Comparison of G-protein activation in the brain by mu-, delta-, and kappa-opioid receptor agonists in mu-opioid receptor knockout mice
Park, Y.; Ma, T.; Tanaka, S.; Jang, C.; Loh, H.H.; Ko, K.H.; Ho, I.K.
Brain Research Bulletin 52(4): 297-302
2000
ISSN/ISBN: 0361-9230
PMID: 10856828
DOI: 10.1016/s0361-9230(00)00265-3
Accession: 010356128
Mice lacking the mu-opioid receptor gene have been developed by a gene knockout procedure. In this study, the activity of opioid receptor coupled G-proteins was examined to investigate whether there is a change in the extent of coupling for mu, delta-, and kappa-opioid receptors in mu-opioid receptor knockout mice. Selective agonists of mu- (DAMGO), delta- (DPDPE), and kappa- (U-69,593) opioid receptors stimulated [(35)S]GTPgammaS binding in the caudate putamen and cortex of wild-type mice. In contrast, only U-69,593 stimulated [(35)S]GTPgammaS binding in these regions of mu-opioid receptor knockout mice. These results confirmed the absence of G-protein activation by a mu-opioid receptor agonist in mu-opioid receptor knockout mice, and demonstrated that coupling of the kappa-opioid receptor to G-proteins is preserved in these mice. However, G-protein activation by the delta-opioid receptor agonist, DPDPE, was reduced in the mu-opioid receptor knockout mice, at least in the brain regions studied using autoradiography.