Functional ultrastructure of cerebrospinal fluid drainage channels in human arachnoid villi

The functional ultrastructure of the human arachnoid villi was studied to clarify drainage channels of cerebrospinal fluid (CSF). The apical portion of each villus was usually covered by the arachnoid cell layer alone with no endothelial investment, whereas most of the stromal central core was further encompassed by a fibrous capsule with an endothelial investment. Accordingly, the CSF-blood interface was assumed to be in both the endothelial cells and the arachnoid cell layer. The former were characterized by abundant micropinocytotic vesicles and occasional intracytoplasmic vacuoles, whereas the latter was characterized by numerous extracellular cisterns measuring 10 micron in maximal diameter. There were no free communications such as endothelial open junctions or endothelium-lined tubules. In the villi affected by subarachnoid hemorrhage, endothelial cells were intact and continuous despite the erythrocyte-packed subendothelial space, which appeared to be on the verge of rupturing. Intracytoplasmic vacuoles, measuring less than 1 micron diameter, sometimes contained serum protein-like substance. Furthermore, the extracellular cisterns were distended by intact or disintegrating erythrocytes that served as a natural tracer, suggesting CSF drainage channels. It is conceivable that, in human arachnoid villi, the extracellular cisterns of the arachnoid cell layer contribute to the passive transport of CSF, whereas micropinocytosis and vacuolization mechanisms of the endothelial cells are available for active transport.     

Arachnoid villi affected by subarachnoid pressure and haemorrhage

The arachnoid villi of 18 dogs were studied. The authors confirmed the pressure gradient changes of the morphology of arachnoid villi of dogs with the scanning electron microscope (SEM). A subarachnoid infusion with 5--10 times higher pressure gradient than the physiological one, tore the superficial endothelial layer from the villi, and the inner part could also be observed stereoscopically. On the surface of the arachnoid villi, the authors observed microvilli, openings of vacuoles and intercellular gaps, but did not find openings of performed channels. After subarachnoid haemorrhage (SAH) generally the villi were blocked but the authors have observed a red blood cell escaping from a villus intercellularly.     

Human arachnoid villi response to subarachnoid hemorrhage: possible relationship to chronic hydrocephalus.

OBJECT: The origin of chronic communicating hydrocephalus following subarachnoid hemorrhage (SAH) is not well understood. Fibrosis of the arachnoid villi has been suggested as the cause for obstruction of cerebrospinal fluid (CSF) flow, but this is not well supported in the literature. The goal of this study was to determine the relationship between blood, inflammation, and cellular proliferation in arachnoid villi after SAH. METHODS: Arachnoid villi from 50 adult patients were sampled at autopsy. All specimens were subjected to a variety of histochemical and immunohistochemical stains. The 23 cases of SAH consisted of patients in whom an autopsy was performed 12 hours to 34 years post-SAH. Fifteen cases were identified as moderate-to-severe SAH, with varying degrees of hydrocephalus. In comparison with 27 age-matched non-SAH controls, the authors observed blood and inflammation within the arachnoid villi during the 1st week after SAH. Greater mitotic activity was also noted among arachnoid cap cells. The patient with chronic SAH presented with ventriculomegaly 2 months post-SAH and exhibited remarkable arachnoid cap cell accumulation. CONCLUSIONS: The authors postulate that proliferation of arachnoidal cells, triggered by the inflammatory reaction or blood clotting products, could result in obstruction of CSF flow through arachnoid villi into the venous sinuses. This does not exclude the possibility that SAH causes generalized fibrosis in the subarachnoid space.     

Origin of the capsule of a chronic subdural hematoma--an electron microscopy study

To understand the early stage of subdural neomembrane (SN) formation, we examined 23 outer SNs and two inner SNs of chronic subdural hematomas in surgical specimens. Ultrastructurally, the cellular component of the outer SN was fibroblasts, myofibroblasts, smooth-muscle cells (in four cases), blood vessels and blood-born cells. Dural border cells were observed only in limited areas. Namely, the outer SN is a simple granulation tissue which originates from multiple sources of mesenchymal cells in dura mater, and dural border cells are only one of constituent sources for SN formation. The inner SN was simply composed of slender spindle cells which were mostly fibroblasts and some were recognized as dural border cells. Our results showed that the subdural hematoma is actually an "intra" dural hematoma which is formed within the split dural border cell layer. The dura mater with rich vascular supply forms thick granulation tissue, that is outer SN and a few dural border cells on the underlying arachnoid membrane form thin fibrous inner SN.     

Involvement of BMP-2 signaling in a cartilage cap in osteochondroma.

This study describes the distributions of bone morphogenetic protein (BMP)-2 as well as mRNAs for BMP receptor type IB (BMPRIB). collagen types II (Col II) and III (Col III) in a growing "cartilage cap" of osteochondroma. In situ hybridization and immunohistochemical study were performed using histological sections obtained during surgery. BMP-2 was detected in mesenchymal cells in the outer fibrous layer and chondrocytes in the inner cartilaginous matrix, positive for Col III and Col II, respectively. BMPRIB mRNA was distributed in chondrocytes. This is the first study to provide observational evidence of the involvement of BMP-2 signaling in the pathogenesis of cartilage cap of osteochondroma. and suggests the role of BMP-2 in the growth of cartilage cap in osteochondroma.     

The fine anatomy of the human spinal meninges. A light and scanning electron microscopy study

The fine anatomy of the human spinal meninges was examined in five postmortem spinal cords taken within 12 hours after death from patients aged 15 months to 46 years. Specimens of spinal cord were viewed in transverse section and from the dorsal and ventral aspects by scanning electron microscopy. Transverse sections of spinal cord and meninges were also examined by light microscopy. The arachnoid mater was seen to be closely applied to the inner aspect of the dura. An intermediate fenestrated leptomeningeal layer was observed attached to the inner aspect of the arachnoid mater and was reflected ventrally to form a series of dorsal septa. As it arborized laterally over the surface of the cord to surround nerves and blood vessels, the intermediate layer became highly fenestrated but remained distinct from the pia and arachnoid mater. The pia mater appeared to form a continuous layer which was reflected off the surface of the cord to coat blood vessels within the subarachnoid space in a manner similar to that described in the leptomeninges over the human cerebral cortex. Each dentate ligament consisted of a collagenous core which was continuous with the subpial connective tissue and was attached at intervals to the dura; pia-arachnoid cells coated the surface of the dentate ligaments. The present study suggests that the fine anatomy of the human spinal meninges differs significantly from that described in other mammals.     

Astroblastoma: electron microscopy and immunohistochemical findings: case report

The clinical, histological, immunohistochemical, and electron microscopic features of a cerebral astroblastoma are reported. The patient is a young woman with a superficial parietal tumor. Macroscopic findings include a well-delineated superficial nodule with a hard central core. Histological study disclosed a predominantly papillary tumor with hyalinized vessels. Tumor cells were scarcely positive with immunohistochemical stain for glial fibrillary acidic protein, extensive and diffusely positive with vimentin and neuron-specific enolase, and intensely positive with S-100 and epithelial membrane antigen in the papillary areas. Ultrastructural study showed abundant intermediate filaments forming bundles in tumoral cytoplasms, membrane junctions, and external laminae when cells were in contact with collagen fibers. Based on immunohistochemical and ultrastructural characteristics, we believe that the filaments seen in tumor cells are mainly vimentin filaments. These peculiar immunohistochemical patterns in a glioma may aid in the histological diagnosis of this rare tumor type.     

The morphology of sensory corpuscles in the joint capsule--ultrastructural and histochemical study

Sensory corpuscles in the cat elbow joint were observed by light and electron microscopy. Two types of corpuscles were identified, i.e. Pacini-type and Ruffini-type corpuscles. Silver impregnation revealed a single straight axon terminal in Pacini-type and highly-ramified fine axons in Ruffini-type corpuscles. Pacini-type corpuscles, 100-200 microns long and 30 microns wide, consisted of dense lamellae of lamellar cells and thick capsule. The lamellar portion contained a centrally-located axon terminal, and was similar in organization to the inner core of the typical Pacini corpuscle. The capsule was the continuation of perineurial sheath. This corpuscle was devoid of outer core structure as seen in a typical Pacini corpuscle. Ruffini-type corpuscles, 50-150 microns long and 25-50 microns wide, had the branched axon terminals with varicosities under the incomplete capsule. Axons, which were surrounded by thin Schwann cell processes, were embedded in the dense layers of collagen fibrils. The interior of the corpuscle was separated into small compartments by cell processes extended from the capsule. The axon varicosities contained numerous mitochondria. These fine structures of the corpuscles were similar to those of Ruffini corpuscles reported so far in other regions. Both Pacini-type and Ruffini-type corpuscles were clearly demonstrated by histochemistry for ChE. Inasmuch as the staining feature of corpuscles was different from each other, the distribution pattern of corpuscles in the joint capsules could be obtained by examining semi-serial sections. Pacini-type corpuscles were mainly found in the synovial layer, while Ruffini-type corpuscles were mainly located in the fibrous layer of the joint capsule. Both types of corpuscles were located near the median nerve on the flexor side of the joint. The reaction products of ChE activity were located in the peri-axonal as well as inter-lamellar spaces of Pacini-type corpuscles, and in the peri-axonal region as well as around Schwann cell processes of Ruffini-type corpuscles. No definite reaction product was found within axon terminals. Some reaction products were also found in the rough endoplasmic reticulum and/or nuclear envelope, suggesting that ChE is synthesized by Schwann cells. The significance of these sensory corpuscles with regard to the deep sensation in the joint capsule was discussed from the point of view of the electro-physiological characteristics of the corpuscles.     

The inner membrane of chronic subdural hematomas: pathology and pathophysiology

There is no clear plane between the dura and arachnoid in situ. Instead of the virtual subdural space, there is a dura-arachnoid interface layer, which is structurally the weakest throughout the meninges. An extravasation of blood within the dural border layer splits it, leaving a few tiers of dural border cells over the arachnoid. These cells cover the internal surface of the hematoma, proliferate, and later on, form the inner membrane. The outer membrane is related to hematoma enlargement because of the repetitive hemorrhages whereas the inner membrane is related to liquefaction of the subdural hematoma. As the inner membrane plays a pivotal role in the pathophysiogenesis and determination of the location of chronic subdural hematoma, histologic, ultrastructural, and clinical analyses were performed with correlations to the dura-arachnoid interface and the so-called "subdural space."     

Ultrastructure of sensory nerve endings in monkey (Macaca fascicularis) knee joint capsule

Ultrastructural studies of sensory endings in monkey posterior medial knee joint capsule were undertaken. Three distinct sensory nerve endings have been identified: free nerve endings, Ruffini corpuscles, and Pacinian corpuscles. The free nerve endings are present in all layers of the joint capsule excluding the synovium. Two types of Ruffini corpuscles have been found in the fibrous layer. The first type is characterized by a thin perineurial capsule, the second type by a thicker perineurial capsule, and extensive intracapsular space. Both types of Ruffini corpuscles are innervated by approximately one to four myelinated axons which lose their sheaths as they course through the corpuscle. They terminate on collagen fiber bundles as distinct swellings with spiny membrane projections that are covered by a thin basal lamina. These terminals contain abundant mitochondria, agranular vesicles, and irregularly arranged neurofilaments and neurotubules. Two types of Pacinian corpuscles were occasionally observed. The first was a small, typically laminated structure with an inner core at the layer between the synovium and the fibrous layer and between the fibrous layer and muscle/ligament; larger Vater-Pacinian corpuscles were noted only at the boundary between the fibrous layer and the muscle/ligament layer.     

Electron microscopic observations of human sperm whole-mounts after extraction for nuclear matrix and intermediate filaments (NM-IF)

The extraction for nuclear matrix and intermediate filaments (NM-IF) is used to reveal, isolate and study these highly resistant structures in different cell types. We applied for the first time this chemical dissection to human spermatozoa and observed them as whole-mounts by unembedded electron microscopy. The general appearance of NM-IF extracted sperm cells was preserved, showing the intermediate filament-like properties of their cytoskeletal components. In most heads, a network was observed in subacrosomal position, consisting of hubs interconnected by filaments. It seemed to be overlaid on another, finer network. The neck retained its integrity, allowing observations of the three-dimensional structure of the segmented columns. More distally, axoneme and outer dense fibres were covered by submitochondrial cytoskeleton in the middle piece and fibrous sheath in the principal piece, with the annulus usually detached from the fibrous sheath. End piece microtubules were retained in most cells and showed a tendency of cohesion, remaining in a parallel bundle or forming flat sheets. In conclusion, our results provided additional structural details of human sperm cytoskeleton and demonstrated the advantages of combining different methodological approaches in ultrastructural research.     

Expression of cell adhesion molecule E-cadherin in human arachnoid villi.

Calcium-dependent epithelial cell adhesion molecules designated as E-cadherin (also known as uvomorulin or L-CAM) were identified in human arachnoid villi by immunoblotting and immunocytochemical analyses using a monoclonal antibody HECD-1 raised against human mammary carcinoma MCF-7 cells. Immunoblot analysis showed that HECD-1 recognizes E-cadherin with a molecular weight of 124 kD. In all arachnoid cells of an arachnoid villus, E-cadherin was detected by immunolight microscopy within the cytoplasm rather than the cellular boundaries as seen in the control group. Furthermore, the extent of expression by immunolight microscopy varied from portion to portion. The expression was usually weak in the syncytial cluster which was ultrastructurally composed of tightly juxtaposed cells characterized by few extracellular cisterns and numerous cell junctions, while it was intense in the reticular cluster and the surface layer which were ultrastructurally characterized by abundant extracellular cisterns and smaller numbers of cell junctions. The cells of the reticular cluster and the surface layer contained more free ribosomes than those of the syncytial cluster. Immunoelectron microscopy showed that E-cadherin was localized not only to the opposing plasma membranes and the cytoplasm around the free ribosomes or the rough endoplasmic reticulum but also to the extracellular cisterns. As the expression of E-cadherin was closely related to the arachnoid cells adjacent to the cerebrospinal fluid pathway, it is suggested that, instead of the cell junctions, E-cadherin may play an important role in the flexible adhesion of arachnoid cells even in the presence of the cerebrospinal fluid.     

Development of arachnoid granulations

The ontogenesis of arachnoid granulations has been analysed in specimens derived from 30 humans, 5 cats and 10 ships. We distinguish the following developmental stages : (i) The arachnoid membrane forms small diverticula that grow toward the superior sagittal sinus. In the majority of cases, this process is followed by an infiltration of mesothelial and connective tissue cells from these diverticula into the dura mater, where it forms the wall of the sinus. (ii) These arachnoid cells form an evagination, giving rise to an arachnoid granulation of simple pediculated form, which, by generating evaginations of second and third order, can become an arachnoid granulation of the so-called complex pediculated form. The wall of the superior sagittal sinus participates in the development of the granulation by the formation of a fibrous capsule. This capsule has openings where arachnoid mesothelium and sinus endothelium are in direct contact.     

Differential phenotypic characteristics of heterogeneous cell population in the rabbit periosteum

BACKGROUND: Periosteum and periosteum-derived progenitor cells have demonstrated the potential for stimulative applications in repair of various musculoskeletal tissues. It has been found that the periosteum contains mesenchymal progenitor cells that are capable of differentiating into either osteoblasts or chondrocytes, depending on the culture conditions. Anatomically, the periosteum is a heterogeneous multilayered membrane, consisting of an outer fibrous and an inner cambium layer. The present study was designed to elucidate the phenotypic characteristics of fibrous and cambium layer cells in vitro. METHODS: Using a sequential enzymatic digestion method, fibrous and cambium layer cells were harvested separately from periosteum-bone explants of the proximal tibia of 6-month-old New Zealand White rabbits. RESULTS: We found that the cells from each layer showed distinct phenotypic characteristics in a primary monolayer culture system. Specifically, the cambium cells demonstrated higher osteogenic characteristics (higher alkaline phosphatase and osteocalcin levels) than the fibrous cells. However, these differences diminished with time in vitro. INTERPRETATION: Our findings suggest that the periosteum has phenotypically distinct heterogeneous cell populations. Care must be taken in order to identify and distinguish the intrinsic phenotypes of the heterogeneous periosteum-derived cell types in vitro.     

Electron microscopic observations of mouse sperm whole mounts after extraction for nuclear matrix and intermediate filaments.

Nuclear matrix and intermediate filaments (NM-IF) can be isolated by sequential treatment with non-ionic detergent, high salt. and nuclease. Extracted cells are easily observed by unembedded whole-mount transmission electron microscopy. Different somatic cell types have been subjected to this procedure and retained their essential architecture. To our knowledge, this work describes the first application of NM-IF extraction to sperm. After chemical dissection the general appearance of mouse sperm cells was preserved, except for head-from-neck separation in some cases. The cell membrane, acrosome and mitochondria were not present. The nucleus showed no apparent changes and revealed no details excepting pore complexes in the posterior part. Tissue-specific cytoskeletal elements (perforatorium, postacrosomal sheath, capitulum, segmented columns, outer dense fibers, submitochondrial reticulum, annulus, and fibrous sheath) were retained, which permitted a parallel between them and intermediate filaments of somatic cells. Tail microtubules were also relatively well preserved, showing high intrinsic stability. Cell structures could be observed well, with some details in the tail even better visible than in ultrathin sections. Observation of mouse sperm whole mounts after NM-IF extraction not only revealed intermediate filament-like properties of their cytoskeletal elements but also offered an additional viewpoint to sperm ultrastructure.     

The periosteum. Part 1: Anatomy, histology and molecular biology

The periosteum is a thin layer of connective tissue that covers the outer surface of a bone in all places except at joints (which are protected by articular cartilage). As opposed to bone itself, it has nociceptive nerve endings, making it very sensitive to manipulation. It also provides nourishment in the form of blood supply to the bone. The periosteum is connected to the bone by strong collagenous fibres called Sharpey's fibres, which extend to the outer circumferential and interstitial lamellae of bone. The periosteum consists of an outer "fibrous layer" and inner "cambium layer". The fibrous layer contains fibroblasts while the cambium layer contains progenitor cells which develop into osteoblasts that are responsible for increasing bone width. After a bone fracture the progenitor cells develop into osteoblasts and chondroblasts which are essential to the healing process. This review discusses the anatomy, histology and molecular biology of the periosteum in detail.     

Differential phenotypic characteristics of heterogeneous cell population in the rabbit periosteum

Background Periosteum and periosteum-derived progenitor cells have demonstrated the potential for stimulative applications in repair of various musculoskeletal tissues. It has been found that the periosteum contains mesenchymal progenitor cells that are capable of differentiating into either osteoblasts or chondrocytes, depending on the culture conditions. Anatomically, the periosteum is a heterogeneous multilayered membrane, consisting of an outer fibrous and an inner cambium layer. The present study was designed to elucidate the phenotypic characteristics of fibrous and cambium layer cells in vitro.

Methods Using a sequential enzymatic digestion method, fibrous and cambium layer cells were harvested separately from periosteum-bone explants of the proximal tibia of 6-month-old New Zealand White rabbits.

Results We found that the cells from each layer showed distinct phenotypic characteristics in a primary monolayer culture system. Specifically, the cambium cells demonstrated higher osteogenic characteristics (higher alkaline phosphatase and osteocalcin levels) than the fibrous cells. However, these differences diminished with time in vitro.

Interpretation Our findings suggest that the periosteum has phenotypically distinct heterogeneous cell populations. Care must be taken in order to identify and distinguish the intrinsic phenotypes of the heterogeneous periosteum-derived cell types in vitro.     

Endothelial seeding of Dacron and polytetrafluoroethylene grafts: the cellular events of healing

To detect cellular differences in the healing of polytetrafluoroethylene (e-PTFE) and Dacron grafts up to 7 months after implantation, we studied 108 aortic graft interpositions in dogs. Each prosthesis was alternately prepared by endothelial seeding or by an unseeded control method. The grafts were perfusion fixed and studied with light, scanning, and transmission electron microscopy at intervals from before to 221 days after implantation. Seeding resulted in the development of an extensive endothelial flow surface in two out of three of the e-PTFE and none out of four of the Dacron grafts by 10 days after implantation (p = 0.053). After 30 days a microfibrillar subendothelial matrix ranging from 5 to 11 mu formed in all but three grafts with endothelial coverage. The inner capsule of mature Dacron grafts was significantly thicker (169 +/- 143 mu) than in e-PTFE grafts (22 +/- 32 mu; p = 0.002). Seeded and unseeded Dacron grafts had predominantly fibroblasts in the outer capsule of the graft by 10 days. Surface endothelium, vasa vasorum, fibroblasts, and myointimal cells appeared in the inner capsule between 10 and 30 days after implantation. In Dacron grafts, fibroblasts and myointimal cells predominated in the inner capsule at 30 days, with smooth muscle cells not being definitely identifiable until after 150 days. Neither fibroblasts nor myointimal cells were common (present but sparse in one of four e-PTFE grafts) at 30 days, and transmural vasa vasorum were never seen. The seeded endothelial cells migrated rapidly from the sites of initial adhesion near the e-PTFE onto the flow surface. Only one of four of the unseeded e-PTFE grafts had surface endothelium after 30 days, and only moderate coverage developed during 180 days. We conclude that endothelial healing is more rapid in seeded e-PTFE grafts than in seeded Dacron grafts and occurs by a different mechanism.     

Contribution of angiotensin-converting enzyme and angiotensin II to ischemic stroke: their role in the formation of stable and unstable carotid atherosclerotic plaques

BACKGROUND: The angiotensin-converting enzyme/angiotensin II (ACE/Ang II) system is a strong contributor to intimal hyperplasia in atherosclerotic lesions. To illuminate its role in ischemic stroke, we examined the expression of ACE/Ang II in stable and unstable carotid atherosclerotic plaques from symptomatic and asymptomatic patients. METHODS: Using immunohistochemical methods, we studied differences between carotid atherosclerotic lesions obtained at carotid endarterectomy (CEA) from symptomatic (n = 36) and asymptomatic (n = 28) patients. The specimens were classified as stable (n = 30) and unstable (n = 34) plaques, and their fibrous cap, lipid core, and shoulder lesion were examined. We used antibodies against smooth muscle cells (SMC), macrophages, endothelial cells (EC), ACE, and Ang II. RESULTS: Of 28 lesions from asymptomatic patients, 20 (71.4%) manifested features characteristic of stable plaques: the expression of ACE/Ang II co-localized with SMC, EC, and macrophages in the shoulder lesion. In contrast, 26 of 36 symptomatic lesions (72.2%) exhibited the typical features of unstable plaques: dense accumulations of macrophages near the luminal surface in the shoulder lesion and weak immunoreactivity for ACE/Ang II, EC, and SMC. Furthermore, most of the lesions were accompanied by early stage atherosclerotic lesions (satellite lesions) that were strongly immunoreactive with macrophages, EC, and ACE/Ang II. CONCLUSIONS: ACE/Ang II expression may induce the proliferation of SMC and EC and result in the formation of carotid atherosclerotic plaques with a thick fibrous cap. Notably, the shoulder lesion of unstable plaques exhibited a thin fibrous cap and faintly expressed ACE/Ang II. Lack of the ACE/Ang II system may contribute to the final step in plaque rupture.     

Arthroscopic Extracapsular Plication to Treat Multidirectional Instability of the Shoulder

Successful arthroscopic treatment of multidirectional shoulder instability requires that the surgeon reduce the volume of the capsule. This goal can be achieved by using the extracapsular plication technique. There are several advantages to using pancapsular plication and an intra-articular knot. Much better potential for capsular healing exists when the outer layer of the capsule, which is composed of fibrous tissue, is tied extra-articularly. With the intra-articular plication technique, the inner layer of the capsule is synovia, which has less healing capacity. The amount of capsule plication that can be achieved with the extra-articular plication technique exceeds what is possible with the intra-articular plication technique. This is very important in patients who have a large degree of instability in the anterior, the posterior, and, particularly, the inferior direction. Thermal capsulorrhaphy enhances other arthroscopic stabilization procedures. Thermal striping helps to reduce capsular redundancy if laxity persists. However, with arthroscopic extracapsular plication, the capsular tissue can be shortened without using thermal energy.