Effects of intracerebroventricular administration of beta-funaltrexamine on DAMGO-stimulated [35S]GTP-gamma-S binding in rat brain sections.
Intracerebroventricular administration of beta-funaltrexamine (beta-FNA) reduces the density of mu opioid receptors as measured by in situ autoradiography by 40-50% throughout the brain, with little regional variation [Martin et al. (1993) J. Pharmacol. Exp. Ther. 267:506-514] Recently an assay has been developed to study opioid stimulation of [35S]GTP-gamma-S binding autoradiographically in situ using slide-mounted brain sections [Sim et al. (1995) Proc. Natl. Acad. Sci. U.S.A. 92:7242-7246]. The present study was undertaken to determine the effect of mu opioid receptor alkylation on G protein activation by the mu opioid agonist DAMGO. Animals were injected intracerebroventricularly with 40 nmol of beta-FNA or saline and sacrificed 24 hours later. DAMGO stimulated [35S]GTP-gamma-S binding with an anatomical specificity consistent with the localization of mu opioid receptors. The percent stimulation by DAMGO ranged from approximately 50 to 100% in the regions studied. beta-FNA significantly decreased G protein activation by DAMGO in regions that are consistent with its reported long-lasting and insurmountable antagonism of the antinociceptive (medial thalamus, central gray) and reinforcing (nucleus accumbens) effects of mu opioid agonists [Adams et al. (1990) J. Pharmacol. Exp. Ther. 255:1027-1032; Martin et al. (1995) J. Pharmacol. Exp. Ther. 272:1135-1140]. However, the effects of beta-FNA were not equal in all brain regions. This may indicate regional differences in the coupling efficiency of mu opioid receptors with G proteins, or in the effects of beta-FNA on mu opioid receptor binding or on mu opioid receptor-stimulated G protein activity.
Martin
T J
TJ
Dept of Physiology and Pharmacology, Bowman Gray School of Medicine of Wake Forest University, Winston-Salem, North Carolina, USA. tjmartin@isnet.is.wfu.edu
Sim
L J
LJ
Selley
D E
DE
deMontis
M G
MG
Childers
S R
SR
D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D004745:Enkephalins / Q000494:pharmacology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism*; D007276:Injections, Intraventricular; D008297:Male; D009271:Naltrexone / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000008:administration & dosage / Q000494:pharmacology*; D051381:Rats; D011916:Rats, Inbred F344; D017450:Receptors, Opioid, mu / Q000819:agonists* / Q000378:metabolism*; D013462:Sulfur Radioisotopes
D004745:Enkephalins; D009292:Narcotic Antagonists; D017450:Receptors, Opioid, mu; D013462:Sulfur Radioisotopes; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D009271:Naltrexone; C024524:beta-funaltrexamine