Ultrastructural development of raphe nuclei in the bat (Myotis myotis)

The development and ultrastructural features of the raphe nuclei of Microchiroptera Myotis myotis have been studied. Fetuses of different ages, newborn, young and adult bats were examined. Important fetal features were abundant mitoses and an incomplete cytokinesis between daughter cells. A medialward migration of reticular formation neurons was observed. The migration began in the third week of intrauterine life and continued through the sixth week of intrauterine life. In six-week-old fetuses it was possible to distinguish neuronal groups, although the delineation of borders for specific raphe nuclei was still arbitrary. Two types of neurons were distinguished at this stage and at all later stages, and both were present at all levels of the raphe complex. In the nine-week-old fetus the eight raphe nuclei were well-delineated. Newborn bats showed a great increase in cytoplasmic organelles and, also, in the myelination of neuronal fibers. No essential differences between young and adult bats were found.