Objectives-Both sensory and sympathetic nerve fibres are depleted in t
he synovium in rheumatoid arthritis (RA). The hypothesis that the indu
ction of an inflammatory response in the synovium is capable of causin
g depletion of nerve fibres was tested. Methods-To investigate this ph
enomenon experimental arthritis in the rat was induced by three differ
ent methods and the synovium was examined for evidence of nerve deplet
ion by immuocytochemistry. Results-In a synovitis induced by latex sph
eres, a mainly macrophage foreign body type reaction, no nerve depleti
on was seen. In contrast both in an antigen-induced and a hydrogen per
oxide-induced model of arthritis nerve fibre depletion was observed. T
his appeared to affect sensory and sympathetic nerve fibres equally. N
erve fibre depletion was only seen in areas of inflammatory cell infil
tration indicating that a mixed lymphocyte and macrophage population o
f cells may be necessary for this effect. Conclusions-An inflammatory
response, containing lymphocytes and macrophages, in the synovium is c
apable of the depletion of the finely myelinated and unmyelinated neur
opeptide-containing nerves.