Peripheral and spinal components of the sensitization of spinal neurons during an acute experimental arthritis.

In cats the injections of kaolin and carrageenan into the knee joint lead to an acute arthritis which develops within 1-3 hours. In parallel articular afferents (low, high threshold and unresponsive ones) are becoming (more) sensitive to movements in the working range of the joint and many show (enhanced) ongoing discharges. Consequently spinal nociceptive-specific and wide dynamic range neurons with afferent input from the inflamed knee develop (increased) responsiveness to gentle stimulation of the joint. But in addition most of these neurons display enhanced reactions to non-inflamed parts of their receptive fields, too, and some neurons show enlargement of their total receptive fields. These latter findings indicate that the sensitization of spinal neurons is not simply reflecting the increased afferent input from the inflamed knee but that intrinsic spinal mechanisms may participate in the sensitization process.