Astrocytes and Sleep
After many decades of research, scientists think they may finally have found the key to how sleep is regulated in the brain. Whilst this is unlikely to lead to a cure for all forms of insomnia, it could be of major significance in the development of medicines aimed at treating chronic sleep regulatory problems. It also helps us understand more about the side effects of sleep deprivation, which may help us to treat them.
What are Astrocytes?The name 'astrocyte' may sound exotic, but these important cells are actually pretty ordinary. They are part of the glial material in the brain, and their name comes from their characteristic star shape. There are three different types of astrocyte distributed through different parts of the brain.
Traditionally, brain research has focused on neurons, the nerve-type cells known to be responsible for transmitting bursts of information as we think (both consciously and subconsciously). The result of this is that much of what glial cells do remains a mystery. Astrocytes do an important job in repairing injuries to the brain and are also thought to play a role in defending against prion diseases like new variant Creutzfeldt-Jakob disease (otherwise known as mad cow disease).
Astrocytes and Sleep PressureWhat makes us feel sleepy? The answer is something called 'sleep pressure', which builds up whilst we are awake. At a chemical level, sleep pressure is managed through the release of a transmitter called adenosine. It is now known that astrocytes trigger the release of adenosine when the brain is overworked. This relieves the strain on other brain cells and prevents damage.
Scientists have long understood that, in people with sleep regulation disorders, something is wrong with the sleep pressure process. When there is too little sleep pressure you will feel the stress that comes from having an overworked brain but you won't be able to relax into sleep in order to recover. Some studies suggest this may be linked to the long term damage to the brain that occurs in people with Alzheimer's syndrome.
The ease with which astrocytes trigger the release of adenosine varies from person to person. Some people have naturally higher levels, so they get sleepy quickly but need less sleep overall. If, however, there is too much sleep pressure, the brain many start to shut down some processes even before you sleep, causing concentration and memory problems and making it hard to think straight. This could happen before sleep becomes strictly necessary for the health of your brain.
Astrocytes, Genetics and StressAs some forms of insomnia are hereditary, it appears that the level of activity of astrocytes can be influenced by genetic factors. It is thought that some genetic conditions interfere with the way astrocytes normally signal to each other, making it difficult for them to co-ordinate their sleep regulation tasks. This may also mean that it takes longer for them to receive the message that the brain needs sleep.
In order to communicate effectively, astrocytes need to be able to send messages in the form of neurotransmitters. Unfortunately, the longer you stay awake, the lower your stockpile of neurotransmitters falls, so insomnia caused by poor astrocyte communication may become a vicious circle. As stress also decreases the supply of neurotransmitters, this may be why stress can contribute to the development of insomnia.
Knowing how genetic factors influence the functioning of astrocytes, it may be possible to develop drugs that influence gene expression (whether or not inherited factors are 'activated'), and thus make people less likely to suffer from hereditary insomnia. In the meantime, we can keep our astrocytes healthy by aiming to have regular sleep (or at least rest) patterns and not making our brains work too hard when we're already overtired.