Influence of fibroblast-like synovial (FLS) cells on the expression of neurokinin 1 (NK1) receptor-like immunoreactivity (IR) in dorsal root ganglion (DRG) neurones. (a) Co-culture of DRG neurones from normal rats and FLS cells isolated from inflamed knee joints three days after induction of antigen-induced arthritis (AIA). The dark cell (see arrow) shows labelling for NK1 receptor-like immunoreactivity. (b) Same cells as in (a) double-labelled with an anti-neurone-specific enolase antibody. Scale bar, 10 μm. (c) Influence of FLS cells from normal and acutely and chronically inflamed knee joints on the expression of NK1 receptor-like immunoreactivity in DRG neurones from normal rats. #Significant difference to DRG mono-cultures. $Significant difference to co-culture with FLS cells from normal knee joints. AIA, antigen-induced arthritis.