N-methyl-D-aspartate Binding Research Articles

TCP binding: A tool for studying NMDA receptor-mediated neurotransmission in kindling

Findings from numerous pharmacological and electrophysiological studies have uniquely implicated the N-methyl-D-aspartate (NMDA) receptor in kindling. Recent findings indicate that this receptor is regulated by ligands acting at both amino acid (NMDA and glycine) and ion (Zn++ and Mg++) binding sites. To examine the role of the NMDA receptor in kindling it will be necessary to understand how ligands for these different binding sites interact to control activation of the NMDA receptor. To this end we examined a biochemical tool for measuring opening of the NMDA receptor-gated ion channel (NMDA channel). [3H]N-(1-[thienyl] cyclohexyl)piperidine (TCP) binding to brain membranes is stimulated by NMDA and glycine receptor agonists. We have shown that NMDA and glycine increase TCP binding by increasing the access of TCP to its site. Moreover, the pharmacology of the NMDA and glycine binding sites regulating TCP binding is identical to that of the sites regulating NMDA evoked currents. These findings strongly suggest that glycine and NMDA regulate TCP binding by increasing the opening of the NMDA channel. That is NMDA and glycine increase the overall time that the channel is open thereby increasing the time available for TCP to diffuse to its binding site. These findings support the use of TCP binding (association rate) as a marker of channel opening and thereby permit measurement of NMDA receptor activation and ligand binding under identical conditions. This will allow direct testing the hypothesis that an alteration in the NMDA receptor/channel complex itself underlies the increased seizure response of kindled animals.

Transient increase of NMDA-binding sites in human hippocampus during development

In the human hippocampus, the density of glutamate and N- methyl- d-aspartate (NMDA) binding sites follows during development a bell-shaped curve with a peak at 23–27 fetal weeks. We suggest that there is a transient increased density of NMDA binding sites during a restricted period of hippocampal development; this may play an important role in developmental plasticity.

Dynamic changes of excitatory amino acid receptors in the rat hippocampus following transient cerebral ischemia

The changes in excitatory amino acid receptor ligand binding induced by transient cerebral ischemia were studied in the rat hippocampal subfields. Ten minutes of ischemia was induced by common carotid artery occlusion combined with hypotension, and the animals were allowed variable periods of recovery ranging from 1 day to 4 weeks. The binding of 3H-AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) to quisqualate receptors, 3H-kainic acid (KA) to kainate receptors, and 3H-glutamate to N-methyl-D-aspartate (NMDA) receptors as determined by quantitative autoradiography. One week following ischemia the CA1 region of the hippocampus displayed a severe (90%) dendrosomatic lesion with preservation of presynaptic terminals. This was associated with a 60% decrease in AMPA binding and a 25% decrease in glutamate binding to NMDA receptors. At 4 weeks postischemia, both AMPA and NMDA sites were greatly reduced. Although the dentate gyrus granule cells are resistant to an ischemic insult of this magnitude, this region showed marked changes in receptor binding. One week following ischemia, the AMPA and NMDA binding decreased by approximately 40 and 20%, respectively. Following 2 weeks of recovery, the NMDA binding was not significantly different from control level, while the AMPA binding remained depressed up to 4 weeks postischemia. The high density of KA binding sites in the inner molecular layer of the dentate gyrus was unaffected by the ischemic insult, despite an extensive degeneration of cells in the hilus of dentate gyrus which projects glutamatergic afferents to this area.(ABSTRACT TRUNCATED AT 250 WORDS)

Anatomic correlation of NMDA and 3H-TCP-labeled receptors in rat brain

Using quantitative autoradiography, we have compared the regional distribution of N-methyl-D-aspartate (NMDA) receptors labeled with 3H-glutamate and dissociative anesthetic binding sites labeled with 3H-N-(1-[2-thienyl]cyclohexyl)3,4-piperidine (3H-TCP). Binding of both ligands was highest in the hippocampal formation, with high concentrations in a number of cortical and olfactory regions. Intermediate amounts of binding for both ligands were measured in several thalamic and basal telencephalic structures. Very little binding was observed in the hypothalamus, some deep forebrain regions, and most brain-stem structures. Linear-regression analysis comparing the binding at both sites revealed a marked concordance (R = 0.95; p less than 0.001; Pearson product-moment). The granule cell layer of the cerebellum was the only region in which this concordance was not observed. Scatchard analysis of 3H-glutamate binding to NMDA receptors in stratum radiatum of hippocampal formation revealed an apparent single binding site with a Bmax of 9.78 +/- 0.84 pmol/mg protein and KD of 158 +/- 37 nM. 3H-TCP also bound to an apparent single site with a Bmax of 2.07 +/- 0.16 pmol/mg protein and KD of 127 +/- 30 nM. Our results are consistent with the hypothesis that the dissociative anesthetic binding site is linked to the NMDA receptor, and the data suggest that there are approximately 4-5 NMDA binding sites for each dissociative anesthetic binding site.

Characterization of motor activity patterns induced by N-methyl-D-aspartate antagonists in gerbils.

A computerized motor activity data collection and analysis system is described. An example of the utilization of the Digiscan system is provided, in which motor activity patterns induced by three N-methyl-D-aspartate (NMDA) antagonists and the dissociative anesthetic, ketamine, are compared. All of these compounds produce a distinct pattern of motor activity characterized by an increase in distance traveled, movement time, speed and perimeter walking, with a decrease in vertical activity. Recently described links between NMDA and phencyclidine (PCP) binding sites may account for these findings. The utility of computerized motor activity apparatus is clearly demonstrated.

Neuropharmacological actions of kynurenic and quinolinic acids on horizontal cells of the isolated fish retina

We have studied the effects of naturally occurring metabolites of tryptophan, kynurenic and quinolinic acids, on the electrophysiological responses of retinal horizontal cells in the fish ( Rutilus rutilus, the roach). Quinolinic acid usually hyperpolarizes the cells and reduces their light evoked responses (S-potentials) but on occasion, it causes a slight depolarization of the membrane potential. These actions are similar to those found with N-methyl- d-aspartate (NMDA) and our results are consistent with the proposal that it acts at NMDA binding sites. Kynurenic acid (⩾1mM) invariably hyperpolarizes horizontal cells to their potassium Nernst equilibrium potential and, more significantly, blocks the depolarizing actions exerted on them by excitatory amino acids, such as kainic and quisqualic acids. We show that this action persists in the presence of the synaptic blocker, cobalt chloride, and thus is not mediated by chemical synaptic activity. Kynurenic acid does not reverse depolarization of horizontal cells by dopamine or γ-aminobutyric acid, thus its inhibitory effects are selective to the actions of excitatory amino acids. Neither xanthurenic acid, a close structural analogue of kynurenic acid, nor quinolinic acid are effective in blocking depolarizations by excitatory aino acids.