Neonatal capsaicin treatment abolishes the modulations by opioids of substance P release from rat spinal cord slices.
The possible modulation by opioids of substance P (SP) release at the spinal level was studied using slices of the dorsal half of the rat lumbar enlargement superfused with an artificial cerebrospinal fluid. Capsaicin (0.5 microM) selectively evoked a Ca2+-dependent overflow of SP-like material (SPLI) from primary afferent fibers which was enhanced in the presence of mu-opioid agonists (DAGO, FK 33824, sufentanyl, morphine), reduced by the delta-opioid agonist DTLET, and unaltered by the kappa-opioid agonist U 50488 H. Selective antagonists (naloxone, ICI 154129) prevented the effects of mu- and delta-opioid agonists. Neonatal capsaicin (50 mg/kg) abolished the stimulatory effect of in vitro capsaicin (0.5 microM) but not that of 30 mM K+ on SPLI outflow. This K+-induced SPLI release was unaffected by opioids. Presynaptic inhibitory control of SPLI release from capsaicin-sensitive primary afferent fibers might account for the analgesic effect of delta- but not mu- and kappa-opioid agonists at the spinal level.
Pohl
M
M
INSERM U. 288, Neurobiologie Cellulaire et Fonctionelle, Faculté de Médecine Pitié-Salpêtrière, Paris, France.
Mauborgne
A
A
Bourgoin
S
S
Benoliel
J J
JJ
Hamon
M
M
Cesselin
F
F
D000818:Animals; D000831:Animals, Newborn; D002211:Capsaicin / Q000494:pharmacology*; D004723:Endorphins / Q000494:pharmacology*; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D004745:Enkephalins / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D009020:Morphine / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000187:drug effects*; D013116:Spinal Cord / Q000187:drug effects / Q000378:metabolism*; D013373:Substance P / Q000378:metabolism*
D004723:Endorphins; D004745:Enkephalins; D011957:Receptors, Opioid; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D013373:Substance P; D009020:Morphine; D002211:Capsaicin