NMDA Receptor-associated Glycine Research Articles

Presence of the N‐Methyl‐D‐Aspartate‐Associated Glycine Receptor Agonist, D‐Seine, in Human Temporal Cortex: Comparison of Normal, Parkinson, and Alzheimer Tissues

The amino acid D-serine (D-Ser), previously recognized as a pharmacological tool for potentiating neuronal activity mediated by the N-methyl-D-aspartate (NMDA) receptor complex, in vitro and in vivo, has been observed in several brain regions of the rat and mouse, most prominently in cortex. In addition to reconfirming the presence and distribution of D-Ser in rat brain, we have observed, for the first time, endogenous, free D-Ser in temporal cortex of normal human brains at a level of 2.18 +/- 0.12 nmol/mg of protein, representing 15 +/- 2% of the free L-Ser pool. The D- and L-Ser specific content and the D/L-Ser ratio obtained from temporal cortex of Parkinson and Alzheimer brains did not differ significantly from those of controls. However, at the levels observed here, and considering its specificity and affinity for the NMDA-associated glycine receptor, endogenous D-Ser is a plausible NMDA receptor glycine site agonist.

Characterization of 3-carboxy-5-phosphono-1,2,3,4-tetrahydroisoquinoline (SC-48981), a potent competitive [formula omitted] (NMDA) receptor antagonist, in vitro and in vivo

(±)-3-Carboxy-5-phosphono-1,2,3,4-tetrahydroisoquinoline (SC-48981), a conformationally restricted analog of the potent competitive N- methyl- d-aspartate (NMDA) antagonist, 2-amino-5-phosphonopentanoate (AP-5), potently inhibited the binding of [ 3H]glutamate to the N- methyl- d-aspartate (NMDA) receptors with a K i of 1.6 mcM, but with minimal affinity for kaininate and quisqualate receptors ( K i > 50 mcM), in vitro. Consistent with its ability to antagonize the NMDA receptor, SC-48981 decreased the binding of [ 3H]glycine and [ 3H]TCP [1-(2-thienyl)cyclohexylpiperidine] to the NMDA-associated glycine and phencyclidine (PCP) recognition sites, in vitro. SC-48981 attenuated levels of basal cGMP and harmaline-induced increases in levels of cGMP in the mouse cerebellum, in vivo, in a competitive manner, with ED 50 values of 5.5 and 8.7 mg/kg, i.p. Direct intracerebellar injection of SC-48981 (0.5 μg) attenuated increases in levels of cGMP induced by central injection of the NMDA-associated glycine receptor agonist, D-serine and by NMDA itself. Parenteral administration of SC-48981 (25 mg/kg, s.c.) decreased basal levels of cGMP for up to 3 h. These results indicate that SC-48981 represents a novel bioavailable competitive NMDA antagonist with a long duration of action.

Effects of sigma ligands on mouse cerebellar cyclic guanosine monophosphate (cGMP) levels in vivo: further evidence for a functional modulation ofN-methyl- d-aspartate (NMDA) receptor complex-mediated events by sigma ligands

In the present investigation, the effects of sigma ligands[WY-47384 {;8-fluoro-2,3,4,5-tetrahydro-2[3-(3-pyridinyl)propyl)1H-pyrido(4, 3b)indole}, (+)-pentazocine, (+)-SFK 10,047 (N-allylnormetazocine), mafoprazine, opipramol, dextromethorphan, dextrorphan, (+)-3-PPP [3-(3-hydroxyphenyl)-N-propylpiperidine], (−)-butaclamol, DTG [1,3-di(2-tolyl)guanidine], rimcazole, ifenprodil and BMY-14802 {α-(fluorophenyl)-4-(5-fluoropyrimidinyl)-1-piperazine butanol}] on harmaline-, pentylenetetrazol (PTZ)-, methamphetamine (MA)- and d-serine-induced increases in mouse cerebellar levels of cGMP were determined. Ifenprodil, BMY-14802, dextromethorphan, dextrorphan, (+)-SKF 10,047, opipramol and mafoprazine reversed harmaline-, PTZ-, MA- and d-serine-induced increases in levels of cGMP. Rimcazole reversed only the harmaline-induced response. WY-47384 reversed harmaline-, MA-, d-serine-, but not PTZ- or quisqualate-induced increases in levels of cGMP. (+)-Pentazocine attenuated harmaline- and d-serine-, but not PTZ- and MA-induced cGMP responses. Haloperidol did not affect harmaline- and d-serine-induced cGMP responses. (+)-3-PPP and (−)-butaclamol did not affect any of the responses studied. Furthermore, (+)-3-PPP-induced increases in levels of cGMP were reversed by the competitiveN-methyl- d-aspartate (NMDA) antagonist, CPP} 3-(2-car☐ypiperazin-4-yl)propyl-1-phosphonic acid, the non-competitive NMDA antagonist, (+)-MK-801 (dizocilipine maleate), the NMDA-associated glycine receptor antagonist, HA-966 (3-amino-1-hydroxypyrrolidin-2-one), the partial glycine agonist, DCS ( d-cycloserine) as well as by the sigma ligands, ifenprodil, WY-47384, (+)-pentazocine, (+)-SKF 10,047, dextromethorphan and dextrorphan but not by rimcazole. These data further support functional modulation by sigma ligands of events mediated by the NMDA receptor complex established in earlier investigations.

Glycine, glycinamide and d-serine act as positive modulators of signal transduction at the N-Methyl-D-Aspartate (NMDA) receptor [formula omitted]: Differential effects on mouse cerebellar cyclic guanosine monophosphate levels

Direct intracerebellar (icb) administration of glycine, glycinamide and D-serine produced time- and dose-dependent changes in mouse cerebellar cGMP levels, indicating a modulation of ongoing neuronal activity through the NMDA receptor complex. Intracerebro-ventricular administration of glycinamide also produced a timedependent change in cGMP levels, indicating a central mechanism of action. The icb dose-response data indicated a unimolecular interaction for these compounds. D-serine-, glycine-, and glycinamide-mediated increases in cGMP levels were reversed by the competitive NMDA antagonist, CPP and the NMDA-associated glycine receptor antagonist, HA-966, indicating mediation via the NMDA receptor complex. Glycine and D-serine were less effective than glycinamide at increasing cerebellar cGMP levels. In contrast, L-and D-serinamide did not affect cGMP levels. These results indicate that glycine receptor is not saturated under physiological conditions and also suggest possible existence of multiple glycine pools.

In vivo antagonism of agonist actions at N-methyl- d-aspartate and N-methyl- d-aspartate-associated glycine receptors in mouse cerebellum: Studies of 1-hydroxy-3-aminopyrrolidone-2

Intracerebellar injections of either NMDA or d-serine dramatically elevated levels of cGMP in the cerebellum of the mouse, in vivo. These actions were both antagonized by simultaneous injection of the NMDA-associated glycine receptor antagonist, HA-966. Intracerebellar injections of d-serine were also antagonized by peripheral (s.c.) injections of HA-966, demonstrating the bioavailability of this glycine receptor antagonist. Parenteral administration of HA-966 was also effective in antagonizing the actions of intravenously injected harmaline, an activator of the cerebellar climbing fiber pathway, on cGMP in the cerebellum. An evaluation of the parenteral dose-response curve for HA-966, revealed no effect on basal activity within the cerebellum. This contrasts sharply with the abilities of both competitive and non-competitive NMDA antagonists to decrease basal levels of cGMP in the cerebellum. In summary, these studies demonstrate that HA-966 is a bioavailable antagonist of the NMDA-associated glycine receptor and that this compound can limit excessive stimulation of the NMDA receptor by exogenous application of agonist, with minimal effects on basal activity. These data suggest that antagonists of the NMDA-associated glycine receptor may be optimal therapies in the treatment of stroke and epilepsy.

Neuropharmacological characterization of 1-Aminocyclopropane-1-carboxylate and 1-Aminocyclobutane-1-carboxylate, Ligands of the N-Methyl-D-Aspartate-associated Glycine Receptor

Following intravenous administration, 1-aminocyclobutane-1-carboxylate (ACBC, 100 mg/kg), a N-methyl-D-aspartate (NMDA)-associated glycine receptor antagonist, was eliminated with a T 1/2 of 5 min in mouse brain and 4 min in rat cerebrospinal fluid (CSF). 1-Aminocyclopropane-1-carboxylate (ACC), a NMDA-associated glycine receptor agonist, was found to have a T 1/2 of less than 5 min in mouse brain. ACC and ACBC did not alter basal cerebellar cGMP. Glycine and D-serine increased cGMP, and 1-hydroxy-3-aminopyrrolidone-2 (HA-966), a glycine antagonist, reversed the D-serine-induced increases in cGMP. In contrast, ACBC did not reverse the D-serine-induced increases in cGMP. These data suggest that despite their brain bioavailability and marked potency at the glycine receptor in vitro. ACC and ACBC are rapidly inactivated and thus have limited in vivo utility.

The polyamines, spermine and spermidine, negatively modulate N-methyl-d-aspartate (NMDA) and quisqualate receptor mediated responses in vivo: Cerebellar cyclic GMP measurements

The effects of the polyamines, spermine and spermidine on basal and d-serine-, harmaline- and quisqualate-induced cyclic GMP (cGMP) were measured in mouse cerebellum. Spermine and spermidine at 200 ?g/mouse, intracerebellar injection (icb), did not alter basal cGMP levels. d-Serine (200 ?g/mouse, icb) and quisqualic acid (5 ?g/mouse, icb) caused 5- and 15-fold increases in cGMP. These increases were significantly reversed by co-injected spermine and spermidine (200 ?g/mouse, icb). Furthermore, direct intracerebellar spermidine (200 ?g) completely reversed harmaline (100 mg/kg, sc) induced increases in cGMP. These data indicate that the polyamines, spermine and spermidine attenuate responses mediated through the N-methyl-D-aspartate (NMDA), NMDA-associated glycine receptor and quisqualate receptors. These results provide an in vivo neurochemical evidence for polyamine modulation of excitatory amino acid receptors. Due to their putative abilities to increase mitochondrial uptake of [Ca(+2)], spermine and spermidine are likely to modulate the responses of several excitatory amino acid agonists. The polyamines spermine and spermidine are widely distributed in neural and non-neural tissues and have been shown to play a key role in cell differentiation and growth (Kremzner et al ., 1970; Harik and Snyder, 1974; Raina and Janne, 1975; Seiler, 1981; Pegg and McCann, 1982). Extensive studies have indicated an important role of the polyamines, spermine and spermidine, in the regulation of intracellular [Ca(+2)] levels (Nicchitta and Williamson, 1984; Iqbal and Koenig, 1985; Jensen Lynch and Baudrey, 1987; 1989 a, b). The precise regulation of intracellular [Ca(+2)] levels and maintenance of [Ca(+2)] gradients across the cell membranes are essential in cell survival as prolonged and excessive exposure to calcium can result in neuronal injury and death (Farber, 1981; Rasmussen and Barnett, 1984). The excitatory amino acid glutamate is known to interact with three subclasses of receptors, N-methyl-D-aspartate (NMDA), quisqualate and kainate (Cotman and Iversen, 1987). The role of excitatory amino acids in the etiology of ischemic neuronal death is also well established (Cotman and Iversen, 1987). Although the precise mechanisms of ischemic injury are unknown, excessive release of glutamate and/or other endogenous excitatory amino acid(s) which result(s) in massive influx of [Ca(+2)] into neurons (Garthwhite et al ., 1986; Choi et al ., 1987) is considered in important event. Due to the pivotal role played by polyamines in the regulation of intracellular [Ca(+2)] levels, it is likely that polyamines may have an important role in the pathophysiology of ischemic injury. Recent in vitro evidence suggests that the NMDA receptor complex has recognition sites for the polyamines, spermine and spermidine, besides the putative sites for glycine, phencyclidine (PCP), and divalent ions such as [Mg(+2)] and [Zn(+2)] (Ransom and Stec, 1988). Recently, ifenprodil, a novel NMDA receptor antagonist, was shown to interact with the polyamines (Reynolds and Miller, 1989) which may explain its unique pharmacological profile. However, the precise functional interactions of polyamines with NMDA and other excitatory amino acids are unknown at this time. The present investigation was aimed at elucidating the in vivo functional interrelationships between polyamines and the excitatory amino acids in general, and with the NMDA receptor complex in particular, by examining the effects of spermine and spermidine on mouse cerebellar cGMP levels, a well characterized excitatory amino acid receptor-mediated second messenger response (Wood et al ., 1982; 1987; 1989; Rao et al ., 1989).

Quinoxaline derivatives are high-affinity antagonists of the NMDA receptor-associated glycine sites

Membranes from rat telencephalon contain strychnine-insensitive glycine binding sites associated with NMDA receptors. Three quinoxaline derivatives, among them the high-affinity AMPA receptor antagonists CNQX and DNQX, were found to inhibit [ 3H]glycine binding to these sites with micromolar affinities. Binding of these compounds to the glycine site also inhibited glutamate-stimulated association and dissociation of [ 3H]TCP. This suggests that these AMPA antagonists, like the structurally related compound kynurenate, act as glycine site antagonists.