Sleep Homeostasis, Metabolism, and Adenosine

Abstract

Sleep is an integral and constitutive part of life, invariably observed in animals with even a simple nervous system. Importantly, sleep is an active and highly regulated state. Sleep propensity or sleep need and its best established biological marker, electroencephalographic (EEG) slow-wave (or delta) activity, is tightly associated to prior wakefulness and sleep and is homeostatically regulated. Sleep need may be considered an essential aspect of life, just like feeding, drinking, and procreation. Sleep, therefore, likely developed in a primordial state of evolution and should either aid or, at least, not interfere with other essential biological aspects of life such as metabolisms and reproduction. Consistent with this view, brain circuitries regulating sleep need, metabolism, and reward appear to involve the basal ganglia and are tightly linked. They may sense changes in the organism’s major cellular energy store, adenosine-tri-phosphate (ATP), and its derivative adenosine, and act in concert with other important neuromodulatory systems including dopamine, glutamate, and hypocretin.