Updates on the sleep-wake cycle

Abstract

In this review, the authors highlight the main findings on the neural mechanisms of the sleep-wake cycle, emphasizing the importance of hypothalamic control of the sleep and wake cycle. The anterior, posterior, and lateral hypothalamic regions are the three divisions involved in this anatomical-functional control. The galaninergic and inhibitory GABAergic systems of the ventrolateral preoptic nucleus of the anterior hypothalamus and the neurons producing melanin concentrating hormone of the lateral hypothalamus are responsible for the inhibition of the waking system and they are, therefore, responsible for the initiation and maintenance of non-rapid-eye-movement and rapid-eye-movement sleep. The neurons of the suprachiasmatic nucleus of the anterior hypothalamus are responsible for the circadian rhythm of the sleep-wake cycle. The histaminergic nuclei of the posterior hypothalamus and hypocretinergic ones of the lateral hypothalamus are active during wakefulness, stimulating the aminergic system of the brainstem and inhibiting both the ventrolateral preoptic nucleus and also the melanin concentrating hormone systems and, thus, establishing a stable waking state. The inhibition-stimulation interaction between the posterior and lateral hypothalamic system of wakefulness and the GABAergic sleep system of the anterior hypothalamus is the base model of the reciprocal interaction, which results in the stability of the wake or sleep states. Changes in these nuclei or pathways result in the instability of the sleep-wake cycle and in sleep disorders.