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System Sensitivity (system + sensitivity)

Distribution by Scientific Domains

Medical Sciences	40%

Selected Abstracts

Plasma serotonin response to carbohydrate-rich food in chronic schizophrenic patients: clozapine versus classic antipsychotic agents

HUMAN PSYCHOPHARMACOLOGY: CLINICAL AND EXPERIMENTAL, Issue 5 2001
Yaffa Vered
Abstract Researchers have reported a stimulatory effect of carbohydrate-rich intake on platelet-poor plasma (PPP) serotonin (5-HT) levels in healthy human subjects. Dietary manipulation may serve as a safer and less invasive means than pharmacologic challenge to provoke serotonergic responsivity in studies of schizophrenia. In the present study, we used the carbohydrate-rich meal test as an indicator of 5-HT activity in 12 patients with chronic schizophrenia maintained for at least 6 months on clozapine. PPP 5-HT levels were measured at baseline and at 1, 2 and 3,h after administration of the test. Findings were compared with those in schizophrenic patients treated with classic antipsychotic agents for the same duration. The maximal PPP 5-HT response was reached 120 min after meal administration in the clozapine-treated group and 60 min after in the classic antipsychotic-treated group (P<0.05 vs baseline for both). The 5-HT level (as percentage of baseline) at 60 min was significantly lower in the clozapine-treated group (P<0.02), as were individual PPP 5-HT peak values (P<0.05). The individual time to reach the peak response was similar in the two groups. Our results indicate that in patients with chronic schizophrenia 5-HT responsivity to the natural challenge of carbohydrate-rich meals is lower in those treated with clozapine than in those given classic antipsychotic agents. Values in both groups were lower than those in an appropriate historical comparative group of healthy subjects. We suggest that both clozapine and classic antipsychotic agents suppress serotonergic system sensitivity, but to a different degree. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Modelling two-dimensional steady-state groundwater flow and flow sensitivity to boundary conditions in blanket peat complexes

HYDROLOGICAL PROCESSES, Issue 2 2005
D. R. Lapen
Abstract This study used a two-dimensional steady-state finite-element groundwater flow model to simulate groundwater flow in two Newfoundland blanket peat complexes and to examine flow system sensitivity to changes in water table recharge and aquifer properties. The modelling results were examined within the context of peat-forming processes in the two complexes. Modelled flow compared favourably with observed flow. The sensitivity analyses suggested that more highly decomposed bog peat along bog margins probably has/had a positive impact on net peat accumulation within bog interiors. Peat with lower hydraulic conductivity along bog margins effectively impedes lateral drainage, localizes water table drawdown to extreme bog margins, and elevates water tables along bog interiors. Peat formation and elevated water tables in adjacent poor fens/laggs currently rely on placic and ortstein horizons impeding vertical drainage and water flow inputs from adjacent bogs. Modest reductions in atmospheric recharge were found to govern bog-flow-system geometries in a way that would adversely affect paludification processes in adjacent fens/laggs. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Low sensitivity of retina to AMPA-induced calcification

JOURNAL OF NEUROSCIENCE RESEARCH, Issue 4 2003
Noemí Andrés
Abstract Glutamate is involved in most CNS neurodegenerative diseases. In particular, retinal diseases such as retinal ischemia, retinitis pigmentosa, and diabetic retinopathy are associated with an excessive synaptic concentration of this neurotransmitter. To gain more insight into retinal excitotoxicity, we carried out a dose,response study in adult rats using ,-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA), a glutamate analogue. AMPA intraocular injections (between 0.27 and 10.8 nmol) caused no morphologic modification, but a 10.8 + 21 nmol double injection in a 10-day interval produced a lesion characterized by discrete neuronal loss, astroglial and microglial reactions, and calcium precipitation. Abundant calcium deposits similar to those present in rat and human brain excitotoxicity or hypoxia-ischemia neurodegeneration were detected by alizarin red staining within the retinal surface and the optic nerve. Glial reactivity, associated normally with astrocytes in the nerve fiber, was assessed in Müller cells. GABA immunoreactivity was detected not only in neuronal elements but also in Müller cells. In contrast to the high vulnerability of the brain to excitotoxin microinjection, AMPA-induced retinal neurodegeneration may provide a useful model of low central nervous system sensitivity to excitotoxicity. © 2003 Wiley-Liss, Inc. [source]

Stimulation Parameters After Vagus Nerve Stimulator Replacement

NEUROMODULATION, Issue 2 2008
Douglas Labar MD
ABSTRACT Objectives., This study aims to assess tolerability and efficacy of stimulation parameters after vagus nerve stimulator (VNS) pulse generator replacement. Materials and Methods., We carried out an observational, retrospective study, reviewing our experience with VNS generator replacements in 28 epilepsy patients. Results., Seven patients had actual end of battery life (EOBL) (with symptoms), and 21 patients had asymptomatic projected EOBL. When we reprogrammed stimulation parameters postoperatively, 17 of the 28 patients could not tolerate the preoperative baseline current settings, even one year later. There were no differences in pre- vs. postoperative seizure rates between patients who did or did not return to baseline settings. Failure to return to baseline current was not related to previous VNS duration, same- vs. different-battery generator replacements, or antiepileptic medication changes. Conclusions., After VNS generator replacement, patients' common inability to tolerate preoperative current settings does not lead to more seizures. A chronic modification of the vagus nerve system's sensitivity to stimulation changes may be hypothesized. [source]

Quantitative analogue flume-model study of river,shelf systems: principles and verification exemplified by the Late Quaternary Colorado river,delta evolution

BASIN RESEARCH, Issue 3 2001
M. W. I. M. Van Heijst
ABSTRACT Physical modelling of clastic sedimentary systems over geological time spans has to resort to analogue modelling since full scaling cannot be achieved within the spatial and temporal restrictions that are imposed by a laboratory set-up. Such analogue models are suitable for systematic investigation of a sedimentary system's sensitivity to allocyclic changes by isolating governing parameters. Until now, analogue models of landscape evolution were mainly qualitative in nature. In this paper, we present a quantitative approach. The quantitative experimental results are verified and discussed by comparison with high-resolution data from the Colorado river,shelf system of the Texas shelf that we used as a prototype. The model's dimensions are proportionally scaled to the prototype, except for a vertical exaggeration. Time is scaled using a Basin Response factor to maintain a similar ratio between the period of change and the system's equilibrium time for model and prototype. A Basin Fill factor was used to compare the ratio between the time-averaged sedimentation rate and the rate of change in accommodation space of model and prototype. The flume-model results are in the form of sediment budgets that are related to shelf cannibalism and fluvial supply, which are compared with the ancestral Colorado river,delta evolution of the last 40 kyr. Model and prototype have similarities in delta evolution in response to one cycle of sea-level change. With sea-level change as the isolated variable, the flume model generates a significant supply pulse caused by headward erosion of the shelf in response to the sea-level fall. This pulse adds to the yield of the hinterland. The supply induced by sea-level change persists during the early rise, although its rate declines. A similar trend is observed on the east Texas shelf. We argue that shelfal and fluvial degradation cycles induced by sea-level changes can significantly influence the timing and amount of sediment supply to basins and must therefore be taken into consideration. [source]