1 Project Summary 2 3 Vagal nerve stimulation (VNS) therapy is approved for three central nervous system disorders. Despite promising 4 preclinical evidence of success amelioration of heart failure, several large patient trials have failed to meet 5 designated endpoints. Remarkably many recommended clinical protocols for VNS therapy appear to violate 6 strong preclinical evidence as well as approved therapies that rely on vagal afferent activation of central nervous 7 mechanisms. Low intensities of clinically tolerated VNS activate myelinated vagal afferents and these activate 8 neurons within the nucleus of the solitary tract (NTS). Preclinical data on vagal NTS neurons outline multiple 9 mechanisms controlling successful vagal transmission but indicate that current clinical VNS protocols likely 10 engage substantial frequency dependent transmission depression within NTS. Our global hypothesis is that VNS 11 drives central nervous system (CNS) pathways that contribute to beneficial therapeutic outcomes. Our goals are 12 to identify the mechanistic basis for processes contributing to optimal VNS therapy. Activation of the CNS by 13 VNS requires successful activation of action potentials in NTS neurons. We found that midcollicular knife cuts 14 eliminate pathways above the medulla and profoundly reduced VNS activation of NTS neurons. Our work will 15 examine the contribution of the paraventricular nucleus of the hypothalamus (PVN). Our experimental design 16 assays cellular mechanisms of NTS activation in brain slices as well as single NTS neurons in intact animals. 17 Hypotheses related to PVN will center on potential mechanisms of NTS modulation including roles for the 18 neuropeptides, vasopressin and oxytocin. New optogenetic experiments will incorporate transfections of PVN 19 neurons that are activated by VNS to expression ChR2 or halorhodopsin to control these neurons via light. Our 20 Aims focus on weak-intensity, vagal afferent activation of the CNS. Our approach relies on our direct assays of 21 NTS neuron activation – both in the intact brain as well as brain slice, intracellular recordings of NTS in vitro. We 22 propose Specific Aims supported by Preliminary Results that will identify the mechanisms for amplification and 23 spread of VNS excitation. Aim 1 focuses on potential mechanisms within NTS with emphasis on vagal timing 24 and synaptic depression while Aim 2 assesses mechanisms related to PVN modulation of NTS neurons with a 25 particular focus on oxytocin and vasopressin. Aim 3 assesses vagal afferent transmission in heart failure animals. 26 Aim 4 evaluates the therapeutic efficacy of VNS to relieve heart failure in a rat model. This proposal embraces 27 an assessment of whether optimizing activation of NTS neurons will enhance VNS efficacy in a heart failure 28 model. This work addresses a fundamental knowledge gap of neuromodulation therapy. Greater knowledge of 29 visceral afferent processing should drive new stimul...