SL 82.0715, an NMDA antagonist acting at the polyamine site, does not induce neurotoxic effects on rat cortical neurons (original) (raw)
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Polyamines modulate the neurotoxic effects of NMDA in vivo
Brain Research, 1993
The ability of polyamines to alter NMDA-induced neurotoxicity in neonatal rats was examined to determine whether polyamines modulate NMDA receptor activity in vivo. Unilateral injections of NMDA and/or polyamines were made into the striatum of 7-day-old rats. After 5 days, the brains were removed and 20/.~m thick coronal sections were cut and stained with Cresyl violet. A computer-based image analysis system was used to densitometrically measure the cross-sectional area of intact tissue in the control and injected hemispheres. Administration of NMDA (5-40 nmol) produced a dose-dependent tissue damage that ranged from 7 to 52% of the area of the uninjected hemisphere. The polyamine agonist spermine (10-500 nmol) dose-dependently exacerbated the toxicity of a 15 nmol dose of NMDA, increasing the size of the lesion by up to 50%. Administration of spermine alone produced dose-dependent tissue damage that ranged from 9 to 52%. The damage produced by both NMDA and spermine could be completely inhibited by co-administration of the NMDA antagonist MK-801. The polyamine inverse agonist 1,10-diaminodecane (DA-10, 50-400 nmol) inhibited the damage produced by NMDA in a dose-dependent manner, with a maximal inhibition of 50%. Administration of DA-10 alone produced limited damage at doses above 100 nmol. The weak partial agonist diethylenetriamine had no effect by itself or on NMDA-induced toxicity at the doses tested. These results indicate that polyamines can modulate the activity of NMDA receptors in vivo and suggest that polyamines or related compounds may have important therapeutic potential as neuroprotective agents.
Regional Heterogeneity of Polyamine Effects on the N-Methyl-D-Aspartate Receptor in Rat Brain
Journal of Neurochemistry, 1993
Abstract: Polyamines have pronounced effects on N-methyl-D-aspartate (NMDA) receptors in vitro and may be important modulators of NMDA receptor activity in vivo. There is considerable regional heterogeneity in the effects of polyamines on [3H]MK-801 binding in rat brain sections. For example, spermidine enhances the binding of [3H]MK-801 to a much greater extent in the striatum than in the cortex. To further explore the basis for this regional heterogeneity, the effects of polyamines on [3H]MK-801 binding were measured in well-washed membranes prepared from frontal cortex and striatum. There was no difference in the concentration-response relationship for spermidine or the KD for [3H]MK-801 in the presence of 75 μM spermidine, suggesting that the regional difference seen in tissue sections is due to an endogenous factor that is either removed or inactivated during the preparation of membranes. Comparison of spermidine concentration-response curves in washed and unwashed tissue sections revealed that washing selectively enhanced the Emax value in the ventromedial caudate putamen without changing the EC50. This is consistent with the possibility that a noncompetitive polyamine antagonist is being removed from this region during washing. There was no regional variability in the effects of the putative inverse agonist 1, 10-diaminodecane, consistent with recent suggestions that this polyamine inhibits the NMDA receptor at a site distinct from the one at which polyamines act to enhance NMDA receptor function. Agents that modulate the redox state of the NMDA receptor did not eliminate the regional heterogeneity of polyamine effects. Furthermore, the stimulatory effect of glycine in these regions did not correlate with that of spermidine. These results suggest the existence of one or more endogenous factors that noncompetitively influence the effects of polyamines in a regionspecific manner.
Brain Research, 1991
Polyamines such as spermidine potentiate activation of the N-methyl-D-aspartate (NMDA)-type excitatory amino acid receptor. The goal of the present study was to investigate interactions between the putative polyamine binding site and previously described sites for glutamate and glycine. Binding of the high-potency PCP receptor ligand [3H]MK-801 to well-washed rat brain membranes was used as an in vitro probe of NMDA receptor activation. Spermidine concentration-response studies were performed in the absence and presence of both glutamate and glycine, with and without D-(-)-2-amino-5-phosphonovaleric acid (D(-)AP-5) or 7-chiorokynurenic acid (7C1-KYN). Incubation in the presence of spermidine alone induced a 20.4-fold increase in [3H]MK-801 binding with an ECs0 value of 13.3/~M. The mean concentration of spermidine which induced maximal stimulation of binding was 130/~M (n = 10, S.E.M. = 24.66, range = 25-250 ktM). Glutamate (10 /zM) decreased the ECs0 value for spermidine-induced stimulation of [3H]MK-801 binding to 3.4/~M. Glycine (10 ktM) did not significantly alter either maximum spermidine-induced [3H]MK-801 binding or the ECso value for spermidine-induced stimulation of [3H]MK-801 binding. Incubation in the presence of the specific glutamate antagonist D(-)AP-5 attenuated [3H]MK-801 binding in a glutamate-reversible fashion. The competitive glycine antagonist 7CI-KYN decreased maximum spermidine-induced [ 3H]MK-801 binding in a glycine-reversible fashion. In addition, 7CI-KYN increased the ECso value for spermidine-induced stimulation of [3H]MK-801 binding while D(-)AP-5 was without effect. These findings suggest that glutamate and glycine regulate the polyamine binding site differentially. PCP-like agents induce a psychotomimetic state closely resembling schizophrenia by inhibiting NMDA receptor-mediated neurotransmission. The ability of polyamines to modulate NMDA receptor functioning suggests a potential site for pharmacological intervention.
Brain Research, 1991
The intrastriatal injection of N-methyl-D-aspartate (NMDA) (250 nmol) produced a delayed and marked increase in striatai ornithine decarboxylase (ODC) activity and putrescine levels which peaked 6-15 h following the injection of NMDA. Striatai ODC activity subsequently returned to normal values while putrescine levels remained significantly elevated for up to 4 days following the lesion. NMDA produced an early and progressive decline in striatal spermine and spermidine levels, preceding the increase in ODC activity, with a maximum effect 2 h following injection. Spermidine levels returned to normal 6 h post-NMDA infusion, and subsequently increased to above normal levels 36 h and 4 days after the infusion of NMDA. This late increase in striatal spermidine levels paralleled an increase in the binding of the glial cell/macrophage marker [3H]PK 11195. Spermine levels tended to return to normal values 6 h after the injection of NMDA but may be further depressed at later intervals (15 h to 4 days). The intrastriatal injection of saline also resulted in a delayed increase in striatal ODC activity and putreseine levels, but these changes were minor compared to those produced by NMDA. Intrastriatal saline injection provoked no consistent change in striatal spermine or spermidine levels. The changes in polyamine metabolism produced by the intrastriatal injection of kainic acid (4 nmol) were only analysed at 6 and 15 h following injection but were qualitatively similar to those produced by NMDA although perhaps following a slightly more delayed time-course. Neurotoxic lesions of the striatum thus provoke changes in ODC activity and increased levels of putrescine that follow closely the time-course of similar events in the ischaemic brain. The initial early changes in spermine and spermidine levels induced by NMDA could perhaps alter the functioning of the NMDA receptor itself via its polyamine-sensitive modulatory site and contribute to a feed-forward activation of NMDA receptors and prolonged NMDA receptor-mediated toxicity.
European Journal of …, 1994
Polyamine potentiation and inhibition of N-methyl-D-aspartate (NMDA) receptor-mediated Ca 2÷ changes was studied in cultured chick cortical neurons. Spermidine and spermine potentiated the effect of saturating concentrations of NMDA and glycine. No effect of spermidine or spermine was observed in the absence of NMDA or in the presence of either kainate or quisqualate. Similarly, antagonism of the NMDA receptor complex with dizociipine (an open channel blocker), or with competitive antagonists to the NMDA or glycine binding sites greatly attenuated or completely abolished the combined effects of polyamines plus NMDA and glycine. N-Acetylspermine and N-acetylspermidine, in the presence or absence of NMDA and glycine, were without effect. These data strongly suggest that spermidine and spermine are potent and selective agonists at the polyamine binding site. Putrescine and diethylenetriamine were ineffective as antagonists of NMDA-mediated intraceilular free Ca z+ increases in the presence or absence of added spermine or spermidine. Arcaine and 1,10-diaminodecane, however, antagonized NMDA-mediated intracellular free Ca a÷ increases in the presence and absence of spermine and spermidine, and therefore appear to act either as inverse agonists at the polyamine binding site or as open channel blockers of the NMDA receptor.
The Journal of neuroscience : the official journal of the Society for Neuroscience, 2002
NMDA receptor antagonists produce region-specific neurodegeneration by an undetermined mechanism, but one proposed mechanism involves disinhibition. In certain areas of the brain, NMDA receptors mediate excitatory drive onto inhibitory interneurons. Thus, NMDA receptor/channel antagonists may reduce inhibition (i.e., produce "disinhibition"). If a sufficient level of disinhibition is produced, enhanced vulnerability to excitotoxicity may result. Furthermore, if there are region-specific differences in NMDA antagonist-induced disinhibition, this could underlie region-specific NMDA antagonist-induced neurotoxicity. In the present study, we tested this hypothesis by exposing rat brain slices to the NMDA receptor antagonist dizocilpine maleate (MK-801) and measuring MK-801-induced disinhibition in areas of higher and lower vulnerability to neurodegeneration [posterior cingulate/retrosplenial cortices (PCC/RSC) and parietal cortex, respectively]. Using whole-cell patch-clamp te...
Neurochemical Research, 1994
The role of polyamines (PA) synthesis in NMDA receptor-mediated 4sCa2+ fluxes and norepinephrine release was studied in rat hippocampal synaptosomes. NMDA (501.tM) caused a sharp (>2fold) transient increase in PA synthesis regulating enzyme, ornithine decarboxylase (ODC) activity with concomitant elevation in PA levels in the order putrescine> spermidine> spermine. ODC inhibitor, u-difluoromethylornithine (DFMO), and NMDA antagonist, 2-amino-5-phosphonovalerie acid (D-AP5), both blocked increases in ODC activity and PA levels. Activation of NMDA receptors induced a sharp (3 to 4-fold) and quick (15 seconds) increase in 45Ca2 § uptake by synaptosomes within 15 seconds of exposure at 37~ The efflux of 45Ca2+ and 3H-norepinephrine (NE) release at 22~ from pre-loaded synaptosomes was also significantly (2 to 4-fold) enhanced by NMDA within 15 seconds. These NMDA receptor-mediated effects on calcium fluxes and NE release were blocked by NMDA receptor-antagonists (DAP-5 and MK-801) and PA synthesis inhibitor, DFMO and the DFMO inhibition nullified by exogenous putrescine. These observations establish that ODC/PA cascade play an important role in transduction of excitatory amino acid mediated signals at NMDA receptors.
Studies of NMDA- and non-NMDA-mediated neurotoxicity in cultured neurons
Neurochemistry international, 1996
The neurotoxic effects of various glutamate agonists were studied using whole fetal rat brain cultures. The results showed that L-glutamate (L-glu) and N-methyl-D-aspartate (NMDA) were the most potent agonists for inducing neurotoxicity, producing significant toxicity at 0.10 and 0.01 mM concentrations, respectively. Kainic acid (KA) and quisqualic acid (QA) also produced neurotoxicity, but only at a relatively high concentration (1.0 mM). No other glutamate agonist tested produced neurotoxicity in the cultures following brief incubations. The effects of each agonist were found to be Ca2+ dependent, and the selective NMDA Ca2+ channel agonist, (5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,1 0-imine hydrogen maleate (MK-801), blocked the toxicity produced by all the glutamate agonists. Thus, the results of this study found little or no evidence for a direct non-NMDA receptor mediated neurotoxicity. These results suggest that the neurotoxicity produced by the non-NM...