Ultrastructural localization of substance P immunoreactivity in the ventral horn of the rat spinal cord

Abstract

At the light microscope level, the minute concentrations of substance P (SP) in rat spinal ventral horn can be visualized best by amplification with the double bridge PAP method of Vacca et al. (1975; 1980) in 5 microns paraffin tissue sections. Morphologically, the immunoreactive sites resemble punctate bodies. They occur in close apposition with the large ventral horn cells and their associated neuronal processes. By the Sternberger PAP procedure, we now describe these punctate bodies at the electron microscope level. Ultrastructurally, they appear as tiny boutons (terminal and preterminal) and small unmyelinated processes. The boutons and processes typically contain one to several immunolabeled dense core vesicles among many immunolabeled clear vesicles. They range in size near the limit of resolution of the light microscope (LM), thereby justifying further the use of LM amplification staining by the double bridge method. The immunolabeled boutons often synapse with large smooth dendrites (which may originate from motoneurons) by asymmetrical or symmetrical synaptic densities. Their synaptic densities appear immunostained as well. The data support the view that the electrophysiological action of SP in the ventral horn occurs in part by synaptic action along the processes of the ventral horn cells. Other mechanisms of action are considered for the peptide as well. Additional types of membrane specializations (synaptoid junctions) and SP neural circuits are described below.

Substance P and 5-hydroxytryptamine immunoreactive presynaptic boutons on presumed .ALPHA.-motoneurons in the chicken ventral horn.

“…VACCA et al (1982) observed in the rat that in the SP immunoreactive bouton, dense cored vesicles were largely circular in profile, though some appeared ellipsoid in shape. In the present study, SP immunoreactivity was confined to the bouton containing spherical dense cored vesicles and spherical clear vesicles.…”

“…At the electron microscopic level, DE LANEROLLE and LAMOTTE (1982) immunoreactivity was observed in "S" (agranular spheroid vesicles) and "G" (densecore vesicles) type boutons in the human and monkey ventral horns, while VACCA et al (1982) reported that in the rat dense cored vesicles were largely circular, though a few appeared ellipsoid in shape. Thus, these two reports are not consistent with each other in detail.…”

Synaptic Control of Motoneuronal Excitability

“…Raphe premotor neurons are either serotonergic (265) or nonserotonergic (1161). Substance P (134,209,495), thyrotropin-releasing hormone (TRH) (134,471), enkephalinlike peptides (134,397,497,531,723), cholecystokinin (792), neurokinin A (907), galanin (41), and glutamate or aspartate (908) colocalize with 5-HT (based on immunohistochemistry) in neuronal cell bodies in the caudal raphe and medial reticular formation, as well as in fibers and terminals in the ventral horn of the spinal cord (39,41,42,133,575,576,907,908,1034,1237,1297,1348). Peptidergic immunoreactivity largely disappears from the inputs to motoneurons after destruction of serotonergic neurons with neurotoxins such as 5,6-dihydroxytryptamine (426,576).…”

Morphological characterization of substance P receptor‐immunoreactive neurons in the rat spinal cord and trigeminal nucleus caudalis

“…Numerous studies have demonstrated supraspinally derived substance P in the ventral horn, and electron microscopic studies have identified SP-immunoreactive inputs to spinal motoneurons (de Lanerolle et al, 1982;Vacca et al, 1983). Furthermore, iontophoresis of SP modifies the responses of motoneurons in vivo (Krivoy et al, 1980) and excites them after bath application in vitro (Otsuka and Yanagisawa, 1980).…”