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.
Ma
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Department of Pharmacology and Therapeutics, McGill University, Montréal, Québec, Canada.
Ribeiro-da-Silva
A
A
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