Increased levels of GMAP, VIP and nitric oxide synthase, and their mRNAs, in lumbar dorsal root ganglia of the rat following systemic resiniferatoxin treatment.

Using in situ hybridization, the expression of mRNA encoding galanin, vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY), and nitric oxide synthase (NOS), respectively, was studied in lumbar dorsal root ganglia of rats given a single s.c. dose of 300 micrograms kg-1 resiniferatoxin (RTX), an ultrapotent capsaicin analogue. In control animals, 10% of the DRG neurones were positive for galanin mRNA, whereas no message for VIP, NPY or NOS could be detected. One week after RTX treatment, a markedly increased number (approximately 30%) of the neurones expressed galanin mRNA. Simultaneously, VIP and NOS mRNA became detectable in 6-8% of the neurones. The number of galanin-positive neurones declined after 2 weeks and returned to control levels by 8 weeks. The increase in number of VIP-, or NOS-positive neurones persisted up to 4 weeks after RTX treatment and declined thereafter. Also, there was a small increase in NPY mRNA-positive neurones. In parallel immunohistochemical experiments, similar increases were observed for galanin message-associated protein (GMAP)-, VIP- and NOS-like immunoreactivities. Our findings suggest that RTX can cause changes (messenger plasticity) in galanin, VIP and NOS expression in capsaicin-sensitive sensory neurones of the rat, similar to those described following axotomy