it was concluded that beta-endorphin and morphine produce inhibitions of the tail-flick response by stimulating epsilon and mu opioid receptors , respectively , and the descending pain modulatory system activated by beta-endorphin from cg involves spinal opioid receptors but not alpha-2 adrenoceptors whereas the descending system activated by morphine from cg involves spinal alpha-2 adrenoceptors but not opioid receptors .
C0066908
mu opioid receptors
C0034801
opioid receptors