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Deep brain stimulation (DBS), which usually utilizes high frequency stimulation (HFS) of electrical pulses, is effective for treating many brain disorders in clinic. Studying the dynamic response of downstream neurons to HFS and its time relationship with stimulus pulses can reveal important mechanisms of DBS and advance the development of new stimulation modes (e.g., closed-loop DBS). To exhibit the dynamic neuronal firing and its relationship with stimuli, we designed a two-dimensional raster plot to visualize neuronal activity during HFS (especially in the initial stage of HFS). Additionally, the influence of plot resolution on the visualization effect was investigated. The method was then validated by investigating the neuronal responses to the axonal HFS in the hippocampal CA1 region of rats. Results show that the new design of raster plot is able to illustrate the dynamics of indexes (such as phase-locked relationship and latency) of single unit activity (i.e., spikes) during periodic pulse stimulations. Furthermore, the plots can intuitively show changes of neuronal firing from the baseline before stimulation to the onset dynamics during stimulation, as well as other information including the silent period of spikes immediately following the end of HFS. In addition, by adjusting resolution, the raster plot can be adapted to a large range of firing rates for clear illustration of neuronal activity. The new raster plot can illustrate more information with a clearer image than a regular raster plot, and thereby provides a useful tool for studying neuronal behaviors during high-frequency stimulations in brain.

The aim of this paper was to investigate the effect of total saponins from Panax japonicus( SPJ) on cognitive decline of natural aging rats and its mechanism. Thirty male SD rats of eighteen month old were randomly divided into three groups: aged group,10 mg·kg~(-1) SPJ-treated group and 30 mg·kg~(-1) SPJ-treated group. The SPJ-treated groups were given SPJ at the dosages of 10 mg·kg~(-1) and 30 mg·kg~(-1),respectively,from the age of 18 to 24 months. Aged group were lavaged the same amount of saline,10 six-month-old rats were used as control group,with 10 rats in each group. The open field test,novel object recognition and Morris water maze were performed to detect the changes of cognitive function in each group. The changes of synaptic transmission of long-term potentiation( LTP) in hippocampal CA1 region were detected by field potential recording. Western blot was used to detect the protein levels of NLRP3,ASC,caspase-1 and the changes of Glu A1,Glu A2,CAMKⅡ,CREB and phosphorylation of CAMKⅡ,CREB in each group.The results showed that SPJ could improve the decline of cognitive function in aging rats,reduce the damage of LTP in the hippocampal CA1 region of aged rats,and decrease the expression of NLRP3,ASC,caspase-1 in aging rats. At the same time,SPJ could enhance the membrane expression of AMPA receptor( Glu A1 and Glu A2),and increase the expression of p-CAMKⅡand p-CREB in aging rats.SPJ could improve cognitive decline of natural aging rats,and its mechanism may be related to regulating NLRP3 inflammasome,thus regulating the membrane expression of AMPA receptor,and enhancing the expression phosphorylation of CAMKⅡ and CREB.

Objective: To explore the role of β2-nicotinic acetylcholine receptor (β2-nAChR) in the development of γ- aminobutyric acid A type receptors (GABA A -Rs) in hippocampal CA1 and CA3 pyramidal neurons of mice., Methods: The hippocampal CA1 and CA3 pyramidal neurons were acutely isolated from β2-nAChR gene knockout (β2-KO group) mice. GABA currents in CA1 and CA3 pyramidal neurons were induced with the selective GABA A -R agonist muscimol and recorded using perforated patch-clamp recording technique. The GABA currents of CA1 and CA3 pyramidal neurons were tested for their equilibrium potentials (E Mus s) and kinetic parameters and were compared with the measurements in wild-type mice (WT group)., Results: The mean E Mus of CA1 neurons ( n =7) of β2-KO mice ( n =4) was -31.7±3.5 mV, showing an obvious depolarizing shift compared with the WT mice ( P < 0.05); the mean E Mus of CA3 neurons ( n =4) was -16.1±4.6 mV, also showing a depolarizing shift ( P < 0.01). The difference in the E Mus s between CA3 and CA1 neurons in β2-KO mice, but not in WT mice, was significant ( P < 0.05). The GABA A -R desensitization was significantly slowed down in both CA1 and CA3 neurons of β2-KO mice, with decay time of 2.2±0.2 s and 3.2±0.1 s, respectively, significantly longer than those in WT mice (1.6±0.1 s and 2.3±0.1 s, respectively; P < 0.05)., Conclusions: β2-containing nAChRs may promote the functional maturation of GABA A -R in CA1 and CA3 pyramidal cells in mouse hippocampus.

The present study was aimed to investigate the electrophysiological characteristics of hippocampal postnatal early development mediated by α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors in rats. Forty-eight Wistar rats were divided into postnatal 0.5-, 1-, 2- and 3-month groups (n = 12). Spontaneous excitatory postsynaptic currents (sEPSCs) and field excitatory postsynaptic potentials (fEPSPs) mediated by AMPA receptors were recorded to evaluate the changes in the intrinsic membrane properties of hippocampal CA1 pyramidal neurons by using patch-clamp and MED64 planar microelectrode array technique respectively. The results showed that, during the period of postnatal 0.5-3 months, some of the intrinsic membrane properties of hippocampal CA1 pyramidal neurons, such as the membrane capacitance (Cm) and the resting membrane potential (RMP), showed no significant changes, while the membrane input resistance (Rin) and the time constant (τ) of the cells were decreased significantly. The amplitude, frequency and kinetics (both rise and decay times) of sEPSCs were significantly increased during the period of postnatal 0.5-1 month, but they were all decreased during the period of postnatal 1-3 months. In addition, the range of evoked fEPSPs in hippocamal CA1 region was significantly expanded, but the fEPSP amplitudes were decreased significantly during the period of postnatal 0.5-3 months. Furthermore, the evoked fEPSPs could be significantly inhibited by extracellular application of the AMPA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). These results suggest that AMPA receptor may act as a major type of excitatory receptor to regulate synaptic transmission and connections during the early stage of hippocampal postnatal development, which promotes the development and functional maturation of hippocampus in rats.

Objective: To investigate the effects of beta-amyloid (Aβ) and apolipoprotein E4(apoE4) on choline acetyl transferase (ChAT) in hippocampus and to explore possible the synergistic effect of both Aβ and apoE4., Methods: Male Wistar rats were divided into four groups: control group, Aβ group, apoE4 group and Aβ + apoE4 group. Rats in different group received injection of normal saline, Aβ1-40, apoE4 and Aβ1-40 + apoE4, respectively, into bilateral hippocampus CA1 regions under the control of a brain stereotaxic apparatus. The learning-memory ability with the escape latency and the times of passing platform and the expression of ChAT in hippocampus CA1 regions were documented., Results: The escape latency at fifth day and the times of passing platform and ChAT mRNA PU values were obtained for the control group (10.75 s ± 2.44 s, 4.13 ± 0.64, and 28.90 ± 4.43), apoE4 group (23.88 s ± 4.32 s, 2.38 ± 0.52, and 20.85 ± 3.98), Aβ group (43.50 s ± 9.78 s, 1.38 ± 0.52, and 16.96 ± 2.53), and Aβ + apoE4 group (70.63 s ± 10.04 s, 0.75 ± 0.71, and 13.01 ± 2.21). Through 5 days of training all animals acquired learning-memory ability with the gradually shortened escape latency, although injection of Aβ1-40 and apoE4 all induced learning-memory damage, due to a significantly prolonged the escape latency at fifth day (P < 0.01) and markedly decreased the times of passing platform (P < 0.01) in both Aβ and apoE4 group than in control group. An interaction between Aβ and apoE4 also was observed, with further prolonged escape latency(P < 0.01). ChAT mRNA PU values were significantly lower in the Aβ group and apoE4 group than in the control group (P < 0.01). Aβ and apoE4 demonstrated interaction in lowering ChAT mRNA level(P < 0.05)., Conclusions: Both Aβ and apoE4 induce an injury to hippocampal cholinergic system and its learning-memory ability, in which Aβ and apoE4 have a synergistic effect in the initiation of such injury.

Objective: To explore the effects of brain-derived neurotrophic factor (BDNF) pretreatment on beta amyloid protein (Abeta) induced impairment of in vivo hippocampal long-term potentiation (LTP) in the CA1 region of rats., Methods: Thirty-six adult male SD rats were randomly divided into six groups (n = 6): control, Abeta25-35, BDNF, (0.02 microg, 0.1 microg, 0.5 microg) BDNF + Abeta25-35. A self-made hippocampal local drug delivery catheter and a parallel bound stimulating/recording electrode were used to deliver drugs/stimulation and record field excitatory post-synaptic potentials (fEPSPs) in the hippocampal CA1 region of rats. High-frequency stimulation (HFS) was used to induce in vivo LTP., Results: (1) Abeta25-35 (2 nmol) injection into CA1 region of rats did not affect the baseline fEPSPs, but inhibited the HFS-induced LTP significantly (P < 0.01). (2) Hippocampal CA1 injection of BDNF (0.1 microg) alone did not affect the baseline fEPSPs and HFS-induced LTP. (3) Compared with Abeta25-35 alone group, the averaged amplitude of LTP in BDNF (0.1 microg and 0.5 microg) plus Abeta25-35 groups significantly increased at 0 min, 30 min, and 60 min after HFS (P < 0.01), indicating that pretreatment with BDNF effectively protected against the Abeta,25-35 induced depression of LTP in a dose-dependent manner., Conclusion: Intrahippocampal injection of BDNF can protect against the Abeta25-35-induced LTP impairment, suggesting that the up-regulation of BDNF in the brain could maintain the normal hippocampal synaptic plasticity and may contribute to the improvement of learning and memory in Alzheimer's (AD) disease patients.

Using 64-channels (8 × 8) multi-electrode array technique (MED-64 system), the modulatory actions of 5-hydroxytryptamine (5-HT) 2C receptor subtype on the entorhinal (EC)-hippocampal synaptic transmission and connections were studied. One of freshly dissociated acute hippocampal slices of rats which was placed on the MED-64 probe, was subject to constant perfusion with oxygenated artificial cerebrospinal fluid (ACSF, 95% O2 and 5% CO2). Two hours after ACSF incubation, simultaneous multi-site electrophysiological recordings were performed. One electrode was selected to be used for perforant path (PP) stimulation, and the remaining 63 electrodes were used for recordings of network field excitatory postsynaptic potentials (fEPSPs) within both CA1 and dentate gyrus (DG) that have been previously proved to be mediated by glutamate non-NMDA receptors. After stability of network fEPSPs was achieved, (±)-1(2, 5-Dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride (DOI, an agonist of 5-HT2C receptor subtype), or SB242084 (6-Chloro-2,3-dihydro-5-methyl-N-[6-[(2-methyl-3-pyridinyl)oxy]-3-pyridinyl]-1H-indole-1-carboxyamide dihydrochloride hydrate) (a selective antagonist of 5-HT2C receptor subtype) was applied for 10 min perfusion, respectively. Two-dimensional current source density (2D-CSD) analysis was also transformed by bilinear interpolation at each point of the 64 electrodes for spatial imaging of the fEPSP network responses. Based upon the polarities of fEPSP and 2D-CSD imaging, it was clearly shown that synaptic activations were evoked to occur within the molecular layer of DG and pyramidal cell layer of CA1 by the PP stimulation in which negative-going field potentials and current sink (blue) could be recorded. While, positive-going field potentials and current source (yellow) were mainly localized within the granule cell layer and hilus of DG and alveus of CA1, reflecting spread of electrical signals derived from depolarized region toward CA3 area or subiculum and fimbria along the axons. Perfusion of the hippocampal slices with DOI resulted in a significant enlargement of synaptic connection size at network level and enhancement of synaptic efficacy. However, on the contrary, perfusion with SB242084 produced reversal effect with either reduction in synaptic network size or decreased magnitude of fEPSPs (amplitude and slope) in the CA1 and DG. These results suggest that endogenous 5-HT causes facilitation of EC-CA1 and EC-DG synaptic transmission and connections via acting on 5-HT2C receptor subtype, leading to gain in synaptic transmission and enlargement of synaptic connections.

To study the influence of behavioral stress on hippocampal spatial learning and memory, we used the freely moving rats that had undergone chronic implantation of a recording electrode in the hippocampus CA1 region and a bipolar stimulating electrode in the ipsilateral Schaffer collateral-commissural pathway. The field excitatory postsynaptic potentials (fEPSPs) were recorded in the absence of exogenous induction of high-frequency stimulation (HFS) or low-frequency stimulation (LFS) and reflected the effect of stress on the hippocampal spatial learning. And we also investigated the change of hippocampal synaptic plasticity when rats were re-exposed to the same environment at 24 h after novelty acquisition. We found that exploration of a novel environment induced the hippocampal synaptic depression in the rats with stress-adaption, whereas exposure to the novel environment induced the hippocampal synaptic potentiation in the behavioral stress rats. Furthermore, re-exposure to the same environment no longer elicited the hippocampal synaptic potentiation or depression at 24 h after the first novel acquisition in the behavioral stress rats. These results demonstrate that behavioral stress induces the hippocampal synaptic potentiation under novelty acquisition and further damages the hippocampal spatial learning and memory. However, the stress can be adapted by re-exposure to the novelty and thus does not further damage the hippocampal spatial learning and memory.

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.

To study the role of long-term depression (LTD) in the mechanisms of learning and memory in hippocampus of rat, recordings were taken from freely moving animals that had undergone chronic implantation of a recording electrode in the hippocampus CA1 region and a bipolar stimulating electrode in the ipsilateral Schaffer collateral-commissural pathway. The recording electrode was inserted 3.8 mm posterior to bregma and 2.8 mm right of the midline, and the stimulating electrode was inserted 4.8 mm posterior to bregma and 3.8 mm right of the midline via holes drilled through the skull. The entire assembly was connected with a rubber socket on the animal's head and then stabilized with dental cement. The correct placement of the electrodes into the hippocampal CA1 area was confirmed via electrophysiological criteria and postmortem histological analysis. After 2 weeks of surgery recovery, the rats were placed in the familiar recording chamber for 3 days. The field excitatory postsynaptic potentials (fEPSPs) were evoked by stimulating with a square wave constant current pulse of 0.2 ms duration, at a frequency of 0.033 Hz and at a stimulation intensity adjusted to given an fEPSP amplitude of 50% of the maximum, and the baseline of fEPSPs were recorded for 3 days in the familiar recording environment at the same time each day. A novelty environment that was made of clear Perspex (40 cm x 40 cm x 40 cm) was prepared and we examined whether exposure to a novelty spatial environment facilitated the expression of activity-dependent persistent decrease in synaptic transmission (namely LTD) at CA1 synapses in the rat hippocampus. The results showed that brief exposure to a novelty environment for 10 min facilitated the expression of LTD in the hippocampal CA1 area under no other exogenous high- or low-frequency stimulation protocol. This facilitatory effect was dependent on the activation of D1/D5 receptors: the D1/D5 receptors antagonist SCH23390 prevented the decrease of synaptic transmission in the hippocampus during the novelty exploration. These data provided important evidence that LTD may underlie certain forms of learning and memory and that dopamine participates in the synaptic plasticity in the process of hippocampal spatial information storage.

Objective: To explore the effect of the total flavonoids of Jiawei Wuzi Yanzong prescription on the Voltage-gated calcium channel of the CA1 pyramidal cell of rat hippocampus., Method: The inward calcium current was recorded by the whole-cell patch clamp and the amplitude of it was thought to observe the effect of Abeta25-35 and the total flavonoids. The hippocampus of rat was separated and cut into slices. Active pyramidal cells of slices were chosen for the whole-cell patch clamp recording. After exposure to Abeta25-35, voltage steps (500 ms) were used to depolarize stepwise in a range from 50 to +50 mV (increment: 5 mV). An inward Ca2+ current which was suggested to be survey was evoked. Application of the total flavonoids was to be observed if it had effect on this voltage-depended inward current., Result: Abeta25-35 could enhance the calcium current to induce intracellular calcium overload. The amplitude of the control group was--(157.1 +/- 19.9) pA, but after application of Abeta25-35 the current enhanced to--(323.2 +/- 23.4) pA. When the total flavonoids at concentration of 125, 250, 500 g x L(-1) were added, the current declined to--(257.9 +/- 31.6), - (196.4 +/- 29.8) and--(169.3 +/- 34.0) pA, respectively., Conclusion: Abeta-induced intracellular calcium overload may be one of neurotoxic of beta-amyloid peptide. The total flavonoids of Jiawei Wuzi Yanzong prescription can suppress inward calcium current to protect neurons.

Objective: Previous studies have demonstrated that vitamin A and its active derivatives function as essential competence factors for long-term synaptic plasticity within the adult brain. But little is known if marginal vitamin A deficiency (MVAD) beginning from embryonic period affects the brain development and the ability of learning and memory in young rats. The aim of this study was to identify the effects of MVAD and vitamin A intervention (VAI) on learning, memory and the hippocampal CA1 long-term potentiation (LTP) in young rats., Methods: Rats were divided into control, MVAD and VAI groups in this study. In control group (10 young rats) the dams and pups were fed with normal diet (VA 6500 IU/kg). In MVAD group (19 young rats) the dams and pups were fed with MVAD diet (VA 400 IU/kg). In VAI group (9 young rats) the dams were fed with MVAD diet and the pups were fed with normal diet from postnatal week 4. All the young rats were killed at the age of 7 weeks. During the last week of the experiment, the shuttle box active avoidance reaction tests were carried out. At week 7, the hippocampal CA1 LTP was detected by electrophysiological technique and relative intensity of fluorescence in cells in hippocampal slices was measured by confocal laser scanning microscopy labeled by fluo-3., Results: (1) The times to reach the learning standard in both VAI group (28.8 +/- 4.1) and MVAD group (45.6 +/- 12.1) were more than control group (17.1 +/- 4.4) (P < 0.01), and that of MVAD group was more than VAI group (P < 0.05) in active avoidance reaction tests. (2) The changes of field excitatory postsynaptic potentials (fEPSP) slope for MVAD group (22.9% +/- 9.4%) and VAI group (29.5% +/- 13.7%) were less than that of control group (57.5% +/- 27.3%), respectively (P < 0.01). No significant difference was found between VAI and MVAD groups (P > 0.05). (3) No significant differences of relative intensity of fluorescence in cells were found among the three groups before the tetanus stimulation. However, the significantly low relative intensity of fluorescence in cells was seen in MVAD (65.1 +/- 17.0) and VAI (85.8 +/- 17.1) groups compared with control group (113.6 +/- 20.5) after the tetanus stimulation (P < 0.01), and that of VAI group was higher than that of MVAD group (P < 0.05)., Conclusion: MVAD beginning from embryonic period impairs learning, memory and LTP in young rats. But the losses might not be reversible if the vitamin A supplementation is late especially missing the critical period of hippocampus development. According to the experimental data, it is speculated that vitamin A may modulate the influx of calcium ion to influence the LTP and lead to the change of learning and memory.

Aim: To investigate the effect of uncaria on evoked field potential of CA1 hippocampal slice in epileptogenic model., Methods: We made rats which were injected by pilocarpine as epileptic-models. The pathway of drug administration is titration adjacent to hippocampal slices. We recorded the evoked field potential of hippocampal slice by glass microelectrode extracellularly, and observed the effect of uncaria on the amplitude of population spike (PS) in CA1 pyramidal cells in hippocampal slices., Results: The uncaria with concentration of 1 g/ml could reduce the amplitude of PS in CA1 of hippocampal slices. The average of fall was 27.64%, and restored in 8.71 minutes on average (n = 14, P < 0.01)., Conclusion: Uncaria could reduce the amplitude of PS in CA1 of epileptic hippocampal slices remarkably. These results show that uncaria can inhabited the synaptic transfer activity of CNS remarkably, suggest that it has the distinct effect of anti-epilepsy.