dizocilpine-maleate and (tetrazol-5-yl)glycine

Autoradiographical studies revealed that 10 nM [3H]N-acetyl-aspartyl-glutamate (NAAG) labelled grey matter structures, particularly in the hippocamus, cerebral neocortex, striatum, septal nuclei and the cerebellar cortex. The binding was inhibited by (2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)-glycine (DCG IV), an agonist at group II metabotropic glutamate receptors (mGluR II). (RS)-alpha-Methyl-4-tetrazolylphenylglycine (MTPG), (RS)-alpha-cyclopropyl-4-phosphonoglycine (CPPG) and (RS)-alpha-methylserine-O-phosphate monophenyl ester (MSOPPE), all antagonists at mGluR II and mGluR III, also inhibited [3H]NAAG binding. Other inhibitors were (1S,3R)-1-aminocyclopentane-1,3-dicarboxylate (ACPD), a broad-spectrum mGluR agonist with preference for groups I and II and the mGluR I agonists/mGluR II antagonists (S)-3-carboxy-4-hydroxyphenylglycine (3,4-CHPG) and (S)-4-carboxy-3-hydroxyphenylglycine (4,3-CHPG). Neither the mGluR I specific agonist (S)-dihydroxyphenylglycine nor any of the ionotropic glutamate receptor ligands such as kainate, AMPA and MK-801 had strong effects (except for the competitive NMDA antagonist CGS 19755, which produced 20-40% inhibition at 100 microM) suggesting that, at low nM concentrations, [3H]NAAG binds predominantly to metabotropic glutamate receptors, particularly those of the mGluR II type. Several studies have indicated that NAAG can interact with mGluR II and the present study supports this notion by demonstrating that sites capable of binding NAAG at low concentrations and displaying pharmacological characteristics of mGluR II exist in the central nervous tissue. Furthermore, the results show that autoradiography of [3H]NAAG binding can be used to quantify the distribution of such sites in distinct brain regions and study their pharmacology at the same time.

Topics: Alanine; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Animals; Binding Sites; Brain; Brain Chemistry; Carboxypeptidases; Cold Temperature; Cycloleucine; Cyclopropanes; Dipeptides; Dizocilpine Maleate; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Female; Glutamate Carboxypeptidase II; Glycine; Kainic Acid; Male; Nerve Tissue Proteins; Phosphoserine; Pipecolic Acids; Rats; Rats, Sprague-Dawley; Receptors, Glutamate; Receptors, Metabotropic Glutamate; Receptors, N-Methyl-D-Aspartate; Tetrazoles

The release of preloaded [3H]glycine from hippocampal slices in developing and ageing mice (from 7 days to 22 months) was characterized using a superfusion system. The release was Ca(2+)-independent in each age group studied. The basal release and the responses to potassium stimulation were fairly constant during the whole life span. The release was potentiated by the glutamate receptor agonists kainate, N-methyl-D-aspartate (NMDA), tetrazolylglycine, quisqualate and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) in developing mice, but only kainate was effective in adult and aged animals. The kainate effect was not modified by the antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) in adult and old mice, indicating that glutamatergic systems may not be involved in the release. On the other hand, hippocampal glycine release in immature mice seems to be subject to regulation by both NMDA and non-NMDA (kainate and AMPA) receptors. The potentiations by NMDA and AMPA were antagonized by dizocilpine (MK-801) and CNQX, respectively. The modulation of glycine release by glutamatergic receptors could be of importance in the regulation of synaptic glycine levels in the developing hippocampus.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Aging; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Animals; Calcium; Dizocilpine Maleate; Female; Glycine; Hippocampus; In Vitro Techniques; Kainic Acid; Male; Mice; N-Methylaspartate; Potassium; Quisqualic Acid; Receptors, Glutamate; Tetrazoles

The purpose of the present study was to examine the effects of N-methyl-D-aspartate (NMDA) receptor blockade on the activity of tuberoinfundibular dopaminergic (TIDA) neurons in male and female rats. TIDA neuronal activity was estimated by measuring either the accumulation of 3,4-dihydroxyphenylalanine (DOPA) 30 min after the administration of the decarboxylase inhibitor NSD-1015 or the concentration of the dopamine metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) in the median eminence. The non-competitive NMDA receptor antagonist MK-801 markedly reduced prolactin secretion in both male and female rats. MK-801 also produced a dose- and time-dependent decrease in the activity of TIDA neurons in female rats, but had no effect on the activity of TIDA neurons in either intact, orchidectomized or orchidectomized, testosterone-treated male rats. Removal of the tonic stimulatory effects of prolactin on TIDA neurons in female rats by immunoneutralization of endogenous prolactin failed to alter the responsiveness of TIDA neurons to the inhibitory effects of MK-801. On the other hand, MK-801 was unable to inhibit TIDA neurons in ovariectomized female rats, but the responsiveness of TIDA neurons to MK-801 in ovariectomized female rats was restored following estrogen replacement, even in the absence of prolactin. Like MK-801, the competitive NMDA receptor antagonist CGS-19755 produced a dose-dependent decrease in TIDA neuronal activity in female rats, which was prevented in a dose-dependent manner by the NMDA receptor agonist D,L-(tetrazol-5-yl) glycine. Taken together, these results reveal a sexual difference in the responsiveness of TIDA neurons to NMDA receptor antagonists, and suggest that estrogen positively modulates NMDA receptor-mediated, tonic stimulation of TIDA neurons in female rats by a prolactin-independent mechanism.

Topics: Animals; Dizocilpine Maleate; Dopamine; Female; Glycine; Hypothalamus, Middle; Male; Neurons; Pipecolic Acids; Prolactin; Rats; Receptors, N-Methyl-D-Aspartate; Sex Characteristics; Tetrazoles

At physiological pH, the spatial arrangement of the three charges of DL-tetrazol-5-ylglycine (5) could be viewed as similar to those found in certain conformations of the two excitatory amino acids (EAAs)--aspartic and glutamic acids. Given significant binding to one or more EAA receptors, 5 would offer unique modeling and perhaps biological opportunities. We have previously shown it to be the most potent NMDA agonist known, with a unique and marked in vitro neutrotoxicity at depolarizing concentrations. Now we report the details required for its synthesis, together with its potency and efficacy in two assays of functional activation of the NMDA receptor, namely agonist-influenced [3H]MK801 binding and agonist-induced release of the neurotransmitter [3H]-norepinephrine from brain slices. In both these assays DL-tetrazol-5-ylglycine proved to be more potent and efficacious than NMDA and cis-methanoglutamate. It was more potent than, and equally efficacious to, L-glutamate in [3H]MK801 binding. The structural features of 5 may well reflect optimal agonist interaction at the NMDA receptor site. (We considered the possibility that some decarboxylation of DL-tetrazol-5-ylglycine may have occurred during testing. This would give 5-(aminomethyl)tetrazole (13), the tetrazole acid analog of glycine; and glycine is involved in NMDA receptor activation. Compound 13 does not affect [3H]glycine binding at the strychnine-insensitive glycine binding site, and [3H]MK801 binding studies showed that the (aminomethyl)-tetrazole, even if is formed, would probably have no effect on the activity of tetrazol-5-ylglycine at the NMDA receptor.

Topics: Animals; Cell Membrane; Cerebral Cortex; Dizocilpine Maleate; Glutamates; Glutamic Acid; Glycine; Hippocampus; Molecular Structure; N-Methylaspartate; Norepinephrine; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Structure-Activity Relationship; Tetrazoles