Journal of Neuroscience, Vol 13, 801-807, Copyright © 1993 by Society for Neuroscience
Neurogenesis and differentiation of sympathetic B and C cells in the bullfrog tadpole
WD Stofer and JP Horn
Department of Physiology, University of Pittsburgh, School of Medicine, Pennsylvania 15261.
The relation between birthdates of sympathetic neurons and their subsequent
differentiation into cutaneous B cells and vasomotor C cells was examined
in paravertebral ganglia 9 and 10 of the bullfrog tadpole. Neurons
undergoing terminal cell division were identified by injecting tadpoles
repeatedly with 5'-bromodeoxyuridine (BRDU) for one to six developmental
stages between III and XXI. After allowing the tadpoles to enter late
metamorphic stages (XX-XXV), the ganglia were double immunostained for BRDU
and neuropeptide Y (NPY). NPY is a marker for mature C-type neurons (Horn
et al., 1987). Double-labeled neurons were readily discerned through use of
distinct black and brown HRP reaction products and also because
immunoreactivity for BRDU was localized in nuclei while that for NPY was
localized in perinuclear cytoplasm. Counts of labeled cells showed that
neurogenesis occurs throughout limb bud and paddle stages, and that it
ceases during early foot stages (XII- XIV), a time coinciding with the
onset of NPY expression. By contrast, the labeling of non-neuronal
satellite cells with BRDU was most common weeks later during metamorphic
stages. Irrespective of their birthdates, about half of the BRDU-labeled
neurons were also positive for NPY immunoreactivity. This proportion of
NPY-positive cells is indistinguishable from that in the entire adult
ganglia (Horn et al., 1987). In addition to establishing that neurogenesis
and gliogenesis occurs during tadpole stages, the results indicate that the
onset of NPY expression by vasomotor C neurons is unrelated to their time
of origin. In other words, the last wave of neurogenesis in sympathetic
ganglia does not give rise to a specific subclass of sympathetic neurons.