Centrally administered orexin A increases motivation for sweet pellets in rats

A. J. Thorpe, J. P. Cleary, A. S. Levine, C. M. Kotz

Research output: Contribution to journalArticlepeer-review

81 Scopus citations


Rationale: Centrally administered orexin A induces both feeding and locomotion in rats. Thus, the feeding response following orexin A administration may be secondary to general increases in activity rather than a specific motivation to eat. Objective: The aim of the study is to determine whether orexin A increases the motivation to eat. Methods: The effect of orexin A (0, 31.25, 62.5, 125, 250, and 500 pmol) on breakpoint was determined in male Sprague-Dawley rats with rostro-lateral hypothalamic cannulae under a progressive ratio of five schedule (PR5). The effect of orexin A (0, 31.25, 125, and 500 pmol) on pressing rate under a fixed ratio (20) schedule was obtained to analyze the time course of orexin-A-induced pressing. The effect of 24-h food deprivation on breakpoint under PR5 and the effect of orexin A (125 pmol) on free feeding (sweet pellets) and on open-field locomotor activity (0, 100, 500, and 1,000 pmol) were also tested. Results: Orexin A significantly augmented free feeding of sweet pellets, open-field locomotor activity, rate of pressing (FR20 schedule), and breakpoint (PR5 schedule), although compared to 24-h deprivation, the effect of orexin A on breakpoint was mild. However, there was a differential dose response relationship and time course of stimulation between orexin A's effects on locomotion and lever pressing. Conclusion: These data indicate that infusion of orexin A enhances free feeding by enhancing and possibly prolonging motivation to eat.

Original languageEnglish (US)
Pages (from-to)75-83
Number of pages9
Issue number1
StatePublished - Oct 2005

Bibliographical note

Funding Information:
This article is supported by the Department of Veterans Affairs, the National Institute of Diabetes and Digestive and Kidney Diseases Grant DK 57573, and the Minnesota Craniofacial Training Program NIDCR T32 DE07288-8.


  • Deprivation
  • Feeding
  • Fixed ratio
  • Hypocretin
  • Lateral hypothalamus
  • Neuropeptide
  • Progressive ratio


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