PONTINE RESPIRATORY NEURONS IN ANESTHETIZED CATS

The pontine respiratory neurons (PRG) in the 'pneumotaxic centre' have been hypothesized to contribute to phase-switching of neural respirat ory activity, especially in terminating inspiration. To define the neu ral elements involved in phase-switching, we recorded respiratory neur ons extra- and intracellularly in anesthetized cats with an intact cen tral nervous system. In total, 54 neurons were recorded: 49 neurons wi th activity modulated by central respiratory rhythm (20 inspiratory, 1 7 postinspiratory and 12 expiratory) and 5 neurons with activity corre lated to tracheal pressure. The recorded neurons were clustered in dor solateral pontine tegmentum within the Kolliker-Fuse (KF) subnucleus o f the parabrachial nuclei. Stable intracellular membrane potential was recorded in 11 of the 49 respiratory neurons (8 postinspiratory, 1 ea rly inspiratory and 2 inspiratory). During continuous injection of chl oride ions (n = 6), synaptic noise increased and IPSPs reversed, inclu ding a wave of IPSPs during stage-2 expiration in postinspiratory neur ons. Further, relative input resistance varied through the respiratory cycle such that the least input resistance occurred during the neuron 's (n = 5) quiescent period. No IPSPs nor EPSPs were evoked in pontine respiratory neurons by vagal stimulation. In conclusion, various type s of respiratory neurons were recorded in the KF nucleus. Prominent ex citatory and inhibitory postsynaptic activities were similar to those described for medullary neurons. These pontine respiratory neurons do not appear to receive a strong afferent input from the vagus. Rather, vagal afferent inputs seem to be directed towards non-respiratory neur ons that are located more medially in the dorsal pens.