-
[show abstract]
[hide abstract]
ABSTRACT: 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.
The Chinese journal of physiology 10/2010; 53(5):328-36. · 0.56 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Late-phase long-term potentiation (L-LTP) plays a very important role in the maintenance of long-term memory in hippocampus. However, studies have shown that L-LTP can be reversed by subsequent neuronal activity. The aim of the present study is to investigate whether the presynaptic mechanism and the change of AMPARs expressions are involved in the reversal of L-LTP in hippocampal CA1 area. Standard extracellular recording technique was used to record the potential change in the stratum radiatum of CA1 area of adult rat hippocampal slices. Two hours after LTP induction, which was induced by high-frequency stimulation (HFS), two episodes of high-intensity paired-pulse low-frequency stimulation (HI-PP-LFS) were delivered to induce L-LTP reversal. Paired-pulse ratios (PPR) were obtained before LTP induction, 2 h after LTP induction and 30 min after LTP reversal. On the other hand, immunofluorescence histochemistry was used to detect AMPARs expressions before and after L-LTP reversal. The results showed that, after 2 h of induction, L-LTP was partially reversed by two episodes of HI-PP-LFS, and the percentage of depotentiation was 61.79%+/-14.51%. PPR obtained before and after LTP induction, and as well that after LTP reversal, are all more than 1, showing paired-pulse facilitation (PPF). Multiple comparison indicated PPR before LTP induction was the greatest one, and PPR after LTP induction was the smallest. In addition, no significant difference was observed in the intensity of AMPAR/GluR2 immunoreactivity in CA1 area among control group, LTP group and LTP reversal group. These results suggest that the presynaptic mechanism is involved in both the maintenance and reversal of L-LTP and there is no change in AMPAR/GluR2 expression before and after the reversal of L-LTP.
Sheng li xue bao: [Acta physiologica Sinica] 02/2010; 62(1):23-9.
-
[show abstract]
[hide abstract]
ABSTRACT: Synaptic depression in the hippocampus at early postnatal stage can be induced by test pulse stimulation (<1 Hz). However, the receptor mechanism for induction of this synaptic depression is unclear. In the present study, we used whole-cell patch clamp recording in vitro to investigate how excitatory and inhibitory synapses onto layer II/III pyramidal neurons of the primary visual cortex adapt to test pulse activation from a previously non-activated (naive) state. We found that excitatory postsynaptic currents (EPSCs) of pyramidal neurons were rapidly depressed by 0.1 Hz stimulation in acutely prepared slices from rats at 11-12 postnatal days, while this phenomena disappeared in slices from young adolescent rats (23-24 postnatal days). By contrast, inhibitory postsynaptic currents (IPSCs) were relatively stable following 0.1 Hz stimulation of rat slices at the same early postnatal stage. Moreover, the test pulse depression of EPSCs was associated with a decrease in 1/coefficient of variation (CV)(2) and no change in the paired-pulse ratio. These data imply silencing of synapses and no significant change either in postsynaptic receptor density or presynaptic terminal release probability. This synaptic depression was unaffected by the competitive NMDA receptor antagonist D-APV. Ca(2+)-permeable AMPA receptor selective antagonists, Naspm or IEM-1460, prevented the induction of the test pulse depression. These data suggest that EPSCs, but not IPSCs, were rapidly depressed by test pulse stimulation in rats at early postnatal stage via a Ca(2+)-permeable AMPA receptor-dependent mechanism.
Neuroscience 11/2009; 165(3):684-91. · 3.38 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Long-term potentiation (LTP) is a well-characterized form of synaptic plasticity that fulfills many of the criteria for the neural correlate of memory. LTP reversal (or depotentiation, DP) is thought to correlate with prevention or elimination of memory storage. LTP during and immediately after induction can be easily reversed by afferent stimulation, when applied within the optimal time window. The aim of the present study was to determine whether later-phase LTP (L-LTP) could be reversed by special patterned stimulation applied at 2 h after LTP induction, as well as to characterize the receptor mechanisms underlying this reversal. Field excitatory postsynaptic potentials evoked by Schaffer collateral stimulation were recorded from the CA1 subfield of adult rat hippocampal slices. Results demonstrated that stable LTP, which was induced by six theta-burst stimulations, was mediated by NR2A-containing N-methyl-d-aspartate receptors (NMDARs). This L-LTP was partially reversed by high-intensity paired-pulse low-frequency stimulation (HI-PP-LFS) and was inhibited by Zn(2+) (30 nm), a voltage-independent NR2A-NMDAR antagonist. However, NR2B-NMDAR antagonists (Ro 25-6981, 1 mum) displayed no effect on L-LTP reversal. L-LTP partial reversal was also induced by HI-PP-LFS, when the protein synthesis inhibitors anisomycin (25 microm) and cycloheximide (60 microm) were applied following LTP induction. These results suggested that NR2A-containing NMDARs are required for L-LTP induction and DP in the hippocampal CA1 area of adult rats. Moreover, HI-PP-LFS was an effective stimulation pattern to induce DP.
European Journal of Neuroscience 06/2009; 29(11):2137-44. · 3.63 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: To investigate the expressions and distributions of N-methyl-D-aspartic acid NMDA/ NR1 and alpha-amino-3-hydroxy-5-methyl-4 isoxazolepropionic acid AMPA/GluR2 subunits in the hippocampal formation.
The immunofluorescence histochemical staining was made on paraformaldehyde fixed hippocampal tissue sections for then observed by confocal laser scanning microscopy.
There were widely positive expressions and basically same distributions of NR1 and GluR2 in the hippocampal formation of adult rats, especially in pyramidal layer of CA1 and CA3 regions and in the interneurons of hilus fascia dentata. Positive expressions, which mainly existed in the cytomembrane and processes of the neurons, also distributed in molecular layer of CA1 and CA3 regions as well as in granule layer of dentate gyrus. However, the immunoreactive intensity of NMDA/NR1 was stronger than that of AMPA/GluR2 in molecular layer of CA3 area and in polymorphic layer of dentate gyrus.
The distributions of NMDA/NR1 and AMPA/GluR2 in the hippocampal formation are basically same, this suggests that they may execute cooperatively some important tasks.
Sichuan da xue xue bao. Yi xue ban = Journal of Sichuan University. Medical science edition 02/2008; 39(1):15-8.
-
[show abstract]
[hide abstract]
ABSTRACT: There is no unambiguous report so far on whether short reinforcing training could establish stable spatial long-term memory and how the NMDA/NR1 expression in the hippocampal formation changes after establishment of short- and long-term memory. In the present study, three spatial memory training modes of Morris water maze were used: spatial long-term memory training mode (LT group), spatial short-term memory training mode (ST group) and short reinforcing training mode (SRT group). The characteristics of those memories established by different training modes were compared. The immunofluorescence histochemical staining technique was used to observe the changes of NMDA/NR1 expression in the hippocampal formation in the three groups. The results showed that, during Morris water maze training, no significant difference was found in the mean latency and the strategies to the target between the LT and SRT groups. The examination of the memories following different trainings indicated that the mean latency and the strategies to the target as well as the times crossing the target in LT group were not significantly different from those in SRT group, except that the mean time remaining in the platform quadrant in LT group was significantly longer than that in SRT group. In addition, no significant difference in the intensity of NMDA/NR1 immunoreactivity in CA1, CA3 and dentate gyrus of the hippocampal formation was observed between the control and ST groups or between LT and SRT groups. However, the intensity of NMDA/NR1 immunoreactivity in CA1 area and dentate gyrus in both LT and SRT groups was significantly increased as compared with that in ST or the control groups. These results suggest that the short reinforcing training mode can establish long-term spatial memory, which is almost the same as that established by the long-term training mode, and that the increase of NMDA/NR1 expression in CA1 area and dentate gyrus of the hippocampal formation may be one of the mechanisms of spatial long-term memory formation.
Sheng li xue bao: [Acta physiologica Sinica] 11/2006; 58(5):442-8.
