Morphological characterization of substance P‐like immunoreactive glomeruli in the superficial dorsal horn of the rat spinal cord and trigeminal subnucleus caudalis: A quantitative study

Abstract

The aim of this work was to study the ultrastructural distribution of substance P-like immunoreactivity in laminae I and II of rat spinal cord and trigeminal subnucleus caudalis in relation to synaptic glomeruli. A bispecific monoclonal antibody directed against substance P and horseradish peroxidase was used, combining sensitive immunocytochemistry with preservation of fine ultrastructural detail. Some of the quantitative observations were carried out with an automated image analysis system. The study revealed that in lamina I of the spinal cord, almost all immunoreactive profiles counted were nonglomerular, and a considerable number of them contacted medium-size or large dendrites or were in direct contact with other vesicle-containing profiles. In ventral lamina II, 9.4% of the labeled axonal varicosities were central boutons of type I glomeruli (CI). They could be identified by their scalloped contour, number and types of peripheral profiles, reduced density of mitochondria, and localization in the dorsal horn. However, these immunoreactive glomerular CI boutons (14.1% of the total number of CI) differed statistically from the prevailing population of nonimmunoreactive CI, by being surrounded by less peripheral neuronal profiles, which established fewer synapses. In addition, they contained more than three dense-core vesicles per central profile. In the trigeminal subnucleus caudalis laminae I and II, the substance P fibers and varicosities had a plexiform orientation at the light microscopic level, which contrasted with the mainly rostrocaudal orientation of the spinal cord's lamina II plexus. However, the main ultrastructural findings were similar. These results demonstrate that substance P-like immunoreactivity occurs in a large number of type I synaptic glomeruli with specific morphological features and reinforce the current concept that the substantia gelatinosa of the spinal cord and trigeminal subnucleus caudalis are homologous structures.

Identifying local and descending inputs for primary sensory neurons

“…Yet the number of labeled spinal neurons in Trpv1-Cre RΦGT mice were 20-fold less than that observed in AvilCre RΦGT (85 versus 1,700; Table 1). Since Trpv1-Cre is expressed primarily in peptidergic nociceptive neurons, the limited labeling of spinal neurons corroborates the fact that peptidergic afferents rarely participate in synaptic glomeruli structures (5,32) and To further confirm the intraganglion spreading of rabies virus, we injected the EnvA-pseudotyped virus (EnvA-RV-GFP) into Trpv1-Cre RΦGT RΦtomato pups ( Figure 2J). In this case, Trpv1-Cre induced the expression of rabies-G, TVA receptor, and also tomato fluorescent protein in these neurons, and only these neurons can be infected by EnvA-RV-GFP (through a TVA receptor).…”

“…+ peptidergic neurons rarely participate in synaptic glomeruli structures (5,32). They instead receive inputs through volume transmission or spillover.…”

CCL2 Released from Neuronal Synaptic Vesicles in the Spinal Cord Is a Major Mediator of Local Inflammation and Pain after Peripheral Nerve Injury

“…The presence of CCL2-IR in SCVs is consistent with its continuous basal secretion from DHSC explants in both control and capsaicin-treated rats. CCL2 therefore resembles the neuropeptides detected in SCVs (Chan-Palay and Palay, 1977;Cuello et al, 1977;Ribeiro-da-Silva et al, 1989). This basal release, mobilizing preferentially SCVs, is a rather passive phenomenon independent of calcium .…”

Pathway-Specific Bidirectional Regulation of Ca2+/Calmodulin-Dependent Protein Kinase II at Spinal Nociceptive Synapses after Acute Noxious Stimulation

“…The majority of peroxidase-labeled terminals contained no or very few dense core vesicles. An important aim of the study was to investigate possible differences in CaMKII regulation between peptidergic and nonpeptidergic nociceptive fiber synapses; thus, to yield a more homogeneous sample of synapses, terminals containing more than three dense core vesicles, and therefore judged to be the central terminals of peptidergic type Ib glomeruli (Ribeiro-da-Silva et al, 1989;Ribeiro-da-Silva, 2004), were discarded from the analysis. The large majority of the remaining sampled terminals could be identified by their dark axoplasm and clear vesicles of heterogeneous size as dense sinusoid axon terminals [i.e., the central terminals of type Ia glomeruli, arising from isolectin B4-binding, nonpeptidergic C-fibers (Gerke and Plenderleith, 2004;Ribeiro-da-Silva, 2004)].…”