Trophic factor modulation of c-Jun expression in supraspinal neurons after chronic spinal cord injury

Brain region changes following a spinal cord injury

Brain-related complications are common in clinical practice after spinal cord injury (SCI); however, the molecular mechanisms of these complications are still unclear. Here, we reviewed the changes in the brain regions caused by SCI from three perspectives: imaging, molecular analysis, and electrophysiology. Imaging studies revealed abnormal functional connectivity, gray matter volume atrophy, and metabolic abnormalities in brain regions after SCI, leading to changes in the structure and function of brain regions. At the molecular level, chemokines, inflammatory factors, and damage-associated molecular patterns produced in the injured area were retrogradely transmitted through the corticospinal tract, cerebrospinal fluid, or blood circulation to the specific brain area to cause pathologic changes. Electrophysiologic recordings also suggested abnormal changes in brain electrical activity after SCI. Transcranial magnetic stimulation, transcranial direct current stimulation, and deep brain stimulation alleviated pain and improved motor function in patients with SCI; therefore, transcranial therapy may be a new strategy for the treatment of patients with SCI.

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.

Transcriptional Factors and Protein Biomarkers as Target Therapeutics in Traumatic Spinal Cord and Brain Injury

Traumatic injury to the spinal cord (SCI) and brain (TBI) are serious health problems and affect many people every year throughout the world. These devastating injuries are affecting not only patients but also their families socially as well as financially. SCI and TBI lead to neurological dysfunction besides continuous inflammation, ischemia, and necrosis followed by progressive neurodegeneration. There are well-established changes in several other processes such as gene expression as well as protein levels that are the important key factors to control the progression of these diseases. We are not yet able to collect enough knowledge on the underlying mechanisms leading to the altered gene expression profiles and protein levels in SCI and TBI. Cell loss is hastened by the induction or imbalance of pro- or anti-inflammatory expression profiles and transcription factors for cell survival after or during trauma. There is a sequence of events of dysregulation of these factors from early to late stages of trauma that opens a therapeutic window for new interventions to prevent/restrict the progression of these diseases. There has been increasing interest in the modulation of these factors for improving the patient’s quality of life by targeting both SCI and TBI. Here, we review some of the recent transcriptional factors and protein biomarkers that have been developed and discovered in the last decade in the context of targeted therapeutics for SCI and TBI patients.

The crossed phrenic phenomenon

The cervical spine is the most common site of traumatic vertebral column injuries. Respiratory insufficiency constitutes a significant proportion of the morbidity burden and is the most common cause of mortality in these patients. In seeking to enhance our capacity to treat specifically the respiratory dysfunction following spinal cord injury, investigators have studied the "crossed phrenic phenomenon", wherein contraction of a hemidiaphragm paralyzed by a complete hemisection of the ipsilateral cervical spinal cord above the phrenic nucleus can be induced by respiratory stressors and recovers spontaneously over time. Strengthening of latent contralateral projections to the phrenic nucleus and sprouting of new descending axons have been proposed as mechanisms contributing to the observed recovery. We have recently demonstrated recovery of spontaneous crossed phrenic activity occurring over minutes to hours in C₁-hemisected unanesthetized decerebrate rats. The specific neurochemical and molecular pathways underlying crossed phrenic activity following injury require further clarification. A thorough understanding of these is necessary in order to develop targeted therapies for respiratory neurorehabilitation following spinal trauma. Animal studies provide preliminary evidence for the utility of neuropharmacological manipulation of serotonergic and adenosinergic pathways, nerve grafts, olfactory ensheathing cells, intraspinal microstimulation and a possible role for dorsal rhizotomy in recovering phrenic activity following spinal cord injury.

Neuroprotective and Neurorestorative Processes after Spinal Cord Injury: The Case of the Bulbospinal Respiratory Neurons

High cervical spinal cord injuries interrupt the bulbospinal respiratory pathways projecting to the cervical phrenic motoneurons resulting in important respiratory defects. In the case of a lateralized injury that maintains the respiratory drive on the opposite side, a partial recovery of the ipsilateral respiratory function occurs spontaneously over time, as observed in animal models. The rodent respiratory system is therefore a relevant model to investigate the neuroplastic and neuroprotective mechanisms that will trigger such phrenic motoneurons reactivation by supraspinal pathways. Since part of this recovery is dependent on the damaged side of the spinal cord, the present review highlights our current understanding of the anatomical neuroplasticity processes that are developed by the surviving damaged bulbospinal neurons, notably axonal sprouting and rerouting. Such anatomical neuroplasticity relies also on coordinated molecular mechanisms at the level of the axotomized bulbospinal neurons that will promote both neuroprotection and axon growth.

Flipping the transcriptional switch from myelin inhibition to axon growth in the CNS

Poor regeneration of severed axons in the central nervous system (CNS) limits functional recovery. Regeneration failure involves interplay of inhibitory environmental elements and the growth state of the neuron. To find internal changes in gene expression that might overcome inhibitory environmental cues, we compared several paradigms that allow growth in the inhibitory environment. Conditions that allow axon growth by axotomized and cultured dorsal root ganglion (DRG) neurons on CNS myelin include immaturity (the first few postnatal days), high levels of cyclic adenosine mono phosphate (cAMP), and conditioning with a peripheral nerve lesion before explant. This shift from inhibition to growth depends on transcription. Seeking to understand the transcriptome changes that allow axon growth in the CNS, we collaborated with the Marie Filbin laboratory to identify several mRNAs that are functionally relevant, as determined by gain- and loss-of-function studies. In this Perspective, we review evidence from these experiments and discuss the merits of comparing multiple regenerative paradigms to identify a core transcriptional program for CNS axon regeneration.

Erythropoietin Attenuates the Apoptosis of Adult Neurons After Brachial Plexus Root Avulsion by Downregulating JNK Phosphorylation and c-Jun Expression and Inhibiting c-PARP Cleavage

In the present study, the effects of erythropoietin (EPO) on preventing adult neurons from apoptosis (introduced by brachial plexus avulsion) were examined, and the mechanism was analyzed. Fifty injury rat models were established in this study by using micro-hemostat forceps to pull out brachial plexus root from the intervertebral foramen in supine position. These models were divided into EPO group (avulsion + 1000 U/kg subcutaneously on alternate days) and control group (avulsion + normal saline). C5-T1 spinal cord was harvested at days 1, 2, 4, 7, and 14. Compared with the control group, the apoptosis of spinal motoneurons was significantly decreased on days 4 and 7 in the EPO group, which was also approved by TUNEL examination results. The detection of p-JNK and expression of c-Jun and cleavage of cleaved PARP (c-PARP) were also examined by immunohistochemistry and were increased immediately at day 1, and peaked at day 2, day 2, and day 4 in control group, respectively. However, the amounts were decreased and delayed by EPO treatment significantly at the same time points. In conclusion, the apoptosis of adult spinal motorneurons was associated with JNK phosphorylation, c-Jun expression, and caspase activity, and EPO-mediated neuronal protective effect is proved by downregulating the JNK phosphorylation and c-Jun expression and inhibiting of c-PARP cleavage.

Valproic acid protection against the brachial plexus root avulsion-induced death of motoneurons in rats

In this study, the role of valproic acid (VPA) in protecting motoneuron after brachial plexus root avulsion was investigated in adult rats. Sixty rats were used in this study, and underwent the brachial plexus root avulsion injury, which was created by using a micro-hemostat forceps to pull out brachial plexus root from the intervertebral foramen. The animals were divided into two groups, VPA group administered with VPA dissolved in drinking water (300 mg/kg) daily, and control group had drinking water every day. The spinal cords (C5-T1) were harvested at day 1, 2, 3, 7, 14, and 28 for immunohistochemistry analysis, TUNEL staining, Nissl staining, and electron microscopy, respectively. The results showed that with VPA administration, the survival of motoneurons was promoted and the cell apoptosis was inhibited. The number of c-Jun and Bcl-2 positive motoneurons was increased immediately after avulsion both in control and VPA group, however, the percent of c-Jun positive motoneurons was decreased and the percent of Bcl-2 positive motoneurons was increased by VPA treatment significantly. Our results indicated that motoneurons were protected by VPA against cell death induced by brachial plexus root avulsion through c-Jun inhibition and Bcl-2 induction.

Descending bulbospinal pathways and recovery of respiratory motor function following spinal cord injury

The rodent respiratory system is a relevant model for study of the intrinsic post-lesion mechanisms of neuronal plasticity and resulting recovery after high cervical spinal cord injury. An unilateral cervical injury (hemisection, lateral section or contusion) interrupts unilaterally bulbospinal respiratory pathways to phrenic motor neurons innervating the diaphragm and leads to important respiratory defects on the injured side. However, the ipsilateral phrenic nerve exhibits a spontaneous and progressive recovery with post-lesion time. Shortly after a lateral injury, this partial recovery depends on the activation of contralateral pathways that cross the spinal midline caudal to the injury. Activation of these crossed phrenic pathways after the injury depends on the integrity of phrenic sensory afferents. These pathways are located principally in the lateral part of the spinal cord and involve 30% of the medullary respiratory neurons. By contrast, in chronic post-lesion conditions, the medial part of the spinal cord becomes sufficient to trigger substantial ipsilateral respiratory drive. Thus, after unilateral cervical spinal cord injury, respiratory reactivation is associated with a time-dependent anatomo-functional reorganization of the bulbospinal respiratory descending pathways, which represents an adaptative strategy for functional compensation.

Are rodents an appropriate pre-clinical model for treating spinal cord injury? Examples from the respiratory system

Because most studies of the effects of spinal cord injury (SCI) and resulting repair and treatments use rodent models, it is important to determine if these models are relevant to humans. In this review, we focus on alterations in respiratory function as a result of SCI. Several injury paradigms have been used in the rat to examine restoration of post-lesion respiratory function and potential benefits from repair strategies designed for humans. Unlike the corticospinal locomotor system, respiratory neural organization is well preserved between rodents and humans, and resembles the general organization of motor pathways in primates. These similarities justify the use of the rodent respiratory system as a model to analyze SCI and putative repair strategies.

c-Jun N-terminal kinase signaling regulates events associated with both health and degeneration in motoneurons

The c-Jun N-terminal kinases (JNKs) are activated by various stimuli and are critical for neuronal development as well as for death following a stressful stimulus. Here, we have evaluated JNK activity in both healthy and dying motoneurons from developing chick embryos and found no apparent difference in overall JNK activity between the conditions, suggesting that this pathway maybe critical in both circumstances. Pharmacological inhibition of JNK in healthy motoneurons supplied with trophic support resulted in decreased mitochondrial membrane potential, neurite outgrowth, and phosphorylation of microtubule-associated protein 1B. On the other hand, in motoneurons deprived of trophic support, inhibition of JNK attenuated caspase activation, and nuclear condensation. We also examined the role of JNK's downstream substrate c-Jun in mediating these events. While c-Jun expression and phosphorylation were greater in cells supplied with trophic support as compared with those deprived, inhibition of c-Jun had no effect on nuclear condensation in dying cells or neurite outgrowth in healthy cells, suggesting that JNK's role in these events is independent of c-Jun. Together, our data underscore the dualistic nature of JNK signaling that is critical for both survival and degenerative changes in motoneurons.

Chronically injured corticospinal axons do not cross large spinal lesion gaps after a multifactorial transplantation strategy using olfactory ensheathing cell/olfactory nerve fibroblast-biomatrix bridges

Transplantation of mixed cultures containing olfactory ensheathing cell (OEC) and olfactory nerve fibroblasts (ONF) has been shown to stimulate regrowth of both acutely and chronically injured corticospinal (CS) axons across small spinal cord lesion gaps. Here, we used a multifactorial transplantation strategy to stimulate regrowth of chronically injured CS axons across large spinal cord lesion gaps. This strategy combined the transplantation of aligned OEC/ONF-biomatrix complexes, as described previously (Deumens et al. [2004] Neuroscience 125:591-604), within the lesion gap with additional OEC/ONF injections rostral and caudal to the lesion site. We show an enhanced presence of injured CS axons directly rostral to the lesion gap, with no effects on injured CS axons at or caudal to the lesion gap. Furthermore, injured CS axons did not penetrate the OEC/ONF-biomatrix complex within the lesion gap. The enhanced presence of CS axons rostral to the lesion gap was not accompanied by any recovery of behavioral parameters assessed with the BBB locomotor rating scale or CatWalk gait analysis. We conclude that our multifactorial transplantation strategy should be optimized to create an OEC/ONF continuum in the injured spinal cord and thereby stimulate regrowth of injured CS axons across large spinal lesion gaps.

Effects of electro-acupuncture on the expression of c-jun and c-fos in spared dorsal root ganglion and associated spinal laminae following removal of adjacent dorsal root ganglia in cats

This study evaluated the plastic changes of c-jun and c-fos in the right sixth lumbar dorsal root ganglion (L6 DRG), Rexed's lamina II in representative spinal segments L3, L5, and L6 and in the nucleus dorsalis (ND) at L3 segments after electro-acupuncture (EA) in cats subjected to removal of L1-L5 and L7-S2 DRG. Following dorsal root ganglionectomy, there was a significant increase in the density of c-jun immunoreactivity in the neurons and glia in spinal lamina II and in the ND; there was also marked elevation in the expression of c-fos in ND. In both cases there was no change in the c-jun and c-fos immunoreactivity in the DRG. After EA in the operated animals, there was an up-regulation in the expression of c-jun in the L6 DRG and the associated spinal lamina II; however, increased c-fos expression was detected only in the L6 DRG. Western blot and RT-PCR were also performed to quantitatively explore the mRNA and protein expression changes in the spinal dorsal horn and associated DRG. Following partial deafferentation, there was a significant increase in the protein level of both c-jun and c-fos in the dorsal horn, while, in both cases there was no change in c-jun and c-fos protein and mRNA in the DRG. After EA in the operated animals, both c-jun protein and its mRNA in the L6 DRG as well as the associated dorsal horn of L6 spinal segment were upregulated, but increased c-fos protein and its mRNA was observed only in the L6 DRG. These findings suggested that c-jun and c-fos might be related to the acupuncture promoted spinal cord plasticity as reported previously.

Regeneration of descending axon tracts after spinal cord injury

Axons within the adult mammalian central nervous system do not regenerate spontaneously after injury. Upon injury, the balance between growth promoting and growth inhibitory factors in the central nervous system dramatically changes resulting in the absence of regeneration. Axonal responses to injury vary considerably. In central nervous system regeneration studies, the spinal cord has received a lot of attention because of its relatively easy accessibility and its clinical relevance. The present review discusses the axon-tract-specific requirements for regeneration in the rat. This knowledge is very important for the development and optimalization of therapies to repair the injured spinal cord.

Axotomized bulbospinal neurons express c-Jun after cervical spinal cord injury

In several central nervous system neuronal populations, axotomy triggers the upregulation of regeneration-associated genes such as c-Jun, which determines neurons ability to regenerate axon in a growth-permissive environment. We analyzed the expression of c-Jun in rat ventral medullary neurons after cervical hemisection in order to investigate their intrinsic regenerative potential. Maximal expression of c-Jun was observed 7 days after injury mainly in axotomized medullary neurons located in the gigantocellularis nucleus, the raphe nucleus and, although less intensively, in the rostral ventral respiratory group. This suggests that after high cervical injury, a large number of medullary neurons projecting to the spinal cord become competent for axonal regeneration, although this regenerating potential may not be equivalent between the various neuronal populations.

Repair of chronic spinal cord injury

Advances in medical and rehabilitative care now allow the 10-12,000 individuals who suffer spinal cord injuries each year in the United States to lead productive lives of nearly normal life expectancy, so that the numbers of those with chronic injuries will approximate 300,000 at the end of the next decade. This signals an urgent need for new treatments that will improve repair and recovery after longstanding injuries. In the present report we consider the characteristics of the chronically injured spinal cord that make it an even more challenging setting in which to elicit regeneration than the acutely injured spinal cord and review the treatments that have been designed to enhance axon growth. When applied in the first 2 weeks after experimental spinal cord injury, transplants, usually in combination with supplementary neurotrophic factors, and possibly modifications of the inhibitory central nervous system environment, have produced limited long-distance axon regeneration and behavioral recovery. When applied to injuries older than 4 weeks, the same treatments have almost invariably failed to overcome the obstacles posed by the neurons' diminished capacity for regeneration and by the increasing hostility to growth of the terrain at and beyond the injury site. Novel treatments that have stimulated regeneration after acute injuries have not yet been applied to chronic injuries. A therapeutic strategy that combines rehabilitation training and pharmacological modulation of neurotransmitters appears to be a particularly promising approach to increasing recovery after longstanding injury. Identifying patients with no hope of useful recovery in the early days after injury will allow these treatments to be administered as early as possible.

Exposure to short-lasting impulse noise causes neuronal c-Jun expression and induction of apoptosis in the adult rat brain

Exposure to impulse noise, above a certain intensity, is harmful to auditory function. Effects of impulse noise on the central nervous system (CNS) are largely unexplored, and there is little information on critical threshold values and time factors. We have recently shown that neurofilament proteins are affected in the cerebral cortex and the hippocampus. Now we show that impulse noise induces expression of the immediate early gene c-Jun products, proposed to play a role in the initiation of neuronal death, and apoptosis as revealed by TUNEL staining. Rat brains were investigated immunohistochemically 2 h to 21 days after exposure to impulse noise of 198 dB or 202 dB. c-Jun was expressed in neuronal perikarya in layers II-VI of the temporal cortex, the cingulate and the piriform cortices at 2 h to 21 days after both exposure levels. Granule neurons of the dentate gyrus and the CA1-3 in the hippocampus pyramidal neurons were similarly affected. The elevated expression of c-Jun products remained high at all postexposure times. TUNEL staining was positive among the same nerve cell populations 6 h after exposure and persisted even at 7 days at both exposure levels.

Protective autoimmunity as a T-cell response to central nervous system trauma: prospects for therapeutic vaccines

Immune activity in general, and autoimmunity in particular, have long been considered as harmful in the context of central nervous system (CNS) trauma. Increasing evidence suggests, however, that the injured CNS can benefit from autoimmune manipulations. Active or passive immunization with CNS-associated self antigens was shown to promote recovery from a CNS insult. It is now also evident that this beneficial 'autoimmunity' is not solely an outcome of immune manipulation but is also a physiological response, evoked by a non-pathogenic insult and apparently designed to counteract the insult-related toxicity which is induced in part by essential physiological compounds present in excess of their normal levels. It appears that when the buffering capacity of constitutive local mechanisms (transporters, enzymes, etc.) that normally regulate these compounds is exceeded, assistance is recruited from the immune system. Like the overactive physiological compounds themselves, the immune system needs to be rigorously regulated in order to produce adequate phagocytic activity and the required quantity of cytokines and growth factors at the right time and place. Boosting of this autoimmune response is potentially a powerful strategy for neuroprotective therapy.

Chronically injured supraspinal neurons exhibit only modest axonal dieback in response to a cervical hemisection lesion

This study examined the extent of axon retraction (dieback) exhibited by injured brain stem neurons in a chronic spinal cord injury (SCI) condition. Adult female rats subjected to a cervical (C3) hemisection lesion were sacrificed 1, 4, 8, or 14 weeks after injury and the spinal cord from C1 to the lesion cavity was removed. One week prior to sacrifice, a microinjection of biotinylated dextran amine (BDA, 0.5 microliter) was made into the red nucleus, lateral vestibular nucleus, or medullary reticular formation of each animal. Horizontal cryostat sections were processed with avidin-HRP to detect supraspinal axons anterogradely labeled with BDA. Terminal end bulbs of axons were identified and their distance from the lesion site was measured by a computerized image analysis program. At all postinjury intervals, numerous rubrospinal, vestibulospinal, and reticulospinal tract axons were found immediately adjacent to the lesion site and over 60% of all terminals were within 500 micrometer at 1 and 4 weeks. The mean axonal distance of 450-500 micrometer from the lesion indicated that many injured axons had retracted farther than 500 micrometer from the lesion site; however, long-term maintenance of the mean axonal distance from the lesion at less than 500 micrometer indicated the absence of progressive dieback after SCI. While some modest changes occur in specific supraspinal pathways following SCI, axonal retraction does not appear to be a contributing factor to the diminished regenerative effort by certain brain stem neurons that has been observed at long postinjury intervals.

Partial functional recovery of paraplegic rat by adenovirus-mediated gene delivery of constitutively active MEK1

Spinal cord injury in adult mammals results in little axonal regeneration, although the mechanism of regeneration failure still remains elusive. Recent research has revealed that activation of the extracellular-signal-regulated kinases (ERKs) plays an important role in the neurite outgrowth. In the present study, we constructed a replication-defective adenovirus vector carrying mutated form of MEK1 (CA-MEK virus), which constitutively activate ERK pathway, and investigated its effect on thoracic spinal cord injury model in young adult rats as well as neurite outgrowth in vitro. In rat pheocromocytoma cell line PC12 cells, CA-MEK virus infection induced sustained activation of ERKs and stimulated neurite outgrowth in the absence of neurotrophic factors. In rat spinal cord transection model, injection of CA-MEK virus into the completely transected spinal cord efficiently activated ERKs in the supraspinal neurons and induced axonal regeneration across the transection site, which was confirmed by anterograde labeling with wheat-germ-agglutinin conjugated peroxidase (WGA-HRP). Spinal cord evoked potentials (SCEP) showed that these regenerated axons were electroconductive. Most importantly, CA-MEK virus-treated rats showed significant recovery of hind limb function 2 weeks after operation compared to the control rats treated with no virus or LacZ virus. These results suggest that adenovirus-mediated CA-MEK gene transduction offers a novel strategy for the gene therapy of spinal cord injury.

Distinct subcellular localization and mRNA expression of neuronal nitric oxide synthase in the nucleus dorsalis and red nucleus and their correlation with inducible transcription factors after spinal cord hemisection

We previously reported on the differential expression of neuronal nitric oxide synthase (nNOS) in neurons of the nucleus dorsalis (ND) and red nucleus (RN), as well as differential roles of nitric oxide (NO) in these two distinct groups' neurons characterized with different nNOS phenotypes after lower thoracic spinal cord hemisection. To further understand the enzyme, nNOS expression was studied at the subcellular and mRNA levels by using electron microscopic immunohistochemistry (EM-IHC) and in situ hybridization respectively. Possible transcriptional regulation by c-Jun or CREB in the differential nNOS expression in both ND and RN neurons was also studied. nNOS mRNA was not found in the normal ND neurons, but was shown in the normal RN neurons. After spinal cord hemisection, nNOS mRNA was induced in the ipsilateral ND, while upregulated on both sides of the RN, which preceded protein induction or upregulation. By EM-IHC, nNOS immunoreaction products were predominantly bound to the membrane of the mitochondria, rough endoplasmic reticulum (rER), Golgi apparatus, and nuclear envelope in the RN neurons of normal rats as well as rats subjected to spinal cord hemisection. In contrast, nNOS-immunoreactive deposits in the experimental ND neurons were found to be mainly granular, being dispersed throughout the cytoplasmic matrix. It is speculated that the differential subcellular localizationof nNOS indicates that axotomy may trigger different nNOS transcripts and lead to different nNOS isoform expression in the normally non-nNOS- and normally nNOS-containing neurons. c-Jun was induced in the ipsilateral ND neuronsand upregulated only in the contralateral RN neurons. Activation of CREB by phosphorylation was occasionally detectable in the ND neurons, but not in the RN neurons. Double-labeling data showed a large proportion of c-Jun and nNOS colocalization in neurons of the ipsilateral ND and contralateral RN after spinal cord hemisection. However, dissociation of nNOS expression kinetics with c-Jun was observed in the ipsilateral RN. The results implied that nNOS expression might not be under the direct transcriptional regulation by c-Jun, although it seemed to be closely related to the c-Jun expression.

Passive or active immunization with myelin basic protein promotes recovery from spinal cord contusion

Partial injury to the spinal cord can propagate itself, sometimes leading to paralysis attributable to degeneration of initially undamaged neurons. We demonstrated recently that autoimmune T cells directed against the CNS antigen myelin basic protein (MBP) reduce degeneration after optic nerve crush injury in rats. Here we show that not only transfer of T cells but also active immunization with MBP promotes recovery from spinal cord injury. Anesthetized adult Lewis rats subjected to spinal cord contusion at T7 or T9, using the New York University impactor, were injected systemically with anti-MBP T cells at the time of contusion or 1 week later. Another group of rats was immunized, 1 week before contusion, with MBP emulsified in incomplete Freund's adjuvant (IFA). Functional recovery was assessed in a randomized, double-blinded manner, using the open-field behavioral test of Basso, Beattie, and Bresnahan. The functional outcome of contusion at T7 differed from that at T9 (2.9+/-0.4, n = 25, compared with 8.3+/-0.4, n = 12; p<0.003). In both cases, a single T cell treatment resulted in significantly better recovery than that observed in control rats treated with T cells directed against the nonself antigen ovalbumin. Delayed treatment with T cells (1 week after contusion) resulted in significantly better recovery (7.0+/-1; n = 6) than that observed in control rats treated with PBS (2.0+/-0.8; n = 6; p<0.01; nonparametric ANOVA). Rats immunized with MBP obtained a recovery score of 6.1+/-0.8 (n = 6) compared with a score of 3.0+/-0.8 (n = 5; p<0.05) in control rats injected with PBS in IFA. Morphometric analysis, immunohistochemical staining, and diffusion anisotropy magnetic resonance imaging showed that the behavioral outcome was correlated with tissue preservation. The results suggest that T cell-mediated immune activity, achieved by either adoptive transfer or active immunization, enhances recovery from spinal cord injury by conferring effective neuroprotection. The autoimmune T cells, once reactivated at the lesion site through recognition of their specific antigen, are a potential source of various protective factors whose production is locally regulated.

JNK and p38 stresskinases--degenerative effectors of signal-transduction-cascades in the nervous system

The c-Jun N-terminal kinases (JNKs, also called stress activated protein kinases. SAPKs) and p38 kinases constitute together with extracellular signal-regulated kinases (ERKs) the family of MAP kinases. Whereas the functions of JNKs under physiological conditions are largely unknown, there is raising evidence that JNKs are potent effectors of apoptosis or degeneration of neurons in vitro and in the brain. The activation of the inducible transcription factor c-Jun by N-terminal phosphorylation is a central event in JNK-mediated degenerative processes that depend on de novo protein synthesis. At the post-translational level, cytoplasmic degenerative actions of JNKs might comprise inhibition of Bcl-2 and steroid hormone-receptor signaling or hyperphosphorylation of tau; and at transcriptional level, JNKs might trigger the induction of the apoptotic effectors p53 and Fas-Ligand by phosphorylation of c-Jun. The role of p38 is the nervous system is poorly understood, but its activation is also considered as part of the neuronal stress response. This review informs about the genetic processing, the regulation of activity and the biochemical actions of JNK and p38 isoforms in general. In the second part, we summarize the findings on expression and activation of JNKs and p38 under neurodegenerative condition. A particular focus is also put on the putative function of JNK under physiological conditions and for neuroprotection.

Repetitive electroconvulsive seizures induce activity of c-Jun N-terminal kinase and compartment-specific desensitization of c-Jun phosphorylation in the rat brain

Electroconvulsive seizures (ECS) are used for therapy of pharmacoresistent depression and are supposed to induce long-lasting neuronal alterations in morphology and gene expression. In this study, we have investigated the phosphorylation of the transcription factor protein c-Jun at its serine 73 residue by immunohistochemistry and the activity of the c-Jun N-terminal kinase 1 (JNK1) by immunocomplex assay following repetitive ECS in adult rats. In untreated controls, nuclear c-Jun immunoreactivity, but not N-terminal phosphorylation, was present in a variety of neuronal populations including the hippocampus, the temporobasal cortex and the amygdalar complex. Daily ECS for 1, 5 or 10 days (1x, 5x or 10x ECS) did not alter the expression of c-Jun but caused a substantial N-terminal phosphorylation of c-Jun (phospho-c-Jun). Nuclear phospho-c-Jun immunoreactivity was maximal within 15 min following ECS, and became absent after 30 min. The highest levels of phospho-c-Jun labeling were found after 1x ECS in the amygdalar complex, the dorsomedial hypothalamus and the piriform cortex. The inducibility of c-Jun N-terminal phosphorylation was preserved in the medial amygdala and piriform cortex, but significantly declined in the basal amygdala and medial hypothalamus with progressive ECS stimulation. One single ECS 3 or 5 days following 10x ECS yielded a pattern of phospho-c-Jun as seen following 10x ECS; thus, a lag of 5 days was not sufficient to provoke the initial level of N-terminal phosphorylation of c-Jun. In the rostral hippocampus, c-Jun was not phosphorylated at any investigated time inspite of its high constitutive expression. In some contrast with this compartment-specific phosphorylation of c-Jun, immunocomplex assays revealed that the JNK1 activity was strongly enhanced in both amygdala and hippocampus. Our findings demonstrate that rapid JNK activation and phosphorylation of c-Jun as stand-by transcription factor characterize the beginning of neuroplastic changes, e.g., following ECS, a classic treatment of mental disorders. The N-terminal phosphorylation is compartment specific and can habituate following repetitive stimulation suggesting that the differential activation of the JNK/c-Jun axis is part of the neuronal strategy to integrate transynaptic excitation.