Dr. Tibor  Toth  Dmd image

Dr. Tibor Toth Dmd

1706 Treasure Hills Blvd
Harlingen TX 78550
956 656-6003
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License #: 21597
NPI: 1538175534
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A three-leg model producing tetrapod and tripod coordination patterns of ipsilateral legs in the stick insect. - Journal of neurophysiology
Insect locomotion requires the precise coordination of the movement of all six legs. Detailed investigations have revealed that the movement of the legs is controlled by local dedicated neuronal networks, which interact to produce walking of the animal. The stick insect is well suited to experimental investigations aimed at understanding the mechanisms of insect locomotion. Beside the experimental approach, models have also been constructed to elucidate those mechanisms. Here, we describe a model that replicates both the tetrapod and tripod coordination pattern of three ipsilateral legs. The model is based on an earlier insect leg model, which includes the three main leg joints, three antagonistic muscle pairs and their local neuronal control networks. These networks are coupled via angular signals to establish intra-leg coordination of the three neuro-muscular systems during locomotion. In the present 3-leg model, we coupled three such leg models, representing front, middle and hind leg, in this way. The coupling was between the levator-depressor local control networks of the three legs. The model could successfully simulate tetrapod and tripod coordination patterns, as well as the transition between them. The simulations showed that for the inter-leg coordination during tripod, the position signals of the levator-depressor neuro-muscular systems sent between the legs were sufficient, while in tetrapod, additional information on the angular velocities in the same system was necessary, and together with the position information also sufficient. We therefore suggest that, during stepping, the connections between the levator-depressor neuro-muscular systems of the different legs are of primary importance.Copyright © 2015, Journal of Neurophysiology.
Investigating inter-segmental connections between thoracic ganglia in the stick insect by means of experimental and simulated phase response curves. - Biological cybernetics
The neuronal networks that control the motion of the individual legs in insects, in particular in the stick insect, are located in the pro-, meso- and meta-thoracic ganglia. They ensure high flexibility of movement control. Thus, the legs can move in an apparently independent way, e.g., during search movements, but also in tight coordination during locomotion. The latter is evidently a very important behavioural mode. It has, therefore, inspired a large number of studies, all aiming at uncovering the nature of the inter-leg coordination. One of the basic questions has been as to how the individual control networks in the three thoracic ganglia are connected to each other. One way to study this problem is to use phase response curves. They can reveal properties of the coupling between oscillatory systems, such as the central pattern generators in the control networks in the thoracic ganglia. In this paper, we report results that we have achieved by means of a combined experimental and modelling approach. We have calculated phase response curves from data obtained in as yet unpublished experiments as well as from those in previously published ones. By using models of the connected pro- and meso-thoracic control networks of the protractor and retractor neuromuscular systems, we have also produced simulated phase response curves and compared them with the experimental ones. In this way, we could gain important information of the nature of the connections between the aforementioned control networks. Specifically, we have found that connections from both the protractor and the retractor "sides" of the pro-thoracic network to the meso-thoracic one are necessary for producing phase response curves that show close similarity to the experimental ones. Furthermore, the strength of the excitatory connections has been proven to be crucial, while the inhibitory connections have essentially been irrelevant. We, thus, suggest that this type of connection might also be present in the stick insect, and possibly in other insect species.
Influence of lowland forests on subsurface salt accumulation in shallow groundwater areas. - AoB PLANTS
In flat sedimentary plains in areas with a sub-humid climate, tree planting on grasslands and arable lands creates strong hydrological shifts. As a result of deep rooting and high water uptake of trees, groundwater levels drop and subsurface salt accumulation increases. Tree planting has expanded globally and in Hungary it reached rates of 15 000 ha year(-1), being focused mainly in the Great Hungarian Plain where forests replace grasslands and crops in a region with widespread shallow groundwater. We performed soil and groundwater observations in 31 pairs of forest and control plots in the region, including gradients of initial water table depth and salinity, soil layering, and tree species and age. Accumulated tree biomass was positively correlated with soil salinization rates following tree planting, being also affected by species (poplar > common oak > black locust) and stand age. Differences among tree species effects appeared to be related to their growth rates. Due to downward deep percolation and salt leaching episodes during the Hungarian winters, the observed salt accumulation rates were lower than those described under similar settings in the warmer Argentine Pampas.Published by Oxford University Press on behalf of the Annals of Botany Company.
A neuro-mechanical model explaining the physiological role of fast and slow muscle fibres at stop and start of stepping of an insect leg. - PloS one
Stop and start of stepping are two basic actions of the musculo-skeletal system of a leg. Although they are basic phenomena, they require the coordinated activities of the leg muscles. However, little is known of the details of how these activities are generated by the interactions between the local neuronal networks controlling the fast and slow muscle fibres at the individual leg joints. In the present work, we aim at uncovering some of those details using a suitable neuro-mechanical model. It is an extension of the model in the accompanying paper and now includes all three antagonistic muscle pairs of the main joints of an insect leg, together with their dedicated neuronal control, as well as common inhibitory motoneurons and the residual stiffness of the slow muscles. This model enabled us to study putative processes of intra-leg coordination during stop and start of stepping. We also made use of the effects of sensory signals encoding the position and velocity of the leg joints. Where experimental observations are available, the corresponding simulation results are in good agreement with them. Our model makes detailed predictions as to the coordination processes of the individual muscle systems both at stop and start of stepping. In particular, it reveals a possible role of the slow muscle fibres at stop in accelerating the convergence of the leg to its steady-state position. These findings lend our model physiological relevance and can therefore be used to elucidate details of the stop and start of stepping in insects, and perhaps in other animals, too.
A neuro-mechanical model of a single leg joint highlighting the basic physiological role of fast and slow muscle fibres of an insect muscle system. - PloS one
In legged animals, the muscle system has a dual function: to produce forces and torques necessary to move the limbs in a systematic way, and to maintain the body in a static position. These two functions are performed by the contribution of specialized motor units, i.e. motoneurons driving sets of specialized muscle fibres. With reference to their overall contraction and metabolic properties they are called fast and slow muscle fibres and can be found ubiquitously in skeletal muscles. Both fibre types are active during stepping, but only the slow ones maintain the posture of the body. From these findings, the general hypothesis on a functional segregation between both fibre types and their neuronal control has arisen. Earlier muscle models did not fully take this aspect into account. They either focused on certain aspects of muscular function or were developed to describe specific behaviours only. By contrast, our neuro-mechanical model is more general as it allows functionally to differentiate between static and dynamic aspects of movement control. It does so by including both muscle fibre types and separate motoneuron drives. Our model helps to gain a deeper insight into how the nervous system might combine neuronal control of locomotion and posture. It predicts that (1) positioning the leg at a specific retraction angle in steady state is most likely due to the extent of recruitment of slow muscle fibres and not to the force developed in the individual fibres of the antagonistic muscles; (2) the fast muscle fibres of antagonistic muscles contract alternately during stepping, while co-contraction of the slow muscle fibres takes place during steady state; (3) there are several possible ways of transition between movement and steady state of the leg achieved by varying the time course of recruitment of the fibres in the participating muscles.
A novel CFHR5 fusion protein causes C3 glomerulopathy in a family without Cypriot ancestry. - Kidney international
C3 glomerulopathy describes glomerular pathology associated with predominant deposition of complement C3 including dense deposit disease and C3 glomerulonephritis. Familial C3 glomerulonephritis has been associated with rearrangements affecting the complement factor H-related (CFHR) genes. These include a hybrid CFHR3-1 gene and an internal duplication within the CFHR5 gene. CFHR5 nephropathy, to date, occurred exclusively in patients with Cypriot ancestry, and is associated with a heterozygous internal duplication of the CFHR5 gene resulting in duplication of the exons encoding the first two domains of the CFHR5 protein. Affected individuals possess both the wild-type nine-domain CFHR5 protein (CFHR5(12-9)) and an abnormally large mutant CFHR5 protein in which the initial two protein domains are duplicated (CFHR5(1212-9)). We found CFHR5(1212-9) in association with familial C3 glomerulonephritis in a family without Cypriot ancestry. The genomic rearrangement was distinct from that seen in Cypriot CFHR5 nephropathy. Our findings strengthen the association between CFHR5(1212-9) and familial C3 glomerulonephritis and recommend screening for CFHR5(1212-9) in patients with C3 glomerulopathy irrespective of ethnicity. Since CFHR5(1212-9) can result from at least two genomic rearrangements, screening is most readily achieved through analysis of CFHR5 protein.
An incidental finding of unicornuate uterus with unilateral ovarian agenesis during laparoscopy in patient who gave birth to eleven children: a case report. - Collegium antropologicum
Congenital uterine anomalies are often asymptomatic. They may present with infertility, recurrent miscarriage, preterm delivery, abnormal lie in pregnancy and other obstetric complications. We report the case of a 38-year old patient with unicornuate uterus without rudimentary horn and with unilateral left ovarian agenesis and unilateral left renal agenesis who gave birth to eleven children. Anomaly was incidentally diagnosed during laparoscopic sterilization.
Factor H autoantibodies in membranoproliferative glomerulonephritis. - Molecular immunology
Factor H autoantibodies are found in ~10% of aHUS patients. Most are associated with complete deficiency of factor H related proteins 1/3 and bind to the C terminal recognition domain. MPGN, like aHUS, is characterised by complement activation. In this study we, therefore, examined the hypothesis that factor H autoantibodies are associated with MPGN. We screened sera from 16 MPGN patients and 100 normal controls using ELISA and detected strongly positive IgG factor H autoantibodies in 2 patients. One patient had type II (DDD) MPGN (male aged 24 yrs) with C3NeF and the other type I (female aged 26 yrs) with no detectable C3NeF. We identified the binding site of the autoantibodies using small SCR domain fragments in the ELISA and showed that the autoantibodies in both patients bound predominately to the N terminal complement regulatory domain of factor H. We measured CFHR 1/3 copy number using MLPA and showed that both patients had 2 copies of CFHR1 and 3. Finally, we examined the functionality of detected factor H autoantibodies using purified patient IgG and observed increased haemolysis when purified IgG from both patients was added to normal human sera prior to incubation with rabbit red blood cells. Thus, in a cohort of MPGN patients we have found a high titre of functionally significant factor H autoantibodies in two patients with MPGN. Antibody depleting therapy may have a role in such patients and we suggest that screening for factor H autoantibodies should be undertaken in all patients with MPGN.Copyright © 2012 Elsevier Ltd. All rights reserved.
Dominance of local sensory signals over inter-segmental effects in a motor system: modeling studies. - Biological cybernetics
Recent experiments, reported in the accompanying paper, have supplied key data on the impact afferent excitation has on the activity of the levator-depressor motor system of an extremity in the stick insect. The main finding was that, stimulation of the campaniform sensillae of the partially amputated middle leg in an animal where all other but one front leg had been removed, had a dominating effect over that of the stepping ipsilateral front leg. In fact, the latter effect was minute compared to the former. In this article, we propose a local network that involves the neuronal part of the levator-depressor motor system and use it to elucidate the mechanisms that underlie the generation of neuronal activity in the experiments. In particular, we show that by appropriately modulating the activity in the neurons of the central pattern generator of the levator-depressor motor system, we obtain activity patterns of the motoneurons in the model that closely resemble those found in extracellular recordings in the stick insect. In addition, our model predicts specific properties of these records which depend on the stimuli applied to the stick insect leg. We also discuss our results on the segmental mechanisms in the context of inter-segmental coordination.
Dominance of local sensory signals over inter-segmental effects in a motor system: experiments. - Biological cybernetics
Legged locomotion requires that information local to one leg, and inter-segmental signals coming from the other legs are processed appropriately to establish a coordinated walking pattern. However, very little is known about the relative importance of local and inter-segmental signals when they converge upon the central pattern generators (CPGs) of different leg joints. We investigated this question on the CPG of the middle leg coxa-trochanter (CTr)-joint of the stick insect which is responsible for lifting and lowering the leg. We used a semi-intact preparation with an intact front leg stepping on a treadmill, and simultaneously stimulated load sensors of the middle leg. We found that middle leg load signals induce bursts in the middle leg depressor motoneurons (MNs). The same local load signals could also elicit rhythmic activity in the CPG of the middle leg CTr-joint when the stimulation of middle leg load sensors coincided with front leg stepping. However, the influence of front leg stepping was generally weak such that front leg stepping alone was only rarely accompanied by switching between middle leg levator and depressor MN activity. We therefore conclude that the impact of the local sensory signals on the levator-depressor motor system is stronger than the inter-segmental influence through front leg stepping.

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