Optogenetic perturbation of preBötzinger Complex inhibitory neurons modulates respiratory pattern

Inhibitory neurons make up a significant fraction of the neurons within the preBötzinger Complex (preBötC), a site critical for mammalian eupneic breathing. The role of glycinergic preBötC neurons in respiratory rhythmogenesis in mice was investigated by optogenetically-targeted excitation or inhibition. Channelrhodopsin-2 (ChR2) or Archaerhodopsin (Arch) was expressed in glycinergic preBötC neurons of glycine transporter 2 (GlyT2)-Cre mice. In ChR2-transfected mice, brief inspiratory-phase bilateral photostimulation targeting the preBötC prematurely terminated inspiration, whereas expiratory-phase photostimulation delayed the onset of the next inspiration. Prolonged photostimulation produced apneas lasting as long as the light pulse. Inspiratory-phase photoinhibition in Arch-transfected mice during inspiration increased tidal volume without altering inspiratory duration, whereas expiratory-phase photoinhibition shortened the latency until the next inspiration. During persistent apneas, prolonged photoinhibition restored rhythmic breathing. We conclude that glycinergic preBötC neurons modulate inspiratory pattern and are important for reflex apneas but that the rhythm can persist after significant dampening of their activity.