Mechanisms of EEG and Cardiovascular Arousal

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In obstructive sleep apnea (OSA), patients repeatedly lose ainway motor tone during sleep, resulting in collapse of the airway and apnea. This results in hypoxia, hypercarbia, and increased respiratory effort, until there is an arousal in which the ainway patency is restored. The EEG arousal causes sleep fragmentation and the autonomic arousal causes increased sympathetic tone, which may have deleterious long term cognitive and cardiovascular consequences, but the mechanisms for these arousals are not know. In Project 1, we hypothesize that glutamatergic neurons in the parabrachial nucleus (PB) and adjacent precoeruleus region (PC) play a key role in causing EEG and autonomic arousals during obstructive sleep apnea OSA. In Specific Aim 1, we will test whether the glutamatergic neurons in the PB/PC that show Fos-activation during repeated brief episodes of hypercarbia during sleep project to key forebrain targets for producing EEG arousal (hypothalamus, thalamus, basal forebrain, amygdala, prefrontal cortex) and key brainstem targets for producing autonomic arousal, by combining retrograde tracing with Fos immunohistochemistry and vesicular glutamate transporter 2 (VGLUT2) in situ hybridization. In Specific Aims 2 and 3, we determine the effects of deleting glutamatergic transmission in subsets of these VGLUT2+ PB/PC neurons, respectively on EEG and autonomic (HR, ECG power spectrum) arousal. We will do this by using VGLUT2 conditional knockout mice and adeno-associated viral vectors (/VAV) containing the genes for Cre recombinase and Green Fluorescent Protein (GFP). We will inject the AAV-Cre/GFP into the PB/PC, deleting VGLUT2 expression and glutamate transmission from subsets of PB/PC neurons, and correlate this with the EEG (duration of arousal, high frequency/low frequency EEG power) and the ECG (HR, low frequency/high frequency ECG power) consequences on arousals during repeated brief C02 exposures. We will then trace the projections from the affected PB/PC neurons with GFP, and determine which targets are critical for the alterations that are seen. These studies will help in deciphering the brain circuitry causing EEG and autonomic arousals during OSA, and in designing interventions to minimize its cognitive and cardiovascular consequences.