Afferent projections to the dorsal and ventral respiratory nuclei in the medulla oblongata of the cat studied by the horseradish peroxidase technique

Abstract

The central afferent projections to cells in the region of the dorsal and ventral groups of respiratory neurones of the medulla were studied in the cat using the retrograde axonal transport of horseradish peroxidase (HRP). HRP was injected electrophoretically either in the ventrolateral nucleus of the solitary tract (the dorsal group), or into the nucleus ambiguus and retroambigualis (the ventral group). Microelectrode recordings of the activity of the respiratory neurones in these locations were obtained prior to the iontophoretic injections of the enzyme. Projections from the parabrachial region of the pons (nucleus locus coeruleus and subcoeruleus, lateral and medial parabrachial nuclei, Kölliker-Fuse nucleus), nucleus reticularis pontis oralis, retrofacial nucleus, nucleus paragigantocellularis lateralis and ventrolateral nucleus of the solitary tract to the nucleus ambiguus and retroambigualis were identified. The ventrolateral nucleus of the solitary tract was found to receive an input from the retrofacial and lateral paragigantocellular nuclei, and to have strong reciprocal connections with the nucleus paragigantocellularis dorsalis of the medulla upon which pontine Kölliker-Fuse nucleus projects, and some of the primary respiratory and cardiovascular afferences are thought to converge.