ISSN:0736-5748    

DOI:10.1016/0736-5748(90)90067-C

出版商:Wiley    

年代:2003

数据来源: WILEY

摘要:

AbstractDifferentiating granule cells develop survival requirements in culture which can be met by treatment with high K+or N‐methyl‐d‐aspartate (NMDA) and, according to our recent findings, also with low concentrations of kainic acid (KA, 50 μM). We have now attempted to elucidate the mechanism(s) underlying the trophic effect of KA.KA rescue of cells was completely suppressed by blockers of voltage‐ sensitive calcium channels, such as nifedipine in low concentrations (5×10−7M), indicating that the promotion of cell survival is mediated through the activation of these channels by membrane depolarization. Thus the trophic influences of KA and NMDA share a common mechanism, increased Ca2+influx (albeit through different routes), a conclusion that is supported by the observation that the effects of these agonists at concentrations causing maximal promotion of cell survival were not additive.Interactive effects involving different classes of excitatory amino acid receptors were revealed by the potentiation of the KA rescue of cells by the NMDA receptor antagonists, 2‐amino 5‐phosphonovalerate (APV) or (+)‐5‐methyl‐10,11‐dihydro‐5H‐dibenzo[a,d]cyclohept‐5,10‐imine hydrogen maleate (MK‐801), which on their own failed to promote, but rather reduced cell survival. The potentiation of the KA effect by the competitive NMDA antagonist APV was counteracted by the weak NMDA agonist, quinolinic acid. These observations suggest that KA alone has both trophic and toxic effects, the latter being mediated secondarily through an NMDA‐like glutamate receptor, which is distinct from the conventional NMDA, KA and quisqualate preferring subtypes.

ISSN:0736-5748    

DOI:10.1016/0736-5748(90)90068-D

出版商:Wiley    

年代:2003

数据来源: WILEY

摘要:

AbstractThe effects of elevating the potassium concentration of the growth medium of neocortical explants was studied. Under control conditions, 10 mM potassium resulted inca20% decrease in the number of surviving neurons. The same potassium concentration, however, was clearly neurotrophic in tetrodotoxin‐grown cultures: tetrodotoxin‐induced neuronal death was significantly reduced. Both effects could be mimicked by the addition of 10 μM N‐methyl‐d‐aspartate (NMDA); lower concentrations were without effect; higher concentrations were neurotoxic under both control and tetrodotoxin conditions. The neurotoxic, as well as the neurotrophic effects of 10 mM potassium appear to be mediated through depolarization‐induced glutamate release since they could be influenced by the application of glutamate receptor antagonists. The addition of the NMDA receptor antagonistd‐2‐amino‐7‐phosphonoheptanoate (APH) blocked the trophic effect of 10 mM potassium in tetrodotoxin‐grown cultures, resulting in low survival. On the other hand, the addition of the non‐NMDA antagonist 6,7‐dinitroquinoxaline‐2,3‐dione (DNQX) resulted in neuronal survival similar to control cultures, indicating that it blocked the toxic effects of glutamate, leaving the trophic effects on the NMDA receptor untouched. Under control (non‐TTX) conditions, neither DNQX nor APH showed significant effects on 10 mM potassium‐induced cell death, indicating that stimulation of the non‐NMDA, as well as the NMDA receptors is neurotoxic. This differential effect of NMDA receptor stimulation on neuronal survival is discussed with respect to the maturational and/or functional state of the neurons in the culture.

ISSN:0736-5748    

DOI:10.1016/0736-5748(90)90069-E

出版商:Wiley    

年代:2003

数据来源: WILEY

摘要:

AbstractNeuronal survival of dorsal root ganglion‐spinal cord cultures was determined after treatment with vasoactive intestinal peptide (VIP) and an antagonist to the N‐methyl‐d‐aspartate receptor (NMDA). Blockade of NMDA receptors with 2‐amino 5‐phosphonovaleric acid (AP5) produced a bi‐phasic response on neuronal survival: low concentrations (0.1 μM) resulting in greater survival and higher concentrations (100 μM) causing cell death. VIP, a substance with demonstrated neurotrophic propertiesin vitro, prevented the neuronal cell death associated with high concentrations of AP5, while having no additive effect on the survival‐promoting action of low levels of AP5. Electrophysiological studies indicated that APS, although reducing high frequency bursting activity, did not significantly reduce the abundant on‐going asynchronous activity present in these cultures of high density neuronal networks. These data indicate that excitatory amino acids have more than one action that can influence neuronal survival during development and that VIP can increase neuronal survival in bioelectrically active cultures when NMDA channels are blocked. Together with previous studies, these data suggest that multiple neurochemical inputs serve to determine the survival of spinal cord neurons during development, perhaps through one final common pathway: intracellular calcium regulation.

ISSN:0736-5748    

DOI:10.1016/0736-5748(90)90070-I

出版商:Wiley    

年代:2003

数据来源: WILEY

摘要:

AbstractThe possible involvement of N‐methyl‐d‐aspartate (NMDA) receptors in the biochemical differentiation of cultured neurons derived from the medial frontal part of the forebrain containing the septum‐diagonal band region was studied in terms of the activities of enzymes important in the synthesis of neurotransmitter compounds. The activity of choline acetyltransferase (ChAT) was used as a marker for cholinergic neurons, glutamate decarboxylase (GAD) for GABAergic neurons and phosphate‐activated glutaminase (GLNase) and aspartate aminotransferase (ASP‐AT) for glutamatergic neruons, while lactate dehydrogenase (LDH) was included as an ubiquitous enzyme. The exposure of cultures to a depolarizing concentration of K+(40 mM) for the last 3 days (i.e. between 2 and 5 daysin vitro) significantly enhanced the expression of ChAT, GAD and GLNase activities, but high K+caused little alteration in the activities of ASP‐AT and LDH. On the other hand, treatment with NMDA markedly elevated the specific activities of GAD and GLNase only, and the compound had no significant effects on the activities of ChAT, ASP‐AT and LDH enzymes. The enhancements of the specific activities of GAD and GLNase were completely blocked by the NMDA receptor antagonist, 2‐amino‐5‐phosphonovaleric acid, and by the NMDA receptor‐linked Ca2+ion channel blocker, MK‐801. On the basis of the present findings it is concluded that, (a) contrary to an earlier proposal, ASP‐AT does not appear to be a good marker for the glutamatergic neurons, (b) the failure of the subcortical cholinergic neurons to respond by an increase in ChAT activity to NMDA may indicate that these nerve cells lack NMDA subtype excitatory amino acid receptors, and (c) as the septal GABAergic input in the hippocampus is involved in the modulation of long‐term potentiation, the presence of NMDA receptors on these neurons would now suggest that NMDA receptors are linked to both the initiation and the modulation of hippocampal plasticity in the mammalian brain.

ISSN:0736-5748    

DOI:10.1016/0736-5748(90)90071-9

出版商:Wiley    

年代:2003

数据来源: WILEY

摘要:

AbstractWe tested glutamate for its ability to modulate neurite outgrowth from isolated neurons of the adult snail,Helisoma trivolvis. Although glutamate did not induce neunte outgrowth from neurons maintained in defined medium, nevertheless it showed a dose‐dependent ability to enhance the activity of conditioned medium. We concluded that glutamate can enhance the release and/or activity of CNS derived sprouting factor(s) present in conditioned medium.The general conclusion to be drawn from this study is that the ability of a neurotrophic factor(s) to promote neunte outgrowth can be regulated by a neurotransmitter. This mechanism may be important in the regulation of trophic factors in the adult nervous system.

ISSN:0736-5748    

DOI:10.1016/0736-5748(90)90072-A

出版商:Wiley    

年代:2003

数据来源: WILEY

摘要:

AbstractLow density cell cultures of embryonic rat hippocampus containing astrocyte‐like glia and neurons were used to test the hypothesis that glia can alter ‘natural’ and excitatory amino acid (EAA)‐induced neuronal death. Neurons contacting glia survived for longer time periods than did neurons not contacting glia. Neurons associated with glia were also protected against glutamate and kainate neurotoxicity. Fibroblast growth factor (FGF)‐like immunoreactivity was associated with the glia. Addition to the cultures of an antiserum raised against an internal peptide fragment of FGF greatly reduced the protective effect of glia against both spontaneous and EAA‐induced neurotoxicity. Contact with glia, or exposure to exogenous FGF, also protected the hippocampal neurons against Ca2+ionophore‐induced degeneration indicating that FGF enhanced the ability of neurons to handle a Ca2+load. Taken together, these results suggest that glia surface‐associated FGF may play important roles in hippocampal development, and in neurodegenerative conditions that involve EAAs.

ISSN:0736-5748    

DOI:10.1016/0736-5748(90)90073-B

出版商:Wiley    

年代:2003

数据来源: WILEY

摘要:

AbstractThe role played by the glycine site associated with the NMDA receptor in inducing long‐term potentiation (LTP) in neonatal hippocampus was examined. An antagonist of the glycine site, 7‐chlorokynurenic acid (Cl‐Kyn), completely blocked both the short‐term and the long‐term potentiation associated with theta burst stimulation (TBS) linked to NMDA receptor activation in slices from hippocampus at postnatal days 10–16; this effect was reversed by the glycine agonist,d‐serine. Analysis of the TBS‐evoked responses showed: (1) a developmental alteration in the burst response morphology that may be related to maturation of GABA‐mediated inhibition; and (2) that, unlike 2‐amino‐5‐phosphonovalerate (APS), Cl‐Kyn did not reduce any portion of the burst response. These results suggest that stimulation of the glycine site coupled to the NMDA receptor complex is necessary to induce LTP in neonatal tissue and that two NMDA receptor types may be present in the hippocampus.

ISSN:0736-5748    

DOI:10.1016/0736-5748(90)90074-C

出版商:Wiley    

年代:2003

数据来源: WILEY

摘要:

AbstractThe existence of Hebb synapses in the visual cortex of young kittens has long been postulated. A mechanism for the correlation of activity in simultaneously active pre‐ and postsynaptic neurons could be provided by the properties of the N‐methyl‐d‐aspartate (NMDA) receptor and its associated Ca2+channel, which opens in a transmitter‐andvoltage‐dependent manner. We have studied the effects on cortical plasticity of blocking NMDA receptors in different ways with competitive and non‐competitive NMDA antagonists.In our first approach, the non‐competitive NMDA antagonist ketamine, a short‐acting dissociative anaesthetic, was injected systemically after each of a series of brief monocular exposures. This procedure prevented the development of an ocular dominance shift towards the experienced eye in the visual cortex. Other short‐acting anaesthetics, such as xylazine or methohexital, while providing the same depth of anaesthesia, did not have the same effect on ocular dominance plasticity. We conclude, therefore, that ketamine quite specifically interferes with synaptic consolidation in the visual cortex.In order to establish a role of NMDA receptors for cortical plasticity directly in the visual cortex, we performed another series of experiments: 2‐amino‐5‐phosphono‐valerate (APV), a competitive NMDA antagonist, was infused intracortically by means of implanted osmotic minipumps in kittens, which were monocularly deprived for 1–2 weeks. Within a radius of 4–5 mm, the expected ocular dominance shift was prevented or reduced. In addition, however, physiologically determined cell density and responsiveness to visual stimuli were grossly abnormal around the infusion site, and histological cell density was also reduced. Similar effects were found when MK801 (a non‐competitive NMDA antagonist) was used in the same type of experiment.The outcome of both experimental approaches makes it very likely that NMDA antagonists somehow interfere with cortical plasticity. Their mode of action, however, remains ambiguous. Although it is quite possible that blocking of the NMDA channel prevents the Hebbian correlative process necessary for synaptic consolidation, more complex effects, such as an interference with a neurotrophic action normally exerted via the NMDA receptor, may have to be taken into account as well.

ISSN:0736-5748    

DOI:10.1016/0736-5748(90)90075-D

出版商:Wiley    

年代:2003

数据来源: WILEY

摘要:

AbstractThe developmental pattern ofl‐[3H]glutamate binding to rat brain in the presence of saturating concentrations of unlabeled N‐methyl‐d‐aspartate (NMDA), kainate (KA) and quisqualate (OQA) was examined in an autoradiographic assay. The unique glutamate binding site defined by this assay displayed four distinct, regionally specific patterns of development. (1) In reticular nucleus of thalamus there was an initial very high level of binding at postnatal day 1 (PND1) followed by a progressive 80% decline in binding during maturation. (2) In entorhinal cortex, a progressive 500–1100% increase in binding was seen during development. (3) In ventral posterior medial nucleus of thalamus, there was an initial transient 200–300% increase in binding, peaking at PND10, followed by a steady decline in binding. (4) In frontal cortex, binding remained relatively stable throughout development. At all stages of development, the distribution of these recognition sites was different from NMDA, KA or QQA receptors. The function of this glutamate binding site remains to be determined, but the distinct regional and temporal patterns of binding suggest that it may be important in normal development of the central nervous system.

ISSN:0736-5748    

DOI:10.1016/0736-5748(90)90076-E

出版商:Wiley    

年代:2003

数据来源: WILEY