Opiate-receptor interactions on single locus coeruleus neurones
Williams, J.T.; North, R.A.
Molecular Pharmacology 26(3): 489-497
1984
ISSN/ISBN: 0026-895X PMID: 6092898 Document Number: 239848
Intracellular recordings were made from neurons of the rat locus coeruleus (LC) which were located in a slice of pons superfused in vitro. Opioid agonists and antagonists were applied by adding them to the superfusing solution; normorphine and enkephalin anlogs were also applied by ejecting a few nl of a solution which contained the drugs from a pipette situated above the tissue slice. Opioid agonists hyperpolarized LC neurons. This results from an increase in the membrane K+ conductance. The lowest concentration of normorphine which was effective was 30 nM, the EC50 enkephalin, with a dissociation equilibrium constant of 2 nM. The opioid hyperpolarization of LC neurons may be mediated by a receptor having a high affinity for naloxone, previously termed a .mu.-receptor. The affinity of this receptor for normorphine appears to be 3-4 orders or magnitude lower than its affinity for naloxone.