Actions of orexins on individual myenteric neurons of the guinea-pig ileum: orexin A or B?
The actions of orexins (orexin A and B, 10-300 nM) on individual myenteric neurons of the guinea-pig ileum in vitro were compared using intracellular recording methods. Both orexins caused membrane depolarizations associated with an increase in input neuronal resistance in S and AH neurons via a direct action. Orexin depolarizations reversed at about -90 mV, indicating they were due to an inactivation of K+ channels. Orexins facilitated fast excitatory postsynaptic potentials without affecting postsynaptic sensitivity to acetylcholine and adenosine 5'-triphosphate, indicating that the peptides may facilitate ganglionic transmission by increasing presynaptic release of neurotransmitters. Orexin B was sometimes more effective than orexin A and vice versa. It is concluded that orexin B increased neuronal activity via mechanisms similar to orexin A in the guinea-pig myenteric plexus.
Katayama
Yoshifumi
Y
Department of Autonomic Physiology, Medical Research Institute, Tokyo Medical and Dental University, Chiyoda-ku, Tokyo 101-0062, Japan. kataauto@tmd.ac.jp
Hirai
Keiji
K
Homma
Tomoo
T
Noda
Yumi
Y
Honda
Kazuki
K
D000818:Animals; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D006168:Guinea Pigs; D007082:Ileum / Q000294:innervation*; D047908:Intracellular Signaling Peptides and Proteins / Q000494:pharmacology*; D008297:Male; D009197:Myenteric Plexus / Q000166:cytology / Q000187:drug effects*; D009474:Neurons / Q000187:drug effects* / Q000502:physiology*; D009479:Neuropeptides / Q000494:pharmacology*; D018377:Neurotransmitter Agents / Q000494:pharmacology; D000068797:Orexins; D015221:Potassium Channels / Q000502:physiology; D017729:Presynaptic Terminals / Q000187:drug effects / Q000502:physiology
D047908:Intracellular Signaling Peptides and Proteins; D009479:Neuropeptides; D018377:Neurotransmitter Agents; D000068797:Orexins; D015221:Potassium Channels