Biomedical subjects

C D Blackstone

Publications and source records attributed to C D Blackstone.

At least 19 recordsLinked to original sources

PubMed1998

AMPA receptor protein in developing rat brain: glutamate receptor-1 expression and localization change at regional, cellular, and subcellular levels with maturation.

We tested the hypothesis that the regional, cellular, and synaptic localizations of the glutamate receptor 1 (GluR 1) subunit of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptor are regulated developmentally in rat brain. By immunoblotting, GluR1 was first detected in whole brain at embryonic day E15.5, and levels increased progressively during late embryonic (E20) and early postnatal (P2-P11) days. Regionally, GluR1 increased in cerebral cortex but decreased in striatum with postnatal maturation. These changes occurred in the presence of increased presynaptic maturation, as determined by synaptophysin detection. By immunocytochemistry, distinct cellular populations showed different temporal profiles of GluR1 expression during postnatal maturation. The neocortex and hippocampus showed a progressive maturation-related enrichment of GluR1, whereas the striatum showed a gradual reduction in GluR1 during maturation. In cerebellum, GluR1 protein was expressed transiently at restricted times postnatally by granule cells (P0-P11) and Purkinje cells (P13-P19), but by P21 and thereafter these neurons had sparse GluR1 immunoreactivity. By immunoelectron microscopy. GluR1 was found in neurites, specifically in both dendritic and axon terminal components of developing synapses. GluR1 was clustered at the plasma membrane of apparent growth cone appositions, neuronal cell bodies, and dendrites of developing neurons. The presence of GluR1 at presynaptic sites dissipated with synaptic maturation, as GluR1 became confined to the somatodendritic compartment as maturation progressed. We conclude that the regional expression as well as the cellular and synaptic localizations of the GluR1 are developmentally regulated and are different in immature and mature brain. Differences in glutamate receptor expression and synaptic localization in immature and mature brain may be relevant to the phenomenon that the perinatal and adult brain differ in their regional vulnerability to hypoxia-ischemia and excitotoxicity.

Aging↗

PubMed1996

Immunocytochemical localization of the mGluR1 alpha metabotropic glutamate receptor in the dorsal cochlear nucleus.

We demonstrate that the metabotropic glutamate receptor mGluR1 alpha is enriched in two interneuron cell populations in the dorsal division of the cochlear nucleus. Electron microscopic analysis confirms that mGluR1 alpha immunoreactivity is concentrated in the dendritic spines of cartwheel cells and in dendrites of the recently described unipolar brush cells. The cartwheel cells, which have many similarities to the Purkinje cells of the cerebellum, participate in a local neuronal circuit that modulates the output of the dorsal cochlear nucleus. Immunostained unipolar brush cells were observed in granule cell regions of the cochlear nucleus and the vestibulocerebellum. The presence of analogous cell types with similar patterns of immunolabeling in the cerebellum and in the dorsal cochlear nucleus suggests that a shared but as yet unknown mode of processing may occur in both structures.

Animals↗

PubMed1995

Non-NMDA glutamate receptors are present throughout the primate hypothalamus.

To determine the distributions of glutamate receptors throughout the macaque hypothalamus, we utilized highly specific antipeptide antibodies to visualize alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptor subunits (GluR1, GluR2 and GluR3 [designated as GluR2/3], and GluR4); kainate receptor subunits (GluR6 and GluR7, [designated as GluR6/7]), and a metabotropic receptor (mGluR1 alpha). The results indicate that these glutamate receptors are distributed differentially throughout the monkey hypothalamus. alpha-Amino-3-hydroxy-5-methyl-4-isoxazole propionate receptors are the dominant non-N-methyl-D-aspartate glutamate receptors within the monkey hypothalamus, and the GluR2 subunit is most abundant. GluR1-immunoreactive neurons and neuropil are observed predominantly in the tuberal and mammillary nuclei. GluR2/3-immunoreactive neurons and neuropil have a broader distribution within preoptic, anterior, tuberal, and caudal regions. Separate (but partially overlapping) distributions of GluR1- and GluR2/3-immunoreactive neurons were found, suggesting that the GluR1, GluR2, and/or GluR3 subunits may be coexpressed in subsets of hypothalamic neurons. In contrast, GluR4 immunoreactivity was expressed minimally within monkey hypothalamus. GluR6/7 immunoreactivity was enriched selectively within the suprachiasmatic nucleus. mGluR1 alpha immunoreactivity was present in the mammillary complex. The localization of non-N-methyl-D-aspartate glutamate receptor subunits to neurons throughout the macaque hypothalamus provides further evidence for the glutamatergic regulation of neuroendocrine, autonomic, and limbic circuits. Differential distributions of glutamate receptor subunits may increase the dynamic range of the effects of presynaptic glutamate, allowing for the regulation of several distinct functions subserved by hypothalamic neurons.

Amino Acid Sequence↗

PubMed1995

The AMPA glutamate receptor GluR3 is enriched in oxytocinergic magnocellular neurons and is localized at synapses.

The cellular localization of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate glutamate receptor, GluR3, was identified using antibodies that recognize the N-terminus of the predicted polypeptide sequence of GluR3. Regional immunoblot analysis of monkey brain homogenates identified a protein of approximately 102,000 mol. wt that was enriched in hypothalamus. Immunocytochemistry demonstrated that GluR3 was enriched within the hypothalamic magnocellular neurosecretory nuclei and axons of the hypothalamo-neurohypophysial tract in rat and monkey. GluR3 immunoreactivity co-localized to oxytocin-containing, but not vasopressin-containing, neurons of the hypothalamic paraventricular nucleus, supraoptic nucleus and accessory magnocellular nuclei. Ultrastructurally, GluR3 immunoreactivity was enriched throughout cytoplasm of the somatodendritic compartment and was associated with postsynaptic and presynaptic structures. GluR3 immunoreactivity was frequently observed to be clustered at the plasma membrane of the somatodendritic compartment, consistent with the predicted localization of a membrane-bound ion channel. Additionally, GluR3-immunoreactive axon terminals in synaptic contact with unlabeled dendrites within the retrochiasmatic area and bed nucleus of the stria terminalis were observed, providing morphological evidence for a presynaptic alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptor. By immunoblot analysis and immunocytochemistry using antibodies directed against a specific alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptor in rat and monkey brain, our findings suggest a highly selective hypothalamic distribution of the GluR3 subunit that may have functional significance in the glutamatergic regulation of oxytocinergic neurons.

Amino Acid Sequence↗

PubMed1995

Distribution of glutamate receptor subtypes in the vertebrate retina.

The distribution of glutamate receptor subunit/subtypes in the vertebrate retina was investigated by immunocytochemistry using anti-peptide antibodies against AMPA (GluR1-4), kainate (GluR6/7) and metabotropic (mGluR1 alpha) receptors. All receptor subtypes examined are present in the mammalian retina, but they are distributed differentially. GluR1 is present in the inner plexiform layer as well as amacrine and ganglion cell bodies. GluR2 is present mainly in the outer plexiform layer and bipolar cells. An anti-GluR2/3 antibody labels both plexiform layers and various cell bodies in the inner nuclear layer and the ganglion cell layer. GluR4 is present on Müller glial cells. In the goldfish retina, GluR2 immunoreactivity is prominent in the Mb type of ON-bipolar cells, including the dendrites and the large synaptic terminal. The putative dendritic localization is surprising, because no depolarizing conductance increase induced by glutamate is thought to be present in these cells. An AMPA receptor at a presynaptic terminal is also unusual, and probably provides feedback control of glutamate release. GluR6/7 is most widespread in the retina, being present in horizontal, bipolar, amacrine and ganglion cells. Ion channels composed of GluR6 are now known to be phosphorylated by protein kinase A, resulting in current potentiation. This property and our present observation together suggest that the glutamate receptors previously studied electrophysiologically by others in horizontal cells may contain GluR6. mGluR1 alpha is found mostly in the inner plexiform layer; its localization partially overlaps with that of the inositol trisphosphate receptor in the retina. Our results suggest that, in the retina, glutamate receptor subtypes may be expressed in selective cell types according to their specific functions.

Animals↗

PubMed1995

Down-regulation of AMPA receptor subunit GluR2 in amygdaloid kindling.

Alterations in glutamatergic transmission are postulated to be important in kindling and epilepsy. The levels of alpha-amino-3-hydroxy- 5-methylisoxazole-4-propionic acid (AMPA) receptor subunits (GluR1, 2, and 4) were compared in amygdala-kindled and sham-operated animals using subunit-specific antibodies and quantitative western blotting. Four limbic regions were examined: limbic forebrain, piriform cortex/amygdala, hippocampus, and entorhinal cortex. When subunit levels were examined 24 h after the last stage 5 seizure, levels of GluR2 were found to be selectively reduced in limbic forebrain (30%) and piriform cortex/amygdala (25%), with no changes in other regions examined. In addition, no changes in the other subunits were observed in any region. The decrease in GluR2 that was observed in kindled animals at 24 h was no longer present at 1 week and 1 month after the last stage 5 seizure. Because the GluR2 subunit uniquely determines the calcium permeability of these receptors and because the piriform cortex has been implicated as a source of excitatory drive for limbic seizures, reduced GluR2 expression may be important in increasing neuronal excitability in kindling-induced epilepsy, or may reflect a compensatory mechanism resulting from kindling.

Amygdala↗

PubMed1994

Selective clustering of glutamate and gamma-aminobutyric acid receptors opposite terminals releasing the corresponding neurotransmitters.

Several immunocytochemical and physiological studies have demonstrated a concentration of neurotransmitter receptors at postsynaptic sites on neurons, but an overall picture of receptor distribution has not emerged. In particular, it has not been clear whether receptor clusters are selectively localized opposite terminals that release the corresponding neurotransmitter. By using antibodies against the excitatory glutamate receptor subunit GluR1 and the inhibitory type A gamma-aminobutyric acid (GABA) receptor beta 2/3 subunits, we show that these different receptor types cluster at distinct postsynaptic sites on cultured rat hippocampal neurons. The GABAA receptor beta 2/3 subunits clustered on cell bodies and dendritic shafts opposite GABAergic terminals, whereas GluR1 clustered mainly on dendritic spines and was associated with glutamatergic synapses. Chronic blockade of evoked transmitter release did not block receptor clustering at postsynaptic sites. These results suggest that complex mechanisms involving nerve terminal-specific signals are required to allow different postsynaptic receptor types to cluster opposite only appropriate presynaptic terminals.

Action Potentials↗

PubMed1994

Localization of non-N-methyl-D-aspartate glutamate receptors in normal and Alzheimer hippocampal formation.

The hippocampi and adjacent temporal cortices of 24 human brains were examined with antibodies to the GluR1, GluR2/3, and GluR4 subunits of the D,L-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-preferring glutamate receptor. GluR1 immunoreactivity was most dense in the dentate gyrus, with lower densities in other hippocampal and cortical regions. GluR2/3 immunoreactivity was the most intense of the three antibodies, with high levels throughout most hippocampal subfields, where it was localized to cell bodies, proximal axons, and dendrites. GluR4 immunoreactivity was very sparse in all regions. In Alzheimer's disease brains, the general pattern of staining was similar to that seen in control brains. GluR1 and GluR4 immunoreactivity was seen in some but not all neuritic plaques. All three antibodies recognized some neurons undergoing neurofibrillary degeneration.

Aged↗

PubMed1994

Human GluR6 kainate receptor (GRIK2): molecular cloning, expression, polymorphism, and chromosomal assignment.

Glutamate receptors mediate the majority of excitatory neurotransmission in the brain, and molecular cloning studies have revealed several distinct families. Because neuropathological states and possibly human disorders may involve kainate-preferring glutamate receptors, we have isolated a cDNA clone for the human GluR6 kainate-preferring receptor. This clone shows a very high sequence similarity with that of the rat, except for a part of the 3' untranslated region in which there is a TAA triplet repeat. When the protein was overexpressed in human embryonic kidney 293 cells, it had a molecular weight, an antibody recognition, and a glutamate ligand-binding profile similar to those of the rat GluR6 receptor. Northern analysis showed expression in both human cerebral and cerebellar cortices. By PCR analysis of rodent-human monochromosomal cell lines, the human GluR6 could be assigned to chromosome 6. The length of the TAA triplet repeat was polymorphic in the normal population, with at least four alleles and an observed heterozygosity of about 45%. These studies should provide the basis for expression or linkage studies of the GluR6 kainate receptor in human disease or neuropathologic states.

Amino Acid Sequence↗

PubMed1994

Glutamate receptor modulation by protein phosphorylation.

Glutamate-gated ion channels mediate most excitatory synaptic transmission in the mammalian central nervous system and play major roles in synaptic plasticity, neuronal development, and in some neuropathological conditions. Recent studies have suggested that protein phosphorylation of neuronal glutamate receptors by cyclic AMP-dependent protein kinase (PKA) and protein kinase C (PKC) may regulate their function and play a role in some forms of synaptic plasticity. To test whether these protein kinase effects are due to direct phosphorylation of the receptors and to further examine the sites and mechanisms by which the receptors are modulated, we transiently expressed recombinant glutamate receptors in HEK-293 cells and studied their biochemical and biophysical properties. Our results indicate that the kainate-preferring receptor GluR6 is phosphorylated by PKA, primarily on a single serine in the proposed major intracellular loop. Moreover, using the whole cell patch clamp recording technique, we have shown that phosphorylation at this site increases the amplitude of the GluR6-mediated glutamate current without significantly altering its dose-response, current-voltage relation or desensitization kinetics. In other experiments, we have demonstrated that the NMDA receptor subunit NR1 is phosphorylated by PKC on several distinct sites, and most of these sites are located within a single alternatively spliced exon in the C-terminal domain. These findings suggest that RNA splicing can regulate NMDA receptor phosphorylation and that, contrary to the previously proposed membrane topology model, the NR1 C-terminus is intracellular. Furthermore, in HEK-293 cells co-transfected with NR2A and NR1 subunits containing the C-terminal exon with the PKC phosphorylation sites, our preliminary studies indicate that the NMDA-evoked current is potentiated by intracellular PKC. We are currently examining PKC effects on the NMDA-evoked current responses of mutant NR1 receptors that lack the C-terminal phosphorylation sites. These studies provide evidence that glutamate receptors are directly phosphorylated and functionally modulated by protein kinases. Moreover, by identifying phosphorylation sites within the receptor proteins, our results provide information about the structure and membrane topology of these receptors.

Animals↗

PubMed1993

Phosphorylation and modulation of recombinant GluR6 glutamate receptors by cAMP-dependent protein kinase.

Glutamate-gated ion channels mediate most excitatory synaptic transmission in the central nervous system and play crucial roles in synaptic plasticity, neuronal development and some neuropathological conditions. These ionotropic glutamate receptors have been classified according to their preferred agonists as NMDA (N-methyl-D-aspartate), AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate) and KA (kainate) receptors. On the basis of sequence similarity and pharmacological properties, the recently cloned glutamate receptor subunits have been assigned as components of NMDA (NMDAR1, 2A-D), AMPA (GluR1-4) and KA (GluR5-7, KA1, KA2) receptors. Protein phosphorylation of glutamate receptors by protein kinase C and cyclic AMP-dependent protein kinase (PKA) has been suggested to regulate their function, possibly playing a prominent role in certain forms of synaptic plasticity such as long-term potentiation and long-term depression. Here we report that the GluR6 glutamate receptor, transiently expressed in mammalian cells, is directly phosphorylated by PKA, and that intracellularly applied PKA increases the amplitude of the glutamate response. Site-specific mutagenesis of the serine residue (Ser 684) representing a PKA consensus site completely eliminates PKA-mediated phosphorylation of this site as well as the potentiation of the glutamate response. These results provide evidence that direct phosphorylation of glutamate receptors modulates their function.

Amino Acid Sequence↗

PubMed1993

Phosphorylation of recombinant non-NMDA glutamate receptors on serine and tyrosine residues.

Glutamate receptors are the major excitatory neurotransmitter receptors in the central nervous system. A variety of data has recently suggested that protein phosphorylation of glutamate receptors regulates their function. To examine at a molecular level the role of protein phosphorylation in the modification of glutamate receptors, we have transiently expressed the non-NMDA glutamate receptor subunit GluR1 (flop) in human embryonic kidney 293 cells. Using a polyclonal antipeptide antiserum directed specifically against GluR1, we have immunoprecipitated a 106 kDa phosphoprotein corresponding to the GluR1 subunit. Phosphoamino acid analysis and thermolytic peptide mapping demonstrate that this basal phosphorylation occurs exclusively on serine residues in two phosphopeptides. Application of activators of endogenous cAMP-dependent protein kinase or protein kinase C revealed no consistent changes in the phosphorylation of GluR1. However, co-expression of the GluR1 subunit with the well characterized protein tyrosine kinase v-src results in phosphorylation of GluR1 on tyrosine residues, in a single thermolytic phosphopeptide. These results suggest that GluR1 may be a substrate for protein serine/threonine kinases as well as protein tyrosine kinases in the central nervous system.

Cell Line↗

PubMed1993

Phosphorylation of amino acid neurotransmitter receptors in synaptic plasticity.

The precise regulation of synaptic efficacy in the mammalian central nervous system is fundamental for learning, memory, motor control and sensory processing, as well as synaptogenesis. Currently, the molecular mechanisms underlying synaptic plasticity involved in these crucial processes are topics of intense investigation. The modulation of neurotransmitter receptors has received considerable attention, since these receptors mediate signal transduction at the postsynaptic membranes of chemical synapses. Over the past several years, evidence has suggested that protein phosphorylation of neurotransmitter receptors is a common mechanism for the regulation of receptor function. In this reaction, protein kinases catalyse the transfer of a highly charged phosphate moiety from ATP to serine, threonine or tyrosine residues of a neurotransmitter receptor, thereby altering the charge and/or conformation of the receptor and regulating its function. Phosphorylation of neurotransmitter receptors is reversible, can occur rapidly, and might result in prolonged changes in receptor function. Thus, this modification might play an important role in both short- and long-term changes in synaptic transmission.

Animals↗

PubMed1993

AMPA glutamate receptor subunits are differentially distributed in rat brain.

To demonstrate the regional, cellular and subcellular distributions of non-N-methyl-D-aspartate glutamate receptors in rat brain, we generated antipeptide antibodies that recognize the C-terminal domains of individual subunits of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)-preferring glutamate receptors (i.e. GluR1, GluR4, and a region highly conserved in GluR2, GluR3 and GluR4c). On immunoblots, antibodies detect distinct proteins with mol. wts ranging from 102,000 to 108,000 in homogenates of rat brain. Immunocytochemistry shows that glutamate receptor subunits are distributed abundantly and differentially within neuronal cell bodies and processes in cerebral cortex, basal ganglia, limbic system, thalamus, cerebellum and brainstem. The precise patterns and cellular localizations of glutamate receptor subunit immunoreactivities are unique for each antibody. In neocortex and hippocampus, pyramidal neurons express GluR1 and GluR2/3/4c immunoreactivities; many non-pyramidal, calcium-binding, protein-enriched neurons in cerebral cortex are selectively immunoreactive for GluR1. In striatum, the cellular localizations of GluR1, GluR2/3/4c and GluR4 immunoreactivities are different; in this region, GluR1 co-localizes with many cholinergic neurons but is only present in a minor proportion of nicotinamide adenine dinucleotide phosphate diaphorase-positive striatal neurons. GluR1 co-localizes with most dopaminergic neurons within the substantia nigra. In several brain regions, astrocytes show GluR4 immunoreactivity. Within the cerebellar cortex, cell bodies and processes of Bergmann glia express intense GluR4 and GluR1 immunoreactivities; perikarya and dendrites of Purkinje cells show GluR2/3/4c immunoreactivity but no evidence of GluR1 or GluR4. Ultrastructurally, GluR subunit immunoreactivities are localized within cell bodies, dendrites and dendritic spines of specific subsets of neurons and, in the case of GluR1 and GluR4, in some populations of astrocytes. This investigation demonstrates that individual AMPA-preferring glutamate receptor subunits are distributed differentially in the brain and suggests that specific neurons and glial cells selectively express glutamate receptors composed of different subunit combinations. Thus, the co-expression of all AMPA receptor subunits within individual cells may not be obligatory for the functions of this glutamate receptor in vivo.

Amino Acid Sequence↗

PubMed1993

The distribution of glutamate receptors in cultured rat hippocampal neurons: postsynaptic clustering of AMPA-selective subunits.

The distribution of several glutamate receptor subunits was investigated in cultured rat hippocampal neurons by in situ hybridization and immunocytochemistry. The AMPA/kainate-selective receptors GluR1-6 exhibited two patterns of mRNA expression: most neurons expressed GluR1, R2, and R6, whereas only about 20% expressed significant levels of GluR3, R4, and R5. By immunocytochemistry, the metabotropic glutamate receptor mGluR1 alpha was detectable only in a subpopulation of GABAergic interneurons. GluR1 and GluR2/3 segregated to the somatodendritic domain within the first week in culture, even in the absence of synaptogenesis. Glutamate receptor-enriched spines developed later and were present only on presumptive pyramidal cells, not on GABAergic interneurons. Clusters of GluR1 and GluR2/3 completely colocalized and were restricted to a subset of postsynaptic sites. Thus, glutamate receptor subunits exhibit both a cell type-specific expression and a selective subcellular localization.

Animals↗

PubMed1993

The striatal mosaic in primates: striosomes and matrix are differentially enriched in ionotropic glutamate receptor subunits.

The cellular and subcellular distributions of the ionotropic alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)-preferring glutamate receptor (GluR) in monkey striatum were demonstrated immunocytochemically using anti-peptide antibodies to individual subunits of the AMPA receptor. These antibodies specifically recognize GluR1, GluR4, and an epitope common to GluR2 and GluR3 (designated as GluR2/3). On immunoblots, the antibodies detect proteins ranging from 102 to 108 kDa in total homogenates of monkey striatum, hippocampus, and cerebellum. By immunoblotting, GluR1 and GluR2/3 are considerably more abundant than GluR4 in the caudate nucleus. Within the caudate nucleus, putamen, and nucleus accumbens, numerous neuronal perikarya, dendrites, and spines show GluR1 and GluR2/3 immunoreactivities. GluR1- and GluR2/3-enriched striatal neurons have the morphology, transmitter specificity, and distribution of medium-sized (10-20 microns) spiny neurons; large (20-60 microns) round neurons exhibit GluR4 immunoreactivity. GluR1 immunoreactivity, but not GluR2/3 or GluR4 immunoreactivity, is more intense in the ventral striatum (i.e., nucleus accumbens) than in the dorsal striatum, and GluR1 is enriched within dendritic spines in the neuropil of the nucleus accumbens and striosomes in the dorsal striatum. In the caudate nucleus, these patches of dense GluR1 immunoreactivity align with regions low in calcium binding protein immunoreactivity and high in substance P immunoreactivity. Within striosomes, GluR1 immunoreactivity is more abundant than GluR2/3 immunoreactivity; GluR4 immunoreactivity is sparse in striosomes, but the matrix contains large, GluR4-positive cholinergic neurons. This study demonstrates that, within monkey striatum, subunits of ionotropic AMPA GluR have differential distributions within striosomes and matrix. Furthermore, the results suggest that neurons within striatal striosomes and matrix may express different combinations of GluR subunits, thus forming receptors with different channel properties and having consequences that may be relevant physiologically and pathophysiologically. Neurons within these two striatal compartments may have different roles in the synaptic plasticity of motor systems.

Amino Acid Sequence↗

PubMed1993

A subpopulation of cerebellar granule neurons in culture expresses a functional mGluR1 metabotropic glutamate receptor: effect of depolarizing growing conditions.

Homogeneous neuronal cultures of cerebellar granule neurons express different levels of metabotropic glutamate receptor mGluR1 mRNA depending on the concentration of KCl present during the culture period. We have studied the effect of KCl on mGluR1 expression at the single neuron level by measuring: i) the effect of mGluR agonist 1S,3R-aminocyclopentane-1,3-dicarboxylic acid, tACPD, on intracellular free calcium concentration, [Ca2+]i; ii) the immunocytochemical quantitation of mGluR1 alpha protein. tACPD-induced increases in cytoplasmic free Ca2+ were pertussis toxin-sensitive. The number of tACPD-responding and mGluR1 alpha-positive neurons was higher in cultures grown in the presence of 15 mM than 25 mM KCl, but it never exceeded 50% of the cells. The measurement of basal intracellular free Ca2+ under the respective growing condition revealed a bigger subpopulation of cells with high basal Ca2+ concentration in neurons maintained in 25 mM KCl respect to 15 mM KCl. Hence, in primary cultures of cerebellar granule neurons, depolarization (possibly via Ca(2+)-regulated mechanisms) modulates the expression of a functional mGluR1 only in a subpopulation of cells and thus may account for a functional heterogeneity of morphologically similar cells.

Animals↗

PubMed1993

Cellular localizations of AMPA glutamate receptors within the basal forebrain magnocellular complex of rat and monkey.

The cellular distributions of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors within the rodent and nonhuman primate basal forebrain magnocellular complex (BFMC) were demonstrated immunocytochemically using anti-peptide antibodies that recognize glutamate receptor (GluR) subunit proteins (i.e., GluR1, GluR4, and a conserved region of GluR2, GluR3, and GluR4c). In both species, many large GluR1-positive neuronal perikarya and aspiny dendrites are present within the medial septal nucleus, the nucleus of the diagonal band of Broca, and the nucleus basalis of Meynert. In this population of neurons in rat and monkey, GluR2/3/4c and GluR4 immunoreactivities are less abundant than GluR1 immunoreactivity. In rat, GluR1 does not colocalize with ChAT, but, within many neurons, GluR1 does colocalize with GABA, glutamic acid decarboxylase (GAD), and parvalbumin immunoreactivities. GluR1- and GABA/GAD-positive neurons intermingle extensively with ChAT-positive neurons. In monkey, however, most GluR1-immunoreactive neurons express ChAT and calbindin-D28 immunoreactivities. The results reveal that noncholinergic GABAergic neurons, within the BFMC of rat, express AMPA receptors, whereas cholinergic neurons in the BFMC of monkey express AMPA receptors. Thus, the cellular localizations of the AMPA subtype of GluR are different within the BFMC of rat and monkey, suggesting that excitatory synaptic regulation of distinct subsets of BFMC neurons may differ among species. We conclude that, in the rodent, BFMC GABAergic neurons receive glutamatergic inputs, whereas cholinergic neurons either do not receive glutamatergic synapses or utilize GluR subtypes other than AMPA receptors. In contrast, in primate, basal forebrain cholinergic neurons are innervated directly by glutamatergic afferents and utilize AMPA receptors.

Animals↗