C-fiber modulation of the rat type I slowly adapting mechanoreceptor.
Effects of C-fiber activation on type I slowly adapting mechanoreceptor responses were investigated in a rat in vitro nerve-skin preparation using controlled mechanical stimuli. Two changes in behavior were evoked by antidromic C-fiber stimulation: (1). The type I response to mechanical stimuli was modulated in a graded fashion by antidromic C-fiber activation. The average decrease in mechanoresponse from baseline discharge was 53% at 20-Hz, 51% at 5-Hz, and 30% at 1-Hz stimulation rate. The type I response recovered to baseline levels following termination of antidromic electrical stimulation. (2). Antidromic C-fiber activation generated a spontaneous ongoing activity in many skin units; this was independent of mechanical stimulation and outlasted electrical stimulation. The fact that neither antidromic electrical stimulation of the crushed nerve trunk nor selective A-fiber activation elicited these reactions suggests that they were mediated via action potentials of slowly conducting (C-fiber) axons. Immunohistochemical staining revealed both substance P- and calcitonin gene-related peptide-like immunoreactivity in small unmyelinated nerve fibers entering the touch dome. These results support the concepts that (1). the type I slowly adapting mechanoreceptor in rat receives input from nociceptive terminals within the touch dome. (2). The function of type I slowly adapting mechanoreceptors is modulated by axon reflex activation of nociceptor terminals, which may play a role in altering the type I response during states of mechanical allodynia and have paracrine and autocrine influences on maintenance of touch dome structure.
Zhang
J
J
Department of Physiology, University of Utah School of Medicine, 410 Chipeta Way, Room 156, Salt Lake City, UT 84108-1297, USA.
Huang
W
W
Tuckett
R P
RP
D000200:Action Potentials / Q000502:physiology; D000220:Adaptation, Biological / Q000502:physiology*; D000818:Animals; D001369:Axons / Q000502:physiology; D015740:Calcitonin Gene-Related Peptide / Q000378:metabolism; D004558:Electric Stimulation; D005071:Evoked Potentials / Q000502:physiology; D007150:Immunohistochemistry; D008465:Mechanoreceptors / Q000502:physiology*; D036421:Nerve Fibers, Unmyelinated / Q000502:physiology*; D009431:Neural Conduction / Q000502:physiology; D009619:Nociceptors / Q000502:physiology*; D010146:Pain / Q000503:physiopathology*; D010812:Physical Stimulation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012867:Skin / Q000294:innervation; D013373:Substance P / Q000378:metabolism; D009435:Synaptic Transmission / Q000502:physiology*; D014110:Touch / Q000502:physiology*
D013373:Substance P; D015740:Calcitonin Gene-Related Peptide