Modulation of integrin antagonist signaling by ligand binding of the heparin-binding domain of vitronectin to the alphaVbeta3 integrin

The interaction between the arginine glycine and aspartic acid motif (RGD) of integrin ligands such as vitronectin and the integrin receptor alphaVbeta3 in mediating cell attachment has been well described. Similarly, the ability of disintegrins, small RGD containing peptides, to inhibit cell attachment and other cellular processes has also been studied extensively. Recently, we characterized a second site of interaction between vitronectin and its integrin partner. We determined that amino acids within the heparin-binding domain of vitronectin bind to a cysteine loop (C-loop) region of beta3 and that this interaction is required for the positive effects of alphaVbeta3 ligand occupancy on IGF-I signaling in smooth muscle cells. In this study we examine the signaling events activated following ligand binding of disintegrins to the alphaVbeta3 and the ability of these signals to be regulated by binding of the heparin-binding domain of vitronectin. We demonstrate that disintegrin ligand binding activates a series of events including the sequential activation of the tyrosine kinases c-Src and Syk. This leads to the activation of calpain and the cleavage of the beta3 cytoplasmic tail. Addition of vitronectin or a peptide homologous to the heparin-binding domain inhibited activation of this pathway. Our results suggest that the signaling events that occur following ligand binding to the alphaVbeta3 integrin reflects a balance between the effects mediated through the RGD binding site interaction and the effects mediated by the heparin binding site interaction and that for intact vitronectin the effect of the heparin-binding domain predominates.     

Low Dose ZD7288 Attenuates the Ischemia/Reperfusion-Induced Impairment of Long-Term Potentiation Induction at Hippocampal Schaffer Collateral-CA1 Synapses

Focal cerebral ischemia can impair the induction of activity-dependent long-term potentiation (LTP) in the hippocampus. This impairment of hippocampal synaptic plasticity can be caused by excitotoxicity and subsequent perturbation of hippocampal LTP-relevant transmitter systems, which include NR2B and PSD-95. It has been suggested that hyperpolarization-activated cyclic-nucleotide-gated (HCN) channels may play an important role in the control of membrane excitability and rhythmic neuronal activity. Our previous study has indicated that the selective HCN channel blocker ZD7288 can produce a dose-dependent inhibition of the induction of LTP at the Schaffer collateral-CA1 synapse of hippocampus by reducing the amount of glutamate released. It has also been demonstrated that ZD7288 can protect against neuronal injury caused by oxygen glucose deprivation. In the present study, we investigated the effect of ZD7288 on the induction of activity-dependent LTP and the expression of NR2B and PSD-95 after focal cerebral ischemia/reperfusion injury. The results showed that the induction of LTP was significantly impaired and the levels of NR2B and PSD-95 mRNA and protein were markedly decreased in the CA1 region of hippocampus following focal cerebral ischemia/reperfusion injury. Administration of low dose ZD7288 (0.25 μg) at 30 min and 3 h after the onset of ischemia attenuated the impairment of LTP induction and alleviated the NR2B and PSD-95 mRNA and protein down-regulation commonly induced by cerebral ischemia/reperfusion injury. These results suggest that low dose ZD7288 can ameliorate the ischemia/reperfusion-induced impairment of synaptic plasticity in the hippocampal CA1 region.     

Using model substrates to study the dependence of focal adhesion formation on the affinity of integrin-ligand complexes

The adhesion of mammalian cells is mediated by the binding of cell-surface integrin receptors to peptide ligands from the extracellular matrix and the clustering of these receptors into focal adhesion complexes. This paper examines the effect of one mechanistic variable, ligand affinity, on the assembly of focal adhesions (FAs) in order to gain mechanistic insight into this process. This study uses self-assembled monolayers of alkanethiolates on gold as a substrate to present either a linear or cyclic Arg-Gly-Asp peptide at identical densities. Inhibition assays showed that the immobilized cyclic RGD is a higher affinity ligand than linear RGD. 3T3 Swiss fibroblasts attached to substrates presenting the cyclic peptide at twice the rate they attached to substrates presenting the linear peptide. Quantitation of focal adhesions revealed that cells on cyclic RGD had twice the number of FAs as did cells on linear RGD and that these focal adhesions were on average smaller. These findings show that affinity affects the assembly of integrins into focal adhesions and support a model based on competing rates of nucleation and growth of FAs to explain the change in distribution of FAs with ligand affinity. This study is important because it provides a model system that is well-suited for biophysical studies of integrin-mediated cell adhesion and reveals insight into one mechanism utilized by cells to perceive environmental changes.     

Facilitation of long-term potentiation by muscarinic M(1) receptors is mediated by inhibition of SK channels

Muscarinic receptor activation facilitates the induction of synaptic plasticity and enhances cognitive function. However, the specific muscarinic receptor subtype involved and the critical intracellular signaling pathways engaged have remained controversial. Here, we show that the recently discovered highly selective allosteric M(1) receptor agonist 77-LH-28-1 facilitates long-term potentiation (LTP) induced by theta burst stimulation at Schaffer collateral synapses in the hippocampus. Similarly, release of acetylcholine by stimulation of cholinergic fibers facilitates LTP via activation of M(1) receptors. N-methyl-D-aspartate receptor (NMDAR) opening during theta burst stimulation was enhanced by M(1) receptor activation, indicating this is the mechanism for LTP facilitation. M(1) receptors were found to enhance NMDAR activation by inhibiting SK channels that otherwise act to hyperpolarize postsynaptic spines and inhibit NMDAR opening. Thus, we describe a mechanism where M(1) receptor activation inhibits SK channels, allowing enhanced NMDAR activity and leading to a facilitation of LTP induction in the hippocampus.     

Inhibition of post-synaptic Kv7/KCNQ/M channels facilitates long-term potentiation in the hippocampus

Activation of muscarinic acetylcholine receptors (mAChR) facilitates the induction of synaptic plasticity and enhances cognitive function. In the hippocampus, M(1) mAChR on CA1 pyramidal cells inhibit both small conductance Ca(2+)-activated KCa2 potassium channels and voltage-activated Kv7 potassium channels. Inhibition of KCa2 channels facilitates long-term potentiation (LTP) by enhancing Ca(2+)calcium influx through postsynaptic NMDA receptors (NMDAR). Inhibition of Kv7 channels is also reported to facilitate LTP but the mechanism of action is unclear. Here, we show that inhibition of Kv7 channels with XE-991 facilitated LTP induced by theta burst pairing at Schaffer collateral commissural synapses in rat hippocampal slices. Similarly, negating Kv7 channel conductance using dynamic clamp methodologies also facilitated LTP. Negation of Kv7 channels by XE-991 or dynamic clamp did not enhance synaptic NMDAR activation in response to theta burst synaptic stimulation. Instead, Kv7 channel inhibition increased the amplitude and duration of the after-depolarisation following a burst of action potentials. Furthermore, the effects of XE-991 were reversed by re-introducing a Kv7-like conductance with dynamic clamp. These data reveal that Kv7 channel inhibition promotes NMDAR opening during LTP induction by enhancing depolarisation during and after bursts of postsynaptic action potentials. Thus, during the induction of LTP M(1) mAChRs enhance NMDAR opening by two distinct mechanisms namely inhibition of KCa2 and Kv7 channels.     

Preservation of plastic properties of synaptic transmission in long-lasting hippocampal slices under the effects of a peptide analog of piracetam, L-pGlu-D-Ala-NH2

The tetanic stimulation of the Schaffer collaterals (SC) in rat hippocamp slices after 6 hrs in vitro conditions did not produce long-term potentiation (LTP) of the field response amplitude in the CA1 pyramidal cell layer. In contrast, LTP after the late tetanization was well preserved in the slices that were perfused for 20 minutes with 0.5 mkM L-pGlu-D-Ala-NH2 (PGAA) after 4-4.5 hrs in vitro. There were no significant reactivity changes during the perfusion of the slices with this drug concentration. Two other drugs with nootropic activity, piracetam (100 mkM) and gamma-hydroxybutyrate (100 mkM, Na-salt) did not prevent the disappearance of LTP in the late period in vitro, while enhanced the reactivity during perfusion period. The maintenance of the plastic properties of the SC-CA1 synaptic transmission under the influence of PGAA is thought to be the result of some specific interaction of the drug with LTP induction mechanisms. LTP damaged in the late period in vitro might be a new model of memory disturbances and this model can turn out to be useful for the comparative estimation of the effectiveness of the drugs with proposed nootropic activity and for the analysis of the possible mechanisms of their action.     

Coincident activity of converging pathways enables simultaneous long-term potentiation and long-term depression in hippocampal CA1 network in vivo

Memory is believed to depend on activity-dependent changes in the strength of synapses, e.g. long-term potentiation (LTP) and long-term depression (LTD), which can be determined by the sequence of coincident pre- and postsynaptic activity, respectively. It remains unclear, however, whether and how coincident activity of converging efferent pathways can enable LTP and LTD in the pathways simultaneously. Here, we report that, in pentobarbital-anesthetized rats, stimulation (600 pulses, 5 Hz) to Schaffer preceding to commissural pathway within a 40-ms timing window induced similar magnitudes of LTP in both pathways onto synapses of CA1 neurons, with varied LTP magnitudes after reversal of the stimulation sequence. In contrast, in urethane-anesthetized or freely-moving rats, the stimulation to Schaffer preceding to commissural pathway induced Schaffer LTP and commissural LTD simultaneously within a 40-ms timing window, without affecting synaptic efficacy in the reversed stimulation sequence. Coincident activity of Schaffer pathways confirmed the above findings under pentobarbital and urethane anesthesia. Thus, coincident activity of converging afferent pathways tends to switch the pathways to be LTP only or LTP/LTD depending on the activity states of the hippocampus. This network rule strengthens the view that activity-dependent synaptic plasticity may well contribute to memory process of the hippocampal network with flexibility or stability from one state to another.     

Participation of syndecan 2 in the induction of stress fiber formation in cooperation with integrin alpha5beta1: structural characteristics of heparan sulfate chains with avidity to COOH-terminal heparin-binding domain of fibronectin

The present study provides direct evidence that syndecan 2 participates selectively in the induction of stress fiber formation in cooperation with integrin alpha5beta1 through specific binding of its heparan sulfate side chains to the fibronectin substrate. Our previous study with Lewis lung carcinoma-derived P29 cells demonstrated that the cell surface heparan sulfate proteoglycan, which binds to fibronectin, is syndecan 2 (N. Itano et al., 1996, Biochem. J. 315, 925-930). We here report that in vitro treatment of the cells by antisense oligonucleotide for syndecan 2 resulted in a failure to form stress fibers on fibronectin substrate in association with specific suppression of its cell surface expression. Instead, localization of actin filaments in the cytoplasmic cortex occurred. A similar response of the cells was observed when the cells were treated to eliminate functions of cell surface heparan sulfates, including exogenous addition of heparin and pretreatment with anti-heparan sulfate antibody, F58-10E4, and with proteinase-free heparitinase I. Size- and structure-defined oligosaccharides prepared from heparin and chemically modified heparins were utilized as competitive inhibitors to examine the structural characteristics of the cell surface heparan sulfates involved in organization of the actin cytoskeleton. Their affinity chromatography on a column linked with a recombinant H-271 peptide containing a C-terminal heparin-binding domain of fibronectin demonstrated that 2-O-sulfated iduronates were essential for the binding. Inhibition studies revealed that a heparin-derived dodecasaccharide sample enriched with an IdoA(2OS)-GlcNS(6OS) disaccharide completely blocked binding of the syndecan 2 ectodomain to immobilized H-271 peptide. Finally, the dodecasaccharide sample was shown to inhibit stress fiber formation, triggered by adhesion of P29 cells to a CH-271 polypeptide consisting of both the RGD cell-binding and the C-terminal heparin-binding domains of fibronectin in a fused form. All these results consistently suggest that syndecan 2 proteoglycan interacts with the C-terminal heparin-binding domain of fibronectin at the highly sulfated cluster(s), such as [IdoA(2OS)-GlcNS(6OS)](6) present in its heparan sulfate chains, to result in the induction of stress fiber formation in cooperation with integrin alpha5beta1.     

Activity-dependent changes of the hippocampal CA3–CA1 synapse during the acquisition of associative learning in conscious mice

Contemporary neuroscientists are paying increasing attention to subcellular, molecular and electrophysiological mechanisms underlying learning and memory processes. Recent efforts have addressed the development of transgenic mice affected at different stages of the learning process, or emulating pathological conditions involving cognition and motor-learning capabilities. However, a parallel effort is needed to develop stimulating and recording techniques suitable for use in behaving mice, in order to grasp activity-dependent neural changes taking place during the very moment of the process. These in vivo models should integrate the fragmentary information collected by different molecular and in vitro approaches. In this regard, long-term potentiation (LTP) has been proposed as the neural mechanism underlying synaptic plasticity. Moreover, N -methyl- d -aspartate (NMDA) receptors are accepted as the molecular substrate of LTP. It now seems necessary to study the relationship of both LTP and NMDA receptors with the plastic changes taking place, in selected neural structures, during actual learning. Here, we review data on the involvement of the hippocampal CA3–CA1 synapse in the acquisition of classically conditioned eyelid conditioned responses (CRs) in behaving mice. Available data show that LTP, evoked by high-frequency stimulation of Schaffer collaterals, disturbs both the acquisition of CRs and the physiological changes that occur at the CA3–CA1 synapse during learning. Moreover, the administration of NMDA-receptor antagonists is able not only to prevent LTP induction in vivo , but also to hinder the formation of both CRs and functional changes in strength of the CA3–CA1 synapse. Thus, there is experimental evidence relating activity-dependent synaptic changes taking place during actual learning with LTP mechanisms and with the role of NMDA receptors in both processes.     

Downregulation of KCC2 following LTP contributes to EPSP-spike potentiation in rat hippocampus

GABAergic synaptic inhibition plays a critical role in regulating long-term potentiation (LTP) of glutamatergic synaptic transmission and circuit output. The K(+)-Cl(-) cotransporter 2 (KCC2) is an important factor in determining inhibitory GABAergic synaptic strength besides the contribution of GABA(A) receptor. Although much knowledge has been gained regarding activity-dependent downregulation of KCC2 in many pathological conditions, the potential change and contribution of KCC2 in LTP expression is still unknown. In this study, we found that downregulation of KCC2 was accompanied with the occurrence of LTP but not that of long-term depression in hippocampal CA1 region. Meanwhile, KCC2 level in CA3/DG and adjacent cortex was stable in the process of LTP expression in Schaffer collateral synapses. Blockade of NMDA receptor with APV not only prevented LTP induction also abolished the reduction of KCC2. Furthermore, the inhibition of KCC2 function with furosemide directly induced EPSP-spike (E-S) potentiation, an important component of LTP in hippocampus. The present data suggest a novel mechanism that LTP formation is accompanied by the downregulation of KCC2, which is underlying GABAergic strength and most likely contributes to the E-S potentiation following LTP.     

Tyrosine phosphatase STEP is a tonic brake on induction of long-term potentiation

The functional roles of protein tyrosine phosphatases (PTPs) in the developed CNS have been enigmatic. Here we show that striatal enriched tyrosine phosphatase (STEP) is a component of the N-methyl-D-aspartate receptor (NMDAR) complex. Functionally, exogenous STEP depressed NMDAR single-channel activity in excised membrane patches. STEP also depressed NMDAR-mediated synaptic currents whereas inhibiting endogenous STEP enhanced these currents. In hippocampal slices, administering STEP into CA1 neurons did not affect basal glutamatergic transmission evoked by Schaffer collateral stimulation but prevented tetanus-induced long-term potentiation (LTP). Conversely, inhibiting STEP in CA1 neurons enhanced transmission and occluded LTP induction through an NMDAR-, Src-, and Ca(2+)-dependent mechanism. Thus, STEP acts as a tonic brake on synaptic transmission by opposing Src-dependent upregulation of NMDARs.     

A novel integrin specificity exemplified by binding of the alpha v beta 5 integrin to the basic domain of the HIV Tat protein and vitronectin

Several studies have addressed the interaction of the HIV Tat protein with the cell surface. Our analysis of the cell attachment-promoting activity of Tat and peptides derived from it revealed that the basic domain of Tat, not the arg-gly-asp (RGD) sequence, is required for cell attachment to Tat. Affinity chromatography with Tat peptides and immunoprecipitation with various anti-integrin antibodies suggest that the vitronectin-binding integrin, alpha v beta 5, is the cell surface protein that binds to the basic domain of Tat. The Tat basic domain contains the sequence RKKRRQRRR. A related sequence, KKQRFRHRNRKG, present in the heparin-binding domain of an alpha v beta 5 ligand, vitronectin, also bound alpha v beta 5 in affinity chromatography and, in combination with an RGD peptide, was an inhibitor of cell attachment to vitronectin. The alpha v beta 5 interaction with these peptides was not solely due to high content of basic amino acids in the ligand sequences; alpha v beta 5 did not bind substantially to peptides consisting entirely of arginine or lysine, whereas a beta 1 integrin did bind to these peptides. The interaction of alpha v beta 5 with Tat is atypical for integrins in that the binding to Tat is divalent cation independent, whereas the binding of the same integrin to an RGD- containing peptide or to vitronectin requires divalent cations. These data define an auxiliary integrin binding specificity for basic amino acid sequences. These basic domain binding sites may function synergistically with the binding sites that recognize RGD or equivalent sequences.     

Disinhibition Mediates a Form of Hippocampal Long-Term Potentiation in Area CA1

The hippocampus plays a central role in memory formation in the mammalian brain. Its ability to encode information is thought to depend on the plasticity of synaptic connections between neurons. In the pyramidal neurons constituting the primary hippocampal output to the cortex, located in area CA1, firing of presynaptic CA3 pyramidal neurons produces monosynaptic excitatory postsynaptic potentials (EPSPs) followed rapidly by feedforward (disynaptic) inhibitory postsynaptic potentials (IPSPs). Long-term potentiation (LTP) of the monosynaptic glutamatergic inputs has become the leading model of synaptic plasticity, in part due to its dependence on NMDA receptors (NMDARs), required for spatial and temporal learning in intact animals. Using whole-cell recording in hippocampal slices from adult rats, we find that the efficacy of synaptic transmission from CA3 to CA1 can be enhanced without the induction of classic LTP at the glutamatergic inputs. Taking care not to directly stimulate inhibitory fibers, we show that the induction of GABAergic plasticity at feedforward inhibitory inputs results in the reduced shunting of excitatory currents, producing a long-term increase in the amplitude of Schaffer collateral-mediated postsynaptic potentials. Like classic LTP, disinhibition-mediated LTP requires NMDAR activation, suggesting a role in types of learning and memory attributed primarily to the former and raising the possibility of a previously unrecognized target for therapeutic intervention in disorders linked to memory deficits, as well as a potentially overlooked site of LTP expression in other areas of the brain.     

Effects of Chronic Stress and Phenytoin on the Long-term Potentiation （LTP） in Rat Hippocampal CA1 Region

Stress is the response to stimulation from inside andoutside with complicated effects on organisms. Appropri-ate stressful reactions are helpful in resisting diseases byactivating unspecific modulation system, while severe orprolonged stresses are harmful and even induce mentaland physical disorders such as recurrent depression, post-traumatic stress disorder (PTSD), Alzheimer’s disease andepilepsy [1]. Hippocampus, a main brain region of keyimportance for learning, memory and emotion, is t…     

Detection and characterization of heparin-binding proteins with a gel overlay procedure.

The binding of 125I-labeled derivatives of heparin has been used by several investigators to identify heparin-binding fragments of different heparin-binding proteins. In this report we utilize the procedure described by J.W. Smith and D.J. Knauer (1987, Anal. Biochem. 160, 105-114) to produce 125I-fluorescein-heparin. Using this derivative, we compare the use of gel overlay procedures with "Western blot" procedures for the detection of heparin-binding proteins following polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. We show that the gel overlay procedure is a relatively simple and sensitive method for visualizing heparin-binding proteins. In addition, we use the procedure to characterize the heparin-binding properties of heparin-binding growth factor 1 (acidic fibroblast growth factor) with synthetic peptide competitors and site-directed mutants of the growth factor.     

Specificity of the VP1 GH loop of Foot-and-Mouth Disease virus for alphav integrins

Foot-and-mouth disease virus (FMDV) can use a number of integrins as receptors to initiate infection. Attachment to the integrin is mediated by a highly conserved arginine-glycine-aspartic acid (RGD) tripeptide located on the GH loop of VP1. Other residues of this loop are also conserved and may contribute to integrin binding. In this study we have used a 17-mer peptide, whose sequence corresponds to the GH loop of VP1 of type O FMDV, as a competitor of integrin-mediated virus binding and infection. Alanine substitution through this peptide identified the leucines at the first and fourth positions following RGD (RGD+1 and RGD+4 sites) as key for inhibition of virus binding and infection mediated by alphavbeta6 or alphavbeta8 but not for inhibition of virus binding to alphavbeta3. We also show that FMDV peptides containing either methionine or arginine at the RGD+1 site, which reflects the natural sequence variation seen across the FMDV serotypes, are effective inhibitors for alphavbeta6. In contrast, although RGDM-containing peptides were effective for alphavbeta8, RGDR-containing peptides were not. These observations were confirmed by showing that a virus containing an RGDR motif uses alphavbeta8 less efficiently than alphavbeta6 as a receptor for infection. Finally, evidence is presented that shows alphavbeta3 to be a poor receptor for infection by type O FMDV. Taken together, our data suggest that the integrin binding loop of FMDV has most likely evolved for binding to alphavbeta6 with a higher affinity than to alphavbeta3 and alphavbeta8.     

The effects of repetitive low frequency stimulation on control and “potentiated” synaptic responses in the hippocampus

Trains of low frequency stimulation (LFS) (1 sec^?1 for 100 sec) were administered to the Schaffer collateral-commissural projections to the regio superior of the rat hippocampus before and after the induction of long-term potentiation (LTP). In 2 of 16 cases (12.5%) these produced a persistent depression of control responses. In 14 of 18 experiments (77.7%) however LFS significantly reduced the “potentiated” responses. The possible basis for these effects and their significance for understanding the LTP effect are discussed.     

Human herpesvirus 8 envelope glycoprotein B mediates cell adhesion via its RGD sequence

Human herpesvirus 8 (HHV-8) or Kaposi's sarcoma-associated herpesvirus, implicated in the pathogenesis of Kaposi's sarcoma, utilizes heparan sulfate-like molecules to bind the target cells via its envelope-associated glycoproteins gB and gpK8.1A. HHV-8-gB possesses the Arg-Gly-Asp (RGD) motif, the minimal peptide region of many proteins known to interact with subsets of host cell surface integrins. HHV-8 utilizes alpha3beta1 integrin as one of the receptors for its entry into the target cells via its gB interaction and induces the activation of focal adhesion kinase (FAK) (S. M. Akula, N. P. Pramod, F.-Z. Wang, and B. Chandran, Cell 108:407-419, 2002). Since FAK activation is the first step in the outside-in signaling necessary for integrin-mediated cytoskeletal rearrangements, cell adhesions, motility, and proliferation, the ability of HHV-8-gB to mediate the target cell adhesion was examined. A truncated form of gB without the transmembrane and carboxyl domains (gBdeltaTM) and a gBdeltaTM mutant (gBdeltaTM-RGA) with a single amino acid mutation (RGD to RGA) were expressed in a baculovirus system and purified. Radiolabeled HHV-8-gBdeltaTM, gBdeltaTM-RGA, and deltaTMgpK8.1A proteins bound to the human foreskin fibroblasts (HFFs), human dermal microvascular endothelial (HMVEC-d) cells, human B (BJAB) cells, and Chinese hamster ovary (CHO-K1) cells with equal efficiency, which was blocked by preincubation of proteins with soluble heparin. Maxisorp plate-bound gBdeltaTM protein induced the adhesion of HFFs and HMVEC-d and monkey kidney epithelial (CV-1) cells in a dose-dependent manner. In contrast, the gBdeltaTM-RGA and DeltaTMgpK8.1A proteins did not mediate adhesion. Adhesion mediated by gBdeltaTM was blocked by the preincubation of target cells with RGD-containing peptides or by the preincubation of plate-bound gBdeltaTM protein with rabbit antibodies against gB peptide containing the RGD sequence. In contrast, adhesion was not blocked by the preincubation of plate-bound gBdeltaTM protein with heparin, suggesting that the adhesion is mediated by the RGD amino acids of gB, which is independent of the heparin-binding domain of gB. Integrin-ligand interaction is dependent on divalent cations. Adhesion induced by the gBdeltaTM was blocked by EDTA, thus suggesting the role of integrins in the observed adhesions. Focal adhesion components such as FAK and paxillin were activated by the binding of gBdeltaTM protein to the target cells but not by gBdeltaTM-RGA protein binding. Inhibition of FAK phosphorylation by genistein blocked gBdeltaTM-induced FAK activation and cell adhesion. These findings suggest that HHV-8-gB could mediate cell adhesion via its RGD motif interaction with the cell surface integrin molecules and indicate the induction of cellular signaling pathways, which may play roles in the infection of target cells and in Kaposi's sarcoma pathogenesis.     

Increased expression of phospho-cofilin in CA1 and subiculum areas after theta-burst stimulation of Schaffer collateral-commissural fibers in rat hippocampal slices

Activity-dependent structural plasticity of dendritic spines of pyramidal neurons in the central neuron system has been proposed to be a cellular basis of learning and memory. Long-term potentiation (LTP) is accompanied by changes in synaptic morphology and structural remodeling of dendritic spines. However, there is considerable uncertainty as to the nature of the adjustment. The present study tested whether immunoreactive phospho-cofilin, an index of altered actin filament assembly, could be increased by theta-burst stimulations (TBS), which is an effective stimulation pattern for inducing LTP in the hippocampus. The slope of fEPSPs evoked by TBS to Schaffer collateral-commissural fibers in hippocampal slices was measured, and p-cofilin expression was examined using immunofluorescence techniques. Results indicated that saturated L-LTP was produced by multiple TBS episodes to Schaffer collateral-commissural fibers in the hippocampal CA1 area, and TBSs also increased immunoreactive p-cofilin expression in the stratum radiatum of the hippocampal CA1 area and pyramidal layer of the subiculum. D-2-amino-5-phosphonovalerate (D-APV) prevented LTP and expression of p-cofilin immunoreactive induced by multiple TBS episodes in the stratum radiatum of the hippocampal CA1 area. Two paired-pulse low-frequency stimulation (PP-LFS) episodes to Schaffer collateral-commissural fibers induced long-term depression (LTD), and did not affect p-cofilin expression in the stratum radiatum of the hippocampal CA1 area. These results suggest that LTP induction is associated with altered actin filament assembly. Moreover, the CA1 and subiculum areas of the hippocampal formation possibly cooperate with each other in important physiological functions, such as learning and memory, or in pathological diseases, such as epilepsy.