The projections to the nucleus ambiguus (Amb) were examined by means of the anterograde and retrograde axonal transport of wheat germ agglutinin -horseradish peroxidase (WGA-HRP) in 89cats. The existence of direct projections from the bilateral nucleus of the tractus solitarius (nTS) (except the rostral portion), the contralateral Amb, the contralateral reticular formation around Amb, the ipsilateral nucleus parabrachialis (nPB) (mainly the nucleus parabrachialis lateralis) and the lateral and

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... entrolateral parts of the bilateral periaqueductal gray (PAG) to Amb was identified. On the other hand, nTS, nPB and PAG were connected to each other directly. Descending fibers from the orbital gyrus to nTS and nPB were observed. Direct neuron connections between the dorsal, ventral lateral cortical bank of the cruciate sulcus (the pericruciate cortex) and PAG were also recognized. However, no cortical fibers directly connected to Amb were determined in this study.