Immunocytochemical localization of substance P receptor in rat periaqueductal gray matter: a light and electron microscopic study.
The distribution of substance P receptor (SPR) protein in the rat periaqueductal gray matter (PAG) was investigated with a polyclonal antibody in the four subdivisions obtained by cytochrome-oxidase histochemistry (Co-hi). At light microscopic analysis, immunoreactivity appeared particularly dense in the dorsal subdivision of the PAG, was less intense in the other subdivisions, and formed several longitudinally organized columns. SPR-like immunoreactivity (SP(R-i)) was localized mostly to cell bodies and dendrites of small and medium-sized neurons, which constituted about 6% of the total neuronal population of the PAG. At the electron microscopic level, SP(R-i) could be observed on postsynaptic as well as on nonsynaptic regions of both cell bodies and dendrites. A small proportion of axons (4.2%) and axon terminals (5.3%) showed SP(R-i), the majority of labeled axon terminals, amounting to about 70% of synapsing elements, formed asymmetric synapses with dendrites. Rare astroglial processes displaying SP(R-i) were also observed scattered throughout the neuropil of all PAG subdivisions. Our observations suggest that 1) also in the PAG, SP may act in a diffuse, nonsynaptic manner, probably on targets that are distant from its sites of release; and 2) SP may modulate excitatory neurotransmission acting presynaptically on those labeled axons that form asymmetric synapses.
Institute of Human Physiology, University of Ancona, Italy. fisiolum@popcsi.unian.it
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Barbaresi
D000818:Animals; D003712:Dendrites / Q000737:chemistry; D003576:Electron Transport Complex IV / Q000032:analysis; D007150:Immunohistochemistry; D008297:Male; D008853:Microscopy / Q000379:methods; D008854:Microscopy, Electron; D008928:Mitochondria / Q000201:enzymology; D009474:Neurons / Q000737:chemistry; D010487:Periaqueductal Gray / Q000737:chemistry* / Q000166:cytology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018040:Receptors, Neurokinin-1 / Q000032:analysis*
D018040:Receptors, Neurokinin-1; D003576:Electron Transport Complex IV