GABAergic neurons in Kölliker-Fuse nucleus and Bötzinger complex with axons projecting to phrenic nucleus.

Experiments were made on 6 adult cats. Brainstem neurons that project to the phrenic nucleus were retrogradely labeled by microinjection of WGA-HRP into phrenic nucleus. The brainstem sections were doubly processed for HRP histochemical staining with the TMB-Co-DAB method, and GABA immunohistochemical staining with anti-GABA primary antibody and FITC conjugated immunofluorescent secondary antibody. HRP-FITC double-labeled neurons were observed in the pontine Kölliker-Fuse nucleus and areas around the retrofacial nucleus (Bötzinger complex). Double-labeled neurons were also observed in the raphe nucleus, the lateral paragigantocellular nucleus, and the vestibular nucleus. The results show that brainstem GABAergic neurons in these structures, especially those in the Kölliker-Fuse nucleus and the B?t.C, send axonal projections to the phrenic nucleus.