Significance of the neuronal morphology for network dynamics

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.