Nerve growth factor antiserum induces axotomy-like changes in neuropeptide expression in intact sympathetic and sensory neurons

Brachial Plexus Root Avulsion Injury-Induced Endothelin-Converting Enzyme-Like 1 Overexpression Is Associated with Injured Motor Neurons Survival

Brachial plexus root avulsion (BPRA) injury arises from challenging delivery during childbirth, sports-related incidents, or car accidents, leading to extensive loss of motor neurons (MNs) and subsequent paralysis, including both motor and sensory impairment. Surgical nerve re-implantation cannot effectively restore motor function, and the survival of injured MNs is vital for axon regeneration and re-innervating the target muscles. Therefore, identifying novel molecular targets to improve injured MNs survival is of great significance in the treatment of BPRA injuries. Endothelin-converting enzyme-like 1 (ECEL1), a membrane-bound metallopeptidase, was initially identified as a molecule associated with nerve injuries. Damaged neurons exhibit a significant increase in the expression of ECEL1 following various types of nerve injuries, such as optic nerve injury and sciatic nerve injury. This study aimed to investigate the relationship between ECEL1 overexpression and the survival of injured MNs following BPRA injury. Our results observed a significant elevation in ECEL1 expression in injured MNs and positively correlated with MNs survival following BPRA injury. The transcription of ECEL1 is regulated by the transcription factors c-Jun and ATF3 in the context of BPRA injury, which is consistent with previous other nerve injuries study. In addition, the expression of TrkA gradually decreases in ECEL1-positive MNs and ECEL1 possibly preserves the activity of downstream AKT-GSK3β pathway of TrkA in injured MNs. In conclusion, our results introduce a promising therapeutic molecular target to assist re-implantation surgery for the treatment of BPRA injury.

A Review of Hand-Arm Vibration Studies Conducted by US NIOSH since 2000

Studies on hand-transmitted vibration exposure, biodynamic responses, and biological effects were conducted by researchers at the Health Effects Laboratory Division (HELD) of the National Institute for Occupational Safety and Health (NIOSH) during the last 20 years. These studies are systematically reviewed in this report, along with the identification of areas where additional research is needed. The majority of the studies cover the following aspects: (i) the methods and techniques for measuring hand-transmitted vibration exposure; (ii) vibration biodynamics of the hand-arm system and the quantification of vibration exposure; (iii) biological effects of hand-transmitted vibration exposure; (iv) measurements of vibration-induced health effects; (iv) quantification of influencing biomechanical effects; and (v) intervention methods and technologies for controlling hand-transmitted vibration exposure. The major findings of the studies are summarized and discussed.

Macrophage biology in the peripheral nervous system after injury

Neuroinflammation has positive and negative effects. This review focuses on the roles of macrophage in the PNS. Transection of PNS axons leads to degeneration and clearance of the distal nerve and to changes in the region of the axotomized cell bodies. In both locations, resident and infiltrating macrophages are found. Macrophages enter these areas in response to expression of the chemokine CCL2 acting on the macrophage receptor CCR2. In the distal nerve, macrophages and other phagocytes are involved in clearance of axonal debris, which removes molecules that inhibit nerve regeneration. In the cell body region, macrophage trigger the conditioning lesion response, a process in which neurons increase their regeneration after a prior lesion. In mice in which the genes for CCL2 or CCR2 are deleted, neither macrophage infiltration nor the conditioning lesion response occurs in dorsal root ganglia (DRG). Macrophages exist in different phenotypes depending on their environment. These phenotypes have different effects on axonal clearance and neurite outgrowth. The mechanism by which macrophages affect neuronal cell bodies is still under study. Overexpression of CCL2 in DRG in uninjured animals leads to macrophage accumulation in the ganglia and to an increase in the growth potential of DRG neurons. This increased growth requires activation of neuronal STAT3. In contrast, in acute demyelinating neuropathies, macrophages are involved in stripping myelin from peripheral axons. The molecular mechanisms that trigger macrophage action after trauma and in autoimmune disease are receiving increased attention and should lead to avenues to promote regeneration and protect axonal integrity.

Chemically induced inflammation and nerve damage affect the distribution of vasoactive intestinal polypeptide-like immunoreactive (VIP-LI) nervous structures in the descending colon of the domestic pig

BACKGROUND

The enteric nervous system (ENS), situated in the wall of the gastrointestinal tract, regulates the majority of intestinal activities in physiological conditions and during pathological processes. Enteric neurons are diversified in terms of active substance expression. One of the most important neuropeptides within the ENS is vasoactive intestinal polypeptide (VIP). It seems to be one among the important inhibitory peptides in addition to neuropeptide Y (NPY), nitric oxide (NO), and adenosine triphosphate (ATP) of the intestinal motility and secretion, however, many issues connected with distribution and roles of VIP in the large intestine, especially during pathological states, still remain unknown.

METHODS

Changes in the VIP-like immunoreactivity of the enteric nervous structures under experimental pathological states, including chemically induced inflammation and nerve damage was examined using the double immunofluorescence technique with commercial antibodies.

KEY RESULTS

Generally, both pathological factors studied caused an increase in the number of VIP-like immunoreactive (VIP-LI) neurons and nerve fibers, but the intensity of fluctuations depended on both the acting factor and the part of the ENS studied.

CONCLUSIONS AND INFERENCES

The obtained results suggest that VIP participates in pathological processes concerning the digestive tract, and its exact functions probably depend on the type of damaging factor acting on the intestine.

PACAP/PAC1 Regulation of Inflammation via Catecholaminergic Neurons in a Model of Multiple Sclerosis

The sympathetic nervous system (SNS) serves to maintain homeostasis of vital organ systems throughout the body, and its dysfunction plays a major role in human disease. The SNS also links the central nervous system to the immune system during different types of stress via innervation of the lymph nodes, spleen, thymus, and bone marrow. Previous studies have shown that pituitary adenylate cyclase-activating polypeptide (PACAP, gene name adcyap1) exhibits anti-inflammatory properties in the experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis. Because PACAP is known to regulate SNS function, we hypothesized that part of the immunoprotective action of PACAP is due to its neuromodulatory effects on sympathetic neurons. To examine this, we used an inducible, targeted approach to conditionally disrupt not only the PACAP-preferring PAC1 receptor gene (adcyap1r1) in dopamine β-hydroxylase-expressing cells, which includes postganglionic sympathetic neurons, but also catecholaminergic neurons in the brain and adrenomedullary chromaffin cells. In contrast to our previous EAE studies using PACAP global knockout mice which developed severe and prolonged EAE, we found that mice with conditional loss of PAC1 receptors in catecholaminergic cells developed a delayed time course of EAE with reduced helper T cell type 1 (Th1) and Th17 and enhanced Th2 cell polarization. At later time points, similar to mice with global PACAP loss, mice with conditional loss of PAC1 exhibited more severe clinical disease than controls. The latter was associated with a reduction in the abundance of thymic regulatory T cells (Tregs). These studies indicate that PAC1 receptor signaling acts in catecholaminergic cells in a time-dependent manner. At early stages of disease development, it enhances the ability of the SNS to polarize the Th response towards a more inflammatory state. Then, after disease is established, it enhances the ability of the SNS to dampen the inflammatory response via T_regs. The lack of concordance in results between global PACAP KO mice and mice with the PAC1 deletion targeted to catecholaminergic cells during early EAE may be explained by the fact that PACAP acts to regulate inflammation via multiple receptor subtypes and multiple targets, including inflammatory cells.

Retrograde influences of SCG axotomy on uninjured preganglionic neurons

There is evidence that neuronal injury can affect uninjured neurons in the same neural circuit. The overall goal of this study was to understand the effects of peripheral nerve injury on uninjured neurons located in the central nervous system (CNS). As a model, we examined whether axotomy (transection of postganglionic axons) of the superior cervical ganglion (SCG) affected the uninjured, preganglionic neurons that innervate the SCG. At 7 days post-injury a reduction in choline acetyltransferase (ChAT) and synaptophysin immunoreactivity in the SCG, both markers for preganglionic axons, was observed, and this reduction persisted at 8 and 12 weeks post-injury. No changes were observed in the number or size of the parent cell bodies in the intermediolateral cell column (IML) of the spinal cord, yet synaptic input to the IML neurons was decreased at both 8 and 12 weeks post-injury. In order to understand the mechanisms underlying these changes, protein levels of brain-derived neurotrophic factor (BDNF) and tyrosine receptor kinase B (TrkB) were examined and reductions were observed at 7 days post-injury in both the SCG and spinal cord. Taken together these results suggest that axotomy of the SCG led to reduced BDNF in the SCG and spinal cord, which in turn influenced ChAT and synaptophysin expression in the SCG and also contributed to the altered synaptic input to the IML neurons. More generally these findings provide evidence that the effects of peripheral injury can cascade into the CNS and affect uninjured neurons.

Regulation of axonal regeneration following spinal cord injury in the lamprey

Following rostral spinal cord injury (SCI) in larval lampreys, injured descending brain neurons, particularly reticulospinal (RS) neurons, regenerate their axons, and locomotor behavior recovers in a few weeks. However, axonal regeneration of descending brain neurons is mostly limited to relatively short distances, but the mechanisms for incomplete axonal regeneration are unclear. First, lampreys with rostral SCI exhibited greater axonal regeneration of descending brain neurons, including RS neurons, as well as more rapid recovery of locomotor muscle activity right below the lesion site, compared with animals with caudal SCI. In addition, following rostral SCI, most injured RS neurons displayed the "injury phenotype," whereas following caudal SCI, most injured neurons displayed normal electrical properties. Second, following rostral SCI, at cold temperatures (~4-5°C), axonal transport was suppressed, axonal regeneration and behavioral recovery were blocked, and injured RS neurons displayed normal electrical properties. Cold temperatures appear to prevent injured RS neurons from detecting and/or responding to SCI. It is hypothesized that following rostral SCI, injured descending brain neurons are strongly stimulated to regenerate their axons, presumably because of elimination of spinal synapses and reduced neurotrophic support. However, when these neurons regenerate their axons and make synapses right below the lesion site, restoration of neurotrophic support very likely suppress further axonal regeneration. In contrast, caudal SCI is a weak stimulus for axonal regeneration, presumably because of spared synapses above the lesion site. These results may have implications for mammalian SCI, which can spare synapses above the lesion site for supraspinal descending neurons and propriospinal neurons.NEW & NOTEWORTHY Lampreys with rostral spinal cord injury (SCI) exhibited greater axonal regeneration of descending brain neurons and more rapid recovery of locomotor muscle activity below the lesion site compared with animals with caudal SCI. In addition, following rostral SCI, most injured reticulospinal (RS) neurons displayed the "injury phenotype," whereas following caudal SCI, most injured neurons had normal electrical properties. We hypothesize that following caudal SCI, the spared synapses of injured RS neurons might limit axonal regeneration and behavioral recovery.

Research progress of the role and mechanism of extracellular signal-regulated protein kinase 5 (ERK5) pathway in pathological pain

Extracellular signal-regulated protein kinase 5 (ERK5), also known as big mitogen-activated protein kinase 1 (MAPK1), is an important member of ERK family, which is a subfamily of the large MAPK family. ERK5 is expressed in many tissues, including the dorsal root ganglion (DRG) neurons and the spinal cord. In this review, we focus on elaborating ERK5-associated pathway in pathological pain, in which the ERK5/CREB (cyclic adenosine monophosphate (cAMP)-response element-binding protein) pathway plays a crucial role in the transduction of pain signal and contributes to pain hypersensitivity. ERK5 activation in the spinal dorsal horn occurs mainly in microglia. The activation of ERK5 can be mediated by N-methyl-D-aspartate (NMDA) receptors. We also elaborate the relationship between ERK5 activation and nerve growth factor-tyrosine kinase A (NGF-TrkA), and the connection between ERK5 activation and brain-derived neurotrophic factor (BDNF) in pathological pain in detail.

Renal denervation in male rats with heart failure improves ventricular sympathetic nerve innervation and function

Heart failure is characterized by the loss of sympathetic innervation to the ventricles, contributing to impaired cardiac function and arrhythmogenesis. We hypothesized that renal denervation (RDx) would reverse this loss. Male Wistar rats underwent myocardial infarction (MI) or sham surgery and progressed into heart failure for 4 wk before receiving bilateral RDx or sham RDx. After additional 3 wk, left ventricular (LV) function was assessed, and ventricular sympathetic nerve fiber density was determined via histology. Post-MI heart failure rats displayed significant reductions in ventricular sympathetic innervation and tissue norepinephrine content (nerve fiber density in the LV of MI+sham RDx hearts was 0.31 ± 0.05% vs. 1.00 ± 0.10% in sham MI+sham RDx group, P < 0.05), and RDx significantly increased ventricular sympathetic innervation (0.76 ± 0.14%, P < 0.05) and tissue norepinephrine content. MI was associated with an increase in fibrosis of the noninfarcted ventricular myocardium, which was attenuated by RDx. RDx improved LV ejection fraction and end-systolic and -diastolic areas when compared with pre-RDx levels. This is the first study to show an interaction between renal nerve activity and cardiac sympathetic nerve innervation in heart failure. Our findings show denervating the renal nerves improves cardiac sympathetic innervation and function in the post-MI failing heart.

Increase of Galanin in Trigeminal Ganglion during Tooth Movement

It is known that nerve fibers containing neuropeptides such as galanin increase in the periodontal ligament during experimental tooth movement. However, the origin of galanin-containing nerve fibers in the periodontal ligament remains unclear. This study was conducted to examine our hypothesis that the increased galanin nerve fibers have a sensory neuronal origin, and that the peptide is associated with pain transmission and/or periodontal ligament remodeling during experimental tooth movement. In control rats, galanin-immunoreactive trigeminal ganglion cells were very rare and were observed predominantly in small ganglion cells. After 3 days of experimental tooth movement, galanin-immunoreactive trigeminal ganglion cells significantly increased, and the most marked increase was observed at 5 days after experimental tooth movement. Furthermore, their cell size spectrum also significantly changed after 3 and 5 days of movement: Medium-sized and large trigeminal ganglion cells began expressing, and continued to express, galanin until 14 days after experimental tooth movement. These findings suggest that the increase of galanin in the periodontal ligament during experimental tooth movement at least partially originates from trigeminal ganglion neurons and may play a role in pain transmission and/or periodontal remodeling.

Neuropeptide profile changes in sensory neurones after partial prepyloric resection in pigs

This report details the first identification of the sources of sensory innervation of the porcine stomach prepyloric region. The Fast Blue (FB) retrograde tracing technique detected the sensory prepyloric neurons in the bilateral nodose ganglia (NGs) as well as thoracic dorsal root ganglia (DRGs). Double-labelling immunofluorescence demonstrated expression of substance P (SP), calcitonin gene-related peptide (CGRP), neuronal isoform of nitric oxide synthase (nNOS), vasoactive intestinal polypeptide (VIP) and galanin (GAL) in both NGs and DRGs. Additionally, we found that partial resection of the stomach prepyloric area increased expression of the SP, CGRP, NOS, VIP and GAL in the prepyloric sensory neurons. In the control left NGs, both a higher total number of FB-positive perikarya as well as a higher percentage of the peptides expressing prepyloric neurons were visualized than in the right NGs. However, compared to the control group, prepyloric resection evoked greater increases in peptide expression in the right-side NGs sensory neurons. In the ganglia of this side, the proportion of the SP-IR perikarya increased by approximately 15%, while CGRP-IR increased by 28%, NOS-IR 14%, VIP-IR 43% and GAL-IR 13%. On the opposite left side, the ganglia proportion of the CGRP-IR perikarya increased by approximately 10%, while NOS-IR increased by 3%, VIP-IR 36% and GAL-IR by 2%. The only decrease (by 5%) was observed in the case of SP expression. We also found that 92% of the sensory neurons originated from NGs and 8% from DRGs. Our results indicate that, in the pig, SP, CGRP, NOS, VIP and GAL participate in the vagal sensory transduction from the stomach prepyloric area. Moreover, increased expression of the peptides and neuronal isoform of nitric oxide synthase in the sensory neurons following transection of their peripheral dendrites suggests their possible participation in the neuronal recovery and/or reinnervation process.

Long-term daily vibration exposure alters current perception threshold (CPT) sensitivity and myelinated axons in a rat-tail model of vibration-induced injury

Repeated exposure to hand-transmitted vibration through the use of powered hand tools may result in pain and progressive reductions in tactile sensitivity. The goal of the present study was to use an established animal model of vibration-induced injury to characterize changes in sensory nerve function and cellular mechanisms associated with these alterations. Sensory nerve function was assessed weekly using the current perception threshold test and tail-flick analgesia test in male Sprague-Dawley rats exposed to 28 d of tail vibration. After 28 d of exposure, Aβ fiber sensitivity was reduced. This reduction in sensitivity was partly attributed to structural disruption of myelin. In addition, the decrease in sensitivity was also associated with a reduction in myelin basic protein and 2',3'- cyclic nucleotide phosphodiasterase (CNPase) staining in tail nerves, and an increase in circulating calcitonin gene-related peptide (CGRP) concentrations. Changes in Aβ fiber sensitivity and CGRP concentrations may serve as early markers of vibration-induced injury in peripheral nerves. It is conceivable that these markers may be utilized to monitor sensorineural alterations in workers exposed to vibration to potentially prevent additional injury.

SP, CGRP changes in pyridoxine induced neuropathic dogs with nerve growth factor gene therapy

BACKGROUND

Nerve growth factor (NGF) is known not only as a major factor for neuronal plasticity but also as a pain stimulator. Although there have been several trials with NGF for its application in the regeneration or protection of the nervous system, the pain induced by NGF remains a challenge to be overcome. In this study, the pain induced by NGF gene therapy was evaluated.

RESULTS

Vehicle or recombinant dog NGF plasmid was administered into the intrathecal space of dogs. Twenty-four hours after the vehicle or NGF plasmid inoculation, dogs were subcutaneously treated with 150 mg/kg pyridoxine every day for 7 days. For pain assessment, physical examination and electrophysiological recording were performed. Only in the vehicle-treated group, weight loss occurred, while NGF plasmid inoculation significantly improved this physical abnormalities. In the vehicle-treated group, electrophysiological recordings showed that H-reflex disappeared at 24 h after the last pyridoxine treatment. However, in the NGF plasmid inoculated group, the H-reflex were normal. In the results of immunohistochemistry, the NGF plasmid administration efficiently expressed in the dorsal root ganglia and significantly increased the pyridoxine-induced reduction of calcitonin gene-related peptide (CGRP) immunoreactive neurons, but not in substance P immunoreactive neurons, in the dorsal root ganglia.

CONCLUSIONS

Given these results, we reason that NGF gene therapy in pyridoxine induced neuropathic dogs does not induce neuropathic pain with this dosage, even with increasing the expression of CGRP.

Alterations of neurochemical expression of the coeliac-superior mesenteric ganglion complex (CSMG) neurons supplying the prepyloric region of the porcine stomach following partial stomach resection

The purpose of the present study was to determine the response of the porcine coeliac-superior mesenteric ganglion complex (CSMG) neurons projecting to the prepyloric area of the porcine stomach to peripheral neuronal damage following partial stomach resection. To identify the sympathetic neurons innervating the studied area of stomach, the neuronal retrograde tracer Fast Blue (FB) was applied to control and partial stomach resection (RES) groups. On the 22nd day after FB injection, following laparotomy, the partial resection of the previously FB-injected stomach prepyloric area was performed in animals of RES group. On the 28th day, all animals were re-anaesthetized and euthanized. The CSMG complex was then collected and processed for double-labeling immunofluorescence. In control animals, retrograde-labelled perikarya were immunoreactive to tyrosine hydroxylase (TH), dopamine β-hydroxylase (DβH), neuropeptide Y (NPY) and galanin (GAL). Partial stomach resection decreased the numbers of FB-positive neurons immunopositive for TH and DβH. However, the strong increase of NPY and GAL expression, as well as de novo-synthesis of neuronal nitric oxide synthase (nNOS) and leu5-Enkephalin (LENK) was noted in studied neurons. Furthermore, FB-positive neurons in all pigs were surrounded by a network of cocaine- and amphetamine-regulated transcript peptide (CART)-, calcitonin gene-related peptide (CGRP)-, and substance P (SP)-, vasoactive intestinal peptide (VIP)-, LENK- and nNOS- immunoreactive nerve fibers. This may suggest neuroprotective contribution of these neurotransmitters in traumatic responses of sympathetic neurons to peripheral axonal damage.

Neurotrophins and Neuropathic Pain: Role in Pathobiology

Neurotrophins (NTs) belong to a family of trophic factors that regulate the survival, growth and programmed cell death of neurons. In mammals, there are four structurally and functionally related NT proteins, viz. nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin 3 and neurotrophin 4. Most research on NTs to date has focussed on the effects of NGF and BDNF signalling via their respective cognate high affinity neurotrophic tyrosine kinase viz TrkA and TrkB receptors. Apart from the key physiologic roles of NGF and BDNF in peripheral and central nervous system function, NGF and BDNF signalling via TrkA and TrkB receptors respectively have been implicated in mechanisms underpinning neuropathic pain. Additionally, NGF and BDNF signalling via the low-affinity pan neurotrophin receptor at 75 kDa (p75NTR) may also contribute to the pathobiology of neuropathic pain. In this review, we critically assess the role of neurotrophins signalling via their cognate high affinity receptors as well as the low affinity p75NTR in the pathophysiology of peripheral neuropathic and central neuropathic pain. We also identify knowledge gaps to guide future research aimed at generating novel insight on how to optimally modulate NT signalling for discovery of novel therapeutics to improve neuropathic pain relief.

Development of non-catecholaminergic sympathetic neurons in para- and prevertebral ganglia of cats

Expression of vasoactive intestinal peptide (VIP), neuronal nitric oxide synthase (nNOS), choline acetyltransferase (ChAT) and calcitonin gene-related peptide (CGRP) in the sympathetic ganglia was investigated by immunohistochemistry in the superior cervical ganglion (SCG), stellate ganglion (SG) and celiac ganglion (CG) from cats of different ages (newborn, 10-day-old, 20-day-old, 30-day-old and 2-month-old). Non-catecholaminergic TH-negative VIP-immunoreactive (IR) and nNOS-IR sympathetic ganglionic neurons are present from the moment of birth. In all studied age groups, substantial populations of VIP-IR (up to 9.8%) and nNOS-IR cells (up to 8.3%) was found in the SG, with a much smaller population found in the SCG (<1%) and only few cells observed in the CG. The percentage of nNOS-IR and VIP-IR neurons in the CG and SCG did not significantly change during development. The proportion of nNOS-IR and VIP-IR neuron profiles in the SG increased in first 20 days of life from 2.3±0.15% to 8.3±0.56% and from 0.3±0.05% to 9.2±0.83%, respectively. In the SG, percentages of nNOS-IR sympathetic neurons colocalizing VIP increased in the first 20 days of life. ChAT-IR and CGRP-IR neurons were not observed in the sympathetic ganglia of newborn animals and did not appear until 10 days after birth. In the SG of newborn and 10-day-old kittens, the majority of NOS-IR neurons were calbindin (CB)-IR, whereas in the SCG and CG of cats of all age groups and in the SG of 30-day-old and older kittens, the vast majority of NOS-IR neurons lacked CB. We conclude that the development of various non-catecholaminergic neurons in different sympathetic ganglia has its own time dynamics and is concluded at the end of the second month of life.

The biology of neurotrophins: cardiovascular function

This chapter addresses the role of neurotrophins in the development of the heart, blood vessels, and neural circuits that control cardiovascular function, as well as the role of neurotrophins in the mature cardiovascular system. The cardiovascular system includes the heart and vasculature whose functions are tightly controlled by the nervous system. Neurons, cardiomyocytes, endothelial cells, vascular smooth muscle cells, and pericytes are all targets for neurotrophin action during development. Neurotrophin expression continues throughout life, and several common pathologies that impact cardiovascular function involve changes in the expression or activity of neurotrophins. These include atherosclerosis, hypertension, diabetes, acute myocardial infarction, and heart failure. In many of these conditions, altered expression of neurotrophins and/or neurotrophin receptors has direct effects on vascular endothelial and smooth muscle cells in addition to effects on nerves that modulate vascular resistance and cardiac function. This chapter summarizes the effects of neurotrophins in cardiovascular physiology and pathophysiology.

CaMKK-CaMK1a, a new post-traumatic signalling pathway induced in mouse somatosensory neurons

Neurons innervating peripheral tissues display complex responses to peripheral nerve injury. These include the activation and suppression of a variety of signalling pathways that together influence regenerative growth and result in more or less successful functional recovery. However, these responses can be offset by pathological consequences including neuropathic pain. Calcium signalling plays a major role in the different steps occurring after nerve damage. As part of our studies to unravel the roles of injury-induced molecular changes in dorsal root ganglia (DRG) neurons during their regeneration, we show that the calcium calmodulin kinase CaMK1a is markedly induced in mouse DRG neurons in several models of mechanical peripheral nerve injury, but not by inflammation. Intrathecal injection of NRTN or GDNF significantly prevents the post-traumatic induction of CaMK1a suggesting that interruption of target derived factors might be a starter signal in this de novo induction. Inhibition of CaMK signalling in injured DRG neurons by pharmacological means or treatment with CaMK1a siRNA resulted in decreased velocity of neurite growth in vitro. Altogether, the results suggest that CaMK1a induction is part of the intrinsic regenerative response of DRG neurons to peripheral nerve injury, and is thus a potential target for therapeutic intervention to improve peripheral nerve regeneration.

Cell intrinsic control of axon regeneration

Although neurons execute a cell intrinsic program of axonal growth during development, following the establishment of connections, the developmental growth capacity declines. Besides environmental challenges, this switch largely accounts for the failure of adult central nervous system (CNS) axons to regenerate. Here, we discuss the cell intrinsic control of axon regeneration, including not only the regulation of transcriptional and epigenetic mechanisms, but also the modulation of local protein translation, retrograde and anterograde axonal transport, and microtubule dynamics. We further explore the causes underlying the failure of CNS neurons to mount a vigorous regenerative response, and the paradigms demonstrating the activation of cell intrinsic axon growth programs. Finally, we present potential mechanisms to support axon regeneration, as these may represent future therapeutic approaches to promote recovery following CNS injury and disease.

Injury-induced HDAC5 nuclear export is essential for axon regeneration

Reactivation of a silent transcriptional program is a critical step in successful axon regeneration following injury. Yet how such a program is unlocked after injury remains largely unexplored. We found that axon injury in peripheral sensory neurons elicits a back-propagating calcium wave that invades the soma and causes nuclear export of HDAC5 in a PKCμ-dependent manner. Injury-induced HDAC5 nuclear export enhances histone acetylation to activate a proregenerative gene-expression program. HDAC5 nuclear export is required for axon regeneration, as expression of a nuclear-trapped HDAC5 mutant prevents axon regeneration, whereas enhancing HDAC5 nuclear export promotes axon regeneration in vitro and in vivo. Components of this HDAC5 pathway failed to be activated in a model of central nervous system injury. These studies reveal a signaling mechanism from the axon injury site to the soma that controls neuronal growth competence and suggest a role for HDAC5 as a transcriptional switch controlling axon regeneration.

STAT3 integrates cytokine and neurotrophin signals to promote sympathetic axon regeneration

The transcription factor STAT3 has been implicated in axon regeneration. Here we investigate a role for STAT3 in sympathetic nerve sprouting after myocardial infarction (MI) - a common injury in humans. We show that NGF stimulates serine phosphorylation (S727) of STAT3 in sympathetic neurons via ERK1/2, in contrast to cytokine phosphorylation of Y705. Maximal sympathetic axon regeneration in vitro requires phosphorylation of both S727 and Y705. Furthermore, cytokine signaling is necessary for NGF-induced sympathetic nerve sprouting in the heart after MI. Transfection studies in neurons lacking STAT3 suggest two independent pools of STAT3, phosphorylated on either S727 or Y705, that regulate sympathetic regeneration via both transcriptional and non-transcriptional means. Additional data identify STAT3-microtubule interactions that may complement the well-characterized role of STAT3 stimulating regeneration associated genes. These data show that STAT3 is critical for sympathetic axon regeneration in vitro and in vivo, and identify a novel non-transcriptional mode of action.

Expression changes and bioinformatic analysis of Wallerian degeneration after sciatic nerve injury in rat

Wallerian degeneration (WD) remains an important research topic. Many genes are differentially expressed during the process of WD, but the precise mechanisms responsible for these differentiations are not completely understood. In this study, we used microarrays to analyze the expression changes of the distal nerve stump at 0, 1, 4, 7, 14, 21 and 28 days after sciatic nerve injury in rats. The data revealed 6 076 differentially-expressed genes, with 23 types of expression, specifically enriched in genes associated with nerve development and axonogenesis, cytokine biosynthesis, cell differentiation, cytokine/chemokine production, neuron differentiation, cytokinesis, phosphorylation and axon regeneration. Kyoto Encyclopedia of Genes and Genomes pathway analysis gave findings related mainly to the MAPK signaling pathway, the Jak-STAT signaling pathway, the cell cycle, cytokine-cytokine receptor interaction, the p53 signaling pathway and the Wnt signaling pathway. Some key factors were NGF, MAG, CNTF, CTNNA2, p53, JAK2, PLCB1, STAT3, BDNF, PRKC, collagen II, FGF, THBS4, TNC and c-Src, which were further validated by real-time quantitative PCR, Western blot, and immunohistochemistry. Our findings contribute to a better understanding of the functional analysis of differentially-expressed genes in WD and may shed light on the molecular mechanisms of nerve degeneration and regeneration.

Axotomy-induced changes in the chemical coding pattern of colon projecting calbindin-positive neurons in the inferior mesenteric ganglia of the pig

The present study examines the response of colon-projecting neurons localized in the inferior mesenteric ganglia (IMG) to axotomy in the pig animal model. In all animals (n = 8), a median laparotomy was performed under anesthesia and the retrograde tracer Fast Blue was injected into the descending colon wall. In experimental animals (n = 4), the descending colon was exposed and the bilateral caudal colonic nerves were identified and severed. All animals were euthanized and the inferior mesenteric ganglia were harvested and processed for double-labeling immunofluorescence for calbindin-D28k (CB) in combination with either tyrosine hydroxylase (TH), neuropeptide Y (NPY), somatostatin (SOM), vasoactive intestinal polypeptide (VIP), nitric oxide synthase (NOS), Leu-enkephalin (LENK), substance P, vesicular acetylcholine transporter, or galanin. Immunohistochemistry revealed significant changes in the chemical coding pattern of injured inferior mesenteric ganglion neurons. In control animals, Fast Blue-positive neurons were immunoreactive to TH, NPY, SOM, VIP, NOS, LENK, and CB. In the experimental group, the numbers of TH-, NPY-, and SOM-expressing neurons were reduced, whereas the number of neurons immunoreactive to LENK was increased. Our data indicate that the colon-projecting neurons of the porcine IMG react to the axotomy in a similar, but not an identical manner in a comparison to other species, especially rodents. Further studies are needed to elucidate the detailed factors/mechanisms involved in the response to nerve injury.

Laser therapy and pain-related behavior after injury of the inferior alveolar nerve: possible involvement of neurotrophins

Nerve-related complications have been frequently reported in dental procedures, and a very frequent type of occurrence involves the inferior alveolar nerve (IAN). The nerve injury in humans often results in persistent pain accompanied by allodynia and hyperalgesia. In this investigation, we used an experimental IAN injury in rats, which was induced by a Crile hemostatic clamp, to evaluate the effects of laser therapy on nerve repair. We also studied the nociceptive behavior (von Frey hair test) before and after the injury and the behavioral effects of treatment with laser therapy (emitting a wavelength of 904 nm, output power of 70 Wpk, a spot area of ∼0.1 cm², frequency of 9500 Hz, pulse time 60 ns and an energy density of 6 J/cm²). As neurotrophins are essential for the process of nerve regeneration, we used immunoblotting techniques to preliminarily examine the effects of laser therapy on the expression of nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF). The injured animals treated with laser exhibited an improved nociceptive behavior. In irradiated animals, there was an enhanced expression of NGF (53%) and a decreased BDNF expression (40%) after laser therapy. These results indicate that BDNF plays a locally crucial role in pain-related behavior development after IAN injury, increasing after lesions (in parallel to the installation of pain behavior) and decreasing with laser therapy (in parallel to the improvement of pain behavior). On the other hand, NGF probably contributes to the repair of nerve tissue, in addition to improving the pain-related behavior.

Development of neuropeptide Y-containing neurons in sympathetic ganglia of rats

Expression of neuropeptide Y (NPY) in the sympathetic ganglia was investigated by immunohistochemistry and tract tracing. The distribution of NPY immunoreactivity (IR) was studied in the superior cervical ganglion (SCG), stellate ganglion (SG) and celiac ganglion (CG) from rats of different ages (newborn, 10-day-old, 20-day-old, 30-day-old, 2-month-old, 6-month-old, 24-month-old). We observed that the percentage of NPY-IR neuronal profiles increased during early postnatal development. In the SCG and SG, the percentage of NPY-IR profiles enlarged in the first month of life from 43±3.6% (SCG) and 46±3.8% (SG) until 64±4.1% (SCG) and 58±3.5% (SG). The percentage of NPY-IR profiles in the CG increased during the period between 20days (65±3.8%) and 30days (82±5.1%) of animals' life and did not change in further development. In newborn and 10-day-old rats, a large portion of NPY-IR neurons was also calbindin D28K (CB)-IR in all sympathetic ganglia. The proportion of CB-IR substantially decreased during next 10days in the SCG, SG and CG. NPY-IR was approximately present in a half of the postganglionic neurons innervating muscle vessels of the neck and forearm, and the percentage of labeled NPY-IR profiles did not change during the development. Only single Ki67-IR neurons were also NPY-IR in the SCG, SG and CG in newborns and not in older animals. No NPY+/caspase 3+IR neurons were observed. Finally, the process of morphological changes in the size and percentages of NPY-IR profiles is complete in rats by the first month of life.

Activation of extracellular signal-regulated protein kinase 5 is essential for cystitis- and nerve growth factor-induced calcitonin gene-related peptide expression in sensory neurons

Background

Cystitis causes considerable neuronal plasticity in the primary afferent pathways. The molecular mechanism and signal transduction underlying cross talk between the inflamed urinary bladder and sensory sensitization has not been investigated.

Results

In a rat cystitis model induced by cyclophosphamide (CYP) for 48 h, the mRNA and protein levels of the excitatory neurotransmitter calcitonin gene-related peptide (CGRP) are increased in the L6 dorsal root ganglia (DRG) in response to bladder inflammation. Cystitis-induced CGRP expression in L6 DRG is triggered by endogenous nerve growth factor (NGF) because neutralization of NGF with a specific NGF antibody reverses CGRP up-regulation during cystitis. CGRP expression in the L6 DRG neurons is also enhanced by retrograde NGF signaling when NGF is applied to the nerve terminals of the ganglion-nerve two-compartmented preparation. Characterization of the signaling pathways in cystitis- or NGF-induced CGRP expression reveals that the activation (phosphorylation) of extracellular signal-regulated protein kinase (ERK)5 but not Akt is involved. In L6 DRG during cystitis, CGRP is co-localized with phospho-ERK5 but not phospho-Akt. NGF-evoked CGRP up-regulation is also blocked by inhibition of the MEK/ERK pathway with specific MEK inhibitors U0126 and PD98059, but not by inhibition of the PI3K/Akt pathway with inhibitor LY294002. Further examination shows that cystitis-induced cAMP-responsive element binding protein (CREB) activity is expressed in CGRP bladder afferent neurons and is co-localized with phospho-ERK5 but not phospho-Akt. Blockade of NGF action in vivo reduces the number of DRG neurons co-expressing CGRP and phospho-CREB, and reverses cystitis-induced increases in micturition frequency.

Conclusions

A specific pathway involving NGF-ERK5-CREB axis plays an essential role in cystitis-induced sensory activation.

Specificity of peripheral nerve regeneration: interactions at the axon level

Peripheral nerves injuries result in paralysis, anesthesia and lack of autonomic control of the affected body areas. After injury, axons distal to the lesion are disconnected from the neuronal body and degenerate, leading to denervation of the peripheral organs. Wallerian degeneration creates a microenvironment distal to the injury site that supports axonal regrowth, while the neuron body changes in phenotype to promote axonal regeneration. The significance of axonal regeneration is to replace the degenerated distal nerve segment, and achieve reinnervation of target organs and restitution of their functions. However, axonal regeneration does not always allows for adequate functional recovery, so that after a peripheral nerve injury, patients do not recover normal motor control and fine sensibility. The lack of specificity of nerve regeneration, in terms of motor and sensory axons regrowth, pathfinding and target reinnervation, is one the main shortcomings for recovery. Key factors for successful axonal regeneration include the intrinsic changes that neurons suffer to switch their transmitter state to a pro-regenerative state and the environment that the axons find distal to the lesion site. The molecular mechanisms implicated in axonal regeneration and pathfinding after injury are complex, and take into account the cross-talk between axons and glial cells, neurotrophic factors, extracellular matrix molecules and their receptors. The aim of this review is to look at those interactions, trying to understand if some of these molecular factors are specific for motor and sensory neuron growth, and provide the basic knowledge for potential strategies to enhance and guide axonal regeneration and reinnervation of adequate target organs.

Altered norepinephrine content and ventricular function in p75NTR-/- mice after myocardial infarction

Cardiac sympathetic neurons stimulate heart rate and the force of contraction through release of norepinephrine. Nerve growth factor modulates sympathetic transmission through activation of TrkA and p75NTR. Nerve growth factor plays an important role in post-infarct sympathetic remodeling. We used mice lacking p75NTR to examine the effect of altered nerve growth factor signaling on sympathetic neuropeptide expression, cardiac norepinephrine, and ventricular function after myocardial infarction. Infarct size was similar in wildtype and p75NTR-/- mice after ischemia-reperfusion surgery. Likewise, mRNAs encoding vasoactive intestinal peptide, galanin, and pituitary adenylate cyclase activating peptides were identical in wildtype and p75NTR-/- cardiac sympathetic neurons, as was expression of the TrkA neurotrophin receptor. Norepinephrine content was elevated in the base of the p75NTR-/- ventricle compared to wildtype, but levels were identical below the site of occlusion. Left ventricular pressure, dP/dt(MAX), and dP/dt(MIN) were measured under isoflurane anesthesia 3 and 7 days after surgery. Ventricular pressure decreased significantly 3 days after infarction, and deficits in dP/dt(MAX) were revealed by stimulating beta receptors with dobutamine and release of endogenous norepinephrine with tyramine. dP/dt(MIN) was not altered by genotype or surgical group. Few differences were observed between genotypes 3 days after surgery, in contrast to low pressure and dP/dt(MAX) previously reported in control p75NTR-/- animals. Seven days after surgery ventricular pressure and dP/dt(MAX) were significantly lower in p75NTR-/- hearts compared to WT hearts. Thus, the lack of p75NTR did not enhance cardiac function after myocardial infarction.

Early postnatal exposure of mice to side-steam tobacco smoke increases neuropeptide Y in lung

Our recent study showed that prenatal and early postnatal exposure of mice to side-steam tobacco smoke (SS), a surrogate to environmental tobacco smoke (ETS), leads to increased airway responsiveness and sensory innervation later in life. However, the underlying mechanism initiated in early life that affects airway responses later in life remains undefined. The concomitant increase in nerve growth factor (NGF) after exposures suggests that NGF may be involved the regulation of airway innervation. Since NGF regulates sympathetic nerve responses, as well as sensory nerves, we extended previous studies by examining neuropeptide Y (NPY), a neuropeptide associated with sympathetic nerves. Different age groups of mice, postnatal day (PD) 2 and PD21, were exposed to either SS or filtered air (FA) for 10 consecutive days. The level of NPY protein in lung and the density of NPY nerve fibers in tracheal smooth muscle were significantly increased in the PD2-11SS exposure group compared with PD2-11FA exposure. At the same time, the level of NGF in lung tissue was significantly elevated in the PD2-11SS exposure groups. However, neither NPY (protein or nerves) nor NGF levels were significantly altered in PD21-30SS exposure group compared with the PD21-30FA exposure group. Furthermore, pretreatment with NGF antibody or K252a, which inhibits a key enzyme (tyrosine kinase) in the transduction pathway for NGF receptor binding, significantly diminished SS-enhanced NPY tracheal smooth muscle innervation and the increase in methacholine-induced airway resistance. These findings show that SS exposure in early life increases NPY tracheal innervation and alters pulmonary function and that these changes are mediated through the NGF.

Roles of membrane trafficking in nerve repair and regeneration

Successful axonal repair following injury is critical for nerve regeneration and functional recovery. Nerve repair relies on three functionally distinct events involving membrane trafficking. First, axonally transported vesicles accumulate, while others are generated at the cut end to restore a selective barrier to the severed axon. Then, retrograde transport of vesicles along microtubules informs the cell body that damage has occurred in the distal axon. Finally, membrane addition to a newly formed growth cone, or to the axonal membrane is required to promote axonal re-growth and elongation. Yet, how these membrane trafficking events are regulated and what are the identities of the molecules and organelles involved remains largely unknown. Several potential factors have been recently identified. Members of the SNARE machinery appear to regulate fusion of vesicles in a calcium-dependent manner to promote axolemmal resealing. Retrograde transport of endosomes powered by the dynein-dynactin molecular motor complex represents a potential injury-signaling platform. Several classes of secretory and endocytic vesicles may coordinate axonal membrane extension and re-growth. Here we discuss recent advances in understanding the mechanisms of the membrane trafficking involved in nerve repair.

Transcribing the path to neurological recovery-From early signals through transcription factors to downstream effectors of successful regeneration

The peripheral nervous system is known to regenerate comparatively well and this ability is mirrored in the de novo expression or upregulation of a wide variety of molecules involved in axonal outgrowth starting with transcription factors, but also including growth-stimulating substances, guidance and cell adhesion molecules, intracellular signaling enzymes and proteins involved in regulating cell-surface cytoskeletal interactions. Recent studies using pharmacological agents, and global as well as neuron-selective gene inactivation techniques have shed light on those endogenous molecules that play a non-redundant role in mediating regenerative axonal outgrowth in vivo. The aim of the current review is to sketch the sequence of molecular events from early sensors of injury to transcription factors to downstream effectors that cooperate in successful regeneration and functional recovery.

Peripheral somatosensation: a touch of genetics

The somatosensory system processes information that organisms 'feel': joint position, muscle stretch, pain, pressure, temperature, and touch. The system is composed of a diverse array of peripheral nerve endings specialized to detect these sensory modalities. Several recent discoveries have shed light on the genetic pathways that control specification and differentiation of these neurons, how they accurately innervate their central and peripheral targets, and the molecules that enable them to detect mechanical stimuli. Here, we review the cadre of genes that control these processes, focusing on mechanosensitive neurons and support cells of the skin that mediate different aspects of the sense of touch.

Axotomy induced changes in neuronal plasticity of sympathetic chain ganglia (SChG) neurons supplying descending colon in the pig

Sympathetic neurons are capable of extensive regeneration following axonal injury. To investigate the response to axotomy of colon-projecting neurons (CPN) localized in the porcine sympathetic chain ganglia (SChG), the retrograde Fast Blue (FB) tracer, axonal transection and double immunohistochemistry methods were applied. The CPN were localized exclusively in the lumbar SChG and displayed a predominantly catecholaminergic [i.e. Tyrosine Hydroxylase (TH)/Dopamine β Hydroxylase (DβH)] and Neuropeptide Y (NPY) positive phenotype under physiological conditions. Axotomy led to a significant decrease in TH/DβH production and a simultaneous increase in the neuropeptides Galanin (GAL) and Somatostatin (SOM), but not NPY or Vasoactive Intestinal Peptide (VIP) expression in retrogradely traced perikarya. Furthermore, the decrease in density of TH-/DβH-, VIP-, Leu(5)-Enkephalin (LENK)-, Choline Acetyltransferase (ChAT)-immunoreactive (-IR) nerve fibers occurred after axotomy. These data suggest a species-specific response to axonal damage of the CPN localized in porcine SChG. Since the SChG neurons supervise the vasculature of gut both in physiological and pathological conditions, and since pig is a more accurate animal model of human gut than a rodent (Swindle et al., 1992), these data may contribute to the understanding of the pathology of several gut illnesses, like Crohn Disease and Irritable Bowel Syndrome which commonly affect western populations.

Peripheral inflammation augments gap junction-mediated coupling among satellite glial cells in mouse sympathetic ganglia

Intercellular coupling by gap junctions is one of the main features of glial cells, but very little is known about this aspect of satellite glial cells (SGCs) in sympathetic ganglia. We used the dye coupling method to address this question in both a prevertebral ganglion (superior mesenteric) and a paravertebral ganglion (superior cervical) of mice. We found that in control ganglia, the incidence of dye coupling among SGCs that form the envelope around a given neuron was 10–20%, and coupling between SGCs around different envelopes was rare (1.5–3%). The dye injections also provided novel information on the structure of SGCs. Following peripheral inflammation, both types of coupling were increased, but most striking was the augmentation of coupling between SGCs forming envelopes around different neurons, which rose by 8–14.6-fold. This effect appeared to be non-systemic, and was blocked by the gap junction blocker carbenoxolone. These changes in SGCs may affect signal transmission and processing in sympathetic ganglia.

Galanin acts as a trophic factor to the central and peripheral nervous systems

The neuropeptide galanin is widely, but not ubiquitously, expressed in the adult nervous system. Its expression is markedly up-regulated in many neuronal tissues after nerve injury or disease. Over the last 10 years, we have demonstrated that the peptide plays a developmental survival role to subsets of neurons in the peripheral and central nervous systems with resulting phenotypic changes in neuropathic pain and cognition. Galanin also appears to play a trophic role to adult sensory neurons following injury, via activation of GalR2, by stimulating neurite outgrowth. Furthermore, galanin also plays a neuroprotective role to the hippocampus following excitotoxic injury, again mediated by activation of GalR2. Most recently, we have shown that galanin expression is markedly up-regulated in multiple sclerosis (MS) lesions and in the experimental autoimmune encephalomyelitis (EAE) model of MS. Over-expression of galanin in transgenic mice abolishes disease in the EAE model, whilst loss-of-function mutations in galanin or GalR2 increase disease severity. In summary, these studies demonstrate that a GalR2 agonist might have clinical utility in a variety of human diseases that affect the nervous system.

Endogenous BDNF regulates induction of intrinsic neuronal growth programs in injured sensory neurons

Identification of the molecule(s) that globally induce a robust regenerative state in sensory neurons following peripheral nerve injury remains elusive. A potential candidate is brain-derived neurotrophic factor (BDNF), the sole neurotrophin upregulated in sensory neurons after peripheral nerve injury. Here we tested the hypothesis that BDNF plays a critical role in the regenerative response of mature rat sensory neurons following peripheral nerve lesion. Neutralization of endogenous BDNF was performed by infusing BDNF antibodies intrathecally via a mini-osmotic pump for 3 days at the level of the fifth lumbar dorsal root ganglion, immediately following unilateral spinal nerve injury. This resulted in decreased expression of the injury/regeneration-associated genes growth-associated protein-43 and Talpha1 tubulin in the injured sensory neurons as compared to injury plus control IgG infused or injury alone animals. Similar results were observed following inhibition of BDNF expression by intrathecal delivery of small interfering RNAs (siRNA) targeting BDNF starting 3 days prior to injury. The reduced injury/regeneration-associated gene expression correlated with a significantly reduced intrinsic capacity of these neurons to extend neurites when assayed in vitro. In contrast, delayed infusion of BDNF antibody for 3 days beginning 1 week post-lesion had no discernible influence on the elevated expression of these regeneration-associated markers. These results support an important role for endogenous BDNF in induction of the cell body response in injured sensory neurons and their intrinsic ability to extend neurites, but BDNF does not appear to be necessary for maintaining the response once it is induced.

The dependence on gp130 cytokines of axotomy induced neuropeptide expression in adult sympathetic neurons

Adult peripheral neurons exhibit dramatic changes in gene expression after axonal injury, including changes in neuropeptide phenotype. For example, sympathetic neurons in the superior cervical ganglion (SCG) begin to express vasoactive intestinal peptide (VIP), galanin, pituitary adenylate cyclase activating polypeptide (PACAP), and cholecystokinin after axotomy. Before these changes, nonneuronal cells in the SCG begin to express leukemia inhibitory factor (LIF). When the effects of axotomy were compared in LIF-/- and wild-type mice, the increases in VIP and galanin expression were less in the former, though significant increases still occurred. LIF belongs to a family of cytokines with overlapping physiological effects and multimeric receptors containing the subunit gp130. Real-time PCR revealed large increases in the SCG after axotomy in mRNA for three members of this cytokine family, interleukin (IL)-6, IL-11, and LIF, with modest increases in oncostatin M, no changes in ciliary neurotrophic factor, and decreases in cardiotrophin-1. To explore the role of these cytokines, animals with selective elimination of the gp130 receptor in noradrenergic neurons were studied. No significant changes in mRNA levels for VIP, galanin, and PACAP were seen in axotomized ganglia from these mutant mice, while the increase in cholecystokinin was as large as that seen in wild-type mice. The data indicate that the inductions of VIP, galanin, and PACAP after axotomy are completely dependent on gp130 cytokines and that a second cytokine, in addition to LIF, is involved. The increase in cholecystokinin after axotomy, however, does not require the action of these cytokines.

Colitis induces calcitonin gene-related peptide expression and Akt activation in rat primary afferent pathways

Previous study has shown that colitis-induced increases in calcitonin gene-related peptide (CGRP) immunoreactivity in bladder afferent neurons result in sensory cross-sensitization. To further determine the effects of colitis on CGRP expression in neurons other than bladder afferents, we examined and compared the levels of CGRP mRNA and immunoreactivity in the lumbosacral dorsal root ganglia (DRG) and spinal cord before and during colitis in rats. We also examined the changes in CGRP immunoreactivity in colonic afferent neurons during colitis. Results showed increases in CGRP mRNA levels in L1 (2.5-fold, p<0.05) and S1 DRG (1.9-2.4-fold, p<0.05). However, there were no changes in CGRP mRNA levels in L1 and S1 spinal cord during colitis. CGRP protein was significantly increased in L1 (2.5-fold increase, p<0.05) but decreased in S1 (50% decrease, p<0.05) colonic afferent neurons, which may reflect CGRP release from these neurons during colitis. In L1 spinal cord, colitis caused increases in the number of CGRP nerve fibers in the deep lamina region extending to the gray commissure where the number of phospho-Akt neurons was also increased. In S1 spinal cord, colitis caused the increases in the intensity of CGRP fibers in the regions of dorso-lateral tract, and caused the increases in the level of phospho-Akt in the superficial dorsal horn of the spinal cord. In spinal cord slice culture, exogenous CGRP increased the phosphorylation level of Akt but not the phosphorylation level of extracellular-signal regulated kinase ERK1/2 even though our previous studies showed that colitis increased the phosphorylation level of ERK1/2 in L1 and S1 spinal cord. These results suggest that CGRP is synthesized in the DRG and may transport to the spinal cord where it initiates signal transduction during colitis.