Organization of the pneumotaxic oscillator in the cat.

The present series concerns the topographical organization of pneumotaxic neurons within the nucleus parabrachialis medialis and adjacent structures according to their respiratory subtype. Results presented were obtained from 1000 units recorded in a region 2.5 mm in height, 1.5 mm in width and 2.5 mm in length. During penetration in the postero-lateral part (mainly in Kolliker-Fuse nucleus) inspiration related cells were found almost exclusively. Phase-spanning inspiratory-expiratory neurons largely predominated in the central core of nucleus parabrachialis medialis. A large majority of expiratory cells was recorded at the antero-medial border of the nucleus. In the intervening regions, clusters of 6 to 10 cells of the inspiratory-expiratory (IE) type alternated with similar clusters of either inspiratory- or expiratory neurons. Phase-spanning expiratory-inspiratory (EI) neurons were mainly found in the intermediary positions between phase-spanning IE and either inspiratory or expiratory columns. A two dimensional reconstruction of pneumotaxic organization is presented and a tentative model of the oscillator is advanced.