Establishment of a Method for the Introduction of Poorly Water-Soluble Drugs in Cells and Evaluation of Intracellular Concentration Distribution Using Resonance Raman Imaging

Label-free measurement is essential to understand the metabolism of drug molecules introduced into cells. Raman imaging is a powerful method to investigate intracellular drug molecules because it provides in situ label-free observation of introduced molecules. In this study, we propose that Raman imaging can be used not only to observe the intracellular distribution of drug molecules but also to quantitatively visualize the concentration distribution reflecting each organelle in a single living cell using the Raman band of extracellular water as an intensity standard. We dissolved poorly water-soluble all-trans-retinoic acid (ATRA) in water using a cytocompatible amphiphilic phospholipid polymer, poly[2-methacryloyloxyethyl phosphorylcholine-co-n-butyl methacrylate] (PMB) as a solubilizing reagent, introduced it into cells, and obtained the intracellular concentration distribution of ATRA. ATRA was concentrated in the cells and mainly localized to mitochondria and lipid droplets, interacting strongly with mitochondria and weakly with lipid droplets. Poorly water-soluble β-carotene was also introduced into cells using PMB but was not concentrated intracellularly, indicating that β-carotene does not interact specifically with intracellular molecules. We established a protocol for the solubilization and intracellular uptake of poorly water-soluble molecules using PMB and obtaining their concentration distribution using Raman microscopy.

Ratiometric analysis of reversible thia-Michael reactions using nitrile-tagged molecules by Raman microscopy

Ratiometric Raman analysis of reversible thia-Michael reactions was achieved using α-cyanoacrylic acid (αCNA) derivatives. Among αCNAs, the smallest derivative, ThioRas (molecular weight: 167 g mol-1), and its glutathione adduct were simultaneously detected in various subcellular locations using Raman microscopy.

Multiple deuteration of triphenylphosphine and live-cell Raman imaging of deuterium-incorporated Mito-Q

All aromatic C-H bonds of triphenylphosphine (PPh3) were efficiently replaced by C-D bonds using Ru/C and Ir/C co-catalysts in 2-PrOH and D2O, an inexpensive deuterium source. Furthermore, non-radioactive and safe deuterium-incorporated Mito-Q (drug candidate) was prepared from deuterated PPh3 and used for the live-cell Raman imaging to evaluate the mitochondrial uptake.

Label-Free Tracking of Nanoprodrug Cellular Uptake and Metabolism Using Raman and Autofluorescence Imaging

Nano-DDS, a drug delivery system using nanoparticles, is a promising tool to reduce adverse drug reactions and maximize drug efficiency. Understanding the intracellular dynamics following the accumulation of nanoparticles in tissues, such as cellular uptake, distribution, metabolism, and pharmacological effects, is essential to maximize drug efficiency; however, it remains elusive. In this study, we tracked the intracellular behavior of nanoparticles of a prodrug, cholesterol-linked SN-38 (CLS), in a label-free manner using Raman and autofluorescence imaging. Bright autofluorescent spots were observed in cells treated with CLS nanoparticles, and the color tone of the bright spots changed with incubation time. The Raman spectra of the bright spots showed that the autofluorescence came from the nanoparticles taken into cells, and the change in color of bright spots indicated that CLS turned into SN-38 via hydrolysis inside a cell. It was found that most of the SN-38 were localized in small regions in the cytoplasm even after the conversion from CLS, and only a small amount of SN-38 was dissolved and migrated into other cytoplasm regions and the nucleus. The massive size growth of cells was observed within several tens of hours after the treatment with CLS nanoparticles. Moreover, Raman images of cells using the cytochrome c band and the fluorescence images of cells stained with JC-1 showed that cellular uptake of CLS nanoparticles efficiently caused mitochondrial damage. These results show that the combination of Raman and autofluorescence imaging can provide insight into the intracellular behavior of prodrug nanoparticles and the cell response and facilitate the development of nano-DDSs.

Label-free autofluorescence lifetime reveals the structural dynamics of ataxin-3 inside droplets formed via liquid-liquid phase separation

Liquid-liquid phase separation is a phenomenon that features the formation of liquid droplets containing concentrated solutes. The droplets of neurodegeneration-associated proteins are prone to generate aggregates and cause diseases. To uncover the aggregation process from the droplets, it is necessary to analyze the protein structure with keeping the droplet state in a label-free manner, but there was no suitable method. In this study, we observed the structural changes of ataxin-3, a protein associated with Machado-Joseph disease, inside the droplets, using autofluorescence lifetime microscopy. Each droplet showed autofluorescence due to tryptophan (Trp) residues, and its lifetime increased with time, reflecting structural changes toward aggregation. We used Trp mutants to reveal the structural changes around each Trp and showed that the structural change consists of several steps on different timescales. We demonstrated that the present method visualizes the protein dynamics inside a droplet in a label-free manner. Further investigations revealed that the aggregate structure formed in the droplets differs from that formed in dispersed solutions and that a polyglutamine repeat extension in ataxin-3 hardly modulates the aggregation dynamics in the droplets. These findings highlight that the droplet environment facilitates unique protein dynamics different from those in solutions.

Concentration Quantification of the Low-Complexity Domain of Fused in Sarcoma inside a Single Droplet and Effects of Solution Parameters

Liquid-liquid phase separation (LLPS) is an important phenomenon in biology, and it is desirable to develop quantitative methods to analyze protein droplets generated by LLPS. This study quantified the change in protein concentration in a droplet in label-free and single-droplet conditions using Raman imaging and the Raman band of water as an intensity standard. Small changes in the protein concentration with variations in pH and salt concentration were observed, and it was shown that the concentration in the droplet decreases as the conditions become less favorable for droplet formation. The effect of exposure to 1,6-hexanediol was also examined, and this additive was found to decrease the protein concentration in the droplet. A model can be proposed in which the addition of 1,6-hexanediol reduces the protein concentration in the droplet, and the droplet disappears when the concentration falls below a certain threshold value.

Regulation of Cell Volume by Nanosecond Pulsed Electric Fields

Stimulation of cells by nanosecond pulsed electric fields (nsPEFs) has attracted attention as a technology for medical applications such as cancer treatment. nsPEFs have been shown to affect intracellular environments without significant damage to cell membranes; however, the mechanism underlying the effect of nsPEFs on cells remains unclear. In this study, we constructed electrodes for applying nsPEFs and analyzed the change in volume of a single cell due to nsPEFs using fluorescence and Raman microscopy. It was shown that the direction of the change depended on the applied electric field; expansion due to the influx of water was observed at high electric field, and cell shrinkage was observed at low electric field. The change in cell volume was correlated to the change in the intracellular Ca²⁺ concentration, and nsPEFs-induced shrinking was not observed when the Ca²⁺-free medium was used. This result suggests that the cell shrinkage is related to the regulatory volume decrease where the cell adjusts the increase in intracellular Ca²⁺ concentration, inducing the efflux of ions and water from the cell.

Observation of liquid-liquid phase separation of ataxin-3 and quantitative evaluation of its concentration in a single droplet using Raman microscopy

Liquid-liquid phase separation (LLPS) plays an important role in a variety of biological processes and is also associated with protein aggregation in neurodegenerative diseases. Quantification of LLPS is necessary to elucidate the mechanism of LLPS and the subsequent aggregation process. In this study, we showed that ataxin-3, which is associated with Machado-Joseph disease, exhibits LLPS in an intracellular crowding environment mimicked by biopolymers, and proposed that a single droplet formed in LLPS can be quantified using Raman microscopy in a label-free manner. We succeeded in evaluating the protein concentration and identifying the components present inside and outside a droplet using the O-H stretching band of water as an internal intensity standard. Only water and protein were detected to be present inside droplets with crowding agents remaining outside. The protein concentration in a droplet was dependent on the crowding environment, indicating that the protein concentration and intracellular environment should be considered when investigating LLPS. Raman microscopy has the potential to become a powerful technique for clarifying the chemical nature of LLPS and its relationship with protein aggregation.

Observation of the changes in the chemical composition of lipid droplets using Raman microscopy

We report the dynamics of lipid droplet formation induced by introducing cis- and/or trans-fatty acids into cells. Raman imaging allows the chemical analysis of each droplet, showing that exogenous fatty acids initially enter original endogenous droplets, then induce additional droplets containing endogenous lipids, and finally form their droplets.

Time-Resolved Structured Illumination Microscopy for Phase Separation Dynamics of Water and 2-Butoxyethanol Mixtures: Interpretation of "Early Stage" Involving Micelle-Like Structures

Phase separation dynamics of a water/2-butoxyethanol (2BE) mixture was studied with newly developed time-resolved structured illumination microscopy (SIM). Interestingly, an employed hydrophobic fluorescent probe for SIM showed spectral shifts up to 500 ns after a laser-induced temperature jump, which suggests 2BE micellar-like aggregates become more hydrophobic at the initial stage of phase separation. This hydrophobic environment in 2BE aggregates, probably due to the ejection of water molecules, continued up to at least 10 μs. Time-resolved SIM and previously reported light scattering data clearly showed that the size of a periodic structure remained constant (ca. 300 nm) from 3 to 10 μs, and then the growth of periodic structures having the self-similarity started. We think that the former and the latter processes correspond to "early stage" (concentration growth) and "late stage" (size growth), respectively, in phase separation dynamics. Here we suggest that, in the early stage, the entity to bear 2BE phase be water-poor 2BE aggregates, and the number density of these aggregates would simply increase in time.

Raman Imaging Microscopy for Quantitative Analysis of Biological Samples

Raman imaging microscopy is a powerful tool for label-free imaging of biological samples. It has the advantage of measuring the spatial distribution of endogenous proteins and lipids in cells, as well as obtaining chemical information on these endogenous molecules, such as hydrogen bonding and electrostatic interactions. However, because Raman intensity is very weak compared with fluorescence intensity, obtaining a reliable Raman image requires fast acquisition of a Raman image and rejection of background fluorescence. In this chapter, we describe the procedure for obtaining images of the Raman band of interest using a multipoint technique, which is the fast acquisition method for obtaining an image.

Experimental Evaluation of the Density of Water in a Cell by Raman Microscopy

We report direct observation of a spatial distribution of water molecules inside of a living cell using Raman images of the O-H stretching band of water. The O-H Raman intensity of the nucleus was higher than that of the cytoplasm, indicating that the water density is higher in the nucleus than that in the cytoplasm. The shape of the O-H stretching band of the nucleus differed from that of the cytoplasm but was similar to that of the balanced salt solution surrounding cells, indicating less crowded environments in the nucleus. The concentration of biomolecules having C-H bonds was also estimated to be lower in the nucleus than that in the cytoplasm. These results indicate that the nucleus is less crowded with biomolecules than the cytoplasm.

Conformational changes in inhibitory PAS domain protein associated with binding of HIF-1α and Bcl-xL in living cells

Inhibitory PAS domain protein (IPAS) is a dual function protein acting as a transcriptional repressor and as a pro-apoptotic protein. Simultaneous dual-color single-molecule imaging of EGFP-IPAS coexpressed with Mit-TagRFP-T in living HeLa cells revealed that fraction of EGFP-IPAS was arrested in the nucleus and on mitochondria. Transiently expressed Cerulean-IPAS in HEK293T cells was present in nuclear speckles when coexpressed with Citrine-HIF-1α or Citrine-HLF. Fluorescence lifetime imaging microscopy (FLIM) analysis of Citrine-IPAS-Cerulean in living CHO-K1 cells clarified the presence of intramolecular FRET. Reduced lifetimes of the donor were partially restored by coexpression of HIF-1α or Bcl-xL, binding proteins of IPAS in the nucleus and mitochondria, respectively. This alteration in lifetimes demonstrates that conformational changes occurred in IPAS by their binding.

Phase behavior of a binary fluid mixture of quadrupolar molecules

We propose a model molecule to investigate microscopic properties of a binary mixture with a closed-loop coexistence region. The molecule is comprised of a Lennard-Jones particle and a uniaxial quadrupole. Gibbs ensemble Monte Carlo simulations demonstrate that the high-density binary fluid of the molecules with the quadrupoles of the same magnitude but of the opposite signs can show closed-loop immiscibility. We find that an increase in the magnitude of the quadrupoles causes a shrinkage of the coexistence region. Molecular dynamics simulations also reveal that aggregates with two types of molecules arranged alternatively are formed in the stable one-phase region both above and below the coexistence region. String structures are dominant below the lower critical solution temperature, while branched aggregates are observed above the upper critical solution temperature. We conclude that the anisotropic interaction between the quadrupoles of the opposite signs plays a crucial role in controlling these properties of the phase behavior.

Picosecond dynamics of hydrogen bond rearrangements during phase separation of a triethylamine and water mixture

A picosecond temperature jump experiment reveals that phase separation in a liquid triethylamine (TEA)–water mixture started from hydrogen bond scission of TEA–water aggregates in TEA-rich regions and then in water-rich regions.

A silver nanowire-based tip suitable for STM tip-enhanced Raman scattering

A chemically synthesized silver nanowire was used for atomic-resolution STM imaging and tip-enhanced Raman scattering (TERS) spectroscopy, yielding excellent reproducibility.

Nano-scale characterization of binary self-assembled monolayers under an ambient condition with STM and TERS

Gold surfaces were modified by benzyl-mercaptan (BM) and then partly replaced with benzenethiol (BT), which formed binary self-assembled monolayers (SAM).

Additive-free size-controlled synthesis of gold square nanoplates using photochemical reaction in dynamic phase-separating media

Ultrafast phase separation of water and 2-butoxyethanol mixture was induced by nanosecond IR laser pulse irradiation. After a certain delay time, a UV laser pulse was introduced to induce photoreduction of aurate ions, which led to the formation of gold nanoparticles in dynamic phase-separating media. The structure and size of the nanoparticles varied depending on the delay time between the IR and UV pulses. For a delay time of 5 and 6 μs, gold square plates having edge lengths of 150 and 100 nm were selectively obtained, respectively. With a delay time of 3 μs, on the other hand, the size of the square plates varied widely from 100 nm to a few micrometers. The size of the gold square plates was also varied by varying the total irradiation time of the IR and UV pulses. The size distribution of the square plates obtained under different conditions suggests that the growth process of the square plates was affected by the size of the nanophases during phase separation. Electron diffraction patterns of the synthesized square plates showed that the square plates were highly crystalline with a Au(100) surface. These results showed that the nanophases formed during laser-induced phase separation can provide detergent-free reaction fields for size-controlled nanomaterial synthesis.

Dynamics of Volume Expansion of De-Mixing Liquids after Pulsed IR Heating

Triethylamine (TEA)–water mixtures have a critical-temperature (Tc). Below Tc the mixture exists as one phase and above Tc it exists in two phases. The de-mixed volume is different to the mixed volume. A nanosecond pulsed-laser heated a TEA–water mixture so that it de-mixed. The resulting dynamics of volume expansion were monitored using interferometry. For T-jumps within the one phase region the dynamics of volume change were limited by the speed of sound. However, T-jumps between the one and two phase regions also manifested a slower volume change associated with the de-mixing process. After 150 ns, the volume of the de-mixed TEA–water was consistent with the equilibrium volume change. This suggests that, within 150 ns, the system had split into phase-domains having equilibrium compositions of TEA and water. Subsequently the phase domains would simply merge and grow resulting in no further volume change to reduce surface tension between the phases.

Photo-controlled phase separation and mixing of a mixture of water and 2-butoxyethanol caused by photochromic isomerisation of spiropyran

Photo induced phase separation of a mixture of water and 2-butoxyethanol, in which spiropyran was dissolved as a photoresponsive molecule, was investigated. It was found that the phase separation temperature of the merocyanine (MC) form solution was higher than that of the spiropyrane (SP) form; therefore phase separation was induced by visible light irradiation to the solution which caused the photoisomerization from the MC form to the SP form. The system also exhibits reversible photoinduced phase mixing by irradiation of UV light. The photo-chemical phase separation was also induced by the nanosecond laser pulse irradiation and the dynamics of the phase domain growth were studied.

Time-resolved brewster angle microscopy for photochemical and photothermal studies on thin-films and monolayers

Transient events in thin films and interfaces have been studied using the technique of time resolved pump-probe nanosecond Brewster angle microscopy. For p-polarized light there is a minimum reflectivity at the Brewster angle. When the interface is viewed with light that is both incident and reflected at the Brewster angle the resulting image is dark. Subsequent small changes is refractive index will then cause an increase in the reflectivity in affected regions providing high contrast images of an altered interface with a dark background level. This is the basis of Brewster angle microscopy. In the present work two synchronized nanosecond pulsed lasers were used in the pump-probe configuration in order to induce changes at an air-liquid interface and to monitor the resulting morphology changes over a range of time delays from nanosecond to milliseconds after laser-excitation. This method can be used to observe morphological changes in phase altering thin-films and molecular monolayers. Further it can be used to obtain information about transient photochemistry even in optically thin materials and nano-films. In the current work the method is used to monitor laser induced processes in phase separating binary liquid mixtures as well as in monolayers of photo-responsive amphiphilic molecules derived from spiropyran on water. The two systems are quite different but provide valuable comparisons.

Normal perfusion pressure hyperperfusion in cerebral arteriovenous malformation surgery: model study on the hemodynamics and mechanisms

A simulation study was undertaken using a compartmental flow model of a large high-flow cerebral arteriovenous malformation to investigate the hemodynamic changes during obliteration procedures. Under certain autoregulatory conditions, marked hyperperfusion (92 ml/100 g/min) could be induced in association with increased wall stress of the arterioles. Narrowing of the autoregulatory pressure range and its shift to a low pressure level are suspected to be among the possible causes of normal perfusion pressure breakthrough phenomenon.

Return to home early days after acute aortic dissection surgery

AIM

The length of hospital stay after acute aortic dissection surgery tends to be prolonged. The aim of this study is to assess the feasibility of our protocol for early discharge after acute aortic dissection surgery.

METHODS

This study enrolled 17 consecutive acute aortic dissection patients who returned to their own home within 2 weeks of surgery. In seven patients total aortic arch replacement was performed and in 7 partial arch replacement. The main aim of the first 24 h after surgery was to achieve early extubation. Patients were encouraged to return to their own home 4 days and later after surgery. The prerequisite criteria for discharge were the following: independent mobility, stable hemodynamics, apyrexia, adequate oral intake, normal bowel function, healthy surgical wound and the patient's agreement for discharge.

RESULTS

The mean age of these patients was 59. The postoperative ventilation time, length of intensive care unit stay and postoperative hospital stay were 11 h, 37 h and 6.9 days, respectively. Two (12%), 13 (76%) and 14 (82%) patients returned to their own home by postoperative day 4, 7 and 10, respectively. Three patients were readmitted to a peripheral hospital in the 4 week postoperative period. The reason for all readmissions was lack of family support. Two other patients underwent pericardiocentesis for pericardial effusion at an other hospital as outpatients. There was no complication caused by early discharge.

CONCLUSIONS

Early discharge after aortic dissection surgery is safe and recommended to patients who have normal bowel function and adequate family support.

Experimentally determined growth exponents during the late stage of spinodal demixing in binary liquid mixtures

Spinodal demixing was initiated in two systems, with critical and off-critical compositions, using nanosecond pulsed laser-induced temperature jumps (T-jumps) of various magnitude. In this way, deep quenches could be imposed on the systems. One system was the simple triethylamine (TEA)/water mixture and the other was the ionic mixture of 2-butoxyethanol (2BE)/water/KCl. The demixing process was followed using the technique of nanosecond time-resolved microscopic shadowgraphy. The growth of the evolving phase-separated domains followed a simple power law with respect to time in every case. For a given composition, the magnitude of the T-jump had little effect on the growth exponent, however the composition was found to influence the rate of domain growth. At off-critical mole fractions of 0.2 with respect to TEA, the domains grew according to the following expression: L(t)=t(0.70) (where L(t)= the domain size) whereas at the critical TEA mole fraction of 0.08 the domains grew as L(t)=t(0.52). 2BE/water/KCl mixtures quenched at the just off-critical composition of fraction with respect to 2BE evolved as L(t)=t(0.63). These results will be compared to theoretical models and simulations and discussed in terms of estimated Reynolds numbers as well as the consumption and conversion of the available surface energy that fuels the demixing process.

Dynamics of Re(2,2'-bipyridine)(CO)3Cl MLCT formation and decay after picosecond pulsed X-ray excitation and femtosecond UV excitation

The dynamics of Re(2,2'-bipyridine)(CO)3Cl MLCT state formation and decay were determined after femtosecond UV laser excitation and picosecond pulsed X-ray excitation, in an N,N-dimethylformamide (DMF) solution as well as in its solid form. At room temperature, after UV excitation, this MLCT excited state emits both in DMF solution and in the solid form. Transient absorption spectra were measured in solution at various delay times following excitation by a 160 fs, 390 nm laser pulse. There was a prompt absorption increase at around 460 nm occurring within the pump probe convolution (<1 ps), which was assigned to the formation of the 3MLCT state. This transient absorbance was constant over 100 ps. In contrast to the solution state, in the solid state, the emission maximum slightly red-shifts with increasing time after laser excitation. In both solid and solution the emission rises within the system response time. The solid sample exhibited a 1.4 ns emission decay that was not observed for the solution sample. The emission rise from a solid sample after 20 ps pulsed X-ray excitation was significantly slower than the system's time resolution. It is proposed that kinetically energetic electrons are ejected following X-ray induced ionisation, creating ionised tracks in which energetic cations and electrons take time to recombine yielding delayed 3MLCT states that emit.

Ultrafast laser-induced molecular and morphological changes during spinodal demixing of water/2-butoxyethanol/KCl

We initiated morphological and molecular level changes in the spinodal decomposition (SD) of H(2)O/2-butoxyethanol/KCl with a pulsed ir laser. Transient Raman spectra gave us a molecular level view of the early stage of this process that could be linked to later morphological events. Chemical changes during SD, such as reorganization of H bonds and forced hydrophobic interactions, ended after 1 micros; however, phase domains continued to grow with self-similarity after 30 micros. The growth of the phase domains satisfied the power law L(t) approximately t(0.55) and was consistent with the late stage of SD. The time scale for the onset of late stage SD is many orders of magnitude faster than previously reported in ionic and nonionic conditions.

Effects of ebselen on cerebral ischemia and reperfusion evaluated by microdialysis

Since ebselen is known to have glutathione peroxidase-like activity and inhibitory effects on lipoxygenase and cyclo-oxygenase, we investigated its protective effects against cerebral ischemia in the rat using microdialysis. Ebselen was given through a gastric tube 30 min before occlusion in the experimental groups. Ischemia was induced using 4-vessel occlusion either transiently (20-min occlusion of the arteries followed by reperfusion), or over a prolonged period (120-min occlusion). Extracellular lactate, pyruvate and purine catabolites were sampled using microdialysis and measured by high performance liquid chromatography. During ischemia, the level of lactate, adenosine, inosine and hypoxanthine in the control group increased markedly. The lactate: pyruvate ratio increased during ischemia and decreased after reperfusion. Although the level of lactate and adenosine decreased immediately after reperfusion, those of inosine and hypoxanthine showed delayed decrease. Ebselen reduced the maximum values of lactate and purine catabolites significantly and markedly in transient ischemia. Although it reduced the values significantly in prolonged ischemia, the decrements were less marked than those in transient ischemia. Based on these results we consider ebselen to protect against ischemic metabolic changes and to accelerate the recovery during reperfusion.

[Hemodynamic simulation study of cerebral arteriovenous malformations: changes of wall stress and early detection of NPPB]

Obliteration procedures for large high-flow arteriovenous malformations (AVM) were simulated using a compartmental flow model to investigate the role of altered autoregulatory conditions in the development of hyperperfusion and normal perfusion pressure breakthrough (NPPB). Since the arterioles are primarily responsible for autoregulatory function, the role of these structural changes on the development of hyperperfusion was also studied by evaluating the wall thickness (T), internal radius (Ri) and tangential wall stress (sigma). As the AVM flow was decreased during the obliteration procedures, the perfusion pressure (delta P) of the brain tissue surrounding the AVM increased. When the autoregulatory condition was impaired [AR (-)] and the lower limit of the autoregulatory pressure range (LAR) was shifted from 60 mmHg (LAR60) to 40 mm Hg (LAR40), the flow volume in the surrounding brain (Fb) increased markedly, from 67 ml/100g/min to 92 ml/100g/min, with the progress of the obliteration procedures. In these conditions, T/Ri was supposed to be constant and sigma value increased uniformly. In the presence of the autoregulatory mechanism [AR (+)], T/Ri increased against increasing delta P, which resulted in smaller sigma value than that under AR (-) conditions. When the contracted vascular wall yielded on the process of increasing wall stress, delta P and feeder pressure (Pf) decreased to some degree. Concomitantly increase of the sigma value and marked hyperperfusion developed in the brain. The yield of the contracted vascular wall would result in the decrease of a pressure gradient across the arteriole and the reciprocal increase of pressure load on the walls of the capillary and venula, which might lead to NPPB. Since the decrease of delta P or Pf during the progress of the obliterating procedures is considered specific to the appearance of hyperperfusion or NPPB, monitoring these parameters would be useful for its early detection. If the upper limit of the autoregulatory pressure range was assumed to decrease and become the yield point in the brain surrounding high flow AVMs, hyperfusion or NPPB could be considered to develop in the conditions with the autoregulatory pressure range being narrowed and/or shifted to the lower pressure level. Induced systemic hypotension was found to be effective in reducing the magnitude of Fb, delta P, and Pf when induction was appropriately performed in stepwise fashion. T/Ri and sigma were kept in narrow ranges compared to those before induction of hypotension.

Hemodynamic simulation study of cerebral arteriovenous malformations. Part 2. Effects of impaired autoregulation and induced hypotension

The hemodynamic changes occurring during obliteration procedures for arteriovenous malformations (AVM) have not been fully elucidated. Therefore, we undertook a simulation study using a compartmental flow model to investigate the role of altered autoregulatory conditions in the development of hyperperfusion during obliteration of large high-flow AVM. Induced hypotension was also simulated to evaluate its usefulness in reducing the incidence and severity of the event. As the AVM flow was decreased during the obliteration procedures, feeder pressure increased and drainer pressure decreased, with a concomitant increase in the perfusion pressure in the brain tissue surrounding the AVM. Cerebral blood flow (CBF) remained constant at 50 ml 100 g-1 min-1 in the presence of autoregulation and increased to 67 ml 100 g-1 min-1 in its absence. When the lower limit of the autoregulatory pressure range (LAR) was shifted from 60 to 50 or 40 mm Hg, the flow volume increased markedly from 67 to 77 ml 100 g-1 min-1 or to 92 ml 100 g-1 min-1 after complete obliteration. Decrease in LAR would be a cause of the hyperperfusion. Induced systemic hypotension was found to be effective in reducing the magnitude of these hemodynamic changes, when induction was appropriately performed in a stepwise fashion. A simulation study is useful in clarifying the various hemodynamic changes that develop during the treatment of AVM.

Dissociated changes of frontal and parietal somatosensory evoked potentials in sleep

We studied the changes of frontal and parietal somatosensory evoked potentials (SEPs) in the awake state versus different stages of sleep in 10 normal adult subjects. Frontal and parietal SEP components were affected differentially as sleep stages progressed. In general, the amplitudes of frontal components, notably P22, were increased in sleep, whereas the amplitudes of parietal components were decreased in sleep. A sensitive waveform change from the awake state to sleep was present in the frontal response, where a subtle notched negativity, termed "N40," was present only in the awake state and quickly dissipated in all stages of sleep, including stage 1. The amplitude changes from the awake state to stage 3/4 sleep were neither linear nor parallel among SEP components. The most discordant changes occurred in stage 3/4. The amplitudes for the frontal N18-P22-N30 complex and parietal N20-P26-N32 complex increased from stage 2 to stage 3/4, while those for frontal N30-fP40 and parietal N32-pP40 decreased. In contrast to these divergent amplitude changes, the latencies of all components except P14 and frontal N18 showed progressive prolongation from the awake state to slow-wave sleep. The SEP waveforms and latencies in REM sleep approximated those in the awake state, although amplitudes for frontal peaks still remained slightly higher and amplitudes for parietal peaks slightly lower. We postulate that interactions of excitatory and inhibitory phenomena are responsible for the component-dependent and sleep-stage-dependent amplitude enhancement or depression in sleep.

High-rate sequential sampling of auditory brain-stem and somatosensory evoked responses in hypoxia

We developed a high-rate sequential recording technique that allowed simultaneous measurements of both auditory brain-stem response (ABR) and somatosensory evoked potential (SEP) every 10 sec. Using this method, a transient increase in amplitude of all the ABR and SEP components in response to hypoxia in dogs could be detected. The increase in amplitude preceded the prolongation of latency. Our study showed that there were successive changes of evoked potentials in response to hypoxia. A transient increase in amplitude is the first to occur, followed by a latency prolongation and an amplitude decrease for both ABRs and SEPs.

[EC-IC bypass surgery using saphenous vein graft: technical improvement in our experience]

We managed ten cases of EC-IC bypass using a vein graft; six cases with multiple cerebral arterial occlusion and four cases with aneurysm necessitating therapeutic occlusion of the parent artery (Table). Patency of the graft was confirmed in seven cases on long-term follow-up ranging from 7 months to 5 years. Of the ten cases, two died within 7 days after surgery from causes unrelated to the bypass and one was lost in follow-up surgery. Hemorrhagic infarction was observed in two cases, one of which underwent removal of the hematoma. In five cases with cerebral occlusive disease, there were no additional ischemic events and two cases with giant aneurysms showed improvement of visual acuity and extraocular movement. We improved on several surgical techniques for vein graft. We used small hemoclips to occlude branches of the saphenous vein instead of ligating them, which shortens the harvesting time of the saphenous vein. Vessel cannula with a small-sized elegant tip and one-directional valve (DLP, INC., USA) was also used to inflate or deflate vein grafts with saline. It was easily attached to the graft and minimized air entrapment in the lumen. Small clips for microvascular anastomosis (Mizuho INC., Japan) were used to temporarily occlude branches or perforators from the recipient artery. One of the branches of the graft was dissected long enough, through which intraluminal air or thrombus was washed out at the final stage of the surgery. These procedures are useful for shortening occlusion time of the recipient artery and decreasing the risk of embolism.

Simulation study on therapeutic vertebral artery occlusion for VA-PICA giant aneurysm

We investigated haemodynamic effects of therapeutic vertebral artery (VA) occlusion on giant aneurysms at the bifurcation of the VA-posterior inferior cerebellar artery (PICA). An hydraulic model of the human vertebro-basilar artery was manufactured from glass and silicone tubes. Glass-spheres 2.5 cm in diameter were placed at the bifurcation as model aneurysms with respective distances of 8.5, 7.5, 6.5 and 5.5 mm between the VA union and aneurysmal neck. A 40% glycerol solution was perfused in this system and the half-life of the dye injected into aneurysms was regarded as an index of intra-aneurysmal stagnation. Flow conditions in aneurysms depended on the presence or absence of the effect of contralateral VA flow as well as the PICA flow. The half-life increased significantly after VA occlusion proximal to the PICA when the aneurysmal neck was more than 7.5 mm away from the VA union and PICA flow volume was less than 12 ml min-1. The half-life in aneurysms located within 6.5 mm from the union changed little after VA occlusion regardless of the PICA flow volumes. The haemodynamic simulation study would be helpful in speculating on the efficacy of this treatment.