Origins of excitatory drive within the respiratory network: anatomical localization.

This study identified several sources of excitatory drive within the rat brain stem respiratory network. Excitatory neuronal projections to the ventral respiratory group (the largest brain stem respiratory neuron population in the rat) were identified by selective retrograde labeling with tritiated aspartate. Neurons were labeled within portions of the nucleus of the tractus solitarius, the region of the ventral respiratory group, superficial to the facial nucleus, the medullary raphe nuclei and the parabrachial/Kölliker-Fuse nuclei. These findings are the first anatomical demonstration of sources of excitatory drive within the respiratory network, and are consistent with electrophysiological data localizing a source of excitatory drive within the pre-Bötzinger complex subdivision of the ventral respiratory group.