BRAINSTEM RESPIRATORY NEURON INTERACTIONS

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The long term goal of this research is to elucidate the neural mechanisms for mammalian respiratory rhythmogenesis and its modulation. The more immediate and realizable aim of this proposal is the detection and evaluation of interactions among brainstem respiratory neurons. Available data suggest the widely held hypothesis that the respiratory rhythm is an emergent property of a neural network located in the brainstem. While rhythmic activity can be generated by the medulla alone, interactions among respiratory neurons of the pons and medulla are thought to play an essential role in the generation of the eupneic respiratory rhythm. Defining the functional interactions among the various types of respiratory related neurons of the pons and medulla is a necessary step in the process of elucidating the mechanism of mammalian respiratory rhythmogenesis. The interpretation of data from single unit, stimulation, anatomical and lesioning studies requires an understanding of such interactions. Interactions among respiratory related neurons of the medulla (n. tractus solitarius, n. ambiguus, n. retorambigualis, retrofacial n., n. paragigantocellauris lateralis) and pons (Kolliker-Fuse n., n. parabrachialis medialis) will be studied in paralyzed, anesthetized or decerebrate cats ventilated with a phrenic triggered respirator. The activities of several neurons in two or more nuclei will be simultaneously recorded with six microelectrodes. The phase relationship of each neuron's activity to phrenic motoneuron activity, responses to changes in lung volume, and when appropriate, axonal projections will be determined. Conventional neurophysiological techniques, including statistical (e.g., cross-correlation) analysis of extracellularly recorded spike trains, microstimulation and spike triggered averaging methods, will be used to detect and evaluate the functional significance of connections among the observed neurons during the respiratory cycle. Our experiments may support current hypotheses or lead to new ideas. In either case they should contribute not only to our understanding of respiratory rhythmogenesis and its modulation, but also to the broader issue of centrally generated motor programs in the mammalian nervous system.