Neurotrophin-3 administration alters neurotrophin, neurotrophin receptor and nestin mRNA expression in rat dorsal root ganglia following axotomy.

In the months following transection of adult rat peripheral nerve some sensory neurons undergo apoptosis. Two weeks after sciatic nerve transection some neurons in the L4 and L5 dorsal root ganglia begin to show immunoreactivity for nestin, a filament protein expressed by neuronal precursors and immature neurons, which is stimulated by neurotrophin-3 (NT-3) administration. The aim of this study was to examine whether NT-3 administration could be compensating for decreased production of neurotrophins or their receptors after axotomy, and to determine the effect on nestin synthesis. The levels of mRNA in the ipsilateral and contralateral L4 and L5 dorsal root ganglia were analyzed using real-time polymerase chain reaction, 1 day, 1, 2 and 4 weeks after unilateral sciatic nerve transection and NT-3 or vehicle administration via s.c. micro-osmotic pumps. In situ hybridization was used to identify which cells and neurons expressed mRNAs of interest, and the expression of full-length trkC and p75NTR protein was investigated using immunohistochemistry. Systemic NT-3 treatment increased the expression of brain-derived neurotrophic factor, nestin, trkA, trkB and trkC mRNA in ipsilateral ganglia compared with vehicle-treated animals. Some satellite cells surrounding neurons expressed trkA and trkC mRNA and trkC immunoreactivity. NT-3 administration did not affect neurotrophin mRNA levels in the contralateral ganglia, but decreased the expression of trkA mRNA and increased the expression of trkB mRNA and p75NTR mRNA and protein. These data suggest that systemically administered NT-3 may counteract the decrease, or even increase, neurotrophin responsiveness in both ipsi- and contralateral ganglia after nerve injury.