Journal
BEHAVIOURAL BRAIN RESEARCH
Volume 233, Issue 1, Pages 224-231Publisher
ELSEVIER
DOI: 10.1016/j.bbr.2012.05.002
Keywords
Inescapable footshock; Median raphe nucleus (MRN); Theta rhythm; Hypocretin; GABAergic pathway
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Funding
- National Science Council [NSC99-2320-B-002-026-MY3]
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The frequency of electroencephalograms (EEGs) is predominant in theta rhythm during stress (e.g., footshock) in rats. Median raphe nucleus (MRN) desynchronizes hippocampal theta waves via activation of GABAergic neurons in the medial septum-diagonal band of Broca (MS-DBB), a theta rhythm pacemaker. Increased hypocretin mediates stress responses in addition to the maintenance of wakefulness. Hypocretin receptors are abundant in the MRN, suggesting a possible role of hypocretin in modulating stress-induced theta rhythm. Our results indicated that the intensity of theta waves was enhanced by footshock and that a hypocretin receptor antagonist (TCS1102) suppressed the footshock-induced theta waves. Administration of hypocretin-1 (1 and 10 mu g) and hypocretin-2 (10 p,g) directly into the MRN simulated the effect of footshock and significantly increased theta waves. Co-administration of GABA(A) receptor antagonist, bicuculline, into the MRN blocked the increase of theta waves induced by hypocretins or footshock. These results suggested that stress enhances the release of hypocretins, activates GABAergic neurons in the MRN, blocks the ability of MRN to desynchronize theta waves, and subsequently increases the intensity of theta rhythm. (C) 2012 Elsevier ay. All rights reserved.
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