Contribution of Gigantocellular neurons of the medullar reticular formation to awakening from a low brain activity state

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 DESCRIPTION (provided by applicant): Neuromodulation is a promising novel methodology deployed to improve the conditions of thousands of patients whose consciousness is impaired after brain injury. Attempts at neuromodulation using deep brain stimulation (DBS) have targeted a number of loci in the brain arousal pathways such as the thalamus, mesencephalon and cervical cord. However, recovery following single location stimulation remains modest, especially in comatose patients. Although some of these pathways can trigger awakening from sleep or light planes of anesthesia upon activation are insufficient to promote arousal from a deeper arousal state like coma. Furthermore, selective damage to one of these regions, even bilateral, rarely results in permanent unconsciousness. Interpretation of these results suggests that arousal pathways are redundant however, they are not functionally interchangeable. While this implies that the full complement of arousal from a deep arousal state requires coordination of multiple pathways, the mechanism through which this coordination is achieved by the brain is poorly understood. We aim to overcome this challenge uncovering novel neuronal circuits that promote wakefulness through basic research. Considering that medullary reticular neurons project to arousal- modulating areas throughout the brain, integrate a broad range of sensory and autonomic inputs, and fire in response to salient stimuli in close association with the initiation of behaviors, we modulated their activity during a pharmacologic induced coma (PIC). Our results showed that activation of an area located at the anterior border of the nucleus gigantocellularis (aNGC)- elicited robust cortical, autonomic and motor arousal during a state of PIC. To understand how this small subpopulation of neurons exerts such widespread activational effects on arousal, we analyzed immunolabeling of c-Fos-a well-established marker of neuronal activation-following pharmacologic activation of aNGC neurons. C-Fos labeling was sparse and largely limited to structures known to participate in arousal including rhombenchephalon (locus coeruleus and parabrachial nucleus); mesencephalon (periaqueductal gray and ventral tegmental area); diencephalon (intralaminar thalamic nuclei as well as posterior and anterior hypothalamus); and basal forebrain. These findings suggest that aNGC is able to recruit these pathways to trigger arousal from a dense PIC. This proposal characterizes aNGC as a new site to promote arousal from a coma-like state and proposes recruitment of multiple arousal pathways through aNGC as new mechanism to produce widespread activational state resulting in wakefulness. Using extracellular in vivo recordings and innovative technology like optogenetic functional magnetic resonance imaging (ofMRI) we will dissect the circuitry involved in aNGC- stimulated arousal and we will visualize the dynamics of multi-area activation. Results of this study will uncover novel mechanisms leading to new approaches for emerging treatments for patients under coma state.