INVOLVEMENT OF SPINAL NK1 AND OPIOIDS RECEPTORS IN MODULATING THE INHIBITORY EFFECT OF CAPSAICIN ON MICTURITION REFLEX IN THE ACUTE SPINALIZED GUINEA PIG

AbstractPurpose: The aim of this work was to study the role of capsaicin-sensitive afferent fibers in modulating the micturition reflex at spinal level in urethane-anesthetized guinea pigs after spinal cord transection at level T3-T4.Materials and Methods: The intravesical effect of capsaicin was investigated in a series of cystometrograms performed in intact and spinalized animals.Results: In both intact and spinalized animals capsaicin, at 30 micro M, induced a significant increase of volume threshold only, whereas at 100 micro M it induced a complete inhibition of the spinal micturition reflex in 60% and 85% of the animals tested, respectively. This capsaicin inhibitory effect (CIE) was unaffected by intravenous phentolamine and propranolol (0.5 and 1 mg./kg., respectively), indomethacin at 100 nmoles intrathecally (i.t.), the CGRP receptor antagonist hCGRP8-37 (3 nmoles i.t.) and the NK2 receptor selective antagonist GR 94800 (1 nmol. i.t.). However, both naloxone (30 micro g. i.t.) and the NK1 antago...