During normal postnatal development, mammalian skeletal muscles undergo an orderly process of synapse elimination, whereby each muscle fiber begins in a state of polyinnervation but eventually loses all except one of its inputs. Dr. Van Essen will study several aspects of synapse elimination and plasticity of connections in the soleus muscle of the rabbit. In one set of projects, Dr. Van Essen and his colleagues will examine the role of nerve and muscle activity in this process of synapse elimination. Previous studies have shown that increased activity accelerates the overall rate of synapse elimination, while differential activity among competing synapses confers an advantage to the less active inputs. Dr. Van Essen is interested in clarifying the mechanisms whereby activity exerts these dual influences and also in ascertaining whether natural activity patterns contribute to sculpting of the distribution of motor unit sizes in the adult. Another set of projects is aimed at understanding the basis of fiber-type specificity, whereby fast- and slow-contracting muscle fibers are selectively innervated by fast and slow motor neurons. Dr. Van Essen has made a number of important contributions to this field over the past ten years. The results of these new studies will certainly add fundamental information about the important developmental phenomenon of synapse elimination.
