Quantitative autoradiographic mapping of opioid receptors in the brain of delta-opioid receptor gene knockout mice.
Using quantitative receptor autoradiography we have determined if deletion of the delta-opioid receptor gene (Oprd1) results in compensatory changes in the expression of other opioid receptors. Gene targeting was used to delete exon 1 of the mouse delta-opioid receptor gene and autoradiography was carried out on brains from wild-type, heterozygous and homozygous knockout mice. Delta-opioid receptors were labeled with [(3)H]deltorphin I (7 nM), mu- with [(3)H]DAMGO (4 nM), and kappa- with [(3)H]CI-977 (2.5 nM) or [(3)H]bremazocine (2 nM in the presence of DPDPE and DAMGO) and non-specific binding determined with naloxone. [(3)H]Deltorphin I binding was reduced by approximately 50% in heterozygous animals. In homozygous animals specific binding could only be detected after long-term film exposure (12 weeks). Regions exhibiting this residual [(3)H]deltorphin I binding correlated significantly with those demonstrating high levels of the mu-receptor and were abolished in the presence of the mu-agonist DAMGO. Autoradiographic mapping showed significant overall reductions in [(3)H]DAMGO and [(3)H]CI-977 binding throughout the brain following loss of both copies of the Oprd1 gene. In contrast, overall levels of [(3)H]bremazocine binding were higher in brains from -/- than +/+ mice. Our findings suggest that residual [(3)H]deltorphin I binding in the brain of delta-receptor gene knockout mice is the result of cross-reactivity with mu-sites and that there are no delta-receptor subtypes derived from a different gene. Changes in mu- and kappa-receptor labeling suggest compensatory changes in these subtypes in response to the absence of the delta-receptor. The differences in [(3)H]CI-977 and [(3)H]bremazocine binding indicate these ligands show differential recognition of the kappa-receptor.
Pharmacology Group, School of Biomedical and Life Sciences, University of Surrey, Guilford, Surrey GU2 7XH, UK.
Robin J
RJ
Goody
Sarah M
SM
Oakley
Dominique
D
Filliol
Brigitte L
BL
Kieffer
Ian
I
Kitchen
D000818:Animals; D001345:Autoradiography; D001572:Benzofurans / Q000378:metabolism; D001575:Benzomorphans / Q000378:metabolism; D001921:Brain / Q000378:metabolism*; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000378:metabolism / Q000494:pharmacology; D005260:Female; D006579:Heterozygote; D006720:Homozygote; D008297:Male; D051379:Mice; D018345:Mice, Knockout / Q000235:genetics* / Q000378:metabolism*; D009842:Oligopeptides / Q000378:metabolism; D011759:Pyrrolidines / Q000378:metabolism; D017465:Receptors, Opioid, delta / Q000235:genetics* / Q000378:metabolism*; D017473:Receptors, Opioid, kappa / Q000378:metabolism*; D017450:Receptors, Opioid, mu / Q000819:agonists / Q000378:metabolism*
D001572:Benzofurans; D001575:Benzomorphans; D009842:Oligopeptides; D011759:Pyrrolidines; D017465:Receptors, Opioid, delta; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; C060208:deltorphin I, Ala(2)-; C027248:bremazocine; C067110:enadoline