What does H-MC stand for?

Endorphins and enkephalins are important opioid neurotransmitters in the CNS that mediate the sensation of itch. Although morphine alleviates pain, it aggravates itch, as itch and pain share common neurological pathways. The central elicitation of itch by morphine results from binding to opioid receptors and this binding may mimic normal physiological binding of endorphins and enkephakins at these receptor sites. Naloxone, an opioid antagonist, has been found to reduce histamine-provoked itch. The heparin-containing tissue cells called mast cells.