Was Cajal right about sleep?

Abstract

Cajal's careful observations of the anatomy of the nervous system led him to some lesser-known predictions about the function of glia as mediators of sleep. Reporting over 120 years later in BMC Biology, Bellesi et al. examine changes in gene expression and morphology of astrocytes with sleep. Their results provide support for and revisions to Cajal's predictions.See research article: doi: 10.1186/s12915-015-0176-7 .

Fig. 1.

Historical and current understanding of the role astrocytes in sleep. Top: Cajal postulated that astrocytes retract their processes during wakefulness to allow normal synaptic transmission. During sleep, he reasoned, astrocyte processes invade the synapse to block synaptic transmission. Bottom: Recent findings revise this model to include astrocyte processes covering the synapse, presumably to enhance glutamate clearance during wake and retracting during sleep. This correlates with changes in gene expression in astrocytes (with ~400 transcripts up-regulated during wake and ~50 during sleep) and could relate to more glutamate spillover and increased glymphatic flow during sleep. Previous findings also showed dendritic spines grow with time awake (and greater sleep debt; reviewed in [3]). The model thus posits that changes in glial gene expression, morphology, and physiology may modulate synaptic transmission to promote sleep