Muscimol injections into the median raphe nucleus increase serum ACTH and corticosterone concentrations via a nonserotonergic mechanism

J. M. Paris, S. A. Lorens, J. M. Lee, H. Mitsushio, J. C. Ritchie, Charles Nemeroff

Research output: Contribution to journalArticle

2 Citations (Scopus)

Abstract

Midbrain raphe serotonin (5-HT) neurons can influence the pituitary-adrenal axis. The midbrain raphe nuclei also contain a number of non-5-HT neurons, including gamma-aminobutyric acid (GABA) interneurons which can modulate 5-HT neuronal activity. We investigated the effects of intraraphe injections of the GABA agonist, muscimol, on serum adrenocorticotropin hormone (ACTH) and corticosterone concentrations. Rats were infused with muscimol (0, 25, 50, and 100 ng in 0.5 μl saline) into the median raphe nucleus (MR). The animals were killed 30 min later, and trunk blood was collected for measurement of serum concentrations of ACTH and corticosterone by radioimmunoassay. Muscimol dose dependently increased plasma concentrations of these two pituitary-adrenal hormones. In order to determine the role of MR 5-HT neurons in these effects, separate groups of implanted animals were infused with either the serotonergic neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT) or ascorbic acid vehicle into the MR. Two weeks later, the animals were infused with muscimol (100 ng in 0.5 μl) and sacrificed as above. Treatment with 5,7-DHT, which markedly reduced hippocampal concentrations of 5-HT (-83%) and 5-HIAA (-73%), did not block intra-MR muscimol-induced elevations in ACTH and corticosterone. Thus, 5-HT neurons within the MR apparently do not mediate the increased activity of the pituitary-adrenal axis produced by stimulation of MR GABAA receptors.

Original languageEnglish
Pages (from-to)765-768
Number of pages4
JournalPharmacology, Biochemistry and Behavior
Volume39
Issue number3
DOIs
StatePublished - Jan 1 1991
Externally publishedYes

Fingerprint

Muscimol
Raphe Nuclei
Corticosterone
Adrenocorticotropic Hormone
Serotonin
Hormones
Injections
Neurons
Serum
Animals
Dihydroxytryptamines
5,7-Dihydroxytryptamine
GABA Agonists
Hydroxyindoleacetic Acid
Pituitary Hormones
Interneurons
GABA-A Receptors
gamma-Aminobutyric Acid
Ascorbic Acid
Radioimmunoassay

Keywords

  • ACTH
  • Corticosterone
  • GABA
  • Median raphe nucleus
  • Muscimol
  • Serotonin

ASJC Scopus subject areas

  • Biochemistry
  • Behavioral Neuroscience
  • Pharmacology

Cite this

Muscimol injections into the median raphe nucleus increase serum ACTH and corticosterone concentrations via a nonserotonergic mechanism. / Paris, J. M.; Lorens, S. A.; Lee, J. M.; Mitsushio, H.; Ritchie, J. C.; Nemeroff, Charles.

In: Pharmacology, Biochemistry and Behavior, Vol. 39, No. 3, 01.01.1991, p. 765-768.

Research output: Contribution to journalArticle

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