MODULATION OF THE SYNAPTIC DRIVE TO RESPIRATORY PREMOTOR AND MOTOR-NEURONS

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.