THE EPIDEMIOLOGY OF GERMINAL MATRIX HEMORRHAGE DURING THE FIRST HALF-DAY OF LIFE

The personal and maternal characteristics of 27 babies with early-onset germinal matrix hemorrhage (EGMH) were compared with those of 280 babies with normal cranial ultrasonograms, studied in a separate clinical trial. None of the mothers of the babies with EGMH had high blood pressure or pre-eclampsia during pregnancy. Gestational age less than 30 weeks and initial pH less than 7.2 indicated increased risks of EGMH, and maternal receipt of steroids indicated reduced risk of EGMH. Thus prenatal and immediately perinatal factors appear to convey much of the information about the risk of EGMH.     

SPINAL CORD TRANSECTION: A QUANTITATIVE ANALYSIS OF ELEMENTS OF THE CONNECTIVE TISSUE MATRIX FORMED WITHIN THE SITE OF LESION FOLLOWING ADMINISTRATION OF PIROMEN, CYTOXAN OR TRYPSIN

Spinal cord transection: a quantitative analysis of elements of the connective tissue matrix formed within the site of lesion following administration of piromen, cytoxan or trypsin
Long-Evans hooded rats were cordotomized at the T-5 level and given either (1) cyclophosphamide (cytoxan), an immunosuppressive, (2) piromen, a bacterial polysaccharide-nucleic acid complex, (3) topical and systemic trypsin, or (4) no further specific treatment. Because of past and present controversy surrounding the proposed ability of these agents to promote spinal cord regeneration, a systematic study, employing light and electron microscopy, and quantitative methods in a single animal model, was done in order to re-evaluate the effects of each treatment upon the connective tissue matrix which forms in the defect left by transection. After an initial inflammatory reaction during the first week after surgery, the lesion zone is characterized either by areas of dense collagenous connective tissue with occasional fibroblasts and macrophages, or a loose areolar tissue with numerous sheets and cords of mesodermal cellular elements but minimal collagen. By 45 days postoperatively (dpo), axons supported by Schwann cells invade and become entangled in the loose connective tissue matrix. With longer postoperative survival, cysts appear craniad and caudad to the lesion and erode much of the scar together with viable neural tissue. Giving cytoxan or piromen did not result in any qualitative alteration of the scar matrix as evidenced by electron microscopy. Quantitative analysis revealed a slight reduction in the fibrous connective tissue component of the scar at 45–90 dpo, but this was transient when longer postoperative periods were studied. Trypsin caused a significant reduction in the amount of fibrous connective tissue with a concomitant increase in loose connective tissue and the appearance of a few distinctive, compact bundles of unmyelinated axons lacking Schwann cells.     

A POTENT INHIBITOR OF NEURITE OUTGROWTH THAT PREDOMINATES IN THE EXTRACELLULAR MATRIX OF REACTIVE ASTROCYTES

In a model of astrogliosis in vitro, cultured cortical astrocytes were triggered into a functionally reactive state by an immobilized fragment of the β-amyloid peptide. Induced astrocytes produced an extracellular matrix that inhibited the outgrowth of embryonic CNS axons. Within the extracellular matrix deposited by reactive astrocytes, we found an overall increase in the deposition of chondroitin sulphate that accounted for the inhibition. Specifically, we have detected an increased biosynthesis of a small chondroitin/heparan sulphate proteoglycan that is a potent inhibitor of axon outgrowth. We further suggest that this proteoglycan, or related molecules yet to be discovered, may play a role in gliosis-mediated regenerative failure of CNS axons. Copyright © 1996 ISDN.     

THE EFFECTS OF EXTRACELLULAR MATRIX AND OSTEOGENIC PROTEIN-1 ON THE MORPHOLOGICAL DIFFERENTIATION OF RAT SYMPATHETIC NEURONS

The growth patterns of axons and dendrites differ with respect to their number, length, branching, and spatial orientation; therefore, it is likely that these processes differ in their growth requirements. To examine this hypothesis, we have been analyzing the responses of cultured rat sympathetic neurons to three types of stimuli: large structural proteins of the extracellular matrix, matrix-associated growth factors, and neurotrophins. Purified structural proteins such as laminin and collagen IV have been found to promote only axonal growth; whereas the matrix associated growth factor, osteogenic protein-1, selectively stimulates dendritic growth. In contrast, nerve growth factor modulates the growth of both types of processes. These data suggest that process-specific interactions with the extracellular environment may be critical determinants of cell shape in neurons. Perinatal rat sympathetic neurons grown in culture in the absence of serum or glial cells extend a single process which is axonal in nature. Exposure to osteogenic protein-1 causes the formation of additional processes which express the morphological, cytoskeletal, and ultrastructural characteristics of dendrites. Consistent with observations on the regulation of dendritic growth in sympathetic neurons in situ, the dendrite-promoting activity of osteogenic protein-1 is independent of synaptic or electrical activity, but is modulated by nerve growth factor. In the presence of optimal concentrations of osteogenic protein-1 and nerve growth factor, the size of the dendritic arbor extended by cultured sympathetic neurons approximates that seen in situ at comparable developmental stages. Osteogenic protein-1 does not promote dendritic growth in cultured neurons obtained from embryonic ciliary, dorsal root, trigeminal or nodose ganglia, suggesting that its morphogenetic effects are cell selective. Since mRNA for osteogenic protein-1 is expressed in mature as well as embryonic target tissues of the sympathetic nervous system, we also examined the effects of osteogenic protein-1 on cultures of sympathetic neurons derived from adult rats. Consistent with results obtained with perinatal neurons, osteogenic protein-1 selectively promoted dendritic growth in adult neurons. These data suggest that this matrix-associated growth factor could play a role not only in the morphogenesis of the developing nervous system, but also in the maintenance and remodeling of dendritic structures in the mature animal. Copyright © 1996 ISDN. Published by Elsevier Science Ltd.     

THE DEVELOPMENT OF THE HUMAN BLOOD-BRAIN AND BLOOD-CSF BARRIERS

The commonly held belief that the fetal blood-brain and blood-CSF barriers are immature is reviewed. Results obtained from carefully conducted experiments with horseradish peroxidase and optimal freeze-fracturing suggest that the chick, rat and monkey brain barrier systems to proteins are tight from the earliest stages of development. Previous studies are reviewed in the light of new information on retrograde axonal transport, circumventricular organs, the proper use of horseradish peroxidase, freeze-fracturing, immunocytochemistry and plasma protein gene expression in the developing human brain. Original data on the development of human brain barrier systems are included. Tight junctions between cerebral endothelial and choroid plexus epithelial cells form the morphological basis for these systems. CSF in the fetus contains a remarkably high concentration of protein in contrast to adult CSF which is characterized by a very low protein concentration. This has previously been interpreted as due to immaturity of barriers in the fetal brain. Tight junctions between cerebral endothelial cells and between choroid plexus epithelial cells have been investigated in human embryos and fetuses by freeze fracture and thin section electron microscopy. As soon as the choroid plexus and the brain capillaries differentiated they exhibited well formed tight junctions. These junctions were very complex at early stages of development. A new barrier consisting of 'strap junctions' was found in the developing germinal matrix. The very high concentration of protein in early human fetal CSF cannot be accounted for by a lack of tight junctions in the developing brain barrier systems. Some transfer of proteins from blood to CSF, possibly via an intracellular route, has been demonstrated in immature experimental animals, but it seems that an important contribution to CSF proteins in the fetus may be synthesis by the developing brain and choroid plexuses with subsequent release into the CSF.     

AXON SPROUTING INTO SEGMENTS OF RAT SPINAL CORD ADJACENT TO THE SITE OF A PREVIOUS TRANSECTION

Axon sprouting into segments of rat spinal cord adjacent to the site of a previous transection
Transection of the spinal cord in adult Long-Evans Hooded rats is followed by the formation of a connective tissue matrix in the lesion site and the rapid erosion of the neural elements above and below this zone particularly within the dorsal white columns. In the period between 15–45 days after operation two significant events begin to occur. First the injured surfaces of the divided cord become invested by a glial limiting membrane (glia limitans) and, concomitantly, large numbers of axons ensheathed by Schwann cells sprout into the scar matrix and along the eroded dorsal column region. The injured surface of the spinal cord is highly irregular with deep, collagen-filled rifts into which the sprouting axons may probe and penetrate into the adjacent normal neuropil. Electron microscopic examination generally reveals the interposed glia limitans and that these fibres are usually restricted to the peripheral environment. However, as some axons approach the reconstituting glia limitans, they are enveloped by an astrocytic cytoplasmic process which may either displace the Schwann cell or encompass it together with the enclosed axons. This last phenomenon appears to precede the entry of some axons into the neuropil and suggests that the glia limitans may not necessarily represent an impenetrable barrier to the passage of regenerating nxons into the CNS. Apparent maintenance of most of these fibres for periods of up to 3 months may suggest that viable, functional synapses were established upon available neuronal elements, but clear evidence of this could not be documented.     

AN IMMUNOHISTOCHEMICAL STUDY OF THE GERMINAL LAYER IN THE LATE GESTATION HUMAN FETAL BRAIN

In the cerebral lateral ventricle of the human fetus, the embryonic ventricular and subventricular zones (VZ and SVZ) persist into the latter half of gestation, particularly in the lateral wall. The SVZ is usually referred to as the germinal layer at this stage. The VZ is gradually replaced by ependyma, a single epithelial layer composed of tanycytes and ciliated columnar cells. In the prematurely born infant, the germinal layer is frequently the site of haemorrhage, the incidence of which diminishes with increasing maturity. There are many contributory pathogenetic factors but the structure of the germinal layer itself is considered important. It contains numerous, thin walled vessels in a cellular matrix which demonstrates little fibrillary background. Immunohistochemical evidence of glial differentiation in the germinal layer was sought in 21 preterm brains, using antibody to glial fibrillary acidic protein (GFAP). Early immunoreactivity was due to GFAP positive tanycyte fibres. Subsequently, associated with astrocyte differentiation, there was progressive development of a glial fibre network. It is suggested that the increase in glial fibres may be a significant factor in capillary stabilization, and in the inverse relationship between gestation of the infant and the risk of intracerebral haemorrhage. The possible structural significance of the tanycyte is also highlighted.     

BINDING OF THE VON WILLEBRAND FACTOR A1 DOMAIN TO HISTONE

Activation of the von Willebrand Factor (vWF) A1 domain is a critical factor in regulating the interaction of vWF with its platelet membrane receptor, the glycoprotein (GP) Ib-IX-V complex. This activation controls vWF-dependent platelet adhesion at high shear. The vWF-GP Ib-IX-V interaction is induced in vivo by exposure of platelet-rich plasma to high shear force, or by association of vWF with one or more unidentified components of the subendothelial matrix. In vitro, soluble vWF is activated to bind to platelets by nonphysiological modulators, such as the bacterial glycopeptide, ristocetin, or the snake venom protein, botrocetin, or by removal of negatively-charged sialic acid residues. Analysis of vWF modulators and the very marked charge asymmetry of amino acid sequences within the A1 domain has led to an electrostatic model for vWF modulation. Endothelial membrane/matrix and detergent-soluble fractions of human placenta were screened for the ability to bind vWF by electrophoresis of extracts on SDS-polyacrylamide gels, electrotransferring to nitrocellulose and probing with fluid-phase ¹²⁵I-labeled vWF or a 39/34-kDa vWF fragment (Leu-480-Gly-718) that encompasses the A1 domain. In the course of these studies, it was found that both vWF and the 39/34-kDa vWF fragment bound strongly to histone. Purified soluble histone also bound vWF since, like ristocetin, it induced vWF flocculation. Histone binding to vWF did not activate or inhibit vWF binding to platelets. While the vWF-histone interaction has no conceivable physiological role, it suggests that binding to the A1 domain of vWF alone is insufficient to modulate vWF adhesive activity. This implies that specific interactions of the vWF A1 domain with either ristocetin or botrocetin are required for GP Ib-IX-V recognition to occur. © 1997 Elsevier Science Ltd     

THE EFFECT OF ETHANOL ON THE CELLULAR COMPOSITION OF THE CEREBELLUM

Borges S. & Lewis P.D. (1983) Neuropathology and Applied Neurobiology 9, 53–60
The effect of ethanol on the cellular composition of the cerebellum
Pregnant Wistar rats were fed on a diet of food pellets and a 10% (v/v) solution of ethanol in water during pregnancy and up to 21 days postnatally. Control groups were given food pellets and water ad libitum. Areal analysis of the cerebellum of neonates showed a significant reduction of 9–7% to 12–4% in three selected lobules of the mid-sagittal vermis. Although there were no significant decreases in the linear frequency and absolute number of Purkinje cells, all three lobules showed a small percentage decrease in the length of Purkinje cell layer. The total number of granule cells was significantly reduced in all three lobules, and the ratio of granule cells to Purkinje cells was reduced by between 8–6% and 13–6%, although not significantly. The pyknotic index in the external granular layer (but not in the internal granular layer) was significantly increased at 21 days, while mitotic activity was unchanged. The extent of the diminution in the cell number of the internal granular layer suggests that besides increased cell death there may be a disturbance of cell proliferation kinetics in the precursor pool of the external granular layer. Although it is known that high blood levels can cause death of Purkinje cells, the moderate alcohol blood levels attained in this study were insufficient to do so.     

THE EFFECTS OF CASTRATION ON THE SUBEPENDYMAL PLATE OF THE RAT

Hopkins B. & Hopewell J. W. (1982) Neuropathology and Applied Neurobiology 8, 189–195
The effects of castration on the subependymal plate of the rat
Earlier studies have shown that glial tumours, produced by the intracerebral implantation of chemical carcinogens, originate from the subependymal plate. In the present study the effects of castration on cell number and proliferation in the subependymal region has been investigated as such treatment has been shown to reduce the incidence of gliomata produced by an implanted carcinogen.
An age-related reduction in mitotic activity and nuclear density was found in the subependymal plate. Castration produced a consistent reduction in mitotic activity but the nuclear density was unchanged.
The results suggest that the reduction in tumour incidence produced by castration cannot be explained simply on the basis of reduced proliferation in the population believed to be at risk and that other, as yet, undefined factors must be involved.
In addition, it appeared that there was also no simple relationship between brain growth and cell proliferation in the subependymal plate.     

THE EFFECTS OF MULTIPLE SEQUENTIAL EPISODES OF DEMYELINATION IN THE SCIATIC NERVE OF THE MOUSE

Intraneural injections of lysophosphatidyl choline were used to examine the effects of multiple episodes of demyelination and repair in the sciatic nerves of adult mice. It was found that the early phases of repair, from initiation of myelinolysis to the appearance of promyelinated fibres, were achieved more rapidly in multiple-injected nerves than in single-injected nerves. However, this lead was temporary, since subsequent remyelination was delayed in the multiple-injected nerves until several days after it had been established in most single-demyelinated nerves. Cell-mediated demyelination was seen in multiple-injected nerves, but never in single-injected nerves. The results are discussed in terms of a the contribution of supernumerary Schwann cells to the acute stage of the programme of cellular repair; and b the possibility that the 'normal' response to an injection of LPC in a nerve which has previously undergone several episodes of demyelination is exacerbated by a local and self-limiting immune-mediated reaction.