Dual orexin actions on dorsal raphe and laterodorsal tegmentum neurons: noisy cation current activation and selective enhancement of Ca2+ transients mediated by L-type calcium channels.
The hypocretin/orexins (Hcrt/Orxs) are hypothalamic neuropeptides that regulate stress, addiction, feeding, and arousal behaviors. They depolarize many types of central neurons and can increase [Ca2+]i in some, including those of the dorsal raphe (DR) and laterodorsal tegmental (LDT) nuclei-two structures likely to contribute to the behavioral actions of Hcrt/Orx. In this study, we used simultaneous whole cell and Ca2+-imaging methods in mouse brain slices to compare the Hcrt/Orx-activated current in DR and LDT neurons and to determine whether it contributes to the Ca2+ influx evoked by Hcrt/Orx. We found Hcrt/Orx activates a similar noisy cation current that reversed near 0 mV in both cell types. Contrary to our expectation, this current did not contribute to the somatic Ca2+ influx evoked by Hcrt/Orx. In contrast, Hcrt/Orx enhanced the Ca2+ transients produced by voltage steps (-60 to -30 mV) by approximately 30% even in neurons lacking an inward current. This effect was abolished by nifedipine, augmented by Bay-K and abolished by bisindolylmaleimide I. Thus Hcrt/Orx has two independent actions: activation of noisy cation channels that generate depolarization and activation of a protein kinase C (PKC)-dependent enhancement of Ca2+ transients mediated by L-type Ca2+ channels. Immunocytochemistry verified that both these actions occurred in serotonergic and cholinergic neurons, indicating that Hcrt/Orx can function as a neuromodulator in these key neurons of the reticular activating system. Because regulation of Ca2+ transients mediated by L-channels is often linked to the control of transcriptional signaling, our findings imply that Hcrt/Orxs may also function in the regulation of long-term homeostatic or trophic processes.
Kohlmeier
K A
KA
Department of Physiology, New York Medical College, Valhalla, NY 10595, USA.
Watanabe
S
S
Tyler
C J
CJ
Burlet
S
S
Leonard
C S
CS
D000818:Animals; D020746:Calcium Channels, L-Type / Q000187:drug effects*; D020013:Calcium Signaling / Q000187:drug effects*; D002412:Cations / Q000378:metabolism; D004594:Electrophysiology; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D047908:Intracellular Signaling Peptides and Proteins / Q000494:pharmacology*; D007473:Ion Channels / Q000819:agonists*; D051379:Mice; D008810:Mice, Inbred C57BL; D009474:Neurons / Q000187:drug effects*; D009479:Neuropeptides / Q000494:pharmacology*; D018377:Neurotransmitter Agents / Q000502:physiology; D000068797:Orexins; D010275:Parasympathetic Nervous System / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D011493:Protein Kinase C / Q000378:metabolism; D011903:Raphe Nuclei / Q000187:drug effects*; D012154:Reticular Formation / Q000166:cytology / Q000502:physiology; D012701:Serotonin / Q000502:physiology; D015222:Sodium Channels / Q000187:drug effects / Q000502:physiology; D013681:Tegmentum Mesencephali / Q000166:cytology* / Q000187:drug effects*
D020746:Calcium Channels, L-Type; D002412:Cations; D047908:Intracellular Signaling Peptides and Proteins; D007473:Ion Channels; D009479:Neuropeptides; D018377:Neurotransmitter Agents; D000068797:Orexins; D015222:Sodium Channels; D012701:Serotonin; D011493:Protein Kinase C