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D G Winder

Publications and source records attributed to D G Winder.

17 recordsLinked to original sources
PubMed2001

Inducible and reversible enhancement of learning, memory, and long-term potentiation by genetic inhibition of calcineurin.

The threshold for hippocampal-dependent synaptic plasticity and memory storage is thought to be determined by the balance between protein phosphorylation and dephosphorylation mediated by the kinase PKA and the phosphatase calcineurin. To establish whether endogenous calcineurin acts as an inhibitory constraint in this balance, we examined the effect of genetically inhibiting calcineurin on plasticity and memory. Using the doxycycline-dependent rtTA system to express a calcineurin inhibitor reversibly in the mouse brain, we find that the transient reduction of calcineurin activity facilitates LTP in vitro and in vivo. This facilitation is PKA dependent and persists over several days in vivo. It is accompanied by enhanced learning and strengthened short- and long-term memory in several hippocampal-dependent spatial and nonspatial tasks. The LTP and memory improvements are reversed fully by suppression of transgene expression. These results demonstrate that endogenous calcineurin constrains LTP and memory.

Animals↗
PubMed2001

Plasticity and behavior: new genetic techniques to address multiple forms and functions.

As the best-studied form of vertebrate synaptic plasticity, NMDA-receptor dependent long-term potentiation (NMDAR-LTP) has long been considered a leading candidate for a cellular locus for some aspects of learning and memory. However, assigning a specific role for this form of plasticity in learning and memory has proven surprisingly difficult. Two issues have contributed to this difficulty. First, a large number of molecules have been shown to in some way mediate or modulate not only NMDAR-LTP but also many forms of plasticity. Indeed, it is increasingly clear that multiple induction and maintenance mechanisms for plasticity exist, often at the same synapse. Second, linking cellular events to behavioral function has been hindered by a lack of sufficiently precise tools. In this review, we will discuss some of the proposed mechanisms of induction and maintenance of changes in synaptic efficacy and their regulation in the context of an attempt to understand their roles in animal behavior. Further, we will discuss recently developed genetic techniques, specifically, inducible transgenic models, which now allow more precise manipulations in the study of the roles plasticity plays in learning and memory.

Animals↗
PubMed1999

ERK plays a regulatory role in induction of LTP by theta frequency stimulation and its modulation by beta-adrenergic receptors.

MAP kinase (ERK) translates cell surface signals into alterations in transcription. We have found that ERK also regulates hippocampal neuronal excitability during 5 Hz stimulation and thereby regulates forms of long-term potentiation (LTP) that do not require macromolecular synthesis. Moreover, ERK-mediated changes in excitability are selectively required for some forms of LTP but not others. ERK is required for the early phase of LTP elicited by brief 5 Hz stimulation, as well as for LTP elicited by more prolonged 5 Hz stimulation when paired with beta1-adrenergic receptor activation. By contrast, ERK plays no role in LTP elicited by a single 1 s 100 Hz train. Consistent with these results, we find that ERK is activated by beta-adrenergic receptors in CA1 pyramidal cell somas and dendrites.

Action Potentials↗
PubMed1998

Rolipram, a type IV-specific phosphodiesterase inhibitor, facilitates the establishment of long-lasting long-term potentiation and improves memory.

In an attempt to improve behavioral memory, we devised a strategy to amplify the signal-to-noise ratio of the cAMP pathway, which plays a central role in hippocampal synaptic plasticity and behavioral memory. Multiple high-frequency trains of electrical stimulation induce long-lasting long-term potentiation, a form of synaptic strengthening in hippocampus that is greater in both magnitude and persistence than the short-lasting long-term potentiation generated by a single tetanic train. Studies using pharmacological inhibitors and genetic manipulations have shown that this difference in response depends on the activity of cAMP-dependent protein kinase A. Genetic studies have also indicated that protein kinase A and one of its target transcription factors, cAMP response element binding protein, are important in memory in vivo. These findings suggested that amplification of signals through the cAMP pathway might lower the threshold for generating long-lasting long-term potentiation and increase behavioral memory. We therefore examined the biochemical, physiological, and behavioral effects in mice of partial inhibition of a hippocampal cAMP phosphodiesterase. Concentrations of a type IV-specific phosphodiesterase inhibitor, rolipram, which had no significant effect on basal cAMP concentration, increased the cAMP response of hippocampal slices to stimulation with forskolin and induced persistent long-term potentiation in CA1 after a single tetanic train. In both young and aged mice, rolipram treatment before training increased long- but not short-term retention in freezing to context, a hippocampus-dependent memory task.

Animals↗
PubMed1998

Genetic and pharmacological evidence for a novel, intermediate phase of long-term potentiation suppressed by calcineurin.

To investigate the role of phosphatases in synaptic plasticity using genetic approaches, we generated transgenic mice that overexpress a truncated form of calcineurin under the control of the CaMKIIalpha promoter. Mice expressing this transgene show increased calcium-dependent phosphatase activity in the hippocampus. Physiological studies of these mice and parallel pharmacological experiments in wild-type mice reveal a novel, intermediate phase of LTP (I-LTP) in the CA1 region of the hippocampus. This intermediate phase differs from E-LTP by requiring multiple trains for induction and in being dependent on PKA. It differs from L-LTP in not requiring new protein synthesis. These data suggest that calcineurin acts as an inhibitory constraint on I-LTP that is relieved by PKA. This inhibitory constraint acts as a gate to regulate the synaptic induction of L-LTP.

Action Potentials↗
PubMed1998

Inducible and reversible gene expression with the rtTA system for the study of memory.

To obtain rapidly inducible and reversible expression of transgenes in the forebrain of the mouse, we have combined the reverse tetracycline-controlled transactivator (rtTA) system with the CaMKIIalpha promoter. We show that doxycycline induces maximal gene expression in neurons of the forebrain within 6 days and that this expression can be reversed by removal of doxycycline. Using calcineurin as a test transgene, we show that doxycycline-induced expression impairs both an intermediate form of LTP (I-LTP) in the hippocampus and the storage of spatial memory. The reversibility of the rtTA system in turn allowed us to examine the effects of the transgene on memory retrieval after normal storage had occurred. This examination suggests that retrieval requires some of the same molecular components required for storage.

Animals↗
PubMed1996

Roles of metabotropic glutamate receptors in glial function and glial-neuronal communication.

The amino acid glutamate plays a key role in brain function. One of the major roles of glutamate is to mediate fast excitatory neurotransmission via activation of ionotropic glutamate receptors (iGluRs). More recently, however, it has become clear that glutamate also serves a regulatory function through activation of receptors coupled to modulation of second messenger systems [metabotropic glutamate receptors (mGluRs)]. A body of evidence suggests that mGluRs regulate neuronal function through modulation of ion channels and enzymes to modulate cellular excitability and synaptic transmission. Interestingly, it has become clear that in addition to activation of neuronal receptors, glutamate can activate both iGluRs and mGluRs on glia. A growing body of evidence suggests that the mGluRs on glia play important roles in both glial function and mediation of intercellular signaling.

Animals↗
PubMed1996

Novel glial-neuronal signalling by coactivation of metabotropic glutamate and beta-adrenergic receptors in rat hippocampus.

1. We have previously reported that activation of group II-like metabotropic glutamate receptors (mGluRs) in rat hippocampus results in a potentiation of the accumulation of cAMP elicited by activation of G-protein Gs-coupled receptors. This large increase in cAMP levels results in release of cAMP or a cAMP metabolite and depression of synaptic transmission at the Schaffer collateral-CA1 pyramidal cell synapse through activation of A1 adenosine receptors. 2. Consistent with these studies, we report that antagonists of group II mGluRs block both the potentiation of cAMP accumulation elicited by activation of mGluRs and the depression of synaptic transmission induced by coactivation of mGluRs and beta-adrenergic receptors. 3. In situ hybridization studies suggest that of the cloned group II mGluRs only mGluR-3 mRNA is present in area CA1. Interestingly, mGluR-3 appears to be present predominantly in glia in this region. Thus, we tested the hypothesis that mGluRs coupled to potentiation of cAMP accumulation were present on glia rather than neurons in area CA1. 4. The selective group II mGluR agonist 2S,1'R,2'R,3'R-2(2,3-dicarboxycyclo-propyl)glycine (DCG-IV) failed to enhance cAMP-mediated electrophysiological responses to the beta-adrenergic receptor agonist isoprenaline (Iso) in CA1 pyramidal cells, suggesting that mGluRs coupled to potentiation of cAMP accumulation may not be present in these cells. 5. Pre-incubation of hippocampal slices with either of the selective glial toxins L-alpha-aminoadipic acid (L-AA) or fluorocitrate (FC) blocked mGluR-mediated potentiation of cAMP accumulation. However, L-AA and FC had no discernible effects on viability of CA1 pyramidal cells, or cAMP-mediated electrophysiological effects in these neurons. 6. Pre-incubation of hippocampal slices with the neurotoxin kainate resulted in disruption of neuronal transmission and degeneration of neurons in area CA1, but had no effect on mGluR-mediated potentiation of cAMP accumulation. 7. Pre-incubation of hippocampal slices with the cAMP/cAMP metabolite transport blocker probenicid blocked the depression of synaptic transmission elicited by coapplication of Iso and DCG-IV, while having no significant effect on cAMP accumulation elicited by these agonists. 8. Taken together, these data suggest that mGluRs coupled to potentiation of cAMP accumulation are present on glia rather than neurons in area CA1 of hippocampus. This suggests that a novel form of glial-neuronal communication may exist, since activation of these mGluRs in concert with beta-adrenergic receptors results in depression of synaptic transmission.

Animals↗
PubMed1996

Differential involvement of group II and group III mGluRs as autoreceptors at lateral and medial perforant path synapses.

1. Previous reports have shown that group III metabotropic glutamate receptors (mGluRs) serve as autoreceptors at the lateral perforant path, but to date there has been no rigorous determination of the roles of other mGluRs as autoreceptors at this synapse. Furthermore, it is not known which of the mGluR subtypes serve as autoreceptors at the medial perforant path synapse. With the use of whole cell patch-clamp and field excitatory postsynaptic potential (fEPSP) recording techniques, we examined the groups of mGluRs that act as autoreceptors at lateral and medial perforant path synapses in adult rat hippocampal slices. 2. Consistent with previous reports, the group III mGluR agonist (D,L)-2-amino-4-phosphonobutyric acid reduced fEPSPs and excitatory postsynaptic currents (EPSCs) in the dentate gyrus. However, the group-II-selective agonist (2S,1'R,2'R,3'R)-2-(2,3-dicarboxycyclopropyl)glycine (DCG-IV) also reduced fEPSPs and EPSCs, suggesting that multiple mGluR subtypes may serve as autoreceptors at perforant path synapses. 3. Selective activation of either medial or lateral perforant pathways revealed that micromolar concentrations of (L)-2-amino-4-phosphonobutyric acid (L-AP4) reduce fEPSPs in lateral but not medial perforant path, suggesting group III involvement at the lateral perforant pathway. Conversely, DCG-IV and 2R, 4R-4-aminopyrrolidine-2,4-dicarboxylate, another group-II-selective mGluR agonist, potently reduced fEPSPs at the medial but not lateral perforant path, suggesting that a group II mGluR may act as an autoreceptor at the medial perforant path-dentate gyrus synapse. 4. Antagonist studies with group-selective antagonists such as (2S,3S,4S)-2-methyl-2-(carboxycyclpropyl)glycine (MCCG; group II) and alpha-methyl-L-AP4 (MAP4; group III) suggest differential involvement of each group at these synapses. The effect of L-AP4 at the lateral perforant path synapse was blocked by MAP-4, but not MCCG. In contrast, the effect of DCG-IV was blocked by application of MCCG, but not MAP4. 5. Previous studies suggest that the effect of L-AP4 at the lateral perforant path synapse is mediated by a presynaptic mechanism. In the present studies, we found that concentrations of DCG-IV that reduce transmission at the medial perforant path synapse reduce paired-pulse depression and do not reduce kainate-evoked currents recorded from dentate granule cells. This is consistent with the hypothesis that DCG-IV also acts by a presynaptic mechanism.

Animals↗
PubMed1995

Pharmacological differentiation of the effects of co-activation of beta-adrenergic and metabotropic glutamate receptors in rat hippocampus.

Activation of metabotropic glutamate receptors (mGluRs) can potentiate the cAMP response elicited by activation of beta-adrenergic receptors (beta ARs) in the hippocampus. We have shown that co-activation of mGluRs and beta ARs induces both an acute depression of excitatory synaptic transmission and a long-lasting excitation of CA1 pyramidal cells. However, these studies were performed using a non-selective mGluR agonist. We have now used subtype selective mGluR agonists, and report that while the acute depression of transmission exhibits a pharmacology consistent with mediation by this mGluR subtype, the lasting excitation of CA1 pyramidal cells may be mediated by an interaction between beta ARs and mGluRs that are coupled to phosphoinositide hydrolysis.

Adrenergic beta-Agonists↗
PubMed1995

Metabotropic glutamate receptor (mGluR)-mediated potentiation of cyclic AMP responses does not require phosphoinositide hydrolysis: mediation by a group II-like mGluR.

Metabotropic glutamate receptors (mGluRs) in the CNS are coupled to a variety of second messenger systems, the best characterized of which is activation of phosphoinositide hydrolysis. Recently, we found that activation of mGluRs in rat brain slices by the selective mGluR agonist 1-aminocyclopentane-1S,3R-dicarboxylic acid (1S,3R-ACPD) potentiates cyclic AMP (cAMP) responses elicited by activation of other receptors coupled to Gs. It has been suggested that mGluR-mediated potentiation of cAMP responses is secondary to activation of phosphoinositide hydrolysis. However, preliminary evidence suggests that this is not the case. Therefore, we designed a series of experiments to test more fully the hypothesis that mGluR-mediated potentiation of cAMP responses is secondary to phosphoinositide hydrolysis. Inhibitors of both protein kinase C and intracellular calcium mobilization failed to antagonize 1S,3R-ACPD-stimulated potentiation of cAMP responses. Further, coapplication of phorbol esters and 1S,3R-ACPD induced a cAMP response that was greater than additive. Finally, (RS)-3,5-dihydroxyphenylglycine, a selective agonist of mGluRs coupled to phosphoinositide hydrolysis, failed to potentiate cAMP responses, whereas (2S,1'R,2'R,3'R)-2-(2,3-dicarboxycyclopropyl)glycine, an mGluR agonist that does not activate mGluRs coupled to phosphoinositide hydrolysis, elicited a robust potentiation of cAMP responses. In total, these data strongly suggest that mGluR-mediated potentiation of cAMP responses is not secondary to activation of phosphoinositide hydrolysis and is likely mediated by a group II mGluR.

Animals↗
PubMed1994

4-Bromohomoibotenic acid selectively activates a 1-aminocyclopentane-1S,3R-dicarboxylic acid-insensitive metabotropic glutamate receptor coupled to phosphoinositide hydrolysis in rat cortical slices.

Glutamate activates a family of receptors, known as metabotropic glutamate receptors (mGluRs), that are coupled to various second messenger systems through G proteins. All mGluR subtypes characterized to date in rat brain slices are activated by the glutamate analogue 1-aminocyclopentane-1S,3R-dicarboxylic acid (1S,3R-ACPD). However, few agonists are available that selectively activate specific mGluR subtypes. We report that the glutamate analogue (R,S)-4-bromohomoibotenate (BrHI) stimulates phosphoinositide hydrolysis in rat cerebral cortical slices in a concentration-dependent manner (EC50 = 190 microM). The response to BrHI is stereoselective and is not blocked by ionotropic glutamate receptor antagonists. It is interesting that the responses to BrHI and 1S,3R-ACPD are completely additive, suggesting that these responses are mediated by different receptor subtypes. Consistent with this, the response to BrHI is insensitive to L-2-amino-3-phosphonopropionic acid (L-AP3), whereas the response to 1S,3R-ACPD is partially blocked by L-AP3. BrHI does not activate metabotropic receptors coupled to changes in cyclic AMP accumulation or activation of phospholipase D. Thus, BrHI seems to activate specifically a phosphoinositide hydrolysis-linked mGluR that is insensitive to 1S,3R-ACPD. This compound may prove useful as a tool for elucidating the roles of different mGluR subtypes in mammalian brain.

Adenylyl Cyclase Inhibitors↗
PubMed1993

Activation of metabotropic glutamate receptors increases cAMP accumulation in hippocampus by potentiating responses to endogenous adenosine.

Metabotropic glutamate receptors (mGluRs) are coupled to effector systems through GTP-binding proteins (G-proteins) and appear to mediate slow synaptic responses in the CNS. Although mGluR-mediated increases in phosphoinositide hydrolysis have been well characterized, other mechanisms for signal transduction employed by mGluRs are poorly understood. We recently reported that the selective mGluR agonist 1-aminocyclopentane-1 S,3R-dicarboxylic acid (1S,3R-ACPD) increases cAMP accumulation in rat hippocampal slices. We have now investigated the mechanisms involved in this response. A number of G-protein-linked receptors that are not directly coupled to adenylate cyclase increase cAMP accumulation by potentiating cAMP responses to other agonists. Furthermore, previous studies suggest that glutamate increases cAMP accumulation by a mechanism that is dependent upon the presence of endogenous adenosine. Therefore, we tested the hypothesis that 1S,3R-ACPD-stimulated increases in cAMP accumulation in rat hippocampal slices are dependent upon the presence of endogenous adenosine and are mediated by an mGluR that potentiates cAMP responses to other agonists. We found that adenosine deaminase abolished 1S,3R-ACPD-stimulated cAMP accumulation whereas the adenosine uptake blocker dipyridamole enhanced this response. Additionally, adenosine receptor antagonists blocked mGluR-mediated increases in cAMP accumulation with potencies that were highly correlated with their potencies at A2 adenosine receptors. Furthermore, we performed a series of studies that suggest that 1S,3R-ACPD activates an mGluR subtype that potentiates responses to agonists of other receptors that are coupled to adenylate cyclase and that 1S,3R-ACPD-stimulated increases in cAMP accumulation in hippocampal slices are mediated by potentiation of the cAMP response to low levels of endogenous adenosine that are continuously present extracellularly.

Adenosine↗
PubMed1993

Pharmacological differentiation of metabotropic glutamate receptors coupled to potentiation of cyclic adenosine monophosphate responses and phosphoinositide hydrolysis.

Activation of metabotropic glutamate receptors (mGluRs) results in multiple second messenger responses in rat hippocampal slices, including stimulation of phosphoinositide hydrolysis and potentiation of cyclic AMP responses induced by agonists of other receptors that are directly coupled to adenylate cyclase. Alpha 1 adrenergic receptors and H1-histaminergic receptors are similar to mGluRs in that agonists of these receptors also induce both phosphoinositide hydrolysis and potentiation of cyclic AMP responses to other agonists. In each of these cases, it is not clear whether activation of phosphoinositide hydrolysis and potentiation of cyclic AMP responses are mediated by the same or different receptor subtypes. In the present studies, the pharmacological profiles of mGluR-mediated potentiation of cyclic AMP responses and mGluR-mediated activation of phosphoinositide hydrolysis were compared to determine whether these responses are mediated by the same or distinct receptor subtypes. In addition, the authors determined the effect of mGluR activation on cyclic AMP responses in various regions of the rat brain and at different stages of postnatal development. It was found that the rank order of efficacies and potencies of mGluR agonists for potentiating cyclic AMP responses is distinct from the rank order of efficacies and potencies of the same compounds at stimulating phosphoinositide hydrolysis. Furthermore, L-serine-O-phosphate competitively blocked mGluR-mediated potentiation of cyclic AMP responses but had little or no effect on activation of phosphoinositide hydrolysis by the active isomer of trans-1-aminocyclopentane-1,3-dicarboxylic acid. These data are consistent with the hypothesis that these two responses are mediated by distinct mGluR subtypes.

Animals↗
PubMed1992

Activation of metabotropic glutamate receptors in the hippocampus increases cyclic AMP accumulation.

The selective metabotropic glutamate receptor agonist trans-1-aminocyclopentane-1,3-dicarboxylic acid (trans-ACPD) stimulates phosphoinositide hydrolysis and elicits several physiological responses in rat hippocampal slices. However, recent studies suggest that the physiological effects of trans-ACPD in the hippocampus are mediated by activation of a receptor that is distinct from the phosphoinositide hydrolysis-linked receptor. Previous experiments indicate that cyclic AMP mimics many of the physiological effects of trans-ACPD in hippocampal slices. Furthermore, recent cloning and biochemistry experiments indicate that multiple metabotropic glutamate receptor subtypes exist, some of which are coupled to yet unidentified effector systems. Thus, we performed a series of experiments to test the hypothesis that ACPD increases cyclic AMP levels in hippocampal slices. We report that 1S,3R- and 1S,3S-ACPD (but not 1R,3S-ACPD) induce a concentration-dependent increase in cyclic AMP accumulation in hippocampal slices. This effect was blocked by the metabotropic glutamate receptor antagonist L-2-amino-3-phosphonoproprionic acid but not by selective antagonists of ionotropic glutamate receptors. Furthermore, our results suggest that 1S,3R-ACPD-stimulated increases in cyclic AMP accumulation are not secondary to increases in cell firing or to activation of phosphoinositide hydrolysis.

Alanine↗
PubMed1992

Amygdala kindling alters protein kinase C activity in dentate gyrus.

Kindling is a use-dependent form of synaptic plasticity and a widely used model of epilepsy. Although kindling has been widely studied, the molecular mechanisms underlying induction of this phenomenon are not well understood. We determined the effect of amygdala kindling on protein kinase C (PKC) activity in various regions of rat brain. Kindling stimulation markedly elevated basal (Ca(2+)-independent) and Ca(2+)-stimulated phosphorylation of an endogenous PKC substrate (which we have termed P17) in homogenates of dentate gyrus, assayed 2 h after kindling stimulation. The increase in P17 phosphorylation appeared to be due at least in part to persistent PKC activation, as basal PKC activity assayed in vitro using an exogenous peptide substrate was increased in kindled dentate gyrus 2 h after the last kindling stimulation. A similar increase in basal PKC activity was observed in dentate gyrus 2 h after the first kindling stimulation. These results document a kindling-associated persistent PKC activation and suggest that the increased activity of PKC could play a role in the induction of the kindling effect.

Amygdala↗