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Biomedical subjects

A Straube

Publications and source records attributed to A Straube.

At least 145 records · Page 8Linked to original sources
PubMed1993

The effect of muscimol micro-injections into the fastigial nucleus on the optokinetic response and the vestibulo-ocular reflex in the alert monkey.

Eye movements of four macaque monkeys were investigated after unilateral micro-injections of the GABA agonist muscimol (1 microgram in 1 microliter NaCl) into the caudal fastigial nucleus, i.e. the fastigial oculomotor region. Spontaneous eye movements in the dark and in the light were tested, as well as those evoked by vestibular stimulation in the dark (sinusoidal: 0.1-0.2 Hz, +/- 40-100 deg/s, velocity trapezoid acceleration 40 deg/s2, constant velocity 120 deg/s), optokinetic stimulation (sinusoidal: 0.1-0.2 Hz, +/- 40-100 deg/s, constant velocity 60-100 deg/s), and visual-vestibular conflict stimulation. With these stimuli, smooth pursuit mechanisms (fast build-up of optokinetic slow phase velocity), the vestibulo-ocular reflex (VOR) and the velocity storage mechanism were investigated. Muscimol injections consistently led to specific eye movement changes which were maximal 30-60 min after the injection and lasted 4-6 h. The fast initial rise of OKN slow phase velocity to the contralateral side decreased by 45% (range 24%-82%) of its pre-injection value, while it was virtually unaltered on the ipsilateral side (average decrease of 1%, range from a decrease of 20% to an increase of 32%). For conflict ramp stimulation, the suppression of vestibular nystagmus was less (decrease of 50%, range 12-82%) towards the contralateral side while it remained unchanged on the ipsilateral side. The VOR in the dark and the velocity storage mechanism were not altered. For the latter, the slow build-up of optokinetic nystagmus velocity, the optokinetic afternystagmus (OKAN) and the time constant of decay for the vestibular nystagmus were evaluated.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Central nervous system involvement in Leber's optic neuropathy.

Six months after the onset of visual loss a 23-year-old male patient with Leber's optic neuropathy associated with a mitochondrial DNA mutation developed brain stem involvement with Parinaud's syndrome and oculopalatal myoclonus. Magnetic resonance imaging (MRI) revealed a high signal area in the brain stem, corresponding to a hypodense area in the CT scan that did not show contrast enhancement. Distinct diminution but not complete remission of the MRI findings was found in the 5-year follow-up, which was not accompanied by clinical improvement. Although the MRI findings were compatible with a demyelinating lesion, neither extensive evoked potential studies nor spinal fluid examination supported this.

Adult↗
PubMed1993

A contrast enhanced lesion of the III nerve on MR of a patient with ophthalmoplegic migraine as evidence for a Tolosa-Hunt syndrome.

A 23-year-old female with a six year history of migraine without aura twice developed a nearly complete internal and external III nerve paresis ipsilateral to her headache, two days after the onset of migraineous headache. An MR scan performed one week after the second episode showed a contrast enhanced lesion of the prepontine III nerve, where it enters the cavernous sinus on the left side. The headache, as well as the paresis ameliorated spontaneously. We suggest this is a further well documented case of "ophthalmoplegic migraine" which might reflect Tolosa-Hunt syndrome.

Adult↗
PubMed1993

Role of the caudal fastigial nucleus in saccade generation. I. Neuronal discharge pattern.

1. The effects of lesions in both human and nonhuman primates have implicated the cerebellum in the control of rapid eye movements, i.e., saccades. To examine the neural substrate of this control, we recorded the discharge patterns of cerebellar output cells in the fastigial nucleus while monkeys tracked a small, jumping spot of light. 2. In the caudal fastigial nucleus, neurons discharged for saccades in one or several directions. All exhibited a burst. Some also exhibited a saccade-related pause in firing either before or after saccades greater than approximately 3-5 degrees. Thirty-seven percent discharged only a burst, 44% also exhibited a pause before bursts in certain directions, and 19% also paused after the saccade-related burst in certain directions. Although many cells discharged steadily during intersaccadic intervals, few exhibited a robust relation between firing rate and eye position. 3. As a measure of directional selectivity, we plotted the burst lead time as a function of saccade direction for saccades of similar (10 degrees) radial amplitudes. Of 20 neurons tested, 17 burst earliest for contralateral saccades and 1 for upward saccades; 2 others showed little dependence on direction. Of 19 additional units tested only in the horizontal direction, 18 burst earlier for contralateral saccades. 4. For contralateral saccades the burst preceded saccades of all sizes by at least 7.7 ms on average. For ipsilateral saccades, the burst preceded small saccades by an average of 10.3 ms. However, as ipsilateral saccade size increased, the burst began later and later relative to saccade onset so that, on average, it always occurred after the onset of 20 degrees saccades but well before the saccade ended. 5. Many fastigial saccade-related units showed increases in the number of spikes with saccade size and in burst duration with saccade duration in one or more directions. For either relation the highest average correlation coefficients ranged from 0.6 to 0.65. In general, the average correlation coefficients and slopes for either relation were slightly larger for contralateral saccades. Pure burst neurons did not display better average correlations than neurons that also paused. For neurons that also paused either before or after saccades, there was a weak tendency for pause duration to increase with the duration of larger saccades. 6. We tested the effect of eye position on unit discharge in 13 cells by requiring the monkey to make 10 degrees ipsilateral and contralateral saccades from a variety of starting positions.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Role of the caudal fastigial nucleus in saccade generation. II. Effects of muscimol inactivation.

1. We studied the effect of temporarily inhibiting neurons in the caudal fastigial nucleus in two rhesus macaques trained to make saccades to jumping targets. We placed injections of the gamma-aminobutyric acid (GABA) agonist muscimol unilaterally or bilaterally at sites in the caudal fastigial nucleus where we had recorded saccade-related neurons a few minutes earlier. 2. Unilateral injections (n = 9) made horizontal saccades to the injected side hypermetric and those to the other side hypometric (mean gain of 1.37 and 0.61, respectively, for 10 degrees target steps, and 1.26 and 0.81 for 20 degrees target steps; normal saccade gain was 0.96). Saccades to vertical targets showed a small but significant hypermetria and curved strongly toward the side of the injection. The trajectories and end points of all targeted saccades were more variable than normal. 3. After unilateral injections, centripetal saccades were slightly larger than centrifugal saccades (mean gains for ipsilateral saccades were 1.42 and 1.31, respectively, for 10 degrees target steps, and 1.37 and 1.15 for 20 degrees target steps). 4. Unilateral injections increased the average acceleration of ipsilateral saccades and decreased the acceleration of contralateral saccades. Injections decreased both the acceleration and deceleration of vertical saccades. 5. After dysmetric saccades, monkeys acquired the target with an abnormally high number of hypometric corrective saccades. Injection increased the average number of corrective saccades from 0.6 to 2.1 after 10 degrees horizontal target steps and from 0.8 to 2.1 after 20 degrees steps. The size of each successive corrective saccade in a series decreased, and the latency from the previous corrective saccade increased. 6. Bilateral injections (n = 2) of muscimol, in which we injected first into the left caudal fastigial nucleus and then, within 30 min, into the right, made all saccades hypermetric (mean gain for 10 degrees right, left, up, and down saccades was 1.18, 1.49, 1.43, and 1.10, respectively). Paradoxically, bilateral injection decreased both saccade acceleration and deceleration. Saccade trajectories and end points were more variable than normal. 7. To account for the effects of our injections, we propose that the activity of caudal fastigial neurons on one side normally helps to decelerate ipsilateral saccades and helps to accelerate contralateral saccades by influencing the feedback loop of the saccade burst generator in the brain stem. Without caudal fastigial activity the brain stem burst generator produces hypermetric, variable saccades. We therefore also propose that the influence of caudal fastigial neurons on the burst generator makes saccades more consistent and accurate.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

[Neuro-ophthalmologic and posturographic studies of patients with idiopathic torticollis].

The pathophysiology of idiopathic spasmodic torticollis is still unknown. In addition to genetic and other factors, one of the possible causes under discussion is a disturbance of the vestibular system. In order to analyse vestibular influences we investigated 40 patients with idiopathic torticollis using electronystagmography, fundus photography, measurement of the subjective visual vertical and posturography. The results of the neuroophthalmological investigations and the measurement of the visual vertical were within the normal range. 53% of the patients examined showed a slight central vestibular preponderance in the electronystagmography, whereas 38% demonstrated a slight pathological monocular torsion in the fundus photography. Posturographically, there were some indications of a slightly decreased gain in visual contribution to the postural control process. None of the results could be correlated to the extent of torticollis in the individual case. We propose that these results do not confirm the hypothesis of primary vestibular lesion in the pathogenesis of torticollis. A possible explanation of the results described could be a common basic lesion which causes the torticollis on the one hand and also affects the central vestibular system on the other hand.

Adult↗
PubMed1992

Postural imbalance: an early sign in HIV-1 infected patients.

We have recorded postural performance in 50 HIV-infected patients in different stages of the disease (Walter Reed (WR) stages I-VI) by means of a force measuring platform. The results were compared with 50 age-matched controls. A significant instability was particularly evident when standing on an unstable foot support. In patients standing with "eyes closed", postural sway was significantly higher in every patient group (WR I-II: P less than 0.02, WR III-V: P less than 0.001, WR VI: P less than 0.001). Patients in stage WR I-II showed no relevant neurological abnormalities. In agreement with other neurophysiological data in the literature we suggest that postural imbalance could be an early sign of central nervous system penetration of HIV. No correlation with electromyographic or cerebrospinal fluid findings could be found.

Adult↗
PubMed1992

Exteroceptive suppression of temporalis muscle activity in various types of headache.

Exteroceptive suppression (ES) of temporalis muscle activity, particularly the multisynaptic ES2, has been reported to be significantly reduced in tension type headache, but not in migraine. We re-evaluated the methods of optimally analysing the single shock technique and its intra- and inter-individual variability in 26 normal subjects. These data were compared with the results in patients with migraine, post-lumbar puncture headache, headache due to meningitis, tension-type headaches in HIV infection and patients with symptomatic headache of various etiologies. ES2 was absent in about 50% of tension-type headache patients, but only in one normal subject. With the methods used here and when patients with absent ES2 were excluded, mean duration of ES2 was not significantly different between the various groups. It seems therefore necessary, in spite of increased discomfort for patients, to use complementary methods, such as averaging 16-32 responses and applying various stimulation sets, if one wants to increase the potency of temporalis ES2 as a diagnostic and pathophysiologic tool in headache.

Adult↗
PubMed1992

["Abducens neuromyotonia" with partial oculomotor paralysis].

Paroxysmal involuntary spasms of extraocular eye muscles which can lead to reversible pathological eye positions and limitations of eye movements are etiologically heterogenous. Despite the diagnostic difficulty, they are important as a neurological sign because of the usually good response to treatment. We report on a patient with the unusual combination of ocular neuromyotonia with brief paroxysmal tonic lateral deviation of the left eye and a concomitant partial third nerve palsy. The paroxysmal episodes disappeared with carbamazepine therapy. Possible pathomechanisms are discussed.

Abducens Nerve↗
PubMed1991

Differential effects of bicuculline and muscimol microinjections into the vestibular nuclei on simian eye movements.

1.) Eye movements were recorded in four Java monkeys (M. fascicularis) after unilateral microinjections (1 microliter, concentration 1 micrograms/microliter) of the GABA antagonist, bicuculline, and the GABA agonist, muscimol, into oculomotor related regions of the vestibular nuclei. Eye movements were investigated in the dark and light during spontaneous eye movements, vestibular stimulation (sinusoidal: 0.2 Hz, +/- 40 deg/s, and velocity trapezoid: 40 deg/s2 acceleration, 120 deg/s constant velocity), and visual-vestibular conflict stimulation. 2.) Bicuculline and muscimol injections consistently led to specific eye movement changes, which were maximal 5-10 min after bicuculline injection (muscimol 10-30 min), and lasted 90-120 min (muscimol 2-4 h). Control injections with NaCl (0.9%) into the responsive area and with bicuculline 2-3 mm more lateral showed no effect. 3.) Bicuculline induced a spontaneous nystagmus of 40.9 deg/s (average, range 10.5-93 deg/s), beating in 60% of the cases to the contralateral and in 40% to the ipsilateral side. The analysis of the slope of the slow phase gave no evidence for an additional gaze holding deficit. The VOR gain in the dark showed a slight decrease (pre: 0.96; post: 0.86) on average. The time constant of decay for slow phase nystagmus velocity after vestibular ramp stimulation was reduced, reflecting a 'velocity storage' deficit. After bicuculline injections nystagmus suppression in the light and during visual-vestibular conflict stimulation was generally well preserved. 4.) After muscimol injections horizontal gaze holding was severely affected. Each saccade was followed by an exponentially decreasing postsaccadic drift with a time constant as short as 250 ms (average 414 ms). The eyes always drifted towards a null-position, which generally did not coincide with the midposition of the eye. The null-position could move up to 35 deg to the contralateral or ipsilateral side. The highly distorted eye movements after muscimol injections prevented VOR-measurements based on eye velocity. Instead vestibular stimulation led to a shift of the null-position with an amplitude corresponding to a gain (eye position/stimulus position) of 0.17 (average) at 0.2 Hz (+/- 40 deg/s). Vertical eye movements did not show a major gaze holding deficit. 5.) From the experiments it can be concluded that the inhibitory transmitter GABA plays an important role for eye movement generation within the vestibular nuclei. Bicuculline induces mainly a vestibular imbalance with little evidence for a neural integrator deficit. In contrast unilateral muscimol injections lead to a complete, reversible loss of function for the common horizontal neural integrator, which converts eye velocity into eye position signals. The accompanying shift of the null-position reflects an additional vestibular imbalance.

Animals↗
PubMed1991

The effects of baclofen and cholinergic drugs on upbeat and downbeat nystagmus.

The GABAergic drug baclofen and the cholinergic drug physostigmine were administered to patients with upbeat and downbeat nystagmus. Baclofen (orally, 5 mg three times daily) reduced nystagmus slow phase velocity and distressing oscillopsia by 25-75% in four out of five patients (two upbeat nystagmus; two downbeat nystagmus). Physostigmine (1 mg single intravenous injection) increased nystagmus in five additional patients with downbeat (1) or positional downbeat nystagmus (4) for a duration of 15-20 minutes. The different interactions of baclofen and physostigmine on neurotransmission subserving vertical vestibulo-ocular reflex could account for these effects. The response to baclofen appears to be a GABA-B-ergic effect with augmentation of the physiological inhibitory influence of the vestibulo-cerebellum on the vestibular nuclei. Similarly baclofen has an inhibitory effect on the velocity storage mechanism. Cholinergic action may cause the increment of nystagmus by physostigmine.

Adult↗
PubMed1990

Influence of visual blur on object-motion detection, self-motion detection and postural balance.

We have compared the influence of visual blurring (either by use of plastic foils or by plus lenses) on detection of object-motion and self-motion, and on visual control of postural balance. Three experiments were performed--in all of which object-motion and self-motion detection latencies (response times) and postural sway (sway path) increased with increasing visual blurring. We conclude that visual blurring either by foils or by glasses affects object- and self-motion perception and postural sway in a similar way.

Attention↗
PubMed1990

Oculo-bulbar myasthenic symptoms as the sole sign of tumour involving or compressing the brain stem.

Four patients with tumours involving or compressing the brain stem are described whose initial clinical symptoms of fluctuating paresis of the external ocular muscles and/or the pharyngeal muscles without other neurological deficits led to the primary diagnosis of focal myasthenia. The combination of an unusual clinical pattern, involvement of muscles of only one ocular nerve or severe dysphagia/dysarthria without extension of the myasthenic symptoms, should lead to further investigation to exclude other reasons of a focal myasthenic syndrome such as a brain-stem tumour.

Adult↗
PubMed1989

Differential effects of retinal target displacement, changing size and changing disparity in the control of anterior/posterior and lateral body sway.

When visual information is provided in addition to input from other sensory systems, normal body sway can be attenuated by about 50%. The essential visual cue is retinal target displacement, which increases as eye-target distance is reduced. As a result, both lateral and anterior/posterior (A-P) sway decrease as eye/target distance decreases. We have investigated the geometrical basis of lateral and fore-aft sway detection by vision, the latter provided by detection of change in disparity of the visual axis of both eyes and change in target size. Using known movement detection thresholds the largest possible distance for visual stabilization of posture can be calculated to be 34 m for lateral sway, and for fore-aft sway 1.50 m for change in disparity and 3.20 m for change in size. Visual stimuli were designed to selectively stabilize fore-aft sway either by change in size or by change in disparity. The experiments revealed that the theoretical prediction overestimates the efficacy of visual stabilization of lateral sway and underestimates the efficacy of fore-aft sway stabilization. It is proposed that microoscillations of the eye increase the threshold for detection of retinal target displacements, leading to less efficient lateral sway stabilization than expected, and that the threshold for detection of self motion in the A-P direction is lower than the threshold for object motion detection used in the calculations, leading to more efficient stabilization of A-P sway.

Form Perception↗
PubMed1989

Visual postural performance in ametropia and with optical distortion produced by bifocals and multifocals.

Visual stabilization of posture depends strongly on the performance of the visual system and declines with experimentally induced reduction of visual image quality. We studied postural performance in subjects with median and high grade hyperopia or myopia. While body sway of median grade ametropic subjects increased slightly when measured without glasses, high grade ametropia showed no significant differences between postural performance with glasses on and off. We concluded that the increase in visual acuity when wearing glasses is outweighted by concurrent dioptric distortions such as size change and prismatic effects. In addition we could not find any difference between bifocal and multifocal lenses in their effect on sway when investigated in normals with either steady fixation or saccades or foveal pursuit.

Adult↗