Opioid receptor impairment--underlying mechanism in "pain diseases"?

The scarce or absent analgesic effect exhibited by morphine on pain from migraine attack and the poor inhibition of the spasmogenic effect of 5-HT (tested on the hand dorsal vein, computerized venotest) suggest the hypothesis of an opioid receptor deficiency in headache sufferers. Since endogenous opioids control the nociception, the sense of well being, and the vegetative balance, an opioid receptoral hypofunction could be the background of the headache and central panalgia, where the trinity pain, anhedonia, and dysautonomia are the characteristic features.