State-dependent effects of orexins on the serotonergic dorsal raphe neurons in the rat.
The serotonergic dorsal raphe (DR) neurons play an important role in sleep-wakefulness regulation. Orexinergic neurons in the lateral hypothalamus densely project to the brainstem sites including the DR. To test the effects of orexins on the serotonergic DR neurons, we applied orexin A (0.1 mM) by pressure to these neurons in unanesthetized and urethane anesthetized rats. Orexin A caused excitation in 10 of 15 neurons under unanesthetized condition. The excitation was characterized by slow onset (0-18 s), long lasting duration (15-150 s) and state-dependency. Orexin A applied during REM sleep or slow wave sleep induced significant excitation while during wakefulness, the similar amount of orexin A did not increase the firing rate any more. In the anesthetized animals, orexin A induced excitation in four of eight neurons. The excitation had slow onset and was long lasting. These results suggest that orexinergic neurons exert excitatory influence on the serotonergic DR neurons to maintain tonic activity of them, thereby participating in regulation of sleep-wakefulness cycles and other functions.
Takahashi
Kazumi
K
Department of Physiology, Fukushima Medical University School of Medicine, 1 Hikari-ga-oka, Fukushima 960-1295, Japan.
Wang
Qing-Ping
QP
Guan
Jian-Lian
JL
Kayama
Yukihiko
Y
Shioda
Seiji
S
Koyama
Yoshimasa
Y
D000818:Animals; D047908:Intracellular Signaling Peptides and Proteins / Q000008:administration & dosage*; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009479:Neuropeptides / Q000008:administration & dosage*; D000068797:Orexins; D011903:Raphe Nuclei / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D012894:Sleep Stages / Q000187:drug effects / Q000502:physiology*; D014851:Wakefulness / Q000187:drug effects / Q000502:physiology*
D047908:Intracellular Signaling Peptides and Proteins; D009479:Neuropeptides; D000068797:Orexins; D012701:Serotonin