Ontogeny of caudal fourth ventricular tanycytes in the rabbit brain: a Golgi study

A Golgi study of the floor of the caudal fourth ventricle in the developing and adult rabbit brain stem revealed the presence of several clusters of tanycytes. These tanycytes possessed ciliated apical surfaces and basal shafts extending into the substance of the medulla and pons where they intermingled with specific neuronal fields. These shafts ended in the serotonergic nuclei raphe obscurus and pallidus, and the noradrenergic locus coeruleus and nucleus intercalatus (group A2). The tanycyte shafts extended into the medullary midline early in ontogeny (day 18 of gestation), following which the neurons of the raphe began to sprout neurites. These shafts then formed the underlying structure for a large medullary dendrite bundle. These shafts developed extensive spines during early neonatal ontogeny, which then diminished in number through adulthood. the tanycyte shafts extending into locus coeruleus and nucleus intercalatus developed later in ontogeny than the midline shafts, just before birth. These shafts also persisted into adulthood in close relationship with the monoamine neurons. We suggest that the tanycytes on the floor of the fourth ventricle may take up substances from the CSF and transport them to the region of the monoamine nuclei where the shafts terminate, in a manner similar to median eminence tanycytes. The early development of shafts from fourth ventricular tanycytes suggests a possible regulatory role for these cells over the neuritic sprouting and maturation of the monoaminergic nuclei.