Prolonged sympathetic innervation of sensory neurons in rat thoracolumbar dorsal root ganglia during chronic colitis

Plp1-expresssing perineuronal DRG cells facilitate colonic and somatic chronic mechanical pain involving Piezo2 upregulation in DRG neurons

Satellite glial cells (SGCs) of dorsal root ganglia (DRGs) are activated in a variety of chronic pain conditions; however, their mediation roles in pain remain elusive. Here, we take advantage of proteolipid protein (PLP)/creERT-driven recombination in the periphery mainly occurring in SGCs of DRGs to assess the role of SGCs in the regulation of chronic mechanical hypersensitivity and pain-like responses in two organs, the distal colon and hindpaw, to test generality. We show that PLP/creERT-driven hM3Dq activation increases, and PLP/creERT-driven TrkB.T1 deletion attenuates, colon and hindpaw chronic mechanical hypersensitivity, positively associating with calcitonin gene-related peptide (CGRP) expression in DRGs and phospho-cAMP response element-binding protein (CREB) expression in the dorsal horn of the spinal cord. Activation of Plp1+ DRG cells also increases the number of small DRG neurons expressing Piezo2 and acquiring mechanosensitivity and leads to peripheral organ neurogenic inflammation. These findings unravel a role and mechanism of Plp1+ cells, mainly SGCs, in the facilitation of chronic mechanical pain and suggest therapeutic targets for pain mitigation.

Electroacupuncture Zusanli (ST36) Relieves Somatic Pain in Colitis Rats by Inhibiting Dorsal Root Ganglion Sympathetic-Sensory Coupling and Neurogenic Inflammation

Referred somatic pain triggered by hyperalgesia is common in patients with inflammatory bowel disease (IBD). It was reported that sprouting of sympathetic nerve fibers into the dorsal root ganglion (DGR) and neurogenic inflammation were related to neuropathic pain, the excitability of neurons, and afferents. The purpose of the study was to explore the potential and mechanism of electroacupuncture (EA) at Zusanli (ST36) for the intervention of colon inflammation and hyperalgesia. Sprague-Dawley (SD) was randomly divided into four groups, including control, model, EA, and sham-EA. Our results showed EA treatment significantly attenuated dextran sulfate sodium- (DSS-) induced colorectal lesions and inflammatory cytokine secretion, such as TNF-α, IL-1β, PGE2, and IL-6. EA also inhibited mechanical and thermal pain hypersensitivities of colitis rats. Importantly, EA effectively abrogated the promotion effect of DSS on ipsilateral lumbar 6 (L6) DRG sympathetic-sensory coupling, manifested as the sprouting of tyrosine hydroxylase- (TH-) positive sympathetic fibers into sensory neurons and colocalization of and calcitonin gene-related peptide (CGRP). Furthermore, EA at Zusanli (ST36) activated neurogenic inflammation, characterized by decreased expression of substance P (SP), hyaluronic acid (HA), bradykinin (BK), and prostacyclin (PGI2) in colitis rat skin tissues corresponding to the L6 DRG. Mechanically, EA treatment reduced the activation of the TRPV1/CGRP, ERK, and TLR4 signaling pathways in L6 DRG of colitis rats. Taken together, we presumed that EA treatment improved colon inflammation and hyperalgesia, potentially by suppressing the sprouting of sympathetic nerve fibers into the L6 DGR and neurogenic inflammation via deactivating the TRPV1/CGRP, ERK, and TLR4 signaling pathways.

Maladaptive consequences of inflammatory events shape individual immune identity

The vertebrate immune system develops in layers, as modes of immunity have evolved on top of each other through time with the expansion of organismal complexity. The maturation timing of immune cell subsets, such as innate immune cells, innate-like cells and adaptive cells, corresponds to their physiological roles in protective immunity. While various cell subsets have specialized roles, they also complement each other to clear pathogens, resolve inflammation and maintain homeostasis, especially at barrier sites with high microbial density. Immune cells adapt to inflammatory insults through mechanisms including epigenetic and metabolic reprogramming, clonal expansion and enhanced communication with the surrounding tissue environment. Over time, these adaptations shape an individual immune identity, reflective of the overlay between the genetic predisposition and the antigenic and environmental exposures of each individual. While some aspects of this immune shaping are natural consequences of immune maturation over time, others are maladaptive and predispose to irreversible pathology. In this Perspective, we provide a framework for categorizing the shaping events of the immune response, in terms of mechanisms, contexts and functional outcomes. We aim to clarify how these terms can be appropriately applied to future findings that impact immune function.

Neuroimmune Interactions in Peripheral Organs

Interactions between the nervous and immune systems were recognized long ago, but recent studies show that this crosstalk occurs more frequently than was previously appreciated. Moreover, technological advances have enabled the identification of the molecular mediators and receptors that enable the interaction between these two complex systems and provide new insights on the role of neuroimmune crosstalk in organismal physiology. Most neuroimmune interaction occurs at discrete anatomical locations in which neurons and immune cells colocalize. Here, we describe the interactions of the different branches of the peripheral nervous system with immune cells in various organs, including the skin, intestine, lung, and adipose tissue. We highlight how neuroimmune crosstalk orchestrates physiological processes such as host defense, tissue repair, metabolism, and thermogenesis. Unraveling these intricate relationships is invaluable to explore the therapeutic potential of neuroimmune interaction. Expected final online publication date for the Annual Review of Neuroscience, Volume 45 is July 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

The Anti-Inflammatory Actions and Mechanisms of Acupuncture from Acupoint to Target Organs via Neuro-Immune Regulation

Inflammation plays a significant role in the occurrence and development of multiple diseases. This study comprehensively reviews and presents literature from the last five years, showing that acupuncture indeed exerts strong anti-inflammatory effects in multiple biological systems, namely, the immune, digestive, respiratory, nervous, locomotory, circulatory, endocrine, and genitourinary systems. It is well known that localized acupuncture-mediated anti-inflammatory effects involve the regulation of multiple populations and functions of immune cells, including macrophages, granulocytes, mast cells, and T cells. In acupuncture stimulation, macrophages transform from the M1 to the M2 phenotype and the negative TLR4 regulator PPARγ is activated to inhibit the intracellular TLR/MyD88 and NOD signaling pathways. The downstream IκBα/NF-κB and P38 MAPK pathways are subsequently inhibited by acupuncture, followed by suppressed production of inflammasome and proinflammatory mediators. Acupuncture also modulates the balance of helper T cell populations. Furthermore, it inhibits oxidative stress by enhancing SOD activity via the Nrf2/HO-1 pathway and eliminates the generation of oxygen free radicals, thereby preventing inflammatory cell infiltration. The anti-inflammatory effects of acupuncture on different biological systems are also specific to individual organ microenvironments. As part of its anti-inflammatory action, acupuncture deforms connective tissue and upregulates the secretion of various molecules in acupoints, further activating the NF-κB, MAPK, and ERK pathways in mast cells, fibroblasts, keratinocytes, and monocytes/macrophages. The somatic afferents present in acupuncture-activated acupoints also convey sensory signals to the spinal cord, brainstem, and hypothalamic neurons. Upon information integration in the brain, acupuncture further stimulates multiple neuro-immune pathways, including the cholinergic anti-inflammatory, vagus-adrenal medulla-dopamine, and sympathetic pathways, as well as the hypothalamus-pituitary-adrenal axis, ultimately acting immune cells via the release of crucial neurotransmitters and hormones. This review provides a scientific and reliable basis and viewpoints for the clinical application of acupuncture in various inflammatory conditions.

Beta 2-adrenergic receptor mediates noradrenergic action to induce cyclic adenosine monophosphate response element-binding protein phosphorylation in satellite glial cells of dorsal root ganglia to regulate visceral hypersensitivity

ABSTRACT

Sympathoneuronal outflow into dorsal root ganglia (DRG) is suggested to be involved in sympathetically maintained chronic pain, which is mediated by norepinephrine (NE) action on DRG cells. This study combined in vitro and in vivo approaches to identify the cell types of DRG that received NE action and examined cell type-specific expression of adrenergic receptors (ARs) in DRG. Using DRG explants, we identified that NE acted on satellite glial cells (SGCs) to induce the phosphorylation of cAMP response element-binding protein (CREB). Using primarily cultured SGCs, we identified that beta (β)2-adrenergic receptor but not alpha (α)adrenergic receptor nor other βAR isoforms mediated NE-induced CREB phosphorylation and CRE-promoted luciferase transcriptional activity. Using fluorescence in situ hybridization and affinity purification of mRNA from specific cell types, we identified that β2AR was expressed by SGCs but not DRG neurons. We further examined β2AR expression and CREB phosphorylation in vivo in a model of colitis in which sympathetic nerve sprouting in DRG was observed. We found that β2AR expression and CREB phosphorylation were increased in SGCs of thoracolumbar DRG on day 7 after colitis induction. Inhibition but not augmentation of β2AR reduced colitis-induced calcitonin gene-related peptide release into the spinal cord dorsal horn and colonic pain responses to colorectal distention. Prolonged activation of β2AR in naive DRG increased calcitonin gene-related peptide expression in DRG neurons. These findings provide molecular basis of sympathetic modulation of sensory activity and chronic pain that involves β2AR-mediated signaling in SGCs of DRG.

Neuro-Immune Modulation Effects of Sacral Nerve Stimulation for Visceral Hypersensitivity in Rats

Background: Visceral hypersensitivity (VH) is one of the underlying pathophysiologies of irritable bowel syndrome. Mast cell overactivation has been found to be one of the main causes of VH. We investigated the effects and mechanisms of actions of sacral nerve stimulation (SNS) on visceral pain in a rodent model of VH.

Methods: The VH was established by an intrarectal infusion of AA in 10-day-old pups. Rats were chronically implanted with electrodes for SNS and recording electromyogram (EMG) and electrocardiogram. The acute study was performed in 2-randomized sessions with SNS (14 Hz, 330 μs, 40% motor threshold or MT, 30 min) or sham-SNS. Later on, rats were randomized into SNS/sham-SNS groups and a chronic study was performed with 2 h-daily SNS or sham-SNS for 21 days. Visceromotor reflexes were assessed by abdominal EMG and withdrawal reflex (AWR). Colon tissues were collected to study colonic acetylcholine (ACh), the enteric neurons (ChAT, nNOS, and PGP9.5), mast cells activity [Tryptase, prostaglandins E2 (PGE2), and cyclooxygenases-2 (COX2)] and pain markers [nerve growth factor (NGF) and Sub-P].

Key Results: Sacral nerve stimulation significantly improved visceromotor reflexes assessed by the EMG and AWR, compared with sham-SNS. SNS normalized the protein expressions of ChAT and nNOS and regulated mast cells activity by downregulating Tryptase, COX2, and PGE2. Neonatal AA administration upregulated NGF and Sub-P; chronic SNS significantly decreased these pain biomarkers. Concurrently, chronic SNS increased ACh in colon tissues and vagal efferent activity.

Conclusions: Sacral nerve stimulation reduces VH in rats and this ameliorating effect might be attributed to the suppression of mast cell overactivation in the colon tissue via the modulation of autonomic nervous system functions.

Review: Pelvic nerves - from anatomy and physiology to clinical applications

A prerequisite for nerve-sparing pelvic surgery is a thorough understanding of the topographic anatomy of the fine and intricate pelvic nerve networks, and their connections to the central nervous system. Insights into the functions of pelvic nerves will help to interpret disease symptoms correctly and improve treatment. In this article, we review the anatomy and physiology of autonomic pelvic nerves, including their topography and putative functions. The aim is to achieve a better understanding of the mechanisms of pelvic pain and functional disorders, as well as improve their diagnosis and treatment. The information will also serve as a basis for counseling patients with chronic illnesses. A profound understanding of pelvic neuroanatomy will permit complex surgery in the pelvis without relevant nerve injury.

Spinal neuron-glia-immune interaction in cross-organ sensitization

Inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS), historically considered as regional gastrointestinal disorders with heightened colonic sensitivity, are increasingly recognized to have concurrent dysfunction of other visceral and somatic organs, such as urinary bladder hyperactivity, leg pain, and skin hypersensitivity. The interorgan sensory cross talk is, at large, termed "cross-organ sensitization." These organs, anatomically distant from one another, physiologically interlock through projecting their sensory information into dorsal root ganglia (DRG) and then the spinal cord for integrative processing. The fundamental question of how sensitization of colonic afferent neurons conveys nociceptive information to activate primary afferents that innervate distant organs remains ambiguous. In DRG, primary afferent neurons are surrounded by satellite glial cells (SGCs) and macrophage accumulation in response to signals of injury to form a neuron-glia-macrophage triad. Astrocytes and microglia are major resident nonneuronal cells in the spinal cord to interact, physically and chemically, with sensory synapses. Cumulative evidence gathered so far indicate the indispensable roles of paracrine/autocrine interactions among neurons, glial cells, and immune cells in sensory cross-activation. Dichotomizing afferents, sensory convergency in the spinal cord, spinal nerve comingling, and extensive sprouting of central axons of primary afferents each has significant roles in the process of cross-organ sensitization; however, more results are required to explain their functional contributions. DRG that are located outside the blood-brain barrier and reside upstream in the cascade of sensory flow from one organ to the other in cross-organ sensitization could be safer therapeutic targets to produce less central adverse effects.

Sacral nerve stimulation with optimized parameters improves visceral hypersensitivity in rats mediated via the autonomic pathway

The purpose of this study was to determine effects and mechanisms of sacral nerve stimulation (SNS) on visceral hypersensitivity in rodent models of colonic hypersensitivity. SNS was performed with different sets of parameters for 30 min in six regular rats. Visceral sensitivity was assessed by the measurement of electromyogram and abdominal withdrawal reflex before and after SNS. Real/sham SNS with optimized parameters was performed in 8 restraint stress-induced visceral hypersensitivity rats and 10 neonatal acetic acid-treated colonic hypersensitivity rats; acute effect of SNS was assessed by comparing electromyogram and heart rate variability. Neonatal acetic acid-treated rats were treated by SNS (n = 10) or sham-SNS (n = 10) daily for seven days for the assessment of the chronic effect of SNS. (1) When the stimulation amplitude was reduced from 90% of motor threshold to 65% or 40% motor threshold, SNS with certain parameters showed an inhibitory effect on abdominal withdrawal reflex. The best stimulation parameters for SNS were “14 Hz, 330 µs, and 40% motor threshold.” (2) SNS significantly reduced visceral hypersensitivity and improved autonomic function in restraint stress-induced rats. The inhibitory effect was blocked by naloxone. (3)Acute and chronic SNS significantly reduced visceral hypersensitivity and improved autonomic function in acetic acid-treated rats. SNS with reduced stimulation strength may be used to treat colonic hypersensitivity and the best stimulation parameters seem to be “14 Hz, 330 µs and 40% motor threshold”. SNS with optimized parameters improved visceral hypersensitivity in rodent models of colonic hypersensitivity mediated via the autonomic and opioid mechanisms.

Electroacupuncture relieved visceral and referred hindpaw hypersensitivity in colitis rats by inhibiting tyrosine hydroxylase expression in the sixth lumbar dorsal root ganglia

Irritable bowel syndrome patients frequently complain of pain in body regions somatotopically distinct from the gut, suggesting the involvement of an exaggerated signaling process in both visceral and somatic sensory pathways. Increasing evidence has shown that sprouting of tyrosine hydroxylase immunoreactive (TH-IR) fibers toward sensory neurons in dorsal root ganglia maintains and exacerbates the neuropathic and inflammatory pain, as well as colonic inflammation. The aim of the present study was to determine whether electroacupuncture could alleviate the visceral and secondary somatic hyperalgesia in colitis rats by suppressing the TH-IR expression in related dorsal root ganglia. After trinitrobenzene sulfonic acid irritation, rats developed inflammatory tissue damage in the distal colon, which was accompanied by visceral hypersensitivity and secondary hind paw hyperalgesia, as indicated by enhanced visceromotor response to colorectal distension and decreased mechanical and thermal withdrawal latency of the hind paw. Additionally, excessive TH-IR fibers sprouted toward calcitonin gene-related peptide immunoreactive sensory neurons, and TH-IR neurons also increased in the sixth lumbar dorsal root ganglia of colitis rats. Both electroacupuncture and guanethidine attenuated visceral and referred hind paw hyperalgesia by inhibiting the over-expression of TH-IR neurons and fibers in the sixth lumbar dorsal root ganglia. Moreover local inflammatory damage in the distal colon was restored after 7 days of electroacupuncture intervention. These results suggest that electroacupuncture relieved visceral and referred hind paw hypersensitivity in colitis rats by inhibiting TH expression in the sixth lumbar dorsal root ganglia.

Neuro-Immune Cell Units: A New Paradigm in Physiology

The interplay between the immune and nervous systems has been acknowledged in the past, but only more recent studies have started to unravel the cellular and molecular players of such interactions. Mounting evidence indicates that environmental signals are sensed by discrete neuro-immune cell units (NICUs), which represent defined anatomical locations in which immune and neuronal cells colocalize and functionally interact to steer tissue physiology and protection. These units have now been described in multiple tissues throughout the body, including lymphoid organs, adipose tissue, and mucosal barriers. As such, NICUs are emerging as important orchestrators of multiple physiological processes, including hematopoiesis, organogenesis, inflammation, tissue repair, and thermogenesis. In this review we focus on the impact of NICUs in tissue physiology and how this fast-evolving field is driving a paradigm shift in our understanding of immunoregulation and organismal physiology.

A role for interleukin 17A in IBD-related neuroplasticity

BACKGROUND

Changes to the structure and function of the innervation of the gut contribute to symptom generation in inflammatory bowel diseases (IBD). However, delineation of the mechanisms of these effects has proven difficult. Previous work on sympathetic neurons identified interleukin (IL)-17A as a novel neurotrophic cytokine. Since IL-17A is involved in IBD pathogenesis, we tested the hypothesis that IL-17A contributes to neuroanatomical remodeling during IBD.

METHODS

Immunohistochemistry for tyrosine hydroxylase was used to identify sympathetic axons in mice with dextran sulphate sodium (DSS)-induced colitis and controls. Axon outgrowth from sympathetic neurons in response to incubation in cytokines or endoscopic patient biopsy supernatants was quantified.

KEY RESULTS

DSS-induced colitis led to an increase in tyrosine hydroxylase immunoreactivity in the inflamed colon but not the spleen. Colonic supernatants from mice with colitis and biopsy supernatants from Crohn's disease patients increased axon outgrowth from mouse sympathetic neurons compared to supernatants from uninflamed controls. An antibody that neutralized IL-17A blocked the ability of DSS-induced colitis and Crohn's disease supernatants to induce axon extension.

CONCLUSIONS AND INFERENCES

These findings identify IL-17A as a potential mediator of neuroanatomical remodeling of the gut innervation during IBD.

Colitis-induced bladder afferent neuronal activation is regulated by BDNF through PLCγ pathway

Patients with inflammatory bowel disease (IBD) or irritable bowel syndrome (IBS) often experience increased sensory responsiveness in the urinary bladder reflecting neurogenic bladder overactivity. Here we demonstrate that colitis-induced up-regulation of the phospholipase C gamma (PLCγ) pathway downstream of brain-derived neurotrophic factor (BDNF) in bladder afferent neurons in the dorsal root ganglia (DRG) plays essential roles in activating these neurons thereby leading to bladder hyperactivity. Upon induction of colitis with 2,4,6-trinitrobenzenesulfonic acid (TNBS) in rats, we found that the phosphorylation (activation) level of cAMP responsive element-binding (p-CREB) protein, a molecular switch of neuronal plasticity, was increased in specifically labeled bladder afferent neurons in the thoracolumbar and lumbosacral DRGs. In rats having reduced levels of BDNF (BDNF^+/-), colitis failed to elevate CREB protein activity in bladder afferent neurons. Physiological examination also demonstrated that colitis-induced urinary frequency was not shown in BDNF^+/- rats, implicating an essential role of BDNF in mediating colon-to-bladder sensory cross-sensitization. We further implemented in vivo and in vitro studies and demonstrated that BDNF-mediated colon-to-bladder sensory cross-activation involved the TrkB-PLCγ-calcium/calmodulin-dependent protein kinase II (CaMKII) cascade. In contrast, the PI3K/Akt pathway was not activated in bladder afferent neurons during colitis and was not involved in BDNF action in the DRG. Our results suggest that colon-to-bladder sensory cross-sensitization is regulated by specific signal transduction initiated by the up-regulation of BDNF in the DRG.

Role of satellite glial cells in gastrointestinal pain

Gastrointestinal (GI) pain is a common clinical problem, for which effective therapy is quite limited. Sensations from the GI tract, including pain, are mediated largely by neurons in the dorsal root ganglia (DRG), and to a smaller extent by vagal afferents emerging from neurons in the nodose/jugular ganglia. Neurons in rodent DRG become hyperexcitable in models of GI pain (e.g., gastric or colonic inflammation), and can serve as a source for chronic pain. Glial cells are another element in the pain signaling pathways, and there is evidence that spinal glial cells (microglia and astrocytes) undergo activation (gliosis) in various pain models and contribute to pain. Recently it was found that satellite glial cells (SGCs), the main type of glial cells in sensory ganglia, might also contribute to chronic pain in rodent models. Most of that work focused on somatic pain, but in several studies GI pain was also investigated, and these are discussed in the present review. We have shown that colonic inflammation induced by dinitrobenzene sulfonic acid (DNBS) in mice leads to the activation of SGCs in DRG and increases gap junction-mediated coupling among these cells. This coupling appears to contribute to the hyperexcitability of DRG neurons that innervate the colon. Blocking gap junctions (GJ) in vitro reduced neuronal hyperexcitability induced by inflammation, suggesting that glial GJ participate in SGC-neuron interactions. Moreover, blocking GJ by carbenoxolone and other agents reduces pain behavior. Similar changes in SGCs were also found in the mouse nodose ganglia (NG), which provide sensory innervation to most of the GI tract. Following systemic inflammation, SGCs in these ganglia were activated, and displayed augmented coupling and greater sensitivity to the pain mediator ATP. The contribution of these changes to visceral pain remains to be determined. These results indicate that although visceral pain is unique, it shares basic mechanisms with somatic pain, suggesting that therapeutic approaches to both pain types may be similar. Future research in this field should include additional types of GI injury and also other types of visceral pain.

Splicing Regulation of Pro-Inflammatory Cytokines and Chemokines: At the Interface of the Neuroendocrine and Immune Systems

Alternative splicing plays a key role in posttranscriptional regulation of gene expression, allowing a single gene to encode multiple protein isoforms. As such, alternative splicing amplifies the coding capacity of the genome enormously, generates protein diversity, and alters protein function. More than 90% of human genes undergo alternative splicing, and alternative splicing is especially prevalent in the nervous and immune systems, tissues where cells need to react swiftly and adapt to changes in the environment through carefully regulated mechanisms of cell differentiation, migration, targeting, and activation. Given its prevalence and complexity, this highly regulated mode of gene expression is prone to be affected by disease. In the following review, we look at how alternative splicing of signaling molecules—cytokines and their receptors—changes in different pathological conditions, from chronic inflammation to neurologic disorders, providing means of functional interaction between the immune and neuroendocrine systems. Switches in alternative splicing patterns can be very dynamic and can produce signaling molecules with distinct or antagonistic functions and localization to different subcellular compartments. This newly discovered link expands our understanding of the biology of immune and neuroendocrine cells, and has the potential to open new windows of opportunity for treatment of neurodegenerative disorders.

Endogenous BDNF augments NMDA receptor phosphorylation in the spinal cord via PLCγ, PKC, and PI3K/Akt pathways during colitis

Background

Spinal central sensitization is an important process in the generation and maintenance of visceral hypersensitivity. The release of brain-derived neurotrophic factor (BDNF) from the primary afferent neurons to the spinal cord contributes to spinal neuronal plasticity and increases neuronal activity and synaptic efficacy. The N-Methyl-D-aspartic acid (NMDA) receptor possesses ion channel properties, and its activity is modulated by phosphorylation of its subunits including the NMDA receptor 1 (NR1).

Methods

Colonic inflammation was induced by a single dose of intracolonic instillation of tri-nitrobenzene sulfonic acid (TNBS). NR1 phosphorylation by BDNF in vivo and in culture was examined by western blot and immunohistochemistry. Signal transduction was studied by direct examination and use of specific inhibitors.

Results

During colitis, the level of NR1 phospho-Ser⁸⁹⁶ was increased in the dorsal horn region of the L1 and S1 spinal cord; this increase was attenuated by injection of BDNF neutralizing antibody to colitic animals (36 μg/kg, intravenous (i.v.)) and was also reduced in BDNF^+/− rat treated with TNBS. Signal transduction examination showed that the extracellular signal-regulated kinase (ERK) activation was not involved in BDNF-induced NR1 phosphorylation. In contrast, the phosphatidylinositol 3-kinase (PI3K)/Akt pathway mediated BDNF-induced NR1 phosphorylation in vivo and in culture; this is an additional pathway to the phospholipase C-gamma (PLCγ) and the protein kinase C (PKC) that was widely considered to phosphorylate NR1 at Ser⁸⁹⁶. In spinal cord culture, the inhibitors to PLC (U73122), PKC (bisindolylmaleimide I), and PI3K (LY294002), but not MEK (PD98059) blocked BDNF-induced NR1 phosphorylation. In animals with colitis, treatment with LY294002 (50 μg/kg, i.v.) blocked the Akt activity as well as NR1 phosphorylation at Ser⁸⁹⁶ in the spinal cord.

Conclusion

BDNF participates in colitis-induced spinal central sensitization by up-regulating NR1 phosphorylation at Ser⁸⁹⁶. The PI3K/Akt pathway, in addition to PLCγ and PKC, mediates BDNF action in the spinal cord during colitis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-015-0371-z) contains supplementary material, which is available to authorized users.

Repeated predictable stress causes resilience against colitis-induced behavioral changes in mice

Inflammatory bowel disease is associated with an increased risk of mental disorders and can be exacerbated by stress. In this study which was performed with male 10-week old C57Bl/6N mice, we used dextran sulfate sodium (DSS)-induced colitis to evaluate behavioral changes caused by intestinal inflammation, to assess the interaction between repeated psychological stress (water avoidance stress, WAS) and colitis in modifying behavior, and to analyze neurochemical correlates of this interaction. A 7-day treatment with DSS (2% in drinking water) decreased locomotion and enhanced anxiety-like behavior in the open field test and reduced social interaction. Repeated exposure to WAS for 7 days had little influence on behavior but prevented the DSS-induced behavioral disturbances in the open field and SI tests. In contrast, repeated WAS did not modify colon length, colonic myeloperoxidase content and circulating proinflammatory cytokines, parameters used to assess colitis severity. DSS-induced colitis was associated with an increase in circulating neuropeptide Y (NPY), a rise in the hypothalamic expression of cyclooxygenase-2 mRNA and a decrease in the hippocampal expression of NPY mRNA, brain-derived neurotrophic factor mRNA and mineralocorticoid receptor mRNA. Repeated WAS significantly decreased the relative expression of corticotropin-releasing factor mRNA in the hippocampus. The effect of repeated WAS to blunt the DSS-evoked behavioral disturbances was associated with a rise of circulating corticosterone and an increase in the expression of hypothalamic NPY mRNA. These results show that experimental colitis leads to a particular range of behavioral alterations which can be prevented by repeated WAS, a model of predictable chronic stress, while the severity of colitis remains unabated. We conclude that the mechanisms underlying the resilience effect of repeated WAS involves hypothalamic NPY and the hypothalamic-pituitary-adrenal axis.

Marrow stromal stem cell autologous transplantation in denervated fracture healing: an experimental study in rats

OBJECTIVE

To investigate the influence of bone marrow stromal stem cell (BMSCs) transplantation on healing of fractures combined with central nerve injuries in rats.

METHODS

Forty-eight healthy adult SD male rats were randomly divided into the following three groups (16 rats in each group): group A, simple (left) tibial fracture; group B, tibial fracture combined with T10 spinal cord transection (SCT); group C, tibial fracture combined with T10 SCT and BMSCs transplantation. The tibial fractures were stabilized with modular intramedullary nails and all operated hind limbs were further immobilized in plaster casts to prevent unequal load bearing. BMSCs were labeled with bromodeoxyuridine and implanted into the fractures of C group rats 2 days after creation of the model. The animals in B and C groups were evaluated by postoperative Tarlov scores. The fractured tibiae were evaluated separately radiographically (X-ray and CT) and immunohistochemically 1, 2, 3 and 4 weeks after injury to assess fracture healing. In addition, the wet weights of the left tibias were measured.

RESULTS

All Tarlov score of the B and C group animals reached the requirements of the experiment. One, 2 and 3 weeks after surgery, the tibial callus widths in B and C group animals were significantly greater than those of group A rats (P < 0.05). At 4 weeks the tibial callus width in group C animals had decreased, but still differed significantly from that in group A rats (P < 0.05). One, 2, 3 and 4 weeks after surgery, the wet weights of B and C group tibias were significantly greater than those of group A (P < 0.05). Hematoxylin-eosin-stained sections showed bony union and increased bone trabecula in B and C groups and areas with particles positive for alkaline phosphatase staining were more abundant in groups B and C, especially in group C.

CONCLUSION

Neural regulation plays an important role in fracture healing. Treatment with BMSCs has a positive effect on defective callus in rats that have been subjected to SCT.

Effects of inflammation on the innervation of the colon

Inflammatory bowel diseases (IBD) such as ulcerative colitis and Crohn's disease lead to altered gastrointestinal (GI) function as a consequence of the effects of inflammation on the tissues that comprise the GI tract. Among these tissues are several types of neurons that detect the state of the GI tract, transmit pain, and regulate functions such as motility, secretion, and blood flow. This review article describes the structure and function of the enteric nervous system, which is embedded within the gut wall, the sympathetic motor innervation of the colon and the extrinsic afferent innervation of the colon, and considers the evidence that colitis alters these important sensory and motor systems. These alterations may contribute to the pain and altered bowel habits that accompany IBD.

Neural networks in intestinal immunoregulation

Key physiological functions of the intestine are governed by nerves and neurotransmitters. This complex control relies on two neuronal systems: an extrinsic innervation supplied by the two branches of the autonomic nervous system and an intrinsic innervation provided by the enteric nervous system. As a result of constant exposure to commensal and pathogenic microflora, the intestine developed a tightly regulated immune system. In this review, we cover the current knowledge on the interactions between the gut innervation and the intestinal immune system. The relations between extrinsic and intrinsic neuronal inputs are highlighted with regards to the intestinal immune response. Moreover, we discuss the latest findings on mechanisms underlying inflammatory neural reflexes and examine their relevance in the context of the intestinal inflammation. Finally, we discuss some of the recent data on the identification of the gut microbiota as an emerging player influencing the brain function.

Effects of sciatic nerve transection on ultrastructure, NADPH-diaphorase reaction and serotonin-, tyrosine hydroxylase-, c-Fos-, glucose transporter 1- and 3-like immunoreactivities in frog dorsal root ganglion

Frogs have been used as an alternative model to study pain mechanisms. Since we did not find any reports on the effects of sciatic nerve transection (SNT) on the ultrastructure and pattern of metabolic substances in frog dorsal root ganglion (DRG) cells, in the present study, 18 adult male frogs (Rana catesbeiana) were divided into three experimental groups: naive (frogs not subjected to surgical manipulation), sham (frogs in which all surgical procedures to expose the sciatic nerve were used except transection of the nerve), and SNT (frogs in which the sciatic nerve was exposed and transected). After 3 days, the bilateral DRG of the sciatic nerve was collected and used for transmission electron microscopy. Immunohistochemistry was used to detect reactivity for glucose transporter (Glut) types 1 and 3, tyrosine hydroxylase, serotonin and c-Fos, as well as nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-diaphorase). SNT induced more mitochondria with vacuolation in neurons, satellite glial cells (SGCs) with more cytoplasmic extensions emerging from cell bodies, as well as more ribosomes, rough endoplasmic reticulum, intermediate filaments and mitochondria. c-Fos immunoreactivity was found in neuronal nuclei. More neurons and SGCs surrounded by tyrosine hydroxylase-like immunoreactivity were found. No change occurred in serotonin- and Glut1- and Glut3-like immunoreactivity. NADPH-diaphorase occurred in more neurons and SGCs. No sign of SGC proliferation was observed. Since the changes of frog DRG in response to nerve injury are similar to those of mammals, frogs should be a valid experimental model for the study of the effects of SNT, a condition that still has many unanswered questions.

Interleukin-17A increases neurite outgrowth from adult postganglionic sympathetic neurons

Inflammation can profoundly alter the structure and function of the nervous system. Interleukin (IL)-17 has been implicated in the pathogenesis of several inflammatory diseases associated with nervous system plasticity. However, the effects of IL-17 on the nervous system remain unexplored. Cell and explant culture techniques, immunohistochemistry, electrophysiology, and Ca2+ imaging were used to examine the impact of IL-17 on adult mouse sympathetic neurons. Receptors for IL-17 were present on postganglionic neurons from superior mesenteric ganglia (SMG). Supernatant from activated splenic T lymphocytes, which was abundant in IL-17, dramatically enhanced axonal length of SMG neurons. Importantly, IL-17-neutralizing antiserum abrogated the neurotrophic effect of splenocyte supernatant, and incubation of SMG neurons in IL-17 (1 ng/ml) significantly potentiated neurite outgrowth. The neurotrophic effect of IL-17 was accompanied by inhibition of voltage-dependent Ca2+ influx and was recapitulated by incubation of neurons in a blocker of N-type Ca2+ channels (ω-conotoxin GVIA; 30 nM). IL-17-induced neurite outgrowth in vitro appeared to be independent of glia, as treatment with a glial toxin (AraC; 5 μM) did not affect the outgrowth response to IL-17. Moreover, application of the cytokine to distal axons devoid of glial processes enhanced neurite extension. An inhibitor of the NF-κB pathway (SC-514; 20 μM) blocked the effects of IL-17. These data represent the first evidence that IL-17 can act on sympathetic somata and distal neurites to enhance neurite outgrowth, and identify a novel potential role for IL-17 in the neuroanatomical plasticity that accompanies inflammation.