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Nuclear calcium sensors reveal that repetition of trains of synaptic stimuli boosts nuclear calcium signaling in CA1 pyramidal neurons.

ABSTRACT: Nuclear calcium is a key signal in the dialogue between synapse and nucleus that controls the genomic responses required for persistent adaptations, including memory and acquired neuroprotection. The amplitude and duration of nuclear calcium transients specify activity-induced transcriptional changes. However, the precise relationship between synaptic input and nuclear calcium output is unknown. Here, we used stereotaxic delivery to the rat brain of recombinant adeno-associated viruses encoding nuclear-targeted calcium sensors to assess nuclear calcium transients in CA1 pyramidal neurons after stimulation of the Schaffer collaterals. We show that in acute hippocampal slices, a burst of synaptic activity elicits a nuclear calcium signal with a regenerative component at above-threshold stimulation intensities. Using classical stimulation paradigms (i.e., high-frequency stimulation (HFS) and ? burst stimulation (TBS)) to induce early LTP (E-LTP) and transcription-dependent late LTP (L-LTP), we found that the magnitude of nuclear calcium signals and the number of action potentials activated by synaptic stimulation trains are greatly amplified by their repetition. Nuclear calcium signals and action potential generation were reduced by blockade of either NMDA receptors or L-type voltage-gated calcium channels, but not by procedures that lead to internal calcium store depletion or by blockade of metabotropic glutamate receptors. These findings identify a repetition-induced switch in nuclear calcium signaling that correlates with the transition from E-LTP to L-LTP, and may explain why the transcription-dependent phase of L-LTP is not induced by a single HFS or TBS but requires repeated trains of activity. Recombinant, nuclear-targeted indicators may prove useful for further analysis of nuclear calcium signaling in vivo.

SUBMITTER: Bengtson CP

PROVIDER: S-EPMC3000507 | biostudies-literature | 2010 Dec

REPOSITORIES: biostudies-literature

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Nuclear calcium sensors reveal that repetition of trains of synaptic stimuli boosts nuclear calcium signaling in CA1 pyramidal neurons.

Bengtson C Peter CP Freitag H Eckehard HE Weislogel Jan-Marek JM Bading Hilmar H

Biophysical journal 20101201 12

Nuclear calcium is a key signal in the dialogue between synapse and nucleus that controls the genomic responses required for persistent adaptations, including memory and acquired neuroprotection. The amplitude and duration of nuclear calcium transients specify activity-induced transcriptional changes. However, the precise relationship between synaptic input and nuclear calcium output is unknown. Here, we used stereotaxic delivery to the rat brain of recombinant adeno-associated viruses encoding ...[more]

PMID: 21156150

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Project description:BackgroundHippocampal CA1 pyramidal neurons receive two excitatory glutamatergic synaptic inputs: their most distal dendritic regions in the stratum lacunosum-moleculare (SLM) are innervated by the perforant path (PP), originating from layer III of the entorhinal cortex, while their more proximal regions of the apical dendrites in the stratum radiatum (SR) are innervated by the Schaffer-collaterals (SC), originating from hippocampal CA3 neurons. Endocannabinoids (eCBs) are naturally occurring mediators capable of modulating both GABAergic and glutamatergic synaptic transmission and plasticity via the CB1 receptor. Previous work on eCB modulation of excitatory synapses in the CA1 region largely focuses on the SC pathway. However, little information is available on whether and how eCBs modulate glutamatergic synaptic transmission and plasticity at PP synapses.Methodology/principal findingsBy employing somatic and dendritic patch-clamp recordings, Ca(2+) uncaging, and immunostaining, we demonstrate that there are significant differences in low-frequency stimulation (LFS)- or DHPG-, an agonist of group I metabotropic glutamate receptors (mGluRs), induced long-term depression (LTD) of excitatory synaptic transmission between SC and PP synapses in the same pyramidal neurons. These differences are eliminated by pharmacological inhibition with selective CB1 receptor antagonists or genetic deletion of the CB1 receptor, indicating that these differences likely result from differential modulation via a CB1 receptor-dependent mechanism. We also revealed that depolarization-induced suppression of excitation (DSE), a form of short-term synaptic plasticity, and photolysis of caged Ca(2+)-induced suppression of Excitatory postsynaptic currents (EPSCs) were less at the PP than that at the SC. In addition, application of WIN55212 (WIN) induced a more pronounced inhibition of EPSCs at the SC when compared to that at the PP.Conclusions/significanceOur results suggest that CB1 dependent LTD and DSE are differentially expressed at the PP versus SC synapses in the same neurons, which may have an impact on synaptic scaling, integration and plasticity of hippocampal CA1 pyramidal neurons.

Project description:Local anesthetics can cause severe toxicity when absorbed systemically. Rapid intravenous administration of lipid emulsion (LE) is the standard of care for severe local anesthetic systemic toxicity which can cause cardiovascular and central nervous system (CNS) injury. The biological mechanism by which LE alleviates CNS toxicity remains unknown and understudied. Previous research has suggested that local anesthetics cause an imbalance of excitatory and inhibitory transmission in the brain. Therefore, this study aimed to observe the effect of LE on glutamate- and GABA-induced currents in CA1 pyramidal neurons after bupivacaine-induced CNS toxicity. We further characterized post-synaptic modifications in these cells to try to elucidate the mechanism by which LE mediates bupivacaine-induced CNS toxicity. Sprague-Dawley rats received intravenous bupivacaine (1 mg kg-1 min-1 ) in either normal saline or LE (or LE without bupivacaine) for 5 min. An acute brain slice preparation and a combination of whole-cell patch clamp techniques and whole-cell recordings were used to characterize action potential properties, miniature excitatory, and inhibitory post-synaptic currents, and post-synaptic modifications of excitatory and inhibitory transmission in CA1 hippocampal pyramidal neurons. The expression level of GABAA receptors were assessed with western blotting, whereas H&E and TUNEL staining were used to assess cytoarchitecture and apoptosis levels respectively. Bupivacaine treatment significantly increased the number of observed action potentials, whereas significantly decreasing rheobase, the first interspike interval (ISI), and hyperpolarization-activated cation currents (Ih) in CA1 pyramidal neurons. LE treatment significantly reduced the frequency of miniature inhibitory post-synaptic currents and enhanced GABA-induced paired pulse ratio with 50 ms interval stimulation in bupivacaine-treated rats. Regulation of GABAA levels is a promising mechanism by which LE may ameliorate CNS toxicity after systemic absorption of bupivacaine.

Dataset Information

Nuclear calcium sensors reveal that repetition of trains of synaptic stimuli boosts nuclear calcium signaling in CA1 pyramidal neurons.

Publications

Nuclear calcium sensors reveal that repetition of trains of synaptic stimuli boosts nuclear calcium signaling in CA1 pyramidal neurons.

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