Paucity of dorsal inspiratory neuron collateral projections to ventral inspiratory neurons

The inspiratory region of the ventral respiratory group was mapped in six Nembutal anaesthetized cats. Records multi-unit activity were taken in five or six locations at 0.5 mm spacings. These locations were then used as stimulating sites to test for the antidromic activation of 40 bulbospinal, inspiratory neurons recorded in the ipsilateral, dorsal respiratory group. Only four (10%) were antidromically activated. In a single anatomical experiment, rhodamine labelled microspheres were injected into the ventral group, and Flurogold was injected into the contralateral spinal cord. No neurons in the dorsal group were found to be double-stained. It was concluded that, ipsilateral collaterals from inspiratory dorsal group neurons to the inspiratory region of the ventral group are rare.