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Localization and projection to the phrenic (PH) nucleus were studied in a sample of premotor neurons that directly projected to hypoglossal motoneurons (XII Mns) and showed respiratory-related patterns of activity. The experiments were carried out in cats, under pentobarbital anesthesia. In the first part of the study, the retrograde double-labeling technique was used to reveal the existence of neurons projecting to both the XII and the PH nuclei. Injection of a fluorescent dye (fast blue, FB) into the XII nucleus and another (nuclear yellow, NY) into the PH nucleus retrogradely labeled, with either FB or NY, medullary reticular neurons mainly in the regions ventrolateral to the nucleus of the tractus solitarius (vl-NTS), ventrolateral to the hypoglossal nucleus (vl-XII), and dorsomedial to the nucleus ambiguus (dm-AMB) bilaterally. In addition, some neurons in these regions were labeled with both FB and NY. In the …