Immunohistochemical, Histochemical and Radioassay Analysis of Nitric Oxide Synthase Immunoreactivity in the Lumbar and Sacral Dorsal Root Ganglia of the Dog

Co-localization of nociceptive markers in the lumbar dorsal root ganglion and spinal cord of dromedary camel

Nociceptive markers in mice have been identified in two distinct peptidergic and nonpeptidergic neurons in the dorsal root ganglion (DRG) and distributed in different laminae of the dorsal horn of the spinal cord. Recently, however, a study in humans showed a significant overlapping in these two populations. In this study, we investigated the distribution of various nociceptive markers in the lumbar DRG and spinal cord of the dromedary camel. Immunohistochemical data showed a remarkable percentage of total neurons in the DRG expressed IB4 binding (54.5%), calcitonin gene-related peptide (CGRP; 49.5%), transient receptor potential vanilloid 1 (TRPV1; 48.2%), and nitric oxide synthase (NOS; 30.6%). The co-localization data showed that 89.6% and 74.0% of CGRP- and TRPV1-labeled neurons, respectively, were IB4 positive. In addition, 61.6% and 84.2% of TRPV1- and NOS-immunoreactive neurons, respectively, were also co-localized with CGRP. The distribution of IB4, CGRP, TRPV1, substance P, and NOS immunoreactivities in the spinal cord were observed in lamina I and outer lamina II (IIo). Quantitative data showed that 82.4% of IB4-positive nerve terminals in laminae I and IIo were co-localized with CGRP, and 86.0% of CGRP-labeled terminals were co-localized with IB4. Similarly, 85.1% of NOS-labeled nerve terminals were co-localized with CGRP. No neuropeptide Y (NPY) or cholecystokinin (CCK) immunoreactivities were detected in the DRG, and no co-localization between IB4, NPY, and CCK were observed in the spinal cord. Our results demonstrate marked convergence of nociceptive markers in the primary afferent neurons in camels, which is similar to humans rather than the mouse. The data also emphasizes the importance of interspecies differences when selecting ideal animal models for studying nociception and treating chronic pain.

Distribution pattern of dorsal root ganglion neurons synthesizing nitric oxide synthase in different animal species

The main aim of the present review is to provide at first a short survey of the basic anatomical description of sensory ganglion neurons in relation to cell size, conduction velocity, thickness of myelin sheath, and functional classification of their processes. In addition, we have focused on discussing current knowledge about the distribution pattern of neuronal nitric oxide synthase containing sensory neurons especially in the dorsal root ganglia in different animal species; hence, there is a large controversy in relation to interpretation of the results dealing with this interesting field of research.

Immunohistochemical characterization of TH13-L2 spinal ganglia neurons in sheep (Ovis aries)

Spinal ganglia (SG) neurons are commonly classified according to various specific features. The most widespread classification based on morphological and ultrastructural features subdivides SG neurons into light and small dark neurons. Using immunohistochemical, histochemical and lectin methods, it is possible to further subdivide the small dark neurons into two subpopulations: peptidergic and nonpeptidergic neurons. The majority of studies on SG neurons were carried out on mice and rats; there are few or no studies on large mammals. In this study, some of the widely used neuronal markers, neurofilament 200 kDa (NF200), substance P (SP), calcitonin gene-related peptide (CGRP) and isolectin B4 (IB4), were employed to characterize neuronal nitric oxide synthase (nNOS)-immunoreactivity (-IR) in sheep (Ovis aries) SG (Th13-L2) neurons. The majority of the SG neurons were IB4-labeled (79 +/- 10%), followed by NF200- (45 +/- 4%), NOS- (44 +/- 10%), SP- (42 +/- 5%) and CGRP-IR (35 +/- 7%) neurons. The triple staining experiments showed that a higher percentage (75 +/- 16%) of NOS-IR neurons bound both IB4 and CGRP, or both IB4 and SP (49 +/- 6%). The IB4 marker showed an unexpected staining pattern; in fact, IB4-labeled neurons largely colocalized with NF200, usually considered a marker of light SG neurons, and with CGRP and SP. For this reason, IB4 cannot be employed in sheep to differentiate between light and dark neurons, or between peptidergic and nonpeptidergic neurons. These results suggest the importance of being cautious when comparing data among different species.

The Distribution of Primary Nitric Oxide Synthase- and Parvalbumin- Immunoreactive Afferents in the Dorsal Funiculus of the Lumbosacral Spinal Cord in a Dog

1. The aim of the present study was to examine the distribution of unmyelinated, small-diameter myelinated neuronal nitric oxide synthase immunoreactive (nNOS-IR) axons and large-diameter myelinated neuronal nitric oxide synthase and parvalbumin-immunoreactive (PV-IR) axons in the dorsal funiculus (DF) of sacral (S1-S3) and lumbar (L1-L7) segments of the dog.2. nNOS and PV immunohistochemical methods were used to demonstrate the presence of nNOS-IR and PV-IR in the large-diameter myelinated, presumed to be proprioceptive, axons in the DF along the lumbosacral segments.3. Fiber size and density of nNOS-IR and PV-IR axons were used to compartmentalize the DF into five compartments (CI-CV). The first compartment (CI) localized in the lateralmost part of the DF, containing both unmyelinated and small-diameter myelinated nNOS-IR axons, is homologous with the dorsolateral fasciculus, or Lissauer tract. The second compartment (CII) having similar fiber organization as CI is situated more medially in sacral segments. Rostrally, in lower lumbar segments, CII moves more medially, and at upper lumbar level, CII reaches the dorsomedial angle of the DF and fuses with axons of CIV. CIII is the largest in the DF and the only one containing large-diameter myelinated nNOS-IR and PV-IR axons. The largest nNOS-IR and PV-IR axons of CIII (8.0-9.2 mum in diameter), presumed to be stem Ia proprioceptive afferents, are located in the deep portion of the DF close to the dorsal and dorsomedial border of the dorsal horn. The CIV compartment varies in shape, appearing first as a small triangular area in S3 and S2 segments, homologous with the Philippe-Gombault triangle. Beginning at S1 level, CIV acquires a more elongated shape and is seen throughout the lumbar segments as a narrow band of fibers extending just below the dorsal median septum in approximately upper two-thirds of the DF. The CV is located in the basal part of the DF. In general, CV is poor in nNOS-IR fibers; among them solitary PV-IR fibers are seen.4. The analysis of the control material and the degeneration of the large- and medium-caliber nNOS-IR fibers after unilateral L7 and S1 dorsal rhizotomy confirmed that large-caliber nNOS-IR and and PV-IR axons, presumed to be proprioceptive Ia axons, and their ascending and descending collaterals are present in large number in the DF of the lumbosacral intumescence. However, in the DF of the upper lumbar segments, the decrease in the number of nNOS-IR and PV-IR fibers is quite evident.

Nitrergic Proprioceptive Afferents Originating from Quadriceps Femoris Muscle are Related to Monosynaptic Ia-Motoneuron Stretch Reflex Circuit in the Dog

1. The aim of the present study was to examine the occurrence of the neuronal nitric oxide synthase immunoreactivity in the stretch reflex circuit pertaining to the quadriceps femoris muscle in the dog. 2. Immunohistochemical processing for neuronal nitric oxide synthase and histochemical staining for nicotinamide adenine dinucleotide phosphate diaphorase were used to demonstrate the presence of neuronal nitric oxide synthase in the proprioceptive afferents issuing in the quadriceps femoris muscle. The retrograde tracer Fluorogold injected into the quadriceps femoris muscle was used to detect the proprioceptive afferents and their entry into the L5 and L6 dorsal root ganglia. 3. A noticeable number of medium-sized intensely nitric oxide synthase immunolabelled somata (1000-2000 microm(2) square area) was found in control animals in the dorsolateral part of L5 and L6 dorsal root ganglia along with large-caliber intraganglionic nitric oxide synthase immunolabelled fibers, presumed to be Ia axons. Before entering the dorsal funiculus the large-caliber nitric oxide synthase immunolabelled fibers of the L5 and L6 dorsal roots formed a massive medial bundle, which upon entering the dorsal root entry zone reached the dorsolateral part of the dorsal funiculus and were distributed here in a funnel-shaped fashion. The largest nitric oxide synthase immunolabelled fibers, 8.0-9.2 microm in diameter, remained close to the dorsal horn, while medium-sized fibers were seen dispersed across the medial portion of the dorsal funiculus. Single, considerably tapered nitric oxide synthase immunolabelled fibers, 2.2-4.6 microm in diameter, were seen to proceed in ventrolateral direction until they reached the mediobasal portion of the dorsal horn and the medial part of lamina VII. In lamina IX, only short fragments of nitric oxide synthase immunoreactive fibers and their terminal ramifications could be seen. Nitric oxide synthase immunolabelled terminals varying greatly in size were identified in control material at the base of the dorsal horn, in the vicinity of motoneurons ventrally and ventrolaterally in L5 and L6 segments and in Clarke's column of L3 and L4 segments. Injections of the retrograde tracer Fluorogold into the quadriceps femoris muscle and cut femoral nerve, combined with nitric oxide synthase immunohistochemistry of the L5 and L6 dorsal root ganglia, confirmed the existence of a number of medium-sized nitric oxide synthase immunoreactive and Fluorogold-fluorescent somata presumed to be proprioceptive Ia neurons (1000-2000 microm(2) square area) in the dorsolateral part of both dorsal root ganglia. L5 and L6 dorsal rhizotomy caused a marked depletion of nitric oxide synthase immunoreactivity in the medial bundle of the L5 and L6 dorsal roots and in the dorsal funiculus of L5 and L6 segments. 4. The analysis of control material and the degeneration of the large- and medium-caliber nitric oxide synthase immunoreactive Ia fibers in the dorsal funiculus of L5 and L6 segments confirmed the presence of nitric oxide synthase in the afferent limb of the monosynaptic Ia-motoneuron stretch reflex circuit related to the quadriceps femoris muscle.

The evidence for nitric oxide synthase immunopositivity in the monosynaptic Ia-motoneuron pathway of the dog

In this study, nitric oxide synthase immunohistochemistry supported by nicotinamide adenine dinucleotide phosphate diaphorase histochemistry was used to demonstrate the nitric oxide synthase immunoreactivity in the monosynaptic Ia-motoneuron pathway exemplified by structural components of the afferent limb of the soleus H-reflex in the dog. A noticeable number of medium-sized intensely nitric oxide synthase immunoreactive somata (1000-2000 microm(2) square area) and large intraganglionic nitric oxide synthase immunoreactive fibers, presumed to be Ia axons, was found in the L7 and S1 dorsal root ganglia. The existence of nitric oxide synthase immunoreactive fibers (6-8 microm in diameter, not counting the myelin sheath) was confirmed in L7 and S1 dorsal roots and in the medial bundle of both dorsal roots before entering the dorsal root entry zone. By virtue of the funicular organization of nitric oxide synthase immunoreactive fibers in the dorsal funiculus, the largest nitric oxide synthase immunoreactive fibers represent stem Ia axons located in the deep portion of the dorsal funiculus close to the dorsomedial margin of the dorsal horn. Upon entering the gray matter of L7 and S1 segments and passing through the medial half of the dorsal horn, tapered nitric oxide synthase immunoreactive collaterals of the stem Ia fibers pass through the deep layers of the dorsal horn and intermediate zone, and terminate in the group of homonymous motoneurons in L7 and S1 segments innervating the gastrocnemius-soleus muscles. Terminal fibers issued in the ventral horn intensely nitric oxide synthase immunoreactive terminals with long axis ranging from 0.7 to >or=15.1 microm presumed to be Ia bNOS-IR boutons. This finding is unique in that it focuses directly on nitric oxide synthase immunopositivity in the signalling transmitted by proprioceptive Ia fibers. Nitric oxide synthase immunoreactive boutons were found in the neuropil of Clarke's column of L4 segment, varying greatly in size from 0.7 to >or=15.1 microm in length x 0.7 to 4.8 microm wide. Subsequent to identification of the afferent nitric oxide synthase immunoreactive limb of the monosynaptic Ia-motoneuron pathway on control sections, intramuscular injections of the retrograde tracer Fluorogold into the gastrocnemius-soleus muscles, combined with nitric oxide synthase immunohistochemistry of L7 and S1 dorsal root ganglia, confirmed the existence of a number of medium-sized nitric oxide synthase immunoreactive somata (1000-2000 microm(2) square area) in the dorsolateral part of both dorsal root ganglia, presumed to be proprioceptive Ia neurons. Concurrently, large nitric oxide synthase immunoreactive fibers were detected at the input and output side of both dorsal root ganglia. S1 and S2 dorsal rhizotomy caused a marked depletion of nitric oxide synthase immunoreactivity in the medial bundle of S1 and S2 dorsal roots and in the dorsal funiculus of S1, S2 and lower lumbar segments. In addition, anterograde degeneration of large nitric oxide synthase immunoreactive Ia fibers in the dorsal funiculus of L7-S2 segments produces direct evidence that the afferent limb of the soleus H-reflex is nitric oxide synthase immunoreactive and presents new immunohistochemical characteristics of the monosynaptic Ia-motoneuron pathway, unseparably coupled with the performance of the stretch reflex.