J Neurosci 7: 2493-501 (1987)
Growth and morphogenesis of an autonomic ganglion. I. Matching neurons with
target.
R. D. Heathcote & P. B. Sargent
Regulation of the number and size of neurons presumably plays a role in the
matching of a group of neurons to their target. In this paper the relationship
of the cardiac ganglion neurons of the frog to their target is examined.
Neurons in this ganglion first appear in the embryo and continue to accumulate
for several months, even after the animal has completed metamorphosis, and
eventually reach a fixed number of cells in the adult. This prolonged period of
neuron production has provided an opportunity to manipulate development and
test various mechanisms of neuronal regulation. Manipulation of animal culture
conditions and hormone levels has shown that the addition of neurons to the
ganglion continues up to the characteristic adult number and depends upon
neither the chronological age nor the developmental stage of the animal. The
size of neurons also changes markedly during development. The average cell body
size initially decreases due to the addition of many smaller cells to the
ganglion. After metamorphosis neuron size increases dramatically. The changes
in size and number complement one another such that the total volume of
neuronal cell bodies increases in proportion with the size of both the target
and the entire body. The relationship holds for changes in animal size that
extend over 4 orders of magnitude and follows a power function of the form y =
bxm. Regulation of cardiac ganglion size can be divided into 3 overlapping
phases: (1) the arrival of neurons and precursors from the neural crest, (2) an
increase in neuron number, (3) and an increase in neuron size. A common
denominator for all phases is that the size of the ganglion is, in a coherent
way, precisely matched to the size of its target.