Decussation of bulbospinal respiratory axons at the level of the phrenic nuclei in adult rats: a possible substrate for the crossed phrenic phenomenon.

The axonal trajectories of inspiratory bulbospinal neurons were examined after deposition of the anterograde neuronal tracer phaseolus vulgaris leucoagglutinin (PHA-L) into the rostral ventral respiratory group in rats. At the level of the phrenic nucleus, PHA-L-labeled bulbospinal axons crossed the midline of the spinal cord in both the anterior gray and the anterior white commissure. These spinally decussating neurons provide a possible anatomical substrate for the respiratory reflex known as the crossed phrenic phenomenon.