Afferent projection to the retrotrapezoid nucleus from respiratory related structures in the brainstem of rabbit--a retrograde CB-HRP tracing study.

Experiments were performed on 10 adult rabbits. After microinjection of cholera toxin B-subunit conjugated horseradish peroxidase (CB-HRP) into the retrotrapezoid nucleus (RTN), retrogradely labeled neurons were mainly observed in the Kölliker-Fuse nucleus (KF), the medial parabrachial nucleus (PBM) and the lateral parabrachial nucleus (PBL). A few labeled neurons were also observed in the ventrolateral solitary tract nucleus, the ambiguus and retroambiguus nuclei, and the ventromedial area of retrofacial nucleus. Labeled terminal fibers were mainly observed in the retrofacial nucleus, the ambiguus and retroambiguus nuclei, the ventrolateral area of solitary tract nucleus, and the PBL-PBM-KF. The above results show that the RTN has axonal connections with the pontine and medullary respiratory related structures.