The role of electrical activity in the development of sensorimotor networks in mammals

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Neural activity plays a role in the development of the nervous system but the mechanisms involved are still largely unknown. Two different forms of this activity can be distinguished: "spontaneous" activity that is intrinsically generated in neural networks during development, and "experience dependent" activity that is generated by extrinsic stimulation of the networks. Spontaneous activity is a very early phenomenon which is associated with several phases of the development of neural structures (axon growth, synaptogenesis). The precocious expression of spontaneous activity explains that in mammals it is mostly studied in structures that develop lately (retina, cortex). Structures that develop very early, such as the spinal motor networks, were largely ignored by fault of an experimental model. We use an original mammalian model, the opossum Monodelphis domestica, allowing experimental studies of the mechanisms underlying spontaneous activity by different approaches (anatomical, physiological, pharmacological and behavioral). Using in vitro brainstem spinal-cord preparations, we have showed that spontaneous activity is expressed in the spinal cord of postnatal embryos and started to study the mechanisms underlying its generation. We will continue to investigate the physiological and pharmacological basis of this activity at different ages. We will also describe the spinal motor networks anatomical and physiological characteristic patterns. Any disturbance of the spontaneous activity by pharmacological means should induce modifications of these patterns, allowing inference to the role of this activity in the maturation of the networks. We will also study the effects of evoked activity on these patterns, using the trigeminal systems as a model, to compare the respective impact of each form of nervous activity. This research program is a necessary groundwork for a more thorough study of the physiological mechanisms underlying spontaneous activity, mechanisms which are largely unknown but which play an essential part in the maturation of the nervous system.