The contribution of capsaicin-sensitive innervation to activation of the spinal vesico-vesical reflex in rats: relationship between substance P levels in the urinary bladder and the sensory-efferent function of capsaicin-sensitive sensory neurons.
In acute spinal rats (C2-C3) the transvesical infusion of saline activates a vesico-vesical excitatory reflex (Brain Res., 380 (1986) 83-93). In bladders containing a subthreshold amount of fluid the topical application of capsaicin on the outer surface of the bladder dome activated this spinal reflex and also produced a transient rise in blood pressure and heart rate. The effects of systemic capsaicin desensitization (50 mg/kg s.c. 5 min, 60 days before) on the sensory (activation of the spinal vesico-vesical reflex) and 'efferent' (tetrodotoxin-insensitive capsaicin-induced contraction) functions mediated by the capsaicin-sensitive sensory fibers were correlated to changes in substance P-like immunoreactivity (SP-LI) content of the urinary bladder in adult rats. Blockade of both sensory and efferent functions was observed at a time (60 min from capsaicin administration) when the SP-LI content of the urinary bladder was unaffected. Four days after capsaicin desensitization the SP-LI levels of the bladder are almost depleted indicating that the neuropeptide(s) are entirely stored in sensory structures. At this time the sensory-efferent functions mediated by these fibers are still blocked. At 15-60 days from systemic capsaicin desensitization there was a progressive, time-related recovery of SP-LI levels in the bladder as well as of the sensory-efferent functions. These findings indicate a role of the capsaicin-sensitive innervation of the urinary bladder in activating the spinal vesico-vesical reflex. The present findings suggest that measurement of SP-LI levels in the rat bladder may be a useful biochemical index for monitoring the function(s) of the capsaicin-sensitive, peptidergic sensory neurons.
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002211:Capsaicin / Q000008:administration & dosage / Q000494:pharmacology*; D003655:Decerebrate State; D006339:Heart Rate / Q000187:drug effects; D018738:Hexamethonium; D006584:Hexamethonium Compounds / Q000494:pharmacology; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009475:Neurons, Afferent / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012018:Reflex / Q000187:drug effects / Q000502:physiology*; D013116:Spinal Cord / Q000502:physiology*; D013373:Substance P / Q000378:metabolism*; D013997:Time Factors; D001743:Urinary Bladder / Q000187:drug effects / Q000294:innervation* / Q000502:physiology
D006584:Hexamethonium Compounds; D013373:Substance P; D018738:Hexamethonium; D002211:Capsaicin