Optogenetic stimulation of Dbx1 neurons promote increase in sympathetic activity in vivo

Abstract

Under resting conditions, breathing is characterized by inspiration and postinspiration. Located in the ventrolateral medulla, the preBötzinger Complex (pre‐BötC) is critical for generating the inspiratory phase of breathing. This microcircuit contains glutamatergic neurons derived from progenitor cells that are characterized by the transcription factor “developing brain homeobox (Dbx1)”, and that are thought to be important for inspiratory rhythmogenesis. Located rostromedial of the preBötC is the so called postinspiratory complex (PiCo), which seems to be critical for the generation of the postinspiratory phase of breathing. Important for generating the postinspiratory phase are glutamateric‐cholinergic PiCo neurons. At resting conditions, sympathetic and parasympathetic activity is modulated by excitatory and inhibitory synaptic inputs from these respiratory networks. It is thought that changes in the respiratory‐sympathetic coupling contribute to imbalances that lead to hypertension, as demonstrated in various animal models of chronic intermittent hypoxia. Here we combine optogenetic and electrophysiological approaches in vivo and in vitro in order to investigate the respiratory‐sympathetic coupling. Spontaneously breathing Dbx1‐ERT2Cre/Ai32 and ChAT‐Cre/Ai32 (ChR2) adult mice were anaesthetized (Urethane 1.5mg/kg), and the ventral surface of their brainstem exposed in order to place an optical fiber bilaterally over the pre‐BötC and/or PiCo, while recording the hypoglossal (HN), cervical vagus (cVN) and cervical sympathetic nerves (cSN). Our preliminary data indicate that continuous light stimulation (10s) of pre‐BötC Dbx1 neurons (~ 9mV, 447nm) significantly increased the respiratory frequency, the amplitude of HN, cSN and cVN in relation to baseline. During the optogenetic stimulation of Dbx1 neurons the respiratory‐sympathetic coupling was enhanced. Using the in vivo approach as well as in vitro horizontal slices we are currently also characterizing the role of PiCo in regulating this coupling under control conditions and following CIH. Our preliminary data suggest that PiCo activity is enhanced following CIH exposure, which also contributes to the regulation of respiratory‐sympathetic coupling. Unraveling how the respiratory microcircuits regulate autonomic control will be critical to understand how CIH leads to increased sympathetic drive and hypertension.Support or Funding InformationFAPESP (2016/23513‐1; 2019/11969‐2), and the NIH: P01 HL090554, R01 HL144801 and R01 HL126523