How do 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 neuron, called cortex-directed releasing hormones (CRF), which is a polypeptide hormone and a neurotransmitter involved in the stress response, which becomes hyperactive when mammals are under stress, which can lead to insomnia and other sleep disturbances.

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

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

However, in the case of life-threatening situations, the circadian rhythm signal is turned off to keep the animal awake so it can escape danger even when it is usually bedtime.

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

“It is well known that the biological clock and stress have an effect on sleep, but it is not clear which nerve pathway is necessary to regulate the circadian rhythm of sleep and wakefulness,” said Dr. Daisuke Ono of the Research Institute at Nagoya University Environmental Medicine. To determine the path, a Nagoya University research team led by Professor Akihiro Yamanaka and Dr. Ono, in collaboration with Takashi Sugiyama of Olympus Corporation in Japan, conducted a study in mice.

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

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

Subsequent research also demonstrated 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 heightened alertness.

Therefore, 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 neuronal pathway in mice, which are nocturnal animals,” says Dr. Ono. “More studies are needed to clarify how the day and night difference is regulated in the brain.”

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

Source: medicalxpress