title: The electrical activity of hippocampal pyramidal neuron is subjected to descending control by the brain orexin/hypocretin system.
abstract: The hippocampus receives sparse orexinergic innervation from the lateral hypothalamus and expresses a high level of orexin receptor. The function of orexin receptor in the regulation of hippocampal neural activity has never been investigated. In this study, in vivo single unit recording was performed in urethane-anesthetized rats. After 15 min of baseline recording from pyramidal neuron within the CA1 region of the dorsal hippocampus, i.c.v. injection of orexin-A 0.5 nmol, SB334867 400 nmol, a selective orexin receptor 1 antagonist, saline, or DMSO, or microinjection of carbachol 250 nmol or saline into the ipsilateral lateral hypothalamus were performed using a Hamilton microsyringe, and the spontaneous firing activity continued to be recorded for 25 min. Results showed that orexin administration into the lateral cerebral ventricle excited 6 out of 8 neurons and inhibited 1 neuron. Chemical stimulation of the lateral hypothalamus by carbachol excited 9 out of 13 hippocampal neurons and inhibited 3 neurons. On the other hand, i.c.v. injection of the SB334867, caused reductions in the firing activity of 6 out of 10 neurons and increases in 4 additional neurons. It seems that orexin neurotransmission in the hippocampus mostly elicits an excitatory response, whereas blockade of orexin receptor has an inhibitory effect. Further studies need to be done to elucidate the underlying mechanism of orexin action on hippocampal neurons.
authors: Physiology Department, School of Medicine, Tehran University of Medical Sciences, Iran; Neuroscience Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
authors: Esmail
authors: E
authors: Riahi
authors: Neuroscience Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
authors: Reza
authors: R
authors: Arezoomandan
authors: Neuroscience Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
authors: Zahra
authors: Z
authors: Fatahi
authors: Neuroscience Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Electronic address: Haghparast@yahoo.com.
authors: Abbas
authors: A
authors: Haghparast
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001583:Benzoxazoles / Q000008:administration & dosage; D002217:Carbachol / Q000008:administration & dosage; D006624:Hippocampus / Q000187:drug effects / Q000502:physiology*; D007026:Hypothalamic Area, Lateral / Q000187:drug effects / Q000502:physiology*; D057967:Infusions, Intraventricular; D008297:Male; D009287:Naphthyridines; D000068796:Orexin Receptor Antagonists; D064446:Orexin Receptors / Q000502:physiology*; D000068797:Orexins / Q000008:administration & dosage / Q000502:physiology*; D017966:Pyramidal Cells / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D014508:Urea / Q000008:administration & dosage / Q000031:analogs & derivatives
chemical_list: C420062:1-(2-methylbenzoxazol-6-yl)-3-(1,5)naphthyridin-4-yl urea; D001583:Benzoxazoles; D009287:Naphthyridines; D000068796:Orexin Receptor Antagonists; D064446:Orexin Receptors; D000068797:Orexins; D014508:Urea; D002217:Carbachol
keywords: Hippocampal pyramidal neuron; Lateral hypothalamus; Orexin system; Orexin-A; SB334867; Single unit recording