Ultrastructural features of rat arcuate nucleus neurons during pregnancy.

: The ultrastructure of the arcuate nucleus was studied in Sprague-Dawley rats sacrificed at 7, 10, 14 and 20 days of gestation, using conventional techniques of electron microscopy. Our results revealed an increase in granular filamentous bodies and whorled bodies that appear in arcuate neurons as early as on the 7th day of gestation. A further increase of these structures was showed by day 10 and, especially, by day 14. In the arcuate nucleus of rats sacrificed on day 14 of gestation, some compact, homogeneous and very large (up to 5.5 microm diameter) granular filamentous bodies may be seen both in neuronal bodies and in dendrites. In some neurons of arcuate nucleus of these gestational phases (days 10 and 14), besides the whorled bodies dense-core vesicles were found. Neurons with cilia were occasionally observed, and some neuronal bodies were in close apposition and joined by intercellular bridges. Open synapses were observed during all the gestational phases. The smallest number of these synapses was seen in the arcuate nucleus of rats sacrificed on day 14 of gestation.