Spinal delta 2 but not delta 1 opioid receptors are involved in intracerebroventricular beta-endorphin-induced antinociception in the mouse.
The antinociception induced by beta-endorphin given intracerebroventricularly (i.c.v.) has been previously demonstrated to be mediated by the release of Met-enkephalin and subsequent stimulation of delta receptors in the spinal cord for antinociception. The present study was designed to determine what type of opioid receptor, delta 1 or delta 2, in the spinal cord is involved in i.c.v. beta-endorphin-induced antinociception. Antinociception was assessed by the tail-flick test in male ICR mice. NTB (0.2-20 nmol) and NTI (0.22-2.2 nmol), selective delta 2 receptor antagonists, given intrathecally (i.t.) dose-dependently attenuated i.c.v. beta-endorphin-induced inhibition of the tail-flick response. On the other hand, BNTX (0.02-2.2 nmol), a selective delta 1 receptor antagonist, given i.t., did not block i.c.v. beta-endorphin-induced antinociception. The tail-flick inhibition induced by DAMGO, a mu receptor agonist, or U50,488H, a kappa receptor agonist, was not blocked by i.t. BNTX, NTB or NTI. It is concluded that delta 2 but not delta 1 receptors in the spinal cord are involved in i.c.v. beta-endorphin-induced antinociception.
Department of Pharmacology and Toxicology, Medical College of Wisconsin, Milwaukee 53226.
L F
LF
Tseng
K A
KA
Collins
P S
PS
Portoghese
D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; D000818:Animals; D001597:Benzylidene Compounds / Q000494:pharmacology; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D004745:Enkephalins / Q000494:pharmacology; D007276:Injections, Intraventricular; D007278:Injections, Spinal; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D009271:Naltrexone / Q000031:analogs & derivatives / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D009619:Nociceptors / Q000187:drug effects* / Q000502:physiology; D010147:Pain Measurement / Q000187:drug effects; D011759:Pyrrolidines / Q000494:pharmacology; D017465:Receptors, Opioid, delta / Q000037:antagonists & inhibitors / Q000145:classification / Q000502:physiology*; D013116:Spinal Cord / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure*; D001615:beta-Endorphin / Q000494:pharmacology*
D001597:Benzylidene Compounds; D004745:Enkephalins; D009292:Narcotic Antagonists; D011759:Pyrrolidines; D017465:Receptors, Opioid, delta; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; C068868:naltrindole benzofuran; C077358:7-benzylidenenaltrexone; D009271:Naltrexone; D001615:beta-Endorphin; D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; C055382:naltrindole