Design of a analog front-end for high-precision acquiring excitatory postsynaptic field potentials in the hippocampal Schaffer-CA1 neuronal pathway

The return of the spike: postsynaptic action potentials and the induction of LTP and LTD.

Spike-Timing-Dependent Potentiation of Sensory Surround in the Somatosensory Cortex Is Facilitated by Deprivation-Mediated Disinhibition

Bidirectional Plasticity Gated by Hyperpolarization Controls the Gain of Postsynaptic Firing Responses at Central Vestibular Nerve Synapses

The complementary nature of long-term depression and potentiation revealed by dual component excitatory postsynaptic potentials in hippocampal slices from young rats.

The present study examines changes in field excitatory postsynaptic potential (EPSP) waveform in association with long-term potentiation (LTP) in the CA1 region of the hippocampal slice preparation. Experiments were performed in the presence of the GABAA-antagonist picrotoxin. With test field EPSP about one-third the size of that evoking spike activity (measured in the cell body layer along the same somatodendritic axis as the dendritic recording) a decreased decay time constant (approximately 8%) was seen in association with LTP. This change in field EPSP waveform was not associated with any apparent spike activity in the cell body recording. Nevertheless, several findings suggest that increased spike activity explains the change in the decay time constant of the field EPSP during LTP. First, when reducing the stimulation strength after the induction of LTP to obtain a field EPSP of the same magnitude as the pretetanus one, the change of the decay time constant was reduced to only 2.8%. Second, when using small test field EPSP (about one-fourth the size of that evoking spike activity) the decay time constant was not significantly affected in association with LTP. Third, when cutting the slice in such a manner that spike activity originating from somatic regions closer to the stimulating electrode was removed, the EPSPs decay time constant was not significantly affected in association with LTP. It is concluded that LTP is not associated with a change in the shape of the field EPSP.

1. Long-term potentiation (LTP) of synaptic efficacy comprises two components: a synaptic component consisting of increased field excitatory postsynaptic potentials (EPSPs), and a component consisting of a larger population spike amplitude for a given EPSP size (E-S potentiation). In hippocampal CA1 neurons, delivery of three weak bursts (5 pulses at 100 Hz, 20 min intervals) induced LTP in both the EPSP and E-S components. In the same cells, reversal of LTP (depotentiation, DP) in the field EPSP and the E-S component was achieved by delivering three trains of low-frequency stimuli (LFS; 200 pulses at 1 Hz, 20 min intervals). 2. The effects of adenosine A1 and A2 receptor antagonists on the synaptic and E-S components of LTP and DP in CA1 neurons were studied by perfusing guinea-pig hippocampal slices with either 8-cyclopentyltheophylline (8-CPT) or CP-66713. 3. When bursts or LFS were applied to CA1 inputs in the presence of the A1 receptor antagonist 8-CPT, the field EPSP was enhanced in LTP and attenuated in DP, while the E-S relationship was not significantly affected in either LTP or DP. 4. When similar experiments were performed using the A2 receptor antagonist CP-66713, the field EPSP was blocked in LTP, but facilitated in DP, while E-S potentiation was enhanced during both LTP and DP. 5. The results show that A1 and A2 adenosine receptors modulate both the synaptic and E-S components of the induction and reversal of LTP. Based on these results, we discuss the key issue of the contribution of these receptors to the dynamics of neuronal plasticity modification in hippocampal CA1 neurons.

<strong>Objective</strong> In the present experiment we investigate the behavior of 4-month-old transgenic <em>APP/PS-1/tau </em>mice model with Alzheimer's disease (3 × Tg-AD mice) to evaluate their abilities of spatial learning and memory. We observe the changes of synaptic plasticity and soluble amyloid-β protein 42 (Aβ42) expression in the CA1 region of hippocampus to explore the mechanism of early cognitive impairment of 3 × Tg-AD mice. <strong>Methods</strong> Ten 4-month-old male 3 × Tg-AD mice and matched ten 129/C57BL/6 hybrid wild type (WT) mice were enrolled. The open field test and Morris water maze test were conducted to observe emotion disorder and ability of spatial learning and memory. Field excitatory postsynaptic potential (fEPSP) and theta burst stimulation (TBS)-induced long-term potentiation (LTP) were recorded in CA1 region of hippocampus. The expression changes of soluble Aβ42 in hippocampus were measured by enzyme-linked immunosorbent assay (ELISA). <strong>Results</strong> The open field test showed that there was no significant differences between 3 × Tg-AD group and control group, which indicated that there was no obvious anxiety tendency in 4-month-old 3 × Tg-AD mice. Compared with control group, 3 × Tg-AD group mice had significantly longer escape latency from the 3rd to 5th day (P = 0.001, 0.003, 0.001) and lower percentage of time through the platform area (P = 0.000). LTP induced by TBS in CA1 region of hippocampus of 3 × Tg-AD group decreased significantly (P &lt; 0.01, for all) compared with that of control group. In contrast to control group, the expression of soluble Aβ42 in the hippocampus of 3 × Tg-AD mice group increased significantly (P = 0.000). <strong>Conclusions</strong> The expression of soluble Aβ42 in the hippocampus of 4-month-old 3 × Tg-AD mice increased significantly, which impaired synaptic plasticity in CA1 region of hippocampus and led to a significant decline in spatial learning and memory ability. <strong>DOI: </strong>10.3969/j.issn.1672-6731.2015.05.012

Neprilysin-sensitive Synapse-associated Amyloid-β Peptide Oligomers Impair Neuronal Plasticity and Cognitive Function

Hypoxia-inducible factors (HIFs) are key transcriptional regulators that play a major role in oxygen homeostasis. HIF activity is tightly regulated by oxygen-dependent hydroxylases, which additionally require iron and 2-oxoglutarate as cofactors. Inhibition of these enzymes has become a novel target to modulate the hypoxic response for therapeutic benefit. Inhibition of prolyl-4-hydroxylase domains (PHDs) have been shown to delay neuronal cell death and protect against ischemic injury in the hippocampus. In this study we have examined the effects of prolyl hydroxylase inhibition on synaptic transmission and plasticity in the hippocampus. Field excitatory postsynaptic potentials (fEPSPs) and excitatory postsynaptic currents (EPSCs) were elicited by stimulation of the Schaffer collateral pathway in the CA1 region of the hippocampus. Treatment of rat hippocampal slices with low concentrations (10 µM) of the iron chelator deferosoxamine (DFO) or the 2-oxoglutarate analogue dimethyloxalyl glycine (DMOG) had no effect on fEPSP. In contrast, application of 1 mM DMOG resulted in a significant decrease in fEPSP slope. Antagonism of the NMDA receptor attenuated the effects of DMOG on baseline synaptic signalling. In rat hippocampal slices pretreated with DMOG and DFO the induction of long-term potentiation (LTP) by tetanic stimulation was strongly impaired. Similarly, neuronal knockout of the single PHD family member PHD2 prevented murine hippocampal LTP. Preconditioning of PHD2 deficient hippocampi with either DMOG, DFO, or the PHD specific inhibitor JNJ-42041935, did not further decrease LTP suggesting that DMOG and DFO influences synaptic plasticity primarily by inhibiting PHDs rather than unspecific effects. These findings provide striking evidence for a modulatory role of PHD proteins on synaptic plasticity in the hippocampus.

The induction of long-term potentiation at CA3-CA1 synapses is caused by an N-methyl-d-aspartate (NMDA) receptordependent accumulation of intracellular Ca(2+), followed by Src family kinase activation and a positive feedback enhancement of NMDA receptors (NMDARs). Nevertheless, the amplitude of baseline transmission remains remarkably constant even though low frequency stimulation is also associated with an NMDAR-dependent influx of Ca(2+) into dendritic spines. We show here that an interaction between C-terminal Src kinase (Csk) and NMDARs controls the Src-dependent regulation of NMDAR activity. Csk associates with the NMDAR signaling complex in the adult brain, inhibiting the Src-dependent potentiation of NMDARs in CA1 neurons and attenuating the Src-dependent induction of long-term potentiation. Csk associates directly with Src-phosphorylated NR2 subunits in vitro. An inhibitory antibody for Csk disrupts this physical association, potentiates NMDAR mediated excitatory postsynaptic currents, and induces long-term potentiation at CA3-CA1 synapses. Thus, Csk serves to maintain the constancy of baseline excitatory synaptic transmission by inhibiting Src kinase-dependent synaptic plasticity in the hippocampus.

Objective To evaluate the effect of hypoxemia factor on hippocampal long-term potentiation(LTP)in newborn rats undergoing propofol anesthesia. Methods Forty-two pathogen-free healthy Sprague-Dawley rats(21 males, 21 females), aged 7 days, weighing 14-18 g, were divided into 3 groups(n=14 each)using a random number table: propofol plus air group(group PA), propofol plus pure oxygen group(group PO)and intralipid plus pure oxygen group(group IO). Propofol 50 mg/kg was injected intraperitoneally once a day for 7 consecutive days in PA and PO groups. Intralipid 5.0 ml/kg was injected intraperitoneally once a day for 7 consecutive days in IO group. The rats were exposed to air or pure oxygen for 6 h after the end of each injection. The arterial oxygen saturation and respiratory rate were determined after administration. The rats were returned to the cage after recovery of righting reflex. Six rats in each group were selected for preparation of hippocampal slices at 24 h after the last injection on 7th day, and the electric stimulation-induced field excitatory post synaptic potential(fEPSP)and success rate of LTP induction were recorded. Morris water maze test was performed in the other rats at 2 weeks after administration to assess the cognitive function. Results Compared with group IO, the respiratory rate, amplitude of fEPSP and success rate of LTP induction were significantly decreased, and the escape latency was prolonged in group PO(P<0.05). Compared with group PO, the arterial oxygen saturation, amplitude of fEPSP and success rate of LTP induction were significantly decreased, the escape latency was prolonged, and the number of crossing the original platform was decreased in group PA(P<0.05). Conclusion Hypoxemia factor increases propofol-induced neurotoxicity in the central nervous system of newborn rats. Key words: Oxygen; Propofol; Hippocampus; Long-term potentiation; Cognition

Associative Hebbian-type synaptic plasticity underlies the mechanisms of learning and memory; however, Hebbian learning rules lead to runaway dynamics of synaptic weights and lack mechanisms for synaptic competition.Heterosynaptic plasticity may solve these problems by complementing plasticity at synapses that were active during the induction, with opposite-sign changes at non-activated synapses. In visual cortex, a potential candidate mechanism for normalization is plasticity induced by a purely postsynaptic protocol, intracellular tetanization. Here we asked if intracellular tetanization can induce long-term plasticity in auditory cortex. We recorded excitatory postsynaptic potentials (EPSPs) of regular (n =76) and all-or-none (n =24) type in layer 2/3 pyramidal cells in slices from rat auditory cortex. After intracellular tetanization, 32 of 76 regular inputs (42%) showed long-term depression, 21 inputs (28%) showed potentiation and 23 inputs (30%) did not change. The direction of plasticity correlated with the initial release probability: inputs with initially low release probability tended to be potentiated, while inputs with high release probability tended to be depressed. Thus, intracellular tetanization had a normalizing effect on synaptic efficacy. Induction of plasticity by intracellular tetanization required a rise of intracellular [Ca(2+)], because it was impaired by chelating intracellular calcium with EGTA. The long-term changes induced by intracellular tetanization involved both pre and postsynaptic mechanisms. EPSP amplitude changes were correlated with changes of release indices: paired-pulse ratio and the inverse of the coefficient of variation (CV(-2)). Furthermore at some all-or-none synapses, changes of averaged response amplitude were correlated with a change of the failure rate, without a change of the synaptic potency, measured as averaged amplitude of successful responses. Presynaptic components of plastic changes were abolished in experiments with blockade of NO-synthesis and spread, indicating involvement of NO signalling. These results demonstrate that the ability of purely postsynaptic challenges to induce plasticity is a general property of pyramidal neurons of both auditory and visual cortices.

Learning to Encode Timing: Mechanisms of Plasticity in the Auditory Brainstem

Objective To investigate the effects of repeated high frequency transcranial magnetic stimulation (rTMS) on spatial learning and memory function,and on long-term potentiation (LTP) after global cerebral ischemia and reperfusion,and to explore the mechanisms involved.Methods Eighty-three male Wistar rats were studied.Five were tested to determine their average motor threshold (Tm).The others were divided into a normal control group,a cerebral ischemia and reperfusion model group and an rTMS group.Cerebral ischemia was induced with the four vessel occlusion method for 10 minutes.The rTMS treatment protocol (10 Hz stimulation for 5 s at the resting threshold,twice a day) was applied over a 2-week period from day 3 post-operation.The Morris water maze test was performed to observe spatial learning and memory at post-operation day 2 and day 4.The field excitatory postsynaptic potentials,population spike and the magnitude of long-term potentiation (LTP) induced by theta burst electric stimulation were recorded from the perforant path to the dentate gyrus (PP-DG).Results At post-operation day 3,rats in the untreated cerebral ischemia and reperfusion model group exhibited a significant decrease in the magnitude of the PP-DG LTP as compared to the normal group.No significant difference in LTP was found between the model group and the rTMS group.After the 2 weeks of treatment the LTP levels in the rTMS treated group were significantly higher than in the two untreated groups.In the Morris water maze testing,the average escape latency in the rTMS group was significantly shorter than that of the cerebral ischemia and reperfusion model group (which was not treated).In the probe trials,the time in the original quadrant of the platform and the time of crossing the platform were both significantly less for the rTMS-treated rats than for those not treated.Conclusions High frequency rTMS can improve spatial learning and memory after global cerebral ischemia and reperfusion by enhancing the LTP induced in the hippocampus.High frequency rTMS might exert this beneficial effect by modulating the function of intermediate neurons in the hippocampal neuronal network and by promoting neurotransmitter release. Key words: Transcranial magnetic stimulation; Cerebral ischemia; Spatial learning; Memory; Long-term potentiation

The entorhinal cortex projects monosynaptically to the granule cells in the dentate gyrus via the lateral and medial perforant paths. These two subdivisions of the perforant path differ with respect to synaptic properties, and recent studies suggest that they also differ with respect to long-term potentiation (LTP). In the present study, using the in vitro slice preparation of the guinea-pig hippocampus, field excitatory postsynaptic potentials (EPSPs) and LTP in the lateral and medial perforant paths were compared. The two pathways were distinguished on the basis of their different termination in the dendritic layer, their different pharmacology and short-term synaptic facilitation. The field EPSP [obtained in the presence of gamma-aminobutyric acid (GABA) A and B receptor antagonists] consisted of a non-N-methyl-d-aspartate (NMDA) component with different time characteristics in the two pathways, the decay being monoexponential in the lateral perforant path and biexponential in the medial one. In addition, the field EPSP in both pathways contained a small NMDA-mediated component that could also be observed after complete blockade of the non-NMDA one. LTP induction in both lateral and medial perforant paths was facilitated by blockade of GABAA inhibition, showed associative properties, and was blocked by NMDA receptor antagonists. Following the induction event, LTP in both pathways developed to a peak value within 30 - 40 s, and the stability of LTP was correlated with the amount of postsynaptic, but not presynaptic, activity during the induction event. During blockade of GABAA inhibition the opioid receptor antagonist naloxone and the beta-adrenergic antagonist timolol had no effect on the magnitude or stability of LTP. It is concluded that LTP in the lateral and medial perforant paths does not differ with respect to induction mechanisms and early temporal characteristics.