Highly read on www.cell.com in November

Certain brain cells can respond not only to changing glucose levels, but also to mixtures of amino acids — the building blocks of proteins. This suggests that the brain can sense the body's nutrient status in addition to its energy needs.

Denis Burdakov at the University of Cambridge, UK, and his colleagues looked at cells in the brain's hypothalamus called orexin/hypocretin neurons, which regulate energy balance and feeding. Working with mice, they found that these cells were activated both in vitro and in vivo when exposed to nutritionally relevant amino-acid mixtures.

Glucose normally suppresses the activity of these neurons, but when the researchers exposed the cells to both glucose and amino acids, the amino acids excited the neurons and blocked the effect of glucose. The authors suggest that this boosts the signal from amino acids, which are typically at lower concentrations in the brain than glucose.

Neuron 72, 616–629 (2011)