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Biomedical subjects

F Hayashi

Publications and source records attributed to F Hayashi.

At least 91 records · Page 5Linked to original sources
PubMed1996

Possible stimulation of retinal rod recovery to dark state by cGMP release from a cGMP phosphodiesterase noncatalytic site.

Cyclic GMP phosphodiesterase, a key enzyme for phototransduction, contains alpha, beta (Palphabeta), and two gamma (Pgamma) subunits. In addition to catalytic sites, Palphabeta has two classes of noncatalytic cGMP binding sites with different affinities (Kd values <100 nM and >1 microM). Pgamma regulates Palphabeta as an inhibitor of cGMP hydrolysis and as a stimulator of cGMP binding to the high affinity noncatalytic sites. Pgamma release from Palphabeta by the GTP-bound alpha subunit of transducin (GTP.Talpha) interrupts these two functions. Here we describe a novel regulation of the Pgamma release by [cGMP] and its physiological implication. We isolated Pgamma mutants that exhibit abnormally one of these two functions, indicating the distinct domains in Pgamma are involved to express these functions. When [cGMP] was high ( approximately 5 microM), Pgamma responsible for the inhibition of cGMP hydrolysis was preferentially released, and cGMP hydrolysis activity of Palphabeta was increased about 10 times. When [cGMP] was low (less than approximately 0.5 microM), Pgamma responsible for the stimulation of cGMP binding to the high affinity sites was released. The Pgamma release resulted in the decrease of relative affinity of cGMP for the high affinity sites to at least (null)/1;10, followed by the rapid release of cGMP from one of the high affinity sites (apparent t1/2 = 3.8 s). cGMP ( approximately 5 microM) inhibited the extraction of Palphabeta from rod membranes by a Mg2+-free hypotonic buffer. The inhibition of Palphabeta extraction was not affected by Pgamma, suggesting that Palphabeta detects on the order of micromolar [cGMP] using low affinity noncatalytic sites on Palphabeta. Because [cGMP] is approximately 5 microM in darkness and lowered by photoexcitation and phosphodiesterase concentration is approximately 30 microM in rod photoreceptors, it is possible that cGMP phosphodiesterase functions to increase cytoplasamic [cGMP] after [cGMP] is reduced to the illuminated level.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed1996

Respiratory neurons mediating the Breuer-Hering reflex prolongation of expiration in rat.

Afferent input from pulmonary stretch receptors is important in the control of the timing of inspiratory and expiratory phases of the respiratory cycle. The current study was undertaken to identify neurons within a column of respiratory neurons in the ventrolateral medulla (termed the ventral respiratory group, VRG) that, when activated by lung inflation, produce the Breuer-Hering (BH) reflex in which lung inflation causes inspiratory termination and expiratory prolongation. Intracellular recordings of VRG neurons revealed three groups of inspiratory (I) and two groups of expiratory (E) neurons similar to previous descriptions: I-augmenting (I-Aug), I-decrementing (I-Dec), I-plateau (I-All), E-augmenting (E-Aug), and E-decrementing (E-Dec) neurons. Low-intensity, low-frequency stimulation of a vagus nerve elicited paucisynaptic EPSPs in E-Dec, I-Aug, and I-All neurons that could be divided into two groups on the basis of latency (2.8 +/- 0.1 msec, n = 10; 4.0 +/- 0.1 msec, n = 17). IPSPs were elicited in I-Aug and I-All neurons (4.8 +/- 0.1 msec, n = 12). However, only E-Dec neurons were depolarized when the BH reflex was activated by lung inflation (7.5 cm H2O) or mimicked by vagus nerve stimulation (50 Hz). All other neurons were hyperpolarized and ceased firing during BH reflex-mediated expiratory prolongation. A subset of E-Dec neurons (termed E-Decearly) discharged before inspiratory termination and could contribute to inspiratory termination. The findings are consistent with the hypothesis that a group of E-Dec neurons receives a paucisynaptic (probably disynaptic) input from pulmonary afferents and, in turn, inhibits inspiratory neurons, thereby lengthening expiration.

Afferent Pathways↗
PubMed1996

Effects of hypoxia on the ventral root motor-evoked potential in the in vitro spinal cord preparation.

STUDY DESIGN: This study investigated the effects of hypoxia and glucose on motor functions of spinal cord, monitoring ventral root motor-evoked potential in the in vitro cervical cord preparations. OBJECTIVE: To study ischemia-induced changes in ventral root motor-evoked potential of spinal cord. SUMMARY OF BACKGROUND DATA: Previous studies demonstrated ischemic changes caused by local circulatory impairment might be a major pathophysiologic basis of neuron damage in cord compression. METHODS: Ventral root motor-evoked potential elicited by stimulation of ventrolateral funiculus was recorded from the ventral root in the isolated spinal cord preparations obtained from a newborn rat. The preparations were exposed to artificial cerebrospinal fluid equilibrated with severe or mild hypoxia for 90 minutes. Inhibitory and excitatory neurotransmitter antagonists were added to artificial cerebrospinal fluid to investigate synaptic transmission. The artificial cerebrospinal fluids containing various concentrations of glucose were used to study the glucose's effects. RESULTS: Ventral root motor-evoked potential consisted of the early and late components, which were excitatory transsynaptic potentials. The amplitudes were increased in the early phase of severe hypoxia and declined in the prolonged exposure. In mild hypoxia, there was a sustained increase of the amplitudes. The application of inhibitory neurotransmitter antagonists abolished the augmentation of the amplitudes in the early phase of severe hypoxia. Hypoxia without glucose accelerated hypoxic change. CONCLUSION: Inhibitory synaptic transmission was depressed preferentially in the early phase of severe hypoxia or in mild hypoxia. Excitatory and inhibitory transmissions were suppressed in prolonged severe hypoxia. Glucose deficiency aggravated hypoxic inhibition of synaptic transmissions.

Animals↗
PubMed1996

MEKA/phosducin attenuates hydrophobicity of transducin beta gamma subunits without binding to farnesyl moiety.

Hydrophobic modifications of transducin (T) gamma, such as farnesyl-and carboxyl-methylation, are essential for the association of T beta gamma with the photoreceptor disc membrane, and MEKA/phosducin is known to inhibit the association. In this study, we examined the effect of MEKA on the hydrophobicity of T beta gamma. MEKA could bind to T beta gamma without farnesyl/carboxyl-methyl moieties as well as native T beta gamma. In the Triton X-114 phase separation assay, T beta gamma-MEKA complex was recovered in the aqueous phase, whereas T beta gamma was recover in the detergent phase. N-terminal portion of MEKA which includes T beta gamma-binding domain was not sufficient to reduce the hydrophobicity of T beta gamma or to dissociate T beta gamma from the membrane. The data suggest that MEKA attenuates the hydrophobicity of T beta gamma to result in the dissociation of T beta gamma from the membrane without directly binding to farnesyl/carboxyl-methyl moieties.

Animals↗
PubMed1996

Recruitment order and dendritic morphology of rat phrenic motoneurons.

The detailed morphology of rat phrenic motoneurons (PMs) was studied in 40 electrophysiologically identified cells with intracellular injection of Neurobiotin. In 15 cells, the dendritic trees were fully analyzed by using path-distance analysis, and total surface area and volume were estimated. Based on their relative onset times (ROT; i.e., the time of firing onset relative to the onset of whole phrenic activity), PMs were classified into three types; early recruited (type E; ROT < 10%), late recruited (type L; ROT > 12.5%), and quiescent (type Q; not recruited under normal conditions). Dendrites constituted 93.3% of the surface area of cells and 38.9% of the cell volumes. The number of primary dendrites (nPD) averaged 10.1, and the mean number of terminations was 38.8. The combined diameters of primary dendrites of PMs correlated well with the total dendritic surface area and the number of dendritic terminations. Comparisons among cell types revealed that type Q cells had greater dendritic surface areas and volumes than type E or type L cells. With path-distance analysis, this difference was found to be due to differences between the cell types in the numbers of their dendrites, their combined dendritic lengths, and the number of their branches. The differences between these data and those available for cat motoneurons are discussed. The input resistance of PMs correlated with their total surface area but did not correlate with their somal surface area, indicating that, in rat, PM input resistance is a function of the entire neuronal membrane rather than of the somal surface alone.

Action Potentials↗
PubMed1996

Cell-mediated cytotoxicity results from, but may not be critical for, primary allograft rejection.

Tumor cells insensitive to lysis through the Fas and TNF pathways were injected either subcutaneously or into the peritoneal cavities of allogeneic perforin-less (P0) and perforin wild-type (P2) mice. In three of four cases, the tumors were rejected equally rapidly in both strains of mice. Rejection was accompanied by vigorous in vitro cytotoxicity in P2, but not in P0 mice. The rapid clearance of allografted cells in mice where all three known cytolytic pathways are seriously compromised raises important questions about the involvement of cell-mediated cytotoxicity, as defined by current assay techniques, in primary allograft rejection.

Animals↗
PubMed1996

Sonic hedgehog is expressed in epithelial cells during development of whisker, hair, and tooth.

Sonic hedgehog (Shh) is a vertebrate gene homologous to a Drosophila segment polarity gene, hedgehog, and functions as a secreted signaling molecule in limb pattern formation, differentiation of motor neurons, and sclerotome induction. We found that Shh is also expressed in epithelia of the developing whisker, hair, tooth, rugae, and thyroid primordium of mouse embryos. In whisker and hair development, Shh is expressed in epithelial cells before condensation of the underlying mesenchymal cells and then in the placode. The expression of Shh continues in the hair bulb surrounding the dermal papilla. Shh is also expressed in epithelial cells of the tooth bud, then localized to the enamel knot. The Shh expression continues in developing ameloblasts. These results suggest that SHH is an essential epithelial signaling molecule in epithelio-mesenchymal interactions for the terminal differentiation.

Animals↗
PubMed1996

Accommodation in primate eyes after implantation of refilled endocapsular balloon.

PURPOSE: To restore accommodation after crystalline lens removal. METHODS: The crystalline lens of one eye of each of four primates was removed by phacoemulsification. Each operated-on eye underwent endocapsular silicone balloon implantation followed by filling with an organosilicone mixture. Seven months postoperatively, the anterior chamber depth and refractive power changes were measured before and after topical application of 4% pilocarpine. RESULTS: In the refilled eyes, the average anterior chamber depth reduction was 0.50 mm and the average maximal myopic change was 6.74 diopters. CONCLUSION: After lens removal, measurable accommodation was restored in the eyes with the endocapsular balloon filled with an organosilicone mixture.

Accommodation, Ocular↗
PubMed1996

Capsular capture of silicone intraocular lenses.

PURPOSE: To examine the incidence of capsular capture in silicone IOL implantation and determine its effect on visual acuity. SETTING: Hayashi Eye Hospital, Fukuoka, Japan. METHODS: This study comprised 144 eyes that had phacoemulsification with three-piece silicone intraocular lens (IOL) implantation that were evaluated about 3 months after surgery. The examination included the status of the haptic and optic placement, extent of posterior capsular opacification (PCO), and the best corrected visual acuity. RESULTS: One hundred twenty-eight eyes had an in-in haptic placement, 15 had in-out placement, and 1 had out-out placement. Capsular capture occurred in 30 eyes (20.8%). The extent of PCO in eyes with capsular capture was greater than in those without capture. The best corrected visual acuity in eyes with capsular capture was worse than in those without capture. In addition, eyes with in-out and out-out haptic placement had significantly worse PCO and visual impairment than the eyes with in-in placement. CONCLUSION: There was a high incidence of capsular capture after silicone IOL implantation. This complication, along with the undesirable placement of the haptics, led to PCO and thus visual impairment.

Humans↗
PubMed1996

Risk factors for corneal endothelial injury during phacoemulsification.

PURPOSE: To determine the principal risk factors for corneal endothelial injury during phacoemulsification. SETTING: Hayashi Eye Hospital, Fukuoka, Japan. METHODS: We prospectively investigated 859 consecutive eyes of 800 patients who had had phacoemulsification surgery. The percentage of corneal endothelial cell loss at 3 months after surgery was quantitated using specular microscopy. The firmness of the nucleus was graded by Emery's classification prior to surgery. We selected nine variables that could be associated with endothelial injury. The univariate associations between the endothelial cell loss and these variables were evaluated using simple correlation coefficients. A multiple linear regression analysis was performed to identify independent predictors of endothelial cell loss. RESULTS: In the simple regression analysis, older age, small pupil diameter, high nucleus grade, large nucleus, greater infusion volume, type of IOL implanted, and a greater amount of total emitted ultrasound energy were univariately associated with endothelial cell loss. In the multiple linear regression analysis, the best final model (R2 = 0.42) identified high nucleus grade, greater infusion volume, type of IOL implanted, and large nucleus as independent predictors of endothelial cell loss. CONCLUSION: Both univariate and multivariate analyses identified the firmness of the nucleus as the most significant risk factor for endothelial cell loss. Therefore, mechanical contact with nuclear fragments is considered the principal cause of endothelial injury.

Adult↗
PubMed1996

Respiratory motor responses to cranial nerve afferent stimulation in rats.

It was hypothesized that, because rats appear to lack a prominent disynaptic projection from the dorsal respiratory group to phrenic motoneurons (Phr), they would lack the short-latency excitation of Phr output seen in cats in response to stimulation of some cranial nerve afferents. Single-pulse superior laryngeal nerve (SLN) stimulation elicited a short-latency bilateral excitation of glossopharyngeal (IX) and hypoglossal (XII) nerves and an ipsilateral excitation of pharyngeal branch of vagus (PhX) in 67% of rats, but no excitation of Phr. Vagus (X) stimulation elicited a bilateral excitation of Phr and a predominantly ipsilateral excitation of IX and PhX. Single-pulse stimulation of SLN or X also elicited longer-latency, bilateral decreases in activity of all recorded nerves. Repetitive stimulation (50 Hz) of SLN or X suppressed inspiratory activity and prolonged expiration. Lung inflation (7.5 cmH2O) inhibited Phr and PhX activity; X stimulation inhibited Phr but prolonged PhX activity. In conclusion, rats predictably lack the SLN-induced short latency Phr excitation but exhibit other short latency reflexes for which the underlying circuitry is not clear.

Afferent Pathways↗
PubMed1996

[Changes in axial length after scleral buckling surgery].

The eye lengthens after scleral buckling surgery for retinal detachment. We investigated the changes in axial length and refraction after scleral buckling. A total of 89 eyes from 88 patients which were all scheduled to undergo scleral buckling were included in this study. The eyes were classified into four groups based on the type of buckling procedures:1 local buckling, 2 encircling, 3 encircling with vitrectomy, and 4 encircling with local buckling. We examined the axial length of these eyes using ultrasonography, preoperatively and at 1, 3, and 6 months postoperatively. The refractive changes were also examined. Depending on the type of scleral buckling procedure employed, the eyes in Groups 2, 3, and 4 clearly lengthened, but those of Group 1 did not. The amount of axial lengthening in Groups 2, 3, and 4 was significantly greater than in Group 1 at 3 and 6 months after surgery. In the spherical equivalent, a myopic shift occurred in the eyes in Groups 2, 3, and 4, and this shift was significantly greater than in Group 1 In addition, the correlation between the extent of axial lengthening and myopic shift was significant. In conclusion, the axial length increases with a myopic shift due to encircling, whereas local buckling changed the axial length only slightly.

Adolescent↗
PubMed1996

Current trends in cataract and refractive surgery in Japan--1995 survey.

A fourth annual survey was carried out by mail in February 1996 to investigate the current trends in cataract and refractive surgery in Japan. A questionnaire was sent to 911 ophthalmologist members of the Japanese Society of Cataract and Refractive Surgery. Data received from 46.7% of the recipients were cross-analyzed and compared with those from the previous surveys.

Adult↗
PubMed1995

Enhancement by peroxisome proliferators of the susceptibility to DNA damage in the liver of male F344 rats.

Effects of [4-chloro-6-(2,3-xylidino)-2-pyrimidinylthio] acetic acid (Wy-14643) or di(2-ethylhexyl) phthalate (DEHP) as peroxisome proliferators on the susceptibility of liver DNA to damage by N-nitrosodimethylamine (DMN) or methyl methane sulfonate (MMS) were investigated. Male F344 rats were administered Wy-14643 or DEHP, orally, for 1 or 10 weeks. At 1 week, the susceptibility to hepatic DNA damage by DMN or MMS was significantly increased in the Wy-14643- or DEHP-treated rats. The enhancement of the susceptibility persisted for up to 10 weeks in both peroxisome proliferator-treated groups. These findings suggest that the high susceptibility to DNA damage caused by peroxisome proliferators would amplify the DNA damage action such as spontaneous damage, leading to an increase in the risk of initiation in the hepatocarcinogenesis.

Animals↗
PubMed1995

Structure of the Oct-3 POU-homeodomain in solution, as determined by triple resonance heteronuclear multidimensional NMR spectroscopy.

The POU-homeodomain (POUH) forms the bipartite DNA-binding POU domain in association with the POU-specific domain. The 1H, 15N, and 13C magnetic resonances of the 67-amino acid long POUH of mouse Oct-3 have almost completely been assigned, mainly through the combined use of three-dimensional triple resonance NMR methods. Based on the distance and dihedral angle constraints derived from the NMR data, the solution structure of the POUH domain has been calculated by the ab initio simulated annealing method. The average RMS deviation for all backbone heavy atoms of the 20 best calculated structures for residues 9-53 of the total 67 amino acid residues is 0.44 A. The POUH domain consists of three alpha-helices (helix-I, 10-20; helix-II, 28-38; and helix-III, 42-53), and helices-II and -III form a helix-turn-helix motif. In comparison with other classical homeodomains, the folding of the three helices is quite similar. However, the length of helix-III is fairly short. In the complex of the Oct-1 POU domain with an octamer site (Klemm JD, et al., 1994, Cell 77:21-32), the corresponding region is involved in helix-III. The structural difference between these two cases will be discussed.

Amino Acid Sequence↗
PubMed1995

The correlation between incision size and corneal shape changes in sutureless cataract surgery.

PURPOSE: To examine the correlation between incision size and corneal shape changes in sutureless surgery using corneal topography. METHODS: Two hundred eyes undergoing sutureless cataract surgery were assigned randomly to three groups according to the incision size: group A, 3.2-mm incision; group B, 4.0-mm incision; and group C, 5.0-mm incision. All eyes were examined by corneal topography preoperatively as well as at 1 week and at 1, 3, and 6 months after surgery. RESULTS: In the average of difference maps of eyes in the 3.2-mm incision group, a wound-related flattening in the peripheral cornea occurred 1 week after surgery, but decreased rapidly thereafter. Subsequently, no significant changes were observed in the cornea after 1 month. In the 4.0-mm incision group, with a reduction of the wound-related peripheral flattening, an irregular steepening appeared in the lower central cornea 6 months after surgery. In the 5.0-mm incision group, a similar steepening in the lower cornea occurred just after surgery. This steepening persisted and even extended to the upper central cornea in its later postoperative periods. CONCLUSION: The 3.2-mm incision hardly produced any irreversible corneal shape changes, whereas both the 4.0- and 5.0-mm incisions caused a persistent irregular steepening in the central cornea.

Adult↗
PubMed1995

Electrophysiological properties of phrenic motoneurons in adult rats.

Electrophysiological properties of phrenic motoneurons (PMs) were studied by intracellular recordings in anesthetized, paralyzed, and artificially ventilated adult rats. Our results revealed that rat PMs, as compared to cat PMs, had a shorter afterhyperpolarization duration (55 +/- 13 ms; mean +/- SD), a narrower half-width of action potential, a larger membrane input resistance (Rm; 2.0 +/- 0.6 M omega), a smaller rheobase (Irh) and a shorter minimum paired pulse interval to provoke the second spike (1.9 +/- 0.6 ms). These features indicate that the rat PMs possess higher frequency responsiveness than cat PMs. Based on the time of firing onset relative to the onset of whole phrenic nerve activity (relative onset time; ROT) or on the absence of discharge during inspiration, the PMs could be classified into four types: early recruited with ROT < 10.0%; late recruited with 12.5% < ROT < 37.5%; very late recruited with ROT > 45%, and quiescent which was not recruited during normal experimental conditions. A number of differences in the membrane properties such as end-expiratory membrane potential, Rm, and Irh among the four cell types are discussed in relation to the recruitment order. Inhibitory postsynaptic potentials (IPSPs) were present during the late expiratory phase (stage II expiration) in all PMs tested.

Animals↗