Catecholamine receptors on locus coeruleus neurons: Pharmacological characterization

Jesse M. Cedarbaum, George K. Aghajanian

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Abstract

There is evidence that the noradrenergic neurons of the locus coeruleus (LC) possess α-adrenoreceptors in the vicinity of their cell bodies. To further characterize this receptor, we studied the responses of LC neurons to a series of catecholamine agonist and antagonist drugs using the techniques of single-unit recording and microiontophoresis. The spontaneous firing of LC neurons was inhibited by microiontophoretic application of norepinephrine, epinephrine, the α-adrenoreceptor agonist clonidine and the β-agonist isoproterenol. These inhibitions were blocked by the α-adrenergic antagonist piperoxane but not by the β-antagonist sotalol. In addition these cells were strongly inhibited by dopamine or α-methylnorepinephrine, but only weakly inhibited by phenylephrine or the dopamine agonist apomorphine. The dopamine antagonist trifluoperazine was ineffective in blocking the inhibitions of LC neurons by both dopamine and norepinephrine. The rank order of potencies of agonist drugs in inhibiting LC neurons was clonidine > > α-methylnorepinephrine ≥ epinephrine = norepinephrine > > phenylephrine. In this respect the LC α-receptor is similar to 'presynaptic' or 'α2' receptors or peripheral sympathetic nerves and differs from the classical postsynaptic α-receptor. The noradrenergic neurons of the LC thus appear to possess catecholamine receptors on or near their cell bodies which have pharmacological characteristics of 'presynaptic' α-adrenergic receptors. The LC receptors are distinct from central dopamine receptors and from norepinephrine receptors areas of the brain receiving their noradrenergic iput fom the LC.

Original languageEnglish
Pages (from-to)375-385
Number of pages11
JournalEuropean Journal of Pharmacology
Volume44
Issue number4
DOIs
StatePublished - 15 Aug 1977
Externally publishedYes

Keywords

  • Locus coeruleus
  • Microiontophoresis
  • Presynaptic receptors
  • α-Adrenoreceptors

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