Three-dimensional anatomical structure formed by granule cell layer and pyramidal cell layer in human hippocampus.

In the human hippocampus, the pyramidal layer consists of the inferior aspect of the hippocampus which is organized segmentally. Each segment, together with granule layer of the dentate gyrus, exhibits structural unity. In humans, ellipsoidal protrusions called pyramidal hillocks (PHs), which consist of a thick pyramidal cell layer (PL), are present in the inferior aspect of the hippocampus, and are segmentally organized along a longitudinal axis. It is also known that the granule cell layer (GL) of the dentate gyrus (DG) is not a smooth but undulated structure. However, the cytoarchitectural relationships between the protrusions and undulation have yet to be studied well. Here, we aimed to clarify the three-dimensional cytoarchitecture of the PL and GL of human hippocampus. For that purpose, the GL and PL were three-dimensionally reconstructed from serial sections of human hippocampus stained with hematoxylin and eosin. The GL was shaped as tubing with an opening in the dorsal part, and undulated especially in the medial part, forming digit-like processes. In the base of a digit-like process, protrusions of the GL extended laterally, with longer ones reaching the lateral edge, whereas shorter ones disappeared around the medial 1/3 of the GL. Consequently, the lateral part of the GL was undulated loosely. In the ventral view of the PL, the ellipsoidal PHs were sagittally aligned, whereas in the top view, each PH formed an ellipsoidal trough. Each structural unit was formed by a trough of the PH along the bottom, and had a longer GL protrusion in the upper-center, and shorter GL protrusions located between the longer protrusions and the lateral edge of the GL. A digit-like process extended into a dens. It is concluded that a unit of the PH and the GL comprises the longitudinal segmental formation of the hippocampus.

A Fiber Dissection Study of the Anterior Commissure: Correlations with Diffusion Spectrum Imaging Tractography and Clinical Relevance in Gliomas.

The anterior commissure, which connects bilateral temporal lobes and olfactive areas, remains elusive in many aspects of its structure and functional role. To comparatively describe anatomical details of the anterior commissure using cadaveric fiber dissection (FD) and diffusion spectrum imaging (DSI) thus refining our knowledge of the tract and exploring its clinical relevance in glioma migration. Twelve normal postmortem hemispheres were treated with Klingler's method and subjected to FD with medial, inferior, and lateral approaches. The FD findings were correlated with DSI tractography results. To illustrate the clinical relevance, two patients with recurrent temporal high-grade glioma are described. Our FD and DSI tractography of the anterior commissure disclosed a new anatomical paradigm. The FD confirmed that the anterior limb (absent sometimes and variable) and the lateral/temporal extension include the rostral portion and caudal portion, respectively, of the anterior commissure fibers. The shape of the lateral/temporal extension predominantly resembles an 'H'. The DSI tractography findings corresponded to these FD results. According to the FD, the Virchow-Robin space is continuous with the subarachnoid space and very close to the anterior commissure. The two clinical cases presented severe disturbances of consciousness and behavior despite good local tumor control. Subsequent magnetic resonance images showed new lesions infiltrating the contralateral temporal lobes. FD combined with DSI provided anatomical details facilitating a better understanding of the anterior commissure. Glioma migration routes to the contralateral temporal lobe included the anterior commissure, Virchow-Robin space, and subarachnoid space and were clinically relevant.

Disconnection of posterior part of the frontal aslant tract causes acute phase motor functional deficit.

The frontal aslant tract (FAT) mainly connects the supplementary motor area (SMA) and inferior frontal gyrus. The left FAT is involved in language-related functions, while the functional role of the right FAT is not fully understood. The aim of this study was to investigate the function of the right FAT by dividing it into three segments according to the anatomical structure. A total of 34 right frontal gliomas who had undergone surgery were studied. Participants were assessed for the acute and chronic phases of several neuropsychological and motor functions. FAT was reconstructed into the anterior, middle, and posterior segments according to the cortical connections as the medial prefrontal cortex, pre-SMA, and SMA proper, respectively. The relationships between the damaged severity of each FAT segment and behavioral scores were analyzed. A significant relationship was observed only in the acute phase motor function and posterior segment of the FAT. The middle segment was involved in motor function, but it did not have a sufficient significance level compared to the posterior segment. Our study revealed that the right FAT can be divided into three segments and that its posterior segment is related to acute phase motor function.

Direct evidence of the relationship between brain metastatic adenocarcinoma and white matter fibers: A fiber dissection and diffusion tensor imaging tractography study.

It is commonly known that brain metastases usually have clear boundaries in magnetic resonance imaging. However, little is known regarding the trajectory of white matter fibers around the tumors, especially using the fiber dissection technique. Here, we focused on the anatomical interaction between white matter fibers and the tumor, using the fiber dissection in a postmortem brain with metastatic tumor and compared the findings with those of diffusion tensor imaging (DTI) tractography. One postmortem human brain hemisphere with metastatic adenocarcinoma in the Broca's area was dissected using fiber dissection following the Klingler's method. In order to compare the in vitro and in vivo results, additional brains from 15 patients with metastatic adenocarcinomas, the volumes of which were comparable to that of the adenocarcinoma in the brain used for fiber dissection, were analyzed using DTI tractographic reconstruction. Morphological findings of white matter bundles running around the tumor were compared between the two techniques. In the fiber dissection technique, the superior longitudinal fascicle, arcuate fascicle, and frontal aslant tract could be dissected, and the white matter bundles were curved and retracted to avoid the tumor. In all the cases analyzed, white matter fibers or streamlines surrounding the tumor avoided the lesion. Using the fiber dissection technique, this is the first direct evidence to elucidate the anatomy of white matter fibers affected by a metastatic brain. This suggests that brain metastatic adenocarcinoma is an intra-axial neoplasm with extra-axial white matter structures.

Pyramid-Shape Crossings and Intercrossing Fibers Are Key Elements for Construction of the Neural Network in the Superficial White Matter of the Human Cerebrum.

Structural analysis of the superficial white matter is prerequisite for the understanding of highly integrated functions of the human cerebral cortex. However, the principal components, U-fibers, have been regarded as simple wires to connect adjacent gyri (inter-gyral U-fibers) but have never been thought as indispensable elements of anatomical structures to construct the cortical network. Here, we reported such novel structures made of U-fibers. Seven human cerebral hemispheres were treated with Klingler's method and subjected to fiber dissection (FD). Additionally, tractography using diffusion spectrum imaging (DSI) was performed. Our FD and DSI tractography succeeded disclosing a new type of U-fibers that was hidden in and ran along the white matter ridge of a gyral convolution (intra-gyral U-fibers). They were distinct from inter-gyral U-fibers which paved sulcal floors. Both intra- and inter-gyral U-fibers converged from various directions into junctional areas of white matter ridges, organizing novel anatomical structures, "pyramid-shape crossings". U-fibers to form pyramid-shape crossings also render routes for communication between crossings. There were 97 (mean, range 73-148) pyramid-shape crossings per lateral cortical surface. They are key structures to construct the neural network for intricate communications throughout the entire cerebrum. They can be new anatomical landmarks, too, for the segmentation of the cerebral cortex.

Does the superior fronto-occipital fascicle exist in the human brain? Fiber dissection and brain functional mapping in 90 patients with gliomas.

The presence of the superior fronto-occipital fascicle (SFOF) has been reported in the Rhesus monkey; however, it is a subject of controversy in humans. The aim of this study is to identify the SFOF using both in vitro and in vivo anatomo-functional analyses. This study consisted of two approaches. First, one acallosal brain and 12 normal postmortem hemispheres (five left and seven right sides) were dissected under a microscope using Klingler's fiber dissection technique. We focused on the medial subcallosal area superior to the Muratoff bundle, which has been indicated as a principal target area of the SFOF in previous studies. Second, 90 patients underwent awake craniotomy for gliomas with direct electrical stimulations. Functional examinations for visual, ataxic, and cognitive tasks were performed and 453 positive mapping sites were investigated by voxel-based morphometry analysis to establish the functions of the SFOF. The corticostriatal fibers, or the Muratoff bundle, and thalamic peduncle fibers joined in the area of the caudate nucleus, making thalamic peduncle/ corticostriatal bundles, which ran antero-posteriorly in the anterior subcallosal area and radiated from the caudate superior margin in the posterior subcallosal area. However, no SFOF fiber bundle crossed perpendicular to the thalamic peduncle/ corticostriatal bundles in the posterior subcallosal area. In the acallosal hemispheres, Probst bundles were confirmed and the subcallosal areas did not show a specific organization different from the normal brain. Hence, we could not detect a long and continuous association fascicle connecting the frontal lobe and occipital or parietal lobe in the target areas. Furthermore, in the in vivo functional mappings of awake surgery and voxel-based morphometry analysis, eight positive points on the SFOF were selected from the total 453 positive points, but their functions were not related with visual processing and spatial awareness, as has been reported in previous studies. In conclusion, in the present study we attempted to investigate the existence of the SFOF using an anatomical and functional approach. According to our results, the SFOF may not exist in the human brain.

The superior longitudinal fascicle: reconsidering the fronto-parietal neural network based on anatomy and function.

Due primarily to the extensive disposition of fibers and secondarily to the methodological preferences of researchers, the superior longitudinal fasciculus (SLF) subdivisions have multiple names, complicating SLF research. Here, we collected and reassessed existing knowledge regarding the SLF, which we used to propose a four-term classification of the SLF based mainly on function: dorsal SLF, ventral SLF, posterior SLF, and arcuate fasciculus (AF); these correspond to the traditional SLF II, SLF III or anterior AF, temporoparietal segment of the SLF or posterior AF, and AF or AF long segment, respectively. Each segment has a distinct functional role. The dorsal SLF is involved in visuospatial attention and motor control, while the ventral SLF is associated with language-related networks, auditory comprehension, and articulatory processing in the left hemisphere. The posterior SLF is involved in language-related processing, including auditory comprehension, reading, and lexical access, while the AF is associated with language-related activities, such as phonological processing; the right AF plays a role in social cognition and visuospatial attention. This simple proposed classification permits a better understanding of the SLF and may comprise a convenient classification for use in research and clinical practice relating to brain function.

Chronic spatial working memory deficit associated with the superior longitudinal fasciculus: a study using voxel-based lesion-symptom mapping and intraoperative direct stimulation in right prefrontal glioma surgery.

OBJECTIVE Although the right prefrontal region is regarded as a silent area, chronic deficits of the executive function, including working memory (WM), could occur after resection of a right prefrontal glioma. This may be overlooked by postoperative standard examinations, and the disabilities could affect the patient's professional life. The right prefrontal region is a part of the frontoparietal network and is subserved by the superior longitudinal fasciculus (SLF); however, the role of the SLF in spatial WM is unclear. This study investigated a persistent spatial WM deficit in patients who underwent right prefrontal glioma resection, and evaluated the relationship between the spatial WM deficit and the SLF. METHODS Spatial WM was examined in 24 patients who underwent prefrontal glioma resection (right, n = 14; left, n = 10) and in 14 healthy volunteers using a spatial 2-back task during the long-term postoperative period. The neural correlates of spatial WM were evaluated using lesion mapping and voxel-based lesion-symptom mapping. In addition, the spatial 2-back task was performed during surgery under direct subcortical electrical stimulation in 2 patients with right prefrontal gliomas. RESULTS Patients with a right prefrontal lesion had a significant chronic spatial WM deficit. Voxel-based lesion-symptom mapping analysis revealed a significant correlation between spatial WM deficit and the region that overlapped the first and second segments of the SLF (SLF I and SLF II). Two patients underwent awake surgery and had difficulties providing the correct responses in the spatial 2-back task with direct subcortical electrical stimulation on the SLF I, which was preserved and confirmed by postoperative diffusion tensor imaging tractography. These patients exhibited no spatial WM deficits during the postoperative immediate and long-term periods. CONCLUSIONS Spatial WM deficits may persist in patients who undergo resection of the tumor located in the right prefrontal brain parenchyma. Injury to the dorsal frontoparietal subcortical white matter pathway, i.e., the SLF I or SLF I and II, could play a causal role in this chronic deficit. A persistent spatial WM deficit, without motor and language deficits, could affect the professional life of the patient. In such cases, awake surgery would be useful to detect the spatial WM network with appropriate task during tumor exploration.

Misexpression experiment of Tbx5 in axolotl (Ambystoma mexicanum) hindlimb blastema.

Axolotls (Ambystoma mexicanum) have the ability to regenerate amputated limbs throughout their life span. In the present study, we attempted to elucidate how axolotls can specify limb type correctly during the regeneration process. We misexpressed Tbx5 in regenerating hindlimb blastema, and consequently a forelimb-like hindlimb regenerated from the hindlimb blastema. On the other hand, no change was observed in Tbx5-overexpressing forelimb blastema, and thus we considered that Tbx5 plays a key role in the specification of forelimb during the regeneration process of axolotl limbs. However, axolotls' fore- and hindlimbs have very similar structures except for the number of fingers, and it was very difficult to judge whether the forelimb-like regenerate was a true forelimb or merely a forelimb-like hindlimb. Therefore, in order to confirm our conclusion, we have to investigate other genes that are expressed differentially between fore- and hindlimbs in future experiments.

Lmx-1b and Wnt-7a expression in axolotl limb during development and regeneration.

Axolotls (Ambystoma mexicanum) have the ability to regenerate amputated limbs throughout their life span. During limb regeneration as well as development, undifferentiated cells in the blastema acquire positional information to reproduce the original pattern along three cardinal limb axes: anteroposterior, proximodistal and dorsoventral. In the present study, we attempted to understand the molecular mechanism involved in patterning of axolotl limb development and regeneration along the dorsoventral (DV) axis. We cloned axolotl Lmx-1b and Wnt-7a, and investigated the expression pattern of these genes in developing and regenerating limbs. In axolotl, unlike in amniotes, Wnt-7a was expressed in a diffuse manner throughout both developing limb bud and regenerating limb blastema. Lmx-1b expression was observed at the dorsal mesenchyme in the developing and regenerating limbs. On the basis of the expression patterns of Lmx-1b and Wnt-7a, it was difficult to identify the interaction between these two genes as reported in amniotes in previous studies. Possibly, with regard to Lmx-1b expression, a Wnt-7a-independent mechanism may exist in axolotl limb development and regeneration.

Gross anatomical tractography (GAT) proposed a change from the 'Two laminae concept' to the 'Neuronal unit concept' on the structure of the human hippocampus.

The three dimensional structure of the human hippocampus was studied using the gross anatomical tractography (GAT) of Klingler technique. Eight hippocampi were obtained from seven donors to the Kanazawa Medical University, fixed in 5% formaldehyde, frozen and thawed twice, then dissected both by naked eye and under a dissecting microscope.The subiculum was segmented into 7-12 hillocks along the antero-posterior axis. The hillocks were organized with the white matter process and its gray matter covering. Cornu ammonis 3 (CA3) was represented by gray matter located in a longitudinal trough about 1 mm wide between the base of the fimbria and fiber bundles of the stratum lacunosum. CA3 was traversed and segmented by numerous short fiber fasciculi extending from the dentes of the margo denticulatus. The stratum radiatum, lacunosum and moleculare were differentially dissected. They not only contained systematically arranged neuronal fibers but also frameworks to allow passage of blood vessels. The polymorphic layer (PL) consisted of many italic L-shaped bars that were segmented, fused side-by-side and arrayed along the antero-posterior axis. The stratum granulosum (SG) lined the superior surface of PL as square plates and inferior surface of PL as thin folds. Thus, the SG was also segmented, although a little arbitrarily. CA4 was found not to be a neuronal plate, but instead comprised numerous neuronal rods that were segmentally arranged in accord with segmentation of CA3.On the basis of these segmentations, we conclude that, structurally, the human hippocampus is an antero-posterior succession of neuronal units, each consisting of the subicular hillock, dens, CA3, granular cell plates and folds, PL bars and CA4 rods.

The human hippocampus observed by scanning electron microscopy (SEM): the dentate gyrus is made of an array of the neuronal lamellae.

Scanning electron microscopy (SEM) was employed to clarify the three dimensional structure of the human hippocampus.The polymorphic layer was L-shaped in coronal histological sections. The superior limb and lateral two thirds of the inferior limb formed a continuous plate. This plate consisted of L-shaped bars that were fused side by side with borders that were, although incompletely, demarcated by the stratum granulosum. The medial one third of the inferior limb was independent part of these L-shaped bars and took part in formation of the dentes. There were 40 to 50 dentes, and each had segmental blood vessels. Thus, the polymorphic layer was organized on a segmental plan, 40- 50 in number, arrayed along the antero-posterior axis.CA4 was surrounded by the L-shaped polymorphic layer and also had the superior and inferior crura. The medial end of the inferior crus was enveloped by the medial one third of the polymorphic tissue and was completely independent from its neighbors. Therefore, CA4, too, may be segmentally constructed following the same plan as the bars of the polymorphic layer. These observations suggest that, first, three major components of the hippocampus, the stratum granulosum, polymorphic layer, and CA4, are constructed based on the same lamellar unit in the dentate gyrus, and, second, the individual lamellae appear as distinct bars in the medial one third, but form a plate in the lateral two thirds of these structures. There were 7 to 12 pyramidal hillocks, organized of the central process and its covering, in the subiculum. Pyramidal cells showed clear polarity in the hillock; the cell apex oriented to the central process and the base to the periphery. The axon emitted from the cell base and formed the alveus. Pyramidal hillocks caused slight waves of the stratum pyramidale on the lateral border of the hippocampus but did not affect the superior surface. Functional aspects of the segmental arrangement of neuronal units along the antero-posterior axis and their medio-lateral diversity were discussed in terms of the three-synapse pathway in the hippocampus.

Wound epithelium function in axolotl limb regeneration.

Axolotls (Ambystoma mexicanum) have the ability to regenerate amputated limbs. The amputation surface is promptly covered by wound epithelium (WE), which is significant for the initiation of limb regeneration. In the present study, we investigated the formation of functional WE by analyzing the migration of WE after amputation. In the center of the amputation surface, epithelial cells migrated from surrounding epidermis to form WE. Therefore, WE around the center of the amputation surface was composed of the cells with dorsal, ventral, anterior and posterior identities, and we tentatively called this WE with radial positional identities, "central WE". When regeneration was complete, central WE became the epidermis around the bifurcation between the first and second digits. In addition, when the artificial rotation of epidermis was performed before amputation, all examined limbs regenerated normally, and central WE formed the epidermis at the bifurcation between first and second digits, similarly to that in normal regeneration. On the basis of our observations, the most important factor for the initiation of regeneration is considered to be the discontinuity of positional identity existing in WE. It is possible that the location of bifurcation between first and second digits is specified by the positional discontinuity in WE.

Association fibers connecting the Broca center and the lateral superior frontal gyrus: a microsurgical and tractographic anatomy.

OBJECT: Recently, intraoperative mapping has disclosed that, in addition to the classic language centers (that is, the Broca and Wernicke centers), other cortical regions may also play an important role in language organization. In the prefrontal cortex, although the lateral superior frontal gyrus (LSFG) could have language-related functions, there are no detailed reports that demonstrate the anatomical connection between the LSFG and other well-known language cortices, such as the Broca center. To show the existence of the structural connection, white matter association fibers between the inferior frontal gyrus (IFG) and the LSFG were examined using fiber dissection (FD) and diffusion tensor (DT) imaging-based tractography. METHODS: Eight cadaveric cerebral hemispheres were dissected to reveal the association fibers between the IFG and LSFG. The DT imaging-based tractography studies targeting the prefrontal cortex were obtained in 53 right-handed patients who had no organic cerebral lesions. RESULTS: The association fiber tract between Brodmann area 44/45 (the Broca center in the dominant hemisphere) and LSFG were detected in all specimens by FD. In the DT imaging-based tractography studies, the tract was identified in all patients bilaterally, except for the 4 in whom the tract was detected only in the left hemisphere. This tract was spread significantly wider in the left than in the right hemisphere, and left lateralization was evident in male patients. CONCLUSIONS: Based on its character, this tract was named the Broca-LSFG pathway. These findings suggest a close relationship between this pathway and language organization. The structural anatomy of the Broca-LSFG pathway may explain speech disturbances induced by LSFG stimulation that are sometimes observed during intraoperative language mapping.

Pitx1 expression in developing and regenerating axolotl limbs.

The expression of the homeobox transcription factor Pitx1 was investigated in the Mexican axolotl (Ambystoma mexicanum) during limb development and regeneration by whole-mount mRNA in situ hybridizations. This clone shares high amino acid identity with Pitx1 from other vertebrates (92% Xenopus; 87% chick; 75% human and mouse) within the region isolated. In the developing limbs, Pitx1 was expressed in hindlimb mesenchyme, as has been reported in other species. The expression pattern in the hindlimb might have been conserved during evolution. In the regenerating limbs, Pitx1 was expressed in both fore- and hindlimb blastemas. Our observations suggest two roles of Pitx1 in the axolotl: one is to determine the hindlimb pattern during development, and the other that relates to proliferation of regenerating tissues without regard to fore- or hindlimb.

RAGE control of diabetic nephropathy in a mouse model: effects of RAGE gene disruption and administration of low-molecular weight heparin.

Diabetic nephropathy is a major microvascular complication in long-standing diabetic patients who eventually undergo renal dialysis or transplantation. To prevent development of this disease and to improve advanced kidney injury, effective therapies directed toward the key molecular target are required. In this study, we examined whether inhibition of the receptor for advanced glycation end products (RAGE) could attenuate changes in the diabetic kidney. Here, we show that inactivation of the RAGE gene in a mouse model of diabetic nephropathy results in significant suppression of kidney changes, including kidney enlargement, increased glomerular cell number, mesangial expansion, advanced glomerulosclerosis, increased albuminuria, and increased serum creatinine compared with wild-type diabetic mice. The degree of kidney injury was proportional to RAGE gene dosage. Furthermore, we show that low-molecular weight heparin (LMWH) can bind RAGE at a mean equilibrium dissociation constant (K(d)) value of approximately 17 nmol/l and act as an antagonist to RAGE. LMWH treatment of mice significantly prevented albuminuria and increased glomerular cell number, mesangial expansion, and glomerulosclerosis in a dose-dependent manner; it also significantly improved the indexes of advanced-stage diabetic nephropathy. This study provides insight into the pathological role of RAGE in both early- and advanced-phase diabetic nephropathy and suggests that RAGE antagonists will be a useful remedy in the treatment of diabetic nephropathy.

Glucocorticoid induces micro-fat embolism in the rabbit: a scanning electron microscopic study.

The objective was to identify fat emboli in the arterioles of the femoral bone marrow by scanning electron microscopy (SEM) after glucocorticoid administration. Female adult rabbits weighing 3.5-4.0 kg received a single injection of prednisolone at a dose of 4 mg/kgBW. The day after injection was designated as day 1. Control rabbits were injected with only physiological saline and killed on day 14. The femoral bone marrow was obtained on days 5, 8, and 14, and processed for SEM. Aortic blood serum was passed through a filter, and the filter was processed for SEM. Some SEM specimens were embedded in a plastic resin and sectioned for correspondence of SEM-photomicroscopy (PM) or SEM-transmission electron microscopy (TEM). In the controls, small fat globules were present in sinusoids and venules but were absent from the arterioles. On day 5, fat globules were found in the lumina of both sinusoids and arterioles, possibly due to the effect of glucocorticoid. Complete arteriolar occlusion was not found. On day 8, fat globules were often encountered in the venous and arteriolar lumina. Some small arterioles were completely occluded by fat emboli. On day 14, fat globules were present in the arterioles, and some small and large arterioles were completely occluded. Blood drawn from the aorta contained fat globules in both the controls and rabbits injected with prednisolone. A small amount of prednisolone induced the presence of fat globules in arterioles as early as day 5, complete occlusion of small arterioles on day 8, and occlusion of large arterioles on day 14.

Receptor for advanced glycation end products is a promising target of diabetic nephropathy.

Advanced glycation end products (AGEs) and the receptor for AGE (RAGE) interactions have been implicated in the development of diabetic vascular complications, which cause various disabilities and shortened life expectancy, and reduced quality of life in patients with diabetes. Diabetes-induced RAGE-overexpressing transgenic mice exhibited the exacerbation of the indices of nephropathy, and this was prevented by the inhibition of AGE formation. We also created RAGE-deficient mice by homologous recombination. They showed marked amelioration of diabetic nephropathy as compared with wild-type mice. Through an analysis of vascular polysomal poly(A)+ RNA, we identified a novel splice variant coding for a soluble RAGE protein and named it endogenous secretory RAGE (esRAGE). esRAGE was able to protect AGE-induced vascular cell injuries as a decoy receptor and was actually detected in human circulation. We conclude that RAGE plays an active role in the development of diabetic vascular complications, especially nephropathy, and is a promising target for overcoming this disease. The esRAGE, an endogenous decoy receptor, may be related to individual variations in resistance to the development of diabetic vascular complications.