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 normally 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 (1000 pmol) 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. Published by Elsevier Science B.V.
Bibliographical noteFunding Information:
We would like to thank Ms. Mary Mullet for her expert technical assistance with stereotaxic surgery. This work was supported by the National Institutes of Health (NIDDK DK57573-01, DK56650, DK50456) and the Department of Veterans Affairs.
Copyright 2008 Elsevier B.V., All rights reserved.
- Feeding behavior
- Hypocretin 1
- Lateral hypothalamus
- Orexin A