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S F Heinemann

Publications and source records attributed to S F Heinemann.

At least 19 recordsLinked to original sources
PubMed2007

Association of the human kainate receptor GluR7 gene (GRIK3) with recurrent major depressive disorder.

The etiology of mood disorders remains elusive, despite our increasing understanding of the neurotransmitter systems and brain regions that are involved. We performed a large family-based association study to test if the human kainate receptor GluR7 gene (GRIK3) is associated with bipolar disorder (BP) or recurrent major depressive disorder (R-MDD). One hundred fifty-three multiplex BP families from the National Institute of Mental Health (NIMH) Genetics Initiative on Bipolar Disorder were analyzed with the transmission disequilibrium test (TDT). We detected a significant linkage disequilibrium (LD) indicated by preferential maternal transmission of the GluR7 S310 allele to R-MDD patients (P = 0.012), but not to bipolar I disorder (BPI) patients (P = 1.00). We performed a second independent study by applying the TDT in 81 parent-offspring triads from families that inherit recurrent early-onset major depressive disorder (RE-MDD). The results from this second study showed only a suggestive maternal association (P = 0.068). Our findings imply that the GluR7 gene is a susceptibility factor in R-MDD and that the glutamatergic receptor system plays a critical role in the disease etiology.

Alleles↗
PubMed2006

Localization of glutamate receptors to distal dendrites depends on subunit composition and the kinesin motor protein KIF17.

Correct glutamate receptor localization in neurons is crucial for neurotransmission in the brain. Here we investigated the mechanisms underlying localization of kainate GluR5 receptors to dendrites in cultured hippocampal neurons. We find that the GluR5 distribution depends on association with GluR6 and KA2 subunits. The GluR5 subunit was expressed in distal dendrites only when GluR6 and KA2 subunits were present, whereas it was restricted to proximal dendrites in the absence of these subunits. The overlap between GluR5 distribution and the organization of microtubules in dendrites led us to examine whether KIF17, a microtubule motor protein expressed in distal dendrites, is involved in GluR5 localization to distal dendrites. We show here, for the first time that the microtubule motor protein KIF17 interacts with GluR6 and KA2 subunits and is required for GluR5 localization to distal dendrites, defining a novel mechanism that controls receptor localization in neurons.

Animals↗
PubMed2004

Role of neuronal nicotinic receptors in the effects of nicotine and ethanol on contextual fear conditioning.

Nicotine can enhance contextual learning while ethanol impairs some forms of learning. Nicotine can overcome some of the impairing effects of ethanol when the two drugs are co-administered. The specific brain nicotinic acetylcholine receptors (nAChRs) that mediate nicotine's effects on contextual learning and whether any of ethanol's actions are mediated by nAChRs are unknown. The potential roles of nAChRs in contextual and cued fear conditioning as well as the effects of nicotine, ethanol, or co-administration of nicotine and ethanol were examined in wild type and homozygous null mutant mice from alpha7, beta2, beta3, and beta4 mouse lines at 24 h after training. Nicotine was given prior to training and testing, whereas ethanol was given only before training. Nicotine enhanced contextual learning in both alpha7 wild types and mutants when mice were trained at 0.17 mA, but not 0.35 mA. Mutants lacking the alpha7 subunit were less sensitive to the memory impairing effects of ethanol trained at 0.35 mA. beta2 Null mutants receiving saline showed a small, but significant, impairment in contextual learning compared with wild type littermates when the shock stimulus was 0.35 mA. Beta2 Null mutant mice also did not respond to the cognitive enhancing effects of nicotine alone, or after ethanol administration. beta3 and beta4 null mutants did not differ from wild types either after saline or any of drug treatments. These results show that beta2-containing nAChRs, but not beta3- or beta4-containing receptors, mediate the enhancing effects of nicotine on contextual learning and confirm previous studies implicating beta2 in other forms of learning. A new role for alpha7 nAChRs in regulating sensitivity to the cognitive disrupting effects of ethanol is proposed.

Animals↗
PubMed2001

alpha10: a determinant of nicotinic cholinergic receptor function in mammalian vestibular and cochlear mechanosensory hair cells.

We report the cloning and characterization of rat alpha10, a previously unidentified member of the nicotinic acetylcholine receptor (nAChR) subunit gene family. The protein encoded by the alpha10 nAChR subunit gene is most similar to the rat alpha9 nAChR, and both alpha9 and alpha10 subunit genes are transcribed in adult rat mechanosensory hair cells. Injection of Xenopus laevis oocytes with alpha10 cRNA alone or in pairwise combinations with either alpha2-alpha6 or beta2-beta4 subunit cRNAs yielded no detectable ACh-gated currents. However, coinjection of alpha9 and alpha10 cRNAs resulted in the appearance of an unusual nAChR subtype. Compared with homomeric alpha9 channels, the alpha9alpha10 nAChR subtype displays faster and more extensive agonist-mediated desensitization, a distinct current-voltage relationship, and a biphasic response to changes in extracellular Ca(2+) ions. The pharmacological profiles of homomeric alpha9 and heteromeric alpha9alpha10 nAChRs are essentially indistinguishable and closely resemble those reported for endogenous cholinergic eceptors found in vertebrate hair cells. Our data suggest that efferent modulation of hair cell function occurs, at least in part, through heteromeric nAChRs assembled from both alpha9 and alpha10 subunits.

Amino Acid Sequence↗
PubMed2001

Assembly with the NR1 subunit is required for surface expression of NR3A-containing NMDA receptors.

Functional NMDA receptors are heteromultimeric complexes of the NR1 subunit in combination with at least one of the four NR2 subunits (A-D). Coexpression of NR3A, an additional subunit of the NMDA receptor family, modifies NMDA-mediated responses. It is unclear whether NR3A interacts directly with NR1 and/or NR2 subunits and how such association might regulate the intracellular trafficking and membrane expression of NR3A. Here we show that NR3A coassembles with NR1-1a and NR2A to form a receptor complex with distinct single-channel properties and a reduced relative calcium permeability. NR3A associates independently with both NR1-1a and NR2A in the endoplasmic reticulum, but only heteromeric complexes containing the NR1-1a NMDA receptor subunit are targeted to the plasma membrane. Homomeric NR3A complexes or complexes composed of NR2A and NR3A were not detected on the cell surface and are retained in the endoplasmic reticulum. Coexpression of NR1-1a facilitates the surface expression of NR3A-containing receptors, reduces the accumulation of NR3A subunits in the endoplasmic reticulum, and induces the appearance of intracellular clusters where both subunits are colocalized. Our data demonstrate a role for subunit oligomerization and specifically assembly with the NR1 subunit in the trafficking and plasma membrane targeting of the receptor complex.

Animals↗
PubMed2001

Kainate receptors are involved in short- and long-term plasticity at mossy fiber synapses in the hippocampus.

Kainate receptors alter the excitability of mossy fiber axons and have been reported to play a role in the induction of long-term potentiation (LTP) at mossy fiber synapses in the hippocampus. These previous studies have relied primarily on the use of compounds whose selectivity is unclear. In this report, we investigate short- and long-term facilitation of mossy fiber synaptic transmission in kainate receptor knockout mice. We find that LTP is reduced in mice lacking the GluR6, but not the GluR5, kainate receptor subunit. Additionally, short-term synaptic facilitation is impaired in GluR6 knockout mice, suggesting that kainate receptors act as presynaptic autoreceptors on mossy fiber terminals to facilitate synaptic transmission. These data demonstrate that kainate receptors containing the GluR6 subunit are important modulators of mossy fiber synaptic strength.

Animals↗
PubMed2001

The role of RNA editing of kainate receptors in synaptic plasticity and seizures.

The ionotropic glutamate receptor subunit GluR6 undergoes developmentally and regionally regulated Q/R site RNA editing that reduces the calcium permeability of GluR6-containing kainate receptors. To investigate the functional significance of this editing in vivo, we engineered mice deficient in GluR6 Q/R site editing. In these mutant mice but not in wild types, NMDA receptor-independent long-term potentiation (LTP) could be induced at the medial perforant path-dentate gyrus synapse. This indicates that kainate receptors with unedited GluR6 subunits can mediate LTP. Behavioral analyses revealed no differences from wild types, but mutant mice were more vulnerable to kainate-induced seizures. Together, these results suggest that GluR6 Q/R site RNA editing may modulate synaptic plasticity and seizure vulnerability.

Animals↗
PubMed2001

A use-dependent tyrosine dephosphorylation of NMDA receptors is independent of ion flux.

Tyrosine phosphorylation can upregulate NMDA receptor activity during pathological and physiological alterations of synaptic strength. Here we describe downregulation of recombinant NR1/2A receptors by tyrosine dephosphorylation that requires agonist binding, but is independent of ion flux. The tyrosine residues involved in this new form of NMDA receptor modulation likely form a 'ring' adjacent to the last transmembrane domain. The downregulation was due to a reduction in the number of functional channels, and was blocked by co-expressing a dominant-negative mu2-subunit of the clathrin-adaptor protein AP-2. Our results provide a mechanism by which synaptic NMDA receptors can be modulated in a use-dependent manner even when the postsynaptic membrane is not sufficiently depolarized to relieve channel block by magnesium ions.

Adaptor Protein Complex 1↗
PubMed2000

Unequal expression of allelic kainate receptor GluR7 mRNAs in human brains.

We describe here the first example of an exonic polymorphism that affects the primary structure of a human ionotropic glutamate receptor. The human kainate receptor GluR7 gene contains a thymine (T)/guanine (G) nucleotide variation that determines a serine or alanine at position 310 in the extracellular region of GluR7 receptor subunits. Our finding contrasts with a previous report that suggested that GluR7 transcripts were RNA-edited at this site. Whole-cell patch-clamp recordings did not detect differences in receptor activation and desensitization between the human GluR7 receptor isoforms expressed in HEK-293 cells. Analysis of 41 tissue samples obtained from 30 human brains revealed expression level differences between GluR7 alleles expressed in the same brain. The expression level of the allelic GluR7 mRNAs differed in 27 samples from 1.2- to 12.7-fold. Unequal expression level of allelic mRNAs is characteristic for genes that are affected by genomic imprinting or that contain mutations. Genomic imprinting in most cases is conserved between human and mice. However, we did not detect unequal expression of allelic GluR7 mRNAs in mice. Our results are important for future studies that explore a potential role or roles for GluR7 receptors in the brain and for neurological disorders.

Alleles↗
PubMed2000

Identification of the kainate receptor subunits underlying modulation of excitatory synaptic transmission in the CA3 region of the hippocampus.

To understand the physiological role of kainate receptors and their participation in seizure induction in animal models of epilepsy, it will be necessary to develop a comprehensive description of their action in the CA3 region of the hippocampus. Activation of presynaptic kainate receptors depresses excitatory synaptic transmission at mossy fiber and associational-commissural inputs to CA3 pyramidal neurons (Vignes et al., 1998; Bortolotto et al., 1999; Kamiya and Ozawa, 2000). In this study, we use gene-targeted mice lacking glutamate receptor 5 (GluR5) or GluR6 kainate receptor subunits to identify the receptor subunits that comprise the kainate receptors responsible for presynaptic modulation of CA3 transmission. We found that bath application of kainate (3 microm) profoundly reduced EPSCs at mossy fiber and collateral synapses in neurons from wild-type and GluR5(-/-) mice but had no effect on EPSCs in neurons from GluR6(-/-) mice. These results therefore contrast with previous studies that supported a role for GluR5-containing receptors at mossy fiber and associational-commissural synapses (Vignes et al., 1998; Bortolotto et al., 1999). Surprisingly, at perforant path synapses kainate receptor activation enhanced transmission; this potentiation was abolished in both GluR5 and GluR6 knock-out mice. Kainate receptors thus play multiple and complex roles to modulate excitatory synaptic transmission in the CA3 region of the hippocampus.

Animals↗
PubMed2000

NMDA-Dependent modulation of hippocampal kainate receptors by calcineurin and Ca(2+)/calmodulin-dependent protein kinase.

Neurotransmitter receptor function can be influenced by the phosphorylation state of the receptor or of associated proteins. Here we show that kainate receptors expressed in cultured hippocampal neurons can be modulated by Ca(2+)/calmodulin-dependent phosphatase (calcineurin) and Ca(2+)/calmodulin-dependent kinase (CaMK). Ca(2+) influx through NMDA receptor or voltage-sensitive calcium channels resulted in a transient depression of the kainate receptor current. This calcium-induced depression of the kainate receptor current depended on the activation of the phosphatase calcineurin. The amplitude of the kainate receptor currents returned to the baseline level in approximately 9 sec (tau = 3.6 sec), and the recovery of the current amplitude depended on CaMK activity. The effect on kainate receptor currents was dependent on the frequency of NMDA receptor activation. Although low-frequency (0.1 Hz) NMDA application induced depression followed by recovery of the kainate receptor currents, higher frequency (1 Hz) NMDA applications induced a more prolonged depression. Kainate receptors have been shown to modulate synaptic transmission by both presynaptic and postsynaptic mechanisms. Our results suggest that synaptic activity mediated by NMDA receptors, or other routes of Ca(2+) influx, may, in turn, modulate the function of kainate receptors.

Animals↗
PubMed2000

Block of the alpha9 nicotinic receptor by ototoxic aminoglycosides.

In the present study, we report that the alpha9 nicotinic acetylcholine receptor (nAChR) expressed in Xenopus laevis oocytes is reversibly blocked by aminoglycoside antibiotics. The aminoglycosides tested blocked the alpha9 nAChR in a concentration-dependent manner with the following rank order of potency: neomycin>gentamicin>streptomycin>amikacin>kanamycin. The antagonistic effect of gentamicin was not overcome by increasing the concentration of acetylcholine (ACh), indicative of a non-competitive type of block. Blockage of ACh-evoked currents by gentamicin was found to be voltage-dependent, being more potent at hyperpolarized than at depolarized holding potentials. Furthermore, gentamicin blockage was dependent upon the extracellular Ca(2+) concentration, shown by the fact that increments in extracellular Ca(2+) significantly reduced the potency of this aminoglycoside to block the alpha9 nAChR. Possible mechanisms of blockage by the aminoglycosides are discussed. The present results suggest that the initial reversible actions of aminoglycosides at the organ of Corti, such as the elimination of the olivocochlear efferent function, are due in part to the interaction with the native alpha9-containing cholinergic receptor of the outer hair cells.

Animals↗
PubMed2000

High calcium permeability and calcium block of the alpha9 nicotinic acetylcholine receptor.

At the synapse between olivocochlear efferent fibers and outer hair cells (OHCs) of the cochlea, a non-classical ionotropic cholinergic receptor allows Ca(2+) entry into the hair cell, thus activating a Ca(2+)-sensitive K(+) current which hyperpolarizes the cell's membrane. In the mammalian ear, this leads to a reduction in basilar membrane motion, altering auditory nerve fiber activity and reducing the dynamic range of hearing. The alpha9 nicotinic acetylcholine receptor (nAChR) subunit mediates synaptic transmission between cholinergic olivocochlear fibers and OHCs. Given that Ca(2+) is a key player at this inhibitory synapse, we evaluated the permeability to Ca(2+) of the recombinant alpha9 receptor expressed in Xenopus laevis oocytes and the modulation of its activity by extracellular Ca(2+). Our results show that the alpha9 receptor is highly permeable to Ca(2+) and that this cation potently blocks monovalent currents through this channel (IC(50)=100 microM, at -70 mV) in a voltage-dependent manner. At a Ca(2+) concentration similar to that found in the perilymph bathing the base of the OHCs, approximately 90% of the Na(+) current through the alpha9 receptor is blocked, suggesting that one of the main functions of this channel could be to provide a pathway for Ca(2+) influx.

Animals↗
PubMed2000

Subunit composition of kainate receptors in hippocampal interneurons.

Kainate receptor activation affects GABAergic inhibition in the hippocampus by mechanisms that are thought to involve the GluR5 subunit. We report that disruption of the GluR5 subunit gene does not cause the loss of functional KARs in CA1 interneurons, nor does it prevent kainate-induced inhibition of evoked GABAergic synaptic transmission onto CA1 pyramidal cells. However, KAR function is abolished in mice lacking both GluR5 and GluR6 subunits, indicating that KARs in CA1 stratum radiatum interneurons are heteromeric receptors composed of both subunits. In addition, we show the presence of presynaptic KARs comprising the GluR6 but not the GluR5 subunit that modulate synaptic transmission between inhibitory interneurons. The existence of two separate populations of KARs in hippocampal interneurons adds to the complexity of KAR localization and function.

Animals↗
PubMed2000

Regulation of GluR2 promoter activity by neurotrophic factors via a neuron-restrictive silencer element.

The AMPA glutamate receptor subunit GluR2, which plays a critical role in regulation of AMPA channel function, shows altered levels of expression in vivo after several chronic perturbations. To evaluate the possibility that transcriptional mechanisms are involved, we studied a 1254-nucleotide fragment of the 5'-promoter region of the mouse GluR2 gene in neural-derived cell lines. We focused on regulation of GluR2 promoter activity by two neurotrophic factors, which are known to be altered in vivo in some of the same systems that show GluR2 regulation. Glial-cell line derived neurotrophic factor (GDNF) and brain-derived neurotrophic factor (BDNF) both induced GluR2 promoter activity. This was associated with increased expression of endogenous GluR2 immunoreactivity in the cells as measured by Western blotting. The effect of GDNF and BDNF appeared to be mediated via a NRSE (neuron-restrictive silencer element) present within the GluR2 promoter. The response to these neurotrophic factors was lost upon mutating or deleting this site, but not several other putative response elements present within the promoter. Moreover, overexpression of REST (restrictive element silencer transcription factor; also referred to as NRSF or neuron restrictive silencer factor), which is known to act on NRSEs in other genes to repress gene expression, blocked the ability of GDNF to induce GluR2 promoter activity. However, GDNF did not alter endogenous levels of REST in the cells. Together, these findings suggest that GluR2 expression can be regulated by neurotrophic factors via an apparently novel mechanism involving the NRSE present within the GluR2 gene promoter.

Animals↗
PubMed1999

LFG: an anti-apoptotic gene that provides protection from Fas-mediated cell death.

Programmed cell death regulates a number of biological phenomena, and the apoptotic signal must itself be tightly controlled to avoid inappropriate cell death. We established a genetic screen to search for molecules that inhibit the apoptotic signal from the Fas receptor. Here we report the isolation of a gene, LFG, that protects cells uniquely from Fas but not from the mechanistically related tumor necrosis factor alpha death signal. LFG is widely distributed, but remarkably is highly expressed in the hippocampus. LFG can bind to the Fas receptor, but does not regulate Fas expression or interfere with binding of an agonist antibody. Furthermore LFG does not inhibit binding of FADD to Fas.

Amino Acid Sequence↗
PubMed1999

Generation and analysis of GluR5(Q636R) kainate receptor mutant mice.

The physiological significance of RNA editing of transcripts that code for kainate-preferring glutamate receptor subunits is unknown, despite the fact that the functional consequences of this molecular modification have been well characterized in cloned receptor subunits. RNA editing of the codon that encodes the glutamine/arginine (Q/R) site in the second membrane domain (MD2) of glutamate receptor 5 (GluR5) and GluR6 kainate receptor subunits produces receptors with reduced calcium permeabilities and single-channel conductances. Approximately 50% of the GluR5 subunit transcripts from adult rat brain are edited at the Q/R site in MD2. To address the role of glutamate receptor mRNA editing in the brain, we have made two strains of mice with mutations at amino acid 636, the Q/R-editing site in GluR5, using embryonic stem cell-mediated transgenesis. GluR5(RloxP/RloxP) mice encode an arginine at the Q/R site of the GluR5 subunit, whereas GluR5(wt(loxP)/wt(loxP)) mice encode a glutamine at this site, similar to wild-type mice. Mutant animals do not exhibit developmental abnormalities, nor do they show deficits in the behavioral paradigms tested in this study. Kainate receptor current densities were reduced by a factor of six in acutely isolated sensory neurons of dorsal root ganglia from GluR5(RloxP/RloxP) mice compared with neurons from wild-type mice. However, the editing mutant mice did not exhibit altered responses to thermal and chemical pain stimuli. Our investigations with the GluR5-editing mutant mice have therefore defined a set of physiological processes in which editing of the GluR5 subunit is unlikely to play an important role.

Animals↗