CaMKII inhibitor 1 (CaMK2N1) mRNA is upregulated following LTP induction in hippocampal slices.

CaMK2N1 and CaMK2N2 (also known as CaMKIINα and β) are endogenous inhibitors of calcium/calmodulin-dependent kinase II (CaMKII), an enzyme critical for memory and long-term potentiation (LTP), a form of synaptic plasticity thought to underlie learning. CaMK2N1/2 mRNAs are rapidly and differentially upregulated in the hippocampus and amygdala after acquisition or retrieval of fear memory. Moreover, CaMK2N2 protein levels increase after contextual fear conditioning.

Fast Decay of CaMKII FRET Sensor Signal in Spines after LTP Induction Is Not Due to Its Dephosphorylation.

Because CaMKII is the critical Ca(2+) sensor that triggers long-term potentiation (LTP), understanding its activation and deactivation is important. A major advance has been the development of a FRET indicator of the conformational state of CaMKII called Camui. Experiments using Camui have demonstrated that the open (active) conformation increases during LTP induction and then decays in tens of seconds, with the major fast component decaying with a time-constant of ~ 6 sec (tau1).

Excitotoxic insult results in a long-lasting activation of CaMKIIα and mitochondrial damage in living hippocampal neurons.

Over-activation of excitatory NMDA receptors and the resulting Ca2+ overload is the main cause of neuronal toxicity during stroke. CaMKII becomes misregulated during such events. Biochemical studies show either a dramatic loss of CaMKII activity or its persistent autonomous activation after stroke, with both of these processes being implicated in cell toxicity.

Measuring CaMKII concentration in dendritic spines.

Here, we present a method for measuring the concentration of endogenous protein in cellular compartments. Importantly, the method is applicable to compartments such as dendritic spines with dimensions often close to the resolution limit of optical microscopy. To our knowledge, a method with such capabilities has not yet been described.

Role of the CaMKII/NMDA receptor complex in the maintenance of synaptic strength.

During long-term potentiation (LTP), synapses undergo stable changes in synaptic strength. The molecular memory processes that maintain strength have not been identified. One hypothesis is that the complex formed by the Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) and the NMDA-type glutamate receptor (NMDAR) is a molecular memory at the synapse.

CaMKII control of spine size and synaptic strength: role of phosphorylation states and nonenzymatic action.

CaMKII is an abundant synaptic protein strongly implicated in plasticity. Overexpression of autonomous (T286D) CaMKII in CA1 hippocampal cells enhances synaptic strength if T305/T306 sites are not phosphorylated, but decreases synaptic strength if they are phosphorylated. It has generally been thought that spine size and synaptic strength covary; however, the ability of CaMKII and its various phosphorylation states to control spine size has not been previously examined.

Autonomous CaMKII can promote either long-term potentiation or long-term depression, depending on the state of T305/T306 phosphorylation.

Ca(2+)/calmodulin-dependent kinase II (CaMKII) is a key mediator of long-term potentiation (LTP). Whereas acute intracellular injection of catalytically active CaMKII fragments saturates LTP (Lledo et al., 1995), an autonomously active form (T286D) of CaMKII holoenzyme expressed in transgenic mice did not saturate potentiation (Mayford et al.

Synaptic strength of individual spines correlates with bound Ca2+-calmodulin-dependent kinase II.

Both synaptic strength and spine size vary from spine to spine, but are strongly correlated. This gradation is regulated by activity and may underlie information storage. Ca2+-calmodulin-dependent kinase II (CaMKII) is critically involved in the regulation of synaptic strength and spine size.

Persistent accumulation of calcium/calmodulin-dependent protein kinase II in dendritic spines after induction of NMDA receptor-dependent chemical long-term potentiation.

Calcium/calmodulin-dependent protein kinase II (CaMKII) is a leading candidate for a synaptic memory molecule because it is persistently activated after long-term potentiation (LTP) induction and because mutations that block this persistent activity prevent LTP and learning. Previous work showed that synaptic stimulation causes a rapidly reversible translocation of CaMKII to the synaptic region. We have now measured green fluorescent protein (GFP)-CaMKIIalpha translocation into synaptic spines during NMDA receptor-dependent chemical LTP (cLTP) and find that under these conditions, translocation is persistent.

Forskolin-induced LTP in the CA1 hippocampal region is NMDA receptor dependent.

Chemically induced long-term potentiation (cLTP) could potentially work by directly stimulating the biochemical machinery that underlies synaptic plasticity, bypassing the need for synaptic activation. Previous reports suggested that agents that raise cAMP concentration might have this capability. We examined the cLTP induced in acute slices by application of Sp-cAMPS or a combination of the adenylyl cyclase activator, forskolin, and the phosphodiesterase inhibitor, rolipram.

Postsynaptic application of a cAMP analogue reverses long-term potentiation in hippocampal CA1 pyramidal neurons.

The molecular mechanisms that underlie the maintenance of long-term potentiation (LTP) remain unclear. We have examined the influence of postsynaptic cAMP-dependent processes on LTP maintenance in CA1 hippocampal cells. After LTP induction, drugs affecting cAMP-dependent processes were perfused into the cell through a patch pipette.

Pathway-specific properties of AMPA and NMDA-mediated transmission in CA1 hippocampal pyramidal cells.

CA1 pyramidal cells receive glutamatergic input from the entorhinal cortex through the perforant path (PP) and from CA3 through Schaffer collaterals (SC). The PP input terminates in the stratum lacunosum molecular approximately 300 microm from the cell body, whereas SC synapses have a more proximal location in the stratum radiatum. We compared the properties of AMPA- and NMDA-mediated transmission at these two inputs.

Is persistent activity of calcium/calmodulin-dependent kinase required for the maintenance of LTP?

Calcium/calmodulin-dependent protein kinase II (CaMKII) is concentrated in the postsynaptic density (PSD) and plays an important role in the induction of long-term potentiation (LTP). Because this kinase is persistently activated after the induction, its activity could also be important for LTP maintenance. Experimental tests of this hypothesis, however, have given conflicting results.

Inhibition of the cAMP pathway decreases early long-term potentiation at CA1 hippocampal synapses.

Long-term potentiation (LTP) has several different phases, and there is general agreement that the late phase of LTP requires the activation of adenylyl cyclase (AC) and cAMP-dependent protein kinase (PKA). In contrast, several studies indicate that the early LTP is not affected by interfering with the cAMP pathway. We have further tested the role of the cAMP pathway in early LTP using several types of inhibitors.

Requirements for LTP induction by pairing in hippocampal CA1 pyramidal cells.

The induction of long-term potentiation (LTP) in the hippocampal CA1 region requires both presynaptic activity and large postsynaptic depolarization. A standard protocol for inducing LTP using whole-cell recording is to pair low-frequency synaptic stimulation (100-200 pulses, 1-2 Hz) with a depolarizing voltage-clamp pulse (1-3 min duration). In this standard protocol, a Cs(+)-based internal solution is used to improve the fidelity of the depolarization produced by voltage-clamp.

Postsynaptic inhibitors of calcium/calmodulin-dependent protein kinase type II block induction but not maintenance of pairing-induced long-term potentiation.

The role of postsynaptic kinases in the induction and maintenance of long-term potentiation (LTP) was studied in the CA1 region of the rat hippocampal slice. A peptide inhibitor for the catalytic domain of calcium/calmodulin-dependent protein kinase type II (CaM-kinase) was applied through a perfused patch pipette. The inhibitor completely blocked both the short-term potentiation and LTP induced by a pairing protocol.

Visualizing hippocampal synaptic function by optical detection of Ca2+ entry through the N-methyl-D-aspartate channel.

Fura-2 and imaging technology were used to detect intracellular Ca2+ changes in CA1 pyramidal cells in hippocampal slices. During focal synaptic stimulation, one or more highly localized regions of Ca2+ elevation (hot spots) were detected in the dendrites. Ca2+ spread from the center of hot spots with properties consistent with diffusion.

[The neuronal network of the hippocampus: a morphological analysis].

The use of new methods of morphologic analysis made it possible to detail significantly already known insights and to formulate the new ones concerning the hippocampal construction. This review discusses in detail the principles of structural organization of all intrahippocampal interneuronal connections and projections to the hippocampus from entorhinal cortex. Also, other afferent and efferent pathways and connections of polymorphic neurons of hippocampus are studied.

Measuring the impact of probabilistic transmission on neuronal output.

We have investigated the impact of stochastic transmission on the input-output relations of neurons in hippocampal slices. A synaptic input that fires a cell has a significant trial-to-trial variability in amplitude, reflecting the probabilistic release of transmitter. By measuring miniature excitatory postsynaptic currents, we estimate that synchronous release of a few vesicles can fire a CA1 cell.

[A comparative analysis of the functional stability (based on electrophysiological criteria) of slices of the suslik and guinea pig brains maintained under deep hypothermia].

The effect of prolonged deep cooling has been investigated in hippocampal and septal slices from the brain of hibernating and active ground squirrels, as well as of the guinea pigs. The slices were kept at low temperatures (2-4 degrees C) for various periods of time (from several hours to 6 days) and were periodically tested in a warm (31 degrees C) incubation medium. Hippocampal field potentials (mainly of the field CA1) and spontaneous activity of single neurones of the medial septum were recorded.

Functional stability of the brain slices of ground squirrels, Citellus undulatus, kept in conditions of prolonged deep periodic hypothermia: electrophysiological criteria.

The brain of hibernating animals, controlling the physiological functions during the hibernation cycles, is itself subject to deep cooling during bouts of hibernation. This suggests its high tolerance to deep hypothermia. Effects of prolonged deep cooling were investigated in hippocampal and septal slices, taken from the brains of three groups of animals: hibernating ground squirrels, actively waking ground squirrels, and guinea-pigs.

[Actin study of the synapses of surviving hippocampal slices during long-term potentiation].

A study was made of the synaptic actin ultrastructural localization in the hippocampal slices at long-lasting potentiation of area CA, using myosin subfragment-1 labeling. A specific qualitative ultrastructural sign of the potentiated hippocampal synapses was revealed for the first time - the formation in spines of rodlike bundles of actin filaments resembling the cilia. They penetrate the spine stalks to pass through the spine core towards the postsynaptic densities of active zones.

[Action of mediators on pyramidal and nonpyramidal neurons in slices of the guinea pig hippocampus].

Effects of acetylcholine (Ach), norepinephrine (NE), 5-hydroxytryptamine (5-HT) and gamma-aminobutyric acid (GABA) on the background activity were tested in the field CA3 in the guinea pig hippocampal slices. Three groups of neurons were investigated: nonpyramidal neurons of stratum radiatum-moleculare (NSR), neurons with single spike discharges of stratum pyramidale (SD-units) and neurons with complex spike discharges (CD-units) in the same stratum. Effects of Ach and NE were tested also on presumed interneurons of str.

[Electrophysiologic study of non-pyramidal neurons of the stratum radiatum in slices of guinea pig hippocampus].

The activity of 67 nonpyramidal neurons of str. radiatum-moleculare (NSRM) and of 8 presumed interneurons of str. oriens-pyramiidale (NSOP) was recorded extracellularly in guinea pig hippocampal slices.

Effects of norepinephrine and serotonin upon spontaneous activity and responses to mossy fiber stimulation of CA3 neurons in hippocampal slices.

Effects of norepinephrine (NE) and 5-hydroxytryptamine (5-HT) upon spontaneous activity and responses to mossy fiber stimulation (mfs) were tested in 192 units of the field CA3 in the guinea pig and rat hippocampal slices. The drugs were added to the incubating medium or ejected by pressure from a micropipette. After NE superfusion firing rate increased in 52% of the reactive units, while activity of 48% was suppressed.