Substance P N-terminus inhibits C-fiber-dependent facilitation of the rat flexor reflex.
Substance P injected intrathecally or a conditioning stimulus (1 Hz, 20 s) at C-fiber strength, which releases substance P from intraspinal primary afferent terminals, each enhance the hamstring muscle flexor reflex elicited by electrical stimulation of the sural nerve in decerebrate, spinalized rats. This suggests a role for substance P in pain transmission. Since substance P N-terminal metabolites are biologically active, we examined the effect of the metabolite substance P-(1-7) on the flexor reflex and the enhancement of the flexor reflex following a conditioning stimulus of the sural nerve. In contrast to the excitatory effect of substance P, intrathecal injection of substance P-(1-7) had no effect on the flexor reflex. However, 10 and 30 min after injection, 0.6 or 6 micrograms of substance P-(1-7) attenuated the facilitation of the flexor reflex by the conditioning stimulus. These data indicate that substance P-(1-7) may modulate the expression of nociception involving repetitive firing of C-fibers while having no significant effect on acute or phasic responses.
Goettl
V M
VM
Department of Veterinary PathoBiology, University of Minnesota, St. Paul 55108.
Xu
X J
XJ
Larson
A A
AA
Wiesenfeld-Hallin
Z
Z
D000818:Animals; D005260:Female; D009412:Nerve Fibers / Q000502:physiology*; D010146:Pain / Q000503:physiopathology*; D010446:Peptide Fragments / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012018:Reflex / Q000187:drug effects*; D013373:Substance P / Q000494:pharmacology*
D010446:Peptide Fragments; D013373:Substance P; C036877:substance P (1-7)