The Journal of Neuroscience, April 1, 2001, 21(7):2380-2392
Formation and Function of Synapses with Respect to Schwann Cells
at the End of Motor Nerve Terminal Branches on Mature Amphibian
(Bufo marinus) Muscle
Greg T.
Macleod,
Paul A.
Dickens, and
Max R.
Bennett
The Neurobiology Laboratory, Department of Physiology and Institute
for Biomedical Research, University of Sydney, NSW 2006 Australia
A study has been made of the formation and regression of synapses
with respect to Schwann cells at the ends of motor nerve terminal branches in mature toad (Bufo marinus) muscle.
Synapse formation and regression, as inferred from the appearance
and loss of
N-(3-triethylammoniumpropyl)-4-(4-(dibutylamino)styryl) pyridinium dibromide (FM1-43)-stained vesicle clusters, occurred at
the ends of terminal branches over a 16 hr period. Multiple microelectrodes placed in an array about FM1-43 blobs at the ends of
terminal branches detected the electrical signs of neurotransmitter being released onto receptors. Injection of a calcium indicator (Oregon
Green 488 BAPTA-1) into the motor nerve with subsequent imaging of the
calcium transients, in response to stimulation, often showed a reduced
calcium influx in the ends of terminal branches. Injection of a
fluorescent dye into motor nerves revealed the full extent of their
terminal branches and growing processes. Injection of the terminal
Schwann cells (TSCs) often revealed pseudopodial TSC processes up to
10-µm-long. Imaging of these TSC processes over minutes or hours
showed that they were highly labile and capable of extending several
micrometers in a few minutes. Injection of motor nerve terminals with a
different dye to that injected into their TSCs revealed that terminal
processes sometimes followed the TSC processes over a few hours. It is
suggested that the ends of motor nerve terminals in vivo
are in a constant state of remodeling through the formation and
regression of processes, that TSC processes guide the remodeling, and
that it can occur over a relatively short period of time.
Key words:
synapses; Schwann cells; motor nerve; formation; regression; Bufo marinus
Copyright © 2001 Society for Neuroscience 0270-6474/01/2172380-13$05.00/0