摘要:

AbstractAcetylcholine and adenosine triphosphate (ATP) raise intracellular Ca2+concentration via muscarinic receptors and P2Upurinoceptors by releasing Ca2+from intracellular Ca2+stores in the neural retina of early embryonic chick. The signal transduction mechanisms for the muscarinic and purinergic Ca2+responses with fura‐2 fluorescence measurements were studied. Li+(1 mM), which inhibits phosphatidylinositol metabolism, enhanced both the Ca2+rises to carbamylcholine (CCh, 30 μM), a muscarinic agonist, and ATP (200 μM). Thapsigargin (250 nM), an inhibitor of Ca2+‐ATPase of inositol trisphosphate (IP3)‐sensitive Ca2+stores, abolished both the Ca2+rises to CCh (100 μM) and ATP (500 μM). U‐73122 (2 μM), an inhibitor of phospholipase Cb, suppressed the Ca2+rise to ATP (500 μM), but its analog U‐73343 (2 μM) did not suppress it. In contrast, both U‐73122 and U‐73343 suppressed the Ca2+rise to CCh (100 μM). Pertussis toxin (250 ng/ml) suppressed the ATP‐induced Ca2+rise at least partly, whereas no inhibition was observed on the CCh‐induced Ca2+rise. Cross‐talk occurred between the muscarinic and purinergic Ca2+mobilizations but they were not occlusive. This study suggests that the muscarinic and purinergic Ca2+mobilizations utilize IP3‐sensitive Ca2+stores, but different signal transduction pathways are involved in between the muscarinic and purinergic Ca2+responses.

ISSN:0736-5748    

DOI:10.1016/S0736-5748(96)00074-3

出版商:Wiley    

年代:1997

数据来源: WILEY

摘要:

AbstractThe effect of GTP concentration on forskolin‐stimulated adenylyl cyclase activity was examined in synaptosomal membranes from 15‐day‐old rats that were hypothyroid due to administration of propylthiouracil and a low‐iodine diet to the mothers during pregnancy and suckling. In membranes from the forebrain hypothyroidism abolished the overall stimulatory effect of GTP, which was seen in the euthyroid case. In membranes from the hindbrain hypothyroidism had the opposite effect in that there was an enhancement of an overall stimulatory effect of GTP. It is suggested that these findings reflect changes during early development of the brain in the expression of various G‐proteins and/or the expression of different isoforms of adenylyl cyclase.

ISSN:0736-5748    

DOI:10.1016/S0736-5748(96)00072-X

出版商:Wiley    

年代:1997

数据来源: WILEY

摘要:

AbstractThese studies demonstrate that murine hippocampal slice cultures possess neural‐immune elements that show responses parallel to comparablein vivomodels of neural‐immune activation. Using immunocytochemical techniques, this study characterized the phenotypes of specific glial elements and the expression of the cytokine, interleukin‐1 (IL‐1β), in the hippocampal dentate gyrus over a period of 10 daysin vitro(DIV). Preparation of organotypic slice cultures of neonatal mouse hippocampus produced cellular damage including axotomy of afferent fibers within the molecular layer of the dentate gyrus. This form of lesion‐induced injury caused activation of neural‐immune elements in the slice cultures. Staining with the microglial specific, biotinylatedGriffonia simplicifoliaB4‐isolectin revealed reactive microglia were most prevalent at 2 DIV and decreased in number from 4 to 10 DIV, whereas the initial population of resting microglia at 2 DIV increased approximately four‐fold from 4 to 10 DIV. The presence of a round IL‐1β‐like immunophenotype closely paralleled the temporal and spatial distribution of the reactive form of microglia observed in the dentate gyrus. In addition, between 4 and 10 DIV, some IL‐1β‐like immunoreactive cells exhibited a stellate‐like morphology with numerous branching processes, similar to resting microglia. At 2 DIV, astrocytes showed minimal labeling with antibodies directed against glial fibrillary acidic protein (GFAP), while from 4 to 10 DIV, a dramatic hypertrophic astrocytic response occurred, resulting in a gliotic scar forming over the entire dentate gyrus. We conclude that neural‐immune activation in the hippocampal organotypic slice culture preparation closely parallels similar responses observedin vivoand thus slice cultures represent an excellent model for further studies of neural‐immune interactions resulting from lesion‐induced injury in the central nervous system.

ISSN:0736-5748    

DOI:10.1016/S0736-5748(96)00071-8

出版商:Wiley    

年代:1997

数据来源: WILEY

摘要:

AbstractAs well as many other hormones and growth factors, insulin is known to influence several processes in the CNS; its specific effects, however, are still poorly understood. Neuroblastoma cell lines represent a useful experimental system for the analysis of the insulin‐specific effect on neurons, in the absence of possible regulatory mechanisms elicited by other neuronal/glial cells and/or soluble factors. The expression and the binding properties of insulin receptors, as well as the insulin effects on both membrane fluidity and cell surface architecture, have been investigated in 41A3 mouse neuroblastoma cells, respectively by radioligand‐binding fluorescence spectroscopy and scanning electron microscopy. In the same cells, insulin‐induced modifications on cytoskeletal organisation also have been studied.Binding studies were performed using125I‐insulin, while the cationic fluorescent probe trimethylammonium 1,6‐diphenyl‐1,3,5‐hexatriene was used for biophysical investigations.The results presented in this paper provide evidence that insulin interacts with 41A3 neuroblastoma cells through a receptor‐mediated mechanism and that, in these cells, insulin binding modifies the cell surface morphology and stimulates endocytosis.

ISSN:0736-5748    

DOI:10.1016/S0736-5748(96)00062-7

出版商:Wiley    

年代:1997

数据来源: WILEY

摘要:

AbstractDuring development, the projections that sensory neurons make within the spinal cord are influenced by the specific targets they contact in the periphery. If sensory ganglia normally supplying principally cutaneous targets are forced to grow into limb muscles, in early stage tadpoles, many sensory neurons within these ganglia innervate limb muscles and subsequently develop spinal projections appropriate for muscle spindle afferents. If the same procedure is performed with adult frogs, however, these novel projections do not form. In this study, we have determined the developmental stages at which this sensitivity to peripheral targets exists. Axons from sensory neurons in thoracic (largely cutaneous) dorsal root ganglia were re‐routed into the front leg at various stages through metamorphosis, and the central spinal projections of these re‐routed fibers were assessed with HRP labeling. We found that thoracic sensory axons could be made to project to limb muscles throughout development, but that the central projections of these neurons were only appropriate for spindle afferents if the fibers were re‐routed before stage XVIII, shortly before metamorphic climax. Because sensory neurons can regenerate specifically into the appropriate spinal laminae even in adult frogs, these results suggest that changes in either the DRG or the arm musculature occur by stage XVII so that DRG neurons cannot respond to novel peripheral targets.

ISSN:0736-5748    

DOI:10.1016/S0736-5748(96)00061-5

出版商:Wiley    

年代:1997

数据来源: WILEY

摘要:

AbstractVimentin is expressed initially by nearly all neuronal precursorsin vivo, and is replaced by neurofilaments shortly after the immature neurons become post‐mitotic. Moreover, both vimentin and neurofilaments can be detected transiently within the same neurite, leaving open the possibility that vimentin may play a role in the early stages of neuritogenesis. In the present study, cultured hippocampal neurons, which transiently express vimentin in culture, were treated with sense‐ and antisense‐oriented deoxyoligonucleotides encoding regions of the vimentin sequence that overlap the translation initiation codon. Antisense oligonucleotide treatment reduced vimentin‐immunoreactivity to background levels. Moreover, while 90–100% of cultured hippocampal neurons elaborated neurites within the first 24 hr following plating, only 24–30% did so in the presence of vimentin antisense oligonucleotides. Inhibition of neurite outgrowth was reversible following removal of antisense oligonucleotide. These findings substantiate earlier studies in neuroblastoma cells, indicating a possible role for vimentin in the initiation of neurite outgrowth.

ISSN:0736-5748    

DOI:10.1016/S0736-5748(96)00053-6

出版商:Wiley    

年代:1997

数据来源: WILEY

摘要:

AbstractVoltage‐gated sodium channels are responsible for the initial depolarizing phase of the action potential. In hippocampal neurons cultured from trisomy 16 (Ts16) mice (a model for Down's syndrome), the maximum inward conductance mediated by these channels was reduced 47% relative to control diploid neurons. This reduced conductance was reflected in a 35% decrease in binding of radiolabeled saxitoxin, a sodium channel‐specific ligand, indicating expression of fewer channels in these neurons. The mRNAs encoding theαandβ1 subunits were, however, present at the same levels in Ts16 neurons and control diploid neurons. Thus, the altered regulation of voltage‐gated sodium channels in Ts16 neurons is apparently a post‐transcriptional event and possible mechanisms are discussed.

ISSN:0736-5748    

DOI:10.1016/S0736-5748(96)00051-2

出版商:Wiley    

年代:1997

数据来源: WILEY

摘要:

AbstractElectron microscopy of the maturing neurons and developing and maturing synapses in the substantia nigra of 14 human embryos/foetuses of 8–24 weeks of gestation are reported. At 8 weeks, cells were immature with very little cytoplasm and cellular organelles. Contact sites of processes appeared more electron dense than the other areas. At 12 weeks, many of the cells had acquired more cytoplasm and cellular organelles and could be identified as neurons. Asymmetric synapses with clear, round synaptic vesicles also were identifiable at this age. Such synapses, first to appear in the developing substantia nigra, are reported to be formed by recurrent collateral nigro‐striatal fibres. Substance P fibres from the striatum also are contributing to this type of synapse. At 15–16 weeks, not only was the number of such synapses increased, but many appeared morphologically mature. Symmetric synapses having clear round vesicles along with a few dense core vesicles also appeared at this stage, suggesting striatal input. By 24 weeks of gestation, most of the neurons had cytological features comparable to that of the mature neurons. There was an increase in the total number of synapses and the individual variety from 15 to 24 weeks of gestation. The present study indicates that synaptogenesis starts at 8 weeks and continues beyond 24 weeks of gestation.

ISSN:0736-5748    

DOI:10.1016/S0736-5748(96)00049-4

出版商:Wiley    

年代:1997

数据来源: WILEY

摘要:

AbstractDetection of catecholamine production by neuroblastoma is a useful tumor marker. The majority of neuroblastoma patients have elevated levels of urinary catecholamines and/or their metabolites, and have tumors, which show histochemical evidence of catecholamines using glyoxylic acid‐induced catecholamine fluorescence. By contrast, continuous cell lines derived from neuroblastomas lack catecholamine fluorescencein vitro. In this study, we report that 11 out of 12 human neuroblastoma cell lines established from catecholamine‐positive tumors displayed histochemical evidence of catecholamines when grown as xenografts in athymic (nude) mice. Catecholamine fluorescence in these xenograft tumors decayed over a 5 day period when the cells were placed into tissue culture. Xenograft tumors of cell lines derived from four catecholamine‐negative neuroblastomas or seven primitive neuroectodermal tumors (PNET) did not show catecholamine fluorescence. Ultrastructural comparisons of cell linesin vitrowith their corresponding tumorsin vivoshowed that six of eight cell lines had fewer dense core (neurosecretory) granulesin vitrocompared to the more readily detectable dense core granules seen in nude mouse tumor tissue. These data indicate that catecholamine synthesis and/or storage in human neuroblastoma cells requires factor(s) not present in thein vitroenvironment. As neuroblastoma cell lines derived from catecholamine‐positive tumors retain the ability to produce and store catecholaminesin vivo, such cell lines can be used to identify factors critical to catecholamine production in human neurons.

ISSN:0736-5748    

DOI:10.1016/S0736-5748(96)00050-0

出版商:Wiley    

年代:1997

数据来源: WILEY

ISSN:0736-5748    

DOI:10.1016/S0736-5748(96)00037-8

出版商:Wiley    

年代:1997

数据来源: WILEY