GABAergic control of the ascending input from the median raphe nucleus to the limbic system

Shaomin Li, V. Varga, Attila Sik, Bernat Kocsis

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

The median raphe nucleus (MRN) is the primary source of serotonergic afferents to the limbic system that are generally considered to suppress hippocampal theta oscillations. GABA receptors are expressed in the MRN by serotonergic and nonserotonergic cells, including GABAergic and glutamatergic neurons. This study investigated the mechanisms by which the fluctuating GABA tone in the MRN leads to induction or suppression of hippocampal theta rhythm. We found that MRN application of the GABAA agonist muscimol (0.05-1.0 mM) or GABAB agonist baclofen (0.2 mM) by reverse microdialysis had strong theta promoting effects. The GABAA antagonist bicuculline infused in low concentrations (0.1, 0.2 mM) eliminated theta rhythm. A short period of theta activity of higher than normal frequency preceded hippocampal desynchronization in 46% of rats. Bicuculline in larger concentrations (0.5, 1.0, 2.0 mM) resulted in a biphasic response of an initial short (<10 min) hippocampal desynchronization followed by stable theta rhythm that lasted as long as the infusion continued. The frequency and amplitude of theta waves were higher than in control recordings and the oscillations showed a conspicuous intermittent character. Hippocampal theta rhythm elicited by MRN administration of bicuculline could be completely (0.5 mM bicuculline) or partially (1.0 mM bicuculline) blocked by simultaneous infusion of the GABAB antagonist CGP35348. Our findings suggest that the GABAergic network may have two opposing functions in the MRN: relieving the theta-generators from serotonergic inhibition and regulating the activity of a theta-promoting circuitry by the fluctuating GABA tone. The two mechanisms may be involved in different functions.

Original languageEnglish
Pages (from-to)2561-2574
Number of pages14
JournalJournal of Neurophysiology
Volume94
Issue number4
DOIs
Publication statusPublished - Oct 2005

Fingerprint

Limbic System
Raphe Nuclei
Bicuculline
Theta Rhythm
gamma-Aminobutyric Acid
GABA-A Receptor Agonists
GABA-A Receptor Antagonists
GABAergic Neurons
Muscimol
Baclofen
GABA Receptors
Microdialysis

ASJC Scopus subject areas

  • Physiology
  • Neuroscience(all)

Cite this

GABAergic control of the ascending input from the median raphe nucleus to the limbic system. / Li, Shaomin; Varga, V.; Sik, Attila; Kocsis, Bernat.

In: Journal of Neurophysiology, Vol. 94, No. 4, 10.2005, p. 2561-2574.

Research output: Contribution to journalArticle

Li, Shaomin ; Varga, V. ; Sik, Attila ; Kocsis, Bernat. / GABAergic control of the ascending input from the median raphe nucleus to the limbic system. In: Journal of Neurophysiology. 2005 ; Vol. 94, No. 4. pp. 2561-2574.
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