Reflections on respiratory rhythm generation.

Knowledge about neuronal mechanisms that control respiration is being advanced rapidly by studies that make use of both mature in vivo animals and in vitro neonates. The available data suggest that particular types of neurons within selected networks of the ventrolateral medulla are essential for respiratory rhythm generation. There are many uncertainties, however, about the correspondence between neurons identified by the above two approaches, because there are virtually no studies that have combined them. In this chapter, I propose a hypothesis that shows how neonatal respiratory neurons, with either retained or modified intrinsic cellular properties, develop into mature, well-characterized respiratory neurons located in medullary areas called the Bötzinger and pre-Bötzinger complex. Currently, the most plausible models of respiratory rhythmogenesis are hybrid ones that include both intrinsic cellular and network properties.