DIFFERENTIAL PROJECTIONS TO THE RAPHE NUCLEI FROM THE MEDIAL PARABRACHIAL-KOLLIKER-FUSE (NPBM-KF) NUCLEAR-COMPLEX AND THE RETROFACIAL NUCLEUS IN CATS - RETROGRADE WGA-HRP TRACING (VOL 45, PG 241, 1993)

After injection of wheat germ agglutinin-conjugated horseradish peroxi dase (WGA-HRP, 2 X 30 nl) into the nucleus raphe magnus (NRM) of 6 cat s, a number of retrogradely labelled neurons were observed in the rost ral pons, mainly in the pontine pneumotaxic area, i.e., the medial par abrachial and Kolliker-Fuse (NPBM-KF) nuclear complex, and the tegment al field. In addition, a cluster of labelled cells was observed in the retrofacial nucleus (RFN) and its adjacent areas in the medulla. Cont rol injections of the same volume of WGA-HRP into the medullary magnoc ellular tegmental field (2 mm lateral to the NRM) resulted in a much l ower number of labelled neurons in the areas described above, and the labelled cells in the tegmental fields were predominant ipsilateral to the injected side. Injections into the nucleus raphe pallidus caudal to the NRM resulted in a diffuse distribution of labelled neurons, mai nly in the tegmental fields of the pons and medulla. This study demons trates that the NRM receives specific convergent projections from the NPBM-KF complex and the RFN in the medulla. It is suggested that these pathways are involved in the control of respiration.