Sleep cycle is a simple neuronal network

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Glial cells
Glial cells

For long the components responsible for sleep in the brain have remained a mystery, but not anymore. Researchers from the Washington State University Spokane were successful in growing a tiny group of brain cells in vitro which could be induced to fall asleep, wake up or could be out into the state of rebound sleep after been subjected to exertion, the classical example being : “staying up late”.

The rationale behind the study performed by James Krueger and doctoral student Kathryn Jewett was that any viable neuronal-glial network, including the ones in vitro exhibit self-organising emerging network properties characteristic of sleep. They simply cultured neurons and glial cells which matured into active neural networks in two weeks. Common parameters such as EEG (electroencephalogram) measurements such as slow wave voltage (SW) and synchronization (SYN) were used determine sleep states of the mature cell cultures.

It is known that neuronal networks release adenosine triphosphate (ATP) which in turn activates interleukin-1 (IL-1) and tumor necrosis factor (TNF) release triggering the sleep phase. This is the first study of its kind to show how TNF, an immune protein , is capable of regulating sleep and how it induces deep-sleep state in increasing doses.

The scientists observed the increasing pattern of SW and SYN in the EEG indicating the deep-sleep phase upon the external addition of TNF, but when these neurons were electrically stimulated, they automatically shifted into the state of being “awake”. Upon prolonged electrical stimulation on one day, the neurons slept in late the following day. This was one of the exciting finding of this study principally proving why lack of good sleep forces us to fall asleep forcefully the next day.

Krueger remarked “Everyone has experienced this type of homeostasis. If you stay up late one night, you sleep more the next night to catch up”. One of the advantages of TNF is, it is known to stabilize synapses, the junction between two neurons, therefore old memories are not lost and new memories are retained simultaneously; indicating there is no harm done when TNF is added externally.

“Before, people viewed sleep as a whole-brain phenomenon – using theories that often invoke “a miracle occurs and then you go to sleep”, Krueger said. But with this in vitro system, due to its simplicity, state characterization and ability to control the intensity of the emergent state properties, offers a novel experimental platform for scientists to see sleep as a small network property.

Through this study whole new hemisphere to understand the genetic, molecular and electrical causality mechanisms of sleep states has been opened and it could perhaps even be applied to the elusive issue of sleep function in the future.

The original publication can be accessed here.

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