The frontiers of sleep

Integrated brain circuits: astrocytic networks modulate neuronal activity and behavior

The past decade has seen an explosion of research on roles of neuron-astrocyte interactions in the control of brain function. We highlight recent studies performed on the tripartite synapse, the structure consisting of pre- and postsynaptic elements of the synapse and an associated astrocytic process. Astrocytes respond to neuronal activity and neurotransmitters, through the activation of metabotropic receptors, and can release the gliotransmitters ATP, d-serine, and glutamate, which act on neurons. Astrocyte-derived ATP modulates synaptic transmission, either directly or through its metabolic product adenosine. d-serine modulates NMDA receptor function, whereas glia-derived glutamate can play important roles in relapse following withdrawal from drugs of abuse. Cell type-specific molecular genetics has allowed a new level of examination of the function of astrocytes in brain function and has revealed an important role of these glial cells that is mediated by adenosine accumulation in the control of sleep and in cognitive impairments that follow sleep deprivation.

Sleep in depression and sleep deprivation: a brief conceptual review

Risk factors for somnipathies are psychological stress or psychiatric illness. More severe sleep difficulties have been found to be clearly related to psychiatric illness such as depression and phobias, as well as to addiction. Somnipathies can objectively be identified by means of polygraphy. Overall, polysomnographic measures in patients with affective disorders differ most frequently and significantly from those in normal control subjects. Persistent sleep disturbances are associated with significant risk of both relapse and recurrence in mood disorders and an increased risk of suicide. In addition to changes in sleep architecture, patients with major depression show profoundly altered patterns of nocturnal hormone secretion, possibly through mechanisms that link regulation of sleep with neuroendocrine activity. Basic and clinical approaches of sleep research established neurobiological models into the underlying pathophysiology associated with psychiatric disorders.