Relative magnitude of tonic and phasic synaptic excitation of medullary inspiratory neurons in dogs

M. Krolo, E. A. Stuth, M. Tonkovic-Capin, F. A. Hopp, D. R. McCrimmon, E. J. Zuperku*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

33 Scopus citations


The relative contribution of phasic and tonic excitatory synaptic drives to the augmenting discharge patterns of inspiratory (I) neurons within the ventral respiratory group (VRG) was studied in anesthetized, ventilated, paralyzed, and vagotomized dogs. Multibarrel micropipettes were used to record simultaneously single-unit neuronal activity and pressure micro-ejected antagonists of GABAergic, glycinergic, N-methyl-D-aspartate (NMDA) and non-NMDA glutamatergic, and cholinergic receptors. The discharge patterns were quantified via cycle-trigger histograms. The findings suggest that two-thirds of the excitatory drive to caudal VRG I neurons is tonic and mediated by NMDA receptors and the other third is ramp-like phasic and mediated by non-NMDA receptors. Cholinergic receptors do not appear to be involved. The silent expiratory phase is produced by phasic inhibition of the tonic activity, and ≃80% of this inhibition is mediated by γ-aminobutyric acid receptors (GABA(A)) and ≃20% by glycine receptors. Phasic I inhibition by the I decrementing neurons does not appear to contribute to the predominantly step-ramp patterns of these I neurons. However, this decrementing inhibition may be very prominent in controlling the rate of augmentation in late-onset I neurons and those with ramp patterns lacking the step component.

Original languageEnglish (US)
Pages (from-to)R639-R649
JournalAmerican Journal of Physiology - Regulatory Integrative and Comparative Physiology
Issue number2 48-2
StatePublished - 2000


  • Central pattern generation
  • Control of breathing
  • Glutamatergic receptors
  • Neurotransmitters
  • γ-Aminobutyric acid receptors

ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)


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