The Tribune

By Bettyjoe Cooper

Sleeping replenishes our energy levels, but it goes far beyond that. Our brains change states when we sleep, clearing away toxic byproducts of neural activity left over from the day.

But in brains that are chronically sleep deprived, the 'cleansing' process overcompensates. Researchers have found that sustained poor sleep causes the brain to clear a significant number of neurons and synaptic connections. And the damage may be irreversible during recovering sleep.

A team led by neuroscientist Michele Bellesi from the Marche Polytechnic University in Italy carried out the research. They examined the mammalian brain's response to poor sleeping habits and found a similarity between well-rested and sleepless mice.

The neurons in your brain are being continually refreshed by two different types of glial cell. These are support cells, a sort of 'glue' for the nervous system.

Microglial cells clear out old and worn cells in a process called phagocytosis (derived from the Greek meaning "to devour"). Astrocytes prune unnecessary synapses (connections) in the brain to reshape its wiring and keep it refreshed.

It is already understood that this process occurs during sleep to clear away the neurological wear and tear of the day. But now it appears that the same thing happens when we start to lose sleep.

It's akin to having your garbage collected whilst you're asleep, versus them coming into the house after several sleepless nights and throwing out your valuables as well.

"We show for the first time that portions of synapses are literally eaten by astrocytes because of sleep loss," Bellesi reported.

The researchers imaged the brains of four groups of mice:

• One group was left to sleep for six to eight hours (well-rested)

• Another had their sleep interrupted periodically (spontaneously awake)

• A third group was kept awake for an extra eight hours (sleep-deprived)

• And a final group was kept awake for five days straight (chronically sleep-deprived)

Astrocytes were present in 5.7 per cent of the synapses in the brains of the well-rested group, and 7.3 per cent in the spontaneously awake group.

However, in the other two sleep deprived groups, they noticed something different: The astrocytes showed increased activity and were eating parts of the synapses, like the microglial cells eat waste. This process is astrocytic phagocytosis.

Astrocytes were active across 8.4 per cent of the synapses in the brains of the sleep-deprived group. In the chronically sleep-deprived group, 13.5 per cent of their synapses showed astrocyte activity.

As Bellesi reported, most of the synapses that were getting eaten in the two groups of sleep-deprived mice were the largest ones, which tend to be the oldest and most heavily used - "like old pieces of furniture" - which is probably a good thing.

Unconstrained microglial activity has been linked to brain diseases like Alzheimer's and other forms of neurodegeneration.

"We find that astrocytic phagocytosis, mainly of presynaptic elements in large synapses, occurs after both acute and chronic sleep loss, but not after spontaneous wake, suggesting that it may promote the housekeeping and recycling of worn components of heavily used, strong synapses," the researchers report.

"By contrast, only chronic sleep loss activates microglia cells and promotes their phagocytic activity ... suggesting that extended sleep disruption may prime microglia and perhaps predispose the brain to other forms of insult."

Further research is required to determine if the process is replicated in the human brain, or if the effects are reversible by catching up on sleep.

Alzheimer's deaths have increased by an astonishing 50 per cent since 1999, according to the US Centre for Disease Control (CDC). In part, this is due to the number of older adults. But given that many of us increasingly struggle to get a good night's sleep, this potential link to Alzheimer's should be a priority area of study.

The research is published in the Journal of Neuroscience.

• Bettyjoe Cooper is an author and founder of Brand New Mattress Co. For more useful information and sleep tips, check out the blog at www.brandnewmattress.com.