title: Selective enhancement of excitatory synaptic activity in the rat nucleus tractus solitarius by hypocretin 2.
abstract: Hypocretin 2 (orexin B) is a hypothalamic neuropeptide thought to be involved in regulating energy homeostasis, autonomic function, arousal, and sensory processing. Neural circuits in the caudal nucleus tractus solitarius (NTS) integrate viscerosensory inputs, and are therefore implicated in aspects of all these functions. We tested the hypothesis that hypocretin 2 modulates fast synaptic activity in caudal NTS areas that are generally associated with visceral sensation from cardiorespiratory and gastrointestinal systems. Hypocretin 2-immunoreactive fibers were observed throughout the caudal NTS. In whole-cell recordings from neurons in acute slices, hypocretin 2 depolarized 48% and hyperpolarized 10% of caudal NTS neurons, effects that were not observed when Cs(+) was used as the primary cation carrier. Hypocretin 2 also increased the amplitude of tractus solitarius-evoked excitatory postsynaptic currents (EPSCs) in 36% of neurons and significantly enhanced the frequency of spontaneous EPSCs in most (59%) neurons. Spontaneous inhibitory postsynaptic currents (IPSCs) were relatively unaffected by the peptide. The increase in EPSC frequency persisted in the presence of tetrodotoxin, suggesting a role for the peptide in regulating glutamate release in the NTS by acting at presynaptic terminals. These data suggest that hypocretin 2 modulates excitatory, but not inhibitory, synapses in caudal NTS neurons, including viscerosensory inputs. The selective nature of the effect supports the hypothesis that hypocretin 2 plays a role in modulating autonomic sensory signaling in the NTS.
authors.affiliation: Department of Cell and Molecular Biology, Tulane University, 6400 Freret Street, New Orleans, LA 70118, USA. bnsmith@tulane.edu
authors.forename: B N
authors.initials: BN
authors.lastname: Smith
authors.forename: S F
authors.initials: SF
authors.lastname: Davis
authors.forename: A N
authors.initials: AN
authors.lastname: Van Den Pol
authors.forename: W
authors.initials: W
authors.lastname: Xu
mesh_terms: D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D018756:GABA Antagonists / Q000494:pharmacology; D058787:GABA-A Receptor Antagonists; D007150:Immunohistochemistry; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology; D009479:Neuropeptides / Q000378:metabolism* / Q000494:pharmacology; D000068797:Orexins; D017729:Presynaptic Terminals / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000378:metabolism; D017470:Receptors, Glutamate / Q000187:drug effects / Q000378:metabolism; D017552:Solitary Nucleus / Q000187:drug effects / Q000378:metabolism*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology; D017833:Visceral Afferents / Q000187:drug effects / Q000378:metabolism*
chemical_list: D018691:Excitatory Amino Acid Antagonists; D018756:GABA Antagonists; D058787:GABA-A Receptor Antagonists; D047908:Intracellular Signaling Peptides and Proteins; D009479:Neuropeptides; D000068797:Orexins; D011963:Receptors, GABA-A; D017470:Receptors, Glutamate; D013779:Tetrodotoxin