Studying rhythmogenesis of breathing: comparison of in vivo and in vitro models

In all mammalian species; breathing is controlled by a neuronal network wit hin the lower brainstem. A component known as the ventral respiratory group produces rhythmic activity, which is transmitted to spinal motoneurons to produce a periodic contraction of respiratory muscles. A dispute about the mechanisms of 'normal' respiratory rhythm generation arose from the differe nces between experimental preparations that have been used to dissect the p rocess. It is,therefore, essential to compare the various experimental appr oaches and to discuss the differences between experimental data. We conclud e that the various preparations all have great value, but that they define different operational conditions of the network, including maturation of ne urons and synaptic processes. We have taken note of these in formulating a 'maturational network-burster model' for rhythm generation that includes mo st features of the existing models of respiratory rhythm generation.