Question

Neurobiology

1.What signaling pathway is activated when enkephalins bind to the m-opioid receptor? What are 2 actions of m-opioid receptor activation that block pain sensation (nociception) at the relay synapse between nociceptive neurons and projection neurons in the spinal cord? Who do these actions block nociception?

Answer 1

When enkephalins bind to m-opioid receptor, intracellular transductional signalling pathway get activated. Opioid receptors are the G protein- Coupled receptors (GPCRs).The different types of M-opioid receptor is responsible for analgesia, dependence, euphoria, respiratory depression, miosis, decreased digestive tract motility, vasodilation. The delta receptors of M-opioid bind to enkephalins and play a major role in analgesia and reduction in gadtrig motility. When the peripheral receptors sense painful stimuli, and impulses get carried to the dorsal horn of the spinal cord for relaying the higher centers of the brain, m- opioid receptor activation by an opioid agonist in the mid brain causes the formation of descending inhibitory impulses which are mediates through inhibition of GABA interneurons to the periaqueductal gray which stimulates descending inhibitory neurons that trigger enkephalin containgin neurons connected directly with the dorsal horn. This subsequently leads the decrease in nocireceptive transmission from the periphery to the thalamus. Exogenously administered Opioids cause analgesia through direct inhibition of substantia gelatinosa of the dorsal horn and through peripheral afferent nerves.