Interrelationship Between Dorsal and Ventral Respiratory Groups

The precise interactions between the DRG and VRG remain unclear. Earlier studies indicated that inspiratory neurons of the DRG projected to the VRG, but a reciprocal connection was not apparent. These studies suggested that the central pattern generator was composed only of inspiratory cells and was located in the DRG. In this view, the DRG was the prime mover in the genesis of the respiratory rhythm, dominating the cells in the VRG and governing their activity. More recent studies indicate that cells from the VRG (Bötzinger complex) may inhibit inspiratory neurons in the DRG. Ablation experiments eliminating either the entire DRG or the Bötzinger complex in the VRG do not eliminate rhythmogenesis, indicating that substantial redundancy is present in the system.
The functional significance of the interconnections between groups of inspiratory cells in the DRG and VRG is also unclear. These interconnections may serve to synchronize the timing of neuronal firing in anatomically separate locations. For example, midline incisions through the medulla are associated with asynchronous firing of the two phrenic nerves.