Fourth ventricular tanycytes: a possible relationship with monoaminergic nuclei

Tanycytes were found in discrete areas on the floor of the fourth ventricle of the developing and adult rabbit. The apical surfaces of the somas extended into the fourth ventricle and the shafts extended into the substance of the rhombencephalon. Shafts from midline tanycytes on the floor of the caudal fourth ventricle entered nuclei raphe obscurus and pallidus and shafts from midline tanycytes on the floor of the rostral fourth ventricle entered nuclei raphe dorsalis and centralis superior. These four raphe nuclei all contained serotonergic neurons and formed dendrite bundles in association with the tanycyte shafts. Shafts of tanycytes on the medial floor of the fourth ventricle entered nucleus intercalatus, and shafts of tanycytes on the lateral floor of the fourth ventricle entered locus coeruleus. Both of these nuclei contained noradrenergic cell bodies. The tanycyte shafts terminated only in these monoaminergic nuclei and did not extend to the pial surface of the ventral brain stem. We suggest that these tanycytes constitute a possible transport system for substances between the cerebrospinal fluid of the fourth ventricle and monoaminergic nuclei of the brain stem, in a role similar to that proposed for tanycytes of the median eminence.