Amygdala-preB?tzinger Complex Monosynaptic Connections for Breathing Depression

About This Grant

PROJECT SUMMARY The amygdala is present in all vertebrate animals because it influences common behaviors that pertain to threat assessment in the natural world (as well as fear, pain, and reward). Neuroscience well understands how the amygdala interacts with neocortical, subcortical and midbrain sites. However, potential links between the amygdala and brainstem respiratory control sites remains mysterious. This proposal will address that knowledge gap by examining how the central amygdala exerts inhibitory control over the breathing core oscillator site, the preBötzinger complex (preBötC) of the lower medulla. Output from the amygdala largely depends on GABAergic neurons of its central subdivision (CeA). Rhythmic breathing movements depend inexorably on the preBötC. Therefore, a CepreBötC projection would be inhibitory and therefore potentially able to perturb or stop breathing. That microcircuit might be important. Why? First, perceived threats, like the presence of a predator, cause arousal in conjunction with arrest of locomotion. Sometimes freezing behavior is accompanied by bradycardia and diminished breathing: bradypnea or apnea. Whereas the microcircuits for vigilance, locomotor arrest and bradycardia are well understood, the mechanisms that diminish breathing are unknown. We propose an explanation that involves – at least in part – CeA neurons that directly inhibit the preBötC. Second, SUDEP (sudden unexpected death in epilepsy) may occur when seizures invade the lateral or basolateral amygdala, which connect to the much smaller CeA and cause long-lasting apneas. Seizure-induced apneas suspend oxygen delivery yet paradoxically fail to cause panic, dyspnea or air hunger in human patients. We hypothesize that seizures invading the lateral or basolateral amygdala activate the CeA preBötC inhibitory pathway, which can stop breathing. The first Aim of the project tests the hypothesis that CeA GABAergic neurons project directly to excitatory preBötC neurons by installing Cre-dependent optogenetic proteins in CeA neurons of VgatCre adult mice and studying the biophysical properties of their synaptic drive onto core preBötC neurons in adult brainstem slice preparations. The second Aim tests that hypothesis that CepreBötC inhibitory synapses can transiently diminish and/or stop breathing. In this context, we photostimulate the CeA with a graded range of intensities during breathing behavior in awake intact adult mice to evaluate its ability to perturb and/or fully stop breathing. Although we acknowledge that the Aims are adversely interdependent, the abundant pilot data in support of Aim 1 make it unlikely to fail and thus undercut Aim 2. This project will reveal a heretofore unknown microcircuit between 2 key nuclei: the central amygdala and the preBötC. Their connection may help explain ethological behaviors like threat assessment common to all mammals and SUDEP (rare but fatal), which can be leveraged for treatment and prevention strategies.