Journal of Neuroscience, Vol 10, 3305-3312, Copyright © 1990 by Society for Neuroscience
Expression of neuropeptide-Y-like immunoreactivity begins after adrenergic differentiation and ganglionic synaptogenesis in developing bullfrog sympathetic neurons
WD Stofer and JP Horn
Department of Physiology, University of Pittsburgh, School of Medicine, Pennsylvania 15261.
Immunoreactivities for tyrosine hydroxylase (TH) and neuropeptide Y (NPY)
were studied in developing sympathetic neurons of bullfrog tadpoles and
adults. At stage III, nearly all ganglion cells are positive for TH. This
suggests early commitment to an adrenergic phenotype, the timing of which
is analogous to that reported for sympathetic neurons in birds and mammals.
During metamorphic stages and in juvenile bullfrogs, the expression of TH
becomes transiently bimodal: many neurons are intensely positive; the
remainder are faintly positive. In adult sympathetic neurons, TH expression
is more uniform. NPY first appears in a few principal neurons (less than
1%) of paravertebral ganglia 9 and 10 at stage XI. The percentage of
ganglion cells containing NPY then increases gradually, reaches adult
levels (approximately 55%) by stage XX, and persists at these levels
through metamorphosis. The development of NPY expression follows a similar
time course in paravertebral ganglion 6. Double-label experiments in late-
stage tadpoles and juvenile bullfrogs revealed that the intensely TH-
positive neurons are negative for NPY. Taken together with recent
electrophysiological data (Horn and Stofer, 1990), these results
demonstrate that the development of NPY expression begins long after the
onset of adrenergic differentiation and ganglionic synapse formation. The
present findings also show that cellular levels of TH and NPY can be
independently altered, and they suggest that the onset of NPY expression is
not linked to maturation of peripheral targets, but rather to some more
global event operating synchronously along the rostro-caudal axis.