Differential tyrosine kinase C mRNA distribution in extensor digitorum longus and soleus motoneurons in adult rats: effect of axotomy and neurotrophin-3 treatment.

Delivery of neurotrophin-3 (NT-3) to severed sciatic nerves results in specific normalization of atrophied fast 2b gastrocnemius muscle fibres, and promotes preferential neuromuscular junction maturation of fast extensor digitorum longus (EDL). To investigate the selective influence on fast muscle reinnervation due to NT-3 delivery, we analyzed tyrosine kinase C (trkC) mRNA differential expression in EDL and slow soleus motor pools of unoperated rats and at 1-week post-axotomy. Motoneurons (Mns) were identified using retrograde tracers. TrkC mRNA quantification was estimated by silver grain counting. TrkC mRNA expression was higher in EDL than in soleus Mns in unoperated rats. Axotomy decreased trkC mRNA expression only in EDL Mns, this downregulation being prevented by NT-3. These results suggest that differential expression of trkC receptor is the morphological correlate of the preferential effect of NT-3 upon EDL Mns.