Stress Induced Neuronal Activation – Impact on Sleep

According to new research, neurons in the preoptic hypothalamus—the part of the brain that regulates sleep and body temperature—are rhythmically engaged during NREM sleep. According to a study published in Current Biology from the Perelman School of Medicine at the University of Pennsylvania, stress stimulates these brain cells out of turn, creating “microarousals” that disrupt sleep cycles and shorten the duration of sleep episodes.

While our bodies are at rest when we sleep, our minds remain quite active throughout the four stages of sleep. There are three stages of NREM sleep and one period of rapid eye movement (REM) sleep in each 90-minute sleep cycle.

Brain waves, heartbeat, and breathing all slow down during the first two stages of NREM sleep, as does body temperature. Spindles and K-complexes, which are brief bursts of activity responsible for processing outside stimuli as well as consolidating memory, are also included in stage two.

The third stage of the NREM sleep cycle is when the body releases growth hormone, which is necessary for bodily repair, immune system health, and memory enhancement.

Brain waves, known as delta waves, are larger during phase three. Memory creation, emotional processing, and brain development all depend on REM sleep, which occurs during this phase when dreaming generally occurs.

“When you have a bad night of sleep, you notice that your memory isn’t as good as it normally is, or your emotions are all over the place—but a bad night of sleep interrupts so many other processes throughout your body. This is even more heightened in individuals with stress-related sleep disorders,” said senior author, Shinjae Chung, Ph.D., an assistant professor of Neuroscience.

Researchers also discovered higher VGLUT2 neuron activity in stressed participants during NREM sleep. Furthermore, when VGLUT2 neurons were inhibited, microarousals during NREM sleep were reduced, and NREM sleep episodes were prolonged.

“The glutamatergic neurons in the hypothalamus give us a promising target for developing treatments for stress-related sleep disorders,” said first author, Jennifer Smith, a graduate researcher in Chung’s lab.

“Being able to reduce interruptions during the important stages of non-REM sleep by suppressing VGLUT2 activity would be groundbreaking for individuals struggling with disrupted sleep from disorders like insomnia or PTSD.”

For more information: Regulation of stress-induced sleep fragmentation by preoptic glutamatergic neurons, Current Biology (2023). DOI: 10.1016/j.cub.2023.11.035.