title: Blockade of alpha 2-adrenoceptors increases opioid mu-receptor-mediated inhibition of the firing rate of rat locus coeruleus neurones.
abstract: In pontine slices of the rat brain, the frequency of spontaneous action potentials of locus coeruleus (LC) neurones was recorded extracellularly. Noradrenaline 0.1-100 mumol/l, UK 14,304 0.01-100 nmol/l, [Met5]-enkephalin 1-10,000 nmol/l and [D-Ala2,D-Leu5]enkephalin 0.1-1,000 nmol/l, all depressed the firing rate. Rauwolscine 1 mumol/l antagonized the effects of both noradrenaline and UK 14,304, but potentiated the effects of [Met5]enkephalin and [D-Ala2, D-Leu5]enkephalin. Idazoxan 1 mumol/l acted in a similar manner. Prazosin 1 mumol/l did not change the effects of either noradrenaline or [Met5]enkephalin. Naloxone 0.1 mumol/l antagonized both [Met5]enkephalin and [D-Ala2, D-Leu5]enkephalin, but failed to alter the effects of either noradrenaline or UK 14,304. Rauwolscine, idazoxan and prazosin, all 1 mumol/l, as well as naloxone 0.1 mumol/l, did not influence the firing rate when given alone. Desipramine 1 mumol/l inhibited the discharge of action potentials in a rauwolscine-antagonizable manner. Noradrenaline 10 mumol/l produced the same depression of firing, both in the presence of noradrenaline 1 mumol/l and [Met5]enkephalin 0.03 mumol/l. Likewise, the effect of [Met5]enkephalin 0.3 mumol/l was the same, irrespective of whether it was added to a medium containing [Met5]enkephalin 0.03 mumol/l or noradrenaline 1 mumol/l. The spontaneous activity of LC neurones is inhibited by somatic alpha 2-adrenoceptors and opioid mu-receptors. We suggest that the two receptors interact with each other at a site located between themselves and not in the subsequent common signal transduction system.
authors.affiliation: Department of Pharmacology, University of Freiburg, Federal Republic of Germany.
authors.forename: P
authors.initials: P
authors.lastname: Illes
authors.forename: W
authors.initials: W
authors.lastname: Nörenberg
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000316:Adrenergic alpha-Agonists / Q000037:antagonists & inhibitors / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000818:Animals; D003891:Desipramine / Q000494:pharmacology; D066298:In Vitro Techniques; D008125:Locus Coeruleus / Q000187:drug effects*; D008297:Male; D009474:Neurons / Q000187:drug effects*; D051381:Rats; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000187:drug effects*; D017450:Receptors, Opioid, mu
chemical_list: D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D011957:Receptors, Opioid; D017450:Receptors, Opioid, mu; D003891:Desipramine