Relationship between neuronal activity and substance P-immunoreactivity inthe rat spinal cord during acute and persistent myositis

The spinal level of substance P (SP) is assumed to be an important determin ant of neuronal activity under pathophysiological conditions. In rat dorsal horn neurones, impulse activity was studied during a carrageenan-induced a cute (2-8 h) and a Freund's adjuvant-induced persistent (12 days) myositis and compared with the spinal substance P-immunoreactivity (SP-IR) of the sa me animals. Myositis-induced changes in responsiveness of the neurones reac hed a maximum within 2-8 h, whereas background activity of the neurones was highest after 12 days of myositis. The area of SP-IR in the superficial do rsal horn decreased during acute and persistent myositis and the integrated density of the staining was largely unchanged. The difference in time-cour se between neuronal activity and SP-IR suggest that during persistent myosi tis factors other than SP gain more influence on the behaviour of the neuro nes. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.