title: Inhibition of neural activity depletes orexin from rat hypothalamic slice culture.
abstract: Orexins (hypocretins) are neuropeptides produced by a small population of hypothalamic neurons whose dysregulation may lead to narcolepsy, a neurological disorder characterized by disorganization of sleep and wakefulness. Excessive stimulation of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptors causes preferential loss of orexin neurons in the hypothalamus, whereas an adequate level of neuronal excitatory activities is generally known to be important for the maintenance of central neurons. By examining the effect of manipulation of neural activity, we found that 24-72 hr application of tetrodotoxin (TTX) caused a substantial decrease in the number of orexin-immunoreactive neurons, but not of melanin-concentrating hormone-immunoreactive neurons, in hypothalamic slice culture. Similar results were obtained when neural activity was arrested by added extracellular Mg(2+). Reduction of orexin expression by TTX and Mg(2+) was also observed at mRNA level. The decrease of orexin-immunoreactive neurons was attributable to depletion of orexin, because it was reversible after washout of TTX or elevated extracellular Mg(2+) and was not associated with induction of cell death. Blockers of voltage-dependent Ca(2+) channels as well as of NMDA receptors also induced a significant and selective decrease of orexin-immunoreactive neurons. Moreover, TTX-induced decrease of orexin immunoreactivity was largely abrogated by concurrent application of a moderate concentration of NMDA. These results suggest that Ca(2+) entry associated with nontoxic levels of spontaneous activity of glutamatergic inputs plays an important role in the maintenance of orexin neurons in a tissue culture model.
authors.affiliation: Department of Chemico-Pharmacological Sciences, Kumamoto University, Kumamoto, Japan.
authors.forename: Shotaro
authors.initials: S
authors.lastname: Michinaga
authors.forename: Akinori
authors.initials: A
authors.lastname: Hisatsune
authors.forename: Yoichiro
authors.initials: Y
authors.lastname: Isohama
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Katsuki
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism; D002452:Cell Count; D016923:Cell Death / Q000502:physiology; D005455:Fluorescent Antibody Technique; D007028:Hypothalamic Hormones / Q000378:metabolism; D007031:Hypothalamus / Q000187:drug effects / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D008543:Melanins / Q000378:metabolism; D016202:N-Methylaspartate / Q000494:pharmacology; D009433:Neural Inhibition / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009479:Neuropeptides / Q000235:genetics / Q000378:metabolism*; D000068797:Orexins; D009924:Organ Culture Techniques; D010907:Pituitary Hormones / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D013779:Tetrodotoxin / Q000494:pharmacology; D013997:Time Factors
chemical_list: D015220:Calcium Channels; D007028:Hypothalamic Hormones; D047908:Intracellular Signaling Peptides and Proteins; D008543:Melanins; D009479:Neuropeptides; D000068797:Orexins; D010907:Pituitary Hormones; D012333:RNA, Messenger; D016194:Receptors, N-Methyl-D-Aspartate; D013779:Tetrodotoxin; D016202:N-Methylaspartate; C019463:melanin-concentrating hormone; D002118:Calcium