Size plasticity of intact motoneurons as reaction to partial denervation of muscle.

It is known that partial denervation of muscle leads to the enlargement of the intact motor units by collateral sprouting of the intramuscular axons. After partially denervating the hind limb muscles in the frog, its effect on the intact motoneuron cell size was investigated. It was found that motoneurons increase in size when their motor unit territory expanded. This increase indicates size plasticity and the dynamic nature of motoneuron size. It is proposed that there are two distinct, but interacting states relating to motoneuron size (the stable in equilibrium labile states). The implications of size plasticity of motoneuron on synaptogenesis/synaptic reorganization on its membrane surface is discussed.