Distribution of the relative grey values of DRG neurons ipsilateral and contralateral to the injected knee with SP–gold binding. (a) Neurons (n = 800, from eight cultures) from control incubations treated with an excess of substance P that was administered together with SP–gold. (b) Neurons (n = 500, from five cultures) from untreated control animals. (c) Neurons (n = 300, from three cultures) from immunized animals without knee injection. (d) Neurons (n = 500, from five cultures) from rats 3 days after the induction of arthritis (3 days). (e) Neurons (n = 500, from five cultures) from AIA rats (21 days). White bars, neurons exhibiting grey densities that were in the range of those observed in neurons from control incubations; black bars, neurons exhibiting grey densities that were higher than those observed in the neurons from control incubations.