Bötzinger-complex, bulbospinal expiratory neurones monosynaptically inhibit ventral-group respiratory neurones in the decerebrate rat

Extracellularly recorded action potentials from 49 Bötzinger-complex, bulbospinal expiratory neurones were used as triggers to compute 162 spike-triggered averages (STAs) of intracellular potentials recorded from 167 respiratory neurones in the ventral respiratory group (VRG) near the obex in 15 vagotomized, paralysed, ventilated and decerebrated rats. All of the Bötzinger-complex expiratory neurones were antidromically activated from the ipsilateral border between the C2/C3 segments of the spinal cord and discharged only during the late part of expiration with an augmenting pattern. We found evidence for monosynaptic inhibitory post-synaptic potentials (IPSPs) in 74 (approximately 44%) of the STAs computed using 34 (approximately 69%) of the trigger neurones. For vagal motoneurones, IPSPs were found in 24 of the 53 STAs of expiratory motoneurones, but in none of the 12 STAs of inspiratory motoneurones. For inspiratory neurones, IPSPs were found in 23 of the 33 STAs of bulbospinal neurones and in 6 of the 26 STAs of not antidromically activated (NAA) neurones. For expiratory neurones, IPSPs were found in one of the two STAs of bulbospinal neurones and in 20 of the 36 STAs of NAA neurones. We conclude that Bötzinger-complex, bulbospinal expiratory neurones monosynaptically inhibit bulbospinal inspiratory neurones, expiratory vagal motoneurones and other unidentified inspiratory and expiratory neurones in the VRG of rats during the late part of expiration.