Ultrastructural connectivity of [leu]5-enkephalin-immunoreactive synapses in the guinea-pig stellate ganglion: involvement of spines and triads.
The ultrastructure of [leu]5-enkephalin-immunoreactive (ENK-IR) nerve fibres in the guinea-pig stellate ganglion was studied by means of pre-embedding immunohistochemistry. ENK-immunoreactivity was primarily contained within large dense core vesicles (91 +/- 21 nm in diameter; n = 259) but was absent from small clear vesicles (47 +/- 9 nm; n = 488) within the same nerve terminal that were concentrated at presynaptic regions. Thus, fast synaptic transmission mediated by ENK-IR terminals most probably does not involve [leu]5-enkephalin which may be released parasynaptically. Evaluating a total number of 123 synapses involving an ENK-IR presynaptic nerve ending, 47% terminated upon a spine, 46% upon a dendritic shaft, and 7% directly addressed a soma of a postganglionic neuron. In 30% of axo-dendritic synapses and 33% of axo-somatic synapses, non-immunoreactive dendrites or somata being postsynaptic to an ENK-IR terminal were in direct but non-synaptic contact to another dendrite/soma. Such arrangements are termed "triads". In view of the current hypotheses concerning the function of spines and triads, these findings indicate that ENK-IR terminals within the guinea-pig stellate ganglion may be involved in the generation of long-lasting synaptic events and modulation of non-synaptic intraganglionic communication.
Asmar
R
R
Institute for Anatomy and Cell Biology, Ruprecht-Karls-University, Heidelberg, Germany.
Kummer
W
W
D000818:Animals; D001369:Axons / Q000648:ultrastructure; D015415:Biomarkers / Q000032:analysis; D004743:Enkephalin, Leucine / Q000032:analysis*; D005260:Female; D006168:Guinea Pigs; D016253:Microscopy, Immunoelectron; D009411:Nerve Endings / Q000648:ultrastructure; D009412:Nerve Fibers / Q000648:ultrastructure; D013233:Stellate Ganglion / Q000648:ultrastructure*; D013569:Synapses / Q000648:ultrastructure*
D015415:Biomarkers; D004743:Enkephalin, Leucine