Three-dimensional morphological study of microvascular regeneration in cavity wall of the rat cerebral cortex using the scanning electron microscope: implications for delayed neural grafting into brain cavities

Rapid and fully automated blood vasculature analysis in 3D light-sheet image volumes of different organs

Light-sheet fluorescence microscopy (LSFM) can produce high-resolution tomograms of tissue vasculature with high accuracy. However, data processing and analysis is laborious due to the size of the datasets. Here, we introduce VesselExpress, an automated software that reliably analyzes six characteristic vascular network parameters including vessel diameter in LSFM data on average computing hardware. VesselExpress is ∼100 times faster than other existing vessel analysis tools, requires no user interaction, and integrates batch processing and parallelization. Employing an innovative dual Frangi filter approach, we show that obesity induces a large-scale modulation of brain vasculature in mice and that seven other major organs differ strongly in their 3D vascular makeup. Hence, VesselExpress transforms LSFM from an observational to an analytical working tool.

Bioscaffold-Induced Brain Tissue Regeneration

Brain tissue lost after a stroke is not regenerated, although a repair response associated with neurogenesis does occur. A failure to regenerate functional brain tissue is not caused by the lack of available neural cells, but rather the absence of structural support to permit a repopulation of the lesion cavity. Inductive bioscaffolds can provide this support and promote the invasion of host cells into the tissue void. The putative mechanisms of bioscaffold degradation and its pivotal role to permit invasion of neural cells are reviewed and discussed in comparison to peripheral wound healing. Key differences between regenerating and non-regenerating tissues are contrasted in an evolutionary context, with a special focus on the neurogenic response as a conditio sine qua non for brain regeneration. The pivotal role of the immune system in biodegradation and the formation of a neovasculature are contextualized with regeneration of peripheral soft tissues. The application of rehabilitation to integrate newly forming brain tissue is suggested as necessary to develop functional tissue that can alleviate behavioral impairments. Pertinent aspects of brain tissue development are considered to provide guidance to produce a metabolically and functionally integrated de novo tissue. Although little is currently known about mechanisms involved in brain tissue regeneration, this review outlines the various components and their interplay to provide a framework for ongoing and future studies. It is envisaged that a better understanding of the mechanisms involved in brain tissue regeneration will improve the design of biomaterials and the methods used for implantation, as well as rehabilitation strategies that support the restoration of behavioral functions.

Optical imaging and modulation of neurovascular responses

The cerebral microvasculature consists of pial vascular networks, parenchymal descending arterioles, ascending venules and parenchymal capillaries. This vascular compartmentalization is vital to precisely deliver blood to balance continuously varying neural demands in multiple brain regions. Optical imaging techniques have facilitated the investigation of dynamic spatial and temporal properties of microvascular functions in real time. Their combination with transgenic animal models encoding specific genetic targets have further strengthened the importance of optical methods for neurovascular research by allowing for the modulation and monitoring of neuro vascular function. Image analysis methods with three-dimensional reconstruction are also helping to understand the complexity of microscopic observations. Here, we review the compartmentalized cerebral microvascular responses to global perturbations as well as regional changes in response to neural activity to highlight the differences in vascular action sites. In addition, microvascular responses elicited by optical modulation of different cell-type targets are summarized with emphasis on variable spatiotemporal dynamics of microvascular responses. Finally, long-term changes in microvascular compartmentalization are discussed to help understand potential relationships between CBF disturbances and the development of neurodegenerative diseases and cognitive decline.

3D visualization and quantification of microvessels in the whole ischemic mouse brain using solvent-based clearing and light sheet microscopy

The visualization of cerebral microvessels is essential for understanding brain remodeling after stroke. Injection of dyes allows for the evaluation of perfused vessels, but has limitations related either to incomplete microvascular filling or leakage. In conventional histochemistry, the analysis of microvessels is limited to 2D structures, with apparent limitations regarding the interpretation of vascular circuits. Herein, we developed a straight-forward technique to visualize microvessels in the whole ischemic mouse brain, combining the injection of a fluorescent-labeled low viscosity hydrogel conjugate with 3D solvent clearing followed by automated light sheet microscopy. We performed transient middle cerebral artery occlusion in C57Bl/6j mice and acquired detailed 3D vasculature images from whole brains. Subsequent image processing, rendering and fitting of blood vessels to a filament model was employed to calculate vessel length density, resulting in 0.922 ± 0.176 m/mm³ in healthy tissue and 0.329 ± 0.131 m/mm³ in ischemic tissue. This analysis showed a marked loss of capillaries with a diameter ≤ 10 µm and a more moderate loss of microvessels in the range > 10 and ≤ 20 µm, whereas vessels > 20 µm were unaffected by focal cerebral ischemia. We propose that this protocol is highly suitable for studying microvascular injury and remodeling post-stroke.

A novel fluorescent imaging technique for assessment of cerebral vasospasm after experimental subarachnoid hemorrhage

Various techniques have been developed to study changes in the cerebral vasculature in numerous neuropathological processes including subarachnoid hemorrhage (SAH). One of the most widely employed techniques uses India ink-gelatin casting, which presents numerous challenges due to its high viscosity, rapid solidification, and its impact on immunohistochemical analysis. To overcome these limitations, we developed a novel technique for assessing cerebral vasospasm using cerebrovascular perfusion with ROX, SE (5-Carboxy-X-Rhodamine, Succinimidyl Ester), a fluorescent labeling dye. We found that ROX SE perfusion achieves excellent delineation of the cerebral vasculature, was qualitatively and quantitatively superior to India ink-gelatin casting for the assessment of cerebral vasospasm, permits outstanding immunohistochemical examination of non-vasospasm components of secondary brain injury, and is a more efficient and cost-effective experimental technique. ROX SE perfusion is therefore a novel and highly useful technique for studying cerebrovascular pathology following experimental SAH.

A Delay between Motor Cortex Lesions and Neuronal Transplantation Enhances Graft Integration and Improves Repair and Recovery

We previously reported that embryonic motor cortical neurons transplanted immediately after lesions in the adult mouse motor cortex restored damaged motor cortical pathways. A critical barrier hindering the application of transplantation strategies for a wide range of traumatic injuries is the determination of a suitable time window for therapeutic intervention. Here, we report that a 1 week delay between the lesion and transplantation significantly enhances graft vascularization, survival, and proliferation of grafted cells. More importantly, the delay dramatically increases the density of projections developed by grafted neurons and improves functional repair and recovery as assessed by intravital dynamic imaging and behavioral tests. These findings open new avenues in cell transplantation strategies as they indicate successful brain repair may occur following delayed transplantation.SIGNIFICANCE STATEMENT Cell transplantation represents a promising therapy for cortical trauma. We previously reported that embryonic motor cortical neurons transplanted immediately after lesions in the adult mouse motor cortex restored damaged cortical pathways. A critical barrier hindering the application of transplantation strategies for a wide range of traumatic injuries is the determination of a suitable time window for therapeutic intervention. We demonstrate that a 1 week delay between the lesion and transplantation significantly enhances graft vascularization, survival, proliferation, and the density of the projections developed by grafted neurons. More importantly, the delay has a beneficial impact on functional repair and recovery. These results impact the effectiveness of transplantation strategies in a wide range of traumatic injuries for which therapeutic intervention is not immediately feasible.

Bilateral internal carotid arteries ligation temporary impairs brain vasculaturev in young rats

Bilateral internal carotid artery ligation (BICL) rat model is one of the chronic cerebral hypoperfusion animal models used for investigating brain dysfunction related diseases. Cerebral blood flow decreases in different cerebral regions in a time-dependent manner after the BICL. However little is known about the cerebral vasculature change in the brain after the BICL. In the current study, the bilateral internal carotid arteries of the juvenile rats were permanently ligated and the change of the cerebral vasculature was studied 7, 14 and 21 days after the BICL. In the juvenile rats, 7 days after the BICL, the functional vascular area was decreased significantly in the anterior half of the cerebral cortex, but it had only little decrease in the posterior half of the cerebral cortex and hippocampus. However, at the time points of 14 and 21 days after the surgery, the functional vascular area throughout the whole cerebral cortex and hippocampus was almost similar to those in the sham control rats. In conclusion, the results from our current study showed that in the BICL hypoperfusion model in young rats, the brain functional vascular area was impaired initially in certain brain regions after the artery ligation, but likely to be quickly self-recovered late after. The results suggest that the brain vasculature in young rats has plasticity to external insult caused by cerebral hypoperfusion.

Improved method of ink-gelatin perfusion for visualising rat retinal microvessels

To visualize completely rat retinal microvessels, the gelatin-ink perfusion condition was systematically optimized using von Willebrand factor (vWf) immunostaining as control. Whether the vessel showed by the new perfusion condition can be used for double label with neurons or glial cells in the same retina was also tested. Our results showed that infusing rats first with 20 ml of 37°C ink plus 3% gelatin at 140% rat mean arterial pressure (MAP), and subsequently with 20 ml of 37°C ink plus 5% gelatin at 180% rat MAP allowed the ink to completely fill the rat retinal microvessels. Rat retinal microvessels labeled by the perfusion method were more in number than that by vWf immunostaining. Moreover, our data, for the first time, displayed that the improved gelatin-ink perfusion had no effect on and caused no contamination to the following fluorogold labeling or immunostaining of retinal neurons or glial cells in the same tissue. These data suggest that the improved gelatin-ink perfusion technique is a superior method for morphological characterization of rat retinal microvessels, compatible to the double labeling of glial cells and neurons, and it extends the practical scale of the classic method.

Enhanced brain angiogenesis in chronic cerebral hypoperfusion after administration of plasmid human vascular endothelial growth factor in combination with indirect vasoreconstructive surgery

OBJECT

Vascular endothelial growth factor (VEGF) is a secreted mitogen associated with angiogenesis. The conceptual basis for therapeutic angiogenesis after plasmid human VEGF gene (phVEGF) transfer has been established in patients presenting with limb ischemia and myocardial infarction. The authors hypothesized that overexpression of VEGF using a gene transfer method combined with indirect vasoreconstruction might induce effective brain angiogenesis in chronic cerebral hypoperfusion, leading to prevention of ischemic attacks.

METHODS

A chronic cerebral hypoperfusion model induced by permanent ligation of both common carotid arteries in rats was used in this investigation. Seven days after induction of cerebral hypoperfusion, encephalomyosynangiosis (EMS) and phVEGF administration in the temporal muscle were performed. Fourteen days after treatment, the VEGF gene therapy group displayed numbers and areas of capillary vessels in temporal muscles that were 2.2 and 2.5 times greater, respectively, in comparison with the control group. In the brain, the number and area of capillary vessels in the group treated with the VEGF gene were 1.5 and 1.8 times greater, respectively, relative to the control group.

CONCLUSIONS

In rat models of chronic cerebral hypoperfusion, administration of phVEGF combined with indirect vasoreconstructive surgery significantly increased capillary density in the brain. The authors' results indicate that administration of phVEGF may be an effective therapy in patients with chronic cerebral hypoperfusion, such as those with moyamoya disease.

Transplantation of human neural stem cells for spinal cord injury in primates

Recent studies have shown that delayed transplantation of neural stem/progenitor cells (NSPCs) into the injured spinal cord can promote functional recovery in adult rats. Preclinical studies using nonhuman primates, however, are necessary before NSPCs can be used in clinical trials to treat human patients with spinal cord injury (SCI). Cervical contusion SCIs were induced in 10 adult common marmosets using a stereotaxic device. Nine days after injury, in vitro-expanded human NSPCs were transplanted into the spinal cord of five randomly selected animals, and the other sham-operated control animals received culture medium alone. Motor functions were evaluated through measurements of bar grip power and spontaneous motor activity, and temporal changes in the intramedullary signals were monitored by magnetic resonance imaging. Eight weeks after transplantation, all animals were sacrificed. Histologic analysis revealed that the grafted human NSPCs survived and differentiated into neurons, astrocytes, and oligodendrocytes, and that the cavities were smaller than those in sham-operated control animals. The bar grip power and the spontaneous motor activity of the transplanted animals were significantly higher than those of sham-operated control animals. These findings show that NSPC transplantation was effective for SCI in primates and suggest that human NSPC transplantation could be a feasible treatment for human SCI.

Transplantation of neural stem cells into the spinal cord after injury

Thanks to advances in the stem cell biology of the central nervous system (CNS), the previously inconceivable regeneration of the damaged CNS is approaching reality. The availability of signals to induce the appropriate differentiation of the transplanted and/or endogenous neural stem cells (NSCs) as well as the timing of the transplantation are important for successful functional recovery of the damaged CNS. Because the immediately post-traumatic microenvironment of the spinal cord is in an acute inflammatory stage, it is not favorable for the survival and differentiation of NSC transplants. On the other hand, in the chronic stage after injury, glial scars form in the injured site that inhibit the regeneration of neuronal axons. Thus, we believe that the optimal timing of transplantation is 1-2 weeks after injury.

Inhibition of endogenous VEGF impedes revascularization and astroglial proliferation: roles for VEGF in brain repair

Vascular endothelial growth factor (VEGF) is upregulated following injury to the CNS. Our previous work has shown that exogenous application of VEGF promotes angiogenesis, blood-brain barrier permeability, and astroglial mitogenicity in the traumatized brain. To develop a model that could link endogenously secreted VEGF to brain tissue repair, a specific neutralizing antibody to VEGF was infused by osmotic minipump directly into the neocortex and striatum for up to 1 week. Tissues adjacent to the infusion/wound site were analyzed for specific vascular and astroglial protein markers and proliferation, necrosis/apoptosis (via TUNEL staining), VEGF, the VEGF receptors flt-1 and flk-1, and bFGF expression using immunohistochemistry and semi-quantitative RT-PCR. Neutralization of native VEGF caused significant decreases in angiogenic activity, astroglial proliferation, and nestin immunoexpression, while vascular and astroglial degeneration was substantially increased, resulting in much larger wound cavities when compared to controls. The hindrance of brain tissue repair occurred despite an increase in bFGF expression at the wound sites. VEGF appears to be an integral factor in CNS wound healing that is essential for vascular endothelial proliferation and survival and may also be necessary for astroglial proliferation and maintenance during the repair of brain injury.

Microvascular structure after embolic focal cerebral ischemia in the rat

OBJECTIVES

We analyze morphological alterations of cerebral neovascularization after stroke using a new 3D imaging software program.

METHODS

Male Wistar rats underwent unilateral embolic middle cerebral artery occlusion (MCAo) by a single fibrin rich clot. Subjects were sacrificed from 1 to 28 days post infarct. Vessel perimeters were measured on coronal sections stained with endothelial cell-specific antibody to von Willebrand's factor. Vessel segment lengths, diameters and number of vessels were analyzed on cerebral microvessels perfused with FITC-dextran 14 days after ischemia using LSCM and a 3-D vessel quantification program.

RESULTS

The mean number of microvessels with enlarged perimeters significantly increased in the ipsilateral cortex at day 7 when compared to the contralateral cortex (29.7+/-14.7 vs. 3.7+/-2.5, P<0.05). Subsequently, differences in the number of microvessels with enlarged perimeters decreased on days 14 and 28. Fourteen days post-MCA occlusion, microvessel segment length (15.0 vs. 26.0 microm, P<0.05) and diameter (3.14 vs. 3.75 microm, P<0.05) significantly decreased in the ipsilateral hemisphere when compared to the contralateral hemisphere, respectively. Furthermore, the mean total number of these smaller microvessels increased in the ipsilateral hemisphere (57.33+/-14.5 vs. 32.22+/-11.7, P<0.05).

CONCLUSIONS

Focal cerebral ischemia induces morphological changes (early dilated microvessels followed by decreased microvessel segment length and diameter) that are consistent with newly generated microvessels.

Microvascular plasticity in aging

Understanding the bases of aging-related cognitive decline remains a central challenge in neurobiology. Quantitative studies reveal little change in the number of neurons or synapses in most of the brain but their ongoing replacement is reduced, resulting in a significant loss of neuronal plasticity with senescence. Aging also may alter neuronal function and plasticity in ways that are not evident from anatomical studies of neurons and their connections. Since the nervous system is dependent upon a consistent blood supply, any aging-related changes in the microvasculature could affect neuronal function. Several studies suggest that, as the nervous system ages, there is a rarefaction of the microvasculature in some regions of the brain, as well as changes in the structure of the remaining vessels. These changes contribute to a decline in cerebral blood flow (CBF) that reduces metabolic support for neural signaling, particularly when levels of neuronal activity are high. In addition to direct effects on the microvasculature, aging reduces microvascular plasticity and the ability of the vessels to respond appropriately to changes in metabolic demand. This loss of microvascular plasticity has significance beyond metabolic support for neuronal signaling, since neurogenesis in the adult brain is regulated coordinately with capillary growth.

Stem cell biology of the central nervous system

Neural stem cells (NSCs) are multipotential progenitor cells that have self-renewal activities. A single NSC is capable of generating various kinds of cells within the central nervous system (CNS), including neurons, astrocytes, and oligodendrocytes. Because of these characteristics, there is increasing interest in NSCs and neural progenitor cells from the aspects of both basic developmental biology and therapeutic applications to the damaged brain. This special issue, dedicated to understanding the nature of the NSCs present in the CNS, presents an introduction to several avenues of research that may lead to feasible strategies for manipulating cells in situ to treat the damaged brain. The topics covered by these studies include the extracellular factors and signal transduction cascades involved in the differentiation and maintenance of NSCs, the population dynamics and locations of NSCs in embryonic and adult brains, prospective identification and isolation of NSCs, the induction of NSCs to adopt particular neuronal phenotypes, and their transplantation into the damaged CNS.

Transplantation of in vitro-expanded fetal neural progenitor cells results in neurogenesis and functional recovery after spinal cord contusion injury in adult rats

Neural progenitor cells, including neural stem cells, are a potential expandable source of graft material for transplantation aimed at repairing the damaged CNS. Here we present the first evidence that in vitro-expanded fetus-derived neurosphere cells were able to generate neurons in vivo and improve motor function upon transplantation into an adult rat spinal-cord-contusion injury model. As the source of graft material, we used a neural stem cell-enriched population that was derived from rat embryonic spinal cord (E14.5) and expanded in vitro by neurosphere formation. Nine days after contusion injury, these neurosphere cells were transplanted into adult rat spinal cord at the injury site. Histological analysis 5 weeks after the transplantation showed that mitotic neurogenesis occurred from the transplanted donor progenitor cells within the adult rat spinal cord, a nonneurogenic region; that these donor-derived neurons extended their processes into the host tissues; and that the neurites formed synaptic structures. Furthermore, analysis of motor behavior using a skilled reaching task indicated that the treated rats showed functional recovery. These results indicate that in vitro-expanded neurosphere cells derived from the fetal spinal cord are a potential source for transplantable material for treatment of spinal cord injury.

Correlation of VEGF and angiopoietin expression with disruption of blood-brain barrier and angiogenesis after focal cerebral ischemia

In an effort to elucidate the molecular mechanisms underlying cerebral vascular alteration after stroke, the authors measured the spatial and temporal profiles of blood-brain barrier (BBB) leakage, angiogenesis, vascular endothelial growth factor (VEGF), associated receptors, and angiopoietins and receptors after embolic stroke in the rat. Two to four hours after onset of ischemia, VEGF mRNA increased, whereas angiopoietin 1 (Ang 1) mRNA decreased. Three-dimensional immunofluorescent analysis revealed spatial coincidence between increases of VEGF immunoreactivity and BBB leakage in the ischemic core. Two to 28 days after the onset of stroke, increased expression of VEGF/VEGF receptors and Ang/Tie2 was detected at the boundary of the ischemic lesion. Concurrently, enlarged and thin-walled vessels were detected at the boundary of the ischemic lesion, and these vessels developed into smaller vessels via sprouting and intussusception. Three-dimensional quantitative analysis of cerebral vessels at the boundary zone 14 days after ischemia revealed a significant (P < 0.05) increase in numbers of vessels (n = 365) compared with numbers (n = 66) in the homologous tissue of the contralateral hemisphere. Furthermore, capillaries in the penumbra had a significantly smaller diameter (4.8 +/- 2.0 microm) than capillaries (5.4 +/- 1.5 microm) in the homologous regions of the contralateral hemisphere. Together, these data suggest that acute alteration of VEGF and Ang 1 in the ischemic core may mediate BBB leakage, whereas upregulation of VEGF/VEGF receptors and Ang/Tie2 at the boundary zone may regulate neovascularization in ischemic brain.

A new method for the investigation of capillary structure

Numerous physiological conditions as well as behavioral conditions have been shown to influence central nervous system vascular structure. Many of the methods used to investigate these structural alterations take advantage of the visibility of viscous substances (e.g. India ink in gelatin) perfused into the vasculature. The high viscosity of the solution, however, can cause incomplete vessel perfusion. The aim of the present study was to test whether or not capillaries seen in tissue perfused with fixative, embedded in celloidin and stained with Methylene Blue-Azure II (n=6) could be a useful alternative for the investigation of brain vascular structure. The method was compared to tissue from six rats perfused with India ink in gelatin and stained with cresyl violet. Qualitatively, vessels in the standard perfused tissue embedded in celloidin yielded clear vessels with stained pericytes. The two methods did not differ in branch point to cell ratio, length of individual capillaries, vessel length per mm(3), and capillary tortuosity. The capillary diameter was greater in the celloidin embedded tissue than in the India ink perfused tissue. Measuring the diameter between vessel walls appears to provide a more accurate measure than the widest distance between India ink pigments. Quantitative comparisons suggest that perfusion with standard fixative followed by embedding in celloidin provides vascular quantification comparable to that from India ink perfused tissue. The present method has several advantages, which include visualization of pericytes, increased probability of complete perfusion, clear view of cells that might otherwise be obscured by opaque vessels, and the possibility of using the alternate cerebral hemisphere for investigation of vascular ultrastructure.

VEGF enhances angiogenesis and promotes blood-brain barrier leakage in the ischemic brain

VEGF is a secreted mitogen associated with angiogenesis and is also a potent vascular permeability factor. The biological role of VEGF in the ischemic brain remains unknown. This study was undertaken to investigate whether VEGF enhances cerebral microvascular perfusion and increases blood-brain barrier (BBB) leakage in the ischemic brain. Using magnetic resonance imaging (MRI), three-dimensional laser-scanning confocal microscope, and functional neurological tests, we measured the effects of administrating recombinant human VEGF(165) (rhVEGF(165)) on angiogenesis, functional neurological outcome, and BBB leakage in a rat model of focal cerebral embolic ischemia. Late (48 hours) administration of rhVEGF(165) to the ischemic rats enhanced angiogenesis in the ischemic penumbra and significantly improved neurological recovery. However, early postischemic (1 hour) administration of rhVEGF(165) to ischemic rats significantly increased BBB leakage, hemorrhagic transformation, and ischemic lesions. Administration of rhVEGF(165) to ischemic rats did not change BBB leakage and cerebral plasma perfusion in the contralateral hemisphere. Our results indicate that VEGF can markedly enhance angiogenesis in the ischemic brain and reduce neurological deficits during stroke recovery and that inhibition of VEGF at the acute stage of stroke may reduce the BBB permeability and the risk of hemorrhagic transformation after focal cerebral ischemia.

Measurement of cerebral microvessel diameters after embolic stroke in rat using quantitative laser scanning confocal microscopy

Perfusion of the microcirculation after stroke is central to preserving neuronal function and improving functional outcome. Using laser scanning confocal microscopy (LSCM) and a novel computer software program, MIRAGE, we measured a reduction in cerebral microvessel diameter after 1 and 4 h of embolic middle cerebral artery (MCA) occlusion. The methodology used by MIRAGE for measurement of blood vessel diameter involves a linearly applied spherical inflation technique. Three-dimensional quantitative analysis revealed a significant (P<0.05) mean 10-12% reduction in vessel diameter in the ipsilateral cortex when compared to the homologous region in the contralateral hemisphere. This reduction was seen only in the cortex and not the striatum. A larger reduction in mean vessel diameter in the ipsilateral cortex, 16-30% (P<0.05) was observed when compared to sham control rats. These results are in strong agreement with other studies using different stroke models and imaging techniques. Our work represents a novel application of LSCM technology to the three dimensional investigation of microvessel diameter changes in acute stroke and identifies its potential as an important tool for investigation of cerebral pathology.

Immunocytochemical basis for a meningeo-glial network

Evidence is presented here for a cellular network that courses through all layers of meninges, the vasculature of both the brain and meninges, and extends into the brain parenchyma. Confocal mapping of calcium-binding protein S100beta immunoreactivity (S100beta-ir) and of the intermediate filament vimentin-ir through serial sections of the meningeal-intact adult rat brain revealed this network. In all tissues examined, S100beta-ir and vimentin-ir were primarily colocalized, and were found in cells with elongated processes through which these cells contacted one another to form a network. The location of labeling and the morphology of the cells labeled were consistent with the possibility that this network consists of fibroblasts in the meninges and the walls of large blood vessels, of pericytes at the level of capillaries, and of ependymocytes and a population of astrocytes in the brain parenchyma. At many sites along the borders of the brain parenchyma itself and of the brain blood vessels, it was possible to detect S100beta-ir and vimentin-ir cell processes that cross the basal laminae. This suggested the probable means by which the S100beta-ir cells of the extraparenchymal tissues anatomically contact the cells that express the same markers in the brain. Privileged anatomical relationships of the S100beta/vimentin network with the glial fibrillary acidic protein (GFAP) astrocytes further suggested that, together, they form the structural basis for a general meningeo-glial network. This organization challenges the current model of brain architecture, calls for a reconsideration of the role of meninges and vascular tissues, and appears to reflect the existence of hitherto unsuspected systems of communication.

Neural transplantation for Parkinson's disease

1. Neural transplantation is one promising approach for the treatment of Parkinson's disease. Fetal substantia nigra cells are a good source of dopamine, but in order to avoid ethical and immunological problems, adrenal medullary chromaffin cells have been investigated as an alternative source. 2. Grafted adrenal medullary chromaffin cells can provide dopamine as well as several neurotrophic factors that affect dopaminergic neurons in the brain. 3. We review experimental studies for application of neural transplantation techniques in Parkinson's disease, including immunological studies, cryopreservation, microvasculature, donor tissue, and direct gene delivery studies performed in our laboratory. Our clinical experience and new approach involving a polymer-encapsulated cell grafting procedure are also described.

VEGF mRNA induction correlates with changes in the vascular architecture upon spinal cord damage in the rat

The multiple cellular and molecular processes induced by injury to the central nervous system (CNS) are still poorly understood. In the present study, we investigated the response of the vasculature and the expression of mRNA for the angiogenic vascular endothelial growth factor (VEGF) following X-irradiation of the spinal cord in the newborn and following traumatic spinal cord injury in the adult rat. Both lesion models induced changes in the density and the distribution pattern of blood vessels: while X-irradiation led to a permanent local increase in vascular density in the fibre tracts of the exposed segments, a transient local sprouting of vessels was induced upon traumatic spinal cord injury. In situ hybridization showed that an increase of VEGF mRNA anticipated and overlapped with the vascular responses in both lesion models. In addition to the temporal correlation of VEGF expression and vascular sprouting, there was a clear correlation in the spatial distribution patterns. Following X-irradiation, the expression of VEGF mRNA was restricted to the fibre tracts, precisely the areas where the changes in the vasculature were observed later on. Upon transection in the adult animal, VEGF was mainly detectable at the border of the lesion area, where the transient increase in vascular density could be observed. Interestingly, according to the type of lesion applied, astrocytes (X-irradiation) or inflammatory cells (presumably microglial cells or macrophages; traumatic lesion) are the cellular sources of VEGF mRNA. Our results strongly indicate that VEGF is crucially involved in mediating vascular changes following different types of injury in the CNS.

Three-dimensional analysis of vasospastic major cerebral arteries in rats with the corrosion cast technique

BACKGROUND AND PURPOSE

Although mice, rats, and other small animals are commonly used for molecular biology research, their use in the evaluation of cerebral vasospasm after subarachnoid hemorrhage is somewhat problematic because of the correspondingly small size of their cerebral vessels. We have already reported that the corrosion cast technique was useful for evaluating newly formed cerebral vessels in neural grafts in these small animals. In the present study we applied the corrosion cast technique to the evaluation of hemolysate-induced cerebral vasospasm in rats and performed three-dimensional analysis for comparison. The casting was done 10 minutes after the hemolysate injection, so that only acute "vasospasm" was assessed.

METHODS

After withdrawal of 0.1 mL cerebrospinal fluid, 0.2 mL hemolysate (n = 9) or saline (n = 10) was injected into the cisterna magna of male Sprague-Dawley rats weighing between 300 and 350 g. Ten minutes later, perfusion of a semipolymerized casting medium was performed at an injection pressure of 100 to 120 mm Hg. The brains were immersed and corroded in 10% NaOH solution. After these procedures, the basilar artery as well as peripheral vessels was analyzed morphologically with scanning electron microscopy. Conventional histological analysis with the use of paraffin-embedded section with hematoxylin-eosin staining was also performed, and the results were compared with those for the corrosion cast methods.

RESULTS

In the saline-injected group, SEM showed that the inner surface of the basilar artery was smooth and the form of the endothelial cell was printed on the surface of the cast. In the hemolysate-injected group, the basilar artery showed an apparent vasospasm over its entire length, and corrugation was observed on the inner surface of the basilar artery in a three-dimensional fashion. Higher magnification revealed that the nuclei of the endothelial cells were distorted. Local narrowing of the basilar artery and vasospasm in the arteries of the anterior circulation and in peripheral arteries were also observed. Measurement of the inner diameter of the basilar artery showed 37.8% contraction in the hemolysate-injected group compared with the saline-injected group by the corrosion cast method. This degree of vasospasm was similar to that observed by the conventional histological method.

CONCLUSIONS

In this report we show that detailed three-dimensional observation in the rat can be performed qualitatively and quantitatively with the corrosion cast technique. We conclude that this method derives an accurate measurement of the diameter of rat major cerebral arteries and is more reliable for analyzing vasospasm in rats than angiography and other conventional procedures.

Analysis of neocortical grafts placed into focal ischemic lesions in adult rats

This study investigated the viability of fetal neocortical block grafts transplanted into adult ischemic cortical lesions. Recipient rats sustained focal ischemic lesions by permanent occlusion of the middle cerebral artery 4-7 days prior to transplantation. Twenty days later, the animals were sacrificed and the brains examined using triphenyltetrazolium chloride, routine Nissl or acetylcholinesterase histochemistry. Ischemic infarctions were localized to the ipsilateral sensorimotor cortex and transplants were integrated with the host cerebral cortex or striatum. Cholinergic fibers were found crossing the host-transplant interface, presumably innervating the graft. This study demonstrates that fetal neocortical block grafts placed into adult focal ischemic lesions following permanent arterial occlusion can survive and establish connections with the host brain.

Neovascularization of rat fetal neocortical grafts transplanted into a previously prepared cavity in the cerebral cortex: a three-dimensional morphological study using the scanning electron microscope

Neovascularization within syngeneic rat fetal neocortical grafts transplanted into a previously prepared cavity in the cerebral cortex was studied 1 to 3 months after transplantation, utilizing scanning electron microscopy of vascular corrosion casts. The grafts were easily identified and the outer surface of the grafts, especially at the host-graft interface, was surrounded by large regenerated vessels of leptomeninges and connective tissue (e.g. dura). Large vessels originating from the choroid plexus also coated the grafts in animals whose lateral ventricles had been opened at the time of cavitation. These large regenerated vessels were mainly observed on the surface of the grafts, and they ramified markedly to form capillary networks in the vicinity of the host-graft interface. Occasionally several relatively large regenerated vessels were noted to extend into the grafts, and to ramify and connect with graft capillary networks having the same features as that of the host brain. Moreover, direct vascular connections between host capillaries and those within the grafts were observed. In some animals, arteries and arterioles which fed the grafts were identified in the perimeter of the grafts with their characteristic morphology. The interior microvasculature structure of the grafts was largely composed of the capillary network of graft origin, and of several relatively large penetrating vessels originating from the regenerated leptomeningeal vessels or the vessels of the choroid plexus. The present study demonstrated that the blood supply to the solid grafts transplanted into the previously prepared cavities originated primarily from the regenerated host vessels. These host vessels perfused the intrinsic graft vessels via new anastomoses which formed predominantly at the host-graft interface.