However, it is noteworthy that essential and nonessential AAs can compete with each other for entry through the

blood-brain barrier (Oldendorf and Szabo, 1976), and thus a rise in nonessential AA levels in the brain may signal a fall in essential AA levels in the blood. Another physiological situation that may, potentially, benefit from increased BMS-777607 cell line stimulation of orx/hcrt neurons by AAs is prolonged starvation, where a rise in extracellular AA levels occurs as proteins are broken down to AAs for fuel (Adibi, 1968 and Felig et al., 1969). More fundamentally, our data suggest that orx/hcrt neurons are under “push-pull” control by glucose and AAs, and that nutrient mixtures dominated by glucose would suppress the orx/hcrt system, while nutrient mixtures dominated by AAs would increase its activity. Interestingly, there is accumulating evidence that underactivity and overactivity of the orx/hcrt system may lead to depression and anxiety, respectively (Boutrel et al., 2005, Brundin et al., 2007, Ito et al., 2008 and Suzuki et al., 2005). While a definitive investigation of behavioral see more effects is beyond the scope of the present study, it is noteworthy that some existing psychological analyses are

consistent with our cellular data. For example, protein-rich meals have been reported to be more effective at promoting cognitive arousal than carbohydrate-rich meals (Fischer et al., 2002 and Spring et al., 1982-1983). In summary, our data show that the activity in the orx/hcrt system is regulated by macronutrient balance, rather than simply by the caloric content of the diet. We propose that the distinct effects of different macronutrients on orx/hcrt cells may allow these neurons to translate different diets into different patterns of activity in

their widespread projection targets. Animal procedures were performed according to the Animals (Scientific Procedures) Act, 1986 (UK). Transgenic orx/hcrt-eGFP mice were used to identify and study orx/hcrt neurons in electrophysiological experiments, as previously described (Williams et al., 2007 and Williams et al., 2008). These mice express eGFP under the control of the prepro-orexin promoter, resulting in highly specific Thiamine-diphosphate kinase targeting of eGFP only to orx/hcrt cells ( Burdakov et al., 2006 and Yamanaka et al., 2003). For lateral hypothalamic control experiments shown in Figure 1D, we used GAD65-GFP mice, which were of C57BL/6 background and expressed GFP gene fused to the first or third exon of the GAD65 gene; these mice express GFP exclusively in GABAergic GAD65-containing neurons, as previously characterized ( Bali et al., 2005 and López-Bendito et al., 2004). Mice were maintained on a 12 hr light:dark cycle (lights on at 0800 hr) and had free access to food and water. Coronal slices (250 μm thick) containing the lateral hypothalamus were prepared from 13- to 29-day-old animals. Experiments in Figures 1G, 7C, and 7D were replicated in adult mice (37–64 days old).