Development of Nystagmus With the Absence of MYOD Expression in the Extraocular Muscles.

Purpose: Myoblast determination protein 1 (MYOD) is a critical myogenic regulatory factor in muscle development, differentiation, myofiber repair, and regeneration. As the extraocular muscles significantly remodel their myofibers throughout life compared with limb skeletal muscles, we hypothesized that the absence of MYOD would result in their abnormal structure and function. To assess structural and functional changes in the extraocular muscles in MyoD-/- mice, fiber size and number and optokinetic nystagmus reflex (OKN) responses were examined. Methods: OKN was measured in MyoD-/- mice and littermate wild-type controls at 3, 6, and 12 months. The extraocular muscles were examined histologically for changes in mean myofiber cross-sectional area, total myofiber number, and nuclei immunostained for PAX7 and PITX2, markers of myogenic precursor cells. Results: The MyoD-/- mice developed nystagmus, with both jerk and pendular waveforms, in the absence and in the presence of moving visual stimulation. At 12 months, there were significant losses in mean myofiber cross-sectional area and in total number of orbital layer fibers in all rectus muscles, as well as in global layer fibers in the superior and inferior rectus muscles. Haploinsufficient mice showed abnormal OKN responses. PITX2-positive cell entry into myofibers of the MyoD-/- mice was significantly reduced. Conclusions: This study is the first demonstration of the development of nystagmus in the constitutive absence of expression of the muscle-specific transcription factor MYOD. We hypothesize that myofiber loss over time may alter anterograde and/or retrograde communication between the motor nerves and extraocular muscles that are critical for maintaining normalcy of extraocular muscle function.

Apamin treatment accelerates equilibrium recovery and gaze stabilization in unilateral vestibular neurectomized cats: Cellular and behavioral aspects.

Sudden and complete unilateral loss of peripheral vestibular inputs evokes characteristic vestibular syndrome comprised of posturo-locomotor, oculomotor, vegetative and cognitive symptoms. Subsequently to the vestibular insult, a neurophysiological process called central vestibular compensation promotes the progressive restoration of the posture and balance. The modulation of the excitability of vestibular secondary neurons has been demonstrated to be a key process of this mechanism. However, the molecular mechanisms that support this modulatory process have thus far not been fully identified. The present study used a combination of a radio-labeled apamin binding experiment and a functional assessment of the vestibular function to demonstrate that unilateral vestibular neurectomy (UVN) induces both ipsi- and contralateral up-regulation of the apamin-sensitive calcium-activated small conductance K+ (SK) channels, within the first days following the insult. We also demonstrate that apamin administration during the acute phase of the vestibular syndrome significantly reduces both the posturo-locomotor and vestibulo-ocular deficits induced by the UVN. This is illustrated by the reduction of both the spontaneous nystagmus and the static and dynamic balance unsteadiness. These data suggest that the regulation of SK channel expression may be part of the vestibular compensation process. It is also indicated that the pharmacological modulation of SK channels may be a potential way to alleviate the vestibular syndrome.

Characterization of the dominant inheritance mechanism of Episodic Ataxia type 2.

Episodic Ataxia type 2 (EA2) is an autosomal dominant neuronal disorder linked to mutations in the Cav2.1 subunit of P/Q-type calcium channels. In vitro studies have established that EA2 mutations induce loss of channel activity and that EA2 mutants can exert a dominant negative effect, suppressing normal Cav2.1 activity through protein misfolding and trafficking defects. To date, the role of this mechanism in the disease pathogenesis is unknown because no animal model exists. To address this issue, we have generated a mouse bearing the R1497X nonsense mutation in Cav2.1 (Cav2.1R1497X). Phenotypic analysis of heterozygous Cav2.1R1497X mice revealed ataxia associated with muscle weakness and generalized absence epilepsy. Electrophysiological studies of the cerebellar circuits in heterozygous Cav2.1R1497X mice highlighted severe dysregulations in synaptic transmission of the two major excitatory inputs as well as alteration of the spontaneous activity of Purkinje cells. Moreover, these neuronal dysfunctions were associated with a strong suppression of Cav2.1 channel expression in the cerebellum of heterozygous Cav2.1R1497X mice. Finally, the presence of Cav2.1 in cerebellar lipid raft microdomains was strongly impaired in heterozygous Cav2.1R1497X mice. Altogether, these results reveal a pathogenic mechanism for EA2 based on a dominant negative activity of mutant channels.

Residual central nervous system damage due to organoarsenic poisoning.

BACKGROUND: Drinking well water contaminated with the organoarsenic compound diphenylarsinic acid (DPAA) causes central nervous system (CNS) disorders that improve within several years after last drinking such water. Subjective symptoms such as lightheadedness and dizziness appear to persist, however, suggesting CNS damage. We evaluated CNS damage due to DPAA by detecting abnormal eye movements. METHODS: Subjects comprised 29 victims of exposure to DPAA in whom this substance had been detected in the nails. Investigations were performed more than 3years following cessation of DPAA exposure. Abnormal eye movements were monitored using electronystagmography. We analysed unpaired t-test between exposure subjects who exhibited upbeat nystagmus and those who did not. Upbeat nystagmus parameters were measured, and mean values were calculated. Associations between the properties of upbeat nystagmus and maximum concentrations of DPAA among DPAA exposure were also investigated. RESULTS: Upbeat nystagmus was common among exposure victims, occurring in 23 of 29 subjects (79.0%). The subjects with upbeat nystagmus had significantly higher ratio than those without upbeat nystagmus in the points of subjective symptoms and DPAA concentration of drinking water (p<0.01). The slow-phase amplitude of upbeat nystagmus enlarged with increasing DPAA concentrations, showing a significant positive correlation (p<0.05). These findings suggest that the level of exposure to DPAA affects the properties of nystagmus. High-frequency pathological square-wave jerks (SWJ) were seen in 14 of 29 patients (48.0%), and mean SWJ frequency was 112.4±16.7/min. CONCLUSIONS: Detection of abnormal ocular movements may be useful in evaluating residual/persistent/chronic CNS damage due to organoarsenic poisoning.

Histaminergic ligands improve vestibular compensation in the cat: behavioural, neurochemical and molecular evidence.

This study analysed the effects of betahistine and thioperamide, two histamine H(3) receptor antagonists, on the recovery process after unilateral vestibular neurectomy (UVN) in the cat. In UVN animals untreated or treated with betahistine or thioperamide, recovery was evaluated by recording the horizontal spontaneous nystagmus and the postural and locomotor performances. The neurochemical effects of these drugs were determined by examining their impact on the histaminergic system. We quantified the mRNA coding for histidine decarboxylase (enzyme synthesizing histamine) by in situ hybridisation in the tuberomammillary nuclei, while binding density to histamine H(3) receptors was assessed using a histamine H(3) receptor agonist ([(3)H]N-alpha-methylhistamine) and autoradiography methods in the tuberomammillary and the vestibular nuclei. Relative to the UVN-untreated group, cats treated with betahistine or thioperamide showed strongly accelerated behavioural recovery. UVN-induced 1) an up-regulation of histidine decarboxylase mRNA in the tuberomammillary nuclei, strongly accentuated under betahistine and thioperamide, 2) a reduction of the binding to histamine H(3) receptors in the vestibular and tuberomammillary nuclei, also strongly enhanced in both groups of treated cats. This study demonstrates that betahistine and thioperamide strongly improve the recovery of vestibular functions in UVN cats by interacting with the histaminergic system.

Unilateral vestibular deafferentation-induced changes in calcium signaling-related molecules in the rat vestibular nuclear complex.

Inquiries into the neurochemical mechanisms of vestibular compensation, a model of lesion-induced neuronal plasticity, reveal the involvement of both voltage-gated Ca(2+) channels (VGCC) and intracellular Ca(2+) signaling. Indeed, our previous microarray analysis showed an up-regulation of some calcium signaling-related genes such as the alpha2 subunit of L-type calcium channels, calcineurin, and plasma membrane Ca(2+) ATPase 1 (PMCA1) in the ipsilateral vestibular nuclear complex (VNC) following unilateral vestibular deafferentation (UVD). To further elucidate the role of calcium signaling-related molecules in vestibular compensation, we used a quantitative real-time polymerase chain reaction (PCR) method to confirm the microarray results and investigated changes in expression of these molecules at various stages of compensation (6 h to 2 weeks after UVD). We also investigated the changes in gene expression during Bechterew's phenomenon and the effects of a calcineurin inhibitor on vestibular compensation. Real-time PCR showed that genes for the alpha2 subunit of VGCC, PMCA2, and calcineurin were transiently up-regulated 6 h after UVD in ipsilateral VNC. A subsequent UVD, which induced Bechterew's phenomenon, reproduced a complete mirror image of the changes in gene expressions of PMCA2 and calcineurin seen in the initial UVD, while the alpha2 subunit of VGCC gene had a trend to increase in VNC ipsilateral to the second lesion. Pre-treatment by FK506, a calcineurin inhibitor, decelerated the vestibular compensation in a dose-dependent manner. Although it is still uncertain whether these changes in gene expression are causally related to the molecular mechanisms of vestibular compensation, this observation suggests that after increasing the Ca(2+) influx into the ipsilateral VNC neurons via up-regulated VGCC, calcineurin may be involved in their synaptic plasticity. Conversely, an up-regulation of PMCA2, a brain-specific Ca(2+) pump, would increase an efflux of Ca(2+) from those neurons and perhaps prevent cell damage following UVD.

Intraspecific hybridization and the recovery of fitness in the native legume Chamaecrista fasciculata.

Genetic incompatibilities and low offspring fitness are characteristic outcomes of hybridization between species. Yet, the creative potential of recombination following hybridization continues to be debated. Here we quantify the outcome of hybridization and recombination between adaptively divergent populations of the North American legume Chamaecrista fasciculata in a large-scale field experiment. Previously, hybrids between these populations demonstrated hybrid breakdown, suggesting the expression of adaptive epistatic interactions underlying population genetic differentiation. However, the outcome of hybridization ultimately rests on the performance of even later generation recombinants. In experiments that compared the performance of recombinant F6 and F2 generations with nonrecombinant F1 and parental genotypes, we observed that increasing recombination had contrasting effects on different life-history components. Lifetime fitness, defined as the product of survivorship and reproduction, showed a strong recovery of fitness in the F6. The overall gain in fitness with increased recombination suggests that hybridization and recombination may provide the necessary genetic variation for adaptive evolution within species. We discuss the mechanisms that may account for the gain in fitness with recombination, and explore the implications for hybrid speciation and phenotypic evolution.

Transtympanic tetrodotoxin alters the VOR and Fos labeling in the vestibular complex.

The sodium channel blocker tetrodotoxin (TTX) is an effective tool for blockade of action potentials. Unilateral transtympanic administration of 3 mM TTX produced behavioral symptoms similar to those following unilateral peripheral vestibular ablation. Complete resolution of visible symptoms occurred between 48 and 72 h post-TTX. Eye-coil recordings indicated a spontaneous nystagmus and a decrease in the VOR in TTX-treated animals. Neuronal activity in the central vestibular complex (VC), as monitored with Fos immunocytochemistry, revealed an asymmetric pattern of Fos labeling in the medial, inferior and superior vestibular nuclei and the prepositus hypoglossal nucleus. Although the spatio-temporal pattern of Fos labeling was consistent and reproducible at each time-point, changes were noted among time-points. Transient blockade with TTX may be useful for studying the central vestibular response to recurrent or episodic vestibular disruption in the intact system.

Protein kinase C inhibition blocks the early appearance of vestibular compensation.

This study tests the hypothesis that activation of protein kinase C (PKC) is a critical step for early recovery from spontaneous nystagmus after unilateral ablation of the vestibular periphery. Halothane-NO(2)-O(2)-anesthetized Long-Evans rats received a 5-microl intracerebroventricular bolus of vehicle (distilled water, six rats), PKC inhibitor [Iso-H-7 (10 mM, four rats; 50 mM, five rats) or bisindolemaleimide I (Bis-I, 10 microM six rats)], PKG and PKA inhibitor (A-3, 1 mM, six rats), or the serine-threonine protein kinase inhibitor H-7 (1 mM, five rats; 10 mM, five rats). Surgical unilateral labyrinthectomy (UL) was completed within 15 min. Sham control groups showed no nystagmus. Bis-I and Iso-H-7 significantly retarded the disappearance of spontaneous nystagmus quick phases for 8 h after UL (p<0.05). The effects of Iso-H-7 were dose-dependent: more nystagmus quick phases (p<0.05) were present in the 50 mM than the 10 mM group at 7 and 8 h post-UL. The rats given A-3 showed a delayed retardation of nystagmus loss, which differed significantly (p<0.05) from controls at 4-8 h after labyrinthectomy. The number of nystagmus quick phases was significantly greater than controls (p<0. 05) in the 10 mM H-7 group at 4, 5, 6 and 48 h post-UL, but only at 6 and 24 h post-UL in the 1 mM H-7 group. Thus, PKC activation is an important early requirement for vestibular compensation during the acute post-labyrinthectomy period, while cyclic-nucleotide dependent kinases may be important in a later time frame.

Metabolic responses of the flocculus to optokinetic stimuli as revealed by the [14C]2-deoxyglucose method in pigmented rats.

By means of the [14C]2-deoxyglucose method, metabolic activity in the flocculus during monocular temporonasal optokinetic stimulation was investigated in alert pigmented rats. Local glucose utilization rates of both flocculi were significantly enhanced in the optokinetically stimulated animals. The flocculus ipsilateral to the stimulated eye showed an enhanced local glucose utilization rate as compared with the contralateral flocculus. The most enhanced activity was localized in the middle part of the rostrocaudal extent of the ipsilateral flocculus, and was characterized by its patchy appearance in the granular layer.

Multisystem degeneration: drugs and square wave jerks.

We studied a 55-year-old woman with macrosquare wave jerks and macrosaccadic oscillations with a vertical component. The oscillations almost completely disappeared after administration of diazepam, clonazepam, thiamylal, or phenobarbital. A disorder of GABAergic tonic inhibitory system from the substantia nigra to superior colliculus probably plays an important the pathogenesis of these abnormal ocular movements. role in the pathogenesis of these abnormal ocular movements.

Joseph disease: protein patterns in fibroblasts and brain.

The separation of brain and fibroblast proteins was analyzed on two-dimensional acrylamide gels. Proteins were examined from skin fibroblast cultures and brain homogenates from the frontal cerebral cortex, putamen, and cerebellum. Protein species from skin fibroblast cultures of controls and patients with Joseph disease or Huntington disease were not significantly different. The proteins from homogenates of the cerebral cortex, putamen, and cerebellum from controls differed from those of one Joseph disease patient. Two major classes of proteins were increased in the patient's putamen and cerebellum. Proteins of 40,000 and 50,000 daltons--including the glial filamentous acidic protein complex (molecular weight 50,000), and two proteins which migrated near actin--were increased in the cerebellum. The glial filamentous acidic protein complex increased 3.7-fold in the putamen of the patient. These protein changes probably represent gliosis, but may also be an expression of the primary genetic mutation.