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D J Linden

Publications and source records attributed to D J Linden.

At least 19 recordsLinked to original sources
PubMed1998

Impaired cerebellar long-term potentiation in type I adenylyl cyclase mutant mice.

Activation of adenylyl cyclase and the consequent production of cAMP is a process that has been shown to be central to invertebrate model systems of information storage. In the vertebrate brain, it has been suggested that a presynaptic cascade involving Ca influx, cAMP production, and subsequent activation of cAMP-dependent protein kinase is necessary for induction of long-term potentiation (LTP) at the cerebellar parallel fiber-Purkinje cell synapse. We have used mutant mice in which the major Ca-sensitive adenylyl cyclase isoform of cerebellar cortex (type I) is deleted to show that this results in an approximately 65% reduction in cerebellar Ca-sensitive cyclase activity and a nearly complete blockade of cerebellar LTP assessed using granule cell-Purkinje cell pairs in culture. This blockade is not accompanied by alterations in a number of basal electrophysiological parameters and may be bypassed by application of an exogenous cAMP analog, suggesting that it results specifically from deletion of the type I adenylyl cyclase.

Adenylyl Cyclases↗
PubMed1998

Expression of a protein kinase C inhibitor in Purkinje cells blocks cerebellar LTD and adaptation of the vestibulo-ocular reflex.

Cerebellar long-term depression (LTD) is a model system for neuronal information storage that has an absolute requirement for activation of protein kinase C (PKC). It has been claimed to underlie several forms of cerebellar motor learning. Previous studies using various knockout mice (mGluR1, GluRdelta2, glial fibrillary acidic protein) have supported this claim; however, this work has suffered from the limitations that the knockout technique lacks anatomical specificity and that functional compensation can occur via similar gene family members. To overcome these limitations, a transgenic mouse (called L7-PKCI) has been produced in which the pseudosubstrate PKC inhibitor, PKC[19-31], was selectively expressed in Purkinje cells under the control of the pcp-2(L7) gene promoter. Cultured Purkinje cells prepared from heterozygous or homozygous L7-PKCI embryos showed a complete blockade of LTD induction. In addition, the compensatory eye movements of L7-PKCI mice were recorded during vestibular and visual stimulation. Whereas the absolute gain, phase, and latency values of the vestibulo-ocular reflex and optokinetic reflex of the L7-PKCI mice were normal, their ability to adapt their vestibulo-ocular reflex gain during visuo-vestibular training was absent. These data strongly support the hypothesis that activation of PKC in the Purkinje cell is necessary for cerebellar LTD induction, and that cerebellar LTD is required for a particular form of motor learning, adaptation of the vestibulo-ocular reflex.

Animals↗
PubMed1998

Synaptically evoked glutamate transport currents may be used to detect the expression of long-term potentiation in cerebellar culture.

Cerebellar long-term potentiation (LTP) is a use-dependent increase in the strength of the granule cell-Purkinje neuron synapse that occurs after brief stimulation of granule cell axons at 2-8 Hz. Previous work has shown that cerebellar LTP also may be seen when synaptic currents are evoked in granule cell-glial cell pairs in culture. This finding suggests a model in which cerebellar LTP is expressed presynaptically and therefore may be detected by either neuronal or glial postsynaptic cells. However, synaptic currents evoked in both granule cell-glial cell pairs and granule cell-Purkinje neuron pairs in culture are mediated primarily by alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate receptors, raising the possibility that cerebellar LTP might be expressed postsynaptically in both glial cells and Purkinje neurons in a similar manner. To address this question, glutamate transport currents were recorded in granule cell-glial cell pairs in culture by pharmacological isolation. These currents were increased by substitution of internal Cl with NO3 and were blocked by -pyrrolidine-2,4-dicarboxylate, both characteristics of the major cloned Bergmann glial cell glutamate transporter, EAAT1. After acquisition of baseline responses, LTP of isolated transport current was evoked by stimulation at 4 Hz (100 pulses) and could be blocked by removal of external Ca during this stimulation. The expression of LTP was associated with a decrease in the rate of synaptic failures and a decrease in the degree of paired-pulse facilitation. These findings, when taken together with the previous observation that both Purkinje neuron and glial AMPA/kainate responses can be used to detect cerebellar LTP, strongly suggest that the expression of cerebellar LTP is, at least in part, presynaptic. This strategy should also be useful in illuminating the locus of expression of other model systems of information storage such as hippocampal LTP/long-term depression.

ATP-Binding Cassette Transporters↗
PubMed1998

Synaptic transmission and hippocampal long-term potentiation in olfactory cyclic nucleotide-gated channel type 1 null mouse.

Field potential recording was used to investigate properties of synaptic transmission and long-term potentiation (LTP) at Schaffer collateral-CA1 synapses in both hippocampal slices of mutant mice in which the alpha-subunit of the olfactory cyclic nucleotide-gated channel (alpha3/OCNC)1 was rendered null and also in slices prepared from their wild-type (Wt) littermates. Several measures of basal synaptic transmission were unaltered in the OCNC1 knockout (KO), including maximum field excitatory postsynaptic potential (fEPSP) slope, maximum fEPSP and fiber volley amplitude, and the function relating fiber volley amplitude to fEPSP slope and paired-pulse facilitation. When a high-frequency stimulation protocol was used to induce LTP, similar responses were seen in both groups [KO: 1 min, 299 +/- 50% (mean +/- SE), 60 min, 123 +/- 10%; Wt: 1 min, 287 +/- 63%; 60 min, 132 +/- 19%). However, on theta-burst stimulation, the initial amplitude of LTP was smaller (1 min after induction, 147 +/- 16% of baseline) and the response decayed faster in the OCNC1 KO (60 min, 127 +/- 18%) than in Wt (1 min, 200 +/- 14%; 60 min, 169 +/- 19%). Analysis of waveforms evoked by LTP-inducing tetanic stimuli revealed a similar difference between groups. The development of potentiation throughout the tetanic stimulus was similar in OCNC1 KO and Wt mice when high-frequency stimulation was used, but OCNC1 KO mice showed a significant decrease when compared with Wt mice receiving theta-burst stimulation. These results suggest that activation of cyclic nucleotide-gated channels may contribute to the induction of LTP by weaker, more physiological stimuli, possibly via Ca2+ influx.

Animals↗
PubMed1997

Neurodegeneration in Lurcher mice caused by mutation in delta2 glutamate receptor gene.

Lurcher (Lc) is a spontaneous, semidominant mouse neurological mutation. Heterozygous Lurcher mice (Lc/+) display ataxia as a result of a selective, cell-autonomous and apoptotic death of cerebellar Purkinje cells during postnatal development. Homozygous Lurcher mice (Lc/Lc) die shortly after birth because of a massive loss of mid- and hindbrain neurons during late embryogenesis. We have used positional cloning to identify the mutations responsible for neurodegeneration in two independent Lc alleles as G-to-A transitions that change a highly conserved alanine to a threonine residue in transmembrane domain III of the mouse delta2 glutamate receptor gene (GluR delta2). Lc/+ Purkinje cells have a very high membrane conductance and a depolarized resting potential, indicating the presence of a large, constitutive inward current. Expression of the mutant GluR delta2(Lc) protein in Xenopus oocytes confirmed these results, demonstrating that Lc is inherited as a neurodegenerative disorder resulting from a gain-of-function mutation in a glutamate receptor gene. Thus the activation of apoptotic neuronal death in Lurcher mice may provide a physiologically relevant model for excitotoxic cell death.

Amino Acid Sequence↗
PubMed1997

Long-term potentiation of glial synaptic currents in cerebellar culture.

Glial cells in the brain express neurotransmitter receptors and can respond appropriately to application of exogenous neurotransmitters such as glutamate. However, activation of receptors by endogenous, synaptically released transmitter has been difficult to demonstrate directly. Using cell-pair recording in cerebellar cultures from embryonic mouse, it is shown that activation of a cerebellar granule neuron can give rise to a rapid inward current in an adjacent glial cell. This current is mediated by activation of Ca2+-permeable AMPA/kainate receptors and is largely independent of glutamate reuptake or gap junctional coupling. Furthermore, prolonged stimulation of the granule neuron at 4 Hz can give rise to long-term potentiation (LTP) of the glial synaptic current that has similar properties to LTP of granule neuron-Purkinje neuron synaptic transmission--its induction is independent of postsynaptic depolarization, postsynaptic Ca2+ influx, or glutamate receptor activation but requires presynaptic Ca2+ influx. These findings suggest a model in which cerebellar LTP is both induced and expressed presynaptically and therefore may be detected by either neuronal or glial postsynaptic cells.

Animals↗
PubMed1996

Reduced nicotinamide adenine dinucleotide-selective stimulation of inositol 1,4,5-trisphosphate receptors mediates hypoxic mobilization of calcium.

To evaluate the relationship of inositol 1,4,5-trisphosphate (IP3) receptor-mediated signal transduction and cellular energy dynamics, we have characterized effects of nucleotides on IP3 receptor (IP3R)-mediated calcium (Ca2+) flux in purified IP3 receptors reconstituted in lipid vesicles (IP3RV) and examined hypoxia-induced augmentation of intracellular Ca2+ in intact cells. Reduced nicotinamide adenine dinucleotide (NADH) increases IP3-mediated Ca2+ flux in IP3RV. This effect is highly specific for NADH. Hypoxia elicited by brief exposure of nerve growth factor-differentiated PC12 cells or cerebellar Purkinje cells to cyanide elicits rapid increased in internal [Ca2+], which derives from IP3-sensitive stores. Blockade of this effect by 2-deoxyglucose and inhibition of glyceraldehyde-3-phosphate dehydrogenase implicates enhanced glycolytic production of NADH in the Ca2+ stimulation. Internal [Ca2+] is markedly and specifically increased by direct intracellular injection of NADH, and this effect is blocked by heparin, further implicating IP3R stores. These findings indicate that direct regulation of IP3R by NADH is responsible for elevated cytoplasmic [Ca2+] occurring in the earliest phase of hypoxia. This link of IP3R activity with cellular energy dynamics may be relevant to both hypoxic damage and metabolic regulation of IP3 signaling processes.

Animals↗
PubMed1996

Defining a minimal computational unit for cerebellar long-term depression.

In cerebellar long-term depression (LTD), conjunctive stimulation of parallel and climbing fiber inputs to a Purkinje neuron (PN) results in a selective depression of parallel fiber-PN synaptic strength. A similar phenomenon may be induced in the cultured PN when glutamate pulses and PN depolarization, which mimic the effects of parallel and climbing fibers, respectively, are coapplied. Here, we show that LTD can be induced in two very reduced preparations of the postsynaptic neuron; an acutely dissociated preparation and a perforated outside-out macropatch of dendritic membrane. LTD in these preparations retains properties of that seen in an intact cultured PN in that it is not induced by either glutamate pulses or depolarization alone and requires calcium influx, mGluR activation, and PKC activation for induction. As both of these preparations lack dendritic spine compartments, these findings suggest that the associative nature of LTD induction does not require this level of morphological organization.

Animals↗
PubMed1996

A protein synthesis-dependent late phase of cerebellar long-term depression.

Synthesis of new protein has been shown to be required for establishment of a late phase in hippocampal long-term potentiation. Whether a similar requirement is needed to produce the late phase of long-term depression (LTD) remains to be determined. Application of transcription inhibitors or of the translation inhibitor anisomycin, immediately, but not 30 min after glutamate/depolarization conjunction, attenuated a late phase of cerebellar LTD in culture. LTD, produced in a perforated outside-out macropatch of Purkinje neuron dendrite, which lacks nuclear material, returned to baseline values with a time course paralleling that observed with protein synthesis inhibitors in intact cultured Purkinje neurons. These findings suggest that there is a distinct late phase of cerebellar LTD that is dependent upon postsynaptic protein synthesis.

Animals↗
PubMed1996

Suppression of the glutamate receptor delta 2 subunit produces a specific impairment in cerebellar long-term depression.

1. The role of the glutamate receptor subunit delta 2 in the induction of cerebellar long-term depression (LTD) was investigated by application of antisense oligonucleotides. The delta 2 subunit is selectively localized to Purkinje cells (PCs), with the highest levels being in the PC dendritic spines, where parallel fibers are received and where cerebellar LTD is expressed. 2. Immunocytochemical analysis of calbindin-positive PCs revealed that both the dendritic and somatic expression of delta 2 was reduced in antisense-but not in sense-treated cultures. An antisense oligonucleotide directed against the related subunit delta 1 did not affect the expression of delta 2 in PCs. 3. Cerebellar LTD may be reliably induced in a preparation of cultured embryonic cerebellar neurons from the mouse when parallel and climbing fiber stimulation are replaced by brief glutamate pulses and strong, direct depolarization of the PC, respectively. Application of an antisense oligonucleotide directed against delta 2 completely blocked the induction of LTD produced by glutamate/ depolarization conjunctive stimulation. A delta 2 sense oligonucleotide or an antisense oligonucleotide directed against the related delta 1 subunit had no effect. 4. The effect of the delta 2 antisense oligonucleotide was not related to attenuation of calcium influx via voltage-gated channels or calcium mobilization via metabotropic glutamate receptors, as assessed with fura-2 microfluorimetry. Current flow through alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-receptor-associated ion channels also appeared unaltered. All three of these processes have previously been shown to be required for cerebellar LTD induction. The observation that delta 2 is involved in a metabotropic-glutamate-receptor-independent signaling pathway that is required for LTD induction supports the view that delta 2 participates in the formation of a novel postsynaptic receptor complex.

Animals↗
PubMed1995

Phospholipase A2 controls the induction of short-term versus long-term depression in the cerebellar Purkinje neuron in culture.

Cerebellar long-term depression (LTD) may be reliably induced in the cultured Purkinje neuron when glutamate pulses and Purkinje neuron depolarization are applied together 6 times. When the number of these conjunctive stimuli was reduced to 2, a short-term depression (STD) lasting 20-40 min was induced in 4/12 cells. The enzyme phospholipase A2 cleaves membrane phospholipids causing liberation of free unsaturated fatty acids, which in turn synergistically activate protein kinase C when present with diacylglycerol and Ca. Application of free unsaturated fatty acids with 2 conjunctive stimuli resulted in an apparent conversion of STD cases to LTD. Application of phospholipase A2 inhibitors during 6 conjunctions converted LTD to STD. These findings suggest a model in which liberation of unsaturated fatty acids by phospholipase A2 contributes to a synergistic activation of protein kinase C, the full activation of which results in LTD induction, and the partial activation of which results in STD induction.

Animals↗
PubMed1995

An evaluation of the nitric oxide/cGMP/cGMP-dependent protein kinase cascade in the induction of cerebellar long-term depression in culture.

Cerebellar long-term depression (LTD) is a model system of information storage in which a persistent attenuation of the parallel fiber-Purkinje neuron (PN) synapse is induced by conjunctive stimulation of parallel fiber and climbing fiber inputs at low frequency. As some studies have suggested that release of the gaseous second messenger, nitric oxide (NO), in the molecular layer and the consequent activation of soluble guanylate cyclase and cGMP-dependent protein kinase (PKG) in the PN, is necessary for LTD induction, we have further examined this hypothesis using a cell culture protocol. In cerebellar cultures made from transgenic mice in which the gene for neuronal nitric oxide synthase (nNOS) has been rendered null, LTD induced by glutamate/depolarization conjunctive stimulation was indistinguishable from that in cultures from wild-type mice in terms of amplitude, rate of onset, and duration. Bath application of cGMP analogs produced a large (80%), transient attenuation of glutamate-gated inward currents. However, application of an activator of soluble guanylate cyclase or an inhibitor of type V cGMP-phosphodiesterase did not mimic the effect of cGMP analogs, and inclusion of cGMP analogs in the patch pipette did not give rise to a slowly developing attenuation, suggesting that these compounds exert their effects at the cell surface. Free Ca was measured in the distal dendritic arbor of single PNs by fura-2 microfluorimetry.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Diphosphate Ribose↗
PubMed1994

Trans-ACPD, a metabotropic receptor agonist, produces calcium mobilization and an inward current in cultured cerebellar Purkinje neurons.

1. 1-aminocyclopentane-trans-1,3-dicarboxylic acid (t-ACPD), a racemic mixture of 1-aminocyclopentane-1S,3R-dicarboxylic acid and 1-aminocyclopentane-1R,3S-dicarboxylic acid, a selective agonist of the metabotropic glutamate receptor, was applied to mouse Purkinje neurons (PNs) in culture. Measurements of free intracellular Ca2+ were made using fura-2 microfluorimetric imaging and of membrane current using perforated-patch voltage-clamp recording in separate experiments. 2. Brief pulses of t-ACPD (< or = 100 microM, 1-5 s) consistently produced a large (200-600 nM) increase in dendritic Ca2+ that was sometimes followed by a somatic increase. The dendrites typically returned to basal Ca2+ levels within 10-30 s. 3. Ca2+ increases produced by t-ACPD were measured in Ca(2+)-free external saline [0.5 mM ethylene glycol-bis(beta-amino-ethyl ether)-N,N,N',N'-tetraacetic acid (EGTA)], suggesting that they result from intracellular mobilization rather than influx. In addition, Ca2+ increases were not attenuated by a mixture of DL-AP5 and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) [antagonists of N-methyl-D-aspartate (NMDA) and AMPA/kainate receptors, respectively], but were almost entirely eliminated by L-AP3 (100 microM), a putative metabotropic receptor antagonist or by preincubation of the cultures in pertussis toxin. 4. Brief pulses of t-ACPD (10 microM) produced a small inward current that was associated with an increase in membrane conductance. This current was reversibly blocked by L-AP3 but not by treatments that attenuate some voltage-gated K+ currents. Thus this current is unlikely to underlie the depolarization that is produced by metabotropic agonists in hippocampal pyramidal cells by K(+)-channel closure. 5. The t-ACPD induced inward current was attenuated by substitution of external Na+ with Li+ or choline, or by application of the membrane-permeable Ca2+ chelator, bis-(2-aminophenoxy)-N,N,N',N'- tetraacetic acid (BAPTA)/AM. One mechanism that could mediate this current is electrogenic Nao/Cai exchange, triggered by Ca2+ mobilization.

Animals↗
PubMed1993

Induction of cerebellar long-term depression in culture requires postsynaptic action of sodium ions.

Cerebellar long-term depression (LTD) is a persistent attenuation of the parallel fiber-Purkinje neuron (PF-PN) synapse induced by conjunctive stimulation of PF and climbing fiber (CF) inputs. A similar phenomenon is seen in the voltage-clamped PN in tissue culture when iontophoretic quisqualate application and PN depolarization are substituted for PF and CF stimulation, respectively. In this model, LTD induction requires activation of both AMPA and metabotropic receptors, together with PN depolarization. We have sought to determine the role of the AMPA receptor in LTD induction. The AMPA receptor does not appear to exert its effect by directly gating Ca2+ influx. Replacement of external Na+ during quisqualate/depolarization conjunction with permeant ions caused a blockade of LTD induction, suggesting that Na+ influx through the AMPA-associated channel is necessary for this process. Similarly, pairing quisqualate pulses with depolarizing steps near ENa also failed to induce LTD. The present results indicate that postsynaptic Na+ influx is necessary for LTD induction. While a portion of the relevant Na+ influx is provided by voltage-gated channels, the AMPA-associated ion channel is most important in this regard.

Animals↗
PubMed1993

Cellular mechanisms of long-term depression in the cerebellum.

Cerebellar long-term depression is a persistent, input-specific attenuation of the parallel fiber-Purkinje neuron synapse induced by co-activation of parallel fibers and climbing fibers. This phenomenon endows the Purkinje neuron with a powerful associative computational ability. Recent investigations have provided strong evidence that two mechanisms, Ca2+ influx via voltage-gated channels, and stimulation of protein kinase C via metabotropic receptor activation, are required for induction of long-term depression. In addition, two other mechanisms, Na+ influx via AMPA receptors, and stimulation of a nitric oxide/cGMP cascade may also be involved in this process.

Animals↗
PubMed1993

Protoporphyrins modulate voltage-gated Ca current in AtT-20 pituitary cells.

1. Zinc-protoporphyrin-IX (ZnPP-IX) is an inhibitor of the enzyme heme-oxygenase-2 (HO-2) and consequently has been used to examine the role of carbon monoxide production in neural tissues. We have measured voltage-gated Ca current in AtT-20 pituitary cells using the whole-cell patch-clamp technique and have assessed the effects of extracellularly applied ZnPP-IX and related compounds. 2. Ca currents evoked by depolarizing steps from a holding potential of -90 mV were of the high-threshold, slowly inactivating type. Fifty-six percent of this current was blocked by 10 microM nifedipine and 16% by 3 microM omega-conotoxin with the remainder resistant to both drugs in combination, suggesting that the total Ca current was a mixture of L, N, and possibly P-type conductances. 3. Bath application of ZnPP-IX resulted in an irreversible, dose-dependent attenuation of Ca current. Five micromolar ZnPP-IX produced a 62% reduction of peak current amplitude with no shift in the current-voltage relation, 0.5 microM produced a 19% reduction, and 0.05 microM produced a variable response, either a small transient attenuation or potentiation. 4. The attenuation of Ca current by 5 microM ZnPP-IX could be nearly completely blocked by co-application of superoxide dismutase in the bath (90 U/ml) but not by addition of an inhibitor of cGMP-dependent protein kinase to the internal saline (KT5823, 1 microM). 5. Other inhibitors of heme-oxygenase with similar potency such as tin-protoporphyrin-IX (Sn-PP-IX) and Zn-deuteroporphyrin-bis-glycol (ZnBG) did not attenuate Ca current when applied at 5microM.(ABSTRACT TRUNCATED AT 400 WORDS)

Calcium↗