Pharmacology of glutamate neurotoxicity in cortical cell culture: attenuation by NMDA antagonists

Abstract

The antagonist pharmacology of glutamate neurotoxicity was quantitatively examined in murine cortical cell cultures. Addition of 1- 3 mM DL-2-amino-5-phosphonovalerate (APV), or its active isomer D-APV, acutely to the exposure solution selectively blocked the neuroexcitation and neuronal cell selectively blocked the neuroexcitation and neuronal cell loss produced by N-methyl-D-aspartate (NMDA), with relatively little effect on that produced by either kainate or quisqualate. As expected, this selective NMDA receptor blockade only partially reduced the neuroexcitation or acute neuronal swelling produced by the broad-spectrum agonist glutamate; surprisingly, however, this blockade was sufficient to reduce glutamate- induced neuronal cell loss markedly. Lower concentrations of APV or D- APV had much less protective effect, suggesting that the blockade of a large number of NMDA receptors was required to acutely antagonize glutamate neurotoxicity. This requirement may be caused by the amplification of small amounts of acute glutamate-induced injury by subsequent release of endogenous NMDA agonists from injured neurons, as the “late” addition of 10–1000 microM APV or D-APV (after termination of glutamate exposure) also reduced resultant neuronal damage. If APV or D-APV were present both during and after glutamate exposure, a summation dose-protection relationship was obtained, showing substantial protective efficacy at low micromolar antagonist concentrations. Screening of several other excitatory amino acid antagonists confirmed that the ability to antagonize glutamate neurotoxicity might correlate with ability to block NMDA-induced neuroexcitation: The reported NMDA antagonists ketamine and DL-2-amino- 7-phosphono-heptanoate, as well as the broad-spectrum antagonist kynurenate, were all found to attenuate glutamate neurotoxicity substantially; whereas gamma-D-glutamylaminomethyl sulfonate and L- glutamate diethyl ester, compounds reported to block predominantly quisqualate or kainate receptors, did not affect glutamate neurotoxicity. The present study suggests that glutamate neurotoxicity may be predominantly mediated by the activation of the NMDA subclass of glutamate receptors--occurring both directly, during exposure to exogenous compound, and indirectly, due to the subsequent release of endogenous NMDA agonists. Given other studies linking NMDA receptors to channels with unusually high calcium permeability, this suggestion is consistent with previous data showing that glutamate neurotoxicity depends heavily on extracellular calcium.

Synapses, NMDA receptor activity and neuronal Aβ production in Alzheimer’s disease

“…This theory was supported by experimental studies showing alterations in calcium signaling both in sporadic and in familial cases of AD (Mattson , 2004 ;Smith et al , 2005 ;Stutzmann , 2005 ). Comparatively to other routes of Ca 2 + entry in neuronal cells, N -methyl-d -aspartate receptors (NMDARs), a subtype of ionotropic glutamate receptors, are of particular interest because of their special ability to gate high levels of Ca 2 + infl ux (Choi et al , 1988 ;Sattler et al , 1998 ). These receptors have been extensively studied for their crucial role in synaptic plasticity and excitotoxicity (Rothman and Olney , 1995 ;Waxman and Lynch , 2005 ).…”

“…Thus, these receptors have been extensively studied for their crucial role in synaptic plasticity and neuronal damage occurring during acute or chronic pathologies (Waxman and Lynch , 2005 ). Dennis Choi was the fi rst to demonstrate that the NMDARs were the primary source of toxic Ca 2 + infl ux mediating glutamate excitotoxicity (Choi et al , 1988 ). Shortly afterwards, it was proposed that Ca 2 + entry through NMDARs was particularly effective at killing neurons as compared with entry through other channels (Tymianski et al , 1993 ).…”

Dopamine receptor activation reveals a novel, kynurenate-sensitive component of striatal N-methyl-d-aspartate neurotoxicity

“…4C). Thus, glutamate excitotoxicity is primarily mediated by NMDA, rather than non-NMDA, receptors (Choi et al, 1988;Monnerie et al, 2003), and KYNA-deficient mice fail to demonstrate enhanced striatal kainate toxicity (Sapko et al, 2006).…”

Potentiation of excitotoxicity in HIV-1-associated Dementia and the significance of glutaminase

“…At normal physiological resting membrane potential, magnesium blocks the channel pore (76); when removed, the ligand activated NMDA receptor allows an influx of calcium, leading to postsynaptic depolarization and action potential in the postsynaptic neuron (77). NMDA receptor antagonists can block most excitotoxic effects of glutamate (78). Calcium entering through over-activated NMDA receptors results in more cell death as opposed to calcium entering through non-NMDA glutamate receptors or voltage-gated calcium channels, suggesting NMDA receptor-mediated neurotoxicity occurs through distinct calcium signaling pathways that may involve the NMDA receptor-specific interaction with PSD, a family of postsynaptic scaffold proteins (75,79).…”

“…Glutamate regulation is critical because improper management of glutamate levels may impair not only its signaling properties, but can lead to cell death via excitotoxicity (78,97). The concept of excitotoxicity was first proposed by Olney in 1969 as a toxic effect of excessive or prolonged activation of receptors by excitatory amino acids (EAA) (98).…”