Optogenetic stimulation of Dbx1 neurons enhances the respiratory‐sympathetic coupling in in vivo CIH mice

Abstract

Under resting conditions, breathing is generated by synchronized activity of a complex respiratory network located in the ventral respiratory column in the brainstem. The preBötzinger Complex (preBötC), critical for generating the inspiratory phase of breathing, contains glutamatergic neurons derived from progenitor cells that are characterized by the transcription factor “developing brain homeobox (Dbx1)”. These neurons are thought to be important for inspiratory rhythmogenesis. Excitatory and inhibitory synaptic inputs from the respiratory networks modulate the sympathetic outflow which is generated by presympathetic neurons from the rostroventrolateral medulla (RVLM). Changes in the respiratory-sympathetic coupling contribute to imbalances as demonstrated in chronic intermittent hypoxia (CIH). To investigate the contribution of Dbx1 neurons in the respiratory-sympathetic coupling, we used an optogenetic in vivo mouse preparation previously exposed to CIH for 10 -12 days (5% O2 – 80 bouts/day). The ventral surface of the brainstem in spontaneously breathing, anaesthetized (Urethane 1.5mg/kg) Dbx1-ERT2Cre/Ai32 adult mice was exposed and an optical fiber positioned bilaterally over the preBötC, while recording the hypoglossal (HN), cervical vagus (cVN) and cervical sympathetic nerves (cSN). Our preliminary data indicate that CIH exposure increased the respiratory frequency and mean sympathetic activity in the baseline conditions. Random light stimulation (200ms) of preBötC Dbx1 neurons (~ 9mV, 447nm) significantly promoted inspiratory activity, increasing the respiratory frequency and amplitude of HN and cSN in relation to baseline in both groups. During optogenetic stimulation of Dbx1 neurons, the respiratory-sympathetic coupling was enhanced in both groups, without significant difference in variability of cSN amplitude. This is possibly due to the increase in mean cSN activity under baseline conditions in CIH mice. Our data demonstrates that stimulation of preBötC Dbx1 neurons aids in regulation of autonomic control modulating the cSN activity, leading to increased sympathetic drive and hypertension in the CIH.