Centrally administered orexin A increases motivation for sweet pellets in rats.
BACKGROUND
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.


CONCLUSIONS
These data indicate that infusion of orexin A enhances free feeding by enhancing and possibly prolonging motivation to eat.
Thorpe
A J
AJ
Department of Neuroscience, University of Minnesota, 1334 Eckles Avenue, Saint Paul, MN 55108, USA.
Cleary
J P
JP
Levine
A S
AS
Kotz
C M
CM
D000818:Animals; D001066:Appetite / Q000187:drug effects*; D001070:Appetitive Behavior / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D005247:Feeding Behavior / Q000187:drug effects*; D007026:Hypothalamic Area, Lateral / Q000187:drug effects*; D047908:Intracellular Signaling Peptides and Proteins / Q000494:pharmacology*; D009043:Motor Activity / Q000187:drug effects; D009415:Nerve Net / Q000187:drug effects; D009479:Neuropeptides / Q000494:pharmacology*; D000068797:Orexins; D051381:Rats; D017207:Rats, Sprague-Dawley; D012055:Reinforcement Schedule; D013649:Taste / Q000187:drug effects*
D047908:Intracellular Signaling Peptides and Proteins; D009479:Neuropeptides; D000068797:Orexins