SENSITIZATION OF ARTICULAR AFFERENTS IN NORMAL AND INFLAMED KNEE JOINTS BY SUBSTANCE-P IN THE RAT

To examine whether substance P (SP) influences the response properties of fine articular afferents in normal and acutely inflamed joints, si ngle units were recorded from the rat knee during normal and noxious j oint rotations. Only three of 39 units were activated by a single bolu s injection of 0.1 mM SP. However, 35% (7/20) of the nerve fibres from the normal joint and 21% (4/19) of the units from the inflamed joint significantly increased their responses to movements after the SP inje ction. This was most prominent during noxious movements in normal join ts, whereas in inflamed joints increase of responses occurred mainly d uring normal movements. These data indicate that SP may also be involv ed in the process of sensitisation of primary afferents during an infl ammation. (C) 1997 Elsevier Science Ireland Ltd.