Development of the human nucleus of the solitary tract: a cyto- and chemoarchitectural study.

The present study investigated the prenatal development of the cyto- and chemoarchitecture of the human nucleus of the solitary tract from 9 to 35 weeks, by using Nissl staining and immunoreactivity to calbindin, calretinin, tyrosine hydroxylase and GAP-43. The nucleus began to gain heterogeneity and show different subnuclei as early as 13 weeks, and approached cytoarchitectural maturation from 21 to 25 weeks. The subnuclear division pattern observed in the fetal nucleus of the solitary tract at 25 weeks was very similar to that of the adult. Neurons immunoreactive to calbindin first appeared in the medial gastrointestinal area of the nucleus at 13 weeks, particularly within a putative gelatinosus subnucleus, while calretinin immunoreactivity during fetal life suggested the possible presence of a central subnucleus. Tyrosine hydroxylase immunoreactive neurons were seen in the medial subdivisions of the nucleus of the solitary tract as early as 13 weeks, but the population continued to increase until 25 weeks. Strong GAP-43 immunoreactivity was also present in the nucleus of the solitary tract at 13 weeks, especially in the dorsolateral and commissural subnuclei, while at 21 weeks there was a significant decline of GAP-43 expression. Results from the chemoarchitectural study showed that the human nucleus of the solitary tract expressed various neurochemical substances at an early developmental age (13 weeks), even before cellular and neuropil maturation was fully attained. Expression of these factors may play an important role in establishment and integration of viscerosensory function in the nucleus.