Development of the cyto- and chemoarchitectural organization of the rat nucleus of the solitary tract

The nucleus of the solitary tract (NST) is the major visceral sensory nucle us in the brainstem. The development of the rat nucleus of the solitary tra ct was followed during late prenatal and early postnatal life in order to d etermine when subnuclear organization and chemoarchitectural features devel op. In Nissl-stained sections, the nucleus of the solitary tract becomes vi sible as a distinct cluster of cells by about E17. Between E17 and E19, a p rofound change in the Nissl-stained appearance of the nucleus occurred, so that by E19 all the subnuclei were discernible. Acetylcholinesterase activi ty in the developing NST showed an early period of rapid differentiation (E 15 to E17), while by E19 the basic adult pattern of distribution of this en zyme had already been achieved. The subnuclei of the NST began to show clea r differential staining for nicotinamide adenine fiucleotide phosphate diap horase at about the same time as reactivity for that enzyme first appeared (E19). With respect to calbindin- and calretinin-immunoreactive neurons wit hin the nucleus, many of the chemoarchitectural features associated with th ese two markers were obvious even by late fetal life. For example, in the c entral subnucleus, a strongly labelled, dense population of calbindin-immun oreactive neurons was present from E17, while in calretinin-immunoreacted m aterial. this subnucleus was prominent because of its immunonegativity also from E17. Nevertheless, the total number of calbindin- and calretinin-immu noreactive neurons in the NST did not peak until late postnatal life. Tyros ine hydroxylase immunoreactive neurons were visible from E15, began differe ntiation by E17 and were distributed in a similar pattern to the adult from E19. Substance P immunoreactivity in the NST was also very similar to the adult pattern by E19, Many of these immunochemical and histochemical marker s indicate a similar pattern of development, i.e. a rapid period of differe ntiation until E19, by which time a relatively stable adult-like pattern ha s been attained. The present findings indicate that many of the cyto- and c hemoarchitectural features of this nucleus are present well before birth, b y which time the nucleus must serve vitally important functions such as rel aying information for control of respiration and the circulation.