Reduced blockade by extracellular Mg²⁺ is permissive to NMDA receptor activation in cerebellar granule neurons that model a migratory phenotype

• Published in: Journal of neurochemistry Vol. 114; no. 1; pp. 191 - 202
• Main Authors: Gerber, Adam M, Beaman-Hall, Carol M, Mathur, Anjili, Vallano, Mary Lou
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01.07.2010; Blackwell Publishing Ltd; Wiley-Blackwell
• Subjects: AMPA receptors; Biological and medical sciences; Brain; CaMK; Central nervous system; Central neurotransmission. Neuromudulation. Pathways and receptors; cerebellum; CREB; Degenerative and inherited degenerative diseases of the nervous system. Leukodystrophies. Prion diseases; explant; Fundamental and applied biological sciences. Psychology; Genotype & phenotype; Medical sciences; Neurology; Neurons; Vertebrates: nervous system and sense organs; CaMK; Granule neuron; Central nervous system; Electrophysiology; Glutamate receptor; Activation; Extracellular; Survival; cerebellum; Encephalon; explant; Depolarization; Phenotype; CREB; Voltage; Development; Models; AMPA receptors; NMDA receptor; Biological receptor
• ISSN: 0022-3042; 1471-4159
• DOI: 10.1111/j.1471-4159.2010.06746.x

J. Neurochem. (2010) 114, 191-202. NMDA receptors (NMDAR) contribute to neuronal development throughout the CNS. However, their mode(s) of activation preceding synaptic maturation is unclear, as they are not co-localized with alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate receptors (AMPARs) which normally provide sufficient depolarization to relieve voltage-dependent blockade by Mg²⁺. We used cerebellar granule neurons (CGNs) cultured at a near-physiological KCl concentration to examine maturation-dependent changes in NMDAR responses. In contrast, most studies use KCl-supplemented medium to promote survival. At 2-4 days in vitro CGNs: (i) express developmental markers resembling the in vivo migratory phenotype; (ii) maintain a basal amount of calcium responsive element-binding protein phosphorylation that requires NMDARs and calcium/calmodulin-dependent kinases, but not AMPARs; (iii) exhibit NMDA-mediated Ca²⁺ influx not effectively blocked by ambient Mg²⁺ (0.75 mM) or AMPARs; (iv) maintain a more depolarized resting membrane potential and increased resistance compared to synaptically-connected CGNs. Moreover, migrating CGNs in explant cultures demonstrate NMDA-mediated Ca²⁺ influx not effectively blocked by 0.75 mM Mg²⁺, and NMDAR but not AMPAR antagonists slow migration. These data suggest the biophysical properties of immature CGNs render NMDARs less sensitive to Mg²⁺ blockade, enhancing the likelihood of activation in the absence of AMPAR depolarization.