Opposing action of conantokin-G on synaptically and extrasynaptically-activated NMDA receptors

• Published in: Neuropharmacology 2012-06, Vol.62 (7), p.2226-2237
• Main Authors: Balsara, Rashna, Li, Neill, Weber-Adrian, Danielle, Huang, Louxiu, Castellino, Francis J.
• Format: Article
• Language: English
• Subjects: Actin; Actin organization; Animals; Antagonists; Calcium influx; Cell survival; Cells, Cultured; Conantokin inhibitors; Conotoxins - pharmacology; Cyclic AMP response element-binding protein; Data processing; Excitatory Amino Acid Antagonists - pharmacology; Excitatory Postsynaptic Potentials - drug effects; Excitatory Postsynaptic Potentials - physiology; Extracellular signal-regulated kinase; Glutamic acid receptors; Glutamic acid receptors (ionotropic); Ion channels; Knockout mice; Mice; Mice, Inbred C57BL; Mice, Knockout; Mitochondria; MK-801; N-Methyl-D-aspartic acid receptors; Neuron signaling; Neurons; Neuroprotection; NMDA receptor subunits; NMDAR inhibition; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate - antagonists & inhibitors; Receptors, N-Methyl-D-Aspartate - physiology; Regulatory sequences; Signal transduction; Synapses - drug effects; Synapses - physiology; Synaptic and extrasynaptic NMDA receptors
• ISSN: 0028-3908; 1873-7064
• DOI: 10.1016/j.neuropharm.2012.01.018

Synaptic and extrasynaptic activation of the N-methyl-d-aspartate receptor (NMDAR) has distinct consequences on cell signaling and neuronal survival. Since conantokin (con)-G antagonism is NR2B-selective, which is the key subunit involved in extrasynaptic activation of the receptor, its ability to specifically elicit distinct signaling outcomes in neurons with synaptically or extrasynaptically-activated NMDARs was evaluated. Inhibition of Ca2+ influx through extrasynaptic NMDAR ion channels was neuroprotective, as it effectively enhanced levels of activated extracellular signal-regulated kinase 1/2 (ERK1/2), activated cAMP response element binding protein (CREB), enhanced mitochondrial viability, and attenuated the actin disorganization observed by extrasynaptic activation of NMDARs. Conversely, the pro-signaling pathways stimulated by synaptically-induced Ca2+ influx were abolished by con-G. Furthermore, subunit non-selective con-T was unable to successfully redress the impairments in neurons caused by extrasynaptically-activated NMDARs, thus indicating that NR2B-specific antagonists are beneficial for neuron survival. Neurons ablated for the NR2B subunit showed weak synaptic Ca2+ influx, reduced sensitivity to MK-801 blockage, and diminished extrasynaptic current compared to WT and NR2A−/− neurons. This indicates that the NR2B subunit is an integral component of both synaptic and extrasynaptic NMDAR channels. Altogether, these data suggest that con-G specifically targets the NR2B subunit in the synaptic and extrasynaptic locations, resulting in the opposing action of con-G on differentially activated pools of NMDARs. ► Separately examined Ca2+ influx into neurons from synaptic and extrasynaptic NMDARs. ► Determined signaling pathways activated by synaptic and extrasynaptic NMDAR activation. ► Assessed neuron cytoskeletal arrangements via synaptic and extrasynaptic NMDAR activation. ► Employed a combination of pharmacological NMDAR inhibitions and gene inactivated NMDAR subunit mice. ► Examined subunit specificity in action of conantokin drug specificity.