Fig. 3.

The transient expression of regeneration-associated genes in injured neurons after transecting the peripheral nerve. (a) The chromatolytic reaction of an injured motoneuron includes the movement of the nucleus to an eccentric position with expression of several growth-associated genes (GAGs) that include the neurotrophic factors and their receptors. There is a switch from the transmitting to the growth state in the axotomized motoneurons that includes the downregulation of transmitter associated genes (choline acetyltransferase and acetylcholinesterase) and the cytoskeletal protein, neurofilament, concurrent with a decline in the size of the axons proximal to the lesion [38]. The cytoskeletal proteins of tubulin and actin are upregulated, as are several growth-associated proteins (GAPs) that include GAP-43. However, this expression is transient as shown by the examples of the decline in the expression of (b) tubulin in chronically axotomized sciatic motoneurons, (c) glial-derived neurotrophic factor (GDNF), and the p75 receptor for the neurotrophic factors in chronically denervated Schwann cells. Mean ± SE bars are plotted in the graphs and the data points are fitted by exponential lines