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At least 721 records · Page 40Linked to original sources

PubMed2000

Convergence pattern of uncrossed excitatory and inhibitory semicircular canal-specific inputs onto second-order vestibular neurons of frogs. Organization of vestibular side loops.

Second-order vestibular neurons of frogs receive converging monosynaptic excitatory and disynaptic excitatory and inhibitory inputs following electrical pulse stimulation of an individual semicircular canal nerve on the ipsilateral side. Here we revealed, in the in vitro frog brain, disynaptic inhibitory postsynaptic potentials (IPSPs) by bath application of antagonists specific for glycine or gamma-aminobutyric acid-A (GABA(A)) receptors. Differences in the response parameters between disynaptic IPSPs and excitatory postsynaptic potentials (EPSPs) suggested that disynaptic IPSPs originated from a more homogeneous subpopulation of thicker vestibular nerve afferent fibers than mono- or disynaptic EPSPs. To investigate a possible size-related organization of these canal-specific, parallel pathways, we combined long-lasting anodal currents of variable intensities with strong cathodal test pulses, to block pulse-evoked responses reversibly in a graded manner according to the size-related sensitivity of vestibular nerve afferent fibers. The anodal current intensity required to block a particular response component was about 15 times lower than the strength of the cathodal test pulse that activated this response component. These large threshold differences were exploited for a selective anodal suppression of the responses from thick vestibular nerve afferent fibers. In fact, response components known to originate exclusively from thick-caliber afferent fibers such as the electrically transmitted monosynaptic EPSP component exhibited the lowest thresholds for cathodal test pulses and were the first to disappear in the presence of small anodal polarization steps. Thresholds for the activation/inactivation of responses and current intensities required for response saturation/blockade were used to assess the fiber spectrum that evoked the different response components. Mono- and disynaptic EPSPs appeared to originate from a broad spectrum of thick and thin vestibular nerve afferent fibers. The spectrum of afferent fibers that activated disynaptic IPSPs on the other hand was more homogeneous and consisted of thick and intermediate fibers. Such a canal-specific and fiber type-related organization of converging inputs of second-order vestibular neurons via feedforward projections was shown for the first time by this study in frogs, but might also prevail in mammals. Similar differences in these feedforward pathways have been proposed earlier in a vestibular side-loop model. Our results are consistent with the basic assumptions of this model and relate to the processing and tuning of dynamic vestibular signals.

Animals↗

PubMed1999

Listing's plane rotation with convergence: role of disparity, accommodation, and depth perception.

Earlier studies have reported temporal rotation of Listing's plane with convergence of the eyes causing torsion, which is dependent on eye elevation. The amount by which the planes rotate differs from study to study. To gain insight into the functional significance of the temporal tilt of Listing's plane for vision, we examined whether the rotation of the plane depends on the visual conditions, namely on the stimuli driving vergence. In different conditions, accommodative vergence, disparity-vergence, combinations of disparity with accommodation or depth perception were used and the resulting rotation of Listing's plane was measured. Our findings show, for the first time, that the relationship between convergence and Listing's-plane temporal rotation depends on the stimuli driving vergence. When the stimulus contains only disparity cues, vergence and Listing's plane rotate immediately and consistently among subjects. Accommodative vergence, the mutual couplings between vergence and accommodation, can influence the orientation of Listing's plane, but they do so in a idiosyncratic way. The largest rotation was elicited by stereograms combining disparity-vergence with depth perception. These findings support the idea of a functional role of Listing's plane rotation for binocular vision, perhaps for depth perception.

Accommodation, Ocular↗

PubMed2006

Mitochondrial genome dynamics in plants and animals: convergent gene fusions of a MutS homologue.

Mitochondrial processes influence a broad spectrum of physiological and developmental events in higher eukaryotes, and their aberrant function can lead to several familiar disease phenotypes in mammals. In plants, mitochondrial genes directly influence pollen development and the occurrence of male sterility in natural plant populations. Likewise, in animal systems evidence accumulates to suggest important mitochondrial functions in spermatogenesis and reproduction. Here we present evidence for a convergent gene fusion involving a MutS-homologous gene functioning within the mitochondrion and designated Msh1. In only plants and soft corals, the MutS homologue has fused with a homing endonuclease sequence at the carboxy terminus of the protein. However, the endonuclease domains in the plants and the soft corals are members of different groups. In plants, Msh1 can influence mitochondrial genome organization and male sterility expression. Based on parallels in Msh1 gene structure shared by plants and corals, and their similarities in reproductive behavior, we postulate that this convergent gene fusion might have occurred in response to coincident adaptive pressures on reproduction.

Adenosine Triphosphatases↗

PubMed2003

Class I molecules with similar peptide-binding specificities are the result of both common ancestry and convergent evolution.

HLA class I molecules can be classified into supertypes associated with overlapping peptide-binding motifs and repertoires. Herein, overlaps in peptide-binding and T-cell recognition repertoires were demonstrated between mouse and human molecules. Since rodent and primate lineages separated before the current allelic variation of mouse and human class I molecules, these data demonstrate that supertypic specificities originated by convergent evolution. Phylogenetic and structural analyses demonstrated that convergent evolution also occurs amongst primates and within the human species, resulting from the selection of different pocket structures having similar specificity or independent repeated selection of the same pocket structure.

Amino Acid Motifs↗

PubMed1999

Convergence of multilocus systems under weak epistasis or weak selection.

The convergence of multilocus systems under viability selection with constant fitnesses is investigated. Generations are discrete and nonoverlapping; the monoecious population mates at random. The number of multiallelic loci, the linkage map, dominance, and epistasis are arbitrary. It is proved that if epistasis or selection is sufficiently weak (and satisfies a certain nondegeneracy assumption whose genericity we establish), then there is always convergence to some equilibrium point. In particular, cycling cannot occur. The behavior of the mean fitness and some other aspects of the dynamics are also analyzed.

Alleles↗

PubMed1998

Phase angle convergence of multiple monophasic action potential recordings precedes spontaneous termination of ventricular fibrillation.

AIMS: To elucidate the mechanism of spontaneous termination of ventricular fibrillation (VF) and to define an indicator of its occurrence, the phase angle, a novel measure to assess synchrony of activation, was evaluated. METHODS AND RESULTS: In 7 isolated rabbit hearts, 7 monophasic action potentials were recorded simultaneously. Ventricular fibrillation was induced by T wave shocks. Cycle lengths (CL) and phase angles between all 7 recordings were analyzed until spontaneous termination or shock-induced defibrillation. Average phase angle was calculated as activation time difference to a reference channel and expressed as a fraction of the reference channel's CL with 1 equaling a complete CL. Initial CLs and phase angles were similar in sustained and terminating episodes (CL: 141 +/- 16 ms vs 142 +/- 24 ms, phase angle: 0.244 +/- 0.11 vs 0.263 +/- 0.1, p = NS). During spontaneous termination, CL increased slightly by 7%. Average phase angle converged gradually over the last three activations before termination of ventricular fibrillation by 22-48% (p < 0.0005), eventually resulting in phase angles similar to paced rhythms directly prior to spontaneous termination of ventricular fibrillation. CONCLUSIONS: Gradual synchronization of activation is part of the electrophysiological mechanism resulting in spontaneous ventricular fibrillation termination and can be detected three activations before termination. Phase angle convergence may be useful to detect spontaneous termination of ventricular fibrillation.

Action Potentials↗

PubMed1998

Convergence of directional vestibular and neck signals on cerebellar purkinje cells.

Convergence of spatially oriented vestibular and neck signals within the cerebellar anterior vermis in decerebrate cats was studied by recording the simple spike discharge of Purkinje (P) cells during wobble either of the whole animal (vestibular input) or of the body under a fixed head (neck input) at 0.156 Hz, 5 degrees and 2.5 degrees , respectively. Both clockwise (CW) and counterclockwise (CCW) rotations were performed. Units that had equal response amplitudes to CW and CCW rotations (narrowly tuned neurons) were described by a single vector (Smax), characterized by a gain, a direction and a temporal phase. Units with different response amplitudes to CW and CCW rotation (broadly tuned neurons) were described by two vectors (Smax and Smin). In addition to these bidirectional units, there were also unidirectional units which responded either to CW or CCW rotation; in these cases the gain of Smax equals that of Smin. On the whole, 77% and 63% of the P cells responding to vestibular and neck stimulation, respectively, showed a bidirectional broadly tuned or unidirectional behavior. These response patterns were attributed to the convergence of signals with different spatial and temporal properties. About 50% of the P cells from which recordings were made responded to stimulation of both sensory systems. However, the gains of the Smax vectors of the neck responses were much greater than those of the vestibular responses, at least for small amplitudes of rotation, and were positively correlated with them. Usually the differences in the orientation components of the neck and vestibular Smax vectors were larger, while the differences in temporal phases were smaller than 90 degrees . These findings suggest that periodic changes in the phase difference and gain ratio of the neck to the vestibular response may occur during dynamic displacement of the head over the body, depending on the stimulus direction. As a result of these data, the P cells of the cerebellar vermis are expected to show prominent responses to head rotation, which could affect the spatially organized postural responses by utilizing vestibular and reticular targets.

Animals↗

PubMed1997

Evidence for convergent evolution of A and B blood group antigens in primates.

To determine whether convergent or trans-specific evolution is responsible for the persistence of the ABO polymorphism in apes, we have sequenced segments of introns 5 and 6 of the ABO gene. Four substitutions and one insertion or deletion group human A, B, and O alleles together, separate from their chimpanzee A and gorilla B counterparts. No shared substitutions support a trans-species mode of evolution for any of the alleles examined. We conclude that the A and B antigens of the chimpanzee and gorilla, respectively, have arisen by convergent evolution. Phylogenetic analysis suggests that the human A and B alleles are ancient, having diverged at least 3 million years ago. These alleles must have therefore been trans-specifically inherited within the genus Homo.

ABO Blood-Group System↗

PubMed2002

Functional convergence in plant responses to the environment.

Much comparative ecophysiological research has focused on contrasting species-specific behavior or ecological strategies with regard to regulation of basic physiological processes such as transpiration, photosynthesis and growth, leading to an emphasis on divergence rather than convergence in plant functioning. This review highlights selected examples in which substantial functional convergence among taxonomically, phylogenetically and architecturally diverse species has been revealed by applying appropriate scaling factors and identifying universal constraints or trade-offs. Recent empirical and theoretical scaling models emphasize the strong role that plant size, architecture, allometry and chemistry play in constraining functional traits related to water and carbon economy and growth. Taken together, the findings summarized here strongly suggest that there are a limited number of physiological solutions to a given problem of plant adaptation to the environment. Comparative ecophysiological studies will therefore benefit from consideration of the constraints that plant anatomical, structural and chemical attributes place on physiological functioning.

Adaptation, Physiological↗

PubMed2026

Shared genetic architecture and cellular convergence between female reproductive disorders and pulmonary function: a genome-wide cross-trait analysis.

Female reproductive disorders (FRDs), including polycystic ovary syndrome, endometriosis, uterine leiomyomata, and infertility, have been epidemiologically associated with impaired pulmonary function. However, it remains unclear whether this cross-organ link reflects shared genetic etiology and, if so, which cellular mechanisms mediate it. We performed a systematic genome-wide cross-trait analysis of three FRDs and lung function traits (FEV₁, FVC, FEV₁/FVC) using GWAS summary statistics from individuals of European ancestry, integrating genetic correlation, bidirectional causal inference, pleiotropy mapping, and single-cell enrichment analyses. We identified significant negative genetic correlations between FRDs and lung volume traits, most prominently for FVC (rg range: - 0.077 to - 0.178). Bidirectional causal analyses indicated that FRDs have a detrimental effect on lung volume, with higher FRD genetic liability associated with reduced lung volume. Cross-trait meta-analysis identified 17 pleiotropic variants across 11 loci, with the 19q13.2 (LTBP4) and 12q13.13 (HOXC6/HOXC9) loci showing strong evidence of shared causal variants. Critically, single-cell analyses revealed that shared genetic risk converged on mesenchymal lineages across organs, specifically alveolar adventitial fibroblasts in the lung and stromal/smooth muscle cells in the endometrium. Transcriptome-wide analyses further nominated the estrogen-responsive gene RERG as a convergent gene linking these conditions with lung function. Our study revealed a shared genetic architecture between female reproductive disorders and lung function traits, providing a basis for further mechanistic investigations and potential clinical evaluation. Furthermore, our findings suggest that shared fibroproliferative and hormone-responsive pathways may offer insights into the biological mechanisms underlying these conditions.

Female↗

PubMed2005

Methods to detect response shift in quality of life data: a convergent validity study.

When measuring changes in quality of life (QL) with a pretest-posttest design, response shift can affect results. We investigated the convergent validity of three approaches to detect response shift. (1) In the thentest approach, response shift is measured using a retrospective judgment of pretest QL-levels (thentest). (2) In the anchor-recalibration approach response shift is measured, assessing shifts in patients' individual definitions of the scale-anchors (worst and best imaginable QL) over time. (3) In the Structural Equation Modeling (SEM) approach response shift is indicated by mathematically defined changes in factor solutions and variance-covariance matrices over time. Prior to and three months after invasive surgery, 170 cancer patients completed the SF-36, the Multidimensional Fatigue Inventory (as pre-, post-, and thentest), and the anchor-recalibration task (as pre-, and posttest). Results showed agreement between the thentest and SEM approach on the absence (6 scales) and presence (2 scales) of response shift in 8 of the 9 scales. For the ninth scale both methods detected response shift, but in opposite directions. Possible explanations for this discrepancy are discussed. The anchor-recalibration task agreed with the other approaches on only the absence of response shift in 4 of the 7 scales. The convergent results of thentest and SEM support their validity, especially because they use statistically independent operationalizations of response shift. In this study, recall bias did not invalidate thentest results.

Activities of Daily Living↗

PubMed1993

Color Doppler echocardiographic determination of mitral regurgitant flow from the proximal velocity profile of the flow convergence region.

Flow rate across an orifice can be determined from color Doppler echocardiographic maps of the flow convergence region proximal to the orifice. Different methods have been developed in vitro. The proximal velocity profile method was prospectively evaluated in patients with mitral regurgitation. Color Doppler echocardiography was performed in 74 patients before cardiac catheterization. The increasing velocities within the flow convergence region were determined in an apical plane on the straight line from the transducer to the leak; thus the proximal velocity profile was established and plotted on a nomogram. Instantaneous regurgitant flow rate was derived from the position of the resulting curve in relation to the nomogram's reference curves, which were derived from in vitro measurements. Regurgitant stroke volume was calculated as regurgitant flow rate.regurgitant velocity-time integral/regurgitant peak velocity, using additional continuous-wave Doppler. The 55 patients with angiographic regurgitation had a close association between regurgitant flow rate (0 to 600 ml/s) and angiographic grade (Spearman's rank correlation coefficient = 0.91; p < 0.0001). Regurgitant flow rate did not overlap between grades < or = 2+, 3+ and 4+. In 16 patients, regurgitant stroke volume by echocardiography correlated well with that by the angiography/Fick method (r = 0.88; SEE = 17.1 ml), with a regression line close to identity (y = 0.89x + 12.7 ml). The proximal velocity profile method enables determination of mitral regurgitant flow and estimation of regurgitant volume.

Blood Flow Velocity↗

PubMed1976

Resection of both medial rectus muscles in organic convergence insufficiency.

Six patients with a prolonged history of severe muscular asthenopia caused by persistent convergence insufficiency underwent resection of both medial rectus muscles. A temporary consecutive esotrapia occurred in each instance and was controlled with prisms. Five weeks after surgery the consecutive esotropia had disappeared in all but one patient who still required prismatic correction for distance fixation. All patients experienced relief from their symptoms. Whereas orthoptic training is useful in most cases of convergence insufficiency a resection of both medial rectus muscles should be considered in persistent cases especially with an associated weakness of accommodation.

Accommodation, Ocular↗

PubMed1982

Convergence-evoked eyelid nystagmus.

We studied two patients with eyelid nystagmus induced by ocular convergence. The first patient, a 29-year-old man, had the signs of a cerebellar syndrome after sustaining severe craniocerebral injuries. The second patient, a 12-year-old girl, had a tumor of the anterior vermis cerebelli. After treatment with corticosteroids (Patient 1) and surgery (Patient 2), the eyelid nystagmus gradually disappeared. An alteration in the cerebellar system is the most likely cause of convergence-evoked nystagmus.

Adult↗

PubMed1995

A study on the convergent and discriminant validity of the Dental Anxiety Inventory.

A correlational design was used to assess the convergent and discriminant validity of the Dental Anxiety Inventory (DAI), a newly developed measurement instrument designed to circumvent shortcomings of other dental anxiety questionnaires. Convergent validity was supported by a high correlation between the DAI and Corah's Dental Anxiety Scale. Discriminant validity was supported by small positive correlations with scales for neuroticism, anxiety, and fear, and nonsignificant correlations with other variables such as extroversion. The results support the construct validity of the DAI.

Adult↗

PubMed1983

Interactions among convergent inputs to somatosensory cortex neurons.

Postsynaptic potentials (psps) produced by electrical stimulation of 4 forelimb nerves were recorded intracellularly from neurons in the primary somatosensory cortex of sodium pentobarbital anesthetized cats. Convergent inputs were found from nerves subserving different modalities and different regions of the forelimb. Psps from separate afferent sources usually did not sum linearly but rather interacted with one another. These interactions could have occurred at the cortical level or earlier in the ascending pathways and are interpreted with regards to the control of somatosensory responsiveness by multiple converging inputs.

Animals↗

PubMed1983

Convergence on reticulospinal neurons mediating contralateral pyramidal disynaptic EPSPs to neck motoneurons.

Convergence upon reticulospinal neurons which mediate disynaptic, contralateral pyramidal EPSPs to neck motoneurons has been examined in cats with contralateral pyramidal transection at the obex. Conditioning stimuli in the contralateral tectum and ipsilateral mesencephalic tegmentum produced monosynaptic facilitation of the disynaptic pyramidal EPSP, whereas facilitation evoked from the ipsilateral pyramid showed a disynaptic time course. These results show that contralateral pyramidal, tectal and ipsilateral tegmental fibers converge onto common reticulospinal neurons which have direct excitatory connections with neck motoneurons.

Animals↗

PubMed1983

An electrophysiological study of convergence of entopeduncular and lateral preoptic inputs on lateral habenular neurons projecting to the midbrain.

Extracellular recordings were made from single neurons in the lateral habenular nucleus of urethane-anesthetized rats. Single pulse stimulation of the entopeduncular nucleus influenced the spontaneous activity of 200 out of 293 (68%) lateral habenular neurons tested, with the most frequent response being suppression of activity and initial activation followed by suppression. Single pulse stimulation of the lateral preoptic area influenced the activity of 140 out of 165 (85%) lateral habenular neurons tested. Response were similar to those for entopeduncular stimulation. In a series of 137 lateral habenular units, 85 (62%) were influenced by stimulation of both sites indicating convergence of inputs from these two forebrain areas. Approximately half of the lateral habenular neurons which received converging inputs from entopeduncular nucleus and lateral preoptic area were activated antidromically by stimulation of the fasciculus retroflexus, indicating that they were output neurons. These electrophysiological findings support the suggestion from recent neuroanatomical studies that the lateral habenular nucleus is a site of integration for entopeduncular and limbic inputs and in turn sends signals to the midbrain.

Afferent Pathways↗