Immunohistochemistry of nitric oxide synthase demonstrates immunoreactive neurons in spinal cord and dorsal root ganglia of man and rat

Distribution and Chemistry of Phoenixin-14, a Newly Discovered Sensory Transmission Molecule in Porcine Afferent Neurons

Phoenixin-14 (PNX), initially discovered in the rat hypothalamus, was also detected in dorsal root ganglion (DRG) cells, where its involvement in the regulation of pain and/or itch sensation was suggested. However, there is a lack of data not only on its distribution in DRGs along individual segments of the spinal cord, but also on the pattern(s) of its co-occurrence with other sensory neurotransmitters. To fill the above-mentioned gap and expand our knowledge about the occurrence of PNX in mammalian species other than rodents, this study examined (i) the pattern(s) of PNX occurrence in DRG neurons of subsequent neuromeres along the porcine spinal cord, (ii) their intraganglionic distribution and (iii) the pattern(s) of PNX co-occurrence with other biologically active agents. PNX was found in approximately 20% of all nerve cells of each DRG examined; the largest subpopulation of PNX-positive (PNX+) cells were small-diameter neurons, accounting for 74% of all PNX-positive neurons found. PNX+ neurons also co-contained calcitonin gene-related peptide (CGRP; 96.1%), substance P (SP; 88.5%), nitric oxide synthase (nNOS; 52.1%), galanin (GAL; 20.7%), calretinin (CRT; 10%), pituitary adenylate cyclase-activating polypeptide (PACAP; 7.4%), cocaine and amphetamine related transcript (CART; 5.1%) or somatostatin (SOM; 4.7%). Although the exact function of PNX in DRGs is not yet known, the high degree of co-localization of this peptide with the main nociceptive transmitters SP and CGRP may suggests its function in modulation of pain transmission.

Neuronal control of the vagina in vertebrates: A review

BACKGROUND

At present, there is an increased interest in the vaginal microbiome. It is believed that microbes play equally important roles in the vagina, including the modulation of neuronal pathways, as in the gut. However, in man as well as in animals, the vagina is the least well-studied part of the female reproductive system. The vagina, a fibromuscular tract, having two main functions, i.e., childbirth and sexual intercourse, is mainly innervated by the pudendal nerve and the pelvic splanchnic nerves (the uterovaginal nerve plexus) containing sympathetic, parasympathetic and nociceptive nerve fibers. Innervation density in the vaginal wall undergoes significant remodeling due to hormonally mediated physiological activity. Knowledge about expression and function of neuropeptides and neurotransmitters in the vaginal fibers is incomplete or not established. Most research concerning the neuroregulation of the vagina and the function and expression of neuropeptides and neurotransmitters, is performed in several vertebrate species, including large farm animals, rodents, domestic fowl and lizards.

METHODS

This review summarizes, on a bibliographic basis, the current knowledge on vaginal innervation and function of neuropeptides and neurotransmitters expressed in vaginal nerve fibers in several vertebrate species, including humans. The presence and role played by the local microbioma is also explored.

CONCLUSION

A thorough knowledge of the vaginal innervation is necessary to unravel the putative communication of the vaginal microbiome and vaginal nerve fibers, but also to understand the effects of vaginal pathologies and of administered drugs on the neuroregulation of the vagina.

Neuromeric Distribution of Nicotinamide Adenine Dinucleotide Phosphate-Diaphorase Activity in the Adult Lamprey Brain

This study reports for the first time the distribution and morphological characterization of nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d; a reliable marker of nitric oxide synthase activity) positive elements in the central nervous system of the adult river lamprey (Lampetra fluviatilis) on the framework of the neuromeric model and compares their cytoarchitectonic organization with that of gnathostomes. Both NADPH-d exhibiting cells and fibers were observed in all major divisions of the lamprey brain as well as in the spinal cord. In the secondary prosencephalon, NADPH-d positive cells were observed in the mitral cell layer of the olfactory bulb, evaginated pallium, amygdala, dorsal striatum, septum, lateral preoptic nucleus, caudal paraventricular area, posterior entopeduncular nucleus, nucleus of the stria medullaris, hypothalamic periventricular organ and mamillary region sensu lato. In the lamprey diencephalon, NADPH-d labeled cells were observed in several nuclei of the prethalamus, epithalamus, pretectum, and the basal plate. Especially remarkable was the staining observed in the right habenula and several pretectal nuclei. NADPH-d positive cells were also observed in the following mesencephalic areas: optic tectum (two populations), torus semicircularis, nucleus M5 of Schöber, and a ventral tegmental periventricular nucleus. Five different cell populations were observed in the isthmic region, whereas the large sensory dorsal cells, some cells located in the interpeduncular nucleus, the motor nuclei of most cranial nerves, the solitary tract nucleus, some cells of the reticular nuclei, and small cerebrospinal fluid-contacting (CSF-c) cells were the most evident stained cells of the rhombencephalon proper. Finally, several NADPH-d positive cells were observed in the rostral part of the spinal cord, including the large sensory dorsal cells, numerous CSF-c cells, and some dorsal and lateral interneurons. NADPH-d positive fibers were observed in the olfactory pathways (primary olfactory fibers and stria medullaris), the fasciculus retroflexus, and the dorsal column tract. Our results on the distribution of NADPH-d positive elements in the brain of the adult lamprey L. fluviatilis are significantly different from those previously reported in larval lampreys and demonstrated that these animals possess a complex nitrergic system readily comparable to those of other vertebrates, although important specific differences also exist.

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.

Antinociceptive Effect of BPC-157 in the Formalin-induced Pain Model

Objectives Body protective compound-157 (BPC-157) is a stable gastric pentadecapeptide that has been effective in trials aiming to increase wound healing capabilities and decrease inflammatory cell influx, including studies on the healing of muscles and tendons. There are no studies about the effect of BPC-157 on pain transmission via nociception. This study examined the antinociceptive effects of BPC-157 using formalin tests and immunohistochemistry. Methods Rats were randomly divided into the control, morphine and BPC-157 groups. Pain behavior was quantified periodically at 5- and 35- min intervals (representative values of phases 1 and 2) by counting the number of flinches exhibited by the injected paw after injection. The dorsal root ganglia (DRG) and spinal cords (SC) were collected, and then, the number of cytokine-positive cells was determined via immunostaining. Results BPC-157 dose-dependently decreased the number of flinches during phase 1 but did not decrease the number of flinches during phase 2. During phase 1, interleukin-1β (IL-1β) in the DRG tissue was significantly different in the morphine, 10 μg/kg BPC-157, and 20 μg/kg BPC-157 groups. During phase 2, statistical significance was achieved in the DRG tissue in the morphine, 20 μg/kg BPC-157, and 40 μg/kg BPC-157 groups. During phase 1, interleukin-6 was significantly different in the DRG tissue in the morphine group and the SC tissue in the 10 μg/kg BPC-157 group. During phase 2, statistical significance was achieved in the morphine group and the BPC-157 20 μg/kg group in both the DRG and SC tissues. There were no significant differences in tumor necrosis factor-α between the DRG and SC tissues. Conclusions BPC-157 was effective during phase 1 but not during phase 2, as determined by the formalin test. BPC-157 decreased the expression of IL-1β in the DRG tissue in phases 1 and 2.

Neuropeptides and neurohormones in immune, inflammatory and cellular responses to ultraviolet radiation

Humans are exposed to varying amounts of ultraviolet radiation (UVR) through sunlight. UVR penetrates into human skin leading to release of neuropeptides, neurotransmitters and neuroendocrine hormones. These messengers released from local sensory nerves, keratinocytes, Langerhans cells (LCs), mast cells, melanocytes and endothelial cells (ECs) modulate local and systemic immune responses, mediate inflammation and promote differing cell biologic effects. In this review, we will focus on both animal and human studies that elucidate the roles of calcitonin gene-related peptide (CGRP), substance P (SP), nerve growth factor (NGF), nitric oxide and proopiomelanocortin (POMC) derivatives in mediating immune and inflammatory effects of exposure to UVR as well as other cell biologic effects of UVR exposure.

Pattern of nitrergic cells and fibers organization in the central nervous system of the Australian lungfish, Neoceratodus forsteri (Sarcopterygii: Dipnoi)

The Australian lungfish Neoceratodus forsteri is the only extant species of the order Ceratodontiformes, which retained most of the primitive features of ancient lobe finned-fishes. Lungfishes are the closest living relatives of land vertebrates and their study is important for deducing the neural traits that were conserved, modified, or lost with the transition from fishes to land vertebrates. We have investigated the nitrergic system with neural nitric oxide synthase (NOS) immunohistochemistry and NADPH-diaphorase (NADPH-d) histochemistry, which yielded almost identical results except for the primary olfactory projections and the terminal and preoptic nerve fibers labeled only for NADPH-d. Combined immunohistochemistry was used for simultaneous detection of NOS with catecholaminergic, cholinergic, and serotonergic structures, aiming to establish accurately the localization of the nitrergic elements and to assess possible interactions between these neurotransmitter systems. The results demonstrated abundant nitrergic cells in the basal ganglia, amygdaloid complex, preoptic area, basal hypothalamus, mesencephalic tectum and tegmentum, laterodorsal tegmental nucleus, reticular formation, spinal cord, and retina. In addition, low numbers of nitrergic cells were observed in the olfactory bulb, all pallial divisions, lateral septum, suprachiasmatic nucleus, prethalamic and thalamic areas, posterior tubercle, pretectum, torus semicircularis, cerebellar nucleus, interpeduncular nucleus, the medial octavolateral nucleus, nucleus of the solitary tract, and the dorsal column nucleus. Colocalization of NOS and tyrosine hydroxylase was observed in numerous cells of the ventral tegmental area/substantia nigra complex. Comparison with other vertebrates, using a neuromeric analysis, reveals that the nitrergic system of Neoceratodus shares many neuroanatomical features with tetrapods and particularly with amphibians.

Human Dorsal Root Ganglia

Sensory neurons with cell bodies situated in dorsal root ganglia convey information from external or internal sites of the body such as actual or potential harm, temperature or muscle length to the central nervous system. In recent years, large investigative efforts have worked toward an understanding of different types of DRG neurons at transcriptional, translational, and functional levels. These studies most commonly rely on data obtained from laboratory animals. Human DRG, however, have received far less investigative focus over the last 30 years. Nevertheless, knowledge about human sensory neurons is critical for a translational research approach and future therapeutic development. This review aims to summarize both historical and emerging information about the size and location of human DRG, and highlight advances in the understanding of the neurochemical characteristics of human DRG neurons, in particular nociceptive neurons.

Endogenous nitric oxide inhibits spinal NMDA receptor activity and pain hypersensitivity induced by nerve injury

The role of nitric oxide (NO) in nociceptive transmission at the spinal cord level remains uncertain. Increased activity of spinal N-methyl-d-aspartate (NMDA) receptors contributes to development of chronic pain induced by peripheral nerve injury. In this study, we determined how endogenous NO affects NMDA receptor activity of spinal cord dorsal horn neurons in control and spinal nerve-ligated rats. Bath application of the NO precursor l-arginine or the NO donor S-nitroso-N-acetylpenicillamine (SNAP) significantly inhibited NMDA receptor currents of spinal dorsal horn neurons in both sham control and nerve-injured rats. Inhibition of neuronal nitric oxide synthase (nNOS) or blocking the S-nitrosylation reaction with N-ethylmaleimide abolished the inhibitory effects of l-arginine on NMDA receptor currents recorded from spinal dorsal horn neurons in sham control and nerve-injured rats. However, bath application of the cGMP analog 8-bromo-cGMP had no significant effects on spinal NMDA receptor currents. Inhibition of soluble guanylyl cyclase also did not alter the inhibitory effect of l-arginine on spinal NMDA receptor activity. Furthermore, knockdown of nNOS with siRNA abolished the inhibitory effects of l-arginine, but not SNAP, on spinal NMDA receptor activity in both groups of rats. Additionally, intrathecal injection of l-arginine significantly attenuated mechanical or thermal hyperalgesia induced by nerve injury, and the l-arginine effect was diminished in rats treated with a nNOS inhibitor or nNOS-specific siRNA. These findings suggest that endogenous NO inhibits spinal NMDA receptor activity through S-nitrosylation. NO derived from nNOS attenuates spinal nociceptive transmission and neuropathic pain induced by nerve injury.

TRPA1 Channels Modify TRPV1-Mediated Current Responses in Dorsal Root Ganglion Neurons

The transient receptor potential vanilloid 1 (TRPV1) channel is highly expressed in a subset of sensory neurons in the dorsal root ganglia (DRG) and trigeminal ganglia of experimental animals, responsible for nociception. Many researches have revealed that some TRPV1-positive neurons co-express the transient receptor potential ankyrin 1 (TRPA1) channel whose activities are closely modulated by TRPV1 channel. However, it is less investigated whether the activities of TRPV1 channel are modulated by the presence of TRPA1 channel in primary sensory neurons. This study clarified the difference in electrophysiological responses induced by TRPV1 channel activation between TRPA1-positive and TRPA1-negative DRG. TRPV1 and TRPA1 channel activations were evoked by capsaicin (1 μM), a TRPV1 agonist, and allyl isothiocyanate (AITC; 500 μM), a TRPA1 agonist, respectively. Capsaicin perfusion for 15 s caused a large inward current without a desensitization phase at a membrane potential of −70 mV in AITC-insensitive DRG (current density; 29.6 ± 5.6 pA/pF, time constant of decay; 12.8 ± 1.8 s). The capsaicin-induced currents in AITC-sensitive DRG had a small current density (12.7 ± 2.9 pA/pF) with a large time constant of decay (24.3 ± 5.4 s). In calcium imaging with Fura-2, the peak response by capsaicin was small and duration reaching the peak response was long in AITC-sensitive neurons. These electrophysiological differences were completely eliminated by HC-030031, a TRPA1 antagonist, in an extracellular solution or 10 mM EGTA, a Ca²⁺ chelator, in an internal solution. Capsaicin perfusion for 120 s desensitized the inward currents after a transient peak. The decay during capsaicin perfusion was notably slow in AITC-sensitive DRG; ratio of capsaicin-induced current 60 s after the treatment per the peak current in AITC-sensitive neurons (78 ± 9%) was larger than that in AITC-insensitive neurons (48 ± 5%). The capsaicin-induced current in the desensitization phase was attenuated by HC-030031 in AITC-insensitive DRG. These results indicate that (1) TRPV1-mediated currents in TRPA1-positive neurons characterize small current densities with slow decay, which is caused by TRPA1 channel activities and intracellular Ca²⁺ mobilization and (2) desensitization of TRPV1-mediated current in TRPA1-positive neurons is apparently slow, due to appending TRPA1-mediated current.

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.

Organization of the nitrergic neuronal system in the primitive bony fishes Polypterus senegalus and Erpetoichthys calabaricus (Actinopterygii: Cladistia)

Cladistians are a group of basal actinopterygian fishes that constitute a good model for studying primitive brain features, most likely present in the ancestral bony fishes. The analysis of the nitrergic neurons (with the enzyme nitric oxide synthase; NOS) has helped in understanding important aspects of brain organization in all vertebrates studied. We investigated the nitrergic system of two cladistian species by means of specific antibodies against NOS and NADPH-diaphorase (NADPH-d) histochemistry, which, with the exception of the primary olfactory and terminal nerve fibers, labeled only for NADPH-d, yielded identical results. Double immunohistochemistry was conducted for simultaneous detection of NOS with tyrosine hydroxylase, choline acetyltransferase, calbindin, calretinin, and serotonin, to establish accurately the localization of the nitrergic neurons and fibers and to assess possible interactions between these neuroactive substances. The pattern of distribution in both species showed only subtle differences in the density of labeled cells. Distinct groups of NOS-immunoreactive cells were observed in pallial and subpallial areas, paraventricular region, tuberal and retromammillary hypothalamic areas, posterior tubercle, prethalamic and thalamic areas, optic tectum, torus semicircularis, mesencephalic tegmentum, interpeduncular nucleus, superior and middle reticular nuclei, magnocellular vestibular nucleus, solitary tract nucleus, nucleus medianus magnocellularis, the spinal cord and amacrine cells in the retina. Large neurons in cranial nerve sensory ganglia were also labeled. The comparison of these results with those from other vertebrates, using a neuromeric analysis, reveals a conserved pattern of organization of the nitrergic system from this primitive fish group to amniotes, including mammals.

[Mechanism of spinal pain transmission and its regulation]

Morphine has been widely used for the treatment of acute, chronic, and cancer pain and is considered the strongest analgesic in clinical care. Conversely, morphine-induced analgesia may be accompanied by several side effects. Animal studies have demonstrated that low doses of morphine administered intrathecally can produce reliable analgesia for thermal, mechanical, and chemical nociceptive stimulation. On the other hand, high doses of morphine administered intrathecally may induce spontaneous nociceptive responses such as scratching, biting, and licking in mice as well as agitation and vocalization in rats. In addition, similar nociceptive responses including hyperalgesia, allodynia, and myoclonus have been observed in humans following intrathecal or systemic administration of high-dose morphine. It has been suggested that the spontaneous nociceptive behaviors evoked by high-dose morphine may be mediated by a non-opioid mechanism that is not yet fully understood. This review describes the mechanisms of spontaneous nociceptive behaviors evoked by high-dose morphine focusing on the neurotransmitters/neuromodulators released from primary afferent fibers.

Development of nNOS-positive neurons in the rat sensory ganglia after capsaicin treatment

To gain a better understanding of the neuroplasticity of afferent neurons during postnatal ontogenesis, the distribution of neuronal nitric oxide synthase (nNOS) immunoreactivity was studied in the nodose ganglion (NG) and Th2 and L4 dorsal root ganglia (DRG) from vehicle-treated and capsaicin-treated female Wistar rats at different ages (10-day-old, 20-day-old, 30-day-old, and two-month-old). The percentage of nNOS-immunoreactive (IR) neurons decreased after capsaicin treatment in all studied ganglia in first 20 days of life, from 55.4% to 36.9% in the Th2 DRG, from 54.6% to 26.1% in the L4 DRG and from 37.1% to 15.0% in the NG. However, in the NG, the proportion of nNOS-IR neurons increased after day 20, from 11.8% to 23.9%. In the sensory ganglia of all studied rats, a high proportion of nNOS-IR neurons bound isolectin B4. Approximately 90% of the sensory nNOS-IR neurons bound to IB4 in the DRG and approximately 80% in the NG in capsaicin-treated and vehicle-treated rats. In 10-day-old rats, a large number of nNOS-IR neurons also expressed TrkA, and the proportion of nNOS(+)/TrkA(+) neurons was larger in the capsaicin-treated rats compared with the vehicle-treated animals. During development, the percentage of nNOS(+)/TrkA(+) cells decreased in the first month of life in both groups. The information provided here will also serve as a basis for future studies investigating mechanisms of sensory neuron development.

Redox and nitric oxide-mediated regulation of sensory neuron ion channel function

SIGNIFICANCE

Reactive oxygen and nitrogen species (ROS and RNS, respectively) can intimately control neuronal excitability and synaptic strength by regulating the function of many ion channels. In peripheral sensory neurons, such regulation contributes towards the control of somatosensory processing; therefore, understanding the mechanisms of such regulation is necessary for the development of new therapeutic strategies and for the treatment of sensory dysfunctions, such as chronic pain.

RECENT ADVANCES

Tremendous progress in deciphering nitric oxide (NO) and ROS signaling in the nervous system has been made in recent decades. This includes the recognition of these molecules as important second messengers and the elucidation of their metabolic pathways and cellular targets. Mounting evidence suggests that these targets include many ion channels which can be directly or indirectly modulated by ROS and NO. However, the mechanisms specific to sensory neurons are still poorly understood. This review will therefore summarize recent findings that highlight the complex nature of the signaling pathways involved in redox/NO regulation of sensory neuron ion channels and excitability; references to redox mechanisms described in other neuron types will be made where necessary.

CRITICAL ISSUES

The complexity and interplay within the redox, NO, and other gasotransmitter modulation of protein function are still largely unresolved. Issues of specificity and intracellular localization of these signaling cascades will also be addressed.

FUTURE DIRECTIONS

Since our understanding of ROS and RNS signaling in sensory neurons is limited, there is a multitude of future directions; one of the most important issues for further study is the establishment of the exact roles that these signaling pathways play in pain processing and the translation of this understanding into new therapeutics.

Uncovering influence links in molecular knowledge networks to streamline personalized medicine

OBJECTIVES

We developed Resource Description Framework (RDF)-induced InfluGrams (RIIG) - an informatics formalism to uncover complex relationships among biomarker proteins and biological pathways using the biomedical knowledge bases. We demonstrate an application of RIIG in morphoproteomics, a theranostic technique aimed at comprehensive analysis of protein circuitries to design effective therapeutic strategies in personalized medicine setting.

METHODS

RIIG uses an RDF "mashup" knowledge base that integrates publicly available pathway and protein data with ontologies. To mine for RDF-induced Influence Links, RIIG introduces notions of RDF relevancy and RDF collider, which mimic conditional independence and "explaining away" mechanism in probabilistic systems. Using these notions and constraint-based structure learning algorithms, the formalism generates the morphoproteomic diagrams, which we call InfluGrams, for further analysis by experts.

RESULTS

RIIG was able to recover up to 90% of predefined influence links in a simulated environment using synthetic data and outperformed a naïve Monte Carlo sampling of random links. In clinical cases of Acute Lymphoblastic Leukemia (ALL) and Mesenchymal Chondrosarcoma, a significant level of concordance between the RIIG-generated and expert-built morphoproteomic diagrams was observed. In a clinical case of Squamous Cell Carcinoma, RIIG allowed selection of alternative therapeutic targets, the validity of which was supported by a systematic literature review. We have also illustrated an ability of RIIG to discover novel influence links in the general case of the ALL.

CONCLUSIONS

Applications of the RIIG formalism demonstrated its potential to uncover patient-specific complex relationships among biological entities to find effective drug targets in a personalized medicine setting. We conclude that RIIG provides an effective means not only to streamline morphoproteomic studies, but also to bridge curated biomedical knowledge and causal reasoning with the clinical data in general.

Topographical distribution and morphology of NADPH-diaphorase-stained neurons in the human claustrum

We studied the topographical distribution and morphological characteristics of NADPH-diaphorase-positive neurons and fibers in the human claustrum. These neurons were seen to be heterogeneously distributed throughout the claustrum. Taking into account the size and shape of stained perikarya as well as dendritic and axonal characteristics, Nicotinamide adenine dinucleotide phosphate-diaphorase (NADPHd)-positive neurons were categorized by diameter into three types: large, medium and small. Large neurons ranged from 25 to 35 μm in diameter and typically displayed elliptical or multipolar cell bodies. Medium neurons ranged from 20 to 25 μm in diameter and displayed multipolar, bipolar and irregular cell bodies. Small neurons ranged from 14 to 20 μm in diameter and most often displayed oval or elliptical cell bodies. Based on dendritic characteristics, these neurons were divided into spiny and aspiny subtypes. Our findings reveal two populations of NADPHd-positive neurons in the human claustrum-one comprised of large and medium cells consistent with a projection neuron phenotype, the other represented by small cells resembling the interneuron phenotype as defined by previous Golgi impregnation studies.

The neurochemical changes in the innervation of human colonic mesenteric and submucosal blood vessels in ulcerative colitis and Crohn's disease

BACKGROUND

Neurogenic inflammation involves vasodilation, oedema and sensory nerve hypersensitivity. Extrinsic sensory nerves to the intestinal wall mediate these effects and functional subsets of these extrinsic nerves can be characterized by immunohistochemical profiles. In this study such profiles were examined in samples from patients with inflammatory bowel disease (IBD), in particular ulcerative colitis (UC) and Crohn's disease (CD).

METHODS

Healthy margins from cancer patients were compared to specimens from IBD patients. All nerve fibres were labelled by PGP 9.5. Double and triple labelling with TH, NPY, SP, SOM, NOS, VIP, VAChT, CGRP, TRPv1 were performed. Perivascular nerve fibres in the mesentery, and submucosa, were examined. The percentage of all labelled nerve fibres was calculated with a transect method.

KEY RESULTS

Total number of varicosities on mesenteric vessels increased in IBD but decreased around submucosal vessels. The percentage of nerve fibres around submucosal arteries labelled by SP increased from 11% in controls to 20% (UC) and 24% (CD) and mesenteric artery nerve fibres were unchanged. Nerve fibres labelled by SOM were markedly reduced surrounding submucosal arteries, from 22% to 1% (UC) and 2% (CD), but not perivascular mesenteric nerve fibres. 87 to 93% of SP immunoreactive nerve fibres were also reactive for TRvP1. TRPv1 labelling without SP was 12%in controls and increased to 40% in CD submucosal specimens.

CONCLUSIONS & INFERENCES

There is an increase in SP and TRPv1, and a reduction in SOM immunoreactive nerve fibres in IBD. Changes in the perivascular functional nerve subclasses may underlie the hyperaemia, and ulceration, characteristic of IBD. Furthermore, pain may relate to underlying neural changes.

Regulation of nociceptive transduction and transmission by nitric oxide

The potential involvement of nitric oxide (NO), a diffusible gaseous signaling messenger, in nociceptive transduction and transmission has been extensively investigated. However, there is no consistent and convincing evidence supporting the pronociceptive action of NO at the physiological concentration, and the discrepancies are possibly due to the nonspecificity of nitric oxide synthase inhibitors and different concentrations of NO donors used in various studies. At the spinal cord level, NO predominantly reduces synaptic transmission by inhibiting the activity of NMDA receptors and glutamate release from primary afferent terminals through S-nitrosylation of voltage-activated calcium channels. NO also promotes synaptic glycine release from inhibitory interneurons through the cyclic guanosine monophosphate/protein kinase G signaling pathway. Thus, NO probably functions as a negative feedback regulator to reduce nociceptive transmission in the spinal dorsal horn during painful conditions.

Sensory and signaling mechanisms of bradykinin, eicosanoids, platelet-activating factor, and nitric oxide in peripheral nociceptors

Peripheral mediators can contribute to the development and maintenance of inflammatory and neuropathic pain and its concomitants (hyperalgesia and allodynia) via two mechanisms. Activation or excitation by these substances of nociceptive nerve endings or fibers implicates generation of action potentials which then travel to the central nervous system and may induce pain sensation. Sensitization of nociceptors refers to their increased responsiveness to either thermal, mechanical, or chemical stimuli that may be translated to corresponding hyperalgesias. This review aims to give an account of the excitatory and sensitizing actions of inflammatory mediators including bradykinin, prostaglandins, thromboxanes, leukotrienes, platelet-activating factor, and nitric oxide on nociceptive primary afferent neurons. Manifestations, receptor molecules, and intracellular signaling mechanisms of the effects of these mediators are discussed in detail. With regard to signaling, most data reported have been obtained from transfected nonneuronal cells and somata of cultured sensory neurons as these structures are more accessible to direct study of sensory and signal transduction. The peripheral processes of sensory neurons, where painful stimuli actually affect the nociceptors in vivo, show marked differences with respect to biophysics, ultrastructure, and equipment with receptors and ion channels compared with cellular models. Therefore, an effort was made to highlight signaling mechanisms for which supporting data from molecular, cellular, and behavioral models are consistent with findings that reflect properties of peripheral nociceptive nerve endings. Identified molecular elements of these signaling pathways may serve as validated targets for development of novel types of analgesic drugs.

The effects of L-NAME on neuronal NOS and SOD1 expression in the DRG-spinal cord network of axotomised Thy 1.2 eGFP mice

Nitric oxide (NO) plays an important role in pathophysiology of the nervous system. Copper/zinc superoxide dismutase (SOD1) reacts with superoxide, which is also a substrate for NO, to provide antioxidative protection. NO production is greatly altered following nerve injury, therefore we hypothesised that SOD1 and NO may be involved in modulating axotomy responses in dorsal root ganglion (DRG)-spinal network. To investigate this interaction, adult Thy1.2 enhanced membrane-bound green fluorescent protein (eGFP) mice underwent sciatic nerve axotomy and received NG-nitro- <l-arginine methylester (L-NAME) or vehicle 7-9 days later. L4-L6 spinal cord and DRG were harvested for immunohistochemical analyses. Effect of injury was confirmed by axotomy markers; small proline-rich repeat protein 1A (SPRR1A) was restricted to ipsilateral neuropathology, while Thy1.2 eGFP revealed also contralateral crossover effects. L-NAME, but not axotomy, increased neuronal NO synthase (nNOS) and SOD1 immunoreactive neurons, with no colocalisation, in a lamina-dependent manner in the dorsal horn of the spinal cord. Axotomy and/or L-NAME had no effect on total nNOS+ and SOD1+ neurons in DRG. However, L-NAME altered SOD1 expression in subsets of axotomised DRG neurons. These findings provide evidence for differential distribution of SOD1 and its modulation by NO, which may interact to regulate axotomy-induced changes in DRG-spinal network.

Mechanisms in cancer-chemotherapeutic drugs-induced peripheral neuropathy

Anti-cancer drugs such as vincristine, paclitaxel, oxaliplatin, cisplatin and bortezomib are well reported to exert direct and indirect effects on sensory nerves to alter the amplitude of action potential, conduction velocity and induce pain. It results in patient suffering and also limits the treatment with potentially useful anticancer drugs. The different scientists have worked in this area to explore the mechanisms responsible for its pathogenesis. Anti-cancer agents activate plasma membrane localized ion channels on dorsal root ganglia and dorsal horn neurons including sodium, calcium, potassium, glutamate activated NMDA receptors to alter cytosolic ionic mileu particularly intracellular calcium that trigger secondary changes to induce neuropathic pain. These may include opening of mPTP pore on mitochondria to induce intracellular calcium release; activation of protein kinase C; phosphorylation of TRPV; activation of calpases/calpains; generation of nitric oxide and free radicals to induce cytotoxicity to axons and neuronal cell bodies. Furthermore, the inflammatory process initiated in glial cells and macrophages also trigger changes in the sensory neurons to alter nociceptive processing. The present review elaborates the role of all these individual targets in the pathogenesis of anticancer agents-induced neuropathic pain to develop effective therapeutic modalities for pain management.

Nitric oxide inhibits nociceptive transmission by differentially regulating glutamate and glycine release to spinal dorsal horn neurons

Nitric oxide (NO) is involved in many physiological functions, but its role in pain signaling remains uncertain. Surprisingly, little is known about how endogenous NO affects excitatory and inhibitory synaptic transmission at the spinal level. Here we determined how NO affects excitatory and inhibitory synaptic inputs to dorsal horn neurons using whole-cell recordings in rat spinal cord slices. The NO precursor L-arginine or the NO donor SNAP significantly increased the frequency of glycinergic spontaneous and miniature inhibitory postsynaptic currents (IPSCs) of lamina II neurons. However, neither L-arginine nor SNAP had any effect on GABAergic IPSCs. L-arginine and SNAP significantly reduced the amplitude of monosynaptic excitatory postsynaptic currents (EPSCs) evoked from the dorsal root with an increase in paired-pulse ratio. Inhibition of the soluble guanylyl cyclase abolished the effect of L-arginine on glycinergic IPSCs but not on evoked monosynaptic EPSCs. Also, inhibition of protein kinase G blocked the increase in glycinergic sIPSCs by the cGMP analog 8-bromo-cGMP. The inhibitory effects of L-arginine on evoked EPSCs and high voltage-activated Ca(2+) channels expressed in HEK293 cells and dorsal root ganglion neurons were abolished by blocking the S-nitrosylation reaction with N-ethylmaleimide. Intrathecal injection of L-arginine and SNAP significantly increased mechanical nociceptive thresholds. Our findings suggest that spinal endogenous NO enhances inhibitory glycinergic input to dorsal horn neurons through sGC-cGMP-protein kinase G. Furthermore, NO reduces glutamate release from primary afferent terminals through S-nitrosylation of voltage-activated Ca(2+) channels. Both of these actions probably contribute to inhibition of nociceptive transmission by NO at the spinal level.

Nitroxidergic system in human trigeminal ganglia neurons: a quantitative evaluation

The trigeminal ganglia are involved in transmission of orofacial sensitivity. The free radical gas nitric oxide (NO) has recently been found to function as a messenger molecule in both central and peripheral trigeminal primary afferent neurons. NO is produced within neurons mainly by two enzymes: a constitutive (neuronal) form of NO synthase (nNOS) or an inducible form of NOS (iNOS). The aim of the study was to evaluate the distribution of trigeminal neurons according to size (small, medium and large neurons) and to correlate the percentage of NOS-immunopositive neurons with regard to neuronal size. The results showed a significant relationship between the percentage of nNOS-immunopositive neurons and the size of neurons. Evaluation of the percentage of nNOS-immunopositive neurons showed that they constitute about 50% of the total number of neurons and that they are represented mainly as large-sized neurons. The iNOS immunolabelling was very faint in all neuronal types. Since the nitroxidergic system is well represented in human trigeminal ganglia, this study indicates that it could play a relevant role in trigeminal neurotransmission.

Acute electroacupuncture inhibits nitric oxide synthase expression in the spinal cord of neuropathic rats

OBJECTIVES

To examine the effects of electroacupuncture stimulation on behavioral changes and neuronal nitric oxide synthase expression in the rat spinal cord after nerve injury.

METHODS

Under pentobarbital anesthesia, male Sprague-Dawley rats were subjected to neuropathic surgery by tightly ligating and cutting the left tibial and sural nerves. Behavioral responses to mechanical stimulation were tested for 2 weeks post-operatively. At the end of behavioral testing, electroacupuncture stimulation was applied to ST36 (Choksamni) and SP9 (Eumleungcheon) acupoints. Immunocytochemical staining was performed to investigate changes in the expression of neuronal nitric oxide synthase-immunoreactive neurons in the L4-5 spinal cord.

RESULTS

Mechanical allodynia was observed by nerve injury. The mechanical allodynia was decreased after electroacupuncture stimulation. Neuronal nitric oxide synthase expression was also decreased in L4-5 spinal cord by electroacupuncture treatment.

DISCUSSION

These results suggest that electroacupuncture relieves mechanical allodynia in the neuropathic rats possibly by the inhibition of neuronal nitric oxide synthase expression in the spinal cord.

Transdermal nitroglycerine enhances postoperative analgesia of intrathecal neostigmine following abdominal hysterectomies

This study was carried out to assess the effect of nitroglycerine (transdermal) on intrathecal neostigmine with bupivacaine on postoperative analgesia and note the incidence of adverse effects, if any. After taking informed consent, 120 patients of ASA Grade I and II were systematically randomised into four groups of 30 each. Patients were premedicated with midazolam 0.05 mg/kg intravenously and hydration with Ringer's lactate solution 10ml/kg preoperatively in the holding room. Group I patients received Intrathecal injection of 15 mg bupivacaine with 1ml of normal saline and transdermal placebo patch. Group II patients received Intrathecal injection of 15 mg bupivacaine with 5 mcg of neostigmine and transdermal placebo patch. Group III patients received Intrathecal injection of 15 mg bupivacaine with 1ml of normal saline with transdermal nitroglycerine patch (5 mg/24 hours). Group IV patients received Intrathecal injection of 15 mg bupivacaine with 5mcg of neostigmine and transdermal nitroglycerine patch (5 mg/24 hours), applied on a non anaesthetised area after 20 minutes. Groups were demographically similar and did not differ in intraoperative characteristics like sensory block, motor block, haemodynamic parameters and SpO(2). The mean duration of analgesia was 202.17 minutes, 407.20 minutes, 207.53 minutes and 581.63 minutes in control group (I), neostigmine group (II), nitroglycerine group (III) and nitroglycerine neostigmine group (IV) respectively (P<0.01). To conclude, our results show that transdermal nitroglycerine itself does not show any analgesic potential but it enhances the analgesic potential of intrathecal neostigmine.

Effects of anaesthesia on the nitrergic pathway during the micturition reflex in rats

OBJECTIVE

To investigate the effects of anaesthesia on the nitrergic pathway during the micturition reflex in rats.

MATERIALS AND METHODS

The effects of N(G)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO) synthase, on bladder and urethral activities were evaluated by infusion cystometrography (CMG) and urethral perfusion pressure under isovolumetric conditions in awake or urethane-anaesthetized rats. L-NAME was administered intravenously (i.v.), intrathecally (i.t.), intracerebroventriculary (i.c.v.) or intravesically in normal rats or rats pre-treated with resiniferatoxin, a potent C-fibre afferent neurotoxin.

RESULTS

L-NAME injected i.v. decreased the intercontraction interval (ICI) in the awake but increased it in the anaesthetized rats. L-NAME injected i.t. increased the ICI in both states and these effects were not apparent after pre-treatment with resiniferatoxin. L-NAME injected i.c.v. decreased the ICI in the awake but increased i.t. in the anaesthetized rats. Intravesical L-NAME decreased the ICI in the awake but not in the anaesthetized rats. L-NAME administered i.v., but not i.t. or i.c.v., increased bladder contraction during CMG. Under isovolumetric conditions, L-NAME administered i.v., but not i.t. or i.c.v., reduced the urethral relaxation without changing bladder contraction.

CONCLUSIONS

These results indicate that spinal NO release facilitates the mechanoceptive C-fibres, and this facilitatory effect is masked by supraspinal (possibly forebrain) and local inhibitory effects of NO during the micturition reflex in awake rats. Urethane seems to inhibit the supraspinal and local inhibitory effects of NO, resulting in unmasking the facilitatory effect of NO in the spinal cord and brain stem. During the voiding phase, urethral relaxation depends on the peripheral but not the central NO system.

NO pain: potential roles of nitric oxide in neuropathic pain

The disabling human syndrome of "neuropathic pain" is an intractable complication of peripheral nerve injury or degeneration. A complex interaction between injured peripheral axons, sensory neurons and central nervous system signaling is thought to account for it. In this brief review, we present evidence that the free radical signaling molecule, nitric oxide (NO) may act at several levels of the nervous system during the development of experimental neuropathic pain. For example, NO may directly influence injured axons in the periphery, may indirectly influence pain by its role in the process of Wallerian degeneration, and may signal in the dorsal horn of the spinal cord. While it is premature to argue for therapeutic approaches that alter NO actions, it may be an important player in the cascade of events that generate neuropathic pain.

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.

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

In this study, immunohistochemistry for neuronal nitric oxide synthase (bNOS-IR), nicotinamide adenine dinucleotide phosphate diaphorase histochemistry (NADPHd) and nitric oxide synthase radioassay were used to study the occurrence, number and distribution pattern of nitric oxide synthesizing neurons in the lumbar (L1-L7) and sacral (S1-S3) dorsal root ganglia of the dog. Nitric oxide synthase immunolabelling was present in a large number of small- (area <1,000 microm(2)) and medium-sized (area 1,000-2,000 microm(2)) as well as in a limited number of large-sized (area >2000 microm(2)) neurons. Although neuronal nitric oxide synthase immunolabelling and histochemical staining provided intense staining of multiple small- and medium-sized neurons in all lumbar and sacral dorsal root ganglia, immuno-labelled or histochemically stained somata exhibited little topographic distribution in individual dorsal root ganglia. Great heterogeneity was noticed in the immunolabelling of medium-sized nitric oxide synthase immunopositive neurons ranging from lightly immuno-labelled somata to heavily immunoreactive ones with completely obscured nuclei. Both staining procedures proved to be highly effective in visualizing intraganglionic fibers of various diameters. In general, the largest fibers revealed at the peripheral end of lumbar and sacral dorsal root ganglia were larger, 6.49-9.35 mum in diameter, while those running centrally and proceeding into the dorsal roots were about 30% reduced, ranging between 5.32 and 8.67 microm in diameter. Peripherally, the occurrence of nitric oxide synthase detected in axonal profiles, and confirmed histochemically, in the specimens of the femoral and sciatic nerves, is the first indication of the presence of nitric oxide synthase in the peripheral processes of somata located in L4-S2 dorsal root ganglia. Large and thin central nitric oxide synthase immunoreactive processes of L1-S3 dorsal root ganglion neurons segregate shortly before entering the spinal cord, the former making a massive medial bundle in the dorsal root accompanied by a slim lateral bundle penetrating Lissauer's tract. Quantitative assessment of the distribution of bNOS-IR and/or NADPHd-stained neurons showed a peculiar pattern in relation to spinal levels. Apparent incongruity was found in the total number of NADPHd-stained versus bNOS-IR neurons, demonstrating a clear prevalence of small bNOS-IR somata in all lumbar ganglia, while medium-sized NADPHd-stained somata clearly prevailed all along the rostrocaudal axis with a peak in L5 ganglion. While the number of small bNOS-IR neurons clearly outnumbered NADPHd-stained and NADPHd-unstained somata in S1-S3 ganglia, an inverse relation appeared comparing the total number of medium-sized NADPHd-stained and NADPHd-unstained somata compared with the number of moderate and intense bNOS-IR neurons. Densitometry of bNOS-IR and NADPHd-stained neurons in lumbar and sacral ganglia revealed two distinct subsets of densitometric profiles, one relating to more often found medium-sized bNOS immuno-labelled and the other, characteristic for moderately bNOS immunoreactive somata of the same cell size. Considerable differences in catalytic nitric oxide synthase activity, determined by conversion of [(3)H]arginine to [(3)H]citrulline were obtained in lumbosacral dorsal root ganglia all along the lumbosacral intumescence, the lowest (0.898+/- 0.2 dpm/min/microg protein) being in the L4 dorsal root ganglion and the highest (4.194+/-0.2 dpm/min/microg protein) in the S2 dorsal root ganglion.

Possible involvement of the spinal nitric oxide/cGMP pathway in vincristine-induced painful neuropathy in mice

The mechanisms that underlie the development of vincristine-induced painful neuropathy are poorly understood. The nitric oxide (NO)-cGMP pathway has been reported to be involved in the spinal transmission of nociceptive information. In the present study, we examined whether alterations in spinal nociceptive processing via the NO-cGMP pathway contribute to vincristine-induced painful neuropathy in mice. Mice were intraperitoneally treated with vincristine at a dose of 0.05 mg/kg 1 day after the measurement of pre-drug latency in the tail-flick test, and then treated with a dose of 0.125 mg/kg twice a week for 6 weeks. In vincristine-treated mice, a significant decrease in tail-flick latencies developed at 4 weeks after treatment. Pretreatment with L-arginine (30-300 mg/kg, s.c.), a substrate of NO synthase (NOS), dose-dependently increased the tail-flick latencies in vincristine-treated mice. The L-arginine-induced increase in tail-flick latencies in vincristine-treated mice was completely reversed by i.t. pretreatment with NG-nitro-L-arginine methyl ester (L-NAME, 3-30 nmol), a NOS inhibitor. Furthermore, i.t. pretreatment with 8-bromoguanosine 3', 5'-cyclic monophosphate (8-Br-cGMP, 0.3-3.0 nmol), a membrane-permeable cGMP analog, dose-dependently increased the tail-flick latencies in vincristine-treated mice. The contents of NO metabolites, cGMP and protein levels of neuronal NOS in the spinal cord in vincristine-treated mice were significantly reduced compared to those in vehicle-treated naive mice. These results indicate that dysfunction of the L-arginine/NO/cGMP cascade in the spinal cord may trigger vincristine-induced thermal hyperalgesia in mice.

Nitric oxide and its modulators in chronic constriction injury-induced neuropathic pain in rats

This study was conducted to examine the role of nitric oxide (NO) in peripheral neuropathy induced by chronic constriction injury of sciatic nerve of rats by using NO precursor, NO donors and nitric oxide synthase (NOS) inhibitors. Chronic constriction injury of sciatic nerve of rats resulted in peripheral neuropathy as confirmed by nociceptive behavioural tests using mechanical, thermal and cold allodynia. NO precursor, L-arginine and NO donors sodium nitroprusside, S-nitroso-N-acetylpenicillamine potentiated the hyperalgesia and allodynia significantly suggesting proalgesic effect in neuropathic rats. Intracerebroventricular (i.c.v.) administration of rats with NOS inhibitors such as L-N(G)-nitroarginine methyl ester, N-iminoethyl lysine and 7-nitroindazole did not show any effect but i.p. administration of NOS inhibitors aminoguanidine, L-N(G)-nitroarginine methyl ester and 7-nitroindazole caused alleviation of pain. The study confirms the involvement of endogenously synthesized and exogenously administered NO in chronic constriction injury-induced neuropathy in rats. Significant increase in the levels of nitrate and nitrite in ligated sciatic nerve suggest that local up regulation of NO in the production and maintenance of neuropathic pain. In conclusion, initial attempt to manipulate L-arginine: NO pathway is indicative of therapeutic potential of these interventions in the management of neuropathic pain.

L-NAME- and ADMA-induced sympathetic neural activation in conscious rats

Although studies in anesthetized, sino-aortic denervated animals indicate that inhibition of central nitric oxide (NO) causes an excitatory influence on efferent sympathetic nerve activity (SNA) that is normally offset by baroreflex activation, studies in conscious animals have not provided clear-cut evidence for a sympathoexcitatory effect of N(omega)-nitro-l-arginine methyl ester (L-NAME) or the endogenous circulating NO synthase (NOS) inhibitor asymmetric dimethylarginine (ADMA). Thus our goals were to 1) use surgical sino-aortic denervation to test for a sympathoexcititatory effect of intravenous l-NAME in conscious rats, and 2) to determine whether SNA responses to intravenous L-NAME can be extrapolated directly to intravenous ADMA. We recorded mean arterial blood pressure and renal SNA in both intact and sino-aortic-denervated conscious rats during 3 h of continuous intravenous infusion with either L-NAME or ADMA. When we eliminated the confounding influence of the sino-aortic baroreceptors, L-NAME produced a progressive increase in SNA with the peak response exceeding the baseline level of nerve firing by 150%. The same type of frank sympathetic activation was observed with intravenous ADMA. Taken together, these data offer straightforward evidence for l-NAME, as well as ADMA-induced sympathetic activation with direct recordings of SNA in conscious animals. These data confirm and extend the concept that circulating endogenous NOS inhibitors can constitute an excitatory signal to SNA.

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.

Inhibition of nitric oxide synthesis blocks the inhibitory response to capsaicin in intestinal circular muscle preparations from different species

Moderate concentrations of the sensory stimulant drug capsaicin caused relaxation in human and animal intestinal circular muscle preparations (guinea-pig proximal, mouse distal colon, human small intestine and appendix) in vitro. With the exception of the guinea-pig colon, the nitric oxide (NO) synthase inhibitor N(G)-nitro-L-arginine (L-NOARG; 10(-4) M) strongly inhibited the relaxant effect of capsaicin. Tetrodotoxin, an inhibitor of voltage-sensitive Na+ channels failed to significantly reduce the inhibitory effect of capsaicin in the guinea-pig colon, human ileum and appendix; it caused an approximately 50% reduction in the mouse colon. The relaxant effect of capsaicin was strongly reduced in colonic preparations from transient receptor potential vanilloid type (TRPV1) receptor knockout mice as compared to their wildtype controls. It is concluded that nitric oxide, possibly of sensory origin, is involved in the relaxant action of capsaicin in the circular muscle of the mouse and human intestine.

Evidence that nitric oxide-glutamate cascade modulates spinal antinociceptive effect of morphine: a behavioural and microdialysis study in rats

We evaluated the ability of spinally administered nitric oxide (NO) synthase inhibitor to modulate antinociceptive action of intrathecal (i.t.) morphine in rats by measuring the early and late phases of flinching and licking/biting in the formalin test. To determine the contribution of spinal NO and glutamate, we measured the release of NO metabolites (nitrite/nitrate) and glutamate from the spinal cord in rats, using a microdialysis probe placed in the lumbar space. The i.t. administration of NG-nitro L-arginine methyl ester (L-NAME) produced a dose-dependent reduction in the number of flinches during the late phase, whereas there were no significant alterations in the late phase licking/biting, and early phase flinching and licking/biting. Spinal administration of morphine at low doses produced a significant antinociceptive activity in the early and late phases of the flinching behaviour, whereas higher doses of morphine were required to obtain a significant effect in the licking/biting behaviour during both phases. Combination of L-NAME with morphine resulted in an enhanced reduction in the early and late phase flinching. Enhanced antinociceptive activity was observed in the late phase licking/biting by i.t. combined administration of L-NAME (400 nmol) and morphine (1.25 nmol). In the present study, we have confirmed our prior results that injection of formalin (5.0%) into the plantar surface of the paw evoked a biphasic spinal release of nitrite/nitrate and a transient release of glutamate. Formalin-evoked release of nitrite/nitrate and glutamate was also reduced markedly by i.t. combined administration of L-NAME and morphine. These behavioural and biochemical results suggest that i.t. administered L-NAME may enhance morphine-induced antinociception through an increased inhibition of nitrite/nitrate and glutamate releases evoked by formalin injection at the spinal cord level.

Neurochemical characterization of extrinsic innervation of the guinea pig rectum

The presence of markers for parasympathetic, sympathetic, and glutamatergic or peptidergic sensory innervation was investigated by using in vitro tracing with biotinamide, combined with immunohistochemistry, to characterise quantitatively extrinsic axons to myenteric ganglia of the guinea pig rectum. Of biotinamide-filled varicose axons, 3.6 +/- 1.3% were immunoreactive for tyrosine hydroxylase (TH) and 16.0 +/- 4.8% for vesicular acetylcholine transporter (VAChT). TH and vesicular monoamine transporter (VMAT1) showed high coexistence (83-100%), indicating that varicosities lacking TH immunoreactivity also lacked VMAT1. VAChT was detectable in 77% of choline acetyltransferase (ChAT)-immunoreactive varicosities. Calcitonin gene-related peptide (CGRP) was detected in 5.3 +/- 1.6% of biotinamide-labeled varicosities, the vesicular glutamate transporter (VGluT) 1 in 2.8 +/- 0.8%, and VGluT2 in 11.3 +/- 4.2% of varicosities of extrinsic origin. Varicosities from the same axon showed consistent immunoreactivity. A novel type of nerve ending was identified, with branching, flattened lamellar endings, similar to the intraganglionic laminar endings (IGLEs) of the proximal gut. Rectal IGLEs were frequently immunoreactive for VGluT1 and VGluT2. Thus most varicose axons of extrinsic origin, which innervate rectal myenteric ganglia, lack detectable levels of immunoreactivity for TH, VMAT1, VAChT, ChAT, VGluT1/2, or CGRP, under conditions in which these markers are readily detectable in other axons. Although some unlabeled varicosities may belong to afferent axons that lack detectable CGRP or VGluT1/2 in the periphery, this suggests that a large proportion of axons do not release any of the major autonomic or sensory transmitters. We speculate that this may vary under particular circumstances, for example, inflammation or obstruction of the gut.

Phosphodiesterase 5 Inhibitors in Rapid Ejaculation

Rapid (premature) ejaculation (RE) is a very common sexual disorder. This condition may be primary or secondary to underlying disease. Control of RE has been primarily focused on behavioural therapy, topical anaesthetics, tricyclic antidepressants and selective serotonin reuptake inhibitors; however, an approved treatment does not exist. Recently, a number of clinical trials have studied the potential effectiveness of the phosphodiesterase (PDE)-5 inhibitor sildenafil in the treatment of RE. Results of most of these studies have been encouraging. Available data indicate that there is clinical, anatomical, physiological, pharmacological and genetic evidence to explain the efficacy of PDE5 inhibitors in RE. The rationale for the use of PDE5 inhibitors in the treatment of RE could be due to possible peripheral and central mechanisms. Possible peripheral ejaculation retarding capabilities may include modulation of the contractile response of the vas deferens (VD), seminal vesicles (SV), prostate and urethra, induction of a state of peripheral analgesia, and prolongation of the total duration of erection. Possible central mechanisms may involve lessening of the central sympathetic output. Furthermore, there is evidence from knockout mice to explain the efficacy of PDE5 inhibitors in RE. Mice lacking the gene for endothelial nitric oxide synthase develop a condition similar to RE. On the other hand, mice lacking the gene for heme oxygenase-2 develop a condition similar to delayed ejaculation. This review also discusses the findings against the use of these agents in RE. In conclusion, a review of the literature suggests the potential usefulness of PDE5 inhibitors as a promising line of therapy in RE but further studies are needed.

Histochemical observation of nitric oxide synthase in trigeminal ganglion of rats with experimental pulpitis

In order to understand the roles of nitric oxide (NO) in pulpalgia and pulpitis, the histochemistry of nitric oxide synthase (NOS) in the neurons of trigeminal ganglion in experimental pulpitis rat and human inflammatory dental pulp tissues were histochemically studied by NADPH-diaphorase (NADPH-D) techniques. Results showed that NADPH-D positive neurons were scattered in rat trigeminal ganglions, but the sizes of positive neurons were not changed. None of NOS-positive fibers was found in human normal and inflammatory dental pulp tissues. The results suggested that NOS in trigeminal ganglion might play an important role in sensory transmission and regulation of pulpalgia. The absence of NOS-positive nerves in human pulp suggested that NO may not be related to inflammatory stimulation and transmission in dental pulp tissues.

Activation and up-regulation of spinal cord nitric oxide receptor, soluble guanylate cyclase, after formalin injection into the rat hind paw

Nitric oxide synthase is expressed abundantly in the spinal cord, and nitric oxide (NO) has been shown to play important roles in the central mechanism of inflammatory hyperalgesia. However, the expression and function of the NO receptor, soluble guanylate cyclase, is not fully understood in this processing at the spinal cord level. In the present study, we report that the soluble guanylate cyclase alpha(1) subunit but not the beta(1) subunit was expressed in rat spinal cord, particularly in the dorsal horn. We showed that intrathecal administration of a selective inhibitor of soluble guanylate cyclase, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, produced a significant anti-nociception demonstrated by the decrease in the number of flinches and shakes in the formalin-induced inflammatory pain model. This was accompanied by a marked reduction in formalin-induced c-fos expression in the spinal cord. During formalin-induced long-lasting inflammation, we found that the expression of the alpha(1) subunit of soluble guanylate cyclase was dramatically increased in the lumbar spinal cord on the second and fourth days after formalin injection into the dorsal side of a hind paw. Intraperitoneal pretreatment with an N-methyl-D-aspartate (NMDA) receptor antagonist, dizocilpine maleate (MK-801), and a neuronal NO synthase inhibitor, 7-nitroindazole, not only significantly blocked formalin-induced secondary thermal hyperalgesia but also suppressed formalin-produced increase in the alpha(1) subunit of soluble guanylate cyclase in the spinal cord. The present results indicate that peripheral inflammation not only initially activates but also later up-regulates soluble guanylate cyclase expression via the NMDA receptor-NO signaling pathway, suggesting that soluble guanylate cyclase might be involved in the central mechanism of formalin-induced inflammatory hyperalgesia in the spinal cord.

Subcutaneous formalin and intraplantar carrageenan increase nitric oxide release as measured by in vivo voltammetry in the spinal cord

The paper describes in vivo voltammetric detection of nitric oxide with carbon fibre microelectrodes at the lumbar spinal dorsal horn level of decerebrated-spinalized rats during peripheral noxious inflammatory processes. At the lumbar (L3-L4) dorsal horn level, a nitric oxide dependent peak of oxidation current (650 mV), remaining stable for up to 4h ((92 +/- 5)% of control) could be detected indicating that significant amounts of nitric oxide are produced continuously. Following subcutaneous injection in the hindpaw of 50 microl of 0.5% formalin the oxidation current rapidly increased ((115 +/- 5)% of control at 25 min) and reached (120 +/- 6)% of control 1h later. Subsequently the voltammograms stabilized for up to 90 min and decreased ((107 +/- 4)% at 124 min). After an injection in the hindpaw of 150 microl of 4% carrageenan, the voltammograms remained at control level for 1h and then the oxidation current increased continuously for up to 4h ((145 +/- 16)% of control at 240 min); such an increase was reversed by ketamine. In these two models of inflammation, the delay in onset and the duration of the increases in NO release within the dorsal horn relate, to some extent, to the time course of the peripheral inflammatory processes, since they are shorter after formalin than after carrageenan. The results provide a direct in vivo demonstration that the intercellular messenger nitric oxide participates in the transmission of noxious afferent messages within the dorsal horn of the spinal cord following peripheral inflammation.

Nitric oxide synthase inhibitors for the treatment of chronic tension-type headache

Chronic tension-type headache may be caused by prolonged painful input from pericranial myofacial tissues, for example tender points, resulting in central sensitisation (increased excitability of neurons in the central nervous system). Animal studies have shown that sensitisation of pain pathways may be caused by or associated with the activation of neuronal nitric oxide synthase and the generation of nitric oxide. Furthermore, it has been shown that nitric oxide synthase inhibitors reduce central sensitisation in animal models of persistent pain. On the basis of this information, the analgesic effect of the nitric oxide synthase inhibitor L-N(G) methyl arginine hydrochloride was investigated. This drug significantly reduced headache and myofacial factors in patients with chronic tension-type headache. These studies show that nitric oxide plays a crucial role in the pathophysiology of tension-type headache. The analgesic effect of nitric oxide synthase inhibition in patients with chronic tension-type headache is probably due to a reduction in central sensitisation at the level of the spinal dorsal horn, trigeminal nucleus or both. Furthermore, inhibition of nitric oxide synthase may become a novel principle in the future treatment of chronic headache.