Structural Plasticity in Lesioned Motoneurons

Abstract

Neurons react to axon lesioning with a number of changes which have been known for almost a century. They are referred to as “chromatolysis”, “retrograde change” or “the axon reaction”. In nerve cells of the peripheral nervous system such as sensory and autonomic ganglia or motoneurons, the retrograde changes are seen as part of the regeneration program that can be triggered in these nerve cells. Under favorable conditions this leads to a regrowth of the lost axon and reinnervation of the target tissue and thus to a restitution of function. In the regenerating neuron many metabolic changes occur concerning RNA and protein synthesis, enzymatic activities, glucose consumption, neurotransmitters and receptors (for review see Lieberman 1971; Grafstein and McQuarrie 1978; Bisby 1980; Kreutzberg 1986; Tetzlaff et al. 1986). There are also changes in the micro-environment of the neuron afflicting local glial cells and the vasculature (Kreutzberg 1982). As a result of the neuronal and glial cell activation, a profound change of the synaptic arrangement on the neurons has been revealed. It shows that the axon lesion can provoke a surprising structural plasticity in the synapse-bearing elements. Several of these alterations will be described in this chapter as they have been studied in motoneurons.