei. However, both ATF3 and pc-Jun were expressed only in degenerative neurons showing severe morphological atrophy after 8 weeks post-lesion, while their expression has been disappeared in neurons with normal morphology. Immunoreactivity of the ED1, a phagocytic marker, was observed as small particles in the soma and cytoplasmic processes of ramified microglia by 2 weeks. Thereafter, relatively large, spheroidal bodies believed to be the phagosomes showed strong ED1 immunoreactivity. Microglial phagocytic activity was thought to precede the expression of major histocompatibility complex II, since the number of ED1-positive microglia was greater than that of the OX-6-positive ones at the early stage of neurodegeneration. Later, many activated microglia were double-labeled with ED1 and OX-6, and they showed ramified form with thick processes. Importantly, the OX-6-positive microglia intimately enclosed the facial motoneurons, and they were thought to be highly phagocytic because they showed strong ED1 immunoreactivity also. There was no amoeboid microglia in the ipsilateral facial motor nucleus. Taken together, these results suggest that the extracranial facial nerve axotomy produces degeneration of the facial motoneurons and the sustained expression of ATF3 and pc-Jun may play an important role in the neurodegenerative cascades caused by nerve injury. Also the present data demonstrates that activated but ramified microglia may phagocytose degenerating neurons.ope

An experimental study of relationship between pool boiling CHF and periodically modified surfaces by LASER processing

MasterBoiling heat transfer is one of the effective heat transfer methods because phase change from liquid to vapor is involved. Critical heat flux (CHF) is considered as an upper limit of boiling heat transfer because when CHF is reached, the heating surface is covered with a vapor layer and then temperature of the heating surface increases drastically. For this reason, there have been various researches to enhance CHF by modifying heating surfaces. Liter et al.(2001) produced modulated porous coated surfaces and their CHF are up to 3 times as high as that of the bare surface. Also, they obtain CHF model by modifying Zuber’s CHF model and its predictions showed good agreement with experimental results. This implies that flow modulation (periodic arrangement of vapor and liquid columns near CHF condition) is induced by periodically modified surface and periodicity of induced flow modulation is exactly identical to that of the surface. In this sense, periodic surface modification can be an effective approach to enhance CHF by changing flow modulation near the heating surface.Accordingly, the objective of this research is defined as to analyze the effects of parameters of periodic surface modification on CHF. Various periodically modified copper surfaces were produced by Nd:YAG laser and corresponding CHFs were obtained by pool boiling experiments for saturated water at atmospheric pressure. As a result, the surface with larger S (size of the modified region) and smaller G (gap between the modified regions) exhibits more enhanced CHF. In other words, virtual surface with high CHF is considered that thin grid of large periodicity is removed from fully modified surface. CHF enhancement by periodic surface modification can be explained that this thin grid disturbs coalescence between vapor columns and it delays complete vapor coverage on the heating surfaceCHF. Also, it is implied that there exist optimum value of parameter G and this means that there is the limit of CHF enhancement by decreasing G for given S