The characteristics of GABAergic inhibitory modulation of respiratory
bulbospinal neuronal activity and short-term potentiation (STP) of phr
enic motoneuronal activity were studied. Extracellular unit recording
and picoejection techniques in anesthetized dogs showed that both the
spontaneous rhythmic and reflexly induced discharge patterns of inspir
atory (I) and expiratory (E) premotor neurons were proportionately amp
lified by the localized application of picomole amounts of bicuculline
(Bic), a competitive GABA(A) antagonist. Intracellular recording and
paired-pulse stimulation techniques in anesthetized rats demonstrated
an STP of phrenic motor output that appears to be mediated by NMDA rec
eptors and is associated with facilitation of EPSPs and prolonged depo
larization of individual phrenic motoneurons. We speculate that both G
ABAergic gain modulation of premotor neuronal activity and NMDA-mediat
ed STP of phrenic activity may be neural substrates which are involved
with the optimization of respiratory and non-respiratory behaviors, v
ia adaptive and/or differential control of breathing. (C) 1997 Elsevie
r Science B.V.