448 research outputs found
Assessing seizure liability in vitro with voltage-sensitive dye imaging in mouse hippocampal slices
Non-clinical toxicology is a major cause of drug candidate attrition during development. In particular, drug-induced seizures are the most common finding in central nervous system (CNS) toxicity. Current safety pharmacology tests for assessing CNS functions are often inadequate in detecting seizure-inducing compounds early in drug development, leading to significant delays. This paper presents an in vitro seizure liability assay using voltage-sensitive dye (VSD) imaging techniques in hippocampal brain slices, offering a powerful alternative to traditional electrophysiological methods. Hippocampal slices were isolated from mice, and VSD optical responses evoked by stimulating the Schaffer collateral pathway were recorded and analyzed in the stratum radiatum (SR) and stratum pyramidale (SP). VSDs allow for the comprehensive visualization of neuronal action potentials and postsynaptic potentials on a millisecond timescale. By employing this approach, we investigated the in vitro drug-induced seizure liability of representative pro-convulsant compounds. Picrotoxin (PiTX; 1–100 μM), gabazine (GZ; 0.1–10 μM), and 4-aminopyridine (4AP; 10–100 μM) exhibited seizure-like responses in the hippocampus, but pilocarpine hydrochloride (Pilo; 10–100 μM) did not. Our findings demonstrate the potential of VSD-based assays in identifying seizurogenic compounds during early drug discovery, thereby reducing delays in drug development and providing insights into the mechanisms underlying seizure induction and the associated risks of pro-convulsant compounds
Electrophysiological studies on thermoreception in paramecium caudatum
Thesis (Ph.D. in Science)--University of Tsukuba, (A), no. 1190, 1994.3.2
ラット大脳皮質における電位オシレーターを駆動するための状況に応じた戦略
Information integration in the brain requires functional connectivity between local neural networks. Here, we investigated the interregional coupling mechanism from the viewpoint of oscillations using optical recording methods. Low-frequency electrical stimulation of rat neocortical slices in a caffeine-containing medium induced oscillatory activity between the primary visual cortex (Oc1) and medial secondary visual cortex (Oc2M), in which the oscillation generator was located in the Oc2M and was triggered by a feedforward signal. During to-and-fro oscillatory activity, neural excitation was marked in layer II/III. When the upper layer was disrupted between Oc1 and Oc2M, feedforward signals could propagate through the deep layer and switch on the oscillator in the Oc2M. When the lower layer was disrupted between Oc1 and Oc2M, feedforward signals could propagate through the upper layer and switch on the oscillator in the Oc2M. In the backward direction, neither the upper layer cut nor the lower layer cut disrupted the propagation of the oscillations. In all cases, the horizontal and vertical pathways were used as needed. Fluctuations in the oscillatory waveforms of the local field potential at the upper and lower layers in the Oc2M were reversed, suggesting that the oscillation originated between the two layers. Thus, the neocortex may work as a safety device for interregional communications in an alternative way to drive voltage oscillators in the neocortex
Network Plasticity Involved in the Spread of Neural Activity Within the Rhinal Cortices as Revealed by Voltage-Sensitive Dye Imaging in Mouse Brain Slices
The rhinal cortices, such as the perirhinal cortex (PC) and the entorhinal cortex (EC), are located within the bidirectional pathway between the neocortex and the hippocampus. Physiological studies indicate that the perirhinal transmission of neocortical inputs to the EC occurs at an extremely low probability, though many anatomical studies indicated strong connections exist in the pathway. Our previous study in rat brain slices indicated that an increase in excitability in deep layers of the PC/EC border initiated the neural activity transfer from the PC to the EC. In the present study, we hypothesized that such changes in network dynamics are not incidental observations but rather due to the plastic features of the perirhinal network, which links with the EC. To confirm this idea, we analyzed the network properties of neural transmission throughout the rhinal cortices and the plastic behavior of the network by performing a single-photon wide-field optical recording technique with a voltage-sensitive dye (VSD) in mouse brain slices of the PC, the EC, and the hippocampus. The low concentration of 4-aminopyridine (4-AP; 40 μM) enhanced neural activity in the PC, which eventually propagated to the EC via the deep layers of the PC/EC border. Interestingly, washout of 4-AP was unable to reverse entorhinal activation to the previous state. This change in the network property persisted for more than 1 h. This observation was not limited to the application of 4-AP. Burst stimulation to neurons in the perirhinal deep layers also induced the same change of network property. These results indicate the long-lasting modification of physiological connection between the PC and the EC, suggesting the existence of plasticity in the perirhinal-entorhinal network
Overall Assay of Neuronal Signal Propagation Pattern With Long-Term Potentiation (LTP) in Hippocampal Slices From the CA1 Area With Fast Voltage-Sensitive Dye Imaging
Activity-dependent changes in the input-output (I-O) relationship of a neural circuit are central in the learning and memory function of the brain. To understand circuit-wide adjustments, optical imaging techniques to probe the membrane potential at every component of neurons, such as dendrites, axons and somas, in the circuit are essential. We have been developing fast voltage-sensitive dye (VSD) imaging methods for quantitative measurements, especially for single-photon wide-field optical imaging. The long-term continuous measurements needed to evaluate circuit-wide modifications require stable and quantitative long-term recordings. Here, we show that VSD imaging (VSDI) can be used to record changes in circuit activity in association with theta-burst stimulation (TBS)-induced long-term potentiation (LTP) of synaptic strength in the CA1 area. Our optics, together with the fast imaging system, enabled us to measure neuronal signals from the entire CA1 area at a maximum frame speed of 0.1 ms/frame every 60 s for over 12 h. We also introduced a method to evaluate circuit activity changes by mapping the variation in recordings from the CA1 area to coordinates defined by the morphology of CA1 pyramidal cells. The results clearly showed two types of spatial heterogeneity in LTP induction. The first heterogeneity is that LTP increased with distance from the stimulation site. The second heterogeneity is that LTP is higher in the stratum pyramidale (SP)-oriens region than in the stratum radiatum (SR). We also showed that the pattern of the heterogeneity changed according to the induction protocol, such as induction by TBS or high-frequency stimulation (HFS). We further demonstrated that part of the heterogeneity depends on the I-O response of the circuit elements. The results show the usefulness of VSDI in probing the function of hippocampal circuits
Electron-capture supernovae exploding within their progenitor wind
The most massive stars on the asymptotic giant branch (AGB), so called
super-AGB stars, are thought to produce supernovae (SNe) triggered by electron
captures in their degenerate O+Ne+Mg cores. Super-AGB stars are expected to
have slow winds with high mass-loss rates, so their wind density is high. The
explosions of super-AGB stars are therefore presumed to occur in this dense
wind. We provide the first synthetic light curves (LCs) for such events by
exploding realistic electron-capture supernova (ecSN) progenitors within their
super-AGB winds. We find that the early LC, i.e. before the recombination wave
reaches the bottom of the H-rich envelope of SN ejecta (the plateau phase), is
not affected by the dense wind. However, after the plateau phase, the
luminosity remains higher when the super-AGB wind is taken into account. We
compare our results to the historical LC of SN 1054, the progenitor of the Crab
Nebula, and show that the explosion of an ecSN within an ordinary super-AGB
wind can explain the LC features. We conclude that SN 1054 could have been a
Type IIn SN without any extra extreme mass loss which was previously suggested
to be necessary to account for its early high luminosity. We also show that our
LCs match Type IIn SNe with an early plateau phase (`Type IIn-P') and suggest
that they are ecSNe within super-AGB winds. Although some ecSNe can be bright
in the optical spectral range due to the large progenitor radius, their X-ray
luminosity from the interaction does not necessarily get as bright as other
Type IIn SNe whose optical luminosities are also powered by the interaction.
Thus, we suggest that optically-bright X-ray-faint Type IIn SNe can emerge from
ecSNe. Optically-faint Type IIn SNe, such as SN 2008S, can also originate from
ecSNe if their H-rich envelope masses are small. Some of them can be observed
as `Type IIn-b' SNe due to the small H-rich envelope mass.Comment: 8 pages, 6 figures, accepted by Astronomy & Astrophysics, abstract
abridge
Evolution of newly formed dust in Population III supernova remnants and its impact on the elemental composition of Population II.5 stars
We investigate the evolution of dust formed in Population III supernovae
(SNe) by considering its transport and processing by sputtering within the SN
remnants (SNRs). We find that the fates of dust grains within SNRs heavily
depend on their initial radii . For Type II SNRs expanding into
the ambient medium with density of cm, grains of
m are detained in the shocked hot gas and are
completely destroyed, while grains of m are injected
into the surrounding medium without being destroyed significantly. Grains with
= 0.05-0.2 m are finally trapped in the dense shell behind
the forward shock. We show that the grains piled up in the dense shell enrich
the gas up to 10 , high enough to form low-mass stars
with 0.1-1 . In addition, [Fe/H] in the dense shell ranges from -6 to
-4.5, which is in good agreement with the ultra-metal-poor stars with [Fe/H] <
-4. We suggest that newly formed dust in a Population III SN can have great
impacts on the stellar mass and elemental composition of Population II.5 stars
formed in the shell of the SNR.Comment: 5 pages, 3 figures and 1 table. To appear in the proceedings of IAU
Symposium 255 "Low-Metallicity Star Formation: From the First Stars to Dwarf
Galaxies", Rapallo, June 2008, eds. L.K. Hunt, S. Madden, & R. Schneider
(Cambridge Univ. Press
Euclid detectability of pair instability supernovae in binary population synthesis models consistent with merging binary black holes
We infer the expected detection number of pair instability supernovae (PISNe)
during the operation of the Euclid space telescope, based on two binary
population models that are consistent with binary black holes (BHs) observed by
gravitational waves. The two models consider different PISN criteria depending
on the CO reaction rate. The fiducial and
models adopt the standard and -smaller CO reaction rate, which predicts that stars with helium core masses
and cause PISNe, respectively. Our fiducial
model predicts that Euclid detects several Type I or hydrogen-poor PISNe. For
the model, detection of Type I PISN by Euclid is expected if
the stellar mass distribution extends to , but the
expected number becomes significantly smaller if .
Thus, we may be able to prove or distinguish the fiducial and models
by the observed PISN rate. This will help us to constrain the origin of binary
BHs and the CO reaction rate. PISN ejecta mass
estimates from light curves and spectra obtained by follow-up observations
would also be important to constrain the CO
reaction rate.Comment: 4 pages, 4 figures, submitte
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