ABSTRACT
The efferent projections of the rostral ventrolateral medulla(RVL) to the hypothalamic paraventricular nucleus(Pa) and the thoracic cord were studied in the adult cat by using WGA-HRP or fluorescent retrograde tract-tracing method. After injection of WGA-HRP or fluorescent tracer Fast blue(FB) into one side of the Pa, retrogradely labelled cells were found in bilateral RVL, with an ipsilateral predominance. The labelled cells decreased in number from the caudal to the rostral level. After injection of FB into one side of the thoracic cord at T_2-T_3 segments, retrogradely labelled cells in the RVL were observed which increased in number from the caudal to the rostral level and reached the peak at 1.0-1.5mm caudal to the trapezoid body. Most of these cells were distributed in the ipsilateral RVL, and clustered in the region 0.0-1.0mm from the ventral surface of the medulla. After Diamino yellow 2HC1 and FB were injected into the Pa and the thoracic cord respectively, only single labelled cells were detected in the RVL, no double labelled cells were found. The above results suggest that the Pa and the thoracic cord receive separate fiber projections from different cells of the RVL.
