Reduced vestibular function is associated with longer, slower steps in healthy adults during normal speed walking.

BACKGROUND: Vestibular signals contribute to balance and walking. With aging, vestibular function declines and gait speed decreases. Vestibular loss contributes to decreasing gait speed, but this influence could be linked to spatial and/or temporal aspects of gait. We investigated the relationship between vestibular function (semicircular canal and otolith function) and spatial and temporal gait parameters in a cohort of adults. METHODS: 113 community-dwelling healthy adults (mean age 72.2 (14.6) years) participating in the Baltimore Longitudinal Study of Aging were tested. Horizontal semicircular canal (SCC) function was evaluated using quantitative vestibulo-ocular reflex gain. Otolith function was measured with cervical and ocular vestibular evoked myogenic potentials. Gait kinematics were collected during normal speed walking. Multiple linear regressions examined the association between spatial and temporal gait parameters and SCC and otolith function separately, controlling for age, gender, height, and either cadence (for spatial gait outcomes) or stride length (for temporal gait outcomes) to account for gait speed effects. RESULTS: Vestibular SCC function was significantly associated with both spatial and temporal gait parameters. Every 0.1 decrease in SCC function resulted in longer stride length (ß = -.04 m, p = 0.004), longer stance time (ß = 15.8 ms, p < 0.003), and a slower cadence (ß = -2.1 steps/minute, p < 0.001). Otolith function was not associated with any gait parameter. CONCLUSIONS: Reduced horizontal SCC function was associated with longer, slower steps in a cohort of healthy adults. These results indicate that vestibular signals contribute to specific spatial and temporal aspects of gait thought to contribute to upright balance.

Correlated firing in macaque visual area MT: time scales and relationship to behavior.

We studied the simultaneous activity of pairs of neurons recorded with a single electrode in visual cortical area MT while monkeys performed a direction discrimination task. Previously, we reported the strength of interneuronal correlation of spike count on the time scale of the behavioral epoch (2 sec) and noted its potential impact on signal pooling (Zohary et al., 1994). We have now examined correlation at longer and shorter time scales and found that pair-wise cross-correlation was predominantly short term (10-100 msec). Narrow, central peaks in the spike train cross-correlograms were largely responsible for correlated spike counts on the time scale of the behavioral epoch. Longer-term (many seconds to minutes) changes in the responsiveness of single neurons were observed in auto-correlations; however, these slow changes in time were on average uncorrelated between neurons. Knowledge of the limited time scale of correlation allowed the derivation of a more efficient metric for spike count correlation based on spike timing information, and it also revealed a potential relative advantage of larger neuronal pools for shorter integration times. Finally, correlation did not depend on the presence of the visual stimulus or the behavioral choice of the animal. It varied little with stimulus condition but was stronger between neurons with similar direction tuning curves. Taken together, our results strengthen the view that common input, common stimulus selectivity, and common noise are tightly linked in functioning cortical circuits.

Inhibitory effects of deferoxamine on UVB-induced AP-1 transactivation.

Production of reactive oxygen species (ROS) by iron can contribute directly to DNA and protein damage and may contribute to cell signaling and proliferation. We have examined the effects of the iron(III) chelator deferroxamine (DFO) and iron (FeCl(3)) on UVB (290-320 nm)-induced activator protein 1 (AP-1) signaling. The ability of DFO to inhibit UVB-induced AP-1 transactivation was tested in a human keratinocyte cell line stably transfected with a luciferase reporter driven by a single AP-1 element. DFO treatment 24 h prior to UVB irradiation reduced UVB-induced AP-1 transactivation by approximately 80%, with the effect of DFO diminishing as pre-treatment time was shortened. Treatment with FeCl(3) a minimum of 6 h prior to UVB potentiated the UVB induction of AP-1 transactivation by 2-3-fold. DFO was able to ablate both the UVB induction of AP-1 transactivation as well as the potentiation by FeCl(3). The antioxidants Trolox and N-acetyl cysteine were both able to inhibit UVB-induced AP-1 transactivation and Trolox was able to inhibit the potentiation of UVB-induced AP-1 by FeCl(3). These results indicate that UVB-induced AP-1 activation may be in part due to oxidant effects of UVB and intercellular iron.

Spike timing in the mammalian visual system.

Evidence is accumulating for the existence of mechanisms that create and detect synchrony among action potentials on short time scales both within and between neurons. Progress is most rapid in the retina, the lateral geniculate nucleus, and cortical slices, where signal flow is better understood or more manipulable. The debate over the functional relevance of spike timing in cortex has gained substance from new computational models but remains unresolved.

The influence of fixational eye movements on the response of neurons in area MT of the macaque.

We analyzed the relationship between eye movements and neuronal responses recorded from area MT in alert monkeys trained to maintain visual fixation during the presentation of moving patterns. The monkeys made small saccades which moved the eyes with velocities that spanned the sensitivity range of MT neurons. The saccades evoked changes in the neuronal response that depended upon (1) the level of stimulus-evoked activity amidst which the saccade occurred and (2) the direction of the saccade relative to the preferred direction of the neuron. Most notably, saccades were able to suppress stimulus-evoked activity when they caused retinal image flow that opposed the neuron's preference and were able to elicit a response or enhance weak activity when they caused flow in the neuron's preferred direction. On average, the disturbance lasted 40 ms beginning about 40 ms following saccade onset. Using these parameters, we simulated synthetic spike trains from an imaginary pair of similarly tuned neurons and determined that the interneuronal correlation due to saccades should be negligible at all but the lowest ongoing firing rates. This conclusion was supported from our data by the observation that response variance for single MT spike trains was not measurably reduced during periods of stable gaze compared to periods when eye movement exceeded a stability criterion (0.1 deg during 0.5 s). While the intrusions caused by saccades are too short-lived and infrequent to account for the variability of MT neuronal response (counter to the finding in V1 of Gur et al., 1997), the clear directional signal that they carry in area MT suggests that motion perception is not blocked during saccades by suppression at early stages in the visual pathway.

(-)-Epigallocatechin-3-gallate inhibition of ultraviolet B-induced AP-1 activity.

Green tea polyphenols have been shown to inhibit cancer in a variety of tumor models, including ultraviolet B (UVB)-induced non-melanoma skin cancer. In green tea extracts, the major dry mass constituent is the family of catechins, of which (-)-epigallocatechin-(3)-gallate (EGCG) is considered to be important for the chemopreventive activity. EGCG has been shown to have antioxidant properties, but there has been little progress toward identifying the specific targets and mechanisms of its action. Using cultured human keratinocytes, we show that UVB-induced AP-1 activity is inhibited by EGCG in a dose range of 5.45 nM to 54.5 microM. EGCG is effective at inhibiting AP-1 activity when applied before, after or both before and after UVB irradiation. EGCG also inhibits AP-1 activity in the epidermis of a transgenic mouse model. This work begins to define a mechanism by which EGCG could be acting to inhibit UVB-induced tumor formation.

Quantitative measurement of improvement in sitting balance in children with spastic cerebral palsy after selective posterior rhizotomy.

Severe muscular spasticity encountered frequently in patients with spastic cerebral palsy not only affects patient locomotor function but also causes musculoskeletal complications. Significant reduction of spasticity over pelvis and lower limbs after selective posterior rhizotomy (SPR) results in improvement of trunk stability, locomotor function, and function of upper limbs also. The purpose of this study was to investigate the difference of sitting balance before and after SPR using a quantitative measurement in sitting stability represented as dispersion index provided by the Chattecx Balance System. Seventeen children with spastic cerebral palsy, ten boys and seven girls, with a mean age of 5.06 yr, underwent SPR. Their sitting stability under static and dynamic, visual and nonvisual testing conditions was assessed before SPR and three mo after SPR. Their sitting balance showed significant improvement at postoperative evaluation except for the static-nonvisual testing condition. Dispersion index under the dynamic testing condition was significantly higher than under the static testing condition, which implies that dynamic sitting balance was worse than static sitting balance in these patients. There was no statistical difference of sitting performance between visual and nonvisual condition both preoperatively and postoperatively. Quantitative measurement of dispersion index provided by the Chattecx Balance System offers an objective evidence of improvement in sitting balance for children after SPR.

Temporal precision of spike trains in extrastriate cortex of the behaving macaque monkey.

How reliably do action potentials in cortical neurons encode information about a visual stimulus? Most physiological studies do not weigh the occurrences of particular action potentials as significant but treat them only as reflections of average neuronal excitation. We report that single neurons recorded in a previous study by Newsome et al. (1989; see also Britten et al. 1992) from cortical area MT in the behaving monkey respond to dynamic and unpredictable motion stimuli with a markedly reproducible temporal modulation that is precise to a few milliseconds. This temporal modulation is stimulus dependent, being present for highly dynamic random motion but absent when the stimulus translates rigidly.

Power spectrum analysis of bursting cells in area MT in the behaving monkey.

It is widely held that visual cortical neurons encode information primarily in their mean firing rates. Some proposals, however, emphasize the information potentially available in the temporal structure of spike trains (Optican and Richmond, 1987; Bialek et al., 1991), in particular with respect to stimulus-related synchronized oscillations in the 30-70 Hz range (Eckhorn et al., 1988; Gray et al., 1989; Kreiter and Singer, 1992) as well as via bursting cells (Cattaneo et al., 1981a; Bonds, 1992). We investigate the temporal fine structure of spike trains recorded in extrastriate area MT of the trained macaque monkey, a region that plays a major role in processing motion information. The data were recorded while the monkey performed a near-threshold direction discrimination task so that both physiological and psychophysical data could be obtained on the same set of trials (Britten et al., 1992). We identify bursting cells and quantify their properties, in particular in relation to the behavior of the animal. We compute the power spectrum and the distribution of interspike intervals (ISIs) associated with individual spike trains from 212 cells, averaging these quantities across similar trials. (1) About 33% of the cells have a relatively flat power spectrum with a dip at low temporal frequencies. We analytically derive the power spectrum of a Poisson process with refractory period and show that it matches the observed spectrum of these cells. (2) About 62% of the cells have a peak in the 20-60 Hz frequency band. In about 10% of all cells, this peak is at least twice the height of its base. The presence of such a peak strongly correlates with a tendency of the cell to respond in bursts, that is, two to four spikes within 2-8 msec. For 93% of cells, the shape of the power spectrum did not change dramatically with stimulus conditions. (3) Both the ISI distribution and the power spectrum of the vast majority of bursting cells are compatible with the notion that these cells fire Poisson-distributed bursts, with a burst-related refractory period. Thus, for our stimulus conditions, no explicitly oscillating neuronal process is required to yield a peak in the power spectrum. (4) We found no statistically significant relationship between the peak in the power spectrum and psychophysical measures of the monkeys' performance on the direction discrimination task.(ABSTRACT TRUNCATED AT 400 WORDS)

Splenic artery aneurysm rupture during pregnancy.

Rupture of a splenic artery aneurysm during pregnancy or delivery is an unusual event. Only 98 previous cases have been reported. The survival of both mother and fetus is even more uncommon. This paper describes the tenth case of maternal-fetal survival after splenic artery aneurysm rupture. The literature is reviewed in detail with emphasis on the epidemiology, etiology, clinical presentation, and treatment of this problem. A high index of suspicion and an awareness of the management options are necessary to achieve a successful outcome.

Human respiratory tract model for radiological protection: a revision of the ICRP Dosimetric Model for the Respiratory System.

In 1984, the International Commission on Radiological Protection (ICRP) appointed a task group of Committee 2 to review and revise, as necessary, the ICRP Dosimetric Model for the Respiratory System. The model was originally published in 1966, modified slightly in Publication No. 19, and again in Publication No. 30 (in 1979). The task group concluded that research during the past 20 y suggested certain deficiencies in the ICRP Dosimetric Model for the Respiratory System. Research has also provided sufficient information for a revision of the model. The task group's approach has been to review, in depth, morphology and physiology of the respiratory tract; deposition of inhaled particles in the respiratory tract; clearance of deposited materials; and the nature and specific sites of damage to the respiratory tract caused by inhaled radioactive substances. This review has led to a redefinition of the regions of the respiratory tract for dosimetric purposes. The redefinition has a morphologic and physiological basis and is consistent with observed deposition and clearance of particles and with resultant pathology. Regions, as revised, are the extrathoracic (E-T) region, comprising the nasal and oral regions, the pharynx, larynx, and upper part of the trachea; the fast-clearing thoracic region (T[f]), comprising the remainder of the trachea and bronchi; and the slow-clearing thoracic region (T[s]), comprising the bronchioles, alveoli, and thoracic lymph nodes. A task group report will include models for calculating radiation doses to these regions of the respiratory tract following inhalation of representative alpha-, beta-, and gamma-emitting particulate and gaseous radionuclides. The models may be implemented as a package of computer codes available to a wide range of users. This should facilitate application of the revised human respiratory tract model to worldwide radiation protection needs.

Thyroidal influence on nuclear accumulation and DNA replication in skeletal muscles of young chickens.

Regulation of DNA accumulation may be a particularly important aspect of the regulation of skeletal muscle growth. Since thyroid hormones influence the growth of chicken skeletal muscle, including DNA accumulation, we ascertained whether triiodothyronine (T3) affects the accumulation of nuclei within muscle fibers and 3H-thymidine uptake into nuclei within the basal lamina and muscle total DNA. The number of nuclei and the diameter of pectoralis muscle fiber segments freed of adhering connective tissue were reduced markedly in cockerels treated with propylthiouracil (PTU) during the first month after hatching. T3 replacement for 1 week increased the number of nuclei per unit length of isolated fiber section by as much as 54%, compared to the value for birds receiving PTU alone, without affecting fiber diameter. There was also a 24% increase in the number of nuclei beneath the basal lamina of fiber cross sections near the origin of anterior latissimus dorsi (ALD) muscles within 48 hr after initiating T3 replacement in 25-day-old, PTU-treated cockerels. The incorporation of 3H-thymidine into nuclei beneath the basal lamina of ALD fiber cross sections was increased approximately two-fold at 24 hr after administering T3 to 8-day-old thyroidectomized (Tx) cockerels. Thymidine (-3H) incorporation into total DNA of ALD muscles incubated in vitro for 1 hr was also markedly enhanced as early as 6-12 hour after T3 administration to Tx chicks during the first week after hatching. Data from this study suggest that T3 enhances DNA replication and the accumulation of nuclei within the basal lamina of muscle fibers of thyroid-deprived chicks.(ABSTRACT TRUNCATED AT 250 WORDS)