Mechanisms of orexin-induced depolarizations in rat dorsal motor nucleus of vagus neurones in vitro.
1. Whole-cell patch-clamp recordings were made from neurones of the dorsal motor nucleus of the vagus (DMNV), including Fluoro-gold-labelled parasympathetic preganglionic neurones (PPNs), in slices of the rat medulla. In the latter case, rats had received an I.P. injection of Fluoro-gold solution (10 microg) 2-3 days earlier. 2. Superfusion of orexin A or B (10-300 nM) caused a slow depolarization in approximately 30% of the DMNV neurones, including PPNs. Orexin-induced depolarizations, which persisted in TTX (0.5 microM)-containing Krebs solution, were reduced by 70% in a low-Na+ (26 mM) Krebs solution, indicating the involvement of Na+ ions. A significant change in orexin-induced depolarizations was not obtained in either a high-K+ (7 mM) or Cd2+ (100 microM) Krebs solution. 3. Inclusion of the hydrolysis-resistant guanine nucleotide GDP-beta-S in the patch solution significantly reduced the orexin A- or B-induced depolarizations. 4. Under whole-cell voltage-clamp conditions, the orexin-induced inward current declined with hyperpolarization, but did not reverse polarity in the potential range between -120 and 0 mV. In low-Na+ solution, the orexin-induced current was reduced, and the I-V curve reversed polarity at about -105 mV; the response was further reduced and the reversal potential shifted to -90 mV in a low-Na+, high-K+ Krebs solution. 5. It is concluded that the peptides orexin A and B, acting on orexin receptors, which are GTP-binding-protein coupled, are excitatory to DMNV neurones. In addition, more than one conductance, which may include a non-selective cation conductance and a K+ conductance, appears to be involved in the orexin-induced depolarization.
Hwang
L L
LL
Department of Pharmacology, James H. Quillen College of Medicine, East Tennessee State University, PO Box 70577, Johnson City, TN 37614, USA.
Chen
C T
CT
Dun
N J
NJ
D000818:Animals; D001933:Brain Stem / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*; D002352:Carrier Proteins / Q000494:pharmacology*; D004594:Electrophysiology; D019204:GTP-Binding Proteins / Q000502:physiology; D005726:Ganglia, Parasympathetic / Q000166:cytology / Q000187:drug effects; D047908:Intracellular Signaling Peptides and Proteins; D009474:Neurons / Q000187:drug effects; D009479:Neuropeptides / Q000494:pharmacology*; D000068797:Orexins; D051381:Rats; D017207:Rats, Sprague-Dawley; D014630:Vagus Nerve / Q000502:physiology*
D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D009479:Neuropeptides; D000068797:Orexins; D019204:GTP-Binding Proteins