Biomedical subjects

W J Ray

Publications and source records attributed to W J Ray.

At least 19 recordsLinked to original sources

PubMed2000

Presenilin complexes with the C-terminal fragments of amyloid precursor protein at the sites of amyloid beta-protein generation.

An unusual intramembranous cleavage of the beta-amyloid precursor protein (APP) by gamma-secretase is the final step in the generation of amyloid beta-peptide (Abeta). Two conserved aspartates in transmembrane (TM) domains 6 and 7 of presenilin (PS) 1 are required for Abeta production by gamma-secretase. Here we report that the APP C-terminal fragments, C83 and C99, which are the direct substrates of gamma-secretase, can be coimmunoprecipitated with both PS1 and PS2. PS/C83 complexes were detected in cells expressing endogenous levels of PS. The complexes accumulate when gamma-secretase is inactivated either pharmacologically or by mutating the PS aspartates. PS1/C83 and PS1/C99 complexes were detected in Golgi-rich and trans-Golgi network-rich vesicle fractions. In contrast, complexes of PS1 with APP holoprotein, which is not the immediate substrate of gamma-secretase, occurred earlier in endoplasmic reticulum-rich vesicles. The major portion of intracellular Abeta at steady state was found in the same Golgi/trans-Golgi network-rich vesicles, and Abeta levels in these fractions were markedly reduced when either PS1 TM aspartate was mutated to alanine. Furthermore, de novo generation of Abeta in a cell-free microsomal reaction occurred specifically in these same vesicle fractions and was markedly inhibited by mutating either TM aspartate. Thus, PSs are complexed with the gamma-secretase substrates C83 and C99 in the subcellular locations where Abeta is generated, indicating that PSs are directly involved in the pathogenically critical intramembranous proteolysis of APP.

Amyloid Precursor Protein Secretases↗

PubMed2000

A complex of iron and nucleic acid catabolites is a signal that triggers differentiation in a freshwater protozoan.

The polymorphic ciliated protozoan Tetrahymena vorax can undergo differentiation from the microstomal form, which normally feeds on bacteria and other particulate matter, into the macrostomal cell type, which is capable of ingesting prey ciliates. The process is triggered by exposure of the microstome to an inducer contained in stomatin, an exudate of the prey. To establish the identity of the signal, stomatin was fractionated by combinations of cation exchange, HPLC, and TLC, and the fractions were assayed for biological activity. Although no single active fraction of purified inducer was obtained, all fractions with activity contained ferrous iron and the nucleic acid catabolites hypoxanthine (6-oxypurine) and uracil (2, 4-dioxopyrimidine), probably in a chelated form. The activity of synthetic complexes containing these three components is equivalent to stomatin. These results indicate a role for ferrous iron and its potential in chelated form to signal differentiation in certain protozoa and, perhaps, in other organisms as well.

Animals↗

PubMed2000

Posttranslational modification and plasma membrane localization of the Drosophila melanogaster presenilin.

Mutations in two genes, presenilin 1 (PS1) and presenilin 2, are linked to early onset cases of familial Alzheimer's disease. The presenilins are thought to contribute to the pathogenesis of Alzheimer's disease by directly or indirectly affecting the proteolytic processing of the amyloid precursor protein. They have also been implicated in the proteolytic processing of Notch. In PS1-deficient mammalian cells, the proteolytic release of the Notch intracellular domain is reduced. Likewise, loss-of-function mutations in Drosophila presenilin (Psn) prevent the production of the intracellular Notch signaling fragment and lead to phenotypes resembling Notch mutants. Here we characterize the Drosophila Psn protein and demonstrate that it undergoes a proteolytic cleavage. We describe Psn expression at different developmental stages of the fly and show Psn localization near both apical and basal plasma membranes. Furthermore, we demonstrate that portions of the Psn protein span the plasma membrane in S2 cells.

Alternative Splicing↗

PubMed2000

A ligand-induced extracellular cleavage regulates gamma-secretase-like proteolytic activation of Notch1.

Gamma-secretase-like proteolysis at site 3 (S3), within the transmembrane domain, releases the Notch intracellular domain (NICD) and activates CSL-mediated Notch signaling. S3 processing occurs only in response to ligand binding; however, the molecular basis of this regulation is unknown. Here we demonstrate that ligand binding facilitates cleavage at a novel site (S2), within the extracellular juxtamembrane region, which serves to release ectodomain repression of NICD production. Cleavage at S2 generates a transient intermediate peptide termed NEXT (Notch extracellular truncation). NEXT accumulates when NICD production is blocked by point mutations or gamma-secretase inhibitors or by loss of presenilin 1, and inhibition of NEXT eliminates NICD production. Our data demonstrate that S2 cleavage is a ligand-regulated step in the proteolytic cascade leading to Notch activation.

Amino Acid Sequence↗

PubMed2000

Cardiovascular reactivity during hypnosis and hypnotic susceptibility: three studies of heart rate variability.

This paper was designed to examine the relationship between hypnotic susceptibility and cardiovascular measures, especially parasympathetic activity, in 3 separate studies. In these studies, neither heart rate nor heart rate variability differed between the high and low hypnotically susceptible individuals at the initial baseline. Furthermore, in the first study, experimental tasks designed to elicit differential sympathetic and parasympathetic cardiac responses demonstrated no interaction with hypnotic susceptibility. Overall, these 3 studies suggest that hypnotic susceptibility in itself is not associated with parasympathetic aspects of either basal cardiac states or cardiac responses. In addition, a hypnotic induction itself did not differentially influence parasympathetic activity for the high versus low susceptible individuals.

Electrocardiography↗

PubMed2000

Rate of force development and the lateralized readiness potential.

We examined the relationship between force and rate of force development aspects of movement dynamics and electroencephalogram motor components as reflected in the lateralized readiness potential (LRP). Using self-paced tasks, in Studies 1 and 3 we investigated whether differential speed and accuracy constraints in discrete and repetitive finger force production tasks influenced the LRP. These studies showed that speed tasks produced larger LRP than accuracy tasks regardless of whether the movement type was discrete or repetitive. In Studies 2 and 4 we studied four conditions with two levels of force and two levels of rate of force development. The largest LRPs were found with the greatest rate of force development. Overall, the four studies demonstrated that preparation for differential rates of force development is a major component reflected in the LRP.

Adult↗

PubMed1999

Cell surface presenilin-1 participates in the gamma-secretase-like proteolysis of Notch.

Presenilin-1 (PS1), a polytopic membrane protein primarily localized to the endoplasmic reticulum, is required for efficient proteolysis of both Notch and beta-amyloid precursor protein (APP) within their trans- membrane domains. The activity that cleaves APP (called gamma-secretase) has properties of an aspartyl protease, and mutation of either of the two aspartate residues located in adjacent transmembrane domains of PS1 inhibits gamma-secretase processing of APP. We show here that these aspartates are required for Notch processing, since mutation of these residues prevents PS1 from inducing the gamma-secretase-like proteolysis of a Notch1 derivative. Thus PS1 might function in Notch cleavage as an aspartyl protease or di-aspartyl protease cofactor. However, the ER localization of PS1 is inconsistent with that hypothesis, since Notch cleavage occurs near the cell surface. Using pulse-chase and biotinylation assays, we provide evidence that PS1 binds Notch in the ER/Golgi and is then co-transported to the plasma membrane as a complex. PS1 aspartate mutants were indistinguishable from wild-type PS1 in their ability to bind Notch or traffic with it to the cell surface, and did not alter the secretion of Notch. Thus, PS1 appears to function specifically in Notch proteolysis near the plasma membrane as an aspartyl protease or cofactor.

3T3 Cells↗

PubMed1999

Human gamma band activity and perception of a gestalt.

Neuronal oscillations in the gamma band (above 30 Hz) have been proposed to be a possible mechanism for the visual representation of objects. The present study examined the topography of gamma band spectral power and event-related potentials in human EEG associated with perceptual switching effected by rotating ambiguous (bistable) figures. Eleven healthy human subjects were presented two rotating bistable figures: first, a face figure that allowed perception of a sad or happy face depending on orientation and therefore caused a perceptual switch at defined points in time when rotated, and, second, a modified version of the Rubin vase, allowing perception as a vase or two faces whereby the switch was orientation-independent. Nonrotating figures served as further control stimuli. EEG was recorded using a high-density array with 128 electrodes. We found a negative event-related potential associated with the switching of the sad-happy figure, which was most pronounced at central prefrontal sites. Gamma band activity (GBA) was enhanced at occipital electrode sites in the rotating bistable figures compared with the standing stimuli, being maximal at vertical stimulus orientations that allowed an easy recognition of the sad and happy face or the vase-faces, respectively. At anterior electrodes, GBA showed a complementary pattern, being maximal when stimuli were oriented horizontally. The findings support the notion that formation of a visual percept may involve oscillations in a distributed neuronal assembly.

Adult↗

PubMed1999

A presenilin-1-dependent gamma-secretase-like protease mediates release of Notch intracellular domain.

Signalling through the receptor protein Notch, which is involved in crucial cell-fate decisions during development, requires ligand-induced cleavage of Notch. This cleavage occurs within the predicted transmembrane domain, releasing the Notch intracellular domain (NICD), and is reminiscent of gamma-secretase-mediated cleavage of beta-amyloid precursor protein (APP), a critical event in the pathogenesis of Alzheimer's disease. A deficiency in presenilin-1 (PS1) inhibits processing of APP by gamma-secretase in mammalian cells, and genetic interactions between Notch and PS1 homologues in Caenorhabditis elegans indicate that the presenilins may modulate the Notch signalling pathway. Here we report that, in mammalian cells, PS1 deficiency also reduces the proteolytic release of NICD from a truncated Notch construct, thus identifying the specific biochemical step of the Notch signalling pathway that is affected by PS1. Moreover, several gamma-secretase inhibitors block this same step in Notch processing, indicating that related protease activities are responsible for cleavage within the predicted transmembrane domains of Notch and APP. Thus the targeting of gamma-secretase for the treatment of Alzheimer's disease may risk toxicity caused by reduced Notch signalling.

Alzheimer Disease↗

PubMed1999

Evidence for a physical interaction between presenilin and Notch.

Genetic analyses in Caenorhabditis elegans demonstrate that sel-12 and hop-1, homologues of the Alzheimer's disease-associated presenilin genes, modify signaling through LIN-12 and GLP-1, homologues of the Notch cell surface receptor. To gain insight into the biochemical basis of this genetic interaction, we tested the possibility that presenilin-1 (PS1) physically associates with the Notch1 receptor in mammalian cells. Notch1 and PS1 coimmunoprecipitated from transiently transfected human embryonic kidney 293 cell lysates in a detergent-sensitive manner, consistent with a noncovalent physical association between the two proteins. The interaction predominantly occurred early in the secretory pathway prior to Notch cleavage in the Golgi, because PS1 immunoprecipitation preferentially recovered the full-length Notch1 precursor. When PS1 was immunoprecipitated from 293 cells that had been metabolically labeled with [35S]methionine and [35S]cysteine, Notch1 was the primary protein detected in PS1 immunoprecipitates, suggesting that this interaction is specific. Furthermore, endogenous Notch and presenilin coimmunoprecipitated from cultured Drosophila cells, indicating that physical interaction can occur at physiological expression levels. These results suggest that the genetic relationship between presenilins and the Notch signaling pathway derives from a direct physical association between these proteins in the secretory pathway.

Alzheimer Disease↗

PubMed1998

Dynamical aspects of motor and perceptual processes in schizophrenic patients and healthy controls.

The present study examined the temporal stationarity of the performance of 16 schizophrenic patients and 16 controls matched for age and sex in a bimanual coordination task and a perceptual task. In the motor task, rhythmic finger oscillations (alternating activity of homologue muscle groups) at increasing speed levels resulted in two measures, the preferred oscillation frequency and the critical frequency at which phase transitions (change towards simultaneous activity of homologue muscle groups) occurred. A measure of local dimensional complexity (pointwise D2 or PD2), which is a measure of non-linear dynamics, was determined for the acceleration profiles of the subjects' movements. Schizophrenics exhibited less stable movement dynamics than controls in horizontal finger cycling, indicated by a lower ratio critical/preferred frequency (critical ratio) and by higher means and standard deviations of the pointwise D2. In vertical cycling, the critical ratio did not differentiate between groups, while PD2 means and standard deviations did. Groups also differed specifically in perception of two ambiguous figures (Schroeder stairs and Rubin vase). Schizophrenics showed significantly higher reversal rates for the Rubin vase and a differential perceptive in comparison to controls in the perception of the Schroeder stairs. Measures of perceptual and motor stability were unrelated, which suggests that perceptual and motor processes are not influenced by a common underlying mechanism.

Adult↗

PubMed1998

Movement-related potentials with reference to isometric force output in discrete and repetitive tasks.

This study investigates whether different speed and accuracy constraints in discrete and repetitive index finger isometric force-production tasks influence the characteristics of the movement-related potentials (MRP) preceding and accompanying these tasks. Three components of MRP (Bereitschaftspotential, BP, motor potential, MP, and movement-monitoring potential, MMP) associated with isometric force output were identified and examined. Our principal finding for the MRP amplitude showed that only MMP, not BP and MP, was enhanced at higher rates of force development for both speed and accuracy tasks. That is to say, there was a high correlation between MMP peak amplitude and the rate of force development for both repetitive and discrete force-production tasks. Additionally, the amplitude of MMP was consistently higher for fast, rather than accurate, force outputs. Moreover, the results from analysis of MRP onset times suggest that, in general, the MRP begin earlier for the fast force output than for the accurate force output.

Adult↗

PubMed1998

Effects of memory load on event-related patterns of 40-Hz EEG during cognitive and motor tasks.

The present study describes a phasic event-related synchronization (ERS) in the gamma band (36-44 Hz) induced by the onset of probe visual stimuli. The experiment consisted of two experimental tasks with high and low memory-load in which a geometrical figure (S1) was held in memory for comparison with a subsequent stimulus (S2). In each task a Go-NoGo paradigm was used with a Same-Different discrimination task. The aim of the study was to examine the influence on 40-Hz ERS of stimulus type ('Same-Different') and of response (Go-NoGo) task as moderated by activation or effort level (high/low memory-load). The investigation was carried out in 27 women. The EEG was recorded from FP1, FP2, F3, F4, P3, P4, O1 and O2 scalp sites referenced to linked earlobes. As a manipulation check for activation level, we recorded heart rate (HR) during the S1-S2 period. A main peak of activity was found around 160 ms with a maximum at occipital sites. The amplitude of this peak was higher in the high memory-load as compared to the low memory-load condition. This difference was manifested mainly at F3 and O2 scalp sites. A larger 40-Hz peak at F3 was also found in the Go compared to the NoGo condition. No 40-Hz ERS differences between Same and Different trials were observed. The HR was found sensitive to the stimulus type showing a greater HR deceleration response to S2 for Same trials, as compared to Different ones. In parallel with 40-Hz ERS response, the HR deceleration was more pronounced for the high memory-load as compared to the low memory-load condition. The results indicate that the 40-Hz ERS is dependent upon both memory-load and motor responding. The influence of memory load on cognitive (Same-Different) and motor response (Go-NoGo) variables is discussed.

Adult↗

PubMed1998

EEG activity and heart rate during recall of emotional events in hypnosis: relationships with hypnotizability and suggestibility.

The purpose of the present research was to find physiological and cognitive correlates of hypnosis, imaginative suggestibility and emotional experiences. After the administration of a standard hypnotic induction, the EEG and heart rate (HR) were recorded during self-generated happy and sad emotions using a relaxation condition as a control. Physiological recordings were also obtained during three eyes-open and eyes-closed baseline periods: (1) waking rest; (2) early-rest in hypnosis (just after the hypnotic induction); (3) late-rest hypnosis (at the end of hypnotic condition). EEG was recorded at frontal (F3, F4), central (C3, C4), and posterior sites (middle of O1-P3-T5 and O2-P4-T6 triangles). Using log transform of mean spectral amplitude, eight EEG frequency bands (4-44 Hz) were evaluated. High hypnotizable subjects, as compared to the lows, produced a higher theta1 amplitude (4-6 Hz) across both left- and right-frontal and right-posterior areas. These subjects also produced smaller alpha1 amplitude (8.25-10 Hz) over both left and right frontal recording sites. High suggestible subjects, during resting conditions, disclosed higher theta2 (6.25-8 Hz) and alpha1 amplitudes in eyes-closed as compared to an eyes-open condition than did low suggestible subjects. High suggestible subjects also showed, in hypnosis-rest condition, higher 40-Hz amplitudes (36-44 Hz) and HR activity than did low suggestible subjects. Hypnotizability and not suggestibility was found to moderate emotional processing: high hypnotizable individuals self-reported greater levels of emotional experiences than did low hypnotizables especially in terms of negative emotion. High hypnotizables, during processing of emotional material, also disclosed opposite 40-Hz hemispheric asymmetries over anterior and posterior regions of the scalp. These subjects during happiness showed an increased production of 40-Hz activity in the left frontal and central regions of the scalp, while during sadness they showed an increased activity in the right central and posterior regions. The hemispheric asymmetries for relaxation condition were similar, but less marked, to those obtained for happiness. No significant interactions involving both hypnotizability and imaginative suggestibility were found for physiological variables considered in this study. This demonstrates that hypnotizability and suggestibility reflect different underlying psychophysiological activities.

Adult↗

PubMed1998

Molecular pathogenesis of sporadic and familial forms of Alzheimer's disease.

Our understanding of the pathogenesis of Alzheimer's disease (AD) comes primarily from the study of rare inherited forms of the disease. Mutations that cause familial AD appear to act by a common mechanism: that of increasing production of A beta 42/43, one of the family of A beta peptides deposited in senile plaques. However, increased A beta 42/43 production has not been demonstrated to occur in most cases of sporadic AD, suggesting that genetic and environmental factors acting at other stages of the disease process can modify the risk for disease. Such factors most likely include those affecting A beta aggregation or clearance, the inflammatory response, cerebrovascular disease, or susceptibility of neurons to injury. Identifying these factors will lead to a better understanding of the etiology of the disease and provide additional targets for therapeutic intervention.

Age of Onset↗

PubMed1998

Movement-related potentials accompanying unilateral finger movements with special reference to rate of force development.

The aim of this study was to examine the relationship between force and rate of force development with electroencephalogram correlates. The primary question was whether the different components of movement related potentials (MRPs) were related to specific properties of force output while subjects performed index finger force production tasks. The peak force and rate of force development (e.g., a product of peak force over time-to-peak force) were manipulated, and the effects of these manipulations on components of MRPs preceding and accompanying force production tasks were examined. The hypothesis was that the rate of force development, rather than level of force itself, would directly influence the later component of MRPs. Consistent with this hypothesis was the finding that the amplitudes of MRP components preceding (MP) and accompanying (MMP, MTP) finger force production movements were significantly correlated with force development rate.

Adult↗

PubMed1997

CYP26, a novel mammalian cytochrome P450, is induced by retinoic acid and defines a new family.

A novel member of the cytochrome P450 superfamily, CYP26, which represents a new family of cytochrome P450 enzymes, has been cloned. CYP26 mRNA is up-regulated during the retinoic acid (RA)-induced neural differentiation of mouse embryonic stem cells in vitro and is transiently expressed by embryonic stem cells undergoing predominantly non-neural differentiation. CYP26 transcript is detectable as early as embryonic day 8.5 in mouse embryos, suggesting a function for the gene in early development. CYP26 is expressed in mouse and human liver, as expected for a cytochrome P450, and is also expressed in regions of the brain and the placenta. Acute administration of 100 mg/kg all-trans-RA increases steady-state levels of transcript in the adult liver, but not in the brain. CYP26 is highly homologous to a Zebrafish gene, CYPRA1, which has been proposed to participate in the degradation of RA, but is minimally homologous to other mammalian cytochrome P450 proteins. Thus, we report the cloning of a member of a novel cytochrome P450 family that is expressed in mammalian embryos and in brain and is induced by RA in the liver.

Amino Acid Sequence↗

PubMed1997

EEG concomitants of hypnotic susceptibility.

Numerous historical attempts have been directed at understanding electrocortical concomitants of hypnosis. Today, with the availability of more sophisticated multichannel recording technologies and signal-processing approaches, it is possible to reconsider and update previous attempts. The most solid relationship between electrocortical activity and hypnotizability exists in the EEG theta frequency range. Given the stable electrocortical differences found in high and low susceptible individuals, the question arises whether we can use additional EEG measures to help understand the nature of these individual differences. One possible alternative is the pointwise or fractal dimension, which we examined during baseline conditions with high and low hypnotic susceptible individuals. The dimensionality measures suggest that high susceptible individuals display underlying brain patterns associated with imagery, whereas low susceptible individuals show patterns consistent with cognitive activity (i.e., mental math). This type of speculation is similar to that of Tellegen, who makes a distinction between imaginative versus realistic responding. Future research should address the exact nature of the underlying process (imagination, effortlessness, suggestibility, etc.) seen in high and low susceptible individuals.

Arousal↗