This means that a lack of muOR renders one closer to threshold, making it easier to fire the nociceptor and to perceive pain. Or, it is more easy to fire a nociceptive neuron if its inhibitory muOR is missing. These authors note that nociceptive thresholds vary in gene dose-dependent fashions in mice. These mice studies provide powerful models for possible sources and consequences of genetic variation in humans. Studies of human twins document that individual differences in several types of pain are likely to have substantial genetic determinants.
Humans differ from one another in muOR densities.
This has been shown in postmortem brain samples and in vivo positron-emission tomography analyses. Elucidation of the genetic bases for these differences in receptor expression would thus represent a substantial advance in our understanding of individual differences in nociceptive behaviors and drug responses. Levels of expression of many, if not most, human genes differ from individual to individual. I believe that this article is hugely relevant to chiropractic. In the whiplash arena, there are some individuals who have voluntarily subjected themselves up to thousands of whiplash collisions, apparently without suffering any pain.