PubMed · 4101801
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G Enăchescu, C David. 1971. [Aging and immunological processes].. https://pubmed.ncbi.nlm.nih.gov/4101801/
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Metabotropic glutamate receptors (mGluRs) couple to heterotrimeric G-proteins and regulate cell excitability and synaptic transmission in the CNS. Considerable effort has been focused on understanding the cellular and biochemical mechanisms that underlie regulation of signaling by G-proteins and their linked receptors, including the mGluRs. Recent findings demonstrate that regulators of G-protein signaling (RGS) proteins act as effector antagonists and GTPase-activating proteins for Galpha subunits to inhibit cellular responses by G-protein-coupled receptors. RGS4 blocks Gq activation of phospholipase Cbeta and is expressed broadly in rat brain. The group I mGluRs (mGluRs 1 and 5) couple to Gq pathways to regulate several effectors in the CNS. We examined the capacity of RGS4 to regulate group I mGluR responses. In Xenopus oocytes, purified RGS4 virtually abolishes the mGluR1a- and mGluR5a-mediated but not the inositol trisphospate-mediated activation of a calcium-dependent chloride current. Additionally, RGS4 markedly attenuates the mGluR5-mediated inhibition of potassium currents in hippocampal CA1 neurons. This inhibition is dose-dependent and occurs at concentrations that are virtually identical to those required for inhibition of phospholipase C activity in NG108-15 membranes and reconstituted systems using purified proteins. These findings demonstrate that RGS4 can modulate mGluR responses in neurons, and they highlight a previously unknown mechanism for regulation of G-protein-coupled receptor signaling in the CNS.
New neurons continue to be born in the ventricular zone (VZ) of the lateral ventricles in the brain of adult birds. On the basis of serial section reconstruction and electron microscopy, we determined that the VZ of the adult canary brain is composed of three main cell types (A, B, and E). Type A cells were never found in contact with the ventricle and had microtubule-rich processes typical of young migrating neurons. Type B cells were organized as a pseudostratified epithelium, all contacted the ventricle, and most had a characteristic single cilium. Type E cells, also in contact with ventricle, were ultrastructurally similar to the mammalian multiciliated ependymal cells. After six injections of [3H]-thymidine (1 every 12 hr), Types A and B cells were found labeled. Type E cells were never [3H]-thymidine labeled. One to two hours after a single injection of [3H]-thymidine, all labeled cells corresponded to Type B cells. At survivals of 5, 24, and 74 hr after [3H]-thymidine injection, the proportion of labeled Type B cells decreased and that of Type A cells increased, indicating that Type B cells were the primary precursors. Most [3H]-labeled nuclei at 1-2 hr after [3H]-thymidine injection were separated from the ventricular cavity, but most of the mitotic cells were adjacent to the ventricle. This observation and measurements of the distance between labeled nuclei and the ventricular surface at 1, 5, 7, and 11 hr after [3H]-thymidine injection indicate that Type B cell nuclei move toward the ventricle to divide. This work reveals the architecture of the VZ in an adult vertebrate brain, identifies the primary precursor of new neurons, and describes nuclear translocation of these precursors during the cell cycle.