Stimulation by nerve growth factor of neuropeptide synthesis in the adult rat in vivo: Bilateral response to unilateral intraplantar injections

Unilateral intraplantar injections (1/day for 3 days) of 4 mu g nerve growth factor (NGF) into the rat hindpaw increased the expression of prepro-tachykinin (PPT)- and prepro-calcitonin gene-related peptide (ppCGRP)-mRNA in bilateral L(5) dorsal root ganglia (DRGs). This was accompanied by an increase of CGRP-like immunoreactivity in the ipsi- and contralateral sciatic nerve but by no detectable change of CGRP-IR in other afferents. NGF injections into the skin of one ear or into the plantar side of one forepaw increased CGRP-IR in the respective afferents (trigeminal ganglion, or nerves arising from the brachial plexus, respectively), but had no effect on sciatic CGRP-IR. This suggests that the NGF-induced symmetrical increase of CGRP synthesis in L(5) DRGs was not caused by systemic action of NGF, which, therefore, may be a useful tool to further investigate mechanisms which are responsible for contralateral effects of unilateral inflammation.