Analysis of concerted sleep control through populations of GABAergic neurons of PZ and VLPO brain regions

• Applicant: Professor Dr. Henrik Bringmann
• Subject Area: Cognitive, Systems and Behavioural Neurobiology
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 530307129

Sleep is a fundamental physiological state in all animals that possess a nervous system. Sleep is essential and disorders of sleep are widespread in modern societies posing an unmet medical and economical problem. Across different species, sleep is induced by sleep-active neurons. These neurons activate specifically during sleep and induce this state by shutting down wakefulness and arousal circuits. Several centers exist in the mammalian brain that contain sleep-active neurons. Populations of GABAergic sleep-active neurons in the Parafacial Zone (PZ) and Ventrolateral Preoptic area (VLPO) are important for NREM sleep induction. The impairment of GABAergic neurons in the PZ and VLPO causes a reduction but not complete removal of sleep. A major unsolved question in the sleep field is how different populations of GABAergic neurons act together to generate a global sleep state. Also, it has been challenging in the past to generate mouse models of severe sleep loss. Such mouse models of severe sleep loss would be tremendously helpful in studying severe insomnia. We hypothesize that GABAergic neurons in the PZ and VLPO act mostly in parallel circuits to shut down different brain wakefulness areas. If this hypothesis is true, double ablation of GABAergic neurons in the PZ and the VLPO will result in severe loss of sleep that is larger than the sleep loss obtained by ablation or inhibition of GABAergic neurons in only one of these key brain regions. In order to test this hypothesis, we will ablate or inhibit GABAergic neurons of the PZ and VLPO separately and in combination. This will be achieved by injection of an Adeno-Associated Virus (AAV) vector expressing either 1) a Cre-dependent Diphtheria Toxin A (DTA) or 2) a chemogenetic inhibitor into the PZ and VLPO of a transgenic mouse that expresses Cre recombinase only in GABAergic neurons. Thus, only GABAergic neurons of the PZ and VLPO will be affected. We will then characterize sleep amount and quality in these mice with an electroencephalogram analysis during undisturbed sleep and during sleep deprivation, and will also investigate gene expression in the cerebral cortex. Together these experiments will reveal whether two major NREM-promoting brain regions, the populations of GABAergic Neurons of the PZ and VLPO, act through a series or parallel circuit for sleep induction. Thus, these results will provide an important step forward in understanding how GABAergic sleep circuits act concertedly for sleep induction. Also, the double ablation/inhibition of both GABAergic neurons in the VLPO and PZ might provide an animal model that will allow to study the consequences of severe sleep loss, and might thus constitute an important model to study the mechanisms of sleep.

• DFG Programme: Research Grants