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At least 55 records · Page 3Linked to original sources
PubMed1997

Intracellular distributions and putative functions of calcium-binding proteins in the bullfrog vestibular otolith organs.

Hair cells in the bullfrog vestibular otolith organs were immunolabeled by monoclonal and polyclonal antisera against calbindin (CaB), calmodulin (CaM), calretinin (CaR), and parvalbumin (PA). S-100, previously shown to immunolabel striolar hair cells in fish vestibular organs, only weakly immunolabeled hair cells in the bullfrog vestibular otolith organs. Immunolabeling was not detected in supporting cells. With the exception of CaR, myelinated axons and unmyelinated nerve terminals were immunolabeled by all of the above antisera. Immunolabeling was seen in all saccular hair cells, although hair cells at the macular margins were immunolabeled more intensely for CaB, CaM, and PA than more centrally located hair cells. As the macula margins are known to be a growth zone, this labeling pattern suggests that marginal hair cells up-regulate their calcium-binding proteins during hair cell development. In the utriculus, immunolabeling for CaM and PA was generally restricted to striolar hair cells. CaR immunolabeling was restricted to the stereociliary array. Immunolabeling for other calcium-binding proteins was generally seen in both the cell body and hair bundles of hair cells, although this labeling was often localized to the stereociliary array and the apical portion of the cell body. CaM and PA immunolabeling in the stereociliary array in saccular and utricular striolar cells suggests a functional role for these proteins in mechanoelectric transduction and adaptation.

Adaptation, Physiological↗
PubMed1996

Motor function in microgravity: movement in weightlessness.

Microgravity provides unique, though experimentally challenging, opportunities to study motor control. A traditional research focus has been the effects of linear acceleration on vestibular responses to angular acceleration. Evidence is accumulating that the high-frequency vestibulo-ocular reflex (VOR) is not affected by transitions from a 1 g linear force field to microgravity (<1 g); however, it appears that the three-dimensional organization of the VOR is dependent on gravitoinertial force levels. Some of the observed effects of microgravity on head and arm movement control appear to depend on the previously undetected inputs of cervical and brachial proprioception, which change almost immediately in response to alterations in background force levels. Recent studies of post-flight disturbances of posture and locomotion are revealing sensorimotor mechanisms that adjust over periods ranging from hours to weeks.

Animals↗
PubMed1996

Perceived visual speed constrained by image segmentation.

Little is known about how or where the visual system parses the visual scene into objects or surfaces. However, it is generally assumed that the segmentation and grouping of pieces of the image into discrete entities is due to 'later' processing stages, after the 'early' processing of the visual image by local mechanisms selective for attributes such as colour, orientation, depth, and motion. Speed perception is also thought to be mediated by early mechanisms tuned for speed. Here we show that manipulating the way in which an image is parsed changes the way in which local speed information is processed. Manipulations that cause multiple stimuli to appear as parts of a single patch degrade speed discrimination, whereas manipulations that perceptually divide a single large stimulus into parts improve discrimination. These results indicate that processes as early as speed perception may be constrained by the parsing of the visual image into discrete entities.

Humans↗
PubMed1996

Use of bed rest and head-down tilt to simulate spaceflight-induce immune system changes.

Bed rest, both with and without head-down tilt, has been extensively used as an earth-bound analog to study physiologic effects mimicking those occurring in weightlessness during spaceflight. We have been able to show in six subjects that 4 weeks of head-down tilt bed rest induces a significant decrease in interleukin-2 secretion by PHA-stimulated T lymphocytes. Another study, lasting 113 days, with two subjects showed a decreased interleukin-2 receptor expression in PHA-stimulated peripheral blood mononuclear cells but a decreased interleukin-2 production in one subject only. Under the same conditions, interleukin-1 production was largely increased in both subjects. Several other immune parameters were also analyzed. Increased interleukin-1 production could contribute to bone mineral loss encountered during bed rest and decreased interleukin-2 secretion could play a role in the appearance of infectious diseases often observed during bed red.

Antibody Formation↗
PubMed1995

Investigations of the pathogenesis of acquired pendular nystagmus.

We investigated the pathogenesis of acquired pendular nystagmus (APN) in six patients, three of whom had multiple sclerosis. First, we tested the hypothesis that the oscillations of APN are due to a delay in visual feedback secondary, for example, to demyelination of the optic nerves. We manipulated the latency to onset of visually guided eye movements using an electronic technique that induces sinusoidal oscillations in normal subjects. This manipulation did not change the characteristics of the APN, but did superimpose lower-frequency oscillations similar to those induced in normal subjects. These results are consistent with current models for smooth (non-saccadic) eye movements, which predict that prolongation of visual feedback could not account for the high-frequency oscillations that often characterize APN. Secondly, we attempted to determine whether an increase in the gain of the visually-enhanced vestibulo-ocular reflex (VOR), produced by viewing a near target, was accompanied by a commensurate increase in the amplitude of APN. Increases in horizontal or vertical VOR gain during near viewing occurred in four patients, but only two of them showed a parallel increase in APN amplitude. On the other hand, APN amplitude decreased during viewing of the near target in the two patients who showed no change in VOR gain. Taken together, these data suggest that neither delayed visual feedback nor a disorder of central vestibular mechanisms is primarily responsible for APN. More likely, these ocular oscillations are produced by abnormalities of internal feedback circuits, such as the reciprocal connections between brainstem nuclei and cerebellum.

Adult↗
PubMed1993

Orientation and movement in unusual force environments.

A manned space mission to Mars might take as long as 1 year each way. Consequently, artificial gravity is being considered as a way of preventing the debilitating effects of long-duration exposure to microgravity on the human body. The present article discusses some of the problems associated with adapting to the rotation levels that might be used to generate artificial gravity. It also describes how exposure to background-force levels greater or less than the 1-G force of Earth gravity affects orientation and movement control. The primary emphasis of the article is that human movement and orientation control are dynamically adapted to the 1-G force background of Earth and that accommodation to altered force levels or to rotating environments requires a wide range of adaptive changes.

Adaptation, Physiological↗
PubMed1996

Evidence of a sensory processing unit in the mammalian macula.

We cut serial sections through the medial part of the rat vestibular macula for transmission electron microscopic (TEM) examination, computer-assisted 3-D reconstruction, and compartmental modeling. The ultrastructural research showed that many primary vestibular neurons have an unmyelinated segment, often branched, that extends between the heminode (putative site of the spike initiation zone) and the expanded terminal(s) (calyx, calyces). These segments, termed the neuron branches, and the calyces frequently have spine-like processes of various dimensions with bouton endings that morphologically are afferent, efferent, or reciprocal to other macular neural elements. The major questions posed by this study were whether small details of morphology, such as the size and location of neuronal processes or synapses, could influence the output of a vestibular afferent, and whether a knowledge of morphological details could guide the selection of values for simulation parameters. The conclusions from our simulations are (1) values of 5.0 k omega cm2 for membrane resistivity and 1.0 nS for synaptic conductance yield simulations that best match published physiological results; (2) process morphology has little effect on orthodromic spread of depolarization from the head (bouton) to the spike initiation zone (SIZ); (3) process morphology has no effect on antidromic spread of depolarization to the process head; (4) synapses do not sum linearly; (5) synapses are electrically close to the SIZ; and (6) all whole-cell simulations should be run with an active SIZ.

Acoustic Maculae↗
PubMed1996

Tactile influences on astronaut visual spatial orientation: human neurovestibular studies on SLS-2.

Human spatial orientation in spaceflight is initially disturbed by the absence of usable graviceptor information from the otolithic organs. Experiments measuring astronaut visually induced motion (vection) strength on various flight days during the first 10 days of the Spacelab Life Sciences-2 mission demonstrated two new phenomena in addition to confirming the initial increased weighting of visual and localized tactile cues. The reliance on tactile and visual noninertial cues apparently declined after a week in space, as the crew became able to utilize their internal reference frame. Subjects also showed that even nondirectional tactile cues served as a direction anchor and inhibited visually induced roll sensation relative to a new loosely tethered test condition. Individual perceptual styles were again revealed among the four astronauts tested. The readaptation to 1 G similarly shows a period of reinterpretation of inertial and visual cues to spatial orientation. The results are discussed in terms of an internal-model representation of body orientation, with time-varying weights applied to extrinsic and intrinsic signals.

Adult↗
PubMed1996

Effect of spaceflight on ability to sense and control roll tilt: human neurovestibular studies on SLS-2.

To measure adaptive changes in the ability to sense tilt after spaceflight, we measured the ability of four astronauts to control roll tilt in the presence of a pseudorandom motion disturbance before and after a 14-day Spacelab mission. The subjects were tested 1) in the dark, 2) with an independent sum-of-sines visual display, and 3) by using a control condition in which the visual cues confirmed the motion cues (counterrotating). The two subjects tested on the landing day exhibited significant decrements (P < 0.05) in their ability to control roll tilt in the dark, whereas no significant performance decrements were observed in the control condition. The absence of changes in the control condition suggests that changes in the neuromuscular component of the task and postflight fatigue were not major factors contributing to the observed performance decrement in the dark. These findings indicate an adaptive change in the way the nervous system interprets tilt cues. Readaptation of all responses appeared to be rapid, with a return to preflight values within 1-2 days after landing.

Adaptation, Physiological↗
PubMed1996

Perceptual responses to linear acceleration after spaceflight: human neurovestibular studies on SLS-2.

Perceptual responses of four astronauts were measured before and after a 14-day Spacelab Life Sciences-2 mission during interaural (y-axis) and rostrocaudal (z-axis) linear acceleration to measure adaptive changes in perceptual responses to inertial cues. In one test, subjects used a joystick to null a pseudorandom velocity disturbance. Postflight, two of three subjects showed a significantly enhanced ability to null linear self-motion in the y-axis and z-axis orientations. In another test, the subjects used a joystick to indicate their direction of motion during a series of low-acceleration steps. The postflight responses of three of the four subjects showed a significant increase in the response latency for both y-axis and z-axis orientations. In a third test, subjects were asked to track a stationary but unseen target with their eyes while they translated linearly in the dark. No significant changes were observed in the postflight responses. The observed changes, when present, may be due to a reinterpretation of inertial cues that are functionally adaptive for the microgravity environment but are not optimal for responses on Earth.

Acceleration↗