Substance P- and GABA-like immunoreactivities are co-localized in axonal varicosities in the superficial laminae of cat but not rat spinal cord.
In the present study, we applied a combination of pre-embedding peroxidase-based immunocytochemistry and post-embedding immunogold staining to examine the synaptic interactions of substance P (SP) and gamma-aminobutyric acid (GABA) in the superficial laminae of the dorsal horn of cat and rat spinal cord. We demonstrate for the first time the co-existence of SP and GABA immunoreactivities in axonal boutons in laminae I-III of cat spinal dorsal horn. In cat, most SP + GABA immunoreactive (IR) axonal boutons established synapses with SP-IR or non-IR dendrites. These synapses were exclusively symmetric. Quantitative analysis showed that the percentage of SP/GABA double labelled bouton profiles was higher (7%) in lamina I but was considerably lower in laminae IIo, IIi and III. Similarly, the density (number of bouton profiles per 100 microns2) of SP + GABA-IR bouton profiles was highest in lamina I. However, in agreement with previous studies, the co-localization of SP and GABA immunoreactivities was never detected in the rat dorsal horn. In both species, SP + GABA-IR or GABA-IR axonal bouton profiles were never seen presynaptic to SP-IR boutons. These findings provide a morphological basis for the interaction of excitatory and inhibitory agents in the nociceptive circuits in the dorsal horn of the cat and rat spinal cord.
Department of Pharmacology and Therapeutics, McGill University, Montréal, Québec, Canada.
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Ribeiro-da-Silva
D000818:Animals; D001369:Axons / Q000378:metabolism* / Q000648:ultrastructure; D002415:Cats; D003712:Dendrites / Q000378:metabolism / Q000648:ultrastructure; D007150:Immunohistochemistry; D008297:Male; D008854:Microscopy, Electron; D051381:Rats; D017208:Rats, Wistar; D017661:Receptors, Presynaptic / Q000378:metabolism; D013116:Spinal Cord / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D013373:Substance P / Q000378:metabolism*; D013569:Synapses / Q000378:metabolism / Q000648:ultrastructure; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D017661:Receptors, Presynaptic; D013373:Substance P; D005680:gamma-Aminobutyric Acid