Journal of Neuroscience, Vol 2, 623-632, Copyright © 1982 by Society for Neuroscience
Conditioned medium from cultures of embryonic neurons contains a high molecular weight factor which induces acetylcholine receptor aggregation on cultured myotubes
AE Schaffner and MP Daniels
The developmental mechanisms involved in the formation of stable arrays of
postsynaptic neurotransmitter receptors near sites of neurotransmitter
release are essentially unknown. However, several recent studies have shown
that cells or tissues of neural origin produce macromolecular factors which
induce an increase in the number of acetylcholine (ACh) receptors or the
number of receptor aggregates on cultured embryonic myotubes. We have
tested primary cultures of embryonic neurons and other cell types for the
release of an ACh receptor aggregation factor. Conditioned medium from the
cultures was applied to cultures of embryonic rat myotubes for 1 day; ACh
receptors on the myotubes were stained with tetramethylrhodamine-labeled
alpha- bungarotoxin and ACh receptor aggregation activity, defined as the
change in the number of receptor aggregates per myotube, was assayed.
Aggregation activity with a molecular weight greater than or equal to
50,000 was released by cultures of neurons from sympathetic ganglia, dorsal
root ganglia, spinal cord, and cerebellum. Little or no activity was
released by glial or other non-neuronal cultures. Release of aggregation
activity by different neuronal cell types varied by up to an order of
magnitude; however, this variation was not well correlated with the
differences in ACh synthesis. The factor(s) in neuronal cell conditioned
medium induced a rearrangement of pre-existing receptors at the cell
surface, and its action was not dependent on new protein synthesis. The
results of this study are consistent with the idea that one or more
receptor aggregation factors secreted by neurons are involved in the
organization of neurotransmitter receptors during synapse formation in
vivo.