μ type opioid receptors in rat periaqueductal gray‐enriched P2 membrane are coupled to G‐protein‐mediated inhibition of adenylyl cyclase

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Abstract
The periaqueductal gray (PAG) region of the midbrain has been implicated in both stimulation-produced and opioid-induced analgesia. High-affinity μu-selective opioid-binding sites associated with μu type opioid receptors have been detected in rat PAG-enriched P2, membranes, and these receptors have been shown to be coupled to guanine nucleotidebinding proteins (G-proteins). In the present study the potential G-protein-mediated coupling of μu type opioid receptors to the inhibition of adenylyl cyclase was examined utilizing in vitro adenylyl cyclase assays. In the presence of Na+, opioid agonists inhibited adenylyl cyclase in aμu selective, naloxone reversible, dose dependent, and pertussis toxin sensitive manner. Overall the data suggests that μu type opioid receptors in the rat PAG are coupled to G-protein-mediated inhibition of adenylyl cyclase.