抄録
Reportedly experimental systemic inflammation produced by injecting complete Freund's adjuvant into the tail of rats (AI rats) increased the level of nerve growth factor (NGF) many fold above normal level in the inflamed tissue and DRGs. Enhanced retrograde transport of NGF to DRGs would lead to a rapid and large increase in the production of neuropeptides such as substance P (SP) and calcitonin gene-related peptide (CGRP), resulting in hyperalgegesia. However, little is known about the time course of changes in NGF and neuropeptides levels during development of persistent inflammation. Therefore we examined changes in these substances at different time points after inoculation of adjuvant. No NGF immunoreactivity (IR) was found in any specific structures in normal rat L4-6 DRGs, but found in AI rat DRGs 7 and 14 days after adjuvant inoculation. NGF-positive cells composed 9% of DRG neurons and were of small and medium size. After 21 days NGF-IR was not detected in any DRGs. Similar to NGF, percentage of SP and CGRP-positive cells were increased in AI rat DRGs after 7 and 14 days, but after 21 days it returned to normal. Trk-A receptor for NGF also showed a similar change as SP and CGRP. However, hind paw swelling begins at nearly 14 days after inoculation and reaches its peak at 21 to 28 days. This controversy between the time course of inflammatory sign and that of changes in NGF and neuropeptides raises a question what maintain inflammatory sing and hyperalgesia when the level of NGF and neuropeptides returned to normal. [Jpn J Physiol 54 Suppl:S174 (2004)]
