Journal of Neurophysiology, Vol 58, Issue 2 288-299, Copyright © 1987 by APS
Neonatal synapse elimination in the rat submandibular ganglion: effect of retarded target growth
M. D. Womble and S. Roper
Department of Anatomy, University of Colorado Health Sciences Center, Denver 80262.
1. We have studied synapse elimination in the submandibular ganglion of
neonatal rats to determine the effects of retarded target growth on
synaptic development. Neurons of this ganglion provide parasympathetic
innervation to the submandibular and sublingual salivary glands. 2.
Ligating the main salivary ducts 2-4 days after birth at a point where
nerve fibers were not damaged reduces gland weight by 55% during the 2nd wk
after birth and 80% by adulthood. 3. In control animals, the average number
of preganglionic inputs/neuron normally declines steadily during the first
few weeks after birth, before stabilizing during the 5th wk at the control
adult level. Between birth and adulthood, the number of ganglionic neurons
increases by 150%. 4. Ganglia from duct-ligated animals showed an
acceleration in the process of synapse elimination. Input number in
experimental ganglia reached the control adult level during the 3rd wk
after birth. This acceleration is confined solely to ganglia that innervate
the underdeveloped glands. 5. The loss of inputs was not further enhanced
by prolonged target atrophy. Thus average input numbers to neurons of 5th
wk or adult experimental ganglia were not different from age-matched
control values. 6. No differences from control values were seen in most
cases for resting potentials, input resistances, or cell size. However, the
increase in neuron number was retarded in experimental animals, and the
number of synapses/neuronal profile was reduced in the adult animals. 7.
Thus subnormal target growth leads to an acceleration in the process of
synaptic elimination in neonatal rats. This acceleration may be mediated by
alterations in the level of trophic factors emanating from the target.
