Differential effects of treatment with nerve growth factor on thermal nociception and on calcitonin gene-related peptide content of primary afferent neurons in the rat.

摘要

We have investigated the effect of repeated systemic administration of nerve growth factor (NGF) to rats on (a) the calcitonin gene-related (CGRP) content of primary afferent neurons and (b) the thermal nociceptive threshold in normal and inflamed hind paws. NGF (0.1 mg/kg s.c.) was administered every other day for 7 days. After each injection of NGF there was transient thermal hyperalgesia lasting less than 23 h. One day after the last of four NGF injections, there was no detectable difference of the thermal nociceptive threshold between the NGF-treated and control group. NGF treatment caused, however, a significant increase of the concentration of immunoreactive (IR) CGRP in the sciatic nerves and paw skin while it had no significant effect on CGRP-IR in the stomach or ureter. A separate set of experiments showed that intraplantar injection of complete Freund's adjuvant (CFA) in NGF-treated rats caused thermal hyperalgesia and edema that was not significantly different from values obtained in the control group. The results suggest that prolonged treatment of rats with moderate doses of NGF is sufficient to stimulate neuropeptide synthesis in primary afferent neurons without causing long-lasting changes in thermal nociceptive threshold.