Biomedical subjects

J M Krum

Publications and source records attributed to J M Krum.

At least 19 recordsLinked to original sources

PubMed2002

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.

Animals↗

PubMed1999

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.

Animals↗

PubMed1999

Vascular, glial and neuronal effects of vascular endothelial growth factor in mesencephalic explant cultures.

Vascular endothelial growth factor is a highly conserved, heparin-binding protein which mediates a number of critical developmental processes in both vertebrates and invertebrates, including angiogenesis, vasculogenesis and hematopoiesis. We employed an organotypic rat explant model (produced from embryonic day 17 fetuses) to assess the effects of vascular endothelial growth factor on brain microvasculature in general and the ventral midbrain specifically. Immunohistochemistry using antisera to rat endothelial cell antigen and laminin demonstrated a robust, dose-dependent effect of vascular endothelial growth factor, resulting in increased vessel neogenesis, branching and lumen size by three days in vitro. This effect was blocked by addition of an anti-vascular endothelial growth factor antibody. At higher doses of vascular endothelial growth factor, the effect was attenuated, though a statistically significant increase in both astrocyte, and neuronal density was observed using antisera to glial and neuronal markers. Tyrosine hydroxylase-immunoreactive (i.e. dopaminergic) neurons, particularly, exhibited increased survival in response to vascular endothelial growth factor application. Vascular endothelial growth factor had a mitogenic effect on endothelial cells and astrocytes, but not dopaminergic neurons, as demonstrated by the addition of [3H]thymidine to the cultures 2 h after the cultures were established. Similarly, results of a radioreceptor assay indicated that specific vascular endothelial growth factor binding sites were present on blood vessels and astrocytes, and were up-regulated by exposure to vascular endothelial growth factor. We conclude that, in explants of the ventral mesencephalon, exogenously applied vascular endothelial growth factor is mitogenic for endothelial cells and astrocytes, and promotes growth/survival of neurons in general and dopaminergic neurons in particular.

Animals↗

PubMed1998

Recycling immunoaffinity chromatography for multiple analyte analysis in biological samples.

The ability to isolate and measure multiple complex analytes in a single biological sample holds great potential in many biomedical fields, especially immunology and diagnostic clinical chemistry. We have developed a procedure involving recycling immunoaffinity chromatography for the simultaneous measurement of a number of analytes in a single sample. The procedure is based on the passage of a fluorochrome-labelled sample through a battery of small immunoaffinity columns, each column extracting a single analyte. Detection is achieved by acid elution of the bound analytes and laser-induced fluorescence. We have applied this system to a number of different biological fluids and found that it is capable of reliably isolating and measuring up to ten different cytokines in a 25-microl sample of human body fluid.

Antibodies↗

PubMed1998

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.

Animals↗

PubMed1998

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.

Animals↗

PubMed1997

Expression of blood-brain barrier characteristics following neuronal loss and astroglial damage after administration of anti-Thy-1 immunotoxin.

In most regions of the CNS, vascular endothelial cells play an important role in maintaining the composition of the neuronal microenvironment by virtue of their blood-brain barrier (BBB) characteristics. The maintenance of the endothelial BBB phenotype in vitro has been attributed primarily to astrocytes but little attention has been paid the potential role of neurons. In this study we have attempted to injure or destroy neurons and fibers of passage in a circumscribed area while leaving vascular and glial elements intact in order to determine if neurons are involved in BBB maintenance in situ. The immunotoxin OX7-SAP, a conjugate of the Thy-1 antibody OX7 and the ribosome-inactivating protein saporin, was injected into the adult rat striatum to effect neuronal death at the injection site. Although neurons and fibers of passage were destroyed within the lesion, glial cells unexpectedly were also severely injured as determined by immunohistochemical expression of several neuronal and astroglial marker proteins and ultrastructural analysis. The microvasculature remained intact, allowing a qualitative immunohistochemical analysis of several BBB markers at time points ranging from 3 to 28 days postinjection. Despite the loss of both neurons and astroglia within the lesions, the microvasculature continued to express the brain-type endothelial glucose transporter GLUT-1 at all time points examined. In contrast, the barrier to endogenous protein (rat serum albumin) and the expression of endothelial barrier antigen (EBA) decreased initially but recovered even in areas that contained minimal numbers of astroglia and neuronal elements. We conclude that intact neuronal or glial cells do not appear to be necessary for the maintenance in situ of the BBB properties examined herein.

Animals↗

PubMed1996

Effect of astroglial degeneration on neonatal blood-brain barrier marker expression.

Numerous studies have demonstrated that astroglial influence is necessary to maintain several blood-brain barrier (BBB) characteristics in CNS-derived endothelial cells in vitro. In the present study, we examined the hypothesis that intact perivascular astrocytes are essential contributors to the maintenance of particular BBB properties within the developing microvasculature of the postnatal rat CNS in situ. Astroglial cells were selectively injured following chronic systemic injections of the antimetabolite 6-aminonicotinamide (6-AN) during the first postnatal week. Throughout the CNS, the majority of perivascular astroglial endfeet were swollen and contained degenerating organelles. The brain microvasculature was examined at Postnatal Days 6-12 and the histochemical and immunohistochemical expressions of the brain endothelial glucose transporter (Glut1), gamma-glutamyltranspeptidase (gamma-GT), and endothelial barrier antigen (EBA) were qualitatively analyzed. Despite the apparent perivascular astroglial degeneration, all of the BBB markers examined were robustly expressed throughout the CNS and were comparable to age-matched controls. Moreover, 3[H]thymidine labeling revealed that the vascular endothelium continued to proliferate, albeit at a decreased rate when compared to age-matched controls. The results suggest that, in contrast to the majority of in vitro studies, the postnatal brain microvasculature continues to express Glut1, gamma-GT, and EBA in situ without the influence of continuously manufactured, astrocyte-derived substances.

6-Aminonicotinamide↗

PubMed1995

Age-dependent susceptibility of CNS glial populations in situ to the antimetabolite 6-aminonicotinamide.

Intraperitoneal injections of the nicotinamide antagonist 6-amino-nicotinamide (6-AN) were used to determine if there are regional differences in putative glial energy metabolism between the developing and adult rat CNS. 6-AN shuts down the hexose monophosphate pathway, which is used preferentially by astrocytes and oligodendrocytes. These cells subsequently undergo cytotoxic edema and cell death. Adult rats and pups ranging in age from 7 to 31 d received a single injection of 6-AN and were sacrificed after 24 h. As demonstrated wit immunocytochemical staining for the astroglia-specific markers GFAP and S-100 beta, the 7-9-d-old animals exhibited a uniform appearance with edematous glial cells located throughout the CNS. However, with advancing age, a consistent pattern of progressively decreasing amounts of injured glia, which has not been previously described, occurred in cerebral and cerebellar structures. After 3 wk postnatal, the adult pattern was manifested in which glial degeneration occurred only in specific regions of the spinal cord, cerebellum, medulla, and thalamus, whereas the remainder of the CNS appeared normal. The results suggest the presence of heterogeneous populations of glia whose preferred use of the hexose monophosphate pathway is predicated on both the age of the animal and their location in the CNS.

6-Aminonicotinamide↗

PubMed1995

An improved autoradiographic coating technique for neurohistopathological stains and electron microscopy.

We describe modifications and improvements to our first report of a new nuclear emulsion coating technique for both light and electron microscopic autoradiography. Although this technique was originally designed to facilitate electron microscopic autoradiography, the methodology also allows pre-staining of plastic-embedded tissue sections prior to coating the slides with nuclear emulsion for light microscopic autoradiography. We now demonstrate that paraffin sections can be autoradiographically processed after being subjected to a combination of immunocytochemical reactions and special neuroanatomical strains. Parlodion film has been found to be more resistant to temperature changes and less prone to contamination than Formvar film. The shape of the double adhesive tape is an important aspect of the electron microscopic technique; it has been modified to minimize contamination and facilitate the removal of the grids from the glass slide. These technical adjustments facilitate the application of the nuclear emulsion and increase radionuclide specificity, thus expanding the investigative horizons of light and electron microscopic autoradiography.

Animals↗

PubMed1994

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.

Animals↗

PubMed1994

Experimental gliopathy in the adult rat CNS: effect on the blood-spinal cord barrier.

The expression of certain blood-brain barrier (BBB) properties in CNS endothelial cells appear to be dependent on astroglial interactions in vitro. However, evidence for direct astroglial support of BBB function in vivo is controversial. To determine if perivascular astroglial damage or loss would compromise BBB function in situ, localized astroglial degeneration was produced in adult rat spinal cords by systemic injections of the anti-metabolite 6-aminonicotinamide (6-AN). Between 1 and 5 days after 6-AN administration, microvessels in the lumbar spinal cord (blood-spinal cord barrier) were examined for the expression of several BBB markers and for leakage of endogenous and exogenous proteins by means of immunocytochemical and histochemical procedures. Glial cells throughout the gray matter were swollen after 24 h, and by 5 days post-injection perivascular astroglia in laminae VI-VIII appeared completely degenerated. Microvessels were undamaged and continued to express BBB markers such as GLUT-I, gamma-glutamyltranspeptidase, and endothelial barrier antigen in this region in a manner comparable to control animals. These results suggest that differentiated, BBB-competent microvascular endothelia in situ may not depend on continuous astroglial support to maintain these particular BBB characteristics. However, the BBB to protein appeared to be compromised; the gray matter was immunoreactive for serum albumin and some areas were permeable to intravascularly injected horseradish peroxidase (HRP). No increase in microvascular transport vesicles was apparent, and no open, tracer-containing interendothelial junctions were detected using standard ultrastructural methods. Some venous structures were surrounded by hemorrhages and HRP reaction product. Thus, astrocytic injury may alter venous, and possibly microvascular, permeability to macromolecules.

6-Aminonicotinamide↗

PubMed1993

Effect of astroglial degeneration on the blood-brain barrier to protein in neonatal rats.

Recent in vitro studies have suggested that astrocytes may be responsible for the induction of several blood-brain barrier (BBB) characteristics. To examine this hypothesis in an in vivo situation, we have investigated the effect of chronic astrocytic deprivation on the BBB to proteins in neonatal rats. Intraperitoneal injections of the gliotoxin 6-aminonicotinamide (6-AN) resulted in cytotoxic edema with subsequent necrobiosis of differentiated astrocytes and oligodendrocytes throughout the CNS. Animals were sacrificed 1-5 days after chronic exposure to 6-AN during the first postnatal week. Animals sacrificed 24 h after the final injection of 6-AN had the greatest depletion of perivascular astroglia. The BBB to exogenous protein, examined by intravascular administration of horseradish peroxidase, remained intact, as did the BBB to endogenous protein as determined by immunocytochemical detection of rat serum albumin. In no case was any leakage of protein found other than in areas that do not normally possess BBB characteristics. These data show that CNS endothelial cells retain BBB characteristics without a full complement of astrocytic contacts. Since the astroglial cytoplasm was destroyed and only membrane fragments remained, we suggest that factors continuously produced by astroglia cannot be responsible for the induction and maintenance of the BBB to protein, but that substances produced during the prenatal period may be the primary determinant of endothelial phenotype.

6-Aminonicotinamide↗

PubMed1992

Immunocytochemical expression of the endothelial barrier antigen (EBA) during brain angiogenesis.

The antibody to the endothelial barrier antigen (anti-EBA) is localized to the luminal plasma membrane of endothelia that have a blood-brain barrier (BBB) but not to other vessels, for instance those in the circumventricular organs, which lack barrier function. We have examined EBA expression in the rat in certain tissues and in brain microvessels in models of brain angiogenesis such as development, wound healing and neural transplantation. All brain microvessels including pial ones stained for anti-EBA whereas those of the dura, median eminence and choroid plexus did not. Vessels of the iris which are characterized by tight junctions and barrier function expressed EBA strongly. Embryonic day 18 brain did not stain at all for anti-EBA although vessels were readily localized with anti-laminin. Following stab wounds to mature brain, directly injured and adjacent microvessels lacked EBA expression for a period of approximately 2 weeks which is a similar time frame of BBB breakdown. Following this period, EBA expression gradually returned to a normal pattern by 3-4 weeks. Likewise, in intraparenchymal transplants of fetal neocortex EBA expression was not observed for 2 weeks and while at later times transplant vessels expressed EBA whereas some interface vessels associated with inflammatory cells did not. Permeable choroid plexus vessels vascularizing intraventricular transplants did not stain for anti-EBA at any time period and neither did vessels in adrenal medulla transplants. The present study shows that while EBA expression is a postnatal event unlike the development of a barrier to serum protein, its expression may be lost or delayed in injured vessels or ones associated with inflammatory cells or reactive astrocytes.

Animals↗

PubMed1992

An innovative coating technique for light and electron microscopic autoradiography.

We describe a modified nuclear emulsion coating technique for both electron and light microscopic autoradiography. We propose that by reversing the application of formvar film so that it adheres to and covers thin sections placed on grids, we have developed a technically accessible methodology that produces optimal conditions for the tracing of specific nuclear activity. A smooth, continuous base is formed over the sections on which a monolayer of evenly packed silver halide crystals can be applied by dip-coating. The same principle is applied to pre-stained 1-micron plastic sections of glass slides. We suggest that the application of formvar film over thin sections does not impede or interfere with the exposure of the emulsion by the labeled tissue. On the contrary, it virtually eliminates contamination and background radiation, enhancing the specificity and quality of resolution at even low magnifications. This technical modification, which facilitates the application of the emulsion, could render electron microscopic autoradiography a routine laboratory procedure, allowing for easily reproducible results and quantitative evaluation. At the light microscopic level, this technique prevents chemical fogging caused by certain stains, and thus allows routine pre-staining before coating with emulsion.

Adrenal Glands↗

PubMed1991

Brain angiogenesis: variations in vascular basement membrane glycoprotein immunoreactivity.

Changes in the distribution and quantity of laminin and fibronectin within the basement membranes of developing or regenerating CNS blood vessels were investigated using two immunocytochemical techniques. Three models of angiogenesis were studied: normal pre- and postnatal development, wound healing, and vascularization of fetal neocortical transplants placed in the adult rat brain. Although all brain vessels were stained in enzymatically pretreated immunoreacted paraffin sections, those associated with wound and transplant sites were the most intensely reactive with both antisera during the first postoperative week. When 40-microns vibratome sections of normal adult brains were immunoprocessed, only the meninges and vessels of the circumventricular organs were stained. The remainder of the brain vasculature was immunoreactive only if sections were enzymatically treated prior to immunoprocessing. In contrast, the nascent vasculature in developing brain and the regenerating vessels at wound and transplant sites were reactive to both antisera without enzymatic pretreatment of the sections. This immunoreactivity decreased by 11 days postnatal in normal animals and 4 weeks postoperative in experimental animals, coinciding with the period of astrocytic contact and complete vascular basement membrane formation in both cases. The variations in staining pattern and intensity may be reflections of differences in the quantity of laminin and fibronectin within the basement membranes of proliferating and/or non-blood-brain barrier vasculature. However, the results of the different experimental protocols suggest that immature vascular basement membranes may have a molecular configuration that does not require an enzymatic unmasking step to react with the antisera. Alternatively, the looseness of the surrounding neuropil inherent in developing and injured CNS could allow the antisera greater access to basement membrane antigens.

Animals↗

PubMed1989

The astroglial response to autonomic tissue grafts.

Autonomic (superior cervical) ganglia were grafted either into the IV ventricle where minimal trauma occurred or directly into the cerebral cortex which was necessarily traumatic. Previous studies have shown that host astroglia may migrate into autonomic tissue grafts. The purpose of the present study was to compare and contrast the astroglial response in allo- and autografts. By monitoring the host response in the two model sites using glial fibrillary acidic protein (GFAP) immunostaining in 1 micron plastic sections we sought to determine the role of injury stimulus in astroglial migration. In addition, these models could be used to investigate any potential differences in glial reactivity produced by allo- or autograft antigenic stimulation. In both ventricular and parenchymal locations, astroglia migrated progressively into allografts. Migration, which could have taken place along anastomotic vascular connections, began after one week and was continual, eventually replacing graft neural tissue. Astrocytic processes appeared enlarged and highly immunoreactive only as they entered the allografts or were in close association with the choroid plexus; adjacent host astrocytes were unaltered. Glial migration was greatly reduced in ventricular autografts but in the parenchymal site was nearly comparable to that of allografts. It was suggested that certain immunological factors may be involved in glial reactivity or migration considering the observed differences in the non-traumatic model whereas tissue damage stimulus played a major role in migration in both allo- and autografts. In no instances were typical astrocytic end-feet found on the autonomic graft vessels. The host astrocytic response to grafted autonomic tissue occurred significantly later (5-7 days) than the host endothelial response. This observation indicates that the graft vessels were original, intrinsic ones and the astrocytic invasion played no role in influencing endothelium with regards to brain-barrier properties.

Animals↗

PubMed1989

The fine structure of vascular-astroglial relations in transplanted fetal neocortex.

The vascular development within allografts of rat fetal neocortex was examined ultrastructurally with particular attention to astroglial-endothelial relationships. Grafts placed in the fourth ventricle exhibited a progressive astrogliosis around the host pial or choroidal vessels incorporated within the transplant which was evident by 1 month postoperative. Immunostaining with antisera to laminin showed intense reactivity around such neovessels at the light microscopic level. Transplants located intraparenchymally within the host parietal cortex also developed reactive astroglial "cuffs" around their marginal vessels by 1 week postoperative, although the degree and location of this reaction varied considerably with time. The origin of the reactive astroglia could not be directly determined from this study, but it is possible that they were stimulated by the collagen and fibroblasts present around vascularizing host pial and choroidal vessels in intraventricular grafts and by meningeal elements that entered the wound created for the intraparenchymal grafts. The marked astroglial reactivity within the grafts raises issues concerning their metabolic activity and their intimate relationship with brain endothelium. The close proximity of reactive astroglia to the graft vasculature would not appear to enhance the blood-brain barrier capabilities of transplant neovasculature, especially in intraventricular transplants, as might be suggested by many in vitro studies.

Animals↗