Galanin receptors inhibit the spontaneous firing of locus coeruleus neurones and interact with mu-opioid receptors.
Electrophysiological experiments were performed in a pontine slice preparation of rat brain containing the locus coeruleus (LC). The extracellular part of this study showed that galanin (0.003-0.1 mumol/l), [Met5]enkephalin (0.01-10 mumol/l) and noradrenaline (0.1-100 mumol/l) concentration dependently inhibited the firing rate. Noradrenaline (1 and 3 mumol/l) had the same effect both before and during the application of galanin (0.001 or 0.01 mumol/l). Similarly, [Met5]enkephalin (0.03 and 0.1 mumol/l) produced identical inhibition, regardless of the presence or absence of 0.01 mumol/l galanin. Whereas rauwolscine (1 mumol/l) potentiated the effect of galanin (0.03 mumol/l), idazoxan (1 mumol/l) was inactive. In contrast, both naloxone (0.1 mumol/l) and beta-funaltrexamine (0.1 mumol/l) facilitated the galanin-induced inhibition. In the intracellular experiments, galanin (0.3 mumol/l) abolished the spontaneous discharge of action potentials, hyperpolarized the cells and decreased their input resistance. In conclusion, galanin may depress the firing rate by increasing a potassium permeability. Moreover, galanin receptors appear to interact with mu-opioid receptors but not with alpha 2-adrenoceptors.
Sevcik
J
J
Department of Pharmacology, University of Freiburg, Germany.
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D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001921:Brain / Q000378:metabolism* / Q000502:physiology; D004347:Drug Interactions; D004594:Electrophysiology; D019004:Galanin; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009474:Neurons / Q000187:drug effects* / Q000502:physiology; D009638:Norepinephrine / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects; D044088:Receptors, Galanin; D011964:Receptors, Gastrointestinal Hormone / Q000378:metabolism*; D017450:Receptors, Opioid, mu / Q000378:metabolism*; D015016:Yohimbine / Q000494:pharmacology*
D010455:Peptides; D011942:Receptors, Adrenergic, alpha; D044088:Receptors, Galanin; D011964:Receptors, Gastrointestinal Hormone; D017450:Receptors, Opioid, mu; D015016:Yohimbine; D019004:Galanin; D009638:Norepinephrine