Patterns of angiogenesis in neural transplant models: II. Fetal neocortical transplants

Donor-derived vasculature is required to support neocortical cell grafts after stroke

Neural precursor cells (NPCs) transplanted into the adult neocortex generate neurons that synaptically integrate with host neurons, supporting the possibility of achieving functional tissue repair. However, poor survival and functional neuronal recovery of transplanted NPCs greatly limits engraftment. Here, we test the hypothesis that combining blood vessel-forming vascular cells with neuronal precursors improves engraftment. By transplanting mixed embryonic neocortical cells into adult mice with neocortical strokes, we show that transplant-derived neurons synapse with appropriate targets while donor vascular cells form vessels that fuse with the host vasculature to perfuse blood within the graft. Although all grafts became vascularized, larger grafts had greater contributions of donor-derived vessels that increased as a function of their distance from the host-graft border. Moreover, excluding vascular cells from the donor cell population strictly limited graft size. Thus, inclusion of vessel-forming vascular cells with NPCs is required for more efficient engraftment and ultimately for tissue repair.

[Restoration of damaged cortical pathways by neural grafting]

The motor cortex plays a central role in the control, planning, and execution of voluntary motor commands in mammals. The loss of cortical neurons is a common feature of many neuropathological conditions such as traumatic and ischemic lesions or several neurodegenerative diseases. Cell transplantation presents a promising therapeutic strategy to overcome the limited abilities of axonal regrowth and spontaneous regeneration of the adult central nervous system. In this review, we will present a historical review of brain transplantation and the current state of research in the field of cortical transplantation.

Developmental Expression of Calcium-Binding Protein-Containing Neurons in Neocortical Transplants

The present study examined the development of calcium binding protein-containing neurons in a timed series of fetal neocortical transplants. The immunoexpression of parvalbumin and calbindin, which are subpopulations of GABAergic neurons, have been widely studied in normal development and in disease and injury states. Because of their purported resistance to oxidative injury by their ability to buffer Ca++ influx, these neurons have been particularly studied following ischemia. Because it is likely that oxidative stress is associated with the grafting procedure, we sought to determine if these neurons displayed enhanced survival characteristics. Normally, parvalbumin and calbindin represent about 5-10% of cortical neurons. Within 2-4 wk after grafting the expression of both proteins increased markedly in that a relatively larger number of neurons (27% for parvalbumin) were immunopositive. This increase was transitory, however, and by 4 mo and beyond, confocal microscopic data showed a reduction of over 50% of parvalbumin (+) neurons and processes. Calbindin (+) processes showed a qualitative change in that they were smaller with less terminal branching. Electron microscopy confirmed a substantial reduction in parvalbumin synaptic contacts. Interestingly, in older grafts, remaining parvalbumin neurons were those that were strongly NSE (+) suggesting a link between normal metabolism and Ca++ buffering in grafted neurons. It is possible that in early grafts certain neuronal populations transiently upregulated calcium binding proteins as a defensive mechanism against Ca++ influx associated with oxidative stress. Over time, however, following physiological normalization within grafts, the calcium binding protein (+) neurons are diminished, possibly due to lack of appropriate afferent input to the interneuronal pool.

Enhanced Vascularization and Survival of Neural Transplants with Ex Vivo Angiogenic Gene Transfer

Restoration of brain function by neural transplants is largely dependent upon the survival of donor neurons. Unfortunately, in both rodent models and human patients with Parkinson's disease the survival rate of transplanted neurons has been poor. We have employed a strategy to increase the availability of nutrients to the transplant by increasing the rate at which blood vessels are formed. Replication-deficient HSV-1 vectors containing the cDNA for human vascular endothelial growth factor (HSVhvegf) and the bacterial β-galacto-sidase gene (HSVlac) have been transduced in parallel into nonadherent neuronal aggregate cultures made of cells from embryonic day 15 rat mesencephalon. Gene expression from HSVlac was confirmed in fixed preparations by staining with X-gal. VEGF expression as determined by sandwich ELISA assay of culture supernatant was up to 322-fold higher in HSVhvegf-infected than HSVlac-infected sister cultures. This peptide was also biologically active, inducing endothelial cell proliferation in vitro. Adult Sprague-Dawley rats received bilateral transplants into the striatum, with HSVlac on one side and HSVhvegf on the other. At defined intervals up to 8 weeks, animals were sacrificed and vibratome sections of the striatum were assessed for various parameters of cell survival and vascularization. Results demonstrate dose-dependent increases in blood vessel density within transplants transduced with HSVhvegf. These transplants were vascularized at a faster rate up to 4 weeks after transplantation. After 8 weeks, the average size of the HSVhvegf-infected transplants was twice that of controls. In particular, the survival of transplanted dopaminergic neurons increased 3.9-fold. Taken together these experiments provide convincing evidence that the rate of vascularization may be a major determinant of neuronal survival that can be manipulated by VEGF gene transduction.

Two-step grafting significantly enhances the survival of foetal dopaminergic transplants and induces graft-derived vascularisation in a 6-OHDA model of Parkinson's disease

Following transplantation of foetal primary dopamine (DA)-rich tissue for neurorestaurative treatment of Parkinson's disease (PD), only 5-10% of the functionally relevant DAergic cells survive both in experimental models and in clinical studies. The current work tested how a two-step grafting protocol could have a positive impact on graft survival. DAergic tissue is divided in two portions and grafted in two separate sessions into the same target area within a defined time interval. We hypothesized that the first graft creates a "DAergic" microenvironment or "nest" similar to the perinatal substantia nigra that stimulates and protects the second graft. 6-OHDA-lesioned rats were sequentially transplanted with wild-type (GFP-, first graft) and transgenic (GFP+, second graft) DAergic cells in time interims of 2, 5 or 9days. Each group was further divided into two sub-groups receiving either 200k (low cell number groups: 2dL, 5dL, 9dL) or 400k cells (high cell number groups: 2dH, 5dH, 9dH) as first graft. During the second transplantation, all groups received the same amount of 200k GFP+ cells. Controls received either low or high cell numbers in one single session (standard protocol). Drug-induced rotations, at 2 and 6weeks after grafting, showed significant improvement compared to the baseline lesion levels without significant differences between the groups. Rats were sacrificed 8weeks after transplantation for post-mortem histological assessment. Both two-step groups with the time interval of 2days (2dL and 2dH) showed a significantly higher survival of DAergic cells compared to their respective standard control group (2dL, +137%; 2dH, +47%). Interposing longer intervals of 5 or 9days resulted in the loss of statistical significance, neutralising the beneficial two-step grafting effect. Furthermore, the transplants in the 2dL and 2dH groups had higher graft volume and DA-fibre-density values compared to all other two-step groups. They also showed intense growth of GFP+ vessels - completely absent in control grafts - in regions where the two grafts overlap, indicating second-graft derived angiogenesis. In summary, the study shows that two-step grafting with a 2days time interval significantly increases DAergic cell survival compared to the standard protocol. Furthermore, our results demonstrate, for the first time, a donor-derived neoangiogenesis, leading to a new understanding of graft survival and development in the field of cell-replacement therapies for neurodegenerative diseases.

Single-cell suspension methodology favors survival and vascularization of fetal striatal grafts in the YAC128 mouse model of Huntington's disease

Cell replacement therapies have yielded variable and short-lived benefits in Huntington's disease (HD) patients. This suboptimal outcome is likely due to the fact that graft survival is compromised long term because grafts are subjected to a host's microglial inflammatory response, to a lack of adequate trophic support, and possibly to cortical excitotoxicity. However, graft demise may also relate to more straightforward issues such as cell preparation methodology (solid grafts vs. cell suspension). Indeed, we recently reported that solid grafts are poorly revascularized in HD patients transplanted 9 and 12 years previously. To evaluate whether methodological issues relating to cell preparation may have an impact on graft viability, we implanted green fluorescent protein (GFP(+)) single-cell suspensions of fetal striatal neuronal cells into the striatum of YAC128 HD mice. Postmortem evaluation yielded comparable graft survival in YAC128 mice and their wild-type littermates (noncarrier) at 1 and 3 months posttransplantation. Additionally, the degrees of graft revascularization in the YAC128 and noncarrier mice were similar, with both capillaries and large-caliber vessels observable within the grafted tissue. Furthermore, GFP(+) cells interacted well with host blood vessels, indicating integration of the donor cells within the recipient brain. These observations, combined with our recent report of poor revascularization of solid grafts in the HD-transplanted patients, suggest that the success of cell transplantation can be improved by optimizing methodological aspects relating to cell preparation.

Short term interactions with long term consequences: modulation of chimeric vessels by neural progenitors

Vessels are a critical and necessary component of most tissues, and there has been substantial research investigating vessel formation and stabilization. Several groups have investigated coculturing endothelial cells with a second cell type to promote formation and stabilization of vessels. Some have noted that long-term vessels derived from implanted cocultures are often chimeric consisting of both host and donor cells. The questions arise as to whether the coculture cell might impact the chimeric nature of the microvessels and can modulate the density of donor cells over time. If long-term engineered microvessels are primarily of host origin, any impairment of the host's angiogenic ability has significant implications for the long-term success of the implant. If one can modulate the host versus donor response, one may be able to overcome a host's angiogenic impairment. Furthermore, if one can modulate the donor contribution, one may be able to engineer microvascular networks to deliver molecules a patient lacks systemically for long times. To investigate the impact of the cocultured cell on the host versus donor contributions of endothelial cells in engineered microvascular networks, we varied the ratio of the neural progenitors to endothelial cells in subcutaneously implanted poly(ethylene glycol)/poly-L-lysine hydrogels. We found that the coculture of neural progenitors with endothelial cells led to the formation of chimeric host-donor vessels, and the ratio of neural progenitors has a significant impact on the long term residence of donor endothelial cells in engineered microvascular networks in vivo even though the neural progenitors are only present transiently in the system. We attribute this to the short term paracrine signaling between the two cell types. This suggests that one can modulate the host versus donor contributions using short-term paracrine signaling which has broad implications for the application of engineered microvascular networks and cellular therapy more broadly.

Contribution of subcutaneous connective tissues to the epithelialization and cyst formation by the skin transplanted subcutaneously

Skins and hollow organs have been shown to form epithelialized cysts when transplanted into subcutaneous tissue of a recipient animal, expanding their surface areas. This system seems to offer a good potential for regenerating organs. We investigated the functional and structural contribution of epithelia and connective tissue compartments in this regeneration system with two experimental systems.

Roles of the endogenous VEGF receptors flt-1 and flk-1 in astroglial and vascular remodeling after brain injury

Following trauma to the brain significant changes occur in both the astroglial and vascular components of the neuropil. Angiogenesis is required to re-establish metabolic support and astrocyte activation encompasses several functions including scar formation and the production of growth factors. VEGF has seminal involvement in the process of brain repair and is upregulated during many pathological events. VEGF signaling is regulated mainly through its two primary receptors: flk-1 (KDR/VEGF-R2) is expressed on vascular endothelium and some neurons and flt-1 (VEGF-R1) in the CNS, is expressed predominantly by activated astrocytes. Using an injury model of chronic minipump infusion of neutralizing antibodies (NA) to block VEGF receptor signaling, this study takes advantage of these differences in VEGF receptor distribution in order to understand the role the cytokine plays after brain injury. Infusion of NA to flk-1 caused a significant decrease in vascular proliferation and increased endothelial cell degeneration compared to control IgG infusions but had no effect on astrogliosis. By contrast infusion of NA to flt-1 significantly decreased astroglial mitogenicity and scar formation and caused some increase in endothelial degeneration. Neutralization of the flt-1 receptor function, but not flk-1, caused significant reduction in the astroglial expression of the growth factors, CNTF and FGF by 7days. These data suggest that after CNS injury, endogenous VEGF upregulation (by astrocytes) induces angiogenesis and, by autocrine signaling, increases both astrocyte proliferation and facilitates expression of growth factors. It is likely that VEGF plays an important role in aspects of astroglial scar formation.

From angiogenesis to neuropathology

Angiogenesis--the growth of new blood vessels--is a crucial force for shaping the nervous system and protecting it from disease. Recent advances have improved our understanding of how the brain and other tissues grow new blood vessels under normal and pathological conditions. Angiogenesis factors, especially vascular endothelial growth factor, are now known to have roles in the birth of new neurons (neurogenesis), the prevention or mitigation of neuronal injury (neuroprotection), and the pathogenesis of stroke, Alzheimer's disease and motor neuron disease. As our understanding of pathophysiology grows, these developments may point the way towards new molecular and cell-based therapies.

Improving the survival of human CNS precursor-derived neurons after transplantation

We have examined the effects of predifferentiation and energy substrate deprivation on long-term expanded human neural precursor cells (HNPCs). The pre-differentiation of HNPC cultures produced large numbers of neurons (>60%) and mature glial cells capable of generating glycogen stores that protected the neuronal population from experimental metabolic stress. When predifferentiated HNPCs were transplanted into intact adult rat hippocampus, fewer cells survived compared to undifferentiated HNPC transplants. This cell death was completely attenuated, however, when predifferentiated HNPC cultures were pretreated to boost glial energy stores and resulted in greatly increased neuronal survival in vivo. The transplanted cells primarily engrafted within the granular layer of the dentate gyrus, where a large proportion of the predifferentiated HNPCs co-expressed neuronal markers whereas most HNPCs outside of the neuronal layer did not, indicating that the predifferentiated cells remained capable of responding to local cues in the adult brain. Undifferentiated HNPCs migrated more widely in the brain after grafting than did the predifferentiated cells, which generally remained within the hippocampus.

Dopaminergic neurons associate with blood vessels in neural transplants

Neural transplantation is an attractive strategy for diseases that result in focal neurodegeneration such as Parkinson's disease, where there is a selective loss of dopaminergic neurons in the substantia nigra of the midbrain. A major drawback to its application, however, is the poor survival of donor dopaminergic neurons. While neurons probably depend on host-derived substances delivered by either diffusion or the establishment of functional vascular connections, the relative importance of each delivery mechanism is not known. We investigated the topography of transplants of embryonic mesencephalic tissue and describe the spatial relationships between transplanted dopaminergic neurons, the host brain, and in-growing blood vessels. Results indicate that transplant vascularization shares features with developmental patterns of brain vascularization. Moreover, the topographical distribution of dopaminergic neurons reflected their proximity to the host brain as well as their distance from vascular elements. Zonal analysis revealed that the majority of dopaminergic neurons were found at or near the host-transplant interface at 1 week after transplantation. Nearest neighbor analysis demonstrated a descending exponential gradient of dopaminergic neurons as a function of their distance from vessels at the same time point. These patterns became more marked with time. Results suggest that rates and patterns of vascularization may be important determinants in the long-term survival of dopaminergic neurons.

Angiogenic and neurotrophic effects of vascular endothelial growth factor (VEGF165): studies of grafted and cultured embryonic ventral mesencephalic cells

The present series of experiments investigated the effects of vascular endothelial growth factor (VEGF165) on adult rat striatal cerebrovasculature and embryonic dopamine (DA) neuron allografts in a rat model of Parkinson's disease (PD). We examined VEGF165's ability to (1) alter the vascular network of the adult rat striatum, (2) influence the vascular growth of solid embryonic day 14 (E14) ventral mesencephalic (VM) grafts when placed into a VEGF-pretreated host striatum, (3) alter the function and survival of E14 VM grafts when transplanted into an adult DA-deleted striatum, and (4) influence cell survival and neurite growth in cultures of E14 VM cells. We demonstrate here that a single bolus injection of VEGF165 into the adult rat striatum significantly increases the amount of vasculature in the vicinity of the injection site in a delayed and transient manner when compared to saline controls. Transplanting solid E14 VM grafts into the VEGF165-pretreated striatum resulted in a homogeneous distribution of small blood vessels throughout the graft, a pattern that closely resembles mature adult vasculature. In contrast, grafts in the control condition contained a patchy distribution of heavily dilated vessels. Behavioral measurements indicate that VEGF pretreatment of the intrastriatal graft site accelerates recovery of amphetamine-induced rotational asymmetry in unilateral 6-OHDA lesioned rats. Unexpectedly, however, VEGF pretreatments failed to increase survival of tyrosine hydroxylase-immunoreactive (THir) neurons in the grafts. In contrast to this finding in vivo, adding VEGF165 to glial-reduced E14 rat VM cultures produced a fourfold increase in THir cell survival and a doubling in the length of THir neurites. We conclude that with the proper method of delivery, VEGF165 may prove to be one of several strategies necessary to significantly improve the survival and function of fetal VM tissue grafts.

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.

Rat nigral xenografts survive in the brain of MHC class II-, but not class I-deficient mice

We have examined the role of the indirect pathway of antigen recognition and T cells in neural xenografts rejection by using major histocompatibility complex (MHC) class II-deficient mice as xenograft recipients. Dissociated embryonic ventral mesencephalic tissue from Sprague-Dawley rats was stereotaxically injected as a cell suspension into the striatum of MHC class II-deficient adult mice as well as MHC class I-deficient and wild-type mice as controls. All of the MHC class II-deficient mice had surviving grafts in the striatum 4 weeks post-grafting. In contrast, only a few of the MHC class I-deficient mice exhibited very small grafts and none of the wild-type mice had any surviving grafts. The mean number of surviving transplanted dopamine neurons in the MHC class II-deficient group was significantly larger than that observed in the other two groups. Moderate levels of MHC class I antigen expression were seen in the transplantation sites of some animals in the MHC class II-deficient group. No helper or cytotoxic T cells were observed infiltrating into the graft sites of this group. However, there were markedly increased levels of expression of MHC class I and class II antigens, and a number of T cells infiltrating in the graft sites in both the MHC class I-deficient and wild-type groups. These results show that rat embryonic nigral tissue can survive transplantation in the brain of the MHC class II-deficient mice for at least 4 weeks without any overt signs of rejection, suggesting that the indirect pathway of foreign antigen recognition mediated by host MHC class II molecules and helper T cells plays an important role in the rejection responses to intracerebral xenografts.

Cellular replacement therapy for Parkinson's disease--where we are today?

The concept of replacing lost dopamine neurons in Parkinson's disease using mesencephalic brain cells from fetal cadavers has been supported by over 20 years of research in animals and over a decade of clinical studies. The ambitious goal of these studies was no less than a molecular and cellular "cure" for Parkinson's disease, other neurodegenerative diseases, and spinal cord injury. Much research has been done in rodents, and a few studies have been done in nonhuman primate models. Early uncontrolled clinical reports were enthusiastic, but the outcome of the first randomized, double blind, controlled study challenged the idea that dopamine replacement cells can cure Parkinson's disease, although there were some significant positive findings. Were the earlier animal studies and clinical reports wrong? Should we give up on the goal? Some aspects of the trial design and implantation methods may have led to lack of effects and to some side effects such as dyskinesias. But a detailed review of clinical neural transplants published to date still suggests that neural transplantation variably reverses some aspects of Parkinson's disease, although differing methods make exact comparisons difficult. While the randomized clinical studies have been in progress, new methods have shown promise for increasing transplant survival and distribution, reconstructing the circuits to provide dopamine to the appropriate targets and with normal regulation. Selected promising new strategies are reviewed that block apoptosis induced by tissue dissection, promote vascularization of grafts, reduce oxidant stress, provide key growth factors, and counteract adverse effects of increased age. New sources of replacement cells and stem cells may provide additional advantages for the future. Full recovery from parkinsonism appears not only to be possible, but a reliable cell replacement treatment may finally be near.

Angiogenic and astroglial responses to vascular endothelial growth factor administration in adult rat brain

The effects of exogenous vascular endothelial growth factor (VEGF) on angiogenesis, blood-brain barrier permeability and astroglial proliferation in the adult rat CNS in situ were investigated. Recombinant human VEGF(165) (25 or 50 ng/ml) was delivered for up to 1 week using either intracerebral osmotic minipumps or less traumatic subdural gelatin sponge placement. By 3 days, VEGF delivery caused significantly increased cerebral angiogenesis (25 ng/ml was most effective) in both experimental models when compared to saline controls; VEGF infusion resulted in a 100% increase in an index of vascular proliferation, and gelatin sponge delivery produced a 65% increase. The blood-brain barrier hallmark endothelial glucose transporter-1 was not present in nascent vascular sprouts. Infusion of VEGF produced extensive protein leakage that persisted after saline-induced permeability was mostly resolved, while gelatin sponge administration caused milder barrier dysfunction. Administration of the angiogenic factor had unexpected proliferative effects on astroglia in both models, resulting in an 80-85% increase in mitotically active astroglia when compared to controls. Immunohistochemical results and semi-quantitative reverse transcriptase-polymerase chain reaction indicated that the VEGF receptors flk-1 and flt-1 were up-regulated in response to the infusion trauma; flt-1 was localized to reactive astroglia, while flk-1 was expressed in vascular endothelium but predominantly in neuronal somata and processes adjacent to the delivery site. mRNA for the VEGF(121), VEGF(165) and VEGF(188) isoforms was also increased after delivery of the recombinant protein. These data show that VEGF application has substantial proliferative effects on CNS endothelium and astroglia and causes up-regulation of its own message. Flt-1 and flk-1 receptor mRNAs and proteins are up-regulated in both vascular and non-vascular cell types following infusion trauma. From these results we suggest that administered VEGF has heretofore unanticipated pleiotrophic effects in the adult CNS.

Changes in astroglial GLT-1 expression after neural transplantation or stab wounds

Uncontrolled release of glutamate from damaged brain initiates events that result in excitotoxic neuronal death. Glutamate uptake by specialized astroglial transporters is essential for control of extracellular glutamate levels. Many studies have demonstrated a reduction in astrocytic GLT-1 expression after different forms of injury. Because extensive neuronal death does not occur after direct cortical stab wounds and viable developing neurons populate fetal CNS grafts, we hypothesized that reactive astroglia associated with these procedures might maintain or up-regulate GLT-1. We examined the temporal and spatial distribution of GLT-1, GFAP and nestin proteins by confocal double-label immunohistochemistry combined with a new methodology in which precise brain areas are microdissected and analyzed for protein content by immunoaffinity chromatography. In stab wounds, GLT-1 protein content did not change compared to normal cortex, as determined by direct protein measurements; GLT-1 colocalized with nestin- and GFAP(+) astroglia adjacent to the lesion. In contrast, host reactive astroglia adjacent to grafts significantly upregulated GLT-1 by 3 days postoperative. The GFAP protein analysis suggests that increased GLT-1 is not the result of greater numbers of activated astroglia around grafts, but that developing graft tissue influences adjacent host astroglia to upregulate GLT-1. GLT-1 protein within grafts was rapidly accelerated to mature levels by just three days, and was expressed by the nestin(+) cell population. These data, which demonstrate immunoexpression of GLT-1 protein combined with a new method for protein measurement in situ indicate that, in contrast to other injury models, astroglial GLT-1 is upregulated or maintained following invasive CNS procedures. (c)2002 Elsevier Science (USA).

Solid human embryonic spinal cord xenografts in acute and chronic spinal cord cavities: a morphological and functional study

While therapeutic spinal cord grafting procedures are of interest in the chronic spinal cord injury stage, previous experimental grafting studies, including human spinal cord tissue, have mainly focused on the acute stage. Therefore, solid human embryonic spinal cord grafts were implanted in acute or chronic spinal cord aspiration cavities of immunodeficient rats to compare the morphological and locomotor outcome to that of lesion alone cases. Locomotor function was assessed using the Basso, Beattie, and Bresnahan open-field locomotor rating scale up to 6 months, while the morphological evaluation of graft survival, growth, and integration was performed at 6 weeks or 6 months after implantation. Graft survival was 94% in both lesion models, while graft growth was enhanced in the chronic compared to the acute cavity group. Human specific Thy-1 and neurofilament immunoreactive fibers were observed up to 7 mm into host white matter, while aminergic fibers were observed up to 1 mm into the grafts. Abundant calcitonin gene-related peptide immunoreactive fibers in the grafts in the absence both of immunoreactive cell bodies and colocalized human-specific neurofilament immunoreactivity, suggested host fiber ingrowth. At 6 months, the grafted cases presented less central canal deformation and lower glial fibrillary acidic protein immunoreactivity at the host cavity border compared to that of the nongrafted cases. The strong compensatory regain of locomotor function after unilateral spinal cord lesions was not affected by the human spinal cord grafts. In conclusion, solid human embryonic spinal cord tissue transplanted to a cavity in the adult injured spinal cord results in beneficial morphological effects in both the acute and chronic spinal cord lesion.

Diminished survival of mesencephalic dopamine neurons grafted into aged hosts occurs during the immediate postgrafting interval

The survival rate of dopamine (DA) neurons in mesencephalic grafts to young adult rats is poor, estimated at 5-20%, and even poorer in grafts to the aged striatum. Grafted cells die in young adult rats during the first 4 days after implantation. The present study was undertaken to determine whether the decreased survival of DA neurons in grafts to aged rats is (1) due to additional cell death during the immediate postgrafting interval or (2) due to protracted cell loss during longer postgrafting intervals. We compared survival rates of tyrosine hydroxylase-immunoreactive (THir) neurons in cell suspension grafts to young adult (3 months) and aged (24 months) male Fischer 344 rats at 4 days and 2 weeks after transplantation. At 4 days after grafting, mesencephalic grafts within the aged rat striatum contain approximately 25% of the number of THir neurons in the same mesencephalic cell suspension grafted to young adult rats. This corroborates the decreased survival of grafted DA neurons we have demonstrated previously at 10 weeks postgrafting. THir neurons in grafts to the intact striatum possessed a significantly shorter "long axis" than their counterparts on the lesioned side. No significant differences in the number of apoptotic nuclear profiles or total alkaline phosphatase staining between mesencephalic grafts to young and aged rats were detectable at 4 days postgrafting. In summary, the present study indicates that the exaggerated cell death of grafted DA neurons that occurs following implantation to the aged striatum occurs during the immediate postgrafting interval, timing identical to that documented for young adult hosts.

Survival of intrastriatal xenografts of ventral mesencephalic dopamine neurons from MHC-deficient mice to adult rats

Previous studies of neural xenografts have used immunosuppressive agents to prevent graft rejection. In the present study we have examined the survival of mouse dopamine neurons lacking either MHC class I or MHC class II molecules transplanted into rat brains and the host immune and inflammatory responses against the xenografts. Survival of neural grafts was immunocytochemically determined at 4 days, 2 weeks, and 6 weeks after transplantation by counting tyrosine hydroxylase (TH)-positive cells in the graft areas. In addition, the host immune and inflammatory responses against neural xenografts were evaluated by semiquantitatively rating MHC class I and class II antigen expression, accumulation of macrophages and activated microglia, and infiltration of CD4- and CD8-positive T-lymphocytes. For the negative controls, the mean number of TH-positive cells in rats that received wild-type mouse tissue progressively decreased at various time periods following transplantation. In contrast, intrastriatal grafting of either MHC class I or MHC class II antigen-depleted neural xenografts resulted in a prolonged survival and were comparable to cyclosporin A-treated rats that had received wild-type mouse tissue. These results indicate that genetically modified donor tissue lacking MHC molecules can be used to prevent neural xenograft rejection.

Time course of apoptotic cell death within mesencephalic cell suspension grafts: implications for improving grafted dopamine neuron survival

The vast majority ( congruent with 90%) of embryonic mesencephalic dopamine (DA) neurons die following transplantation to the striatum. Recent reports indicate that at least a subpopulation of grafted cells undergo apoptotic cell death at early times following implantation. This study examines the temporal pattern and magnitude of apoptotic cell death following the implantation of mesencephalic cell suspension grafts. Two techniques, a modified terminal deoxynucleotide-mediated nucleotide end labeling (TUNEL) technique and cresyl violet staining, are used to assess apoptotic cell death by detection of its biochemical and morphological identifiers, respectively. Male, Fischer 344 rats were examined at 1, 4, 7, and 28 days following implantation of embryonic day 14 (E14) ventral mesencephalic cells to the DA-denervated striatum. Results indicate that the overwhelming majority of apoptotic cell death occurs within the first 7 days after transplantation. However, the impact of the apoptosis that occurs over the first week following grafting only appears to limit grafted tyrosine hydroxylase-immunoreactive (THir) neuron survival during the first 4 days. No significant differences between the survival rates of THir neurons at 4 days after grafting and at 28 days after grafting were found. Therefore, it appears that the critical interval during which an estimated 90% of grafted DA neurons die is during the first 4 days postimplantation and that a major contributor to this cell death is apoptosis.

Imaging the rat brain on a 1.5 T clinical MR-scanner

Magnetic resonance imaging (MRI) offers a noninvasive technique for studying neurodegenerative events in the rat brain, however, most of the studies are performed on small bore purpose dedicated MR scanners of limited availability and at high cost. The present study explored the feasibility of using a clinical whole body MR-scanner to perform imaging in rat brain and specifically in models of Parkinson's (PD) and Huntington's disease (HD). For that purpose rats were placed into a specially designed PVC device equipped with a flexible surface coil-and T2-weighted spin echo sequences were acquired on a Siemens Magnetom Vision at 1.5 T. In the experimental protocols of PD and HD, animals underwent 6-hydroxydopamine (6-OHDA) and quinolinic acid (QA) injections, respectively and were subsequently grafted with fetal tissue. T2-weighted images showed a small hyperintense area at the 6-OHDA lesion site and a diffuse hyperintensity in the striata with QA lesions. Transplants were seen as a hypointense area surrounded by a hyperintense rim on T1-weighted images. Moreover, disturbances of the blood-brain-barrier and its time of restoration could be monitored. In conclusion, high-resolution in vivo imaging of small animals is feasible with clinical MR-scanners and hence allows the study of various experimental protocols.

Protein synthesis inhibition in neocortical grafts evaluated by systemic amino acid uptake autoradiography

The temporal pattern of protein synthesis inhibition was examined in grafted neocortical neurons using [(3)H]valine in vivo autoradiography. Neuronal uptake levels of systemically administered (3)H-labeled amino acids which cross the blood-brain barrier (BBB) via endothelial cell neutral carriers have long been a hallmark in studies of experimental ischemic pathology; there is likely a strong correlation between persistent protein synthesis inhibition and the progression of cell damage. Because the grafting procedure involves the loss of blood flow and the subsequent reperfusion of the donor tissue there are, mechanistically, important similarities to reversible ischemia models. The effects of ischemic injury on grafted CNS neurons are not fully understood. Quantitative analysis of grain distribution in individual graft or control (adjacent host cortex) neurons indicated an initial breakdown of the amino acid barrier system, subsequent recovery, and progressive reduction of amino acid uptake by 1 year. Up to 3 weeks after surgery grafts were flooded with the [(3)H]valine tracer but individual neurons contained relatively few silver grains. After this time, the tracer was normally distributed within graft neurons but at significantly lower levels than in controls. Grain density gradually decreased over time such that 12-month grafted neurons had approximately half that compared to control and only 58% of that in 2-month grafts; the 12-month levels were comparable to those observed at early (10 days) postoperative times. Autoradiography of immunostained sections for MAP-2, SMI 311 (neurofilament marker), and neuron-specific enolase showed reduced expression of these proteins in neurons coupled with weak amino acid tracer uptake. The results further suggest that grafted neurons bear intriguing similarities to neurons placed at ischemic risk, particularly "penumbral" neurons, which are affected by reduced blood flow and are metabolically weakened. The loss of BBB properties in early grafts may also extend to the endothelial cell amino acid carrier system, and the delayed revascularization process could affect neuronal uptake mechanisms.

Transient coexpression of nestin, GFAP, and vascular endothelial growth factor in mature reactive astroglia following neural grafting or brain wounds

The spatial and temporal immunoexpression of the intermediate filament (IF) protein nestin and its relationship to glial fibrillary acidic protein (GFAP), vascular endothelial growth factor (VEGF), and its receptor flt-1 (VEGF-R1) in reactive astroglia was examined following stab wounds or transplants of fetal CNS tissue into the adult brain. Since developmentally regulated proteins and gene transcripts can be reexpressed in reactive astroglia following certain brain injuries, we analyzed the nestin profile in these experimental paradigms in order to more fully understand the nature of the gliotic "scar." Nestin expression was transiently up-regulated in some but not all astrocytes which often had a different morphology than the typical stout, stellate GFAP (+) cells; the processes of the nestin (+) cells tended to be slender and elongated. In reactive astroglia from the mature brain, nestin expression was robust but generally localized to the wound or graft site, peaked at 7-10 days postoperative, and was absent by 28 days, whereas GFAP (+) astrocytes were far more widespread and persisted for many months. Only nestin was strongly expressed immediately adjacent to early stab wounds, whereas GFAP (+) cells were located further from the wound sites. In contrast, there was marked nestin/GFAP colocalization at the graft/host interface. Semiquantitative analysis combined with confocal microscopy revealed a unique compartmentalization of protein expression; processes from single astrocytes could be entirely nestin (+), GFAP (+), or could show coexpression. At 4, 7, and 14 days postoperative, 41, 58, and 32% of the immunoexpression, respectively, was accounted for by nestin at the graft/host interface, and it was essentially undetectable at 28 days postoperative. In situ hybridization studies showed nestin transcripts within GFAP (+) cells primarily between 4 and 10 days postoperative and absent by 28 days. Many nestin (+) astrocytes, as shown by electron microscopy, were closely related to the vasculature. Therefore we further examined the expression of vascular endothelial growth factor (VEGF), an endothelial cell mitogen associated with angiogenesis. Nestin colocalized with VEGF in some astrocytes (7%) but far more prominently with the VEGF flt-1 receptor (25%). Early astroglial activation may involve several different IF components and possibly a distinct astrocytic population that shows a rapid, transient nestin expression adjacent to injury sites. Expression of the nestin IF phenotype within affected astrocytes in the surgical vicinity may be indicative of a reversion to an immature phenotype that might be less susceptible to attendant hypoxia after injury. Since injured astrocytes are well known to express many bioactive compounds, such transient reexpression of early, developmentally regulated proteins may be a hallmark for the elaboration of growth factors such as VEGF.

Human natural antibodies cytotoxic to pig embryonic brain cells recognize novel non-Galalpha1,3Gal-based xenoantigens

Transplantation of porcine embryonic brain cells, including dopaminergic neurons, from ventral mesencephalon (VM) is considered a potential treatment for patients with Parkinson's disease. In the present study, we characterized the distribution among VM cells of the major porcine endothelial xenoantigen, the Galalpha1,3Gal epitope, and evaluated the cytotoxic effect of anti-Galalpha1,3Gal antibody-depleted and nondepleted human AB serum on VM cells. Overall levels of Galalpha1,3Gal-epitope expression was very low on the VM cell population using Bandeiraea simplicifolia IB(4) lectin staining of resuspended VM cells in flow cytometric analyses or staining of SDS-PAGE-separated, solubilized VM cell membrane proteins in Western blot analyses. Lectin-histochemical staining of sections of pig embryonal VM regions with BSA IB(4) lectin showed staining restricted to endothelial cells and microglia. In the presence of complement, both nondepleted and anti-Galalpha1,3Gal antibody-depleted AB sera were shown to be cytotoxic to VM cells as assessed in microcytotoxicity- and flow cytometry-based cytotoxicity assays. Purified IgM and IgG were both cytotoxic in the presence of complement. Three major VM cell membrane antigens of approximately 210, 105, and 50 kDa were reactive with natural IgM antibodies present in pooled human AB sera. Thus, antibody-dependent cytotoxicity may contribute to pig to human brain cell xenorejection, necessitating donor tissue modifications prior to a more widespread utilization of neural tissue xenografting.

Striatal grafts in a rat model of Huntington's disease: time course comparison of MRI and histology

Survival and integration into the host brain of grafted tissue are crucial factors in neurotransplantation approaches. The present study explored the feasibility of using a clinical MR scanner to study striatal graft development in a rat model of Huntington's disease. Rat fetal lateral ganglionic eminences grown as free-floating roller-tube cultures were grafted into the quinolinic acid-lesioned striatum, and T1- and T2-weighted sequences were acquired at 2, 7, 21, and 99 days posttransplantation. MR images were then compared with images of corresponding histological sections. The lesion-induced striatal degeneration caused a progressive ventricle enlargement, which was significantly different from controls at 21 days posttransplantation. Seven days posttransplantation, T1-weighted images revealed a defined liquid-isointense signal surrounded by a hyperintense rim at the site of graft placement, which was found unaltered for the first 21 days posttransplantation, whereas a hypointense graft signal was detected at 99 days posttransplantation. At 2 days posttransplantation, T2-weighted images showed the graft region as a hyperintense area surrounded by a rim of low signal intensity but at later time-points graft location could not be further verified. Measures for graft size and ventricle size obtained from MR images highly correlated with measures obtained from histologically processed sections (R = 0.8, P < 0.001). In conclusion, the present study shows that fetal rat lateral ganglionic eminences grown as free-floating roller-tube cultures can be successfully grafted in a rat Huntington model and that a clinical MR scanner offers a useful noninvasive tool for studying striatal graft development.

VEGF mRNA and its receptor flt-1 are expressed in reactive astrocytes following neural grafting and tumor cell implantation in the adult CNS

Significant angiogenesis occurs only after injury in the adult mammalian brain; capillaries proliferate and astrocytes are activated by presently unresolved cellular mechanisms. Because of the intimate relationship between astrocytes and brain capillaries we examined the expression of the specific endothelial mitogen vascular endothelial growth factor (VEGF) in reactive astrocytes following CNS trauma models: neural grafting, stab wounds, and glioma implantation. In situ hybridization was combined with GFAP immunohistochemistry to delineate VEGF mRNA expression in reactive astrocytes. In addition, VEGF and its receptor flt-1 protein expression were detected immunohistochemically. In all three models we found unexpectedly that only reactive astrocytes, not endothelium, expressed the VEGF receptor flt-1, VEGF mRNA, and VEGF protein in a spatiotemporal manner, suggesting that activated astroglia may have a direct role in the induction of angiogenesis or permeability in mature brain. In addition, secreted VEGF may play a part in astroglial signalling by the induction of its own receptor in reactive astroglia following injury. These findings may have significant implications with regard to growth and reparative mechanisms of the adult cerebrovasculature.

Quinolinic acid-induced inflammation in the striatum does not impair the survival of neural allografts in the rat

It has been suggested that inflammation related to intracerebral transplantation surgery can affect the survival of intrastriatal neural allografts. To test this hypothesis, we transplanted dissociated embryonic mesencephalic tissue from one of two rat strains, Lewis (allogeneic grafts) or Sprague-Dawley (syngeneic grafts), to the striatum of Sprague-Dawley rats. The target striatum was either intact or had received a local injection of quinolinic acid 9 days earlier, in order to induce a marked inflammation. At 6 or 12 weeks after transplantation, there was no significant difference between the different groups regarding the number of surviving grafted tyrosine hydroxylase immunoreactive neurons. However, the graft volume of both the syngeneic and allogeneic implants was significantly larger in the quinolinate-lesioned than in the intact striatum. There were dramatically increased levels of expression of major histocompatibility complex class I and II antigens, marked infiltrates of macrophages, activated microglia and astrocytes, and accumulation of large numbers of CD4 and CD8 positive T-lymphocytes in the quinolinate-lesioned striatum. In contrast, these immunological markers were much less abundant around both syngeneic and allogeneic grafts placed in intact striatum. We conclude that severe inflammation caused by quinolinic acid does not lead to rejection of intrastriatal neural allografts.

Patterns of brain angiogenesis after vascular endothelial growth factor administration in vitro and in vivo

Vascular endothelial growth factor (VEGF) is a secreted endothelial cell mitogen that has been shown to induce vasculogenesis and angiogenesis in many organ systems and tumors. Considering the importance of VEGF to embryonic vascularization and survival, the effects of administered VEGF on developing or adult cerebrovasculature are unknown: can VEGF alter brain angiogenesis or mature cerebrovascular patterns? To examine these questions we exposed fetal, newborn, and adult rat cortical slice explants to graduated doses of recombinant VEGF. The effects of another known angiogenic factor, basic fibroblast growth factor (bFGF), were evaluated in a comparable manner. In addition, we infused VEGF via minipump into the adult cortex. Significant angiogenic effects were found in all VEGF experiments in a dose-responsive manner that were abolished by the addition of VEGF neutralizing antibody. Fetal and newborn explants had a highly complex network of branched vessels that immunoexpressed the flt-1 VEGF receptor, and flk-1 VEGF receptor expression was determined by reverse transcription-PCR. Adult explants had enlarged, dilated vessels that appeared to be an expansion of the existing network. All bFGF-treated explants had substantially fewer vascular profiles. VEGF infusions produced both a remarkable localized neovascularization and, unexpectedly, the expression of flt-1 on reactive astrocytes but not on endothelial cells. The preponderance of neovascularization in vitro and in vivo, however, lacked the blood-brain barrier (BBB) phenotype marker, GLUT-1, suggesting that in brain the angiogenic role of VEGF may differ from a potential BBB functional role, i.e., transport and permeability. VEGF may serve an important capacity in neovascularization or BBB alterations after brain injury.

Neurotransmitter and amino acid analysis and ultrastructural observations of fetal brain cortex transplantation to adult rat brain under the effect of dexamethasone

OBJECTIVE

To conduct an investigation of fetal cortical tissue graft survival using transmission electron microscopy and analyzing neurotransmitters and amino acids and their function, with special reference to the effect of dexamethasone.

METHODS

Transplantation of fetal cortical brain tissue to 100 adult Wistar albino rats weighing 170 to 220 g was performed. The rats were divided into three groups. Only transplantation of fetal cortical brain tissue was performed in the first group (n=36). In the second group (n=48), dexamethasone was administered in addition to fetal cortical tissue transplantation. The third group (n=16) was used as the surgical control group. The rats were allowed to live for 6 weeks and were then decapitated. The grafts were examined by electron microscopy. Additionally, quantitative analyses of the neurotransmitters and amino acids of the grafts were conducted using high-pressure liquid chromatography.

RESULTS

Electron microscopic observations revealed that the grafts were still surviving at the end of the 6th week in both groups. However, in the group that received dexamethasone, neurons and their organelles were better developed than in the group that did not receive dexamethasone. Concommitantly, results of quantitative analysis in the dexamethasone group revealed statistically extremely significant higher amino acid values for glutamic acid, aspartic acid, beta-alanine, and lysine and significantly higher values for gamma-aminobutyric acid, glutamine, glycine, and serine when compared to the nondexamethasone group.

CONCLUSION

Dexamethasone is effective in increasing the survival and in developing the ultrastructural and functional outcome of transplanted neurons in fetal grafts.

Characteristics of human fetal spinal cord grafts in the adult rat spinal cord: influences of lesion and grafting conditions

The present study evaluated the growth potential and differentiation of human fetal spinal cord (FSC) tissue in the injured adult rat spinal cord under different lesion and grafting conditions. Donor tissue at 6-9 weeks of gestational age was obtained through elective abortions and transplanted either immediately into acute resection (solid grafts) or into chronic contusion (suspension and solid grafts) lesions (i.e., 14-40 days after injury) in the thoracic spinal cord. The xenografts were then examined either histologically in plastic sections or immunocytochemically 1-3 months postgrafting. Intraspinal grafts in acute lesions demonstrated an 83% survival rate and developed as well-circumscribed nodules that were predominantly composed of immature astrocytes. Solid-piece grafts in chronic contusion lesions exhibited a 92% survival rate and also developed as nodular masses. These grafts, however, contained many immature neurons 2 months postgrafting. Suspension grafts in chronic contusion lesions had an 85% survival rate and expanded in a nonrestrictive, diffuse pattern. These transplants demonstrated large neuronally rich areas of neural parenchyma. Extensive neuritic outgrowth could also be seen extending from these grafts into the surrounding host spinal cord. These findings show that human FSC tissue reliably survives and differentiates in both acute and chronic lesions. However, both the lesion environment and the grafting techniques can greatly influence the pattern of differentiation and degree of host-graft integration achieved.

Rat intrastriatal neural allografts challenged with skin allografts at different time points

The present study was designed to address two questions. First, can an intrastriatal neural allograft exhibit long-term survival (18 weeks) if the host is immunized by an orthotopic skin graft 6 weeks after neural transplantation (the 6w-Long group)? Second, can an intrastriatal neural allograft survive when the host is challenged by an orthotopic skin allograft either simultaneously (Sim) with the intracerebral graft surgery or 2 (2w) weeks later? Dissociated embryonic ventral mesencephalic tissue from Lewis rats was stereotaxically injected into the striatum of Sprague-Dawley rats with unilateral 6-hydroxydopamine lesions. Six weeks after neural grafting, no reduction in amphetamine-induced motor asymmetry was observed in the Sim and 2w groups. At 6 weeks after skin grafting, the mean motor asymmetry scores had returned to the initial pretransplantation levels in the 6w-Long group. All the neural allografts in the Sim group were completely rejected, and the mean number of tyrosine hydroxylase immunoreactivity neurons in the grafts was significantly reduced in the 2w and the 6w-Long group, when compared to the no-skin control group. There were very high levels of expression of MHC class I and II antigens, marked cellular infiltrates containing macrophages and T-lymphocytes, and several activated microglia and astrocytes in and around the surviving intracerebral transplants in the 2w and the 6w-Long groups. The results suggest that intrastriatal neural allografts are more likely to be rejected rapidly if the host is efficiently immunized with the same alloantigens simultaneously or soon after the neural transplantation than at a later time point. When established neural allografts are subjected to a strong immunological challenge, they undergo protracted rejection.

Cytoskeletal Protein Immunoexpression in Fetal Neural Grafts: Distribution of Phosphorylated and Nonphosphorylated Neurofilament Protein and Microtubule-Associated Protein 2 (Map-2)

The present study examined the immunocytochemical expression of important cytoskeletal proteins within the neurons of an extended series of neocortical grafts and smaller group of ventral mesencephalic (nigral) grafts. Using antibodies that were directed at all three neurofilament (NF) epitopes, NF-L, NF-M, and NF-H, we attempted to determine whether these neurons would have an altered cytoskeletal profile following the stress of transplantation, because previous studies have shown such changes following ischemia or direct brain injury. We studied phosphorylated NF protein, which is found predominantly in axons, nonphosphorylated NF protein, which is found predominantly in the somata-dendritic compartment, and MAP-2, a specific microtubule marker that is localized exclusively in the somato-dendritic compartment. The results show that in all neocortical grafts examined, both phosphorylated and nonphosphorylated NF immunoexpression was significantly downregulated and appeared only in relatively few axons and somatic profiles, respectively, even though there were numerous Nissl-stained neuronal profiles in the grafts. There was no particular pattern to the immunopositive profiles. At later times occasional neuronal profiles were positive for phosphorylated NF protein, suggesting a reaction to cellular injury. In contrast to neocortical grafts, the cytoskeletal profiles of MAP-2 and phosphorylated NF protein in nigral grafts appeared very similar to age-matched control although the nonphosphorylated NF protein expression did appear somewhat lessened at 1-2 mo postoperative. Because cytoskeletal proteins play important roles in neuronal size, shape, and structural stability, they may subserve key cellular issues in neural grafting. These results show a significant loss of cytoskeletal protein expression in neocortical grafts that does not occur in nigral grafts. These results suggest that fetal neurons from different brain regions (i.e., graft source) may respond differently to the grafting procedure insofar as their cytoskeletal makeup is concerned. In addition, a potential lack of appropriate growth substrates or synaptic contacts may also produce cytoskeletal alterations. As such, the cytoskeletal protein profiles in central nervous system (CNS) grafts may be useful markers for functional performance, perhaps reflecting a degree of cellular injury.

Cytoskeletal protein immunoexpression in fetal neural grafts: distribution of phosphorylated and nonphosphorylated neurofilament protein and microtubule-associated protein 2 (MAP-2)

The present study examined the immunocytochemical expression of important cytoskeletal proteins within the neurons of an extended series of neocortical grafts and smaller group of ventral mesencephalic (nigral) grafts. Using antibodies that were directed at all three neurofilament (NF) epitopes, NF-L, NF-M, and NF-H, we attempted to determine whether these neurons would have an altered cytoskeletal profile following the stress of transplantation, because previous studies have shown such changes following ischemia or direct brain injury. We studied phosphorylated NF protein, which is found predominantly in axons, nonphosphorylated NF protein, which is found predominantly in the somata-dendritic compartment, and MAP-2, a specific microtubule marker that is localized exclusively in the somato-dendritic compartment. The results show that in all neocortical grafts examined, both phosphorylated and nonphosphorylated NF immunoexpression was significantly downregulated and appeared only in relatively few axons and somatic profiles, respectively, even though there were numerous Nissl-stained neuronal profiles in the grafts. There was no particular pattern to the immunopositive profiles. At later times occasional neuronal profiles were positive for phosphorylated NF protein, suggesting a reaction to cellular injury. In contrast to neocortical grafts, the cytoskeletal profiles of MAP-2 and phosphorylated NF protein in nigral grafts appeared very similar to age-matched control although the nonphosphorylated NF protein expression did appear somewhat lessened at 1-2 mo postoperative. Because cytoskeletal proteins play important roles in neuronal size, shape, and structural stability, they may subserve key cellular issues in neural grafting. These results show a significant loss of cytoskeletal protein expression in neocortical grafts that does not occur in nigral grafts. These results suggest that fetal neurons from different brain regions (i.e., graft source) may respond differently to the grafting procedure insofar as their cytoskeletal makeup is concerned. In addition, a potential lack of appropriate growth substrates or synaptic contacts may also produce cytoskeletal alterations. As such, the cytoskeletal protein profiles in central nervous system (CNS) grafts may be useful markers for functional performance, perhaps reflecting a degree of cellular injury.

Quantitative analysis of vascularization and cytochrome oxidase following fetal transplantation in the contused rat spinal cord

In the normal adult central nervous system, a coupling between energy consumption and vascular density is well established. Likewise, the survival of fetal neural tissue grafts is highly dependent on the establishment of functional vascular integration with the host. However, to what degree graft vascularization and tissue metabolism influence the normal host response to traumatic injury has not been extensively studied. In the present report, embryonic day 14 fetal spinal cord suspension grafts were made into the lesion epicenter of subchronic (10 days) contusion-injured rats. Three months later, intraspinal transplants were analyzed using correlative cytochrome oxidase histochemistry and vascular morphometric analysis. The same approaches were applied to the host spinal cord and injured, non-transplanted animals in order to determine the ability of a graft to alter the level of post-injury vascularization and/or metabolism. In general, graft vascular density was increased over that measured in normal or injured gray matter. Vascular density in gray matter near the host/graft interface was markedly increased when compared to either gray matter of the same spinal level in injured non-grafted animals or normal control spinal gray matter. Vascular changes were not noted in gray matter 3 mm distal to the lesion epicenter (rostral or caudal) in all groups analyzed. Cytochrome oxidase was up-regulated at this time in the graft and gray matter at the host/graft interfaces when compared to either gray matter of the same spinal level in injured, non-grafted animals or that of uninjured controls. These data indicate that an intraspinal transplant placed into the contused adult rat spinal cord reaches a metabolic capacity that is likely to be associated with high levels of oxidative metabolism in the well-vascularized graft neuropil. In addition, transplantation chronically alters vascularization and metabolic patterns of adjacent spinal gray matter following contusion injury.

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.

Immune reactions following systemic immunization prior or subsequent to intrastriatal transplantation of allogeneic mesencephalic tissue in adult rats

We have previously found that dissociated mesencephalic tissue, which differs from the host at both major histocompatibility complex and non-major histocompatibility complex gene loci, can survive stereotaxic transplantation to the striatum of adult rats. We have now studied the outcome of intrastriatal neural allografts in rats that were systemically immunized by an orthotopic skin allograft either prior or subsequent to intracerebral implantation surgery. Dissociated mesencephalic tissue from Lewis rat embryos was stereotaxically injected into the dopamine-depleted striatum of hemi-parkinsonian Sprague-Dawley rats. One group was immunized by an orthotopic allogeneic skin graft of the same genetic origin as the neural graft, six weeks before the neural transplantation (the pre-immunized group). Another group was post-immunized by an orthotopic skin allograft, six weeks after the neural transplantation (the post-immunized group). A control group of rats was not challenged by a skin allograft. Marked behavioural recovery was observed in six of seven rats in the control group, in six of eight rats in the post-immunized group, and in none of the pre-immunized rats. Tyrosine hydroxylase-immunopositive cells were found in rats from the two behaviourally compensated groups, but not in the pre-immunized group. The immune responses were evaluated by OX-18 (monoclonal antibody against major histocompatibility complex class I antigen), OX-6 (major histocompatibility complex class II antigen), OX-42 (microglia and macrophages), glial fibrillary acidic protein (astrocytes), OX-8 (cytotoxic T-lymphocytes) and W3/25 (helper T-lymphocytes) immunocytochemistry. All the neural allografts in the pre-immunized group were rejected, leaving scars only. There were more intense immune responses to the allografts in the post-immunized group than the control group, in terms of immunocytochemically higher expression of major histocompatibility complex class I and II antigens and more intense cellular reactions consisting of macrophages, activated microglia and astrocytes, in addition to CD8- and CD4-positive lymphocytes. In summary, the results show the following: (i) systemic pre-immunization leads to complete rejection of intrastriatal neural allografts, implying that the status of the host immune system before transplantation determines the outcome for intrastriatal neural allografts; (ii) established intrastriatal neural allografts can survive for at least six weeks after systemic immunization, in spite of increased host immune responses in and around the allografts; (iii) there are no marked immune reactions against intrastriatal neural allografts 13 weeks after implantation in rats which have not been systemically immunized by a skin allograft; (iv) pre-immunized rats may provide a very useful animal model to investigate the role of inflammatory lymphokines in immune rejection and to test alternative immunosuppressive drugs.

Diminished Expression of Microtubule-Associated Protein (MAP-2) and β-Tubulin as a Putative Marker for Ischemic Injury in Neocortical Transplants

The present study examined the immunoexpression of the neuronal cytoskeletal proteins, MAP-2 and β-tubulin within a timed series of rat fetal neocortical transplants. β-tubulin is a major component of microtubules and MAP-2 regulates the assembly and stability of neuronal microtubules and is a major site for the phosphorylation cAMP dependent protein kinase in neurons. Both proteins are strongly expressed in the soma and dendrites of normal neurons. MAP-2 has been shown to be a sensitive marker for ischemia in neurons and is downregulated in this form of injury. Immunoexpression of both MAP-2 and β-tubulin in grafted cortical neurons was markedly reduced when compared to age-matched or even perinatal specimens at all postoperative times. Dendritic staining was confined to random, thin processes with no laminar patterns and staining within somata was very weak. In some specimens, somatic expression was increased and dendrites were more robustly stained when a portion of the graft was juxtaposed to a fiber tract even though in other regions of the same graft there was very weak immunostaining. The present results corroborate previous studies of cortical transplants indicating an immature structure and metabolism, and it is suggested here that the primary factor is a sublethal form of ischemic injury. Another possibility for the relative paucity of cytoskeletal protein expression could be that transplanted neurons undergo a new developmental scheme (neodevelopment) that is brought about by truncated migration patterns and abnormal synaptic connections.

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

The present study was carried out to quantify the subsequent vascular regeneration around a lesion cavity made in the rat cerebral cortex and to decide the origin of the regenerated microvessels. A quantitative study utilizing computerized image analysis after microvascular perfusion with India ink indicated approximately 25 and 160% increase of the vascular density adjacent to the cavity compared to the contralateral cortex at 4 and 21 days, respectively, after lesioning. The microvasculature around the cavity was also evaluated by scanning electron microscopy of vascular corrosion casts. Newly formed leptomeningeal vessels began to grow down toward the floor of the cavity 4 days after lesioning and nearly covered the walls of the cavity 21 days after lesioning. A neovascular network of leptomeninges and connective tissue (e.g., dura) was formed as a roof over the cavity. Numerous branches of these newly formed vessels and prominent anastomoses with the capillary network in the walls and floor of the cavity were observed. Newly formed vessels also originated from the choroid plexus in cases where the lateral ventricle had been opened at the time of lesioning. These results document the plasticity of the vascular system in the cerebral cortex after a mechanical injury. The regenerated vascular network may offer a suitable condition for survival of transplanted tissues.

Immunocytochemical expression of the blood-brain barrier glucose transporter (GLUT-1) in neural transplants and brain wounds

The present study examined the immunocytochemical expression of the blood-brain barrier glucose transporter (GLUT-1) in a series of fetal neocortical transplants, autonomic tissue transplants, and stab wounds to the rat brain. GLUT-1 is one of a family of different glucose transporters and is found exclusively on barrier-type endothelial cells. In the brain it is responsible for the regulated facilitative diffusion of glucose across the blood-brain barrier. This investigation is the first to determine if this important molecule is altered during the process of angiogenesis that occurs following neural transplantation procedures or direct brain injury. Beginning in late fetal brain, e.g., E18 and continuing into maturity, GLUT-1 was strongly and exclusively expressed on normal cerebral vessels. In solid fetal central nervous system (CNS) transplants up to around 3 weeks postoperative, GLUT-1 was only weakly expressed, particularly as exemplified by colloidal gold immunostaining when compared with the host. At later times examined, up to 15 months postoperative, GLUT-1 immunoexpression was comparable with the normal adjacent brain. In autonomic tissue transplants, where the vessels do not have a blood-brain barrier, as expected, GLUT-1 was not expressed. In stab wounds, at 1 week there was extensive gliosis, and the injured vessels appeared fragmented and collapsed but still expressed GLUT-1, although to a somewhat lesser extent than normal brain. Between 3 and 6 weeks, GLUT-1 was expressed on tortuous vessels and in apparently fibrillar processes in the wound vicinity with a similar pattern to astrocyte (GFAP) reactivity. These results suggest the occurrence of a down-regulation of GLUT-1 in early transplants, perhaps related to reduced glycolytic activity or transient ischemia, or possibly due to the utilization of alternative energy sources. That GLUT-1 expression was not entirely lost in stab wounds to the mature brain suggests that the protein may be more labile in fetal or perinatal brain than in the adult and may not be affected by direct injury. Coupled with previous transplantation studies that have shown reduced neuronal glycolysis and potential barrier alterations, the reduction of GLUT-1 activity within nearly the identical time frame could indicate a relatively early critical period in cellular metabolism following transplantation of CNS tissue.

Angiogenesis and the blood-brain barrier in intracerebral solid and cell suspension grafts

Solid and suspension grafts of fetal central nervous system (CNS) tissue rapidly reform an intact blood-brain barrier (BBB), whereas solid grafts of peripheral nervous system (PNS) tissue fail to establish a BBB as detected by horseradish peroxide (HRP) leakage, administrated intravenously. We examined the acute changes in the BBB after grafting of fetal CNS tissue in solid and suspension form and superior cervical ganglion (SCG) and PNS tissue in the same manner. Adult rats (n = 20) received fetal (day 14-15) forebrain grafts (either solid or cell suspension) to their rostral corpus callosum bilaterally. A second group (n = 20) received SCG solid and cell suspension grafts at the same coordinates with the same technique. The animals were killed on first, third, seventh, and tenth days after grafting. Intravenous HRP (Sigma, type VI, 75 mg/5-g rat) was given 1 hour before perfusion with mixed aldehydes. Fifty-micron coronal sections were examined for the presence and location of the graft by cresyl violet and AChE staining and Mesulam's TMB method to detect HRP leakage. HRP leakage was detected in the parenchyma in all groups on the first and the third days post-transplantation indicating a disrupted BBB. No HRP reaction was seen at days 7 and 10 in groups receiving fetal forebrain tissue whether solid or cell suspension. Solid grafts of SCG consistently demonstrated HRP leakage from the first through the tenth day. However, cell suspension of SCG established a BBB by 7 days. These results suggest that within the solid grafts of CNS and PNS tissue, the permeability of the vessels is dictated by the transplanted tissue itself. When cell suspensions of the same tissue are introduced, host CNS tissue dominates as the local environment resulting in non-leaky vasculature within the graft.

Architectural alterations in rat cerebral microvessels after hypobaric hypoxia

We performed 3-dimensional studies of vascular casts of the microvasculature of the cerebral cortex of rats that were exposed to three weeks of hypobaric hypoxia and of control rats. Scanning electron microscopy of the casts gave the qualitative impression of increased vascularity of the cerebral cortex, particularly the deeper layers, in hypoxic rats. Quantitative analysis of capillary segment lengths revealed a significant shift in the frequency distribution to longer lengths (from 77 +/- 8 to 90 +/- 14 microns) in the deep, but not in the superficial, layers of the cerebral cortex of hypoxic rats. These findings agree with previous results reporting increased capillary density in the brain after exposure to prolonged hypobaric hypoxia and suggest that capillary segment elongation plays a role in the increased capillary density in the deeper layers of the cerebral cortex.

Immunocytochemical distribution of the brain glucose transporter (GLUT 1) in experimental gliosis

The present study has examined the immunocytochemical expression of the blood-brain barrier glucose transporter GLUT 1 as compared with GFAP in models of experimental gliosis. In neocortical grafts, gliosis was prominent at the graft-host interface mostly associated with blood vessels. Consecutive sections examined for anti-GLUT 1 showed that the protein was distributed in nearly an identical pattern to the anti-GFAP, staining fibrillar processes and all vessels and also appeared extracellularly. In stab wounds, GLUT 1 immunoexpression was similar to GFAP reactivity and stained injured vessels and glial-like processes that were reminiscent of astrocytic end-feet. Normal glial cells and processes in unaffected neuropil, however, were never stained. This report suggests that GLUT 1 protein may be upregulated in non-endothelial components, such as reactive astroglia or possibly microglia, that are associated with injured or angiogenic vessels.

Vascularization and microvascular permeability in solid versus cell-suspension embryonic neural grafts

Vascularization and microvascular permeability were assessed in a comparative study of solid (organized) and cell-suspension (dissociated) fetal nigral grafts implanted in the dopamine-deprived striatum of adult rats. Both graft types were analyzed by chromogen detection of intravenously injected horseradish peroxidase (HRP), which outlined vessel walls, and, in cases in which the blood-brain barrier was compromised, permeated the graft and host parenchyma. Survival of graft-derived dopaminergic cells was assessed using tyrosine hydroxylase (TH) immunocytochemistry. Glial reactivity to cell-suspension grafts was similarly assessed with an antibody directed against glial fibrillary acidic protein. Morphometry revealed significantly higher microvessel density in the cell-suspension grafts (p < 0.001), which effectively equaled that found in the contralateral striatum despite rather prominent surrounding glial reactivity. Capillaries in the cell-suspension grafts were not permeable to blood-borne HRP at postimplantation study times of 7, 14, and 30 days whereas, in the solid grafts, permeability in some cases could be detected for up to 30 days. Large numbers of cells immunoreactive for TH were seen in cell-suspension grafts; in contrast, few if any were found in the majority of solid transplants. The multiple-fragment solid graft implant model used clinically compares poorly with the cell-suspension model because it lacks consistency in early revascularization and shows a greater (albeit temporary) tendency for blood-brain barrier dysfunction. Delayed and inadequate vascularization of the solid graft is likely to account for graft failure more often than in the cell-suspension graft. Similarly, a certain critical number of specific grafted cells are required to achieve sufficient expression to bring about a favorable response in the disabled host, and this expression appears to be achieved less consistently with the solid implant technique.