Optogenetic stimulation of C1 neurons activates breathing in mice

Abstract

The C1 neurons regulate sympathetic tone and blood pressure, contribute to glucose homeostasis and regulate the CRF/ACTH/glucocorticoid cascade. Here, we tested whether the C1 cells also regulate respiration. We used a mouse line in which the Cre recombinase is expressed by dopamine‐beta hydroxylase synthesizing neurons. A Cre‐dependent AAV2 that expresses ChR2‐mCherry under promoter ef1‐alpha was injected unilaterally into the C1 region. The transgene was exclusively expressed by C1 neurons (>98% co‐localization with TH‐ir somata). We found that mouse C1 neurons express VGLUT2. Their projections were indistinguishable from those of the rat and included several regions involved in breathing regulation (pre‐Botzinger complex, retrotrapezoid nucleus, dorsal parabrachial and locus coeruleus). Photostimulation of the ChR2‐expressing C1 neurons with 473nm laser light (30 s; 5–20Hz; 1–10 ms pulses) increased diaphragm EMG frequency and/or amplitude in anesthetized mice (N=7) and increased breathing frequency in unanesthetized mice (N=7; plethysmography). These observations indicate that the C1 neurons have reciprocal connections with the respiratory network. They imply that breathing stimulation elicited by hypotension (barorespiratory reflex), carotid body stimulation, central hypoxia and nociception could also be partially relayed via C1 neurons. Support: HL 028785.