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At least 217 records · Page 12Linked to original sources

PubMed2001

Fast acceleration-encoded magnetic resonance imaging.

Direct acceleration imaging with high spatial resolution was implemented and tested. The well-known principle of phase encoding motion components was applied. Suitable gradient switching provides a signal phase shift proportional to the acceleration perpendicular to the slice in the first scan of the sequences. An additional scan serving as a reference was recorded for compensation of phase effects due to magnetic field inhomogeneities. The first scan compensated for phase shifts from undesired first- and second-order motions; the second scan was completely insensitive to velocity and acceleration in all directions. Advantages of the proposed two-step technique compared to former approaches with Fourier acceleration encoding (with several phase encoding steps) are relatively short echo times and short total measuring times. On the other hand, the new approach does not allow us to assess the velocity or acceleration spectrum simultaneously. The capabilities of the sequences were tested on a modern 1.5 T whole body MR unit providing relatively high gradient amplitudes (25 mT/m) and short rise times (600 micros to maximum amplitude). The results from a mechanical acceleration phantom showed a standard deviation of 0.3 m/s2 in sequences with an acceleration range between -12 and 12 m/s2. This range covers the expected maximum acceleration in the human aorta of 10 m/s2. Further tests were performed on a stenosis phantom with a variable volume flow rate to assess the flow characteristics and possible displacement artifacts of the sequences. Preliminary examinations of volunteers demonstrate the potential applicability of the technique in vivo.

Acceleration↗

PubMedDate not supplied

X-ray sources of medical linear accelerators: focal and extra-focal radiation.

A computerized tomography (CT) reconstruction technique has been used to make quantitative measurements of the size and shape of the focal spot in medical linear accelerators. Using this technique, we have measured the focal spots in a total of nine accelerators, including (i) two Varian Clinac 2100c's, (ii) two Atomic Energy of Canada Ltd. (AECL) Therac-25's, (iii) two AECL Therac 6's, (iv) a Siemens KD-2, (v) a Varian Clinac 600c (4 MV), and (vi) an AECL Therac-20. Some of these focal spots were monitored for changes over a 2-yr period. It has been found that (i) the size and shape of the source spot varies greatly between accelerators of different design ranging from 0.5 to 3.4 mm in full width at half maximum (FWHM); and (ii) for accelerators of the same design, the focal spots are very similar. In addition to the measurements of the focal spot, a new technique for measuring the magnitude and distribution of extra-focal radiation originating from the linear accelerator head (flattening filter, primary collimator) has also been developed. The extra-focal radiation produced by a Varian Clinac 2100c accelerator was measured using this technique and it was found that the extra-focal radiation accounts for as much as 8% of the total photon fluence reaching the isocenter. The majority (75%) of this extra-focal radiation originates from within a circle 6 cm in diameter at the target plane. The source MTFs for each of the measured focal spots have been calculated in order to assess their influence on the spatial resolution of verification images. The limiting spatial resolution (i.e., 10% modulation) for all the source MTFs is 1.8 mm-1 or greater when used for transmission radiography at a magnification of 1.2. The extra-focal radiation, which produces a low-frequency drop in the source MTFs of up to 8%, changes with field size. As a result, the source MTFs of linear accelerators depend not only on the design of individual accelerators and image magnification, but also on the field size used when forming an image.

Biophysical Phenomena↗

PubMed1999

Mauthner and reticulospinal responses to the onset of acoustic pressure and acceleration stimuli.

We determined how the Mauthner cell and other large, fast-conducting reticulospinal neurons of the goldfish responded to acoustic stimuli likely to be important in coordinating body movements underlying escape. The goal was to learn about the neurophysiological responses to these stimuli and the underlying processes of sensorimotor integration. We compared the intracellularly recorded postsynaptic responses (PSPs) of 9 Mauthner cells and a population of 12 other reticulospinal neurons to acoustic pressure and acceleration stimuli. All recorded cells received both pressure and acceleration inputs and responded to stimuli regardless of initial polarity. Thus these cells receive acoustic components necessary to determine source direction. We observed that the Mauthner cell was broadly tuned to acoustic pressure from 100 to 2,000 Hz, with a Q(10dB) of 0.5-1.1 over the best frequency range, 400-800 Hz. This broad tuning is probably due to input from S1 afferents and is similar to tuning of the behavioral audiogram. Our data suggest that cells have relatively more sustained responses to acceleration than to pressure stimuli, to which they rapidly adapted. For a given cell, PSP latencies and amplitudes varied inversely with stimulus intensity. For the entire population of cells studied, minimum onset latencies (i.e., those at the highest intensities) ranged from 0.7 to 7.6 ms for acoustic pressure and 0.7 to 9.8 ms for acceleration. This distribution in minimum onset latencies is consistent with earlier EMG and kinematic findings and supports our previous hypothesis that escape trajectory angle is controlled, in part, by varying the activation time of neurons in the escape network. While the Mauthner cell latency did not differ to both onset polarities of pressure and acceleration, this was not true of all cells. Also, the Mauthner cell responses to pressure were approximately 0.6 ms faster than to acceleration; for the other cells, this difference was 1.1 ms with some cells having differences </=3 ms. To both pressure and acceleration, the average, minimum Mauthner cell latency was approximately 1 ms faster than the average of the 12 other cells. These data are consistent with the hypothesis that the Mauthner cell fires first, followed by other reticulospinal neurons, which more finely regulate escape trajectory. Finally, analysis of our results suggests that while pressure is more important in depolarizing the cell near threshold, high levels of acceleration, perhaps from fluid flow, may be very important in activating the system in a directional manner.

Acceleration↗

PubMed2001

Horizontal vestibuloocular reflex evoked by high-acceleration rotations in the squirrel monkey. IV. Responses after spectacle-induced adaptation.

The horizontal angular vestibuloocular reflex (VOR) evoked by sinusoidal rotations from 0.5 to 15 Hz and acceleration steps up to 3,000 degrees /s(2) to 150 degrees /s was studied in six squirrel monkeys following adaptation with x2.2 magnifying and x0.45 minimizing spectacles. For sinusoidal rotations with peak velocities of 20 degrees /s, there were significant changes in gain at all frequencies; however, the greatest gain changes occurred at the lower frequencies. The frequency- and velocity-dependent gain enhancement seen in normal monkeys was accentuated following adaptation to magnifying spectacles and diminished with adaptation to minimizing spectacles. A differential increase in gain for the steps of acceleration was noted after adaptation to the magnifying spectacles. The gain during the acceleration portion, G(A), of a step of acceleration (3,000 degrees /s(2) to 150 degrees /s) increased from preadaptation values of 1.05 +/- 0.08 to 1.96 +/- 0.16, while the gain during the velocity plateau, G(V), only increased from 0.93 +/- 0.04 to 1.36 +/- 0.08. Polynomial fits to the trajectory of the response during the acceleration step revealed a greater increase in the cubic than the linear term following adaptation with the magnifying lenses. Following adaptation to the minimizing lenses, the value of G(A) decreased to 0.61 +/- 0.08, and the value of G(V) decreased to 0.59 +/- 0.09 for the 3,000 degrees /s(2) steps of acceleration. Polynomial fits to the trajectory of the response during the acceleration step revealed that there was a significantly greater reduction in the cubic term than in the linear term following adaptation with the minimizing lenses. These findings indicate that there is greater modification of the nonlinear as compared with the linear component of the VOR with spectacle-induced adaptation. In addition, the latency to the onset of the adapted response varied with the dynamics of the stimulus. The findings were modeled with a bilateral model of the VOR containing linear and nonlinear pathways that describe the normal behavior and adaptive processes. Adaptation for the linear pathway is described by a transfer function that shows the dependence of adaptation on the frequency of the head movement. The adaptive process for the nonlinear pathway is a gain enhancement element that provides for the accentuated gain with rising head velocity and the increased cubic component of the responses to steps of acceleration. While this model is substantially different from earlier models of VOR adaptation, it accounts for the data in the present experiments and also predicts the findings observed in the earlier studies.

Acceleration↗

PubMed1999

[Measurement and evaluation of three-dimensional acceleration signals for rate adaptation of cardiac pacemakers].

The aim of this study was to determine which of the one-dimensional acceleration signals best correlates with the heart rate under the conditions of daily activities, or whether such correlation is shown by three-dimensional acceleration signals. A commercially available biosignal system (ZAK, Germany) was used to record electrographic data and acceleration caused by body movements in the three directions vertical, sagittal and lateral. The evaluation was performed on 12 young healthy volunteers and 4 elderly volunteers with cardiovascular disorders but adequate chronotropic function. Informed consent was given by all participants. Activity signals and heart rate were recorded while walking under two different conditions. For analysis, the pathways were divided into segments with different gradients. All the acceleration signals were analysed statistically and temporally with regard to peak-to-peak value, root mean square value, and step frequency by means of cross correlation. Both statistical and temporal analysis showed that the correlation of heart rate and all one-dimensional acceleration signals and the three-dimensional acceleration signal was relatively low (r < or = 0.6). Walking uphill even showed a negative correlation between acceleration signals and heart rate. Despite the widespread use of activity-controlled pacemakers, the correlation between heart rate and acceleration signals is not satisfactory.

Acceleration↗

PubMed1990

Pulsatile flow of power-law fluid model for blood flow under periodic body acceleration.

A mathematical model has been proposed to study the pulsatile flow of a power-law fluid through rigid circular tubes under the influence of a periodic body acceleration. Numerical solutions have been obtained by using finite difference method. The accuracy of the numerical procedure has been checked by comparing the obtained numerical results with other numerical and analytical solutions. It is found that the agreement between them is quite good. Interaction of non-Newtonian nature of fluid with the body acceleration has been investigated by using the physiological data for two particular cases (coronary and femoral arteries). The axial velocity, fluid acceleration, wall shear stress and instantaneous volume flow rate have been computed and their variations with different parameters have been analyzed. The following important observations have been made: (i) The velocity and acceleration profiles can have more than one maxima, this is in contrast with usual parabolic profiles where they have only one maximum at the axis. As n increases, the maxima shift towards the axis; (ii) For the flow with no body acceleration, the amplitude of both, wall shear and flow rate, increases with n, whereas for the flow with body acceleration, the amplitude of wall shear (flow rate) increases (decreases) as n increases; (iii) In the absence of body acceleration, pseudoplastic (dilatant) fluids, with low frequency pulsations, have higher (lower) value of maximum flow rate Qmax than Newtonian fluids, whereas for high frequencies, opposite behavior has been observed; for flow with body acceleration pulsations gives higher (lower) value of Qmax for pseudoplastic (dilatant) fluids than Newtonian fluids.

Acceleration↗

PubMed2006

The effect of gender and body size on linear accelerations of the head observed during daily activities.

The purpose of this study was to determine the effect of gender and body size on peak linear head accelerations during daily activities. Head accelerations were measured for 18 volunteers using a biteplate system. Each subject performed seven activities: sitting in a chair, sitting quickly in a chair, walking at 1.3 m/s, running at 2.7 m/s, performing jumping jacks, doing a vertical leap, and jumping off a step approximately 20 cm high. Peak resultant head accelerations for each subject and activity were compared to determine if there were statistically significant differences based on variables such as gender and size. All measured accelerations were below 10 g with a maximum peak acceleration of 9.54 g recorded during the vertical leap activity. Larger head accelerations were measured during the jumping activities, while lower accelerations occurred during the sitting, walking, and running events. Based on the statistical analysis, it was determined that gender and size do not have a statistically significant effect on peak linear accelerations of the head during daily activities.

Acceleration↗

PubMed2006

Thoracic and lumbar spine accelerations in everyday activities.

The purpose of this study was to quantify thoracic and lumbar spine accelerations for men and women of different body sizes during daily activities. Measured spine accelerations were compared to determine if there were significant differences in peak accelerations based on gender, size, and spine location. Each subject performed seven activities, which included sitting in a chair, sitting quickly in a chair, walking at 1.3 m/s, running at 2.7 m/s, performing jumping jacks, achieving maximum vertical leap, and jumping off a step approximately 20 cm high. Overall, the peak lumbar spine accelerations were significantly greater than the thoracic spine accelerations. Based on the statistical analysis, it was determined that gender and body size did not have a significant effect on peak accelerations of the thoracic and lumbar spine. The findings from the present study are of great value to researchers in order to understand the acceleration patterns of the human body during low impact accelerations.

Acceleration↗

PubMed1979

Head acceleration and psychomotor performance.

Concussion resulting from head acceleration could explain the poor survival rates in some types of accidents. Experiments have been conducted on a decelerator using a tracking task to determine whether high head acceleration could affect psychomotor performance. Human subjects were exposed to impact acceleration of O (sham), 5, 10 and 12 -Gx facing forwards. Measurements were made of the linear and angular accelerations experienced at the head and a step tracking task was used to examine psychomotor performance. Electroencephalographs were also recorded. Both the linear and angular accelerations at the head were increased at the higher levels of impact acceleration. At -5Gx there were no significant differences in psychomotor performance when compared with controls, but at -10Gx, and especially -12Gx, significant differences were found. The EEG activity did not vary significantly and no concussive effects were observed in any subject. These results suggest that impairment of psychomotor performance severe enough to jeopardise survival could be produced by high accelerations of the head, though neither linear nor angular acceleration appear to have special significance.

Acceleration↗

PubMed1996

+Gz acceleration affects the trace minerals zinc, copper, and chromium in serum and urine of humans.

BACKGROUND: Research investigating the relationship between physical training and trace mineral concentrations has primarily focused on athletes. Few investigations, however, have specifically examined the alterations of trace mineral concentrations occurring in humans exposed to +Gz acceleration. Exercise alters mineral content; G-exposure is a form of exercise; therefore, G-exposure may elicit changes in mineral content. HYPOTHESIS: Exposure to +Gz acceleration may affect the concentrations of the trace minerals zinc, copper, and chromium in human serum and urine. METHODS: Blood samples were obtained from 7 men and 3 women, before and immediately after +Gz acceleration. Urine samples were obtained before, 30 min after, and 2 h after +Gz acceleration. RESULTS: The serum zinc concentration was significantly different after +Gz acceleration, decreasing from 90.6 +/- 21.0 micrograms.dl-1 to 80.8 +/- 14.4 micrograms.dl-1. The serum copper concentration was also significantly altered immediately after +Gz acceleration, decreasing from 111.7 +/- 27.5 micrograms.dl-1 to 98.5 +/- 35.2 micrograms.dl-1. The urinary zinc and copper concentrations, and the serum chromium concentration were not significantly affected by +Gz acceleration. CONCLUSIONS: The circulating levels of these minerals presumably change as they are transported to the tissues requiring greater amounts due to the increased physiological work associated with +Gz acceleration.

Acceleration↗

PubMed1998

Oculomotor response to linear acceleration as induced by counter-rotation in supine subjects.

BACKGROUND: Horizontal nystagmus occurs in response to sinusoidal linear accelerations directed along an upright subject's Y (interaural) axis, and is proposed to be mediated by an utricular otolith mechanism. HYPOTHESIS: The otolith organs, composed of the utricles and saccules, provide a unique set of signals for any linear acceleration in 3-dimensional space. A supine subject under alternate changing directions of linear acceleration as induced by counter-rotation will receive alternate stimulation along the Y as well as the Z (dorsoventral) axis. We hypothesized that alternate horizontal and vertical nystagmus would be elicited as a result of the changing direction of linear acceleration. METHODS: A group of eight subjects in the supine position were exposed to counter-rotation at 0.16, 0.25, and 0.33 Hz. Vertical and horizontal eye movements were recorded simultaneously using the El-Mar eye and head tracking system. RESULTS: Horizontal nystagmus was observed in all supine subjects. The direction of the slow phase of nystagmus changed with directional changes in linear acceleration. Reversals in the direction of eye movements lagged behind the reversals in the direction of the acceleration. However, only two subjects exhibited alternating horizontal and vertical nystagmus as a result of changing axis of linear acceleration, from "along the Y axis" to "along the Z axis." CONCLUSION: We propose that the nystagmus induced in the supine subject was provoked by linear acceleration and largely an otolith-mediated reflex. The lack of vertical response could be due to the relative paucity of vestibular afferents information along the dorsoventral axis.

Acceleration↗

PubMed2006

The tactile-stimulated startle response of tadpoles: acceleration performance and its relationship to the anatomy of wood frog (Rana sylvatica), bullfrog (Rana catesbeiana), and American toad (Bufo americanus) tadpoles.

I described the tactile-stimulated startle response (TSR) of wood frog (Rana sylvatica), bullfrog (Rana catesbeiana), and American toad (Bufo americanus) tadpoles. One purpose was to rank species in terms of maximum acceleration performance. Also, I tested whether anatomical indicators of performance potential were predictive of realized performance. TSRs were elicited in a laboratory setting, filmed at 250 Hz, and digitally analyzed. TSRs began with two, initial body curls during which tadpoles showed a broad spectrum of movement patterns. TSR performance was quantified by maximum linear acceleration and maximum rotational acceleration of the head/body, both of which tended to occur immediately upon initiation of motion (< 0.012 sec into the response). Bullfrog tadpoles had higher maximum acceleration than the other species, but other interspecific differences were not significant. The species' rank order for the anatomical indicator of linear acceleration potential was bullfrog > wood frog > American toad. The species' rank order for the anatomical indicator of rotational acceleration potential was bullfrog > wood frog = American toad. Thus, the anatomical indicators roughly predicted the rank order of interspecific average performance. However, the anatomical indicators did not correlate with individual tadpole performance. Variability in behavioral patterns may obscure the connection between anatomy and performance. This is seen in the current lack of intraspecific correlation between a morphological indicator of acceleration capacity and acceleration performance.

Animals↗

PubMed2006

Cardiac CINE MR imaging with a 32-channel cardiac coil and parallel imaging: impact of acceleration factors on image quality and volumetric accuracy.

PURPOSE: To assess the impact of parallel imaging algorithms on image quality and volumetric accuracy of CINE magnetic resonance imaging (MRI) with high temporal and spatial resolution using a new 32-channel dedicated cardiac phased array coil. MATERIALS AND METHODS: Fourteen individuals underwent steady-state free precession (SSFP) CINE MRI using a 32-element phased-array coil and parallel imaging acceleration using spatiotemporal sensitivity encoding (TSENSE). Acquisition acceleration ranged from R = 2 to 7. In conjunction with data extracted from phantom measurements, contrast-to-noise ratio (CNR) performance was evaluated for each acceleration factor and subjective image quality was evaluated by two independent readers. In addition, volumetric assessment was performed for each acceleration factor based on a single breath-hold multi-slice data acquisition. Results were compared to nonTSENSE measurements. RESULTS: CNR for non-accelerated CINE (R = 1) was 45.7 +/- 12.8 and showed a constant decrease with increase in acceleration of 51% at R = 4 and 86% at R = 7. CNR losses accompanied reductions in subjective image quality. Volumetric evaluation was accurate for R <or= 4, with significant underestimation of ejection fraction (EF) at higher accelerations. CONCLUSION: This study shows that one-dimensional acceleration factors up to R = 4 allow accurate SSFP CINE MRI even though CNR is significantly reduced. This allows for a marked reduction in scan time and allows for multi-slice CINE imaging with high spatial and temporal resolution.

Adult↗

PubMed1998

High acceleration impulsive rotations reveal severe long-term deficits of the horizontal vestibulo-ocular reflex in the guinea pig.

While there is agreement that unilateral vestibular deafferentation (UVD) invariably produces an immediate severe horizontal vestibulo-ocular reflex (HVOR) deficit, there is disagreement about whether or not this deficit recovers and, if so, whether it recovers fully or only partly. We suspected that this disagreement might mainly be due to experimental factors, such as the species studied, the means chosen to carry out the UVD, or the nature of the test stimulus used. Our aim was to sort out some of these factors. To do this, we studied the HVOR of alert guinea pigs in response to low and high acceleration sinusoidal and high acceleration impulses after UVD by either labyrinthectomy or by vestibular neurectomy. The HVOR in response to high acceleration impulsive yaw rotations was measured before, and at various times after, either unilateral labyrinthectomy or superior vestibular neurectomy. Following UVD, there was a severe impairment of the HVOR for ipsilesional rotations and a slight impairment for contralesional rotations, after either operation. This asymmetrical HVOR deficit in the guinea pig parallels the deficit observed in humans. Between the first measurement, which was made 1 week after UVD, and the last, which was made 3 months after UVD, there was no change in the HVOR. This lack of recovery was the same after labyrinthectomy as after vestibular neurectomy. The HVOR to low and high acceleration sinusoidal yaw rotations were measured after UVD, and the results were compared with those in response to impulsive rotations. For low acceleration sinusoidal rotations (250 degrees/s2), the gain was symmetrical, although reduced bilaterally. As the peak head acceleration increased, the HVOR became increasingly asymmetric. The HVOR asymmetry for sinusoidal rotations was significantly less than for impulsive rotations that had the same high peak head acceleration (2500 degrees/s2). Our results show that the HVOR deficit after UVD is the same in guinea pigs as in humans; that it is the same after vestibular neurectomy as after labyrinthectomy; that it is lasting and severe in response to high acceleration rotations; and, that it is more obvious in response to impulses than to sinusoids.

Afferent Pathways↗

PubMed1990

Effect of beta adrenoceptors and thyroid hormones on velocity and acceleration of peripheral arterial flow in hyperthyroidism.

Brachial artery flow patterns were studied in 10 hyperthyroid and 10 normal subjects. Mean blood velocity and flow were evaluated by pulsed Doppler, and peak systolic acceleration was calculated by computer-assisted digitization of the instantaneous velocity curve. Compared to control subjects, hyperthyroid patients had higher velocity and flow (p less than 0.01, p less than 0.02) and higher peak systolic acceleration (p less than 0.01). In hyperthyroid patients, measurements were repeated after (1) mechanical exclusion of the hand from brachial circulation, (2) short-term beta-blocker treatment and (3) inducement of the euthyroid state. Exclusion of the hand reduced velocity and flow (p less than 0.001) but did not change peak systolic acceleration. Beta blockade induced disparate changes of velocity and flow but reduced peak systolic acceleration (p less than 0.05). In the euthyroid state, decreased blood velocity (p less than 0.01), flow (p less than 0.02) and acceleration (p less than 0.02) were observed. A hyperkinetic arterial circulation consisting of an increase in both velocity and acceleration is thus observable in hyperthyroidism. Hand exclusion showed that velocity seems to be influenced by peripheral factors while beta blockade suggests that acceleration is dependent of beta 1 adrenoceptors. Comparison between euthyroidism and hyperthyroidism indicates that both mean blood velocity and peak systolic acceleration are influenced by thyroid hormones.

Adrenergic beta-Antagonists↗

PubMed2005

Right ventricular pre-ejection myocardial velocity and myocardial acceleration in normal fetuses assessed by Doppler tissue imaging.

Myocardial acceleration during isovolumic contraction obtained from Doppler tissue imaging has been introduced as an index of right ventricular contractile function that is unaffected by the shape of the ventricle and loading conditions, but normal value of myocardial acceleration during isovolumic contraction and the effect of aging on the index are not known in normal fetuses. We studied 61 normal fetuses aged 20 to 39 weeks (29.8 +/- 5.1 weeks). Fetuses were divided into 4 age groups: 20 to 24 weeks (n = 11); 25 to 29 weeks (n = 20); 30 to 34 weeks (n = 20); and 35 to 39 weeks (n = 10). Using Doppler tissue imaging, peak pre-ejection myocardial velocity was measured at the base of right ventricular free wall from 4-chamber view. Myocardial acceleration was calculated by dividing pre-ejection velocity by the time interval from onset of the pre-ejection myocardial velocity to the time at peak velocity of this wave. The mean pre-ejection myocardial velocity was 5.0 +/- 1.1 cm/s. There was a stepwise increase in the pre-ejection myocardial velocity from the fetuses of 20 to 24 weeks to the fetuses of 35 to 39 weeks. The mean myocardial acceleration was 160 +/- 30 cm/s 2 . The mean myocardial acceleration did not differ between the fetuses aged 20 to 24 weeks (139 +/- 13 cm/s 2 ) and the fetuses aged 25 to 29 weeks (143 +/- 21 cm/s 2 ), but after 30 weeks increased with gestational age. For the total group combining the 4 different gestational age groups, the pre-ejection myocardial velocity and myocardial acceleration correlated with gestational age ( r = 0.85 and 0.75). This study demonstrated the gestational age-related changes in pre-ejection myocardial velocity and myocardial acceleration. The load-independent index of contractility, myocardial acceleration, increased mainly after 30 weeks' gestation.

Echocardiography, Doppler↗

PubMed2005

Acceleration characteristics of human ocular accommodation.

Position and velocity of accommodation are known to increase with stimulus magnitude, however, little is known about acceleration properties. We investigated three acceleration properties: peak acceleration, time-to-peak acceleration and total duration of acceleration to step changes in defocus. Peak velocity and total duration of acceleration increased with response magnitude. Peak acceleration and time-to-peak acceleration remained independent of response magnitude. Independent first-order and second-order dynamic components of accommodation demonstrate that neural control of accommodation has an initial open-loop component that is independent of response magnitude and a closed-loop component that increases with response magnitude.

Accommodation, Ocular↗

PubMed2000

Arachidonic acid and prostaglandin D2 cooperatively accelerate desensitization of nicotinic acetylcholine receptor channel in mouse skeletal muscles.

To clarify the effects of arachidonic acid (AA) and its metabolites on desensitization of nicotinic acetylcholine (ACh) receptor channel in mouse skeletal muscle cells, we investigated the time-dependent decrease in the channel opening frequency of ACh (1 microM)-activated channel currents by the cell-attached patch clamp technique. AA (30-100 microM) applied to a patched membrane or to non-patched membrane accelerated the decrease in the channel opening frequency. A cyclooxygenase inhibitor, indomethacin (10 microM), prevented the acceleration elicited by 30 microM AA, but not by 100 microM AA. A lipoxygenase inhibitor, nordihydroguaiaretic acid (10 microM), and a cytochrome P-450 inhibitor, ketoconazole (3 microM), did not affect the acceleration by 30 microM AA. Prostaglandin (PG) D2 at 10 microM alone and at 25 nM in combination with 10 microM AA accelerated the decrease in the channel opening frequency. No acceleration was observed with PGE2 at 10 microM alone and at 25 nM in combination with 10 microM AA. Pretreatment with a protein kinase (PK) C inhibitor, staurosporine (10 nM), but not with a PKA inhibitor, H-89 (3 microM), prevented the acceleration elicited by AA + PGD2. These results suggest that AA, and PGD2 of its metabolites, cooperatively accelerate desensitization of nicotinic ACh receptor channel. The activation of PKC by AA and PGD2 may be involved in the mechanism of the cooperative acceleration of desensitization.

Acetylcholine↗