Go figure.
Leptin modulates orexin-mediated functions at the behavioral and cellular level in mice
The two orexin hypothalamic neuropeptides play an important role in energy homeostasis as well as arousal and narcolepsy. Leptin is putatively involved in the regulation of orexin neuronal activity. Using neurochemical, behavioral and histological methods the in vivo and in vitro interactions between the leptin and orexin systems were studied. Results indicate that there are higher levels of serum orexin A and increased locomotor activity during the active period of the light-dark cycle in female as compared to male mice. Both elevated orexin serum levels and locomotion were decreased following subchronic exposure to a physiological dose of leptin in female mice. In addition, stereological brain analysis revealed that leptin reduced the number of orexin immunoreactive neurons in the lateral hypothalamus of female but not male mice. Leptin also reduced the activation of these neurons in both genders as measured by c-fos activation. ... In summary, these data support the notion that the leptin and orexin systems interact centrally, and indicate how leptin could modulate the orexin-mediated regulation of vigilance states.
