Delta opioid receptors in the rat olfactory bulb stimulate (rather than inhibit) adenylate cyclase, with deltorphin I being the most potent agonist at EC50 of 6.7 nM.
EC50 = 6.7 nMDeltorphin I was an extremely potent stimulator of adenylate cyclase through delta opioid receptors in the olfactory bulb
What the researchers found
Delta opioid receptors primarily mediate adenylate cyclase stimulation in olfactory bulb. Deltorphin I EC50 = 6.7 nM. Mu receptors contribute. Kappa receptors inactive.
Why it matters
Identifying the specific receptor (delta) responsible for unusual stimulatory opioid signaling helps explain how the same receptor family can produce opposite effects in different brain regions.
How the study worked
Rat olfactory bulb homogenates treated with selective opioid agonists and antagonists. Adenylate cyclase activity measured. Concentration-response curves and antagonist profiles determined.
What this study cannot tell us
In vitro tissue homogenate study. Cannot identify the specific cell types responsible. The G-protein coupling mechanism for stimulation was not fully characterized.
How to read the evidence
Preliminary — in vitro tissue homogenate study providing clear pharmacological characterization but not identifying specific cell types or in vivo relevance.
When this study was published
Published in 1992 (34 years ago). Stimulatory opioid signaling is now recognized as a real phenomenon in specific brain regions.
The bigger picture
This shows opioid receptors aren't one-trick ponies. The same receptor type can produce opposite effects depending on where in the brain it's located. This flexibility makes the opioid system far more versatile — and drug design more challenging.
Questions still open
- Why do delta receptors stimulate rather than inhibit signaling in the olfactory bulb?
- Do opioids affect the sense of smell through this mechanism?
Common questions
How can the same receptor do opposite things?
Does this affect how we smell?
Read the original research
Characterization of opioid receptors mediating stimulation of adenylate cyclase activity in rat olfactory bulb.
Molecular pharmacology, 42(1), 109-15
Citation
Olianas, M C; Onali, P. (1992). Characterization of opioid receptors mediating stimulation of adenylate cyclase activity in rat olfactory bulb.. Molecular pharmacology, 42(1), 109-15.