The pia mater at the site of the entry of blood vessels into the central nervous system

Summary The entry of blood vessels into the central nervous system (CNS) has been studied at the surface of the brain stem and the spinal cord of two cats and two rabbits. The study was carried out by scanning electron microscopy (SEM). The results obtained by SEM concerning the layers of the pia mater corresponded to those obtained by other authors who used transmission electron microscopy. Between the basal lamina of the superficial glial membrane of the CNS and the cells lining the subarachnoid space, a pial connective tissue space could be clearly recognized. The blood vessles crossing the subarachnoid space were also covered by leptomeningeal lining cells. At the site of entry of these blood vessels into the pia mater their cellular coverings were reflected onto the pial surface. At this point, some vessels were partly surrounded by a small depression of the surface of the pia mater. Having crossed the pial connective tissue space the vessel enters a funnel-shaped channel that leads into the CNS. Within this channel, the vessel is surrounded by pial connective tissue. The outer wall of the channel consists of the basal lamina of the superficial glial membrane. The outer surface of the vessel is also covered by a homogeneous membrane, interpreted as being the basal lamina of the tunica media or, if the tunica media was absent, that of the tunica intima. Only in two instances could it be noted that an entering vessel was surrounded by deep recesses of the surface of the pia mater. In one of these cases, not too deep in the recess to prevent examination by SEM, it could be seen that the cellular coverings of the outer wall of the vessel were reflected onto the layer of the pial lining cells. This observation would indicate that also the deeper perivascular depressions of the pial surface probably do not conform to the classic concept of the Piatrichter (funnel-shaped perivascular depression of the subarachnoid space communicating with the perivascular space of intracerebral vessels). This mode of entry of blood vessels, commonly described in text-books, could not be substantiated by this study.     

Morphological indications for considerable diffuse reabsorption of cerebrospinal fluid in spinal meninges particularly in the areas of meningeal funnels

Transmission and scanning electron microscopical observations in the rat indicate a considerable capacity of the spinal meninges to reabsorb cerebrospinal fluid. The density of blood vessels and lymphatics in the duramater is extremely high, particularly in the areas of meningeal funnels and spinal nerve root sleeves. Arterioles with closely related unmyelinated nerve fibres, many fenestrated capillaries and venules predetermine these areas as sites where absorption processes could take place. At certain sites of the meningeal angle region, the arachnoid membrane, mostly multilayered, is reduced to only three or four layers. Intercellular discontinuities and cytoplasmic fenestrations occurring in the arachnoid lining cell layer result in direct communications between the subarachnoid space and cisterns of the arachnoid reticular layer. These cisterns are partly fluid-filled, partly occupied by a net of collagen fibre bundles. Some cisterns harbour macrophages that often project filiform processes through the lining cell layer into the subarachnoid space, contacting cerebrospinal fluid. Desmosomes and gap junctions are present in all layers of the arachnoid. However, tight junctions and the continuous electrondense intercellular gap, known to occur normally within the arachnoid barrier layer, were not seen in many sites of the meningeal angle region. Numerous arachnoid cells display a high degree of vesiculation. Cationized ferritin, introduced in vivo into the rat subarachnoid space, passes inter- and intracellularly from the cerebrospinal fluid compartment through the arachnoid membrane, reaching durai blood vessels and lymphatics. Tracer could be visualized both in the cytoplasm of the endothelium and on the luminal surface of the cells. Tracer also passed through pial cell layers into pial vessels, through leptomeningeal sheaths into vessels crossing the subarachnoid space, into the connective tissue compartment and into vessels of spinal dorsal root ganglia. In the angle region, a particularly large number of macrophages can be found on the surface of leptomeninges, within the arachnoid reticular layers, and in close relation to dural and epidural capillaries, venules and lymphatics. Their possible role in the process of cerebrospinal fluid reabsorption is discussed.     

Glial bridges and Schwann cell migration during chronic demyelination in the C.N.S.

Summary The formation of fibrotic bridges from subpial astrocytes into the subarachnoid space of the spinal cord and the migration of Schwann cells to the central nervous system (C.N.S.) is appraised in chronically demyelinated C.N.S. lesions. Spinal cord tissue was studied from inbred, Strain 13 guinea pigs with chronic experimental allergic encephalomyelitis (EAE). It has been found that uncommitted Schwann cells are present around remyelinated fibres in nerve root entry zones, between meningeal cells at a distance from the roots and along blood vessels within the spinal cord parenchyma. It is speculated that these cells migrate via the above route to the C.N.S. In the present model, this invasion might be aided by glial fibrosis, a process which leads to surface irregularities in the spinal cord, an extensive extracellular space and possible breaches in the glia limitans through which Schwann cells might penetrate.     

Blood vessels and tissue space associated with the brain of the rat

Tissues from adult Sprague-Dawley rats fixed by perfusion with buffered aldehydes for a combined study of the vascular system of the brain are described in light and electron microscopy. In these preparations lack of shrinkage prevents the formation of perineuronal and perivascular spaces. However, connective tissue stains indicate restricted tissue space along the course of small arteries and veins. In fine structure this space is found within the walls of the vessels. It consists of a tubular extension of tissue space bounded inwardly by the endothelial boundary (basement) membrane and outwardly by the neural boundary membrane. Between these boundaries the formed elements of the media and the adventitia are found. The media consists of a thin layer of smooth muscle cells; each cells being enclosed in its own boundary membrane. The adventitia consists of cells and fibrous elements of the connective tissues which are derived, near the surface of the brain, from the intermingling of pial and vascular leptomeninges. This “neural” portion of the tissue space extends from the depths of the capillary bed (where it is obliterated by the fusion of boundary membranes), along the course of the blood vessels, through the subarachnoid space and into the general tissue space of the body.     

Electron microscopic study of cat meninges

The intervascular portions of the encephalic dura mater, arachnoid membrane and pia mater were studied with special reference to their spatial relationships. The cell types were analyzed at electron microscopic level. An outer dural layer, composed of typically elongated fibroblasts and large intercellular spaces was identified. The middle dural layer was composed of collagenous connective tissue matrix together with some fibrocytes scattered in it. The inner dural layer showed epithelium-like arranged cells with light cytoplasm and long processes. The electron-dense band, measuring about 20 nm in width, located between dura mater and arachnoid was not so prominent as in the previously investigated experimental animals. The intercellular contacts among the cells of the outer arachnoid layer included maculae and zonulae adherentes and gap junctions mainly, while the tight junctions observed were quite rare. Following the arachnoid trabecular layer, an inner arachnoid layer could be hardly demonstrated. The pial cells were differentiated into 2 distinct layers, bordering the narrow and discontinuous pial space.     

与胸12,腰1椎骨对应的腰骶神经根的应用解剖

在２０具（男１６，女４）成人尸体上，对胸１２、腰１椎骨对应的蛛网膜下隙内脊髓节、脊神经前、后根进行了应用解剖学研究。结果胸１２椎骨多与腰２￣５脊髓节、胸１２￣腰５神经根对应；腰１椎骨与骶１￣尾脊髓节、腰１￣尾脊神经根对应，据此，损伤时利于定位诊断。腰１￣３脊神经根远侧段与腰４￣骶３的近侧段之间常有一定长度的重叠，重叠的长度供神经缝接参考。文内还对神经根排列位置，前、后根的数目、长度和外径等进行了观     

Microscopic morphology and histology of the human meninges

The meninges comprise the dura mater and the leptomeninges (arachnoid and pia mater). Dura forms an outer endosteal layer related to the bones of the skull and spine and an inner layer closely applied to the arachnoid mater. Leptomeninges have multiple functions and anatomical relationships. The outer parietal layer of arachnoid is impermeable to CSF due to tight intercellular junctions; elsewhere leptomeningeal cells form demosomes and gap junctions. Trabeculae of leptomeninges compartmentalize the subarachnoid space and join the pia to arachnoid mater. In bacterial meningitis leptomeningeal cells secrete cytokines. Pia mater is reflected from the surface of the brain and spinal cord onto arteries and veins, thus separating the subarachnoid space from the brain and cord. A sheath of leptomeninges accompanies arteries into the brain and is related to the pathways for the drainage of interstitial fluid that play a role in inflammatory responses in the brain and appear to be blocked by amyloid-beta in Alzheimer's disease. Specialised leptomeningeal cells in the stroma of the choroid plexus form collagen whorls that become calcified with age. Leptomeningeal cells also form channels in the core and apical cap of arachnoid granulations for the drainage of CSF into venous sinuses. In the spine, leptomeninges form highly perforated intermediate sheets of arachnoid and delicate ligaments that compartmentalize the subarachnoid space; dentate ligaments anchor subpial collagen to the dura mater and stabilize the spinal cord. Despite the multiple anatomical arrangements and physiological functions, leptomeningeal cells retain many histological features that are similar from site to site.     

大鼠松果体分泌物释放到蛛网膜下隙脑脊液途径的电镜研究

为探讨松果体分泌物在细胞外转运到蛛网膜下隙脑脊液途径的结构基础,本研究运用透射电镜技术对成年大鼠松果体浅部进行了观察。结果显示:(1)大鼠松果体毛细血管为有孔型(孔径50nm),借基膜与宽阔的血管周隙分隔;(2)松果体细胞借基膜与结缔组织间隙分隔,松果体细胞之间形成与松果体囊结缔组织间隙及血管周隙相通的细胞间小管;(3)松果体囊表面为扁平上皮,上皮下为疏松结缔组织间隙,其内可见松果体细胞的胞体和突起。囊上皮细胞间存在瓣膜样连接(叶瓣间宽处可达1μm)和囊上皮孔(2.5μm)。以上结果提示,松果体细胞表面可分为结缔组织间隙面、连接面和细胞间小管面三个功能面,松果体分泌物可能通过血管周隙-细胞间小管-松果体囊结缔组织间隙-囊上皮瓣膜样连接或囊上皮孔,释放入蛛网膜下隙脑脊液中转运。     

Observations of vascularization in the spinal cord of mouse embryos, with special reference to development of boundary membranes and perivascular spaces

The early stages of vascularizations of the spinal cord of the mouse were studied by graphic reconstruction techniques and electron microscopy. Vascular sprouts arise from the perineural vascular plexus (PNVP) to invade the cord of 10-day embryos. These enter the cord most frequently via the lateral surface between the dorsal root and the ventral root; less frequently, they enter via the ventral and/or dorsal surfaces and anastomose with sprouts that have entered via the lateral surface. During the development of intramedullary blood vessels there are essential changes both in the basal laminae covering the neural parenchyma of the cord and in the relationship between the neural tissue and vascular walls. The basal laminae of the developing spinal cord were classified into three categories. The first is the perineural, external, or primary neural, basal lamina (PNBL), which is the earliest of the three in formation and covers the entire external surface of the cord. The second one is the internal, or secondary neural, basal lamina (INBL), which invests the internal surface of the neural tissue facing the walls of invading blood vessels. The third type is the perivascular basal lamina (PVBL), which surrounds the vascular wall. Blood vessels enter the spinal cord by penetrating the PNBL. Since the PVBL and INBL are absent or incomplete in early stages of vascularization, the neural tissue is in direct contact with intramedullary blood vessels. However, following their development, boundary membranes are formed, separating the neural tissue from neighboring vessels, a situation characteristic of capillaries in the mature CNS. Perivascular spaces are seen along the course of developing vessels and secondarily become continuous with the extramedullary connective tissue space. They are neither artifact nor intramedullary extensions of extramedullary connective tissue space along invading sprouts. The boundary membranes are formed by connection of membrane plaques or by fusion of the INBL and PVBL.     

Plastic repair of the deferent duct with a silicone tubular prosthesis under conditions of a chronic experiment on laboratory animals

A connective tissue capsule consisting of a thin layer of the connective tissue envelopes the prosthesis by the end of week 1 after replacement of a part of the deferent duct with a silicone tubular prosthesis under conditions of a chronic experiment. By days 17–20 postoperation, two layers are clearly differentiated in the capsule: the outer layer consisted of a thin layer of connective tissue and the inner one consisted of compact connective tissue. The space between the silicone prosthesis and the connective tissue capsule is filled with the seminal fluid. Obturation of the deferent duct forms because of formation of internal spermatogranulomas and atypical growth of the deferent duct epithelium adhering to the prosthesis wall. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 144, No. 7, pp. 103–107, July, 2007     

Distribution of connective tissue proteins in chick muscle spindles as revealed by monoclonal antibodies: A unique distribution of brachionectin/tenascin

The distribution in chick muscle spindles of eight connective tissue proteins (collagen types I, IV, V, and VI, laminin, heparan sulfate, fibronectin, and brachionectin/tenascin) was examined by immunofluorescent histochemistry. Intrafusal fibers were surrounded by layers of collagen type VI and fibronectin, and by an external lamina containing collagen type IV, laminin, and heppran sulfate. Most of these layers displayed a different pattern of staining at the sensory region of the equator than at the polar region. The crescent-like sheath that caps each intrafusal fiber and sensory terminal at the equator was strongly positive for collagen type I and weakly positive for collagen type V. The outer spindle capsule contained laminin, heparan sulfate, collagen types IV and VI, brachionectin/tenascin, fibronectin, and to a lesser degree also collagen types I and V. Brachionectin/tenascin had the narrowest distribution of any of the connective tissue macromolecules studied. It was found only in the outer capsule and in the coverings of blood vessels and nerves associated with the outer capsule.     

The elasmobranch kidney

Summary In the kidney of two elasmobranch fish, the little skate (Raja erinacea) and the spiny dogfish (Squalus acanthias), each tubular bundle is wrapped by a continuous sheath of extremely flattened cells which are ordered in several closely superimposed layers. Thin sections and freeze-fracture replicas demonstrate that extensive tight functions exist between the cells of this peritubular sheath. The sheath cells lie on a discontinuous basement membrane which suggests that they do not belong to the connective tissue. Conceivably, each peritubular sheath segregates the milieu inside the sheath (surrounding the bundle of 5 tubules bules and capillaries which form the countercurrent system) from the milieu outside the sheath (connective tissue matrix in which the bundles are embedded).Supported in part by National Institutes of Health AM 06345 and by Deutsche Forschungsgemeinschaft (Sonderforschungs-bereich 146)Alexander von Humboldt Fellow     

The association of octopamine with specific neurones along lobster nerve trunks.

Octapamine and its synthetic enzyme, tyramine beta-hydroxylase (TBH), are found in high concentrations at two points along second thoracic nerve roots in lobsters. The first is in the proximal section of the second root between the ventral nerve cord and the bifurcation of the root into medial (to flexor muscles) and lateral (to extensors) branches. The second region of high concentration is within a well known crustacean neurosecretory system, the pericardial organ, located close to the ends of the lateral branches of the roots. 2. With several different staining procedures, small clusters of nerve cell bodies are found within the connective tissue sheath in the proximal regions of the second roots. No cell bodies are seen in the pericardial organ regions. Cell bodies are variable in number and position between corresponding roots in the same animal and homologous roots among different animals. The average numbers of cell bodies, however, correlate well with TBH and octopamine content, and with the synthesis of octopamine in these same regions of roots. 3. Small clusters of root cell bodies dissected from preparations have greater than 500-fold higher activities of TBH than isolated efferent excitatory and inhibitory or afferent sensory axons. 4. Along with octopamine, the preferential synthesis of acetylcholine and serotonin is also seen in proximal segments of roots. Acetylcholine synthesis in these regions may represent transmitter synthesized in the nerve terminals innervating the root cells. The role of serotonin in these regions is not understood at this time but the amounts of endogenous serotonin found are only a tenth of the amounts of octopamine present. 5. Dopamine is not synthesized from tyrosine in second thoracic roots. However, if DOPA or dopamine are used as precursor compounds, then noradrenaline, which is usually not found in lobsters, can be accumulated in proximal segments of roots. 6. Phenolamines are converted to two further metabolites by lobster tissues. The compounds are unidentified and are named fast and slow product on the basis of their migration on electrophoresis at acid pH. Some partial characterization of slow product reveals that it is a mixture of compounds that can be converted on mild acid hydrolysis to fast product and the parent phenolamine. 7. The several lines of evidence presented suggest that nerve cells found in the proximal segments of the second thoracic roots contain and can synthesize octopamine. Since not all the cells in any single root have been analysed for octopamine or TBH, however, the possibility that one or more of the cells contain physiologically interesting substances other than octopamine is not eliminated.     

Innervation of the vibrissae of the California sea lion,Zalophus californianus

The vibrissae of the California sea lion are richly innervated with myelinated fibers that terminate in three distinctly different endings. Large nerve bundles enter the base of the follicle and immediately branch into smaller bundles that traverse the connective tissue trabeculae below the large ring sinus. Some neurons terminate in a lamellated corpuscle in close relationship to the venous sinuses of the proximal cavernous tissues. The remainder of the nerves continue distally parallel to the glassy membrane terminating in two specific types of endings arranged in a ring about the shaft of the vibrissae at the level of the upper portion of the ring sinus. One type of ending is on the outer surface of the glassy membrane where the myelin sheath terminates abruptly and the sensory ending is flattened into a thick, lancet-shaped structure. An extension of cytoplasm from a specialized supportive cell covers this terminal segment of the nerve on two sides, while numerous finger-like extensions protrude into the connective tissue from the narrow, uncovered sides. The second type of ending penetrates the glassy membrane, branches, and terminates in close apposition to the Merkel cells in the outer root sheath. Amyelinated nerves of various sizes are frequently observed in the same bundles as the larger myelinated fibers, but to date, the position of their termination has not been established.     

The role of fasciae in Civinini–Morton's syndrome

This study evaluates the pathogenetic role of the perineural connective tissue and foot fasciae in Civinini–Morton's neuroma. Eleven feet (seven male, four female; mean age: 70.9 years) were dissected to analyse the anatomy of inter‐metatarsal space, particularly the dorsal and plantar fasciae and metatarsal transverse ligament (DMTL). The macrosections were prepared for microscopic analysis. Ten Civinini–Morton neuromas obtained from surgery were also analysed. Magnetic resonance images (MRIs) from 40 patients and 29 controls were compared. Dissections showed that the width of the inter‐metatarsal space is established by two fibrous structures: the dorsal foot fascia and the DMTL, which, together, connect the metatarsal bones and resist their splaying. Interosseous muscles spread out into the dorsal fascia of the foot, defining its basal tension. The common digital plantar nerve (CDPN) is encased in concentric layers of fibrous and loose connective tissue, continuous with the vascular sheath and deep foot fascia. Outside this sheath, fibroelastic septa, from DMTL to plantar fascia, and little fat lobules are present, further protecting the nerve against compressive stress. The MRI study revealed high inter‐individual variability in the forefoot structures, although only the thickness of the dorsal fascia represented a statistically significant difference between cases and controls. It was hypothesized that alterations in foot support and altered biomechanics act on the interosseous muscles, increasing the stiffness of the dorsal fascia, particularly at the points where these muscles are inserted. Chronic rigidity of this fascia increases the stiffness of the inter‐metatarsal space, leading to entrapment of the CDPN.     

胸腰骶段脊神经根鞘结构的解剖学和组织学研究

目的　明确胸腰骶部不同节段脊神经根鞘的解剖学和组织学结构及其分布特点,探讨其临床意义。 方法　取7例成人脊柱标本,解剖观察胸腰骶部不同节段神经根鞘的硬脊膜囊开口方式,并制成组织切片后显微镜下观察神经根鞘的结构。 结果　胸腰段神经根鞘存在单孔和双孔两种硬脊膜囊开口方式,而骶段神经根鞘只存在单孔开口方式;单孔根鞘又根据前、后根之间有无双层袖套结构分为Ⅰ型和Ⅱ型。较之神经根其他部位,神经节处硬脊膜袖套的胶原纤维层少且结合疏松。腰4/5和骶1~5节段神经节处的硬脊膜袖套的厚度比其他节段更薄（F=37.31,P<0.01）。神经根袖套下腔隙终止于神经节。 结论　Ⅰ型和Ⅱ型神经根鞘在各节段的分布规律,解释了腰骶部神经根受压时多表现为感觉和运动功能同时受累的现象;而神经节处的硬脊膜袖套在下腰骶节段最薄的特点,也和腰腿痛高发的现象相关系。脊神经节是脊神经根开始转化为脊神经的标志。     

Scanning electron microscopy of the subarachnoid space in the dog: Evidence for a non-hematogenous origin of subarachnoid macrophages

Injection of viable BCG into the subarachnoid space of immunized and non-immunized dogs produced a 10-fold increase in the populations of pial free cells. In immunized animals injected three days previously with BCG, stereoscopic SEM revealed that many pial cells had rounded up and were protruding into the subarachnoid space. With continued rounding these cells took on amoeboid characteristics, with shapes that suggested a capacity for cell movement. Internally, these pial cells possessed an increased volume of perinuclear cytoplasm and organelles. Reactive pial cells could be distinguished from macrophages of presumed hematogenous origin on the basis of their surface morphology. These findings suggested that pial cells had the ability to alter their normal structural and behavioral characteristics and to become macrophage-like under these conditions of secondary challenge by BCG.     

Spatial distribution of postotic crest cells defines the head/trunk interface of the vertebrate body: embryological interpretation of peripheral nerve morphology and evolution of the vertebrate head

Vascular arrangements allowing a bulky transfer of venous blood from the skin of the head and from nasal and paranasal mucous membranes to the dura mater provide an excellent anatomical basis for the convection process of cooling, caused by evaporation of sweat or mucus. The dura mater, with its extraordinarily high vascularization controlled by a potent vasomotor apparatus, may transmit temperature changes to the cerebrospinal fluid (CSF) compartment. Temperature gradients of the CSF may in turn influence the temperature of brain parenchyma (1) directly, along the extensive contact area between the cerebrocortical surface and the CSF-compartment, or (2) indirectly, via brain arteries that extend over long distances and arborize within the subarachnoid space before entering the pial vascular network and brain parenchyma. Numerous subarachnoid and pial arterial branches exposed to the CSF have diameters in the range of the vessels of the retia mirabilia of animals in which selective brain cooling has been clearly established experimentally. It is also shown that the arrangements of venous plexuses within the vertebral canal provide anatomical preconditions for a cooling of the spinal cord via the CSF. The possibility of spinal cord and spinal ganglia cooling by temperature convection via venous blood — cooled in the venous networks of the skin of the backflowing through numerous anastomoses to the external and internal vertebral plexuses and, finally, into the vascular bed of the spinal dura is discussed on the basis of anatomical facts.     

椎管与内容物相互关系的研究

用30条已防腐的成人脊柱,从椎间盘处横锯,测量了各段椎管与内容物的矢径。椎管内硬膜前组织较薄,一般不超过2.0mm,硬膜后组织,由上向下逐渐变厚。椎管与硬膜囊的比值(矢状径)颈段为1:0.73,胸段1:0.68,腰段为1:0.60。从本组材料看,C_(3-5)椎骨段有50％以上椎管矢径较细窄,蛛网膜下腔亦较窄,故受压后缓冲余地小,易出现症状。腰段由上向下硬膜囊的逐渐变小,周围组织逐渐增多,故不易受压。