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PubMed1990

A developmental analysis of spontaneous and reflexive reversals in the nematode Caenorhabditis elegans.

Reversals of forward locomotion in the nematode Caenorhabditis elegans are thought to be mediated by a common neural circuit, the touch withdrawal circuit. Despite substantial neuroanatomical changes over post-embryonic development, one reversal behavior, the head-touch withdrawal reflex, does not appear to change over development (Chalfie and Sulston, 1981). The experiments reported here indicate that two other reversal behaviors, spontaneous reversals and the tap reversal reflex to vibratory stimuli, show developmental changes. Young adult animals showed higher frequencies of spontaneous reversals than all other developmental stages, while larval stages differed from adults in their pattern of responses to tap. Although animals of all stages reversed in response to touch, taps elicited both reversals and accelerations of forward movement. In response to single taps, larval stages reversed on approximately half the occasions; young adult and 4-day-old adults almost always reversed. Increasing stimulus magnitudes increased the probability of accelerations at all developmental stages, but larval stages showed fewer reversals and more accelerations than adults. The behavioral changes observed coincide with known periods of neuroanatomical change in the touch withdrawal circuit. The addition of a late-developing sensory neuron, AVM, is implicated in the behavioral differences between juveniles and adults.

Animals↗
PubMed2000

SR calcium depletion following reversal of the Na+/Ca2+-exchanger in rat ventricular myocytes.

We previously reported that cytosolic calcium transiently increases after reversal of the sarcolemmal Na+/Ca2+-exchanger. Calcium released from sarcoplasmic reticulum (SR) constituted the major part of this cytosolic transient. The aim of this study was to test whether reversal of the Na+/Ca2+-exchanger affects SR calcium content, and whether altered SR calcium content is associated with direct triggering of SR calcium release or calcium release secondary to SR calcium overload. To this purpose we studied the change of SR calcium content after reversal of the Na+/Ca2+-exchanger and the dependence on the magnitude of change of its free energy (delta Gexch) in isolated rat ventricular myocytes. The Na+/Ca2+-exchanger was reversed by abrupt reduction of extracellular sodium ([Na+]o). The magnitude of change of deltaGexch was varied with [Na+]o. Cytosolic free calcium ([Ca2+]i) was measured with indo-1 and SR calcium content was estimated from the increase of [Ca2+]i after rapid cooling (RC). SR function was manipulated either by blockade of the SR Ca2+-ATPase with thapsigargin or by blockade of SR calcium release channels with tetracaine. Reversal of the Na+/Ca2+-exchanger caused a transient increase of [Ca2+]i of about 180 s duration with a time to peak of about 30 s. During the first 30 s rapid small amplitude cytosolic calcium fluctuations were superimposed on this transient. The magnitude of the response of [Ca2+]i to RC, during the course of the cytosolic [Ca2+]i transient, also transiently increased from 174 in control myocytes to 480 nmol/l at the time of the peak value. After correction of [Ca2+]i data for the fraction of mitochondrially compartmentalized indo-1 and mitochondrial calcium, total calcium released from SR after RC was calculated with the use of literature data on cytosolic calcium buffer capacity. Contrary to the measured RC-dependent increase of measured [Ca2+]i, after reversal of the Na+/Ca2+-exchanger, calculated total calcium released from SR transiently decreased. The extent of SR calcium depletion after reversal of the Na+/Ca2+-exchanger increased with the magnitude of change of deltaGexch. Restitution of [Na+]o 30 s after reversal of the Na+/Ca2+-exchanger, greatly accelerated both recovery of [Ca2+]i and SR calcium content. Pretreatment of myocytes with thapsigargin caused almost entire depletion of SR and substantial reduction of the cytosolic transient of [Ca2+]i following reversal of the Na+/Ca2+-exchanger. Application of tetracaine hardly affected SR calcium content, but caused an increase of the SR calcium content following reversal of the Na+/Ca2+-exchanger, while the cytosolic transient increase of [Ca2+]i was substantially reduced. We conclude that reversal of the Na+/Ca2+-exchanger directly triggers SR calcium release and decreases SR calcium content in a deltaGexch dependent manner.

Animals↗
PubMed1998

Prediction of post-revascularization functional recovery of asynergic myocardium using quantitative thallium-201 rest-redistribution tomography: has the reverse redistribution pattern an independent significance?

The significance of reverse redistribution on rest-redistribution thallium-201 myocardial scintigraphy is unclear. Previous studies suggested that reverse redistribution segments with normal resting activity include viable myocardium, whilst resting defects with further worsening correspond to scar. We evaluated whether reverse redistribution has an independent significance for the prediction of post-revascularization recovery, particularly as compared with the quantification of redistribution activity. We studied 26 coronary artery disease patients with left ventricular dysfunction, who underwent 201Tl rest-redistribution single-photon emission tomography (SPET) and echocardiography before revascularization. Viability was defined by the detection of wall motion improvement on follow-up echocardiography. 201Tl activity was considered normal if >/=80%, moderately reduced if <80% but >/=50%, and severely decreased if <50%. Reverse redistribution was defined as a defect in redistribution images with >/=10% decrease in relative 201Tl activity compared with the resting value. Reverse redistribution was detected in 33 segments (10%). Baseline dysfunction was equally observed in the reverse redistribution and in the non-reverse redistribution segments (64% vs 56%, P=0.40) and the rate of asynergic segments with post-revascularization recovery was not different between the two groups (33% vs 54%, P=0.11). The rate of functional recovery in redistribution defects without reverse redistribution was 53% in moderate and 30% in severe defects; the corresponding values for the reverse redistribution segments were 50% and 27% (all non-significant versus non-reverse redistribution segments). For the prediction of post-revascularization recovery in asynergic segments, the detection of reverse redistribution on rest-redistribution 201Tl SPET does not add any information to the quantitative analysis of redistribution activity.

Aged↗
PubMed1995

A random trial comparing recovery after midazolam-alfentanil anesthesia with and without reversal with flumazenil, and standardized neurolept anesthesia for major gynecologic surgery.

STUDY OBJECTIVE: To compare the recovery characteristics of total intravenous anesthesia (TIVA) using midazolam-alfentanil, with or without reversal with flumazenil to a standardized neurolept anesthesia with nitrous oxide (N2O). DESIGN: Randomized, double-blinded clinical study. SETTING: University medical center. PATIENTS: 80 ASA physical status I and II women scheduled for major elective gynecologic surgery. INTERVENTIONS: Patients were anesthetized with one of three different anesthetic techniques. Patients in the TIVA group with reversal received midazolam-alfentanil reversed with flumazenil (Group 1), the TIVA group without reversal received midazolam-alfentanil reversed with placebo (Group 2), and patients in the neurolept group received anesthesia using thiopental sodium, droperidol, fentanyl, and N2O (Group 3). MEASUREMENTS AND MAIN RESULTS: Recovery was assessed by an observer blinded to the treatment allocation, using a Modified Steward Recovery Score and judgment of orientation and comprehension, collaboration and degree of sedation for the first 4 hours after extubation. Arterial blood gases were measured 30 minutes after extubation. A questionnaire regarding the degree of perioperative amnesia was presented to the patients 4 and 24 hours after surgery. The recovery scores were better in the TIVA group with reversal than in the other two groups from 0 to 30 minutes postoperatively. No difference between the groups could be found thereafter, although after 30 minutes some resedation occurred in the TIVA group with reversal. The median injected amount of flumazenil in Group 1 was 0.5 mg. Respiratory depression (breathing frequency below 10 breaths/min) was reversed with naloxone in one patient in the TIVA group with reversal, five patients in the TIVA group without reversal, and no patient in the neurolept group (p < 0.001). On blood gas analysis, there was no evidence of hypoxemia or carbon dioxide retention. No difference was seen between the groups regarding consumption of analgesics, degree of amnesia, or patient rating of the quality of anesthesia. One patient in Group 2, however, recorded awareness at skin incision when questioned 4 hours after the operation, but could not recall this 20 hours later. CONCLUSIONS: TIVA with midazolam and alfentanil can be used for major gynecologic surgery. Recovery in the neurolept group was equal to recovery in the TIVA group without reversal, and flumazenil improves the recovery after midazolam anesthesia. Overall, in comparison with the neurolept technique no major advantage could be demonstrated using TIVA with midazolam-alfentanil.

Adult↗
PubMed2005

Isolation and quantification of dinucleoside polyphosphates by using monolithic reversed phase chromatography columns.

In former studies, dinucleoside polyphosphates were quantified using ion-pair reversed-phase perfusion chromatography columns, which allows a detection limit in the micromolar range. The aim of this study was both to describe a chromatographic assay with an increased efficiency of the dinucleoside separation, which enables the reduction of analytical run times, and to establish a chromatographic assay using conditions, which allow MALDI-mass spectrometric analysis of the resulting fractions. We compared the performance of conventional silica reversed phase chromatography columns, a perfusion chromatography column and a monolithic reversed-phase C18 chromatography column. The effects of different ion-pair reagents, flow-rates and gradients on the separation of synthetic diadenosine polyphosphates as well as of diadenosine polyphosphates isolated from human platelets were analysed. Sensitivity and resolution of the monolithic reversed-phase chromatography column were both higher than that of the perfusion chromatography and the conventional reversed phase chromatography columns. Using a monolithic reversed-phase C18 chromatography column, diadenosine polyphosphates were separable baseline not only in the presence of tetrabutylammonium hydrogensulfate (TBA) but also in the presence of triethylammonium acetate (TEAA) as ion-pair reagent. The later reagent is useful because, in contrast to TBA, it is compatible with MALDI mass-spectrometric methods. This makes TEAA particularly suitable for identification of unknown nucleoside polyphosphates. Furthermore, because of the lower backpressure of monolithic reversed-phase chromatography columns, we were able to significantly increase the flow rate, decreasing the amount of time for the analysis close to 50%, especially using TBA as ion-pair reagent. In summary, monolithic reversed phase C18 columns markedly increase the sensitivity and resolution of dinucleoside polyphosphate analysis in a time-efficient manner compared to reversed-phase perfusion chromatography columns or conventional reversed-phase columns. Therefore, further dinucleoside polyphosphate analytic assays should be based on monolithic silica C18 columns instead of perfusion chromatography or conventional silica reversed phase chromatography columns. In conclusion, the use of monolithic silica C18 columns will lead to isolation and quantification of up to now unknown dinucleoside polyphosphates. These chromatography columns may facilitate further research on the biological roles of dinucleoside polyphosphates.

Blood Platelets↗
PubMed2000

Possible mechanisms of action in melatonin reversal of morphine tolerance and dependence in mice.

In our earlier study, we reported the ability of melatonin to reverse the development of morphine tolerance and dependence in mice. In the present study, we attempted to analyse the possible involvement of putative melatonin receptors, central and peripheral benzodiazepine receptors and the nitric oxide (NO) system in the mechanism of melatonin reversal of morphine tolerance and dependence in mice. Co-administration of L-N(G)-nitro arginine methyl ester (L-NAME) or melatonin with morphine during the induction phase (days 1-9) delayed the development of tolerance to the anti-nociceptive action of morphine and also reversed naloxone precipitated withdrawal jumpings. L-arginine administration during the induction phase enhanced the development of tolerance to the anti-nociceptive effect of morphine but had no effect on the naloxone-precipitated withdrawal response. During the expression phase (day 10), acute administration of melatonin or L-NAME reversed, whereas L-arginine facilitated, naloxone-precipitated withdrawal jumping in morphine-tolerant mice, but none of these drugs affected the nociceptive threshold in morphine-tolerant mice. Further, co-administration of melatonin or L-NAME with L-arginine during the induction phase antagonized later the effects on the development of morphine tolerance. Also, prior administration of melatonin or L-NAME reversed the L-arginine potentiation of naloxone-precipitated withdrawal jumping in morphine tolerant mice. Among the antagonists for putative melatonin receptors studied, neither luzindole (melatonin MT1 and MT2 receptor antagonist) nor prazosin (melatonin MT3 receptor antagonist) antagonized the melatonin reversal of morphine tolerance and dependence. 1-(2-Chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinolinecarboxam ide (PK11195), a peripheral but not central benzodiazepine receptor antagonist, flumazenil, partially antagonized the melatonin reversal of naloxone-precipitated withdrawal jumping in morphine-dependent mice, but had no effect on the reversal of morphine tolerance induced by melatonin. Overall, the present observations suggest that the melatonin-induced reversal of morphine tolerance and dependence may involve its ability to suppress nitric oxide synthase (NOS) activity. Further, the melatonin-induced reversal of morphine tolerance and dependence is not mediated through its actions via putative melatonin receptors. The agonistic activity of melatonin towards peripheral benzodiazepine receptors may partially contribute to the suppression of morphine dependence but not to the reversal of tolerance to the analgesic activity of morphine.

Animals↗
PubMed1993

Pronoun reversals: who, when, and why?

Seventeen of a sample of 30 precocious talkers aged 1;8 produced at least one pronoun reversal (I/you) during unstructured play. This finding led to an examination of the role of cognitive and linguistic individual differences as well as contextual factors and processing complexity as determinants of pronoun reversal. Contrary to predictions derived from previous hypotheses, there were few differences between reversers and non-reversers, other than higher use of second person forms by reversers. Reversals were more likely to occur in certain contexts: semantically reversible predicates with two noun phrases, and in imitations (though the rate of imitation was lower overall in reversers). We propose that pronoun reversals commonly result from a failure to perform a deictic shift, which is especially likely when children's psycholinguistic processing resources are taxed. Children who did not produce any pronoun reversals tended to avoid pronoun use, especially second person forms. Overt reversal may thus reflect a risk-taking approach to language acquisition, which may be particularly characteristic of precocious children.

Child Development↗
PubMed1975

Protein kinase and its regulatory effect on reverse transcriptase activity of Rous sarcoma virus.

We have studied the effect of protein phosphokinase (EC 2.7.1.37; ATP:protein phosphotransferase) and phosphoprotein phosphatase (EC 3.1.3.16; phosphoprotein phosphohydrolase) on reverse transcriptase (RNA-dependent DNA nucleotidyltransferase) activity of Rous sarcoma virus. Protein kinase from Rous sarcoma virus-transformed chick embryo fibroblasts was purified by DEAE-cellulose chromatography, Sephadex gel filtration, and isoelectric focusing. Purified reverse transcriptase from Rouse sarcoma virus was preincubated with protein kinase and ATP under conditions allowing incorporation of phosphate into substrate protein. After the preincubation, reverse transcriptase activity was assayed in the presence of poly(rA).oligo(dT) as template. A 2- to 5-fold increase of reverse transcriptase activity was found after the preincubation of reverse transcriptase with protein kinase and ATP. Incubation of reverse transcriptase with heat-treated, inactive protein kinase and ATP had no effect on transcriptase activity. When the transcriptase preparation was incubated with protein kinase and [gamma-32P]ATP and subsequently purified by chromatography on phosphocellulose and Sephadex gel filtration, significant amounts of 32P-labeled proteins were found in the fractions exhibiting reverse transcriptase activity, suggesting 32P incorporation into transcriptase or transcriptase-associated proteins. A 20-60% decrease of reverse transcriptase activity was observed after incubation of reverse transcriptase with phosphatase. The results suggest that phosphorylative modification of reverse transcriptase may be critical in the regulation of reverse transcriptase-catalyzed DNA synthesis.

Alkaline Phosphatase↗
PubMed2003

An algorithm to enumerate sorting reversals for signed permutations.

The rearrangement distance between single-chromosome genomes can be estimated as the minimum number of inversions required to transform the gene ordering observed in one into that observed in the other. This measure, known as "inversion distance," can be computed as the reversal distance between signed permutations. During the past decade, much progress has been made both on the problem of computing reversal distance and on the related problem of finding a minimum-length sequence of reversals, which is known as "sorting by reversals." For most problem instances, however, many minimum-length sequences of reversals exist, and in the absence of auxiliary information, no one is of greater value than the others. The problem of finding all minimum-length sequences of reversals is thus a natural generalization of sorting by reversals, yet it has received little attention. This problem reduces easily to the problem of finding all "sorting reversals" of one permutation with respect to another - that is, all reversals rho such that, if rho is applied to one permutation, then the reversal distance of that permutation from the other is decreased. In this paper, an efficient algorithm is derived to solve the problem of finding all sorting reversals, and experimental results are presented indicating that, while the new algorithm does not represent a significant improvement in asymptotic terms (it takes O(n(3)) time, for permutations of size n; the problem can now be solved by brute force in Theta(n(3)) time), it performs dramatically better in practice than the best known alternative. An implementation of the algorithm is available at www.cse.ucsc.edu/~acs.

Algorithms↗
PubMed1997

Tat is required for efficient HIV-1 reverse transcription.

The ability of human immunodeficiency virus-1 (HIV-1) to undergo efficient reverse transcription is dependent on a number of parameters. These include the binding of the tRNA(3)(Lys) to the HIV-1 primer binding site and the subsequent interaction with the heterodimeric reverse transcriptase. Recently, we demonstrated that TAR RNA was also necessary for efficient HIV-1 reverse transcription. Given the fact that the Tat protein is involved in the activation of HIV-1 gene expression in conjunction with TAR, we wished to determine whether Tat might also be involved in the control of HIV-1 reverse transcription. HIV-1 virions deleted in the tat gene were unable to initiate reverse transcription efficiently upon infection of peripheral blood mononuclear cells (PBMCs). This defect was not due to decreased amounts of genomic RNA, reverse transcriptase or other HIV-1 proteins which were incorporated into the virion. Following transfection of wild-type but not mutant tat genes into cell lines producing HIV-1 lacking tat, the virions produced could be complemented for defects in reverse transcription upon subsequent infection of PBMCs. In contrast, the defect in reverse transcription seen with HIV-1 lacking the tat gene could not be complemented when the target cells rather than the producer cells contained tat. Viruses lacking tat were also defective in endogenous assays of reverse transcription, although these viruses contained similar levels of reverse transcriptase. These results indicate that the Tat protein, in addition to regulating the level of gene expression, is also important for efficient HIV-1 reverse transcription.

Amino Acid Sequence↗
PubMed2001

Breaking of time reversal invariance in nonlinear acoustics.

Time-reversal invariance of nonlinear acoustic wave propagation is experimentally investigated. Reversibility is studied for propagation shorter or longer than shock formation distance. In the first case, time-reversal invariance holds and a sinusoid distorted by nonlinearities during forward propagation progressively recovers its initial shape after the time-reversal operation. In the second case, reversibility is broken locally at the shock front as a time-reversal operation transforms a stable compression shock into an unstable expansion shock. Achieving experimentally the time-reversal process with a time-reversal mirror made of reversible piezoelectric transducers for very broadband signals, would require transducers with huge bandwidths. To date, such transducers remain unavailable. In order to overcome this technical limitation, we restricted ourselves in this study to one-dimensional (1D) propagation, for which an experimental ersatz of a time-reversal mirror can be used. Indeed, in a 1D case, the time-reversal operation applied on a plane wave can be mimicked for an antisymmetric wave form by a reflection of the plane wave onto a pressure-release interface.

Journal Article↗
PubMed1992

The pH in reversed micelles as imposed by the dihydrogen/proton redox couple and indicated by viologens and cytochrome c3 using hydrogenase as redox catalyst.

The pH values in reversed micelles were measured, making use of the hydrogenase enzyme as redox catalyst short-circuiting the viologen oxidized/semiquinone redox states. The hydrogenases from Desulfovibrio vulgaris (Hildenborough) and from Megasphaera elsdenii were applied. The observed pH values in reversed micelles were not dependent on the type of hydrogenase. Two cationic [cetyltrimethylammonium bromide and dodecylammonium propionate (DAP)] and two anionic sodiumdodecyl sulphate, sodium di(ethylhexyl)sulfosuccinate types of reversed micelles were used in combination with viologens having distinguishable valencies. It was observed that, in the cationic-reversed micelles, the dissociation constant for the semiquinone dimer had about the same value as compared to bulk water, while this value was significantly higher in the anionic-reversed micelles. Furthermore, the dissociation constant was independent of the concentration of viologen semiquinone in the reversed micelle, indicating that exchange kinetics are faster than the dimerisation process. With the exception of DAP, a linear relation exists, pH = a.pHrm + b, between the pH of the bulk water and the pH as measured in the reversed micelle (pHrm). In all these cases the value of a is smaller than unity, the value of b ranges between 1.6-2.7. For DAP the pHrm is always around 7. In DAP-reversed micelles, the counter-ion propionate probably serves as an internal buffer. Using cytochrome c3 as pH indicator in combination with N,N'-di(3-aminopropyl)-4,4'-bipyridinium)4+ to take care of electron transfer, in cetyltrimethylammonium-bromide-reversed micelles the pHrm is about the same as indicated by the viologen; in SDS-reversed micelles the pHrm is always lower than that indicated by N,N'-di(3-aminopropyl)4,4'-pyridinium4+. In contrast to cytochrome c3 from D. vulgaris, which in reversed micelles cannot become reduced directly by its D. vulgaris hydrogenase, the hydrogenase of M. elsdenii is able to reduce its ferredoxin directly.

Bromides↗
PubMed1977

A radioimmunoassay for 3,3',5'-L-triiodothyronine (reverse T3): assessment of thyroid gland content and serum measurements in conditions of normal and altered thyroidal economy and following administration of thyrotropin releasing hormone (TRH) and thyrotropin (TSH).

The present report describes the development of a radioimmunoassay for 3,3',5'-L-triiodothyronine (reverse T3) which is performed on unextracted serum. Utilizing this radioimmunoassay, 21 normal subjects had a mean (+/-SD) serum reverse T3 level of 60 +/- 12 ng/100 ml, 17 of 19 hyperthyroid patients had elevated serum reverse T3 levels, and 10 of 11 hypothyroid subjects had decreased serum reverse T3 concentrations. Thyroidal secretion of reverse T3 was assessed by measurements in samples obtained from the internal carotid artery and jugular vein of sheep following the administration of thyrotropin releasing hormone (TRH) or bovine thyrotropin (TSH). Reverse T3 levels were increased 45-60 min after TRH administration, but TSH administration produced inconsistent alterations in reverse T3, although 18 of 27 samples obtained after TSH injection were higher than their average respective baseline concentration and the mean peak reverse T3 level was 14% higher than baseline. Following TRH administration to 10 normal human subjects, mean serum reverse T3 levels significantly increased from 53.6 ng/100 ml to 56.3ng/100 ml (P less than .05). The thyroid gland content of reverse T3 in human autopsy material was 6.5 +/- 1.5 microng/g tissue. Both pregnancy and estrogen administration were associated with increases in serum reverse T3 concentrations presumably because of their ability to augment thyroxine binding globulin synthesis.

Adult↗
PubMed1996

Celiac disease: how common is jejunoileal fold pattern reversal found at small-bowel follow-through?

OBJECTIVE: Celiac disease, or nontropical sprue, is a cause of mucosal malabsorption. A decreased number of jejunal folds and an increased number of ileal folds (jejunoileal fold pattern reversal) found at small-bowel follow-through have been reported for patients with celiac disease. We asked three questions regarding jejunoileal fold pattern reversal found at small-bowel follow-through in patients with celiac disease. (1) How often is it present, either partially or completely? (2) How often is it associated with other findings of malabsorption? (3) How reliably can it be distinguished from the normal pattern? MATERIALS AND METHODS: Twenty-eight small-bowel follow-through examinations performed on 25 adult patients with celiac disease (confirmed by characteristic small-bowel biopsy and clinical response to a gluten-free diet) were reviewed retrospectively by two authors, who agreed by consensus on partial or complete jejunoileal fold pattern reversal and on other findings of malabsorption. Two methods were used to control for retrospective bias. (1) The prospective and retrospective readings of fold pattern reversal were compared for agreement. (2) The author who had not participated in the retrospective review was asked to distinguish, on the basis of the presence or absence of fold pattern reversal, 24 cases of celiac disease (all of which showed partial or complete fold pattern reversal on retrospective review) from 25 normal control cases (patients with diarrhea) (conformed by normal small-bowel biopsy). RESULTS: Partial or complete jejunoileal fold pattern reversal was identified retrospectively in 24 of the 28 small-bowel examinations (86%) performed on patients with celiac disease. One-half lacked other findings of malabsorption. The prospective and retrospective readings of fold pattern reversal agreed in 21 of the 28 examinations (75%). Forty-four of 49 examinations (90%) were correctly identified by the third author on the basis of fold pattern reversal. CONCLUSION: In patients with celiac disease, partial or complete jejunoileal fold pattern reversal discovered at small-bowel follow-through is common, is often not associated with other findings of malabsorption, and can be reliably distinguished from the normal pattern. Identification of jejunoileal fold pattern reversal found at small-bowel follow-through should prompt an appropriate clinical evaluation for celiac disease.

Adult↗
PubMed1999

Second-order reversed phi.

In a first-order reversed-phi motion stimulus (Anstis, 1970), the black-white contrast of successive frames is reversed, and the direction of apparent motion may, under some conditions, appear to be reversed. It is demonstrated here that, for many classes of stimuli, this reversal is a mathematical property of the stimuli themselves, and the real problem is in perceiving forward motion, which involves the second- or third-order motion systems or both. Three classes of novel second-order reversed-phi stimuli (contrast, spatial frequency, and flicker modulation) that are invisible to first-order motion analysis were constructed. In these stimuli, the salient stimulus features move in the forward (feature displacement) direction, but the second-order motion energy model predicts motion in the reversed direction. In peripheral vision, for all stimulus types and all temporal frequencies, all the observers saw only the reversed-phi direction of motion. In central vision, the observers also perceived reversed motion at temporal frequencies above about 4 Hz, but they perceived movement in the forward direction at lower temporal frequencies. Since all of these stimuli are invisible to first-order motion, these results indicate that the second-order reversed-phi stimuli activate two subsequent competing motion mechanisms, both of which involve an initial stage of texture grabbing (spatiotemporal filtering, followed by fullwave rectification). The second-order motion system then applies a Reichardt detector (or equivalently, motion energy analysis) directly to this signal and arrives at the reversed-phi direction. The third-order system marks the location of features that differ from the background (the figure) in a salience map and computes motion in the forward direction from the changes in the spatiotemporal location of these marks. The second-order system's report of reversed movement dominates in peripheral vision and in central vision at higher temporal frequencies, because it has better spatial and temporal resolution than the third-order system, which has a cutoff frequency of 3-4 Hz (Lu & Sperling, 1995b). In central vision, below 3-4 Hz, the third-order system's report of resolvable forward movement of something salient (the figure) dominates the second-order system's report of texture contrast movement.

Adult↗
PubMed1975

The effect of streptomycin resistance, caffeine and acriflavine on ultraviolet light-induced reversion to tryptophan independence in strains of Escherichia coli B/r.

When the excision proficient strain E. coli WP2 Hcr+ trp- was grown to stationary phase by glucose starvation in M-9 minimal medium before UV -irradiation, the ability of nutrient broth enrichment of minimal medium to enhance trp- leads to Trp+ reversion was greatly reduced. Less than 50% of the Trp+ revertants were found to be ochre suppressors. However, in the WWP2 Hcr- strain, 75-86% of the tested revertants were ochre suppressors. This indicates that, under the cultural conditions employed, many potential suppressor mutations were removed by excision repair in the presence of broth enrichment. Broth enhancement of reversion also occurred in the Hcr- strain, which indicates that a less error-prone mode of recombination repair functions under minimal growth conditions. An Hcr+ strr derivative of WP2 Hcr+ was more resistant than its strs parent to the lethal effect of UV light and showed a lower UV-induced Trp+ reversion frequency. The percentage of Trp+ revertants that were due to ochre suppressors was markedly reduced in the strr strain. The Hcr- strr strain also had a lower UV-induced Trp+ reversion frequency than its strs parent. The excision repair inhibitor caffeine had little effect at lower UV doses on increasing Trp+ reversion in both Hcr+ strains. Acriflavine, however, was effective at lower UV doses in enhancing reversiin of the Hcr+ strains and the degree of enhancement increased with the dose. Acriflavine appeared to specifically enhance the number of ochre suppressing Trp+ revertants. In both Hcr- strains (strs and strr) caffeine (500 mug/ml) had no effect on survival but reduced the UV-induced Trp+ reversion frequency acting as an antimutagen. In contrast, acriflavine (2 mug/ml) decreased survival and increased the Trp+ reversion frequency of the Hcr- strains. The data on spontaneous Trp+ reversion frequencies show that the Hcr+ strs strain had a higher spontaneous reversion frequency than the Hcr- strs strain on all plating media. Further, caffeine was shown to reduce spontaneous Trp+ reversion in both Hcr+ and Hcr- strains while acriflavine increased the spontaneous reversion frequencies of both strains.

Acridines↗
PubMed1989

[Electromyographic study of masticatory dysfunction in patients with unilateral cleft lip and palate and reversed occlusion].

UNLABELLED: Masticatory dysfunction in patients with unilateral cleft lip and palate was studied on the basis of electromyograms of the masticatory muscles. The purpose of the study was to elucidate the origin of the dysfunction by means of comparisons among electromyograms of masticatory muscles in cases of normal occlusion, reversed occlusion and reversed occlusion caused by unilateral cleft lip and palate. Subjects were 10 cases of normal occlusion (10y2m-11y10m), 10 cases of reversed occlusion (7y2m-11y2m) and 20 cases of unilateral cleft lip and palate (8y0m-14y3m). In each subject, electromyograms of the masseter and anterior venters of the temporal muscles at the isometric-contraction phase were recorded by means of the surface-electrode method with mandible loads of 1-5 kg. The electromyograms were analyzed quantitatively by means of an electromyographic device called a Turn Counter. Relations between loads and amplitude as well as numbers of turns were examined. At the same time maximum masticatory pressure and occlusal contact points were measured and then examined in comparison with electromyographic findings. RESULTS: 1. Correlation coefficients between loads and amplitudes as well as numbers of turns decreased among the groups in this order: normal occlusion, reversed occlusion and cleft-caused reversed occlusion. Significant differences were observed between the normal-occlusive group and the reversed and cleft-caused reversed-occlusive groups. 2. No. difference was observed between the normal-occlusive and reversed-occlusive groups in terms of correlation coefficients between total sums of amplitudes and turns of the 4 masseter muscles (right and left masseters and anterior venters of the temporal muscles) and loads. Correlation coefficients in the cleft group were significantly smaller than those in the other 2 groups. 3. Because of great differences in regression coefficient among individuals, no synergic contraction pattern of the 4 mastication muscles (right and left masseter and temporal muscles) could be specified. 4. The A/T ratio of masseters in the cleft group was significantly smaller than those in the normal- and reversed-occlusive groups. 5. Under maximum load, the activity ratio of the 4 masseter and temporal muscles was 1:1 in the normal- and reversed-occlusive groups, whereas temporal-muscle activity predominated over masseter-muscle activity in the cleft group. 6. Maximum masticatory pressure decreased in the order: normal-occlusive, reversed-occlusive, and cleft caused occlusive. No correlation with electromyographic findings was observed.(ABSTRACT TRUNCATED AT 400 WORDS)

Child↗
PubMed1981

Specific reversal of cytolytic T cell-target cell functional binding is induced by free target cells.

Reversal of specific cell-cell adhesions between allogeneic cytolytic T lymphocytes (CTL) and 51Cr-labeled target cells has been studied by using a functional assay for specific target cell binding. Functional adhesions between CTL and a tumor cell target, the P815 mastocytoma, were stable in suspension for greater than 5 hr. Addition of unlabeled target cells, however, resulted in rapid reversal of functional binding. This reversal appeared to be specific in that no reversal was induced by tumor cells of other H-2 types. Functional reversal of conjugates between CTL and labeled spleen cells syngeneic with P815 also occurred in the presence of unlabeled P815 cells or normal spleen cells of the appropriate H-2 type. The reversal by P815 was substantially more efficient than by normal spleen cells. Furthermore, normal spleen cells of the appropriate H-2 type did not induce reversal of CTL-P815 target conjugates. Purified plasma membranes from P815 cells did not specifically reverse functional binding of CTL to either P815 or normal spleen cell targets. These results demonstrate that functional CTL-target cell binding can be specifically reversed by interaction with free target cells. The rate of reversal appears to be dependent on the relative affinity of the CTL for the bound versus the free target cell. CTL may provide a useful system for studying reversal of specific cell-cell adhesions.

Animals↗