The role of the dorsolateral pons in the control of expiratory duration (TE) and breathing frequency is incompletely understood. A subregion of the pontine parabrachial/Kölliker-Fuse (PB-KF) complex of dogs was identified via microinjections, in which localized pharmacologically-induced increases in neuronal activity increased breathing rate, while decreases in neural activity decreased breathing rate. This subregion is very sensitive to local and systemic opioids. The object of this study was to precisely characterize the relationship between the PB-KF subregion pattern of altered neuronal activity and the control of respiratory phase timing and the time-course of the phrenic nerve activity/neurogram (PNG). Pulse-train electrical stimulation patterns synchronized with the onset of the expiratory (E) and/or inspiratory (I) phase were delivered via a small concentric bipolar electrode while recording the PNG in decerebrate, vagotomized, dogs. Step-frequency patterns during the E-phase produced a marked frequency-dependent decrease in TE, while similar step inputs during the I-phase increased inspiratory duration (TI) by 14±3%. Delayed pulse trains were capable of pacing the breathing rate by terminating the E-phase and also of triggering a consistent stereotypical inspiratory PNG pattern, even when evoked during apnea. This property suggests that the I-phase pattern generator functions in a monostable circuit mode with a stable E-phase and a transient I-phase. Thus the I-pattern generator must contain neurons with nonlinear pacemaker-like properties, which allow the network to rapidly obtain a full on-state followed by relatively slow inactivation. The activated network can be further modulated and supplies excitatory drive to the neurons involved with pattern generation.
- control of breathing
- rhythm generation
- phrenic neurogram
- expiratory off-switch
- Copyright © 2016, Journal of Neurophysiology