Acta Biologica Hungarica

, Volume 53, Issue 4, pp 435–443 | Cite as

Effect of Orexin-A on Discharge Rate of Rat Suprachiasmatic Nucleus Neurons In Vitro

  • B. Farkas
  • Ildikó VilágiEmail author
  • L. Détári


The suprachiasmatic nuclei (SCN) constitute the principal pacemaker of the circadian timing system in mammals. The generated rhythm is forwarded mostly through projections to various hypothalamic nuclei. On the other hand, the regulated processes feedback to the SCN. One of the possible feedback pathways is the orexinergic projection from the lateral hypothalamus. Orexins are recently identified neuropeptides with an overall facilitatory effect on waking behaviors. Orexinergic fibers are widely distributed throughout the brain and are also present in the SCN. In this study we examined the effect of orexin-A on the spontaneous activity of rat SCN cell in vitro. Neurons showed 2 different firing pattern (continuous-regular, intermittent-irregular). Orexin-A increased firing rate in both cell types at 10−8 M concentration, but caused a clear supression of neuronal activity at 10−7 M. Continuously firing neurons were less responsive than those firing intermittently. These results show that orexin-A may play a role in the modulation of the circadian pacemaker function. The neuropeptide might exert both direct, postsynaptic effects on SCN neurons and indirect, presynaptic effects on excitatory and inhibitory terminals. The dose-dependent modification of the firing rate indicate that the weight of these factors changes with the concentration of orexin-A.


Circadian rhythms cortical slices orexin-A SCN single unit activity 


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© Akadémiai Kiadó, Budapest 2002

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Authors and Affiliations

  1. 1.Department of Physiology and NeurobiologyEötvös Loránd UniversityBudapestHungary

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