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Subcellular organization of camkii in rat hippocampal pyramidal neurons.

ABSTRACT: Calcium/calmodulin-dependent protein kinase II (CaMKII) plays a key role in N-methyl-D-aspartate (NMDA) receptor-dependent long-term synaptic plasticity; its location is critical for signal transduction, and may provide clues that further elucidate its function. We therefore examined the subcellular localization of CaMKII in CA1 stratum radiatum of adult rat hippocampus, by using immuno-electron microscopy after chemical fixation. When tissue was fixed quickly, the concentration of CaMKII? (assessed by pre-embedding immunogold) was significantly higher in dendritic shafts than in spine heads. However, when tissue was fixed 5 minutes after perfusion with normal saline, the density of labeling decreased in dendritic shaft while increasing in spine heads, implying rapid translocation into the spine during brief perimortem stress. Likewise, in quickly fixed tissue, CaMKII within spine heads was found at comparable concentrations in the "proximal" half (adjacent to the spine neck) and the "distal" half (containing the postsynaptic density [PSD]), whereas after delayed fixation, label density increased in the distal side of the spine head, suggesting that CaMKII within the spine head moves toward the PSD during this interval. To estimate its distribution at the synapse in vivo, we performed postembedding immunogold staining for CaMKII in quick-fixed tissue, and found that the enzyme did not concentrate primarily within the central matrix of the PSD. Instead, labeling density peaked ?40 nm inside the postsynaptic membrane, at the cytoplasmic fringe of the PSD. Labeling within 25 nm of the postsynaptic membrane concentrated at the lateral edge of the synapse. This lateral "PSD core" pool of CaMKII may play a special role in synaptic plasticity.

SUBMITTER: Ding JD

PROVIDER: S-EPMC4409980 | biostudies-literature | 2013 Oct

REPOSITORIES: biostudies-literature

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Subcellular organization of camkii in rat hippocampal pyramidal neurons.

Ding Jin-Dong JD Kennedy Mary B MB Weinberg Richard J RJ

The Journal of comparative neurology 20131001 15

Calcium/calmodulin-dependent protein kinase II (CaMKII) plays a key role in N-methyl-D-aspartate (NMDA) receptor-dependent long-term synaptic plasticity; its location is critical for signal transduction, and may provide clues that further elucidate its function. We therefore examined the subcellular localization of CaMKII in CA1 stratum radiatum of adult rat hippocampus, by using immuno-electron microscopy after chemical fixation. When tissue was fixed quickly, the concentration of CaMKIIα (asse ...[more]

PMID: 23749614

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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:An important consequence of gliotransmission, a signaling mechanism that involves glial release of active transmitter molecules, is its manifestation as N-methyl-d-aspartate receptor (NMDAR)-dependent slow inward currents in neurons. However, the intraneuronal spatial dynamics of these events or the role of active dendrites in regulating their amplitude and spatial spread have remained unexplored. Here, we used somatic and/or dendritic recordings from rat hippocampal pyramidal neurons and demonstrate that a majority of NMDAR-dependent spontaneous slow excitatory potentials (SEP) originate at dendritic locations and are significantly attenuated through their propagation across the neuronal arbor. We substantiated the astrocytic origin of SEPs through paired neuron-astrocyte recordings, where we found that specific infusion of inositol trisphosphate (InsP3) into either distal or proximal astrocytes enhanced the amplitude and frequency of neuronal SEPs. Importantly, SEPs recorded after InsP3 infusion into distal astrocytes exhibited significantly slower kinetics compared with those recorded after proximal infusion. Furthermore, using neuron-specific infusion of pharmacological agents and morphologically realistic conductance-based computational models, we demonstrate that dendritically expressed hyperpolarization-activated cyclic-nucleotide-gated (HCN) and transient potassium channels play critical roles in regulating the strength, kinetics, and compartmentalization of neuronal SEPs. Finally, through the application of subtype-specific receptor blockers during paired neuron-astrocyte recordings, we provide evidence that GluN2B- and GluN2D-containing NMDARs predominantly mediate perisomatic and dendritic SEPs, respectively. Our results unveil an important role for active dendrites in regulating the impact of gliotransmission on neurons and suggest astrocytes as a source of dendritic plateau potentials that have been implicated in localized plasticity and place cell formation.

Dataset Information

Subcellular organization of camkii in rat hippocampal pyramidal neurons.

Publications

Subcellular organization of camkii in rat hippocampal pyramidal neurons.

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