title: Modulation of cannabinoid agonist binding by 5-HT in the rat cerebellum.
abstract: Cross-talk between cannabinoid CB1 and serotonin 5-HT receptors in rat cerebellar membranes was investigated using radioligand binding. In competition against the CB1 antagonist, [3 H]SR141716A, the agonist, WIN 55,212-2 yielded a biphasic isotherm. The majority of binding was to a high-affinity state that was significantly reduced by the GTP analogue, Gpp(NH)p. Interestingly, 5-HT enhanced the high-affinity binding constant of WIN 55,212-2 while attenuating the proportion of high-affinity binding. 5-HT also significantly reduced the proportion of high-affinity binding of the cannabinoid agonist, HU 210, but had no effect on the agonist, CP 55,940. The effect of 5-HT on WIN 55,212-2 binding was inhibited by the 5-HT2 receptor antagonist ritanserin as well as Gpp(NH)p, suggesting a dependence on the 5-HT2 receptor and on G protein-receptor interactions, respectively. Subsequent [3 H]WIN 55,212-2 dissociation kinetic experiments revealed that 5-HT promoted a slower-dissociating species of radiolabelled agonist-receptor complex. Our findings support a membrane-delimited cross-talk between two G protein-coupled receptors that are co-localized in certain cells of the central nervous system. Intriguingly, the cannabinoid agonist dependence of the 5-HT modulatory effect suggests that agonist-specific conformations of the CB1 receptor may also be important in determining the extent of this cross-talk.
authors.affiliation: Department of Pharmacology, University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Mark G
authors.initials: MG
authors.lastname: Devlin
authors.forename: Arthur
authors.initials: A
authors.lastname: Christopoulos
mesh_terms: D000818:Animals; D048588:Benzoxazines; D001667:Binding, Competitive / Q000187:drug effects; D002186:Cannabinoids / Q000819:agonists* / Q000378:metabolism*; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D002531:Cerebellum / Q000737:chemistry* / Q000378:metabolism*; D003511:Cyclohexanols / Q000378:metabolism; D013759:Dronabinol / Q000031:analogs & derivatives / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism; D008297:Male; D009025:Morpholines / Q000378:metabolism; D009281:Naphthalenes / Q000378:metabolism; D011869:Radioligand Assay; D051381:Rats; D017207:Rats, Sprague-Dawley; D020239:Receptor Cross-Talk / Q000187:drug effects / Q000502:physiology; D043882:Receptors, Cannabinoid; D011955:Receptors, Drug / Q000737:chemistry / Q000378:metabolism; D011985:Receptors, Serotonin / Q000378:metabolism; D012701:Serotonin / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D048588:Benzoxazines; D002186:Cannabinoids; D003511:Cyclohexanols; D009025:Morpholines; D009281:Naphthalenes; D043882:Receptors, Cannabinoid; D011955:Receptors, Drug; D011985:Receptors, Serotonin; D012701:Serotonin; C070417:(3R)-((2,3-dihydro-5-methyl-3-((4-morpholinyl)methyl)pyrrolo-(1,2,3-de)-1,4-benzoxazin-6-yl)(1-naphthalenyl))methanone; D013759:Dronabinol; C054649:3-(2-hydroxy-4-(1,1-dimethylheptyl)phenyl)-4-(3-hydroxypropyl)cyclohexanol; D019204:GTP-Binding Proteins; C062018:HU 211