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PubMed1985

Neurological findings in patients with the fragile-X syndrome.

We report two brothers with previously unexplained mental retardation and seizures who had dysmorphic facial features, macro-orchidism, and a fragile site at the X chromosome. This recently described syndrome is the second most common chromosome aberration associated with mental retardation after Down's syndrome. In order to determine the prevalence of seizures and the frequency of specific neurological features, we studied a total of 17 patients with the fragile X syndrome. 41% had grand mal seizures; 41% had extensor plantar responses; 47% had hyperactive behaviour and 65% exhibited stereotypics; 59% had incoordination and 35% had blepharospasm. We emphasise the need for chromosome analysis of patients with unexplained mental retardation, specific phenotypic abnormalities, and large testes.

Adult↗
PubMed2004

Observer-rated ataxia: rating scales for assessment of genetic differences in ethanol-induced intoxication in mice.

Identification of genetic and physiological mechanisms underlying a drug's or mutation's effects on motor performance could be aided by the existence of a simple observation-based rating scale of ataxia for mice. Rating scales were developed to assess ataxia after ethanol (2.75, 3.0, and 3.25 g/kg) in nine inbred mouse strains. Each scale independently rates a single behavior. Raters, blinded to dose, scored four behaviors (splay of hind legs, wobbling, nose down, and belly drag) at each of four time points after injection. The severities of hind leg splaying and wobbling were quantifiable, whereas nose down and belly dragging were expressed in all-or-none fashion. Interrater reliabilities were substantial (0.75 0 at some time), but all doses were equally effective. Incidence of nose down and belly dragging behaviors increased strain dependently after ethanol, but strains did not differentially respond to dose. Ethanol-induced splaying was modestly, and negatively, genetically correlated with wobbling. Nose down and belly dragging tended to be associated with splaying and wobbling at later times. Four distinct ataxia-related behaviors were sensitive to ethanol. Strains differed in ethanol sensitivity for all measures. Modest strain mean correlations among behaviors indicate that these behaviors are probably under control of largely different genes and that ataxia rating scales should rate separate behaviors on discrete scales.

Alcoholic Intoxication↗
PubMed2006

Interaction between acoustic startle and habituated neck postural responses in seated subjects.

Postural and startle responses rapidly habituate with repeated exposures to the same stimulus, and the first exposure to a seated forward acceleration elicits a startle response in the neck muscles. Our goal was to examine how the acoustic startle response is integrated with the habituated neck postural response elicited by forward accelerations of seated subjects. In experiment 1, 14 subjects underwent 11 sequential forward accelerations followed by 5 additional sled accelerations combined with a startling tone (124-dB sound pressure level) initiated 18 ms after sled acceleration onset. During the acceleration-only trials, changes consistent with habituation occurred in the root-mean-square amplitude of the neck muscles and in the peak amplitude of five head and torso kinematic variables. The subsequent addition of the startling tone restored the amplitude of the neck muscles and four of the five kinematic variables but shortened onset of muscle activity by 9-12 ms. These shortened onset times were further explored in experiment 2, wherein 16 subjects underwent 11 acceleration-only trials followed by 15 combined acceleration-tone trials with interstimulus delays of 0, 13, 18, 23, and 28 ms. Onset times shortened further for the 0- and 13-ms delays but did not lengthen for the 23- and 28-ms delays. These temporal and spatial changes in EMG can be explained by a summation of the excitatory drive converging at or before the neck muscle motoneurons. The present observations suggest that habituation to repeated sled accelerations involves extinguishing the startle response and tuning the postural response to the whole body disturbance.

Acceleration↗
PubMed2006

Responses of reticulospinal neurons in the lamprey to lateral turns.

When swimming, the lamprey maintains a definite orientation of its body in the vertical planes, in relation to the gravity vector, as the result of postural vestibular reflexes. Do the vestibular-driven mechanisms also play a role in the control of the direction of swimming in the horizontal (yaw) plane, in which the gravity cannot be used as a reference direction? In the present study, we addressed this question by recording responses to lateral turns in reticulospinal (RS) neurons mediating vestibulospinal reflexes. In intact lampreys, the activity of axons of RS neurons was recorded in the spinal cord by implanted electrodes. Vestibular stimulation was performed by periodical turns of the animal in the yaw plane (60 degrees peak to peak). It was found that the majority of responding RS neurons were activated by the contralateral turn. By removing one labyrinth, we found that yaw responses in RS neurons were driven mainly by input from the contralateral labyrinth. We suggest that these neurons, when activated by the contralateral turn, will elicit the ipsilateral turn and thus will compensate for perturbations of the rectilinear swimming caused by external factors. It is also known that unilateral eye illumination elicits a contralateral turn in the yaw plane (negative phototaxis). We found that a portion of RS neurons were activated by the contralateral eye illumination. By eliciting an ipsilateral turn, these neurons could mediate the negative phototaxis.

Action Potentials↗
PubMed2005

Dissociated hysteresis of static ocular counterroll in humans.

In stationary head roll positions, the eyes are cyclodivergent. We asked whether this phenomenon can be explained by a static hysteresis that differs between the eyes contra- (CE) and ipsilateral (IE) to head roll. Using a motorized turntable, healthy human subjects (n = 8) were continuously rotated about the earth-horizontal naso-occipital axis. Starting from the upright position, a total of three full rotations at a constant velocity (2 degrees/s) were completed (acceleration = 0.05 degrees/s2, velocity plateau reached after 40 s). Subjects directed their gaze on a flashing laser dot straight ahead (switched on 20 ms every 2 s). Binocular three-dimensional eye movements were recorded with dual search coils that were modified (wires exiting inferiorly) to minimize torsional artifacts by the eyelids. A sinusoidal function with a first and second harmonic was fitted to torsional eye position as a function of torsional whole body position at constant turntable velocity. The amplitude and phase of the first harmonic differed significantly between the two eyes (paired t-test: P < 0.05): on average, counterroll amplitude of IE was larger [CE: 6.6 +/- 1.6 degrees (SD); IE: 8.1 +/- 1.7 degrees), whereas CE showed more position lag relative to the turntable (CE: 12.5 +/- 10.7 degrees; IE: 5.1 +/- 8.7 degrees). We conclude that cyclodivergence observed during static ocular counterroll is mainly a result of hysteresis that depends on whether eyes are contra- or ipsilateral to head roll. Static hysteresis also explains the phenomenon of residual torsion, i.e., an incomplete torsional return of the eyes when the first 360 degrees whole body rotation was completed and subjects were back in upright position (extorsion of CE: 2.0 +/- 0.10 degrees; intorsion of IE: 1.4 +/- 0.10 degrees). A computer model that includes asymmetric backlash for each eye can explain dissociated torsional hysteresis during quasi-static binocular counterroll. We hypothesize that ocular torsional hysteresis is introduced at the level of the otolith pathways because the direction-dependent torsional position lag of the eyes is related to the head roll position and not the eye position.

Adult↗
PubMed1975

Unit activity in vestibular nucleus of the alert monkey during horizontal angular acceleration and eye movement.

Single units were recorded from the vestibular nuclei of unanesthetized monkeys that were rotated in the horizontal plane while simultaneously pressing individual buttons in a controlled array which turned with hem. Using this behavioral paradigm, it was possible to 1) determine the relationship of unit discharge to eye movements measured by the DC-coupled electrooculogram and calibrated by the button-press task, and 2) determine the relationship of unit discharge to horizontal acceleration, either with or without the compensatory eye movements evoked by vestibular stimulation. Based on their responses during vestibular stimulation and/or eye movements, neurons in the vestibular nuclei (77% of our sample was in the medial nucleus) could be divided into four groups...

Acceleration↗
PubMed1980

Recovery of function in dorsal horn following partial deafferentation.

1. Collateral sprouting of L6 dorsal root afferents within the dorsal horn of the L6 spinal cord segment has been shown anatomically to occur following transection of all other lumbosacral dorsal roots in the cat. The present study was performed to examine a possible physiological correlate of that sprouting, namely, an altered somatotopic organization of the dorsal horn at L6. This was evaluated by microelectrode mapping of the L6 dorsal horn in normal cats and in cats with L6 spared, lumbosacral dorsal rhizotomies performed 2 days (subacute spared root) or more than 8 wk (chronic spared root), prior to recording. 2. In normal cats the mediolateral somatotopic sequence of hindlimb representation in the L6 dorsal horn is ventral digits 2 and 3, dorsal digits 2 and 3, dorsal foot, rostral and lateral ankle, lateral leg, lateral thigh, and back. In both subacute and chronic spared-root cats the somatotopic sequence is similar to that of normal cats, but there is a loss of proximal thigh and back representation. This proximal body region is represented at the lateral edge of the dorsal horn in normal animals. 3. There was a partial loss of responsiveness of cells in the dorsal horn in the subacute spared-root group and a partial recovery of responsiveness in the chronic group. In the subacute group punctures exhibiting no responses to tactile input tended to be clustered in the lateral dorsal horn. 4. The lateral one-fourth of the dorsal horn in each animal was analyzed in terms of the percentage of recording loci occurring within it. The percentages of recording loci having receptive fields proximal to, distal to, and spanning the middle of the thigh (proximal, distal, and intermediate RFs) were tabulated for each animal. Subacute animals had a significantly lower-than-normal overall percentage of responsive loci in the lateral dorsal horn, but chronic animals did not. The percentage of distal fields therein was not different for the normal versus the subacute group, signifying that the loss of proximal and intermediate fields was responsible for the difference in overall percentage. Chronic animals, however, had significantly more distal fields than did normals. When all fields having any distal component were compared (i.e., distal and intermediate), the difference between the chronic and normal groups did not reach significance. One possible explanation of these findings is that loci having both proximal and distal RF components are unresponsive 2 days after partial denervation, but recover responsiveness to their spared distal input over an 8-wk period. One possible mechanism mediating these changes is localized sprouting of intact, spared axons. Other mechanisms of functional recovery, such as interneuronal sprouting, denervation supersensitivity, and unmasking of latent synapses, are discussed in relation to these and other data.

Animals↗