Benzodiazepine receptors in the mammalian central nervous system

A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 20, No. 2, pp. 269–279, March–April, 1988.     

Cancer stem cells in the mammalian central nervous system

Malignant tumours intrinsic to the central nervous system (CNS) are among the most difficult of neoplasms to treat effectively. The major biological features of these tumours that preclude successful therapy include their cellular heterogeneity, which renders them highly resistant to both chemotherapy and radiotherapy, and the propensity of the component tumour cells to invade, diffusely, the contiguous nervous tissues. The tumours are classified according to perceived cell of origin, gliomas being the most common generic group. In the 1970s transplacental administration of the potent neurocarcinogen, N-ethyl-N-nitrosourea (ENU), enabled investigation of the sequential development of brain and spinal neoplasms by electron microscopy and immunohistochemistry. The significance of the primitive cells of the subependymal plate in cellular origin and evolution of a variety of glial tumours was thereby established. Since then, the development of new cell culture methods, including the in vitro growth of neurospheres and multicellular tumour spheroids, and new antigenic markers of stem cells and glial/neuronal cell precursor cells, including nestin, Mushashi-1 and CD133, have led to a reappraisal of the histological classification and origins of CNS tumours. Moreover, neural stem cells may also provide new vectors in exciting novel therapeutic strategies for these tumours. In addition to the gliomas, stem cells may have been identified in paediatric tumours including cerebellar medulloblastoma, thought to be of external granule cell neuronal derivation. Interestingly, while the stem cell marker CD133 is expressed in these primitive neuroectodermal tumours (PNETs), the chondroitin sulphate proteoglycan neuronal/glial 2 (NG2), which appears to denote increased proliferative, but reduced migratory activity in adult gliomas, is rarely expressed. This is in contrast to the situation in the histologically similar supratentorial PNETs. A possible functional 'switch' between proliferation and migration in developing neural tumour cells may exist between NG2 and ganglioside GD3. The divergent pathways of differentiation of CNS tumours and the possibility of stem cell origin, for some, if not all, such neoplasms remain a matter for debate and continued research, but the presence of self-renewing neural stem cells in the CNS of both children and adults strongly suggests a role for these cells in tumour initiation and resistance to current therapeutic strategies.     

Stem cells in the adult mammalian central nervous system

Over the past year, evidence has accrued that adult CNS stem cells are a widespread progenitor cell type. These cells may normally replace neurons and/or glia in the adult brain and spinal cord. Advances have been made in understanding the signals that regulate stem cell proliferation and differentiation. A deeper understanding of the structure of germinal zones has helped us move towards identifying stem cells in vivo. Recent studies suggest that the fate of stem cell progeny in vivo may be linked to the complexity of the animal's environment.     

Substance P receptors in mammalian central nervous system.

1. Multiple distinct affinity states or sites of substance P (SP) receptors exist in freshly-prepared rat brain membranes. 2. Substance P receptors may couple with islet-activating protein (pertussis toxin) sensitive GTP-binding protein(s). 3. Substance P receptors may be regulated Mg2+ and Na+ in an opposite manner. 4. Some important factor(s), in addition to GTP-binding protein, appear to be involved in SP binding activity. 5. An apparent molecular weight of the SP binding site is approximately 46,000 Da.     

The role of astrocyte-secreted matricellular proteins in central nervous system development and function

Matricellular proteins, such as thrombospondins (TSPs1-4), SPARC, SPARC-like1 (hevin) and tenascin C are expressed by astrocytes in the central nervous system (CNS) of rodents. The spatial and temporal expression patterns of these proteins suggest that they may be involved in important developmental processes such as cell proliferation and maturation, cell migration, axonal guidance and synapse formation. In addition, upon injury to the nervous system the expression of these proteins is upregulated, suggesting that they play a role in tissue remodeling and repair in the adult CNS. The genes encoding these proteins have been disrupted in mice. Interestingly, none of these proteins are required for survival, and furthermore, there are no evident abnormalities at the gross anatomical level in the CNS. However, detailed analyses of some of these mice in the recent years have revealed interesting CNS phenotypes. Here we will review the expression of these proteins in the CNS. We will discuss a newly described function for thrombospondins in synapse formation in the CNS in detail, and speculate whether other matricellular proteins could play similar roles in nervous system development and function.     

Fibroblast growth factors as regulators of central nervous system development and function

Fibroblast growth factors (FGFs) are multifunctional signaling proteins that regulate developmental processes and adult physiology. Over the last few years, important progress has been made in understanding the function of FGFs in the embryonic and adult central nervous system. In this review, I will first discuss studies showing that FGF signaling is already required during formation of the neural plate. Next, I will describe how FGF signaling centers control growth and patterning of specific brain structures. Finally, I will focus on the function of FGF signaling in the adult brain and in regulating maintenance and repair of damaged neural tissues.     

Subcellular localization and function of mouse radial spoke protein 3 in mammalian cells and central nervous system

Radial spoke protein 3 (RSP3) was first identified in Chlamydomonas as a component of the radial spoke. The mammalian homologue of the Chlamydomonas RSP3 gene is mainly expressed in testis and developing central nervous system (CNS). However, the subcellular localization and function of mammalian RSP3 in the developing brain and mammalian cells remain poorly understood. Here we show that the mouse RSP3 accumulates at the perinuclear region of Chinese hamster ovary (CHO) and 293T cells. Detailed analysis shows that the mouse RSP3 is not co-localized with the endoplasmic reticulum or Golgi apparatus markers in CHO cells. Using in utero electroporation, we found that over-expression of mammalian RSP3 increases the percentage of neurons reaching the upper cortical plate. In vivo analysis shows that the mouse RSP3 mainly accumulates in the proximal cytoplasmic dilation of the leading process of the migrating cortical neurons. Furthermore, we find that the mammalian RSP3 concentrates in the ependymal cilia as a component of the cilia. Thus, our data provide the first evidence for the subcellular localization and function of mammalian RSP3 in mammalian cells and developing CNS.     

The distribution of tau in the mammalian central nervous system

We have determined the biochemical and immunocytochemical localization of the heterogeneous microtubule-associated protein tau using a monoclonal antibody that binds to all of the tau polypeptides in both bovine and rat brain. Using immunoblot assays and competitive enzyme-linked immunosorbent assays, we have shown tau to be more abundant in bovine white matter extracts and microtubules than in extracts and microtubules from an enriched gray matter region of the brain. On a per mole basis, twice-cycled microtubules from white matter contained three times more tau than did twice-cycled microtubules from gray matter. Immunohistochemical studies that compared the localization of tau with that of MAP2 and tubulin demonstrated that tau was restricted to axons, extending the results of the biochemical studies. Tau localization was not observed in glia, which indicated that, at least in brain, tau is neuron specific. These observations indicate that tau may help define a subpopulation of microtubules that is restricted to axons. Furthermore, the monoclonal antibody described in this report should prove very useful to investigators studying axonal sprouting and growth because it is an exclusive axonal marker.     

The mast cells of the mammalian central nervous system

Summary The uptake and turnover of the precursors of heparin and heparan sulphate (³⁵S), and of serotonin (³H-5-hydroxytryptophan; ³H-5-HTP) by mast cells (MCs) and neurolipomastocytoid cells (NLMs) of the mammalian CNS were studied. Rats of varying age from 1 day to early adulthood were injected with ³⁵S (as a solution of sodium sulphate) and ³H-5-HTP, and allowed to survive for different periods. Several fixatives, as well as lengths of exposure to photographic emulsion, were tested. The monoamine oxidase inhibitor, nialamide, needed to be given before uptake of ³H-5-HTP could be adequately demonstrated especially in the CNS. ³⁵S was taken up by structures known to contain a great deal of sulphate, viz., cartilage and goblet cells, as well as by MCs of adult liver and thymus, but not by MCs of adult CNS. All of these structures, including the MCs of CNS, took it up much more avidly in babies than in adults. ³H-5-HTP had a similar effect in that the MCs of younger animals took it up more strongly than did those of adults. In the MCs of the CNS uptake seemed to increase up to 15 days of age but then to decrease as maturity was reached. The MCs are located in the leptomeninges of the cerebral hemispheres as well as the choroid fissures and dorsal thalamus. The NLMs, ubiquitously distributed in the leptomeninges as well as perivascularly, showed less radioactivity with both markers in fewer cells and only in babies. The possible significance of these results is discussed. It is concluded that MCs, and to a lesser extent NLMs, of the CNS do permit entry of these markers, and that the more immature the cells, the heavier the load that enters. Adult cells do not seem to take up precursor suggesting little or no turnover.Supported in part by a grant from the Incentive Plan of the Medical School, American University of Beirut, and by Research Support Grant MA-004 from the College of Graduate Studies, University of Kuwait     

Dual function of polysialic acid during zebrafish central nervous system development.

Polysialic acid (PSA), a carbohydrate epitope attached to the neural cell adhesion molecule, serves as a modulator of axonal interactions during vertebrate nervous system development. We have used PSA-specific antibodies and whole-mount immunocytochemistry to describe the spatiotemporal expression pattern of PSA during zebrafish central nervous system development. PSA is transiently expressed on all cell bodies and, except for the posterior commissure, it is not found on axons. Floorplate cells in the spinal cord and hindbrain strongly express PSA throughout development. Enzymatic removal of PSA leads to a defasciculated growth pattern of the posterior commissure and also affects distinct subsets of commissural axons in the hindbrain, which fail to cross the midline. Whereas the disordered growth pattern of hindbrain commissures produced by PSA-removal could be mimicked by injections of soluble PSA, the growth of axons in the posterior commissure was unaffected by such treatment. These results suggest that there are distinct mechanisms for PSA action during axon growth and pathfinding in the developing zebrafish CNS.