Synaptic interactions between respiratory neurons during inspiratory on-switching evoked by vagal stimulation in decerebrate cats.
To elucidate neuronal mechanisms underlying phase-switching from expiration to inspiration, or inspiratory on-switching (IonS), postsynaptic potentials (PSPs) of bulbar respiratory neurons together with phrenic nerve discharges were recorded during IonS evoked by vagal stimulation in decerebrate and vagotomized cats. A single shock stimulation of the vagus nerve applied at late-expiration developed an inspiratory discharge in the phrenic neurogram after a latency of 79+/-11 ms (n = 11). Preceding this evoked inspiratory discharge, a triphasic response was induced, consisting of an early silence (phase 1 silence), a transient burst discharge (phase 2 discharge) and a late pause (phase 3 pause). During phase 1 silence, IPSPs occurred in augmenting inspiratory (aug-I) and expiratory (E2) neurons, and EPSPs in postinspiratory (PI) neurons. During phase 2 discharge, EPSPs arose in aug-I neurons and IPSPs in PI and E2 neurons. These initial biphasic PSPs were comparable with those during inspiratory off-switching evoked by the same stimulation applied at late-inspiration. In both on- and off-switching, phase-transition in respiratory neuronal activities started to arise concomitantly with the phrenic phase 3 pause. These results suggest that vagal inputs initially produce a non-specific, biphasic response in bulbar respiratory neurons, which consecutively activates a more specific process connected to IonS.
Haji
A
A
Department of Pharmacology, Faculty of Medicine, Toyama Medical and Pharmaceutical University, Japan. mp04ah@ms.toyama-mpu.ac.jp
Okazaki
M
M
Takeda
R
R
D000818:Animals; D001933:Brain Stem / Q000502:physiology; D002415:Cats; D003655:Decerebrate State / Q000503:physiopathology*; D004558:Electric Stimulation; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology*; D005260:Female; D008297:Male; D008526:Medulla Oblongata / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D009433:Neural Inhibition / Q000502:physiology; D010791:Phrenic Nerve / Q000502:physiology; D011930:Reaction Time / Q000502:physiology; D015656:Respiratory Mechanics / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology; D014630:Vagus Nerve / Q000502:physiology*