The stress surrounding being defeated by another mouse activates mouse midbrain cells, promoting sleep and reducing anxiety, according to a new study. The results highlight a neurological circuit in the brain, targeting of which "may help steer future interventions in rodents and perhaps even humans after stressful experiences, be it through cognitive therapy or pharmacotherapy or maybe, one day, genetic interference," write Marian Joëls and E. Ronald de Kloet in a related Perspective.
Although stress can cause insomnia, the opposite is also true; chronic stress is known to increase rapid eye movement (REM) sleep. These observations have led some to hypothesize that sleep is an important adaptive response to stressful situations, helping ameliorate its negative physiological and mental impacts. In mice, social defeat stress (SDS) – a stress response caused by losing a social confrontation – is often used as a model for psychosocial stress. Researchers have found that SDS can cause some defeated animals to subsequently fall asleep. However, the mechanisms underlying how these events trigger enhanced sleep remain elusive. Here, Xiao Yu can colleagues evaluated the brain circuits involved in SDS-induced sleep in mice.
Yu et al. discovered a small group of neurons in the ventral tegmental area (VTA) of the midbrain that is dedicated to detecting stress after SDS and inducing restorative sleep. According to the findings, a subset of gamma-aminobutyric acid (GABA)-somatostatin neurons receive stress input, which, when activated, promote enhanced REM and non-REM sleep for several hours while also inhibiting the release of corticotropin-releasing factor (CRF). Together, sleep initiated through this process alleviated stress levels and mitigated stress-induced anxiety in mice, restoring mental and body functions. Anxiety and corticotrophin levels remained heightened after stress for mice deprived of SDS-induced sleep.
In the related Perspective, Joëls and de Kloet note that "Not all individuals may respond to social defeat with a bout of sleep." They say this individual variation "requires further investigation in larger groups of mice, which would also be helpful to probe the robustness of the current explorative study."
Yu, X., et al. (2022) A specific circuit in the midbrain detects stress and induces restorative sleep. Science. doi.org/10.1126/science.abn0853.