The Roles of Genetically Distinct Cortical Neuron Types in General-Anesthesia- and Sleep-Induced Slow Waves

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Project Summary/Abstract. Reversible loss of consciousness is a crucial part of two major medical fields: general anesthesia and sleep. General anesthetics and non-rapid-eye-movement (NREM) sleep both induce slow waves (0.1-4 Hz) in the cortical electroencephalogram (EEG). It is unknown whether slow waves generated with different anesthetic agents and during NREM sleep are generated with the same neural circuit activity. Dr. Melonakos’ preliminary data suggests that anesthetic agents with different molecular targets have distinct slow wave mechanisms (Aim 1 Hypothesis). In addition, although dexmedetomidine anesthesia shares neural circuits with NREM sleep, it may also have distinct direct cortical effects, possibly leading to different slow wave activity (Aim 2 Hypothesis). The purpose of this research is to test these hypotheses by mapping cortical neural activity with respect to the EEG slow waves of both anesthesia and NREM sleep. In order to do this, Dr. Melonakos will learn how to perform calcium imaging experiments in freely behaving rodents. He will then record calcium images from Ca2+/calmodulin-dependent protein kinase IIa-positive (CaMKIIa+), parvalbumin-positive (PV+), somatostatin-positive (SST+), and vasoactive intestinal peptide-positive (VIP+) cortical neurons during anesthesia- and sleep-induced slow waves. Propofol, ketamine, and dexmedetomidine anesthesia will be tested. Dr. Melonakos will then compare the neural activity between the anesthetics and between general anesthesia and sleep. Finally, he will identify the role of SST+ neurons in slow waves (Aim 3 Hypothesis) by (1) looking at the activity of cortical neurons following disruption of slow waves by stimulation of the parabrachial nucleus, an arousal area in the brainstem, and (2) inhibiting SST+ neurons during anesthesia- and sleep-induced slow waves. During the K99 phase of this project, Dr. Melonakos will be mentored by Drs. Christa Nehs and Emery Brown, experts in anesthesia and sleep neurocircuitry and faculty at Harvard Medical School, Massachusetts General Hospital (MGH), and Massachusetts Institute of Technology (MIT). Dr. Melonakos will also collaborate with Drs. Michael Hasselmo (Boston University), Nancy Kopell (Boston University), and Daniel Aharoni (University of California, Los Angeles). He will be trained in calcium imaging by Drs. Hasselmo and Aharoni, and statistical analysis by Dr. Brown. Dr. Kopell will guide Dr. Melonakos as he orients his findings within hypothesized slow wave mechanisms from the field of computational neuroscience. Dr. Melonakos will also learn optogenetics stimulation techniques from Dr. Nehs and in a course at MIT. The mentors, collaborators, and other members of the MGH community will also provide him with professional guidance as he nears independence, including training in grant writing, peer review, teaching, and the faculty job search. The scientific and professional training Dr. Melonakos receives will enable him to develop an independent research program to study anesthetics’ direct vs. indirect effects. The resulting understanding of slow wave mechanisms has potential to improve the protocols used to monitor general anesthesia and treat sleep disorders, thus benefiting patient safety and health.