The ultrastructural localization of enkephalin and substance P immunoreactivities in the nucleus tractus solitarii of the cat.
In the medial and commissural subdivisions of the nucleus tractus solitarii enkephalin and substance P immunoreactivities were localized within synaptic terminals, unmyelinated axons, and neuronal cell bodies. Both enkephalin and substance P immunoreactivities were contained within synaptic terminals which had a mixture of small clear vesicles and dense core vesicles. The presence of dense core vesicles within both the enkephalin- and substance P-immunoreactive terminals was a consistent feature, although they were not associated with the actual synaptic junction. While enkephalin- and substance P-immunoreactive terminals shared a similar morphology, their respective distributions along the dendritic tree were quite distinct. Enkephalin-immunoreactive terminals contacted mainly the cell body and proximal portions of the dendritic tree. In contrast, substance P-immunoreactive terminals synapsed predominantly with spines and shafts of small to medium-sized dendrites. Few substance P-immunoreactive terminals contacted proximal dendrites and they were never presynaptic to the neuronal cell body. This apparent segregation of synaptic terminals on neurons suggests that enkephalin synapses have a more pronounced effect than substance P terminals.
Maley
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BE
D000818:Animals; D002415:Cats; D004744:Enkephalin, Methionine / Q000378:metabolism; D004745:Enkephalins / Q000378:metabolism*; D007124:Immunoenzyme Techniques; D008526:Medulla Oblongata / Q000378:metabolism* / Q000648:ultrastructure; D008854:Microscopy, Electron; D013373:Substance P / Q000378:metabolism*; D013572:Synaptic Vesicles / Q000378:metabolism
D004745:Enkephalins; D013373:Substance P; D004744:Enkephalin, Methionine