The mammalian ionotropic glutamate receptor family encodes 18 gene products that coassemble to form ligand-gated ion channels containing an agonist recognition site, a transmembrane ion permeation pathway, and gating elements that couple agonist-induced conformational changes to the opening or closing of the permeation pore. Glutamate receptors mediate fast excitatory synaptic transmission in the central nervous system and are localized on neuronal and non-neuronal cells. These receptors regulate a broad spectrum of processes in the brain, spinal cord, retina, and peripheral nervous system. Glutamate receptors are postulated to play important roles in numerous neurological diseases and have attracted intense scrutiny. The description of glutamate receptor structure, including its transmembrane elements, reveals a complex assembly of multiple semiautonomous extracellular domains linked to a pore-forming element with striking resemblance to an inverted potassium channel. In this review we discuss International Union of Basic and Clinical Pharmacology glutamate receptor nomenclature, structure, assembly, accessory subunits, interacting proteins, gene expression and translation, post-translational modifications, agonist and antagonist pharmacology, allosteric modulation, mechanisms of gating and permeation, roles in normal physiological function, as well as the potential therapeutic use of pharmacological agents acting at glutamate receptors.

/pdf/glutamate-receptor-ion-channels-structure-regulation-and-148yts0p6h.pdf

Glutamate Receptor Ion Channels: Structure, Regulation, and Function

The principles of classification and a classification of mammals. Bulletin of the AMNH ; v. 85

Glial cells were long considered end products of neural differentiation, specialized supportive cells with an origin very different from that of neurons. New studies have shown that some glial cells—radial glia (RG) in development and specific subpopulations of astrocytes in adult mammals—function as primary progenitors or neural stem cells (NSCs). This is a fundamental departure from classical views separating neuronal and glial lineages early in development. Direct visualization of the behavior of NSCs and lineage-tracing studies reveal how neuronal lineages emerge. In development and in the adult brain, many neurons and glial cells are not the direct progeny of NSCs, but instead originate from transit amplifying, or intermediate, progenitor cells (IPCs). Within NSCs and IPCs, genetic programs unfold for generating the extraordinary diversity of cell types in the central nervous system. The timing in development and location of NSCs, a property tightly linked to their neuroepithelial origin, appear to be the key determinants of the types of neurons generated. Identification of NSCs and IPCs is critical to understand brain development and adult neurogenesis and to develop new strategies for brain repair.

The glial nature of embryonic and adult neural stem cells

Precise patterns of cell division and migration are crucial to transform the neuroepithelium of the embryonic forebrain into the adult cerebral cortex. Using time-lapse imaging of clonal cells in rat cortex over several generations, we show here that neurons are generated in two proliferative zones by distinct patterns of division. Neurons arise directly from radial glial cells in the ventricular zone (VZ) and indirectly from intermediate progenitor cells in the subventricular zone (SVZ). Furthermore, newborn neurons do not migrate directly to the cortex; instead, most exhibit four distinct phases of migration, including a phase of retrograde movement toward the ventricle before migration to the cortical plate. These findings provide a comprehensive and new view of the dynamics of cortical neurogenesis and migration.

Cortical neurons arise in symmetric and asymmetric division zones and migrate through specific phases

NMDA receptors (NMDARs) are glutamate-gated ion channels and are crucial for neuronal communication. NMDARs form tetrameric complexes that consist of several homologous subunits. The subunit composition of NMDARs is plastic, resulting in a large number of receptor subtypes. As each receptor subtype has distinct biophysical, pharmacological and signalling properties, there is great interest in determining whether individual subtypes carry out specific functions in the CNS in both normal and pathological conditions. Here, we review the effects of subunit composition on NMDAR properties, synaptic plasticity and cellular mechanisms implicated in neuropsychiatric disorders. Understanding the rules and roles of NMDAR diversity could provide new therapeutic strategies against dysfunctions of glutamatergic transmission.

NMDA receptor subunit diversity: impact on receptor properties, synaptic plasticity and disease

Levo-dihydroxyphenylalanine (L-DOPA) therapy for Parkinson's disease (PD) patients improves motor symptoms, but long-term treatment induces side effects such as abnormal involuntary movements (levodopa-induced dyskinesia – LID). Increasing evidence has linked LID with neuroinflammatory reaction in the striatum involving microglia and astrocytes. The nerve/glial antigen-2 cells (NG2-glia) are recognized as a glial cell whose function in the adult brain is poorly understood. Here, we used immunohistochemistry, confocal microscopy, and western blot to characterize the cellular distribution of NG2-glia in the dorsal striatum of unilaterally 6OHDA-lesioned rats presenting LID. The effect of doxycycline on NG2-glia cells was determined. Dopamine depletion revealed a minor density increase of NG2-glia in the dorsolateral striatum and an activated phenotype. LID development promotes a decrease in NG2-glia cell density and protein level, maintaining the cell-activated feature. Doxycycline antidyskinetic therapy restores the cells to the control density profile. These results indicated the cellular distribution of NG2-glia in the striatum, but the interaction between these cells and other glial types in this model was unanswered and therefore we carried out a double labeling of NG2 and OX-42 (microglia) and GFAP (astrocyte). In LID, there was a decrease in the possible NG2 and OX-42 positive cells interaction, with no effect in the astrocytes. Doxycycline treatment restored the control characteristic. The ability of NG2-glia to regulate their dynamics in response to PD and LID is the first indication of an active link between them. The results suggest that NG2 cells may play important roles other than serving as oligodendrocyte precursor cells. Summary Statement NG2-glia alters its dynamics in response to L-DOPA-induced dyskinesia. In these animals, striatal NG2-glia density was reduced with cells presenting activated phenotype while doxycycline antidyskinetic therapy promotes a return to NG2-glia cell density and protein to a not activated state.

Laura López-Mascaraque

Papers

Dynamic Involvement of Striatal NG2-glia in L-DOPA Induced Dyskinesia in Parkinsonian Rats: Effects of Doxycycline