Biomedical subjects

W G Wright

Publications and source records attributed to W G Wright.

At least 19 recordsLinked to original sources

PubMed2006

Subjective somatosensory vertical during dynamic tilt is dependent on task, inertial condition, and multisensory concordance.

To investigate how visual and vestibular cues are integrated for the perception of gravity during passive self-motion, we measured the ability to maintain a handheld object vertical relative to gravity without visual feedback during sinusoidal roll-tilt stimulation. Visual input, either concordant or discordant with actual dynamic roll-tilt, was delivered by a head-mounted display showing the laboratory. The four visual conditions were darkness, visual-vestibular concordance, stationary visual scene, and a visual scene 180 degrees phase-shifted relative to actual tilt. Tilt-indication performance using a solid, cylindrical joystick was better in the presence of concordant visual input relative to the other visual conditions. In addition, we compared performance when indicating the vertical by the joystick or a full glass of water. Subjects indicated the direction of gravity significantly better when holding the full glass of water than the joystick. Matching the inertial characteristics, including fluid properties, of the handheld object to the glass of water did not improve performance. There was no effect of visual input on tilt performance when using the glass of water to indicate gravitational vertical. The gain of object tilt motion did not change with roll-tilt amplitude and frequency (+/-7.5 degrees at 0.25 Hz, +/-10 degrees at 0.16 Hz, and +/-20 degrees at 0.08 Hz), however, the phase of object tilt relative to subject tilt showed significant phase-leads at the highest frequency tested (0.25 Hz). Comparison of the object and visual effects observed suggest that the task-dependent behavior change may be due to an attentional shift and/or shift in strategy.

Attention↗

PubMed2005

Interaction of involuntary post-contraction activity with locomotor movements.

Involuntary post-contraction muscle activity may occur after performing a strong long-lasting (about 30 s) isometric muscle contraction (Kohnstamm phenomenon). Here we examined how this putative excitatory state may interact with a locomotor movement. The subjects stood upright and were asked to oppose a rotational force applied to the pelvis for about 30 s either in the clockwise or in the counterclockwise direction. After that, they were asked to perform various motor tasks with the eyes closed. During quiet standing, we observed an involuntary post-contraction torsion of the trunk. During walking, the post-contraction facilitatory effect of body torsion was not overridden by the voluntary activity, but instead significantly influenced the forward locomotor program such that subjects walked along a curved trajectory in the direction of the preceding torsion. In contrast, we did not observe any rotational component when subjects were asked to step in place. We conclude that the post-contraction rotational aftereffect does not transfer to just any motor task but apparently manifests itself in those movements that incorporate the activated axial muscle synergy or rotational component. We argue that central excitability changes following the voluntary effort may contribute to the phenomenon and highlight the role of tonic influences in fine-tuning of the spinal cord.

Adult↗

PubMed2005

Vertical linear self-motion perception during visual and inertial motion: more than weighted summation of sensory inputs.

We evaluated visual and vestibular contributions to vertical self motion perception by exposing subjects to various combinations of 0.2 Hz vertical linear oscillation and visual scene motion. The visual stimuli presented via a head-mounted display consisted of video recordings of the test chamber from the perspective of the subject seated in the oscillator. In the dark, subjects accurately reported the amplitude of vertical linear oscillation with only a slight tendency to underestimate it. In the absence of inertial motion, even low amplitude oscillatory visual motion induced the perception of vertical self-oscillation. When visual and vestibular stimulation were combined, self-motion perception persisted in the presence of large visual-vestibular discordances. A dynamic visual input with magnitude discrepancies tended to dominate the resulting apparent self-motion, but vestibular effects were also evident. With visual and vestibular stimulation either spatially or temporally out-of-phase with one another, the input that dominated depended on their amplitudes. High amplitude visual scene motion was almost completely dominant for the levels tested. These findings are inconsistent with self-motion perception being determined by simple weighted summation of visual and vestibular inputs and constitute evidence against sensory conflict models. They indicate that when the presented visual scene is an accurate representation of the physical test environment, it dominates over vestibular inputs in determining apparent spatial position relative to external space.

Adolescent↗

PubMed2002

Sialochemistry in juvenile idiopathic arthritis.

OBJECTIVES: To investigate whether there are any differences in salivary flow rates and saliva composition that may contribute to the reported increase in caries prevalence in patients with juvenile idiopathic arthritis (JIA). DESIGN: Randomized controlled trial. SETTING: The sialochemistry of children with JIA has rarely been investigated. METHODS: Unstimulated and stimulated whole saliva was collected from 17 randomly selected JIA patients and 17 age and sex matched controls. Both samples were analysed for salivary flow rate, pH, calcium and phosphate. RESULTS: Unstimulated and stimulated JIA saliva flow rates, and the flow rate change from unstimulated to stimulated in JIA saliva were all significantly lower than the controls. There were no significant differences in the pH of unstimulated and stimulated JIA saliva compared with the controls, however, the change in pH (from unstimulated to stimulated) in the study group was significantly greater. The JIA patients had non-significantly lower levels of both calcium and phosphate ions in the unstimulated and stimulated samples. CONCLUSIONS: This data would suggest that there is both a reduced resting salivary flow and a reduced response to stimulation in JIA patients, which may contribute to a previously reported higher caries prevalence.

Adolescent↗

PubMed2000

Adaptation of dental plaque to metabolise maltitol compared with other sweeteners.

UNLABELLED: There is some evidence that plaque can adapt to regular exposure to some bulk sweeteners, leading to increased metabolism and acidogenic potential of the sweetener. This potential for adaptation varies between non-sugar sweeteners and has important implications for manufacturers of food, confectionery and medicines used long-term. Maltitol (99% purity crystalline D-maltitol) is a relatively newly approved non-sugar sweetener and appears to have potentially good dental properties. OBJECTIVES: To compare plaque adaptation to pure sucrose, sorbitol, xylitol or maltitol and the effect of their prolonged use on acid production by plaque from sucrose, in vivo. METHODS: Two series of plaque pH experiments were carried out. Each experiment involved a 14 day adaptive period when four 5 g lozenges of the sweetener were taken between meals each day. Each experiment was separated by a 14 day wash-out period. Acid production was quantified as: (a) minimum pH; and (b) cH area (difference between plaque pH curve and resting value, expressed as cH units). RESULTS: Thirteen adults, of mean age 41 years completed the study. When adaptation of dental plaque to the metabolism of sweeteners was compared, there was a statistically significant difference (p = 0.033) between xylitol and sorbitol, and between xylitol and sucrose but not between xylitol and maltitol. When the effect of prolonged use of sweeteners on acid production after sucrose rinsing was compared, there were no statistically significant differences between the sweeteners. CONCLUSION: Dental plaque does not adapt to metabolise xylitol or maltitol following prolonged exposure over 14 days.

Adaptation, Physiological↗

PubMed1999

Dissociation between sensitization and learning-related neuromodulation in an aplysiid species.

Previous phylogenetic analyses of learning and memory in an opisthobranch lineage uncovered a correlation between two learning-related neuromodulatory traits and their associated behavioral phenotypes. In particular, serotonin-induced increases in sensory neuron spike duration and excitability, which are thought to underlie several facilitatory forms of learning in Aplysia, appear to have been lost over the course of evolution in a distantly related aplysiid, Dolabrifera dolabrifera. This deficit is paralleled by a behavioral deficit: individuals of Dolabrifera do not express generalized sensitization (reflex enhancement of an unhabituated response after a noxious stimulus is applied outside of the reflex receptive field) or dishabituation (reflex enhancement of a habituated reflex). The goal of the present study was to confirm and extend this correlation by testing for the neuromodulatory traits and generalized sensitization in an additional species, Phyllaplysia taylori, which is closely related to Dolabrifera. Instead, our results indicated a lack of correlation between the neuromodulatory and behavioral phenotypes. In particular, sensory neuron homologues in Phyllaplysia showed the ancestral neuromodulatory phenotype typified by Aplysia. Bath-applied 10 microM serotonin significantly increased homologue spike duration and excitability. However, when trained with the identical apparatus and protocols that produced generalized sensitization in Aplysia, individuals of Phyllaplysia showed no evidence of sensitization. Thus, this species expresses the neuromodulatory phenotype of its ancestors while appearing to express the behavioral phenotype of its near relative. These results suggests that generalized sensitization can be lost during the course of evolution in the absence of a deficit in these two neuromodulatory traits, and raises the possibility that the two traits may support some other form of behavioral plasticity in Phyllaplysia. The results also raise the question of the mechanistic basis of the behavioral deficit in Phyllaplysia.

Action Potentials↗

PubMed1999

How body asymmetries determine accessibility in spatial frameworks.

Spatial frameworks are a class of spatial mental model that code locations of objects relative to the body axes. Spatial frameworks predict accessibility of spatial relations from memory primarily on the basis of the relative asymmetry of the body axes, such that highly asymmetric axes lead to faster retrieval of information. The present research examined how bodily asymmetries affect retrieval. Experiment 1 contrasted two theoretical accounts. The Salience Account proposes that relative degrees of asymmetry render axes differentially salient, and hence differentially foregrounded in one's mental model. The Direction Decision Account proposes that an explicit decision process is necessary to access specific locations along body axes. The ease of the decision process presumably depends on the degree of asymmetry that exists to discriminate poles along a body axis. The spatial framework pattern of accessibility was observed both when subjects identified specific directions of objects and when subjects identified just the axis to which objects were associated, supporting the Salience Account. Experiment 2 investigated whether lateralization affects accessibility from spatial frameworks. Performance of highly lateralized individuals did not differ from that of weakly lateralized individuals.

Adult↗

PubMed1998

Evolution of nonassociative learning: behavioral analysis of a phylogenetic lesion.

A recent phylogenetic analysis of two learning-related neuromodulatory traits in mechanosensory neurons of species related to the marine mollusk Aplysia californica identified one species, Dolabrifera dolabrifera, which lacked both neuromodulatory traits. Since these traits are thought to contribute importantly to certain forms of learning and memory in the defensive withdrawal reflexes of Aplysia, in the present study, I tested the prediction that facilitatory nonassociative learning would be reduced or absent in Dolabrifera. I tested the tail-mantle withdrawal reflex in Dolabrifera and size-matched Aplysia for three forms of nonassociative learning and memory: dishabituation and short- and long-term sensitization. I found that the same protocols that produced significant dishabituation, short-term sensitization, and long-term sensitization in Aplysia failed in all three cases to produce significant learning in Dolabrifera. Thus, the prediction from the prior mechanistic analysis is confirmed: Dishabituation and short- and long-term sensitization are significantly reduced and perhaps abolished in Dolabrifera. Although not conclusive, this phylogenetic correlation between the absence of behavioral changes and the absence of neural mechanisms thought to underlie the behavioral changes gives support to the contemporary neuromodulatory model of dishabituation and sensitization in Aplysia. Furthermore, these results raise the possibility that evolutionary alteration of two specific neuromodulatory mechanisms may have directly contributed to evolutionary change in behavioral plasticity.

Animals↗

PubMed1998

Acid production from lactulose by dental plaque bacteria.

Representative strains of oral streptococci, lactobacilli and bifidobacteria were incubated overnight with lactulose or other carbohydrates and the final pH recorded. Most bacteria tested were able to metabolize lactulose with the exception of strains of Streptococcus salivarius, Lactobacillus acidophilus and Lact. fermentum. Streptococcus mutans produced most acid overnight but the initial rate of acid production from lactulose by uninduced cultures was very low. Plaque pH was monitored in 12 volunteers following rinsing the mouth with lactulose, sucrose or sorbitol or Lactulose BP. These studies in vivo showed both lactulose and Lactulose BP to exhibit low acidogenic potential. Thus, although plaque bacteria are capable of fermenting lactulose, the results suggest that lactulose is likely to pose a small acidogenic challenge to teeth under normal conditions of use.

Bifidobacterium↗

PubMed1998

Parasite-altered behavior in a crustacean intermediate host: field and laboratory studies.

The effects of the acanthocephalan parasite Pomphorhynchus laevis on the behavior of its crustacean intermediate host, the amphipod Echinogammarus stammeri, were studied. A drift study revealed that infected amphipods were disproportionately represented in drift samples taken throughout a 24-hr period; infection with more than 1 parasite enhanced this effect. Infection also interacted with the daily timing of drift, with parasitized amphipods beginning to drift earlier in the evening. Two distinct behaviors quantified in laboratory settings may play a role in this increased drifting behavior: parasitized amphipods showed (1) an increased preference for an illuminated environment and (2) increased activity in comparison to nonparasitized conspecifics. These results are consistent with previous studies on the effects of P. laevis on another amphipod host, Gammarus pulex, and provide new data on the activity level of P. laevis-infected amphipods.

Acanthocephala↗

PubMed1996

Developmental emergence of long-term memory for sensitization in Aplysia.

Adult Aplysia exhibit both short-term and long-term memory for sensitization in the gill and siphon withdrawal reflex. Previous developmental studies showed that short-term memory for sensitization emerges late in juvenile development (stage 12; Rankin and Carew, 1988; Wright et al., 1991). In the present study, we examined the development of long-term memory for sensitization. Long-term sensitization of the siphon withdrawal reflex was quantified as an increase in mean response duration observed 20-24 h after receiving a training regime of one or more 90-min sessions of electrical shock to the tail. In the first three experiments we assessed the capacity for long-term sensitization in adults and in juveniles of stages late 12 and early 12. Animals in all three age classes showed long-term sensitization. In a fourth experiment we simultaneously trained and tested both early stage 12 animals and stage 11 animals with identical stimulus parameters that were scaled down to a level appropriate to the smaller stage 11 animals. Under these conditions, the early stage 12 animals demonstrated long-term sensitization, while the stage 11 animals still showed no evidence of long-term sensitization. These results indicate that long-term sensitization first emerges at early stage 12, which is the same developmental stage in which short-term sensitization first emerges. Although these behavioral data do not elucidate underlying mechanisms, the fact that short-term and long-term memory emerge according to the same developmental timetable is consistent with the possibility that these two forms of memory may share at least some common mechanistic features.

Animals↗

PubMed1996

A comparison of the relative acidogenic potential of infant milk and soya infant formula: a plaque pH study.

Soya infant formulas contain glucose syrups instead of lactose, which has led to concern that they are potentially more cariogenic than standard infant milk formulas, which contain lactose. However, the cariogenic potential of soya infant formulas has not been tested. The aim of this study was, therefore, to compare the effect of a soya infant formula and an infant milk on the pH of dental plaque. The study group consisted of 19 adults in whom plaque pH was measured before, and 3, 7, 11, 15, 19, 23 and 27 minutes after, rinsing the mouth with each of the formulas. pH curves were compiled and acidogenicity expressed as 'pH area', minimum pH reached, and maximum pH decrease. No statistically significant differences were observed between the acidogenicity of the soya infant formula and the infant milk.

Adult↗

PubMed1996

Gammarus lacustris harboring Polymorphus paradoxus show altered patterns of serotonin-like immunoreactivity.

The pattern of serotonin-like immunoreactivity in the central nervous system of individuals of the amphipod Gammarus lacustris harboring polymorphid cystacanths was compared to the pattern seen in individuals not infected with acanthocephalans. Ventral nerve cords from both parasitized and nonparasitized amphipods showed the same bilateral pair of immunoreactive cell bodies in the third thoracic ganglion. Significant differences were noted in the fine structure of these cell bodies, with nerve cords from Polymorphus paradoxus-parasitized amphipods showing a greater number of bright spots or localized points of storage of serotonin. The results of this study indicate that infection of G. lacustris by cystacanths of P. paradoxus, but not P. marilis, is correlated with changes in the anatomy of the serotonergic neurons of the amphipod's central nervous system.

Acanthocephala↗

PubMed1995

Widespread anatomical projections of the serotonergic modulatory neuron, CB1, in Aplysia.

Although sensitization-related changes in the neural circuitry of withdrawal reflexes in Aplysia are well studied, relatively few studies address the organization of the modulatory components of sensitization. In particular, it is not known whether individual modulatory loci can simultaneously influence multiple reflex circuits. There is, however, evidence that a single modulatory transmitter, serotonin, plays a pivotal role in facilitating different reflex circuits during sensitization. Furthermore, it is known that activation of a pair of serotonergic neurons, the CB1s, produces heterosynaptic facilitation of the sensorimotor connections of one of these reflex circuits. These data together raise the possibility that the CB1s may produce sensitizing changes in the neural elements of multiple reflex systems simultaneously. In the present study, we utilized immunocytochemistry and intracellular labeling to obtain anatomical evidence of CB1's possible role in modulating multiple reflex circuits. We found that two distinct neurons satisfy previously published physiological criteria for CB1. One of these, CB1, is immunoreactive to serotonin. The second cell, here named CB2, has a different neuroanatomy and is not serotonin immunoreactive. Focusing on CB1, we found (1) profuse fine processes given off by its axons in the posterior neuropil of the cerebral ganglion, (2) extensive branching and fine processes in the pleural ganglion, and (3) a branch of CB1 that projects into the pedal ganglion. These three observations are consistent with the hypothesis that, in addition to its already established role in modulating the siphon withdrawal circuit, CB1 may also modulate synaptic connections between (1) the sensory and motor neurons of the tentacle withdrawal reflex (2) the sensory neurons and interneurons of the tail and tail-elicited siphon withdrawal reflex, and (3) the sensory and motor neurons of the tail withdrawal reflex. These observations support further physiological investigations of a possible global role of CB1 in modulating the tail and tentacle withdrawal reflexes.

Animals↗

PubMed1995

A single identified interneuron gates tail-shock induced inhibition in the siphon withdrawal reflex of Aplysia.

The marine mollusc Aplysia has proven very useful for a mechanistic analysis of behavioral modification. Among the stimuli used to modify the behavior of Aplysia, a noxious stimulus, tail shock, is one of the most effective. In addition to the extensively analyzed facilitatory effects of tail shock, recent work has demonstrated that it also produces marked transient inhibition in reflex responses. Here we report that functional removal (by hyperpolarization or voltage clamp) of a single inhibitory interneuron, L16, can eliminate most, if not all, of the inhibition in the siphon withdrawal reflex circuit produced by tail shock. In addition, this interneuron is strongly activated by tail shock. Finally, direct intracellular activation of L16 does not, in itself, reliably produce inhibition, suggesting that L16 plays a gating role which is necessary for the expression of inhibition in the siphon withdrawal circuit. These results support the idea that behaviorally relevant neural modulation can be gated by a small number of neurons, in this case, by a single identified cell. Moreover, they indicate that in Aplysia, as in many other systems, the modulatory effects of a noxious stimulus are often funneled through a restricted neural locus before being distributed to the circuits actually responsible for generating the behavioral output.

Animals↗

PubMed1993

Urinary fluoride excretion in 4-year-old children in Sri Lanka and England.

Urine was collected over 24 h from children aged 4 years in Sri Lanka and England. Fifty-three children were from Dambulla, Sri Lanka, and 44 from Newcastle, England, both localities receiving drinking water containing 0.8-1.1 mgF/l. Urine volume was measured immediately after the 24-hour collection and samples of the collection from each child were frozen for transportation prior to 'blind' analysis in one laboratory for fluoride content. The mean 24-hour urine volumes were 504 ml (SD 198) in Sri Lanka and 449 ml (SD 196) in England (p = 0.17). The mean F concentrations were 1.19 ppm (SD 0.63) in Sri Lanka and 1.02 ppm (SD 0.42) in England (p = 0.12). The mean weights of fluoride excreted were 0.55 mgF/day (SD 0.30) in Sri Lanka and 0.42 mgF/day (SD 0.19) in England (p = 0.009). The distributions of weight of fluoride excreted were also dissimilar in shape between the two countries. The extent to which these small differences in fluoride excretion in urine reflect differences in fluoride intake needs to be investigated.

Child, Preschool↗

PubMed1992

Delayed-onset sensitization emerges after dishabituation in developing Aplysia.

A recent study of the development of nonassociative learning in the siphon withdrawal reflex of Aplysia showed that dishabituation (facilitation of an habituated response) and sensitization (facilitation of a nonhabituated response) emerge according to different developmental timetables: dishabituation precedes sensitization by approximately 60 days (Rankin & Carew, 1988). Both forms of facilitation of the reflex were observed within 90 s of an electrical shock to the tail. However, more recent work by Marcus and colleagues (1988) in adult animals revealed that sensitization can have a delayed onset of 20-30 min after a strong tail shock. Since the developmental study of Rankin and Carew (1988) only tested the reflex for 10 min after tail shock, it is possible that sensitization was in fact present at earlier developmental stages, but was undetected. To examine this question, in the present study we utilized a longer (40-50 min) post-shock observation period to determine whether delayed-onset sensitization is exhibited in juvenile Aplysia, and if so, when it is expressed during development. In our first experiment, we found that Early Stage 12 juveniles (80-95 days after metamorphosis) showed significant delayed-onset sensitization 30-50 min after a strong tail shock. In a second experiment, we found that delayed-onset sensitization was absent in Stage 11 animals (20-70 days after metamorphosis). Thus delayed-onset sensitization emerges in Early Stage 12. The fact that the birthdate of delayed-onset sensitization is at least 30 days after that of dishabituation (Rankin & Carew, 1987, 1988) supports the hypothesis that these two forms of nonassociative learning may have at least partly different underlying mechanisms.

Animals↗

PubMed1991

A cellular analysis of inhibition in the siphon withdrawal reflex of Aplysia.

Recent behavioral experiments examining the siphon withdrawal reflex of Aplysia have revealed inhibitory effects of strong tail shock, a stimulus commonly used as an unconditioned stimulus in studies of associative and nonassociative learning in Aplysia. We utilized a reduced preparation to perform a cellular analysis of tail shock-induced inhibition in the siphon withdrawal reflex. First, we carried out behavioral studies that showed that the reduced preparation exhibits a siphon withdrawal reflex to water jet stimuli, and that tail shock produces inhibitory behavioral effects comparable to those in the intact animal: (1) strong shock produces transient inhibition of nonhabituated responses, and (2) a habituated response is facilitated by weak shock, but not by strong shock, suggesting that increasing tail shock intensity recruits the inhibitory process that competes with facilitation of habituated reflexes. Next, we carried out cellular studies that showed that the amplitude of the complex EPSP in siphon motor neurons elicited by water jet stimuli to the siphon also exhibits the inhibitory patterns produced by tail shock: (1) the nondecremented complex EPSP (a neural correlate of a nonhabituated siphon withdrawal reflex) is significantly inhibited 90 sec after strong tail shock and recovers to preshock levels 10 min later, and (2) the decremented complex EPSP (a neural correlate of a habituated reflex) is significantly facilitated by weak shock, but is not facilitated by strong shock. In addition to the complex EPSP, we simultaneously examined the monosynaptic connection between siphon sensory neurons and siphon motor neurons. The monosynaptic EPSP does not show the pattern of inhibitory modulation by tail shock exhibited by the siphon withdrawal reflex and the complex EPSP: (1) the nondecremented monosynaptic EPSP is not inhibited 90 sec after strong shock, but tends to be above preshock levels; and (2) the decremented monosynaptic EPSP is facilitated by weak as well as strong tail shock. Our results suggest that an important component of the inhibitory process triggered by strong tail shock is mediated by neural elements presynaptic to the siphon motor neurons. Because modulation of the monosynaptic connection between identified siphon sensory and siphon motor neurons does not parallel the tail shock-induced inhibitory patterns observed in the siphon withdrawal reflex and in the complex EPSP, other synaptic connections are likely to play an important role in mediating tail shock-induced inhibition in the siphon withdrawal reflex.

Animals↗