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  • 1
    Electronic Resource
    Electronic Resource
    Evidence for the heterogeneity of glycol lignin (1991)
    s.l. : American Chemical Society
    Industrial & engineering chemistry research 30 (1991), S. 232-240 
    Details
    ISSN: 1520-5045
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ie00049a036
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  • 2
    Electronic Resource
    Electronic Resource
    Modulation of glycine receptor subunits and gephyrin expression in the rat facial nucleus after axotomy (2005)
    Oxford, UK : Blackwell Science Ltd
    European journal of neuroscience 21 (2005), S. 0 
    Details
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: In the last decade, numerous studies have investigated molecular changes in excitatory glutamatergic receptors in axotomized motoneurons, but few data are available concerning the modulation of inhibitory amino acid receptors. We report here the effect of axotomy on the expression of glycine receptors, gephyrin, vesicular inhibitory amino acid transporter (VIAAT) and synapsin I in rat facial motor neurons as demonstrated by in situ hybridization and immunohistochemistry. The facial nerve trunk was sectioned unilaterally and rats were killed 1, 3, 8, 30 or 60 days after surgery. We investigated the mechanisms underlying the changes in production of these proteins following axotomy by perfusing the facial nerve with colchicine or tetrodotoxin, and injecting cardiotoxin or botulinum toxin independently and unilaterally into the whisker pads of normal rats. Animals were killed 8 days later and processed for immunohistochemistry. The abundance of GlyR subunits and gephyrin fell sharply in the axotomized facial nucleus. This decrease began 1 day after axotomy and was lowest at 8 days, with protein levels returning to normal by day 60. Abnormal synapsin immunolabelling was also observed between days 8 and 60 after axotomy but we detected no change in VIAAT immunoreactivity. The effect of colchicine was similar to, but weaker than, that of axotomy. In contrast, tetrodotoxin, cardiotoxin and botulinum toxin had no significant effect. Thus, axotomy-induced changes probably resulted from a loss of trophic factor transported from the periphery or a positive injury signal, or both. They did not seem to depend on the disruption of activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1460-9568.2005.03887.x
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  • 3
    Electronic Resource
    Electronic Resource
    Neuronal correlates of vestibulo-ocular reflex adaptation in the alert guinea-pig (1999)
    Oxford, UK : Blackwell Science Ltd
    European journal of neuroscience 11 (1999), S. 0 
    Details
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The spiking behaviour of 66 second-order vestibular neurons was studied in alert, chronically prepared guinea-pigs during the horizontal vestibulo-ocular reflex (VOR). Among the 66 studied neurons, seven were held long enough (〉 1 h) to compare their spiking behaviour before and after a training procedure inducing a decrease in the gain of the VOR. When tested in darkness following adaptation, five of them showed a significant decrease of their sensitivity to head rotation. However, the resting discharge of these five neurons remained unchanged. This suggests that VOR adaptation is mediated not only by changes in synaptic efficacities but also by modifications in the spike generator which transforms synaptic inputs into a pattern of action potentials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1460-9568.1999.00572.x
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  • 4
    Electronic Resource
    Electronic Resource
    In vitro effects of acetyl-dl-leucine (tanganil®) on central vestibular neurons and vestibulo-ocular networks of the guinea-pig (2001)
    Oxford, UK : Blackwell Science Ltd
    European journal of neuroscience 13 (2001), S. 0 
    Details
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: For 40 years, the amino acid acetyl-dl-leucine (or isoleucine/Tanganil®) has been used in clinical practice to reduce the imbalance and autonomic signs associated with acute vertigo crises. In animal models, acetyl-dl-leucine was shown to accelerate vestibular compensation following unilateral labyrinthectomy, while having only minor effects on normal vestibular function. However, the underlying mechanisms are unknown. In this study, the effect of acetyl-dl-leucine on the activity of central vestibular neurons of the medial vestibular nucleus (MVN) and/or the overall activity of vestibular-related networks was electrophysiologically measured in brainstem slices and in the isolated, in vitro whole brain (IWB) of guinea-pig. Only moderate effects were obtained in normal animals, where both excitatory and inhibitory actions of acetyl-dl-leucine were obtained. However, intracellular recordings from MVN neurons revealed that the nature of the response depended on the resting membrane potential. The neurons excited by acetyl-dl-leucine were significantly hyperpolarized compared to nonsensitive cells, whereas the neurons inhibited by this compound tended to display higher than normal membrane potentials. In accordance with these data, acetyl-dl-leucine reduced the prominent asymmetry characterizing the vestibular-related networks of IWBs taken from previously labyrinthectomized animals, by decreasing the activity of the abnormally depolarized neurons on the hyperactive side. Altogether, our results suggest that acetyl-dl-leucine might act mainly on abnormally hyperpolarized and/or depolarized MVN neurons, by bringing back their membrane potential towards a mean value of −65 to −60 mV. Since in animal models, acute vestibular disorders are associated with asymmetrical spontaneous activities of MVN neurons, this study suggests how acetyl-dl-leucine may reduce acute, vestibular-related imbalances in humans.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.0953-816x.2000.01447.x
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  • 5
    Electronic Resource
    Electronic Resource
    Modification of the pacemaker activity of vestibular neurons in brainstem slices during vestibular compensation in the guinea pig (2001)
    Oxford, UK : Blackwell Science Ltd
    European journal of neuroscience 13 (2001), S. 0 
    Details
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: In the guinea pig, unilateral labyrinthectomy causes an immediate and severe depression of the spontaneous activity of the ipsilateral central vestibular neurons, which subsequently recovers completely within one week. A possible underlying mechanism could be an increase in the endogenous activity of the neurons deprived of their labyrinthine input. Here, we addressed this hypothesis. The endogenous activity of the neurons was assessed by their spontaneous activity recorded extracellularly in brainstem slices in the presence of a cocktail of neurotransmitter blockers (CNQX, d-APV, bicuculline and strychnine) which freed them from their main synaptic influences. The left medial vestibular nucleus (MVN) was explored in a very systematic way and strict methodological precautions were taken in order to validate comparisons between the numbers of spontaneously active neurons recorded in the MVN of distinct slices. In the presence of neurotransmitter antagonists, the mean number of spontaneously active neurons detected in a single MVN increased dramatically from 9.5 in slices from control guinea pigs to 26.3 in slices from animals labyrinthectomized on the left side one week beforehand. The mean firing rate of the recorded neurons also increased from 7.5 ± 5.6 spikes/s in slices from control animals to 12.3 ± 7.6 spikes/s in slices from guinea pigs labyrinthectomized one week beforehand. These results show that deprivation of the vestibular neurons of their labyrinthine input caused a change in the deprived neurons themselves. They suggest that an increase in pacemaker activity might be a factor responsible for the restoration of spontaneous activity in the vestibular neurons after labyrinthectomy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.0953-816x.2001.01603.x
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  • 6
    Electronic Resource
    Electronic Resource
    Effects of Substance P on Medial Vestibular Nucleus Neurons in Guinea-pig Brainstem Slices (1996)
    Oxford, UK : Blackwell Publishing Ltd
    European journal of neuroscience 8 (1996), S. 0 
    Details
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The undecapeptide substance P (SP) has been recently implicated in the control of vestibular function. In particular, it seems to be co-localized with glutamate in approximately half of the primary vestibular afferents in mammals. Using intracellular recordings in guinea-pig brainstem slices, we have investigated the effects of SP and of several agonists of the three known tachykinin receptor subtypes (NK1, NK2 and NK3) on the three main types (A, B and B+LTS) of guinea-pig medial vestibular nucleus neurons (MVNn) that we had previously described. SP could induce two distinct kinds of effects on all types of MVNn. Whereas around half of them were depolarized and had their membrane resistance increased by SP, ∼ 10% of all MVNn were in contrast hyperpolarized and inhibited while their membrane resistance was decreased. Both responses persisted under conditions of blockade of synaptic transmission, and were thus due to the activation of postsynaptic binding sites. The SP-induced membrane depolarization could not be reproduced with any one of the specific agonists of the three tachykinin receptor subtypes, nor was it blocked by the specific NK1 receptor antagonists GR 82334 and CP 99994. This effect might therefore be due to the activation of a new, pharmacologically distinct, ‘NK1-like’ receptor. Only the hyperpolarizing effects, which were in contrast mimicked by the specific NK1 receptor agonists GR 73632 and [Sar9, Met (O2)11]-SP, would be mediated by the few typical NK1 receptors which have been demonstrated in the medial vestibular nucleus.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1460-9568.1996.tb01589.x
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  • 7
    Electronic Resource
    Electronic Resource
    Purification and characterization of a chitosanase from Streptomyces N174 (1992)
    Springer
    Applied microbiology and biotechnology 38 (1992), S. 188-193 
    Details
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract A highly efficient chitosanase producer, the actinomycete N174, identified by chemotaxonomic methods as belonging to the genus Streptomyces was isolated from soil. Chitosanase production by N174 was inducible by chitosan or d-glucosamine. In culture filtrates the chitosanase accounted for 50–60% of total extracellular proteins. The chitosanase was purified by polyacrylic acid precipitation, CM-Sepharose and gel permeation chromatography. The maximum velocity of chitosan degradation was obtained at 65° C when the pH was maintained at 5.5. The enzyme degraded chitosans with a range of acetylation degrees from 1 to 60% but not chitin or CM-cellulose. The enzyme showed an endo-splitting type of activity and the end-product of chitosan degradation contained a mixture of dimers and trimers of d-glucosamine.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00174466
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  • 8
    Electronic Resource
    Electronic Resource
    Neck muscle activity after unilateral labyrinthectomy in the alert guinea pig (1999)
    Springer
    Experimental brain research 124 (1999), S. 159-165 
    Details
    ISSN: 1432-1106
    Keywords: Key words Vestibular system ; Labyrinthectomy ; Vestibular compensation ; Neck muscles ; Vestibulocollic reflex
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  In the guinea pig, lateral deviation of the head is a cardinal symptom of the vestibular syndrome caused by unilateral labyrinthectomy. In the course of recovery from this syndrome (vestibular compensation), lateral deviation of the head disappears completely in 2–3 days. Because this symptom is known to be due to the lesion of the horizontal semicircular canal system, and since obliquus capitis inferior (OCI) muscle is activated predominantly by yaw rotation (horizontal vestibulocollic reflex), we hypothesized that changes in the activity of this muscle could be at least in part responsible for the lateral head deviation caused by unilateral labyrinthectomy. In order to test this hypothesis, electromyographic (EMG) activities of the right and left OCI muscles, as well as eye movements, were recorded in 12 head-fixed alert guinea pigs at various times after left surgical labyrinthectomy (performed with the animals under halothane anesthesia). After the operation, a decrease in tonic EMG activity was observed in the right (contralateral to the lesion) OCI muscle while an increase in tonic EMG activity was detected in the left (ipsilateral) OCI muscle. In addition, phasic changes in EMG activity associated with ocular nystagmic beats occurred in the OCI muscles. These phasic changes were in the opposite direction to those of the tonic changes. There were bursts of activity in the right OCI and pauses in the left OCI. From measurements of rectified averaged EMG activities which took into account both parts (tonic and phasic) of the phenomenon, it was concluded that the labyrinthectomy-induced asymmetry between the activities of the left and right OCI muscles was high enough and lasted long enough to be an important mechanism in the lateral deviation of the head caused by unilateral labyrinthectomy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002210050610
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  • 9
    Electronic Resource
    Electronic Resource
    Direct and indirect effects of muscimol on medial vestibular nucleus neurones in guinea-pig brainstem slices (1995)
    Springer
    Experimental brain research 104 (1995), S. 351-356 
    Details
    ISSN: 1432-1106
    Keywords: GABAergic receptors ; Vestibulo-ocular reflex ; GABAergic interneurones ; Guinea-pig
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Inhibitory amino acids are considered as major transmitters in the vestibular system. Using intracellular recordings in slices, we applied gamma-aminobutyric acid (GABA) and muscimol (a specific agonist of the GABAA receptor) to the two main types of medial vestibular nucleus neurones (A and B MVNn). In either a high Mg2+/low Ca2+ solution, or a solution containing tetrodotoxin, all MVNn were hyperpolarized by GABA and muscimol. This indicates that both types of MVNn are endowed with postsynaptic, hyperpolarising GABAA receptors. In a normal medium, about half of A and B MVNn were, in contrast, depolarised by GABA and muscimol, whereas the remaining cells were hyperpolarised. These results could be due to a modulation by GABA and muscimol of a tonic GABA release in the slice. Such a release was, indeed, suggested by results showing the depolarising effect of either tetrodotoxin (TTX) or bicuculline, when applied alone. The cells that were depolarised by GABA or muscimol in control conditions were always hyperpolarised in the presence of TTX. Our data therefore suggest that GABA acting at GABAA receptors in the medial vestibular nucleus can play a role either through a postsynaptic hyperpolarising action or indirectly by inhibiting a tonic GABA release, probably resulting from the spontaneous activity of local inhibitory interneurones. A GABAergic regulation of these interneurones could be important in processes of vestibular habituation and/or adaptation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00242021
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  • 10
    Electronic Resource
    Electronic Resource
    Intrinsic membrane properties and dynamics of medial vestibular neurons: a simulation (1999)
    Springer
    Biological cybernetics 80 (1999), S. 383-392 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract. The vestibulo-ocular and vestibulo-spinal network provides the ability to hold gaze fixed on an object during passive head movement. Within that network, most of the second-order neurons of the medial vestibular nucleus (MVNn) compute internal representations of head movement velocity in the horizontal plane. Our previous in vitro studies of the MVNn membrane properties indicated that they may play a major role in determining the dynamic properties of these neurons independently of their connectivity. The present study investigated that hypothesis at a theoretical level. Biophysical models of type A and B MVNn were developed. Two factors were found to be important in modeling tonic and phasic firing activity: the activation of the delayed potassium current and the rate of calcium flux. In addition, the model showed that the strength of the delayed potassium current may determine the different forms of action potentials observed experimentally. These two models (type A and B cells) were examined using depolarizing stimulation, random noise, step, ramp and sinusoidal inputs. For random noise, type A cells showed stable (regular) firing frequencies, while type B cells exhibited irregular activity. With step stimulation, the models exhibited tonic and phasic firing responses, respectively. Using ramp stimulations, frequency versus current curves showed a linear response for the type B neuron model. Finally, with sinusoidal stimulation of increasing frequencies, the type A model demonstrated a decrease in sensitivity, while the type B model exhibited an increase in sensitivity. These theoretical results support the hypothesis that MVNn intrinsic membrane properties specify various types of dynamic properties amongst these cells and therefore contribute to the wide range of dynamic responses which characterize the vestibulo-ocular and vestibulo-spinal network.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004220050533
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