title: NMDA-receptor-mediated sensory responses of brain noradrenergic neurons are suppressed by in vivo concentrations of extracellular magnesium.
abstract: Recent studies reveal at least three receptor subtypes for excitatory amino acid (EAA) neurotransmitters. Activation of one of these, the N-methyl-D-aspartate (NMDA) receptor-channel complex, has been strongly implicated in neuronal mechanisms of several important brain processes, including learning and memory. As NMDA receptors are highly sensitive to extracellular magnesium (Mg++), we tested whether in vivo concentrations of this ion are sufficient to suppress NMDA-receptor-mediated responses. We show that slow, local microinfusion of Mg(++)-free artificial cerebrospinal fluid onto noradrenergic locus coeruleus (LC) neurons reveals an NMDA-receptor-mediated component of their response to a sensory stimulus. This is the first demonstration that the in vivo concentration of extracellular Mg++ ions suppresses synaptically mediated NMDA receptor activation. We also present evidence that unmasking this NMDA receptor activity induces prolonged enhancement of the EAA-mediated sensory response of LC neurons.
authors.affiliation: Department of Mental Health Sciences, Hahnemann University, Philadelphia, Pennsylvania 19102-1192.
authors.forename: R
authors.initials: R
authors.lastname: Shiekhattar
authors.forename: G
authors.initials: G
authors.lastname: Aston-Jones
mesh_terms: D000596:Amino Acids / Q000494:pharmacology; D000818:Animals; D001921:Brain / Q000166:cytology* / Q000502:physiology; D004594:Electrophysiology; D066298:In Vitro Techniques; D008125:Locus Coeruleus / Q000166:cytology / Q000502:physiology; D008274:Magnesium / Q000494:pharmacology*; D008297:Male; D009475:Neurons, Afferent / Q000187:drug effects / Q000502:physiology*; D009638:Norepinephrine / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects / Q000502:physiology*; D013569:Synapses / Q000187:drug effects / Q000378:metabolism
chemical_list: D000596:Amino Acids; D016194:Receptors, N-Methyl-D-Aspartate; D008274:Magnesium; D009638:Norepinephrine