Pain aid by electrical stimulation in the central grey make a difference in people and its reversal by naloxone. Nothing at all is understood about how these stimuli activate nociceptors. The nociceptive nerve endings are so compact and scattered that they're challenging to find, let alone research. Even so, https://pukkabookmarks.com/story18218917/what-are-pain-receptors-things-to-know-before-you-buy