Responses of cutaneous C-fiber afferents and spinal microglia after hindlimb cast immobilization in rats

Previous studies have shown that persistent limb immobilization using a cast increases nociceptive behavior to somatic stimuli in rats. However, the peripheral neural mechanisms of nociception remain unclear. Using single-fiber electrophysiological recordings in vitro, we examined the general characteristics of cutaneous C-fiber afferents in the saphenous nerve and their responsiveness to mechanical and heat stimuli in a rat model of immobilization-induced pain by subjecting the rats to hindlimb cast immobilization for 4 weeks. The mechanical response of C-fibers appeared to increase in the model; however, statistical analysis revealed that neither the response threshold nor the response magnitude was altered. The general characteristics and heat responses of the C-fibers were not altered. The number of microglia and cell diameters significantly increased in the superficial dorsal horn of the lumbar spinal cord. Thus, activated microglia-mediated spinal mechanisms are associated with the induction of nociceptive hypersensitivity in rats after persistent cast immobilization. Keywords: Cast immobilization, Hyperalgesia, C-fiber afferents, Single-fiber recording, Spinal microglia, Rats
Author(s): Hiroki Ota[sup.1,2], Haruna Takebe[sup.1], Kazue Mizumura[sup.3] and Toru Taguchi[sup.1,2] Background Experimental cast immobilization of the wrist for 4 weeks led to the development of pain during movement in 90% [...]