How does stress and the biological clock affect sleep?

A research team led by the University of Nagoya in Japan has discovered a new neural pathway that links the biological clock, stress and wakefulness in mammals.

The team identified a nerve cell, called cortical direct-releasing hormones (CRF), which is a polypeptide hormone and neurotransmitter involved in the stress response, which becomes hyperactive when mammals are under stress, which can lead to insomnia and other disorders. of sleep.

The Japanese team’s findings were recently published in the journal Science Advances.

Living things exhibit a 24-hour fluctuation, called a circadian rhythm. In mammals, the central circadian clock, found in neurons in the suprachiasmatic nucleus (SCN), regulates the sleep-wake cycle.

However, in the event of life-threatening situations, the circadian rhythm signal is deactivated to keep the animal awake so that it can escape danger even when it is usually time to go to sleep.

And although suspending the sleep-wake cycle is essential for survival, excessive or prolonged stress caused by such dangers can lead to insomnia and other sleep disturbances.

“The biological clock and stress are known to have an effect on sleep, but it is unclear which nerve pathway is needed to regulate the circadian rhythm of sleep and wakefulness,” said Dr. Daisuke Ono of the Research Institute of environmental medicine at the University of Nagoya. To determine the path, a research team from the University of Nagoya led by Professor Akihiro Yamanaka and Dr Ono, in collaboration with Takashi Sugiyama at the Olympus Corporation in Japan, conducted a study using mice.

The researchers focused on neurons in the cortex-directed hormone-releasing hormone (CRF), which is known to play a role in the stress response, found in the paraventricular nucleus of the hypothalamus. They studied how sleep and wakefulness in mice were affected by the activation of these neurons.

The results showed that active CRF neurons kept the animals awake and made them move vigorously, indicating increased alertness. The researchers also noted that CRF neurons remained active when the mice were awake and that when neuronal activity was suppressed, the animals’ alertness and motor activities decreased.

Further investigations also showed that inhibitory neurons in the suprachiasmatic nucleus, called GABAergic neurons, play an important role in regulating the activity of CRF neurons and that activation of these neurons stimulates orexin cells in the lateral hypothalamus. , Which leads to increased vigilance.

So the team concluded that GABAergic neurons in the suprachiasmatic nucleus control the activity of corticotropin-releasing factor neurons, which ultimately regulate the sleep-wake cycle.

“We have identified this neural pathway in mice, which are nocturnal animals,” says Dr. Ono. “More studies are needed to clarify how the difference between night and day is regulated in the brain.”

“In today’s society, sleep disorders are a serious problem. We hope our findings will contribute to the development of new treatments for insomnia and other sleep disorders caused by stress or circadian rhythm disorders,” he added.

Source: medicalxpress