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Biomedical subjects

G F Wilson

Publications and source records attributed to G F Wilson.

At least 19 recordsLinked to original sources
PubMed1995

A potassium channel beta subunit related to the aldo-keto reductase superfamily is encoded by the Drosophila hyperkinetic locus.

Genetic and physiological studies of the Drosophila Hyperkinetic (Hk) mutant revealed defects in the function or regulation of K+ channels encoded by the Shaker (Sh) locus. The Hk polypeptide, determined from analysis of cDNA clones, is a homologue of mammalian K+ channel beta subunits (Kv beta). Coexpression of Hk with Sh in Xenopus oocytes increases current amplitudes and changes the voltage dependence and kinetics of activation and inactivation, consistent with predicted functions of Hk in vivo. Sequence alignments show that Hk, together with mammalian Kv beta, represents an additional branch of the aldo-keto reductase superfamily. These results are relevant to understanding the function and evolutionary origin of Kv beta.

Amino Acid Sequence↗
PubMed1995

Cognitive task classification based upon topographic EEG data.

EEG from 19 electrodes was used to classify which of 14 tasks each of seven subjects had performed. Stepwise discriminant analysis (SWDA) was used to classify the tasks based upon training on one half of the spectrally analyzed 1 min of data. Eighty six percent correct classification was achieved using principle components analysis (PCA) to determine the EEG bands to be used by the SWDA. Other approaches to deriving the EEG bands met with lower levels of success. The results indicate that frequency and topographical information about the EEG provides useful knowledge with regard to the nature of cognitive activity. Higher frequencies provided much of the information used by the classifier. The utility of this approach is discussed with regard to evaluating operator state in the work environment.

Adult↗
PubMed1994

Task decision difficulty: effects on ERPs in a same-different letter classification task.

A "same-different" letter pair choice reaction time task was used to compare reaction time, performance accuracy, and P3 amplitude and latency at three levels of task difficulty. Stimulus set was held constant across tasks, and task difficulty was manipulated by instructions to the subject. Subjects delivered a button-press response to designate whether members of each letter pair matched or mismatched on the basis of their physical identity (low difficulty), name identity (medium difficulty), or category identity (vowels/consonants, high difficulty). Task decision difficulty was confirmed by slower reaction times and reduced response accuracy. P3 amplitude was inversely related to task decision difficulty; relatively larger P3s were associated with matched (vs. mismatched) letter pairs. These findings evidence direct effects of task difficulty on P3 amplitude, possibly as the result of "equivocation" related to more difficult task judgments.

Adult↗
PubMed1994

Psychophysiological measures of workload during continuous manual performance.

Twelve subjects (six female) participated in an experiment designed to separate the effects of perceptual/central and physical demands on psychophysiological measures of peripheral nervous system activity. The difficulty of a single-axis continuous manual tracking task was varied in two ways: order of control was manipulated to vary perceptual/central processing demand, and disturbance amplitude was manipulated to vary physical demand. Physiological measures were sensitive to the imposition of a task and were more sensitive to physical than to perceptual/central demands. A principal components analysis identified five factors (three of them physiological) that accounted for 83.1% of the observed variance. Perceptual/central processing demands specifically affected the component identified with sympathetic cardiovascular control, whereas physical demands were reflected in the component identified with parasympathetic cardiovascular control. This finding suggests that dissociations observed among cardiovascular measures in manual performance tasks are attributable to differential activation of the autonomic control systems.

Adolescent↗
PubMed1994

Topographical analysis of cortical evoked activity during a variable demand spatial processing task.

This experiment studied changes in brain activity as subjects performed a variable demand spatial rotation task. The task involved the sequential presentation of a template histogram and a spatially rotated comparison histogram. Task difficulty was manipulated by varying the number of bars and the degree of rotation. Topographical analysis of the brain event-related activity data indicated the presence of negative components that were maximal at the vertex within 80 ms and bilaterally in the temporal lobes within 140 ms of stimulus onset and that appeared to be insensitive to changes in task difficulty. Demand-sensitive potentials were recorded, however. Positive components corresponding to P200 and P300 activity were recorded symmetrically around site PZ. The P200 component declined in amplitude, but showed no changes in latency as task demand increased. P300 activity declined in both amplitude and latency as the task became more difficult. Finally, a positive component was recorded over right central cortex approximately 490 ms after stimulus onset. This component declined in amplitude but increased in latency as task difficulty increased.

Adult↗
PubMed1994

Evoked potential, cardiac, blink, and respiration measures of pilot workload in air-to-ground missions.

Brain evoked potentials were successfully recorded from F-4 pilots during air-to-ground training missions. They were recorded during two flight segments. During one the pilot was flying, and during the other, the weapon systems officer was flying the aircraft. The P2 component of the brain-evoked potential evidenced reduced amplitude during the pilot-flying segment, while the N1 component was reduced during both flight tasks compared to ground-based tasks. These data indicate that the P2 amplitude is sensitive to the level of pilot workload. These results were further substantiated using simultaneously recorded physiological data and subjective workload measures. For example, cardiac inter-beat intervals decreased during flight segments relative to those recorded when performing a tracking task, and further reduced for the pilot-flying vs. the weapon systems officer-flying segment. Eye blink measures were sensitive to the visual demands of the various tasks. These data show that evoked potentials can be recorded during flight, and that, together with cardiac and eye blink data, they provide a composite picture of operator state.

Aerospace Medicine↗
PubMed1993

Mode-switching of a voltage-gated cation channel is mediated by a protein kinase A-regulated tyrosine phosphatase.

Tyrosine kinases and tyrosine phosphatases are abundant in central nervous system tissue, yet the role of these enzymes in the modulation of neuronal excitability is unknown. Patch-clamp studies of an Aplysia voltage-gated cation channel now demonstrate that a tyrosine phosphatase endogenous to excised patches determines both the gating mode of the channel and the response of the channel to protein kinase A. Moreover, a switch in gating modes similar to that triggered by the phosphatase occurs at the onset of a prolonged change in the excitability of Aplysia bag cell neurons.

Animals↗
PubMed1993

Mitogenic factors regulate ion channels in Schwann cells cultured from newborn rat sciatic nerve.

1. Patch clamp studies were carried out in Schwann cells cultured from newborn rat sciatic nerve to determine the effects of mitogens on voltage-gated currents without the confounding influences of axonal contact and myelin present in vivo. The relevance of the various Schwann cell currents to proliferation was assessed using assays of [3H]thymidine incorporation. 2. Treatment of cultured Schwann cells with known mitogens, namely axon fragments (AF), myelin fragments (MF), or glial growth factor in combination with forskolin (GGF+F), increased the magnitudes of delayed rectifying potassium (K+) and sodium (Na+) currents. 3. In both control and mitogen-treated cells, the magnitude of net outward current paralleled clearly the magnitude of the cells' proliferative response. 4. The K+ channel-blocking quaternary ammonium ions, tetrabutylammonium (TBuA), tetrapentylammonium (TPeA) and tetrahexylammonium (THeA), but not the Na+ channel blocker tetrodotoxin (TTX), reduced proliferation in a dose-dependent fashion offering further evidence for a role for K+ channels in Schwann cell proliferation. 5. Voltage-gated chloride (Cl-) currents were observed in both control and mitogen-treated cells. Addition of the Cl- channel blockers, 4-acetamido-4'-isocyanatostilbene-2,2'-disulphonate (SITS) or 4,4'-diisothiocyanatostilbene-2,2'-disulphonate (DIDS), to the culture media enhanced proliferation. 6. The possible intermediary role of the Schwann cell resting potential was explored in ion substitution experiments by increasing the K+ concentration of the media and by adding ouabain. Both manipulations inhibited Schwann cell mitosis. 7. Comparison of the expression of functional ion channels in vitro with that previously described for Schwann cells in vivo suggests a difference in the Schwann cell response to the membrane fragment mitogens and their intact counterparts in regard to the regulation of ion channels. MF up-regulates the number of functional channels, whereas the elaboration of myelin (or a factor related to its presence) in vivo appears to down-regulate channel expression, at the cell soma of myelinating Schwann cells. In addition, axonal contact may be required for normal expression of functional inwardly rectifying K+ channels.

Animals↗
PubMed1992

Topographical changes in the ongoing EEG related to the difficulty of mental tasks.

An experiment was carried out to investigate the hypothesis that task difficulty is reflected in changes in the topographical distribution of the ongoing EEG. Subjects had to perform three different tasks at two difficulty levels each; the Sternberg memory scanning task in an auditory and in a visual mode and a task whose performance required mainly visual scanning. Task difficulty was verified by the measurement of response times. Using a commercial Brain Electrical Activity Mapping device, EEG was recorded from 19 scalp electrodes while the subjects performed the tasks. Spectral matrices of the EEG were calculated to investigate spatial relationships in the EEG. Compared to the lower level, higher task difficulty resulted in EEG changes that led to the identification of two factors. One was the reduction of parietal and occipital alpha activity due to the amount of visual scanning and the other an increase of theta activity in the left frontal electrodes which may be associated with the amount of general mental processing.

Adult↗
PubMed1992

Applied use of cardiac and respiration measures: practical considerations and precautions.

Cardiac and respiratory measures can be successfully applied to "real world" environments and these measures have certain advantages over both performance and subjective measures that are typically used to monitor operator state and workload. However, because of large differences between laboratory and "real world" environments one must utilize caution in directly applying laboratory data and theories to the day-to-day world environment. While most workers are highly over-trained in their jobs, laboratory subjects are often under-trained in the cognitive tasks that are used to study cognitive activity. It is possible that a substantial portion of experimental effects reported in laboratory studies is due to learning effects. In addition, relatively small changes in cardiac and respiration measures are reported to experimental manipulations in the laboratory while a much larger range of changes are reported in "real world" environments. These differences highlight questions about laboratory/real world similarities and the need to develop a database of actual work environment data. A third area of concern is the relative lack of control over the experimental situation that is the case with most applied research. The possible confounding of changes due to cognitive and physical activity levels is a major concern and strategies for overcoming these problems are suggested. The potential for valuable contributions by cardiac and respiratory measures to applied research make overcoming these difficulties worthwhile.

Arousal↗
PubMed1991

The use of cardiac and eye blink measures to determine flight segment in F4 crews.

Discriminant analysis techniques were used to classify 8 flight segments for 19 F4 crewmembers and to classify pilots from Weapons Systems Officers (WSOs). Heart rate and eye blink data were used as variables. Pilots and WSOs were correctly classified 84% of the time, while 92% of the flight segments were correctly classified for pilots and 89% for WSOs. The percent correct classifications of flight segments using the jackknife procedure were 69% and 68%, respectively. The advantage of collecting multiple physiological signals was demonstrated. Combined cardiac and eye blink data produced better classifications than when each was used alone. Application of this technique to the flight environment is discussed.

Aerospace Medicine↗
PubMed1991

Mapping of evoked magnetic field with visual stimulation: a secondary projection and processing area.

Visual evoked fields (VEFs) were measured in four subjects, using magnetoencephalography (MEG) and a flashed checkerboard pattern stimulation with a duration of 20 ms. The left hemisphere was searched for the primary and the secondary projection areas with a full-field stimulus. Typical VEFs were found in the occipital area, which is considered to be the primary projection; and a secondary projection area was found in the dorsal temporal area in all subjects. The negative VEF in the secondary projection area was robust and stable, with a range of latencies from 200 to 230 ms. The amplitude was more than -400 femtotesla (fT), as high as the VEF in the occipital area. However, we were unable to localize the position of a dipole, since only one amplitude maxima was found.

Adult↗
PubMed1990

Ion channels in axon and Schwann cell membranes at paranodes of mammalian myelinated fibers studied with patch clamp.

While recent studies have established the presence of voltage-gated ion channels on Schwann cells in culture and on freshly isolated fibers from mature mammals, an important issue not yet explored is whether Schwann cell channels are regionally specialized. In the nodal region, the intimate association between the Schwann cell and its axon suggests that this is a likely site for functional specialization. Here, we examine whether there is a localized expression of channels in the Schwann cell paranodal regions, in a manner similar to that already shown for the nodal axon. Cell-attached and outside-out patch-clamp recordings were made from paranodal regions of rat myelinated sciatic nerve fibers where the myelin on both sides of the node was retracted by enzymatic treatment. Even though no myelin was visible on the surface of the retracted paranode, significant portions of this surface were found to stain positively with a marker (anti-galactocerebroside) for Schwann cell membranes, suggesting that part of the axon still was covered by glial membranes. Using Lucifer yellow in the recording pipettes, we observed that the dye diffused into either axons or Schwann cells when the membrane under the tip was ruptured. Using this as a criterion to identify membranes obtained from retracted paranodes, we found delayed and inwardly rectifying potassium channels on both axon- and Schwann-derived patches. However, sodium channels were detected only in axon patches. This is the first report that voltage-gated glial channels are present in immediate vicinity to axons of the PNS. This finding, coupled with earlier reports that functional channels are absent in soma of mature myelinating Schwann cells, suggests that ion channels in these cells are regionally specialized for functional interaction with axons.

Animals↗
PubMed1990

Potassium channel regulation in Schwann cells during early developmental myelinogenesis.

The presence of neuronal-like, voltage-gated ion channels on glia has raised questions concerning their physiological roles. Insights into glial channel function can be gained by examining regulation of channel expression during axoglial interactions. We examine the regulation of Schwann cell potassium channels in developing sciatic nerves of newborn rats when myelin is first laid down. During the initial postnatal week, cell-attached patch-clamp recordings at soma of Schwann cells with visible myelin revealed an inward rectifying potassium channel (KIR), to date described only in CNS glia but not Schwann cells, as well as an outward potassium channel (KO). Around the resting potential, the KO channel is virtually closed, while the KIR channel appears maximally open. Compared with the KO channel, the KIR channel is blocked by low concentrations of Cs+ and exhibits higher sensitivity to 4-aminopyridine (4AP). Further, the KIR channel appears similar to other mammalian inward rectifiers and rectification depends, in part, on cytoplasmic Mg2+. Channel regulation bears an interesting relation to early myelination: as the average number of myelin lamellae increases from 6 to 21 from day 2 to day 8, currents decrease by 80-90%. The reduction in KO current also parallels the known decrease in proliferation of Schwann cells as they are being committed to myelination, supporting the recently proposed notion of a functional link between potassium channels and proliferation. The KIR channels, by virtue of being open at the resting potential, may play a role in buffering activity-dependent K+ accumulation during early myelin formation. The subsequent reduction in somal channel density may parallel a diminished need for K+ buffering as electrogenesis is restricted to nodal regions.

Animals↗
PubMed1989

The role of potassium channels in Schwann cell proliferation in Wallerian degeneration of explant rabbit sciatic nerves.

1. Patch clamp studies of whole-cell ionic currents and biochemical studies of proliferation were carried out on Schwann cells of myelinated axons in explant segments of sciatic nerves of adult rabbit maintained in culture for 0-10 days. 2. Schwann cell proliferation, as assayed by [3H]thymidine incorporation and by electron microscopic autoradiography, showed an increase following nerve explant. Proliferation proceeded in parallel with a gradual hyperpolarization of the resting potential and an increase in K+ currents in Schwann cells of myelinated axons. 3. The relation between K+ channels and proliferation was studied by incubating explant nerves in the presence of various K+ channel blockers. Quinine, TEA and 4-aminopyridine (4-AP), which blocked K+ currents in Schwann cells, were found also to block Schwann cell proliferation in a dose-dependent fashion and over similar concentrations. Electron microscopy showed that TEA did not retard myelin and axonal break-down which is thought to be the source of mitogens for Schwann cell proliferation. 4. The relation between resting potential and proliferation was studied by incubating explant nerves in depolarizing culture media. Depolarizing monovalent cations (K+ and Rb+) led to a marked inhibition of Schwann cell proliferation. However, Cs+ and NH4+, which did not depolarize Schwann cells in patch clamp studies, also inhibited proliferation. Gramicidin and veratridine also inhibited proliferation. 5. The results suggest that the expression of K+ channels is functionally important for Schwann cell proliferation in Wallerian degeneration. A possible link between K+ channel and proliferation might be via a hyperpolarization of the resting membrane potential which occurs when Schwann cells proliferate.

4-Aminopyridine↗
PubMed1988

Sensitivity of auditory cortical neurons of kittens to monaural and binaural high frequency sound.

The experiments reported here describe the abilities of young auditory cortical neurons to encode information about tone bursts having frequencies above 2.5 kHz. The studies were carried out in anesthetized kittens ranging from 8 to 44 days of age. At all ages studied, stimulation of the contralateral ear was most effective in evoking spikes. Typically the response was confined to stimulus onset. Thresholds were comparatively high and response latencies were comparatively long in the youngest kittens studied. The time course of threshold development was very similar to that of the auditory nerve and cochlear nuclei indicating that most, if not all, age related thresholds and threshold changes at the cortical level are accounted for by mechanisms operating at the level of the cochlea and auditory nerve. Response latency shortened progressively over the first month of postnatal life and while the absolute change in response latency differed considerably from that of cells in the cochlear nuclei the proportional changes were very similar. These data indicate that the comparatively long response latency and latency changes recorded at the cortex are imposed by underdeveloped central auditory processes. Response areas of kitten cortical neurons resembled those of the adult. At all ages studied, binaural interactions were robust and similar in kind to those recorded in adult cats. We conclude that cortical neurons of kittens preserve the results of interactions occurring at lower brainstem levels and that the development of the circuits of which these neurons are a part develop as a functional unit.

Age Factors↗
PubMed1988

Importance of body tissues as sources of nutrients for milk synthesis in the cow, using 13C as a marker.

1. The proportions of carbon in individual milk constituents derived from feed and body tissues in dairy cows, were estimated by taking advantage of the natural variations which occur in the ratio, 13C:12C present in C3- and C4-plant species. 2. Four cows, which had previously grazed C3 plants (ryegrass (Lolium spp.) and white clover (Trifolium repens)), were accustomed to indoor feeding on a ration of C3-plant material (cut pastures and barley meal). The ration was then changed abruptly to one of C4-plant material (paspalum (Paspalum dilatatum) hay, maize silage and meal) for a period of 8 or 9 d in early and again in late lactation. 3. During early lactation it was estimated that 54% of the C in milk fat was derived from the body fat reserves of high genetic merit cows. Corresponding values for casein and lactose were 34 and 24% respectively, if it is assumed they were derived from body protein reserves. In contrast steam-volatile fatty acids in milk fat were almost entirely derived from dietary sources. 4. The proportional contribution of body-tissue C to individual milk constituents varied considerably between animals, possibly associated with genetic merit or the size of the body reserves available for mobilization. 5. In late lactation, when cows were close to energy and protein balance, contributions of body-tissue C to milk fat, casein and lactose ranged up to 19, 19 and 8% respectively. 6. Estimates of endogenous losses of C in faeces averaged 12 and 9% in early and late lactation respectively, and corresponding values for endogenous urinary C were 23 and 15%.

Animal Feed↗