dizocilpine-maleate and 1-10-diaminodecane

Polyamines are thought to modulate the activation of NMDA receptors through a unique allosteric regulatory site. The effects of polyamines on the binding of [3H]MK-801 were measured in cortical and hippocampal tissue surgically removed from patients with temporal lobe epilepsy (TLE). The polyamine agonist spermidine increased the binding of [3H]MK-801 in the cortex in a dose-dependent manner and this effect could be blocked by the weak partial agonist diethylenetriamine (DET). Spermidine decreased the Kd of [3H]MK-801 for the NMDA receptor but did not alter the density of receptors. Spermidine had essentially the same effect on Kd and Bmax measured in the dentate gyrus of TLE subjects and the cortex and dentate gyrus of postmortem controls. Moreover, there was no difference in the density of binding sites between postmortem and TLE subjects in either region. The binding of [3H]MK-801 in human cortex was decreased by 30% by incubation with DET or by prewashing the tissue sections. In contrast, DET did not alter the binding of [3H]MK-801 in rat cortex and prewashing sections produced an increase rather than a decrease in binding. These results suggest that there are different endogenous modulators for the polyamine site in rat and human tissue. The inverse agonist 1,10-diaminodecane decreased the binding of [3H]MK-801 in a dose-dependent manner. These results suggest that the fundamental modulatory properties of polyamines in rat and human tissues are essentially the same and that endogenous polyamines may regulate human NMDA receptors.

Topics: Adult; Animals; Brain; Cadaver; Cerebral Cortex; Diamines; Dizocilpine Maleate; Dose-Response Relationship, Drug; Epilepsy, Temporal Lobe; Female; Hippocampus; Humans; Male; Middle Aged; Polyamines; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Spermidine

N-Methyl-D-aspartic acid (NMDA, 500 microM) stimulated the net release of [3H]norepinephrine from rat hippocampal slices. The putative polyamine inverse agonist 1,10-diaminodecane (DA10) dose-dependently inhibited NMDA-stimulated release with a calculated IC50 value of 33 microM. The putative polyamine competitive antagonist diethylenetriamine (DET) partially inhibited (maximum effect 40%) NMDA-stimulated release at 1 mM which was the highest concentration tested. DET (1 mM) but not DA10 also partially inhibited potassium-stimulated release of norepinephrine from hippocampal slices. Neither DET or DA10 significantly altered the nonstimulated basal efflux of neurotransmitter. The inhibition of NMDA-stimulated release produced by 100 microM DA10 or 1 mM DET was not attenuated by addition of the polyamines spermine or spermidine up to 1 mM. In addition, the IC50 value for DA10-induced inhibition of NMDA-stimulated neurotransmitter release was not altered by the addition of DET (100-1000 microM). The combination of the glycine antagonist 7-chlorokynurenic acid (3 microM) and DA10 (100 microM) inhibited NMDA-stimulated release by approximately 70%. The addition of the glycine agonist D-serine (3-100 microM) partially attenuated the inhibition produced by these two compounds. No further enhancement was observed when D-serine was added in the presence of spermine or spermidine. Finally, the NMDA open channel blocker (+)-5-methyl-10,11- dihydro-5H-dibenzo[1,d]cyclo-hepten-5,10-imine maleate dose-dependently inhibited NMDA-stimulated release with an IC50 value of 25 nM. The inhibitory potency of (+)-5-methyl-10,11- dihydro-5H-dibenzo[1,d]cyclo-hepten-5,10-imine maleate was not significantly altered by the presence of either DET (100 microM) or DA10 (30 or 100 microM).(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Diamines; Dizocilpine Maleate; Hippocampus; In Vitro Techniques; Male; N-Methylaspartate; Norepinephrine; Polyamines; Rats; Rats, Sprague-Dawley

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 microns 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.

Topics: Animals; Brain; Corpus Striatum; Diamines; Dizocilpine Maleate; Dose-Response Relationship, Drug; Female; Male; N-Methylaspartate; Neurotoxins; Polyamines; Rats; Rats, Sprague-Dawley; Spermine

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 microM 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 region-specific manner.

Topics: Analysis of Variance; Animals; Autoradiography; Brain; Cell Membrane; Cerebral Cortex; Corpus Striatum; Diamines; Dizocilpine Maleate; Dose-Response Relationship, Drug; Hypothalamus; Kinetics; Male; Organ Specificity; Polyamines; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Spermidine; Tritium

The endogenous polyamines spermine and spermidine increase the binding of [3H]MK-801 to NMDA receptors. This effect is antagonized by diethylenetriamine (DET). We report here that spermine increases the rates of both association and dissociation of binding of [3H]MK-801, suggesting that it increases the accessibility of the binding site for MK-801 within the ion channel of the receptor complex. 1,10-Diaminodecane (DA10) inhibited the binding of [3H]MK-801. This effect was due to a decrease in the rate of association with no change in the rate of dissociation of [3H]MK-801. The effect of DA10 was not mediated by an action of DA10 at the binding sites for glutamate, glycine, Mg2+, or Zn2+, and was attenuated by DET. This suggests that DA10 acts at the polyamine recognition site. In hippocampal neurons the NMDA-elicited current was decreased by DA10, an effect opposite to that of spermine. The effects of spermine and DA10 were selectively blocked by DET. It is concluded that DA10 acts as a negative allosteric modulator or inverse agonist at the polyamine recognition site of the NMDA receptor.

Topics: Animals; Binding Sites; Cells, Cultured; Diamines; Dibenzocycloheptenes; Dizocilpine Maleate; Electric Conductivity; Glutamates; Glycine; Hippocampus; Kinetics; Magnesium; Polyamines; Rats; Receptors, N-Methyl-D-Aspartate; Receptors, Neurotransmitter; Spermidine; Spermine; Zinc