Abstract
Both orexin and serotonin (5-HT) have important roles in the regulation of sleep-wakefulness, as well as in feeding behavior. We examined the effects of 5-HT on orexin/hypocretin neurons, using hypothalamic slices prepared from orexin/enhanced green fluorescent protein (EGFP) transgenic mice in which EGFP is expressed exclusively in orexin neurons. Patch-clamp recording from EGFP-expressing cells showed that 5-HT hyperpolarized all orexin neurons in a concentration-dependent manner. The response was inhibited by the 5-HT1A receptor antagonist WAY100635. A 5-HT1A receptor agonist, 8-hydroxy-2-(dl-N-propyl-amino)tetralin, also evoked hyperpolarization on orexin neurons with potency comparable with 5-HT. A low concentration of Ba2+ (30 microM) inhibited 5-HT-induced hyperpolarization. Single-channel recording revealed that the conductance of 5-HT-induced channel activity was 33.8 pS, which is in good agreement with that of the G-protein-coupled inward rectifier potassium channel (GIRK). Moreover, 5-HT1A receptor-like immunoreactivity was observed on orexin neurons, and 5-HT transporter immunoreactive nerve endings are in close apposition to orexin neurons. Intracerebroventricular injection of the 5-HT1A receptor-selective antagonist WAY100635 (100 ng) increased locomotor activity during the latter half of dark phase in wild-type mice but not in orexin/ataxin-3 mice in which orexin neurons are specifically ablated, suggesting that activation of orexin neurons is necessary for the WAY100635-induced increase in locomotor activity. These results indicate that 5-HT hyperpolarizes orexin neurons through the 5-HT1A receptor and subsequent activation of the GIRK and that this inhibitory serotonergic input to the orexin neurons is likely to be important for the physiological regulation of this neuropeptide system.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Animals
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Ataxin-3
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Female
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G Protein-Coupled Inwardly-Rectifying Potassium Channels
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Green Fluorescent Proteins / genetics
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Hypothalamus / cytology
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Hypothalamus / metabolism
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Immunohistochemistry
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In Vitro Techniques
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Injections, Intraventricular
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Intracellular Signaling Peptides and Proteins / genetics
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Intracellular Signaling Peptides and Proteins / metabolism*
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Male
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Membrane Glycoproteins / metabolism
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Membrane Transport Proteins / metabolism
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Mice
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Mice, Inbred C57BL
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Mice, Transgenic
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Motor Activity / drug effects
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Nerve Tissue Proteins / genetics
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Nerve Tissue Proteins / metabolism
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Neurons / metabolism
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Neurons / physiology*
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Neuropeptides / genetics
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Neuropeptides / metabolism*
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Nuclear Proteins
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Orexin Receptors
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Orexins
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Patch-Clamp Techniques
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Potassium Channels, Inwardly Rectifying / agonists
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Receptor, Serotonin, 5-HT1A / biosynthesis
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Receptor, Serotonin, 5-HT1A / physiology*
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Receptors, G-Protein-Coupled
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Receptors, Neuropeptide
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Repressor Proteins
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Serotonin / pharmacology
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Serotonin Antagonists / administration & dosage
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Serotonin Antagonists / pharmacology
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Serotonin Plasma Membrane Transport Proteins
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Serotonin Receptor Agonists / pharmacology
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Tetrodotoxin / pharmacology
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Transcription Factors
Substances
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G Protein-Coupled Inwardly-Rectifying Potassium Channels
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Intracellular Signaling Peptides and Proteins
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Membrane Glycoproteins
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Membrane Transport Proteins
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Nerve Tissue Proteins
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Neuropeptides
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Nuclear Proteins
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Orexin Receptors
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Orexins
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Potassium Channels, Inwardly Rectifying
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Receptors, G-Protein-Coupled
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Receptors, Neuropeptide
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Repressor Proteins
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Serotonin Antagonists
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Serotonin Plasma Membrane Transport Proteins
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Serotonin Receptor Agonists
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Slc6a4 protein, mouse
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Transcription Factors
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enhanced green fluorescent protein
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Receptor, Serotonin, 5-HT1A
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Green Fluorescent Proteins
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Serotonin
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Tetrodotoxin
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ATXN3 protein, human
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Ataxin-3
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Atxn3 protein, mouse