| Purpose Ependyma is lined in lumen surface of brain's ventricles which is composed of single ciliated cuboidal epithelium and a major component of brain csf barrier(BCB) and blood csf barrier(BlCB).It plays an important role in production of csf,signal traiisttiission,maintainance of homeostasis within the brain ,and so on ,and a focus of developing pathway both for administration of some drugs into the brain and treatment of brain's diseases.Ependyma may be specified in some sites perhaps owing to functional need and modified its structures of cells and tissue,which hasbeen called circumventricular organs(CVOs)since 50 of 20 century. In mammals CVOs include subfomical organ(SFO), organum vesolum lamina terminalis(OVTT), median eminence (MR) , subcommissural organ(SCO),recess of pineal gland(RPG),paraventricular organ(PVO),and area postrema(AP).Also neurohypophysis,choroids plexes,and pineal gland are recognized as CVOs by some researchers. PVO located at central part of lateral wall of the third ventricle on a line between anterior commissure and posterior border of mammillary body.Ependyma of PVO is an epithelium with multiple layers,and in subependymal layer neuroglial cells are fewer, dendrites of some neurons could extend into the cavity of the third ventricle via a gap between ependymal cells.In fishes angio-capsule and urophyse are believed also as CVOs,the former locates just behind neurohypophysis and posterior end of infundibulum stem,ependyma of it is composed of so-called royal-crown cells and supporting cells ;and the latter locates ventral to the central canal of caudal spinal cord and is an eminence of hemispherical form.In birds the lumbalwulst also belongs to CVO and locates at posterior median sulcus oflumbosacral spinal cord,which may contain large amount of glycogen and gelatin-like tissue .Up to now it has been known functional roles ofependyma and CVOs not enough.Until 90 of 20 center studies on CVOs had been concentrated in their roles of maintaining homeostasis and neuroendocrine modulation. Since 90th of 20 centery it has began to interest in their roles in neuroimmune modulation.As far as the supraependymal structures are concerned,such as supraependymal cells,fibers,and csf-contacting neurons they has been interest in their functions of neurohumoral modulation and in roles within neuro-endoerine-immune network.Because CVOs locate just at signal exchanging sites among blood,brain tissue and csf ,their special locations may determine their decisive roles in neuro-endocrine-immune modulation. So lateral recess of Ihe foulh ventricle and median eminence of the third ventricle were observed in young,adult and aging rats with light and electron microscopy systemically.MATERIAL AND METHODS Normal rats of male SD were divided into young,adult, and aging groups.Preparation of samples for light microscopy: animals were anesthetized by peritoneal injection of 6% chloral hydrate(0.5ml/100g body weight).Perfusion and fixation of animals were carried out by a common procedure: 37 normal saline 50-100 ml and then 4% paraformaldehyde PBS 100-400ml were perfused through the left ventricle of the heart,the whole procedure was lasted for about SOmin.the entire brain was dissected out and dipped in the fixative solution for 12h at 4.Brain pieces targeted were choosen and then passed the graded alcohols for dehydration,dipping into paraffin for embeding,and reshaping the pieces. Serial paraffin sections were cut with paraffin microtome(LEICA),thickness of which were 5 y m and 2 n m.Mounting the sections on slides with protein and glycerol and then put them in 60 baker overnight. The mounted sections were dewaxed in xylene and passed in graded alcohols for pcrmutation,dip in distilled watcr.H.E staining was proceeded,then dehydrated in graded alcohols , cleared in xylene, and sealed8with neutralized resin. The sections were observed under microscope of Olympus New Vanox.ana Preparation of samples for SEM observation:anaesthesia and perfusion and fixation procedures were same as that...
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