Feeding and activity induced by orexin A in the lateral hypothalamus in rats


Orexin A injected into the lateral hypothalamus (LH) stimulates feeding and activates neurons in brain sites regulating feeding and arousal.  The feeding effects of orexin A have been demonstrated during the light cycle, a time when rats are normaly resting, and the effect of orexin A on activity after injection into the LH has not been previously measured.  Thus, it is unclear whether LH orexin A-induced feeding is secondary to enhanced arousal.  To address this, LH-cannulated rats habituated to a running wheel were injected with either orexin A (1000pmol) or vehicle during light and dark cycles.  Food intake and running wheel rotations were measured for 2 h.  Spontaneous physical activity (SPA) was also measured during the dark cycle.  During the light cycle, orexin A in the LH stimulated feeding in the presence and absence of a running wheel and increased number of running wheel rotations in the presence and absence of food. During the dark cycle, orexin A in the LH induced SPA (± presence of food), but had no effect on feeding.  These data show that LH orexin A stimulation of feeding is not always coincident with increased activity, suggesting that feeding induced by LH-injected orexin A is not consequent to enhanced arousal.  

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Catherine M. Kotz, Jennifer A. Teske, James A. Levine, ChaunFeng Wang