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1

Significance of the neuronal morphology for network dynamics

Meyrand P.

Biocybernetics and Biomedical Engineering

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2006

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Vol. 26, no. 2

15-23

EN

One of the striking features of the Nervous System is the complexity and diversity of the neuronal shapes. Extensive morphological studies associated with modeling approaches have emphasized a close relationship between the neuron structure and its bioelectrical properties. However, structural implications of the synaptic connectivity (spatial distribution, number of synapses) in the context of the network operation are far less studied. To explore this issue, the chemical inhibitory synapses between identified motoneurones belonging to the stomatogastric nervous system of the lobster Homarus gammarus were examined. Using multiple intracelIular dyes injected in both pre- and post synaptic motoneurones, the sites of the appositions between these two celIs were localized under the laser-scanning confocal microscopy, and then the synaptic release sites were visualized under the electron microscopy. Such analysis indicates that only one or two zones of apposition exist between the two celIs studied, and only one release site exists per zone. Moreover, these synaptic sites are always located in the same position within the dendritic arbor. Modeling studies suggest that such a specific localization may play an important role in the operation of the network.

2

Progressive die-back and death of motoneurons in a transgenic mouse model of amyotrophic lateral sclerosis

Gordon T., Tam S. L., Sharp P. S., Hegedus. J.

Biocybernetics and Biomedical Engineering

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2005

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Vol. 25, no. 4

17-26

EN

Fischer et al. [1] commented that the longest and largest nerve fibers with the highest metabolic demand appear to be the most susceptible to "dying-back" in a wide variety of degenerative and toxic conditions of the central and peripheral nervous systems. In the high copy number G93AmSOD1 transgenic mouse model of familial amyotrophic lateral sclerosis (ALS) we tested the hypothesis that the largest motoneurons which have the most terminal connections are the most susceptible to the disease. In a time course study of motoneuron, muscle and motor unit properties in fast - and slow-twitch hindlimb muscles of G93A and wild type mice, we found a rapid decline in numbers of functional motor units and motoneurons that progresses from birth to a plateau after 90-100 days of life with surprisingly Iittle compensatory axonal sprouting. Fast motoneurons are the most susceptible, contrasting with the slow motoneurons. Preliminary evidence of loss of S100 reactive perisynaptic Schwann cells at the denervated endplate regions of the affected muscles indicate loss paralIeIs rapid progression of disease with consequent decline in muscle force and motor unit numbers, folIowed closely in time by motoneuron death.

3

Computer system for identification and analysis of motor unit potential trains

Mazurkiewicz Ł., Piotrkiewicz M.

Biocybernetics and Biomedical Engineering

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2004

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Vol. 24, no. 3

15-23

EN

The paper presents a computerized system for identification and analysis of electromyographic signals recorded from muscle by needle electrodes. The system provides information on human motoneuron activity as time sequences of identified single motor unit potentials. This information can afterwards be statistically processed to obtain data on motoneuron properties in healthy subjects and in some neuromuscular diseases. A special attention has been paid to the description of the methods of spike identification, including extraction of spikes from the signal and automatic classification, which is based on the statistical pattern recognition approach. The system described is also an example of adaptation of modern computer technology for biomedical research.

4

Computer system for analysis of recurrent inhibition between human motoneurons

Jakubiec M., Piotrkiewicz M.

Biocybernetics and Biomedical Engineering

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2004

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Vol. 24, no. 3

3-14

EN

Despite years of extensive research, the physiological role of recurrent inhibition (RI) is still far from being clear. We decided to study RI between human motoneurons (MNs) during isometric constant force contractions, which has never been systematically analyzed before. The paper presents a description of a system for detection of RI. In the system several methods for analysis of correlations between single motor units (MUs) were implemented. The software was developed in environment DELPHI 6. The results of evaluation of the system on the basis of the data obtained in the computer simulations are presented. The system detects recurrent IPSPs of amplitudes as low as 50 /mi V.