摘要:

AbstractEndocytosis is the process by which cells take in fluid and components of the plasma membrane. In this way cells obtain nutrients and trophic factors, retrieve membrane proteins for degradation, and sample their environment. In neuronal cells endocytosis is essential for the recycling of membrane after neurotransmitter release and plays a critical role during early developmental stages. Moreover, alterations of the endocytic pathway have been attributed a crucial role in the pathophysiology of certain neurological diseases. Although well characterized at the ultrastructural level, little is known of the dynamics and molecular organization of the neuronal endocytic pathways. In this respect most of our knowledge comes from studies of non‐neuronal cells. In this review we will examine the endocytic pathways in neurons from a cell biological viewpoint by making comparisons with non‐neuronal cells and in particular with another polarized cell, the epithelial cell. © 1993 Wiley‐Lis

ISSN:0360-4012    

DOI:10.1002/jnr.490360102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe synthesis of nerve growth factor (NGF) by the hippocampus raises the possibility that NGF may play a role in the regulation of the hypothalamic‐pituitary‐adrenal axis (HPAA). Subchronic cold stress has been shown to activate the HPAA in a mild noninvasive manner, to stimulate serum glucocorticoid levels, and to perturb NGF binding in hippocampus and basal forebrain. One or repeated episodes of cold stress increased NGF mRNA levels in the hippocampus and p75NGFRmRNA levels in the basal forebrain. These changes were not due to elevated serum glucocorticoid levels since treatment with exogenous corticosterone had no effect on NGF and p75NGFRmRNA levels. Adrenalectomy did not prevent the stress induced increases in NGF and p75NGFRmRNA. © 1993 Wiley‐Lis

ISSN:0360-4012    

DOI:10.1002/jnr.490360103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractExpression of the metabotropic glutamate receptor type 1α (mGluR1α) and the non‐N‐methyl‐D‐aspartate (NMDA) ionotropic glutamate receptor type 1 (GluR1) in mouse brain was investigated using the antibodies raised against the synthetic peptides corresponding to their C‐terminal amino acid sequences. Both receptor proteins are glycosylated predominantly in an asparagine‐linked manner, and are abundant in post‐synaptic membranes. We showed that mGluR1α and GluR1 expression within the first 3 postnatal weeks undergoes dramatic changes in time and space, i.e., in the hippocampus and cerebellum. These spatio‐temporal expression patterns appear to be correlated with the postnatal ontogenesis and establishment of the glutamatergic neurotransmission system in the hippocampus and cerebellum, cell migration, dendritic and axonal growth, spine formation, and synaptogenesis. In the adult cerebellum, mGluR1α is intensely expressed in Purkinje neurons and GluR1 in Bergmann glial cells. Both receptors are expressed to a fair degree inweavermutant cerebellum despite granule cell degeneration. However, the intrinsic expression levels of both mGluR1α and GluR1 are markedly reduced in the cerebellum of the Purkinje cell‐deficient and underdeveloped mutant mice,Purkinje‐cell‐degeneration,Lurcher, andstaggerer, suggesting that GluR1 expression in Bergmann glia cells may be correlated with the sustained interaction with adjacent Purkinje neuro

ISSN:0360-4012    

DOI:10.1002/jnr.490360104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe cadherins are calcium‐dependent cell adhesion molecules which regulate cell–cell interactions during morphogenesis. During development, cadherin expression is subject to dynamic patterns of regulation. We have previously demonstrated that expression of N‐cadherin, the predominant cadherin of neural tissues, is sharply down‐regulated during development of the retina and brain during later stages of histogenesis (Lagunowich and Grunwald,Dev Biol135:158–171, 1989; Lagunowich et al., JNeurosci Res32;202–208, 1992), and that this down‐regulation is due to multiple factors, including decreased mRNA levels and turnover apparently mediated by endogenous metalloproteolytic activity (Roark et al.,Development114:973–984, 1992). In the present study, we describe metabolic studies which provide direct biochemical evidence for turnover of 130‐kDa N‐cadherin in embryonic retina tissues, yielding a soluble 90‐kDa N‐terminal fragment. We demonstrate that this form of N‐cadherin, which we refer to as NCAD90, accumulates in vivo during development. We further demonstrate that purified NCAD90, obtained from embryonic vitreous humor, retains biological function and promotes cell adhesion and neurite growth in a dose‐dependent fashion among chick embryo neural retina cells when present in a substrate‐bound form. The morphology of retinal cells and neurites grown on a substrate of NCAD90 differs strikingly from that seen on a laminin substrate, in a manner similar to that described for intact 130‐kDa N‐cadherin. We conclude that proteolysis of N‐cadherin at the cell surface during embryonic retinal histogenesis is an endogenous mechanism for regulating N‐cadherin expression which generates a novel and functional from of the protein. The results further indicate that an intact cytoplasmic domain is not essential for all cadhe

ISSN:0360-4012    

DOI:10.1002/jnr.490360105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractNascent neural crest cells derived from explanted E12 embryonic rat caudal neural tubes were used as an assay system to investigate the effects of fibroblast growth factors on neural crest cell (NCC) survival, proliferation, migration, and differentiation. In vitro and in vivo all NCC express low affinity nerve growth factor receptors (p75‐LNGFR), whereas a subpopulation of NCC expresses the carbohydrate epitope recognized by the monoclonal antibody HNK‐1 (Bannerman and Pleasure, manuscript in preparation). Both acidic and basic fibroblast growth factor (FGF) promoted the survival of proportionally greater numbers of p75‐LNGF+/HNK‐1−than P75‐LNGFR+/HNK‐1+NCC. An as yet uncharacterized factor present in neural tube‐conditioned medium was also required for NCC survival. Mitosis was frequent in those NCC closest to the neural tube, less so as the cells migrated away. Neither basic nor acidic fibroblast growth factor (FGF) influenced rates of NCC mitosis in either of these locations, nor did these FGFs alter the rate at which nascent NCC migrated away from the neural tube. However, acidic and basic FGFs did delay the differentiation of neural crest derived neurons in the cultures. FGF is abundant in the embryonic rat neural crest outgrowth zone, and the present study strongley supports an essential role for fgf in early development of the mammalian neural crest. © 1993

ISSN:0360-4012    

DOI:10.1002/jnr.490360106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractAlthough epidermal growth factor (EGF) and nerve growth factor (NGF) have markedly different biological effects on PC‐12 cells, many of the signaling events following ligand binding are similar. Both EGF and NGF result in the induction of the primary response gene egr‐1/TIS8 and increased methylation of a variety of membrane‐associated proteins as early as 5 min after EGF or NGF treatment using a methylation assay that detects methyl esters as well as methylated arginine residues. At 20 min after stimulation with these factors, the stimulation of methylation by NGF is greater than that of EGF, especially in the polypeptides of 36–42 and 20–22 kDA. To help dissect the pathways involved in these cellular responses, the protein kinase inhibitor K252a and the methyltransferase inhibitor 5′methylthioadenosine (MTA) were used. Both K252a and MTA inhibit NGF‐, but not EGF‐mediated, primary response gene expression. In contrast, MTA, but not K252a, can block NGF‐induced membrane associated protein methylation. These data suggest a role for differential protein methylation reactions in EGF and NGF signal transduction. © 19

ISSN:0360-4012    

DOI:10.1002/jnr.490360107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractVimentin is initially expressed by nearly all neuronal precursors in vivo, and is gradually replaced by neurofilaments shortly after the immature neurons become postmitotic (Cochard and Paulin, 1984,J Neurosci4:2080; Tapscott et al., 1981,Dev Biol86:40). A transient increase in neuritic vimentin filaments occurs within the first day of dbcAMP‐mediated neurite induction in NB2a/d1 neuroblastoma, after which vimentin levels rapidly decline and neurofilaments increase (Shea, 1990,Brain Res521:343). In the present study, we tested the possibility that vimentin filaments may function in neurite elaboration by inducing neuritogenesis under conditions where vimentin expression and assembly was inhibited. Intracellular delivery of anti‐vimentin antiserum into transiently permeabilized NB2a/d1 cells prevented the initial elaboration of neurites, but did not retract existing neurites. By contrast, intracellular delivery of antiserum directed against the low molecular weight neurofilament subunit or normal rabbit antiserum did not affect neurite outgrowth. Treatment with vimentin antisense oligonucleotides reversibly depleted vimentin synthesis and steady‐state levels, and prevented neurite initiation, but did not induce retraction of existing neurites. These findings point toward an hitherto undetected role for vimentin in the initiation of neurite outgrowth. © 1993 Wiley‐L

ISSN:0360-4012    

DOI:10.1002/jnr.490360108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractMultiple processes lead to neuronal death after ischemia, but the generation of nitric oxide (NO) is a key component in this cascade of events. The mechanisms that regulate the extent of neuronal degeneration during anoxia and NO toxicity are multifactorial. Neuronal death may be modulated by the activity of signal transduction systems that influence the toxicity of NO or its metabolic products such as cGMP. The enzyme responsible for the production of NO, nitric oxide synthase (NOS), is phosphorylated by protein kinase C (PKC), the cAMP‐dependent protein kinase (PKA), and the calcium/calmodulin‐dependent protein kinase II (CaM‐II). We examined in primary cultured hippocampal neurons whether the protein kinases PKC, PKA, CaM‐II, and cGMP‐dependent protein kinase modified the toxic effects of anoxia and NO. Down‐regulation of PKC activity with PMA (1μM) increased hippocampal neuronal survival during anoxia and NO exposure from approximately 22% to 88%. Inhibitors of PKC activity 9H‐7, H‐8, sphingosine, and staurosporine also were neuroprotective. Down‐regulation of PKC activity increased survival during anoxia even in the presence of the NOS inhibitor, Nω‐methyl‐L‐arginine. Thus, although down‐regulation of PKC activity may increase neuronal survival by decreasing NOS activity, it also is likely that PKC contributes to ischemic neuronal death by mechanisms that are independent of NOS. Inhibition of the cGMP‐dependent protein kinase activity, but not the activity of the CaM‐II also was neuroprotective during NO administration. In contrast to the protective effects of inhibition of PKC and the cGMP‐dependent protein kinase, activation rather than inhibition of PKA increased hippocampal neuronal survival during NO exposure. These results indicate that neuronal survival during anoxia and NO exposure is linked to the modulation of PKC, PKA, and cGMP‐dependent protein kinase activity but is not dependent on the CaM‐II pathway. Understanding the involvement of PKC, PKA, and the cGMP‐dependent protein kinase in modulating the effect of neuronal death during ischemia and NO toxicity may help in directing future therapeutic modalities for cerebrov

ISSN:0360-4012    

DOI:10.1002/jnr.490360109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractBacterial β‐galactosidase is widely used as a marker for gene expression and in cell tracing experiments. In a survey of three transgenic mouse lines expressing β‐galactosidase in the central nervous system (CNS) under the control of different promotors, we find substantial variation in the intracellular distribution of thelacZ protein. In line MβP5, transgene β‐galactosidase expression is driven by a promoter/enhancer fragment from the oligodendrocyte‐specific myelin basic protein gene; however, electron microscopy of histochemically stained preparations revels transgene expression not only in oligodendrocytes but also in some neurons. Immunofluorescence and immunoperoxidase staining show the β‐galactosidase protein distributed throughout the perikaryal cytoplasm of oligodendrocytes and in processes reaching to myelin sheaths. By contrast, immunoreactive protein appears restricted in neurons to one or a few small perikaryal immunoreactive granules. The granules are visible in the electron microscope as amorphous inclusion bodies of moderate electron density and lack a limiting membrane. Histochemical staining patterns with X‐gal and Bluo‐gal echoed the protein distribution: diffuse distribution of enzyme protein yielded cells filled with substrate, while punctate enzyme distribution yielded restricted or punctate histochemical staining. Examination of two other lines using different promoter/enhancers to drive expression in the CNS showed both diffuse and punctate β‐galactosidase immunolocalization and histochemical staining. The amount of protein synthesized or other properties, yet unidentified, intrinsic to the target cells may determine the intracellular distribution of β‐galactosidase. In retroviral marking studies, clone members have been identified as those cells filled with X‐gal reaction product. This approach may underestimate both clone size and the minimum number of divisions separating the members of each clo

ISSN:0360-4012    

DOI:10.1002/jnr.490360110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractMyelin basic protein (MBP) mRNAs are translocated from cell bodies into the slender processes connecting oligodendrocyte somas with the myelin sheath in vivo. This translocation was observed in mixed glial cultures prepared from newborn mouse brains and it occurred in approximately 25% of the cells expressing the gene. However, when “enriched” oligodendrocytes were prepared by shaking them free of other glial cells, MBP mRNA translocation occurred into the processes of essentially all of the cells. When enriched oligodendrocytes were plated back onto astrocytes, MBP mRNA was observed to be confined to the cell bodies of almost all the cells, indicating a marketd inhibition of translocation of the mRNA. This inhibition of mRNA translocation did not appear to be mediated through soluble factors secreted by astrocytes or by “astromatrix,” but rather through physical contact between the oligodendrocytes and astrocytes. Intact, but not necessarily live, astrocytes were required for the inhibition of mRNA translocation in the oligodendrocytes. Fibroblasts and a neuroblastoma cell line, SKN‐SH, did not inhibit MBP mRNA translocation in oligodendrocytes suggesting that astrocyte surface‐specific components might be involved in the interaction between astrocytes and oligodendrocytes in culture. These results suggest that contact between these two cell types can influence intramolecular events related to myelinogenesis. © 1993 Wil

ISSN:0360-4012    

DOI:10.1002/jnr.490360111

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY