Norepinephrine and serotonin-induced antinociception are blocked by naloxone with different dosages.
The effects of intrathecally (IT) administered naloxone (Nal) on the antinociception produced by IT norepinephrine (NE), serotonin (5-HT), or morphine (Mor) were observed and compared in rats using the tail-flick (TF) assay. The results show that: a) NE, 5-HT, and Mor in doses of 1 nmol, 240 nmol, and 0.5 nmol, respectively, produce similar increases in amplitude and time in TF latency (TFL); b) Nal treatment of 240 and 360 nmol has no effects on TFL; c) the antinociception produced by NE (1 nmol) can be blocked by Nal (240 nmol); d) antinociception produced by Mor (0.5 nmol) can also be blocked by Nal (240 nmol); e) 240 nmol of Nal does not affect the 5-HT (120 nmol)-produced antinociception, while 360 nmol of Nal show a delayed blockade to the 5-HT (120 nmol)-produced antinociception. The results suggest that endogenous opiate-like substances may be involved in both NE- or 5-HT-produced antinociception at the spinal level, and these effects may be mediated through different types of opiate receptors.
Department of Neurobiology, Shanxi Medical College, Taiyuan, P.R. China.
S W
SW
Yang
Z H
ZH
Zhang
R
R
Wang
Y F
YF
Xie
J T
JT
Qiao
N
N
Dafny
D000818:Animals; D004305:Dose-Response Relationship, Drug; D005260:Female; D007278:Injections, Spinal; D008297:Male; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology; D009270:Naloxone / Q000008:administration & dosage / Q000494:pharmacology*; D009638:Norepinephrine / Q000008:administration & dosage / Q000494:pharmacology*; D010146:Pain / Q000503:physiopathology*; D051381:Rats; D017208:Rats, Wistar; D012018:Reflex / Q000187:drug effects; D012701:Serotonin / Q000008:administration & dosage / Q000494:pharmacology*; D013116:Spinal Cord / Q000187:drug effects / Q000502:physiology*; D013997:Time Factors
D012701:Serotonin; D009270:Naloxone; D009020:Morphine; D009638:Norepinephrine