The connections between the dorsal raphe nucleus and other nuclei in the CNS were studied with Nauta degeneration method and HRP retrograde transport method.After dorsal raphe nucleus had been lesioned the degenerating efferent fibers could be divided into dorsal, intermediate and ventral groups. Via the dorsal group the ascending fibers passed through the periaqueductal gray matter and terminated in the substantia grisea centralis, substantia grisea periventricularis, and substantia grisea paraventricularis of the ventricularis tertius. The intermediate group, lying in the raphe of tegmental and reticular formation, was projected to the mesencephalic reticular formation, substantia nigra bilaterally. The ventral group, passing through the area tegmentalis ventralis, medial forebrain bundle (MFB), zona inserta, was projected to the lateral hypothalamic region, thalamus and telencephalon.The descending projections mainly from the intermediate and ventral groups, could be traced in the lateral region of the periaqueductal gray. The degenerating fibers passed through the ventral aspect of tegmentum along both sides of the raphe, and finally continued to the lower brain stem, and the dorsal horn of spinal cord.In the lower brain stem, the descending degenerated fibers terminated in the nucleus raphe pontis, nucleus raphe magnus, nucleus raphe pallidus, nucleus raphe obscurus, nucleus reticularis tegmenti pontis, nucleus reticularis gigantocellulari, nucleus reticularis paramedianus, nucleus olivaris inferior accessoris medialis, and nucleus tractus spinalis nervi trigemini.After the injection of HRP into the dorsal raphe nucleus, labelled neurons were found in forebrain structures, consisting of nucleus periventricularis, nucleus anterior medialis thalami,nucleus habenularis lateralis,nucleus anterior hypothalami,nucleus dorsomedialis hypothalami, nucleus preopticus medialis, nucleus mamillaris lateralis, ventral tegmental area of Tasi, zona inserta, nucleus supraopticus, and nucleus interpeduncularis. Below the level of injection site, labeled neurons were found in substantia nigra (zona reticularis and compacta), periaqueductal gray, nucleus interpeduncularis, locus coeruleus, nucleus tegmenti dorsalis, nucleus centralis superior, nucleus raphe pontis, nucleus raphe magnus, and nucleus reticularis lateralis.

Studies of the afferent connections of the nucleus accumbens in 56 rats were carried out by retrograde transport method of horseradish peroxidase (HRP). The microinjection or microiontophoretic delivery was performed either through ipsilateral vertical or through contralateral oblique approach into the nucleus. Labelled neurons were found in nucleus caudatus and putamen, nucleus septi lateralis, nucleus amygdaloideus basalis lateralis, nucleus periventricularis thalami, nucleus paratenialis, periventricular gray hypothalami, nucleus medialis thalami, nucleus reuniens, substantia nigra and area ventralis tegmenti (Tsai) in all cases. In addition, the HRP labelled neurons were observed in the cinguIate gyrus, hippocampus, nucleus parafascicularis, nucleus anterior thalami, nucleus dorsal raphe and interpeduncular nucleus in most cases.