The development of sensorimotor networks in mammals

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Motor systems attain the highest complexity in mammals, as evidenced by the sophistication of their motor behaviors and the array of nervous structures controlling them. Locomotion is produced by motoneurons in the spinal cord that cause muscle contractions and are coordinated by interneuronal networks. The central pattern generators (CPGs) located in the cervical and lumbar enlargements of the spinal cord regulate forelimb and hindlimb movements, respectively. For locomotion to be adapted to the external environment and to the animal's internal state and motivation, the CPGs are modulated by sensory inputs from the periphery, and inputs from other spinal levels and from the brain. How all these systems are put in place during development is the object of my research program. A major difficulty of investigating motor systems development in mammals is that they form largely prenatally. We use an original mammalian model, the opossum Monodelphis domestica, which at birth corresponds to a rodent embryo of about one week before birth. We have developed in vitro preparations of their neuraxis with the limbs attached on which we use anatomical, physiological, pharmacological and behavioral approaches to address motor development. Recently we have shown that facial mechanosensory inputs mediated by the trigeminal nerve influence forelimb movements. Herein we propose to investigate the influence of facial thermosensation and of vestibular inputs on motor development and to determine how they integrate with descending central systems known to affect the CPGs, such as the reticular formation and some midbrain areas. Finally, purinergic receptors being involved in mechanosensation, we will study in detail the expression of their different subtypes in the head and neuraxis of developing opossums and determine the involvement of each subtype in the control of motor behaviors. This fundamental research program (previous, present and future terms) will give us a thorough understanding of how motor systems are put in place during development and will serve research aimed at investigating regeneration.