Journal of Neuroscience, Vol 9, 167-174, Copyright © 1989 by Society for Neuroscience
Ultrastructural analysis of substance P-immunoreactive nerve fibers in myenteric ganglia of guinea pig small intestine
IJ Llewellyn-Smith, JB Furness and M Costa
Department of Anatomy, School of Medicine, Flinders University, Bedford Park, South Australia.
Electron microscopic immunocytochemistry has been used to study the
distribution and synaptic relationships of substance P (SP)- immunoreactive
nerve fibers in ultrathin sections from whole-mount preparations of
myenteric ganglia from guinea pig small intestine. At the light microscopic
level, myenteric ganglia stained for ultrastructural study contained dense
arrays of SP-immunoreactive nerve fibers around and between the neuronal
and glial cell bodies. At the electron microscopic level, SP-containing
nerve fiber profiles occurred throughout the neuropil of the myenteric
ganglia. Both vesicle- containing and nonvesiculated nerve fiber profiles
were immunoreactive. The positive vesiculated profiles contained variable
proportions of small clear and large granular vesicles. Two-thirds of the
vesicle- containing nerve fiber profiles in myenteric ganglia were
immunoreactive for SP. Many vesiculated SP-immunoreactive nerve fiber
profiles were directly apposed to each myenteric neuron. However, only
about 0.6% of these vesiculated profiles formed synapses that showed the
ultrastructural specializations of vesicle clustering presynaptically and
fuzzy electron-dense material on the postsynaptic membrane. On the other
hand, morphologically identifiable synapses with SP-immunoreactivity
comprised about half the total number of synapses in the ganglia.
SP-immunoreactive synapses were observed on nonvesiculated nerve processes
in the periphery of the ganglia and on nerve cell bodies. Most of the
axosomatic SP synapses occurred on small neurons that lay either on the
surfaces of the ganglia or near the fibers of the internodal strands where
they traveled through the ganglia. Both SP-positive and SP-negative nerve
cell bodies received SP synapses.(ABSTRACT TRUNCATED AT 250 WORDS)