Ken-ichi Oshio et al. (2002) Japanese Worm Meeting "Revision of synaptic connectivity database"

Eizo Akiyama, Yuishi Iwasaki, Yuko Osana, Ken-ichi Oshio, Sohei Gomi, Satoru Morita, Kotaro Oka, Kazumi Omata

[Japanese Worm Meeting, 2002]

The synaptic connectivity of C. elegans is well known from observations of the somatic system by White et al. and those of the pharyngeal system by Albertson et al. So far, three databases were constructed for computational usage by Achacoso et al. and Durbin, and recently in WormBase. However, they lack some data such as those in tables of White's paper and those in figures of Albertson's book. Our database (K. Oshio, S. Morita, Y. Osana and K. Oka: Technical Report of CCEP, Keio Future No.1, 1998) includes all data described in White's paper and Albertson's book. Unfortunately, some mistakes were found in the database through private communications with John White who is the author of White's paper and with the users of the database. Thus we have been proceeding with the revision to make it perfect one. We are planning to complete the revision in September 2002. The database should be worthwhile not only for neurophysiological studies, but also for post-genomic interests mediating genomes and behavior.

Kiyoshi Kawamura et al. (2002) Japanese Worm Meeting "Pathways from sensory neurons to motor neurons determined by McCulloch-Pitts algorithm."

Ken-ichi Oshio, Kotaro Oka, Satoru Morita, Yuko Osana, Kiyoshi Kawamura

[Japanese Worm Meeting, 2002]

The following two hypotheses are employed :(1) The coupling coefficient in the McCuloch-Pitts equation for C. elegans is proportional to multiplicity of synaptic connection among neurons. (2) Threshold of excitation is the same for every neuron. Under the condition that a given sensor neurons are always excited, excited interneurons and motor neurons have been determined for various threshold values. Assuming that those neurons which are excited for threshold value more than seven are used for native responses concerned with the sensory neuron, pathways from the sensory neuron to various motor neurons have been determined. Pathways along which signals for refrecting response like foreward and backward movement by posterior and anterior part are different from those used for chemotaxis and thermotaxis. To identify pathways for positive and negative chemotaxis, however, connection by elctrical junction is speculated essentially important. We will present circuit from all sensory neurons to motor neurons from this analysis.

Kiyoshi Kawamura et al. (2004) East Asia Worm Meeting "Anatomical Data of Synaptic Connectivity of C. elegans are Almost Perfectly Self-contained."

Satoru Morita, Kiyoshi Kawamura, Sohei Gomi, Yuishi Iwasaki, Yuko Osana, Kazumi Omata, Ken-ichi Oshio, Eizo Akiyama

[East Asia Worm Meeting, 2004]

The anatomical data of synaptic connectivity of C. elegans has been degitized for research with computers. The set of files are entitled 'The database of Synaptic Connectivity of C. elegans for Computaiton' and electronicaly delivered to request. The data files describe all items involved in the paper of Albertson and Thomson (1976) and that of White et al. (1986). The policy we empolyed on creating the data base was that diagrams and tables in the original paper can be reconstructed uniquely up to topology from the degitized data. Since our database is equivalent to the anatomical data, quality of the latter can be investigated on analysing the former by computer. It has been found that the anatomical data is almost perfectly self-contained except a few inconsistent descriptions such that the neuron class PDE sends 61 synapses to the class DVA while the latter receives only 36 synapses from the former. This is an exceptionally extreme case of inconsistency and number of erroneously described synaptic contacts are several hundred among eight thousand contacts. In addition, it has been found that several inconsistent description can be corrected from consideration of topological nature of processes in a three dimensional space, which is also suggested by the database.

Kotaro Oka et al. (2003) International Worm Meeting "Neuronal Circuit and Native Responses of C. elegans"

Kiyoshi Kawamura, Yasuhiro Funabashi, Sohei Gomi, Yuishi Iwasaki, Eizo Akiyama, Kotaro Oka, Ken-ichi Oshio, Satoru Morita, Kazumi Omata, Yuko Osana

[International Worm Meeting, 2003]

The ultimate goal of the present work is to determine pathways of neuronal signal from sensory neurons to motoneurons in occasion of native responses of C. elegans. The fundamental hypothesis is that the pathways consists of highly multiple synaptic connection among interneurons. The McCulloch-Pitts equation is employed to find out sequence of much synaptic connection from each sensory neuron. Although the McCulloch-Pitts equation cannot be used for simulation of propagation of neuronal signal without knowledge about physical parameters within it, it is useful for the present purpose. The point of the algorithm is ; (i) threshold of menbrain potential is replaced by an integer s which is independent of the neuron and (ii) the coupling coefficient between a pair of neurons is replaced with number of synapses between them. When a sensory neuron is always excited, a stationary distribution of excited neurons is realized. Excited neurons in the stationary state are connected to the sensory neuron by pathways which consist of synaptic connection of multiplicity larger than s. A neuron, which is connected with more than one excited neurons, is also excited when the sum of multiplicity of joined synapses are larger than s. A plan of the neuronal circuit is constructed from neurons, which are excited for s more than six, and synapses connecting them. Interneurons are classified into three groups. Three elementary motions of the worm are defined in terms of motoneurons which are simultaneously excited and its behavior in occasion of native responses is combination of such elementary motions. The number of synapses have been counted using the database constructed by our research group. It is translation from the sketch of neurons published by White et al.. into a digital form.

K Omata et al. (1999) International C. elegans Meeting "Habituation of C. elegans for the touch sensitivity"

K Kawamura, F Yonezawa, K Omata

[International C. elegans Meeting, 1999]

In order to study the habituation of C. elegans for the touch sensitivity, we carry out computer simulations, in which the neural circuit is formed by making use of the data table constructed recently by Oshio et al [1]. The i -th neuron is connected with the neighboring j -th neuron through the coupling strength K ij , which is varied dynamically by the Hebb rule. Note that K ij is not necessarily equal to K ji because there are one-way connections between the neurons by chemical synapses. As a reference state, we first deal with the neural circuit consisting only of the neurons ALM, AVM, PLM, PVM, AVA, AVB, PVC, AVD, A and B, that are related to the forward and backward movement directly. We give periodic stimuli to the sensory neurons PLM, PVM, and monitor the response of the motor neuron A. We find that the frequency of the response decreases with time, which indicates that the habituation to the touch sensitivity actually takes place. As one deviation from the reference state, we kill the inter-neuron AVD, and perform the same analysis described in the above. There is a tendency that the decay of the response curve becomes faster, and the habituation is enhanced. As the other deviations, there are several possibilities of killing the inter-neurons AVA, AVB, PVC and/or AVD. We discuss the enhancement of the habituation in relation with the recent experimental results by Hosono. [1.] K. Oshio, S. Morita, Y. Osana and K. Oka; C. elegans synaptic connectivity data'', Technical Report, CCEP, Keio Future No.1 (1998)

K Kawamura et al. (1999) International C. elegans Meeting "Structure of Neural Network of C. elegans Observed by a Random Walker"

Y Osana, K Kawamura, K Oka, K Oshio, Y Funabashi, S Morita

[International C. elegans Meeting, 1999]

A database of synaptic connectivity of 302 neurons of the C. elegans has been constructed[1] from the observations of Albertson and Thomson[2] and White et al.[3] by some of the present authors. A network formed by 302 neurons of the C. elegans is represented on a computer by a network which consists of 302 dots combined by (arrowed) bonds. To analyse the structure of the neural network, behavior of a random walker on it is studied. The walker is displaced among dots which represent neurons over bonds which model synaptic connection. In terms of walking distance defined by minimum time steps which is necessary for the random walker to be displaced between neurons, distances among all neurons, whose synaptic connectivity are described by the above authors, have been determined. Almost all neurons are located within the walking distance of three time steps but walking distance among phalingeal neurons and somatic neurons are more than four time steps. The network is extended in a (more than) nine dimensional space around three nanohedra which are mutually combined by manifolds of less dimension. Each nanohedron consists of nine dots representing interneurons mutually connected by synapses and these nanohedra are located near the center of the network. The lattice is biased by the rectification of the chemical synapse in the sence that a random walker prefers to be displaced from sensory neurons to motor neurons. [1] K. Oshio, S. Morita, Y. Osana and K. Oka: C. elegans connectivity data, Technical report of CCEP, Keio Future No.1 (1998) [2] D. G. Albertson and J. N. Thomson: Phil. Trans R. Soc. Lond. B. 275 (1976) 299 [3] J. G. White, E. Southgate, J. N. Thomson and S. Brenner: Phil. Trans. R. Soc. Lond. B 314 (1986) 1.