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PubMed1998

Vestibular adaptation: how models can affect data interpretations.

Vestibular adaptation can be induced optically or by chemical or physical injury to the vestibular apparatus or the brain stem. In searching for the sites or mechanisms of vestibular adaptation, neurophysiologists often rely on comparing central resting (background) activities and central modulations (sensitivity) during vestibular stimulation, before and after motor learning or vestibular compensation. It is assumed that adapted central sites must exhibit modulation changes that parallel vestibulo-ocular reflex changes. Using model simulations and analysis, we will show that such presumptions may be misleading. First, using a simple schematic of interconnected cells or nuclei, one can show that modulation depth and background "tone" can be modified (or fixed) independently, using weightings on direct or indirect afferent projections. That is, if synaptic weights along all stimulus pathways are altered, one may fix or strongly modify central premotor characteristics in a manner apparently unrelated to global reflex changes. In the vestibulo-ocular reflex, the dominant premotor pathways contain position-vestibular-pause cells and eye-head-velocity cells (which are behaviorally similar to floccular-target neurons). Several experiments have reported negligible changes in the velocity sensitivity of position-vestibular-pause cells, despite large gain changes in the vestibulo-ocular reflex induced by training with visual-vestibular conflict. On the other hand, the modulation changes on floccular-target neurons (position-vestibular-pause) can be much larger than the changes in reflex gain. Using a bilateral vestibulo-ocular reflex model, we show that overall increases or decreases in reflex gain can be expressed (even overexpressed) in one particular subgroup of premotor neurons. Nevertheless, such observations are theoretically compatible with synaptic changes on all primary projections in a widely interconnected central network. Hence, stable neural responses during reflex adaptation are not sufficient to exclude a potential site of sensory-motor adaptation. Similarly, modified neural responses (as in cerebellum) need not necessarily imply a direct role in supporting the adapted state. Model predictions should help to design additional experimental protocols, to test hypotheses, and to refine diagnostic measures of recovery after vestibular lesions.

Adaptation, Physiological↗

PubMed1987

Adaptation of the jejunal mucosa in the experimental blind loop syndrome: changes in paracellular conductance and tight junction structure.

Self-filling blind loops of rat jejunum exhibit hyperregenerative transformation of the mucosa. We used this experimental model to characterise mechanisms, which may occur under similar conditions in man (stagnant loop syndrome). Epithelial and subepithelial resistance were measured in the Ussing-chamber by voltage divider ratio measurements after positioning a microelectrode between epithelium and subepithelial tissue layers. In the blind loop, epithelial resistance increased from 8 +/- 1 to 23 +/- 1 omega cm2 and subepithelial resistance from 39 +/- 4 to 86 +/- 8 omega cm2 as compared with control jejunum. The increase in the subepithelial resistance was paralleled anatomically by an increase in the thickness of the subepithelial tissue layers from 63 +/- 4 microns to 177 +/- 19 microns. Ultrastructural analysis of the tight junction area by freeze fracture electron microscopy revealed an increase in the total junctional 'depth' in the crypts from 243 +/- 9 nm in control jejunum to 396 +/- 17 nm in the blind loop, while the number of horizontally oriented 'strands' remained unchanged. Villus tight junctions did not differ between blind loop and control. We interpret the alterations in the self-filling blind loop as an adaptive response of the epithelium which reduces backleakage of already absorbed electrolytes across the tight junction into the intestinal lumen. This mechanism is suitable to support the intestine in maintaining body electrolyte and water contents during cellular electrolyte malabsorption.

Adaptation, Physiological↗

PubMed2001

The development of the Ocutech VES-autofocus telescope and a future binocular version.

Conventional optical low-vision devices are hampered by the physical constraints of magnification-shallow depth of field and narrow field of view, and for telescopes, the need to change focus for different distances. These characteristics make low-vision telescopic aids difficult to use, especially at important midrange distances. The Ocutech VES Autofocus bioptic telescope (VES-AF) funded with National Institutes of Health-Small Business Innovation Research and Ontario (Canada) Ministry of Health grants, eliminates the need to manipulate the device to maintain focus. Clinical experience with the VES-AF has shown that autofocus (AF) enhances the acceptance and utilization of telescopic devices. Difficulty ignoring the fellow eye while sighting through the device has been a complaint of users that has undermined device acceptance. Although occlusion is an option to alleviate the diplopia experienced, the development of a binocular version may further enhance the acceptance, adaptation to, and utilization of telescopic devices and may offer wider fields of view as well.

Adult↗

PubMedDate not supplied

Keratinocyte growth factor enhances early gut adaptation in a rat model of short bowel syndrome.

OBJECTIVE: To evaluate the effects of keratinocyte growth factor (KGF) on intestinal adaptation after resection of 85% of the small intestine and consider its potential application in short bowel syndrome (SBS). STUDY DESIGN: Experimental study using a known model of SBS. ANIMAL POPULATION: Thirty male Sprague Dawley rats. METHODS: Four groups of animals were designated. Two groups underwent 85% resection of the small intestine, while the other two groups were sham-operated, undergoing transection and reanastomosis. Resected and sham-operated groups then received either 3 mg/kg KGF or vehicle subcutaneously daily for 3 days. Gut adaptation was evaluated by measurements of mucosal cellularity and biochemical activity in duodenal, jejunal, and ileal segments. RESULTS: Significant small intestinal growth after bowel resection alone was confirmed in resected versus sham-operated rats. KGF further augmented this growth in the resected animals. Mucosal wet weight of the small intestine increased with resection and was further increased (by 20% or more) with KGF administration. Mucosal thickness, villus length, and crypt depth exhibited similar patterns of response. The KGF-induced increase in mucosal morphology was accompanied by increased mucosal DNA and protein content, followed by a trend toward increased mucosal enzyme activity. Histology demonstrated an increase in goblet cells in KGF-treated animals. In situ hybridization analysis demonstrated that KGF markedly increased mucosal expression of intestinal trefoil protein (ITF) mRNA. CONCLUSIONS: KGF enhances gut growth, differentiation, and gene regulation during adaptation in rat small intestine after massive resection. CLINICAL RELEVANCE: KGF may be beneficial in the management of veterinary and human patients undergoing massive intestinal resection.

Adaptation, Physiological↗

PubMed1995

Effect of dimension of luting space and luting composite on marginal adaptation of a class II ceramic inlay.

This study evaluated the in vitro marginal quality at the interproximal cervical margin of class II Cerec restorations. Marginal quality was evaluated separately by (1) SEM analysis before and after simultaneous thermocycling and mechanical loading for the integrity of the restoration surface and (2) dye penetration after thermocycling and mechanical loading to evaluate the strength of the bond within the depth of the cavity. The results reveal that marginal integrity is influenced by the width of the luting space and the luting composite. With a luting space of 100 microns, marginal quality with as little as 3% to 14% loss of adhesion can be obtained. Luting spaces greater than 100 microns can partially be compensated by the luting composite. For Cerec inlays, highly filled luting composites with a high viscosity are recommended.

Adhesiveness↗

PubMed2005

Primary health-care teams as adaptive organizations: exploring and explaining work variation using case studies in rural and urban Scotland.

It is acknowledged, internationally, that health-care practitioners' work differs between and urban areas. While several factors affect individual teams' activities, there is little understanding about how patterns of work evolve. Consideration of work in relation to local circumstances is important for training, devising contracts and redesigning services. Six case studies centred on Scottish rural and urban general practices were used to examine, in-depth, the activity of primary health-care teams. Quantitative workload data about patient contacts were collected over 24 months. Interviews and diaries revealed insightful qualitative data. Findings revealed that rural general practitioners and district nurses tended to conduct more consultations per practice patient compared with their urban counterparts. Conditions seen and work tasks varied between case study teams. Qualitative data suggested that the key reasons for variation were: local needs and circumstances; choices made about deployment of available time, team composition and the extent of access to other services. Primary care teams might be viewed as adaptive organization, with co-evolution of services produced by health professionals and local people. The study highlights limitations in the application of workload data and suggests that understanding the nature of work in relation to local circumstances is important in service redesign.

Humans↗

PubMed2006

Stereopsis in refractive surgery.

PURPOSE: To examine stereopsis in myopic refractive surgery patients undergoing sequential bilateral and unilateral treatment. DESIGN: Prospective, observational, cohort study. METHODS SETTING: Clinical practice. PATIENTS: Eighty-three patients were studied; 55 had sequential bilateral and 28 had unilateral treatment. Mean age was 32 years. Stereopsis was measured using a multitarget red-green anaglyph stereo vision test. Only patients with fine preoperative stereopsis were included in the study. Repeat measurements were taken one week laser-assisted in situ keratomileusis (LASIK) or three weeks laser epithelial keratomileusis (LASEK) after treatment of one eye in all patients. Further measurements were taken at six and 12 weeks in unilaterally treated patients and after treatment of the fellow eye in bilaterally treated patients. RESULTS: A total of 38.6% of patients retained fine stereopsis (28 to 41 seconds of arc) over a range of anisometropia from 0.625 to 4.375. Moderate stereopsis (66 to 526 seconds of arc) was recorded 28.9% in the presence of 1.375 to 5.525 diopters of anisometropia. Poor/absent stereopsis (< or =2000 seconds of arc) was found in 32.5% in the presence of 2.1 to 8.0 diopters of anisometropia. A strong correlation was found between stereopsis and anisometropia, but interpatient variability was found. Uncorrected visual acuity (UCVA) in the untreated eye of > or =20/200 was associated with retention of fine stereopsis. Unilaterally treated patients showed improvement in stereopsis at six weeks after surgery. Sequential bilateral treatment had no deleterious effect on stereopsis. CONCLUSIONS: Loss of stereopsis was strongly correlated with anisometropia. UCVA in the untreated eye was a good indicator of postoperative stereopsis. Stereopsis improved during the postoperative adaptation period in unilateral treatments. Bilateral sequential treatment has no long-term effect on stereopsis.

Adult↗

PubMed2005

Electrokinetic generation of temporally and spatially stable concentration gradients in microchannels.

Generating stable microscale concentration gradients is key to numerous biological and chemical analyses. Microfluidic systems offer the ability to maintain laminar fluid diffusion interfaces ideal for the production of temporally stable concentration gradients. Previous efforts have focused on pressure driven flows and have relied on networks of branching channels to create streams of varying concentrations which can subsequently be combined to form the desired gradients. In this study, we numerically and experimentally demonstrate a novel electrokinetic technique which utilizes applied voltages and surface charge heterogeneity in simpler channel geometries to control and manipulate microscale concentration gradients without the need for parallel lamination. Flow rates ranged from 30 to 460 nl min(-1) for Peclet numbers between 70 and 1100. Spatial stability of 0.6 mm or greater was obtained for a wide range of gradient shapes and magnitudes over lateral dimensions of 400-450 microm. Sensitivity analysis determined that this technique is largely independent of channel depth and species electrophoretic mobility, however channel width and the diffusion coefficient of the analyte are critical. It was concluded that by adjusting applied voltages and/or channel width, this approach to concentration gradient generation can be adapted to a wide range of applications.

Journal Article↗

PubMed2006

Online detection and sorting of extracellularly recorded action potentials in human medial temporal lobe recordings, in vivo.

Understanding the function of complex cortical circuits requires the simultaneous recording of action potentials from many neurons in awake and behaving animals. Practically, this can be achieved by extracellularly recording from multiple brain sites using single wire electrodes. However, in densely packed neural structures such as the human hippocampus, a single electrode can record the activity of multiple neurons. Thus, analytic techniques that differentiate action potentials of different neurons are required. Offline spike sorting approaches are currently used to detect and sort action potentials after finishing the experiment. Because the opportunities to record from the human brain are relatively rare, it is desirable to analyze large numbers of simultaneous recordings quickly using online sorting and detection algorithms. In this way, the experiment can be optimized for the particular response properties of the recorded neurons. Here we present and evaluate a method that is capable of detecting and sorting extracellular single-wire recordings in realtime. We demonstrate the utility of the method by applying it to an extensive data set we acquired from chronically implanted depth electrodes in the hippocampus of human epilepsy patients. This dataset is particularly challenging because it was recorded in a noisy clinical environment. This method will allow the development of "closed-loop" experiments, which immediately adapt the experimental stimuli and/or tasks to the neural response observed.

Action Potentials↗

PubMed1988

Periodontal health at first permanent molars adjacent to primary molar stainless steel crowns.

The present investigation was designed to study the effect of stainless steel crowns (SSC), placed on second primary molars, on the periodontal tissues of neighbouring first permanent molars. 36 children (9-12 years old) with an SSC on a second primary molar on one side of the mouth only, were selected for the study. A clinical and radiographic examination was performed at the mesial surface of the first permanent molar, adjacent to the SSC, and at the corresponding area on the contralateral side of the mouth. The clinical examination included gingival and plaque index scores and probing depth measurements. In the radiographic examination, the marginal bone level was assessed. No statistically significant differences in plaque index scores, gingival index scores and probing pocket depth were noted between the mesial surface of first permanent molars and the contralateral control area. Nor were any significant differences in bone level seen. The present findings suggest that the presence of a well-adapted SSC on a second permanent molar does not affect the periodontal health of the neighbouring first permanent molar.

Alveolar Process↗

PubMed1999

Marital quality among couples living under the threat of forced relocation: the case of families in the Golan Heights.

This study aims to explore how the long period of uncertainty about possible relocation affects the marital quality of the population in the Golan Heights and what forms of coping with this ongoing stress are used. The results, based on both quantitative and qualitative data, indicate a circular process in which the level of stress generated by the uncertainty varies with marital quality and with other personal and family resources, such as potency and an appreciation of the spouse's ability to cope with the stress. Four ways of coping with the uncertainty were observed in in-depth interviews: fighting, ignoring, postponing, and planning. The results are discussed in terms of their meaning for possible systemic interventions.

Adaptation, Psychological↗

PubMedDate not supplied

A helium-ion beam for stereotactic radiosurgery of central nervous system disorders.

A new radiation beamline configuration for stereotactic heavy-ion Bragg peak radiosurgery of patients with intracranial deep arteriovenous malformations, including carotid-cavernous fistulas, has been developed using the 230 MeV/u helium ion beam at the 184-in. Synchrocyclotron at the University of California, Berkeley. The modified beam has five characteristics: uniform field between 10 and 40 mm in diameter; variable depth of penetration between 40 and 140 mm; stopping region for primary ions that can be broadened up to 40 mm; sharply defined lateral and distal borders; and dose rate greater than 2 Gy/min. It is adapted to the ISAH (irradiation stereotactic apparatus for humans) at the 184-in. Synchrocyclotron, with effective stereotactic localization of defined volumes within the brain, and is designed to reach all intracranial targets. It has proven suitable for all patients with intracranial vascular disorders treated with stereotactic radiosurgery at our laboratory.

Biophysical Phenomena↗

PubMed1991

Sexual concerns of adolescents with cancer.

The sexually related concerns of adolescents with cancer were compared with those of healthy adolescents. Forty-one adolescents age 12 to 19 years participated. A sexual concerns questionnaire was used. The study had three primary objectives: (1) to identify concerns related to physical, emotional, and behavioral aspects of sexuality present among all adolescents in the study; (2) to determine if there were differences between sexual concerns of adolescents with cancer and those of healthy adolescents; and (3) to determine whether a relationship existed between age and the concerns adolescents had about sexuality. Results of the study indicate that although no age-linked trends in sexually related concerns existed for the adolescents studied, adolescents had concerns regarding sexuality. Adolescents with cancer did not seem to be any more concerned about common developmental aspects of sexuality than healthy adolescents. However, adolescents with cancer had numerous sexually related concerns not identified by healthy adolescents. These concerns seem to relate to being treated for cancer. They included worries about hair loss, feeling isolated, ability to have children, and children having genetic or congenital defects. Nurses who care for adolescents with cancer can provide education and support regarding sexual concerns to help adolescents cope with and resolve some of these treatment-related anxieties. Further research that includes in-depth, narrative interviews could give better insight into the concerns that both adolescents with cancer and healthy adolescents have about sexual issues.

Adaptation, Psychological↗

PubMed2000

Effects of early onset brain injury on the development of cognition and behavior: introduction to the special issue.

The effects of brain injury acquired early in life on the development of cognition and behavior are not well understood. Deciphering these effects and modeling their neurodevelopmental trajectories are major concerns for clinicians and scientists. Historically, a prevailing notion has been that early-onset brain damage has a more favorable prognosis than does brain damage acquired in adulthood. However, there is growing evidence suggesting that early-onset damage to prefrontal brain structures may have devastating consequences on the emergence of adaptive behavior throughout development. Particularly prominent are disorders of personality, social behavior, and executive functions such as planning and decision making. This special issue presents a series of new empirical studies that address these issues in depth, from several different perspectives, and in both human and animal participants. The findings promise to shed further light on both the neurobiology of development, and diverse neurodevelopmental disorders. Such advances may also enhance clinical diagnosis and facilitate the design of more effective interventions to help reduce the tremendous burden that neurodevelopmental disorders place on personal well-being, family structure, educational systems, and social resources.

Adolescent↗

PubMed1999

Light and choroidal PO2 modulation of intraretinal oxygen levels in an avascular retina.

PURPOSE: To determine the influence that choroidal oxygen level and outer retinal oxygen demand have on oxygen availability to the inner retina when the choroid is the only source of retinal oxygenation. This condition prevails in avascular retinas and in vascularized retinas suffering vascular occlusion. METHODS: Oxygen-sensitive microelectrodes were used to measure the oxygen tension as a function of depth in the naturally avascular retina of anesthetized and mechanically ventilated guinea pigs (n = 6). Choroidal PO2 was manipulated by varying the ventilation gas mixture, and outer retinal oxygen consumption was modulated by light-dark adaptation. Individual PO2 profiles were fitted to a multilayer mathematical model of PO2 distribution, and pairs of profiles at different choroidal PO2 levels, or under light and dark conditions, were fitted to an intraretinal PO2 difference model. Both models reflect the purely choroidal supply of retinal oxygenation. RESULTS: An increase in choroidal PO2 produced an equivalent increase in all retinal layers. Light induced a decreased oxygen consumption in the region of the inner segments of the photoreceptors, which resulted in a significant increase in PO2 in this layer, flowing on unattenuated to all inner retinal layers. The intraretinal PO2 distribution and the light- and ventilatory-induced changes in PO2 were consistent with theoretical predictions of the mathematical models. CONCLUSIONS: The present experimental studies confirm that when the choroid is the only source of retinal oxygenation, the full effect of increased choroidal oxygen level or reduced uptake in the outer retina passes through to the inner retinal layers if the oxygen utilization by the inner retina remains constant.

Animals↗

PubMedDate not supplied

[A. A. Ukhtomskiĭ and I. P. Pavlov: a controversy or a dialogue?].

Pavlov's concept of conditioned reflexes and Ukhtomskii theory of dominanta fall within the biological line in physiology. They unravel the integral adaptive and active nature of the organism behavior in the environment. It is impossible to develop modern concepts about the determinants of goal-directed behavior of animals and voluntary activity of humans without in-depth study of the achievements of these Russian physiological schools which not only formed the methodological basis for the current studies but also directed the way for their further development.

Conditioning, Classical↗

PubMed1992

[Forum: dermopigmentation or medical tattooing. Brief notes on technical aspects of dermopigmentation].

Tattooing is a very old procedure widespread throughout the world. Recently dermatologists and plastic surgeons have applied this procedure for medical dermography. Incarcerating a pigment in the depth of the dermis has caused no problems for professionals and aestheticiens performing tattoos. Medical ethics oblige us to specify the nature of the pigment used. The instrument used for injecting the pigment should be well adapted for safety, technically, ergonomically and for asepsis.

Humans↗

PubMed1992

Heritable disorders of connective tissue and disability and chronic disease in childhood.

The heritable disorders of connective tissue encompass a broad range of diseases, many of which occur in childhood and present to the pediatric rheumatologist's attention. The underlying theme of these disorders is fragility of connective tissue components such as bone, cartilage, and blood vessels. Over the past few years, investigations of patients with the major forms of heritable disorders of connective tissue, osteogenesis imperfecta, Marfan syndrome, and Ehlers-Danlos syndrome have revealed genetic mutations of collagen genes as the cause of the diseases. Review of the newest genetic information in these three disorders is presented. The rheumatic disorders of childhood present a paradigm for the effects of chronic disease on children and families. New work, discussed in this review, continues to suggest changes in psychosocial adaptation in children with chronic rheumatic diseases and their families, but these data are conflicting. The development of arthritis impact measures may help workers in pediatric rheumatology care to have a broader and more in-depth understanding of the effect of this chronic disease on functioning, psychosocial development, and family and peer interactions.

Arthritis, Juvenile↗