Simultaneous measurement of plasma and brain extracellular fluid concentrations of catechols after yohimbine administration in rats

Katalin Szemeredi, Samuel Komoly, Irwin J. Kopin, Gyorgy Bagdy, Harry R. Keiser, David S. Goldstein

Research output: Article

41 Citations (Scopus)


The present study examined whether systemic injection of the α2 adrenoceptor blocker, yohimbine, affects concentrations of norepinephrine (NE) and its metabolites in extracellular fluid in the brain and in blood. Microdialysis probes were inserted into the posterior hypothalamus, medulla, and caudate/putamen in rats. Microdialysate and arterial blood were sampled after intravenous administration of yohimbine. In the hypothalamus yohimbine produced significant increases in extracellular fluid concentrations of NE, its intraneuronal metabolite, dihydroxyphenylglycol (DHPG), and methoxyhydroxyphenylglycol (MHPG), a major neuronal and extraneuronal metabolite of NE. The increases in these levels were small or absent in the caudate/putamen, where dopamine is the primary catecholamine transmitter. During systemic infusion of tracer amounts of [3H]NE, little if any radioactive NE or DHPG appeared in the microdialysate, whereas substantial levels of [3H]MHPG were present and increased as plasma [3MHPG levels rose. The results support the view that α2 adrenoceptor blockade in the brain increases hypothalamic and medullary release, reuptake, and metabolism of NE. The findings cannot be explained by disruption of the blood-brain barrier for catecholamines by insertion of the microdialysis probes. Enhanced sympathetic outflow and peripheral release of NE when α2 adrenoceptors are blocked appears to be attended by enhanced central NE release, presumably as a results of presynaptic α2 adrenoceptor blockade at noradrenergic terminals in the brain. This is consistent with the hypothesis that central noradrenergic NE release is regulated by presynaptic α2 adrenoceptors.

Original languageEnglish
Pages (from-to)8-14
Number of pages7
JournalBrain research
Issue number1
Publication statusPublished - febr. 22 1991

ASJC Scopus subject areas

  • Neuroscience(all)
  • Molecular Biology
  • Clinical Neurology
  • Developmental Biology

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