OBJECTIVE To explore whether the interaction occures between MOR and imidazoline receptor antisera-selected (IRAS) and that is responsible for I1 R regulating the function of MOR.METHODS Immunocytochemistry was used for detec ting the colocalization of IRAS and MOR.Co-immunoprecipitati on followed by Western blot was used to analyze whether forma tion of heterodimerization or oligomers.