Brain Stem Circuit Operations during Baroreceptor Modulation of the Motor Pattern for Breathing

Abstract

Circuit operations in the raphe‐pontomedullary network for breathing remain incompletely understood (Nuding et al. J Neurophysiol 101: 2943, 2009; Lindsey et al., Physiology, 33: 281, 2018). Current models for baroreceptor tuning of the respiratory motor pattern include parallel raphe‐ventral respiratory column (VRC) “push‐pull” circuits for regulation of respiratory phase timing and inspiratory drive (Lindsey et al. J Physiol, 512: 863, 1998; Segers et al. J Neurophysiol 113: 352, 2015). To extend prior work, we tested the hypothesis that inter‐regional loop circuits among neurons of the VRC, pons, and raphe nuclei have altered activities appropriate for roles in the tuning of respiratory drive and rhythm during changes in systemic arterial blood pressure. In 7 decerebrate vagotomized neuromuscular‐blocked cats, we used multi‐electrode arrays to record the activities of VRC (n=88), pontine (n=87), and raphe (n=188) neurons during baroreceptor‐evoked perturbations of breathing, as measured by altered peak activity in integrated efferent phrenic nerve activity and changes in respiratory phase durations. Blood pressure was transiently (30 sec.) elevated or reduced by inflations of an embolectomy catheter in the descending aorta or vena cava, respectively. Trials were separated by 1.5‐min intervals to allow the mean systemic arterial pressure to return to pre‐stimulus levels. Spike trains of 10,530 pairs of neurons were evaluated for changes in firing rate and short‐time scale correlational signatures indicative of functional connectivity. The results include evidence for: (i) baroreceptor modulation of a VRC‐pontine inspiratory off‐switch loop; (ii) a VRC inspiratory neuron chain disinhibitory microcircuit for baroreceptor tuning of the drive to breathe that operates in parallel with VRC tonic expiratory (t‐E) “hub” neurons; (iii) multiple push‐pull control pathways between baroresponsive raphe assemblies and the VRC t‐E neurons; (iv) divergent paths from the VRC to raphe circuits, including routes through the pons. Overall, the results provide additional support for parallel chain and loop operations in the brain stem network that controls breathing (Morris et al. J Neurophysiol 119:700, 2018).Support or Funding InformationSupport: NIH Grant NS19814 and Common Fund OT2OD023854.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.