Mitogen-Activated Protein Kinase Pathways Following Traumatic Brain Injury

Naoki Otani, Hiroshi Nawashiro, Kimihiro Nagatani, Satoru Takeuchi, Hiroaki Kobayashi, Katsuji Shima

.

DOI: 10.4236/nm.2011.23028                

Abstract

The mechanisms underlying the secondary or delayed cell death in the hippocampus and cerebral hemisphere after traumatic brain injury (TBI) have been poorly understood. Recent data suggesting that TBI may have relationship with both an inflammatory and a neurodegenerative factors are also presented. Mitogen-activated protein kinases (MAPK), which play a crucial role in signal transduction, are activated by phosphorylation in response to a variety of mitogenic signals. In this article, we review the clinical and experimental evidence for brain damage after TBI. In addition, the MAPK pathways, closely involved in signal transduction after TBI, which could therefore be a new and potentially effective therapeutic target in TBI. Further investigations are therefore necessary to better understand cerebral traumatic damage and delineate the best practice strategies needed to improve the patient outcomes after TBI.

Keywords

Traumatic Brain Injury, Mitogen-Activated Protein Kinase, Cell Signaling

1. Introduction

Posttraumatic amnesia is a common symptom after TBI, and may be related to hippocampal dysfunction [1]. Particularly, memory deficits were found in 90% of patients had made a good recovery after mild and moderate TBI [2]. Patients with mild TBI and persistent postconcussive symptoms have a high incidence of medial temporal lobe injury [3]. Magnetic resonance imaging (MRI) volumetric studies showed that predicting the association between TBI and premature loss of brain parenchyma is important in determining the most serious injuries [4-7]. However, the pathology of neuronal cell death after TBI and the mechanism of MAPK regulation have not yet to be fully understood. Further investigations will be necessary to elucidate the mechanism of neuronal injury after TBI. We herein review the pathophysiology of TBI and alteration of MAPK after TBI. These findings suggested that a distinct MAPK cascade might participate in the pathophysiological disorder after TBI. In addition, the MAPK cascades could therefore be a new and potentially effective therapeutic target in TBI.

2. Discussion

2.1. Selective Vulnerability in the CA3 Neurons after Experimental TBI

In the review by Lighthall et al. [8] regarding experimental TBI models, the authors described and characterized the pathophysiologic changes using a fluid percussion injury (FPI) method and a controlled cortical impact (CI) technique. Chen et al. [9] described the characterization of an experimental model of closed head injury in a mouse model. The posttraumatic accumulation of cerebral edema, the disruption of the blood-brain barrier, histopathology, motor and cognitive functions were investigated up to 30 days following closed head (CH) injury. In addition, Dixon et al. [10] characterized a new FPI model of experimental brain injury to systematically examine the physiologic and histopathologic responses in rats at two levels of injury severity. These reports suggested that the modified injury model could reproduce the posttraumatic sequelae observed in rats and that some of the data obtained in this model were essentially similar to those observed in human brain injuries. Hicks et al. [11] systematically characterized the pattern of neuronal injury at sequential time points to identify the selectively vulnerable regions and to determine the temporal contribution of primary and delayed neuropathological events following LFP brain injury in rats. The frequency of injured neurons was greatest in the ipsilateral cortex, hippocampus, and thalamus, and a visible loss of Nissl-stained neurons was observed in these regions starting at 12 hours after injury. Several experimental studies have suggested that a selective vulnerability to TBI was observed in hippocampal CA3 neurons [11-13]. Immonen et al. [14] suggested that the assessment of early quantitative MRI changes in the hippocampus and in the perifocal area might help to predict the long-term outcome after experimental TBI. The injured neurons were shown as Nissl-stained dark neurons. Ooigawa et al. [15] studied the fate of Nissl-stained dark neurons after TBI. In the hippocampus the number of dead neurons was approximately the same number as that of the Nissl-stained dark neurons. The data suggested that not all Nisslstained dark neurons inevitably died after TBI. Lowenstein et al. [16] showed that neurons of the dentate hilus were vulnerable to a brief, unilateral impact to the extradural surface of the brain using FPI model. This neuronal loss was highly selective since the adjacent dentate granule and pyramidal neurons appeared relatively unaffected. In particular, the mechanism of posttraumatic selective vulnerability of hippocampal CA3 neurons has not yet been fully elucidated.

2.2. Calcium-Dependent Excitotoxic Processes after TBI

Several studies suggested that TBI induced acute neurodegeneration [17] which lead to progressive atrophic changes of the injured cerebral hemisphere [18]. Calciumdependent excitotoxic processes and induction of inflammatory cytokines significantly contribute to pathologic responses, such as apoptotic programmed cell death [19] and glial reaction following TBI [20]. However, the biochemical cascades underlying posttraumatic signal transduction, which causes these pathological alterations are poorly understood. Matsushita et al. [21] suggested that TBI induced neuronal depolarization and excessive excitatory neurotransmitter release, which enhanced glutamate toxicity and led to an increase in intracellular calcium levels [22]. The surge of glutamate might be derived from cortical impact depolarization [23], which immediately induced cytokine genes [24] and neurotrophic genes expression within the bilateral cerebral hemisphere [25, 26]. The NMDA receptor is clearly involved in the pathophysiology of TBI [27,28], thus suggesting that an injury-induced reduction in the expression of the NMDA receptor was one likely mechanism for the impaired experience-dependent neuroplasticity observed in the immature brain following TBI. Calcium-dependent excitotoxic processes and induction of inflammatory cytokines significantly contribute to pathological responses such as apoptotic cell death and glial reactions after TBI. As reviewed by Raghupathi et al. [29], the apoptosis of neurons and glia contributed to the overall pathology of TBI in both humans and animals. While excitatory amino acids, increases in intracellular calcium, and free radicals can all cause cells to undergo apoptosis, in vitro studies have determined that neuronal cells can undergo apoptosis via many other pathways. However, the biochemical cascades underlying posttraumatic signal transduction, which causes these pathological alterations are poorly understood. The surge of glutamate might be derived from cortical impact depolarization [30], which immediately induced cytokine gene expression [31] and neurotrophic gene expression within the bilateral cerebral hemisphere [32,33].

2.3. Mitogen-Activated Protein Kinase Pathways after TBI

Recent studies have indicated that TBI induced the expression of neurotrophin-related mRNA and receptors [34-36] in the rat hippocampus, which triggered downstream mitogen-activated protein kinases (MAPK) cascades through interactions with specific high-affinity tyrosine kinase receptors [37]. The MAPKs are serine/ threonine protein kinases that promote a large diversity of cellular functions in many cell types, which play a crucial role in signal transduction, are activated by phosphorylation in response to a variety of mitogenic signals. The cascades are composed of extracellular signal-regulated protein kinase (ERK), c-Jun NH(2)-terminal kinase (JNK), and p38 pathways (Figure 1). ERK is activated in response to growth factors [38], oxidative stress [39], and intracellular calcium influx [40]. Activated ERK can interact with cytoplasmic components or can translocate to the nucleus. Evidence has shown that sustained ERK is translocated to the nucleus [41,42] and nuclear translocated ERK can promote neuronal cell death, regulating transcription [43], which plays an important role in the survival, proliferation, and differentiation of various cells [44]. Recently, a new member of MAPKs, ERK5 has been identified and implicated in neuronal survival [45]. Rapid ERK5 activation was observed in the hippocampal CA3 and dentate gyrus regions after cerebral ischemia [46]. On the other hand, JNK and p38 are activated in response to the presence of inflammatory cytokines [47], glutamate toxicity [48]. JNK and p38 cause alterations in transcription factors which lead to neuronal apoptosis [49]. Several studies suggested the activation of JNK and p38 cascades induced neuronal injury following cerebral ischemia [50,51] and spinal cord injury [52]. Mandell et al. [53] demonstrated that the focal mechanical injury induced a rapid activation and spreading of astroglial ERK activation in a defined in vitro model and suggested that the similar mechanism may result in astroglial activation following TBI. However, there has been no reports focusing on the expression and distribution of phosphorylated-MAPKs following TBI in vivo. Otani et

Figure 1. Mitogen-activated protein kinases (MAPKs) play a crucial role in the transduction of signals through protein kinases and protein phosphatases. The MAPK pathways are a ubiquitous group of protein serine and threonine kinases that regulate gene expression through transcription factor activity. The stimulus may transduce to the nucleus to regulate gene expression through a distinct set of MAPK signal transduction cascades, including extracellular signalregulated kinases 1 and 2 (ERK1, ERK2), p38 mitogenactivated protein (p38), and the c-Jun NH2-terminal kinase (JNK). These pathways are important mediators of the signal transduction responsible for cell growth and proliferation. The nuclear targets of these MAPK signaling pathways are transcriptional factors, such as transcriptional factor activator protein-1 (AP-1) and nuclear factor-kappa B (NFκB), which regulate the expression of various genes.

al. [53] demonstrated that the focal mechanical injury induced a rapid activation and spreading of astroglial ERK activation in a defined in vitro model and suggested that the similar mechanism may result in astroglial activation following TBI. However, there has been no reports focusing on the expression and distribution of phosphorylated-MAPKs following TBI in vivo. Otani et al. [54] demonstrated that the immunoreactivity of ERK and JNK significantly increased following TBI in the rat hippocampus. The data presented in that article suggested ERKand JNK-, but not p38-phosphorylation, to be associated with the molecular sequelae of TBI, and that the discrepancy in the MAPK alterations reflected differences in selective vulnerability between the mechanical and ischemical events in the rat hippocampus. Thus, recent studies have suggested that the activation of JNK and p38 pathways without an activating ERK pathway induced selective CA1 vulnerability to transient forebrain ischemia [55,56]. In addition, the authors investigated, for the first time, the activation of the MAPK pathways in the rat hippocampus following experimental TBI. These findings suggest that a distinct MAPKs cascade might therefore participate in the selective vulnerability of hippocampal CA3 neurons following TBI. Raghupathi et al. [57] demonstrated the regional activition of JNK and ERK signaling pathways using immunoblotting and immunohistochemistry following TBI. Most of the pharmacological studies implicating ERK have been carried out using PD98059 or U0126 (which inhibits mitogenactivated protein kinase/ERK kinase, an upstream activator of ERK1). Initially, ERK activation was considered as a promoter of neuronal survival and memory [58]. However, it is now clear that ERK activition can also participate in a variety of neuronal death signals [59]. Mori T et al. [60] provided the evidence that perturbations in MAPK signal-transduction pathways were involved in the pathophysiology of TBI. Treatment with PD98059, which inhibits the ERK pathway, significantly increased cell survival in vitro. ERK pathway inhibition with PD98059 resulted in a significant reduction in the cortical lesion volume 7 days after trauma. The p38 kinase and JNK inhibitor SB203580 had no detectable beneficial effect. These data indicated that critical perturbations in MAPK pathways mediated cerebral damage after acute injury, and that ERK was a novel therapeutic target in TBI. Otani N et al. [61] studied the effects of inhibition of ERK phosphorylation using MAPK/ERK (MEK) inhibitor U0126 on the histopathological and behavioral outcome after TBI. Thus, the administration of U0126 improved the histopathological and motor functional performance 3, 4, and 5 days after TBI. The authors suggested that the inhibition of the ERK phosphorylation could therefore be a new and potentially effective therapeutic target in TBI. Several studies have shown that U0126 enhanced the regional cerebral blood flow by inducing smooth muscle cells to block the effects of endothelin-mediated vasoconstriction [62]. U0126 has also been shown to reverse the permeability of endothelial cell monolayers increased by vascular endothelial growth factor [63]. In addition, ERK upregulates the extracellular matrix degrading enzyme matrix metalloproteinase-9, which exacerbates the histopathological findings and motor performance after TBI [64]. These results suggest that the neuroprotective effects induced by U0126 may be mediated through a reduction in the vascular permeability thus leading to edema formation after TBI. Accumulating data indicate that extracellular proteolysis also plays a critical role in the pathophysiology of neuronal cell death after TBI. The two major systems that modify the extracellular matrix in the brain are the plasminogen activator (PA) and matrix metalloproteinase (MMP) axes. Deleterious effects include the disruption of blood-brain barrier integrity, amplification of inflammatory infiltrates, demyelination, and possible interruption of cell-to-cell and cell-to-matrix interactions that may trigger cell death. In contrast, PA-MMP actions may contribute to the extracellular proteolysis that mediates parenchymal and angiogenic recovery after TBI [65]. Asahi et al. [66] showed that the MMP is involved in the pathophysiology of TBI. In particular, MMP-9 knockout mice were protected against TBI. Several authors have so far demonstrated that the resident brain cells secrete MMP after injury, astrocytes are the main source of MMP-9 activity, and the MAPK pathway is activated after mechanical injury, mediating the secretion of MMP-9. These data indicate that the MAPK pathway triggers the upregulation in MMP-9 after trauma, and further suggest that targeting the upstream signaling mechanisms that regulate deleterious MMP-9 activity may reveal new therapeutic opportunities for TBI [64,67].

2.4. Induction of Inflammatory Cytokines after TBI

Brain trauma results in neuronal apoptosis and axonal tract damage. These pathologies are worsened by the inflammatory cascade set into motion by the initial injury [68]. Two pro-inflammatory cytokines released after TBI are tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) [69,70], which induced astrogliosis [71]. Several studies have documented rapid increases in TNF-α and IL-1β levels after TBI [72-74]. These pro-inflammatory cytokines stimulated inflammatory cells to release damaging reactive oxygen and nitrogen species, to raise the glutamate levels to excitotoxic levels, to impair the ability of glia cells to buffer extracellular potassium, to compromise the blood-brain barrier, and to attract more inflammatory cells into the brain [75,76]. Interestingly, recent study showed that over-expression of GFAP induced by TNF-α was significantly attenuated by the ERK inhibitor PD98059. The authors in this article suggested that TNF-α might upregulate GFAP through the ERK pathway [77]. Double immunostaining results in the present study showed that the immunoreactivity for p-ERK was almost exclusively localized in astrocytes surrounding the contusional region after 6 hours of TBI. We speculated that the induction of p-ERK in astrocytes in the late period of TBI has an important role of astroglial reaction led to astrogliosis, which are beneficial for neuronal survival and repairment of damaged blood-brain barrier [78]. Cyclooxygenase-2 (COX-2), a rate-limiting enzyme converting arachidonic acid to prostaglandins and a key player in neuroinflammation, has been implicated in the pathogenesis of TBI, which modulate synaptic transmission and plasticity and cause neurodegeneration after TBI. The actions of these COX-2 metabolites are likely mediated by MAPK and inositol 1,4,5-trisphosphate (IP3) signal transduction pathways. In addition, recent work [79,80] shows that PGE2-G-enhanced hippocampal GABAergic and glutamatergic synaptic transmissions are not mediated via PKA and PKC pathways, but appear to be mediated through ERK, p38, IP3, and NF-κB signal transduction pathways. Yang et al. [81] demonstrated that the PGE2-G-induced increase in hippocampal LTP is attenuated by an IP3 inhibitor, indicating the involvement of the IP3-mediated mobilization of intracellular Ca²⁺ in PGE2-G-induced increase in LTP. The involvement of ERK and p38 pathways is further supported from the molecular evidence. PGE2-G induces a time-dependent phosphorylation of ERK and p38MAPK, and this phosphorylation is attenuated by ERK and p38 inhibitors. TBI leads to the development of gliosis, but little is known about the signal transduction mechanisms that underlie this process. Gliosis is characterized by hypertrophic and hyperplastic changes of astrocytes in response to brain injury. ERK was widely expressed in adult brain with high levels apparent in neocortical neuronal cell bodies and dendrites [82]. Johanson et al. [83] suggested a retrograde axonal transport of p-ERK might play a role in neurotrophic signal transmission from the nerve terminal to the cell body in the rat sciatic nerve. The retrograde axonal transport of p-ERK is of limited value because it may take much time to reach the soma of neurons [84]. An induction of p-ERK was observed in astrocytes surrounding pyramidal CA3 neurons and contusional area at 6 hours after TBI [54,85], which might be derived from intracellular signal transduction in response to TBI. Mandell et al. [86] assessed that ERK phosphorylation triggered an astroglial reaction which led to reactive astrogliosis, which has both beneficial and detrimental consequences for the functional recovery of neurons. A recent study indicated that reactive astrocytes have a beneficial effect on both neuronal survival and the repair of the damaged blood-brain barrier [87]. The prolonged phosphorylation of p-ERK in astrocytes might thus play a crucial role in the promotion of cell survival in the late period of TBI. Reactive astrogliosis is the most prominent response to diverse forms of TBI. TBI induced GFAP gene expression, which might be a sensitive molecular marker for evaluating the global response in progressive glial scarring in the rat brain [88]. On the other hand, several reports showed that there were close relationships between inflammation, cytokine production, and astrogliosis [89]. Reactive astrocytes induced the expression of a variety of molecules such as neurotrophin and growth factor families [90]. Mandell et al. [53] investigated the mechanism of ERK activation with the primary cultured astroglial monolayers subjected to focal mechanical injury and demonstrated that cortical focal lesion induced a rapid spreading of astroglial ERK activation.

3. Conclusions

We herein review the pathophysiology of TBI and alteration of MAPK after TBI. These findings suggested that a distinct MAPK cascade might participate in the pathophysiological disorder after TBI. In addition, the MAPK cascades could therefore be a new and potentially effective therapeutic target in TBI. However, the pathology of neuronal cell death after TBI and the mechanism of MAPK regulation has not yet to be fully understood. Further investigations will be necessary to elucidate the effect of MAPK pathway after TBI.

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	S. W. Scheff, S. A. Baldwin and R. W. Brown, “Morris Water Maze Deficits in Rats Following Traumatic Brain Injury: Lateral Controlled Cortical Impact,” Journal of Neurotrauma, Vol 14, No. 9, 1997, pp. 615-627. doi:10.1089/neu.1997.14.615
[2]	R. W. Rimel, B. Giordani, J. T. Barth and J. A. Jane, “Moderate Head Injury: Completing the Clinical Spec- trum of Brain Trauma,” Neurosurgery, Vol. 11, No. 3, 1982, pp. 344-351.
[3]	E. M. Umile, M. E. Sandel, A. Alavi, C. M. Terry and R. C. Plotkin, “Dynamic Imaging in Mild Traumatic Brain Injury: Support for the Theory of Medial Temporal Vul- nerability,” Archives of Physical Medicine and Rehabili- tation, Vol. 83, No. 11, 2002, pp. 1506-1513. doi:10.1053/apmr.2002.35092
[4]	D. D. Blatter, E. D. Bigler, S. D. Gale, S. C. Johnson, C. V. Anderson, B. M. Burnett and D. Ryser, “MR-Based Brain and Cerebrospinal Fluid Measurement After Trau- matic Brain Injury: Correlation with Neuropsychological Outcome,” American Journal of Neuroradiology, Vol. 18, No. 1, 1997, pp. 1-10.
[5]	E. D. Bigler, D. D. Blatter, C. V. Anderson, S. C. Johnson, S. D. Gale, R. O. Hopkins and B. Burnett, “Hippocampal Volume in Normal Aging and Traumatic Brain Injury,” American Journal of Neuroradiology, Vol. 18, No. 1, 1997, pp. 11-23.
[6]	E. D. Bigler, C. V. Anderson and D. D. Blatter, “Tempo- ral Lobe Morphology in Normal Aging and Traumatic Brain Injury,” American Journal of Neuroradiology Vol. 23, No. 2, 2002, pp. 255-266.
[7]	F. Tomaiuolo, G. A. Carlesimo, M. Di Paola, M. Petrides, F. Fera, R. Bonanni, R. Formisano and P. Pasqualetti, “Gross Morphology and Morphometric Sequelae in the Hippocampus, Fornix, and Corpus Callosum of Patients with Severe Non-Missile Traumatic Brain Injury without Macroscopically Detectable Lesions: a T1 Weighted MRI Study,” Journal of Neurology, Neurosurgery & Psy- chiatry, Vol. 75, No. 9, 2004, pp. 1314-1322. doi:10.1136/jnnp.2003.017046
[8]	J. W. Lighthall, C. E. Dixon and T. E. Anderson, “Ex- perimental Models of Brain Injury,” Journal of Neuro- trauma, Vol. 6, No. 2, 1989, pp. 83-97. doi:10.1089/neu.1989.6.83
[9]	Y. Chen, S. Constantini, V. Trembovler, M. Weinstock and E. Shohami, “An Experimental Model of Closed Head Injury in Mice: Pathophysiology, Histopathology, and Cognitive Deficits,” Journal of Neurotrauma, Vol. 13, No. 10, 1996, pp. 557-568.
[10]	C. E. Dixon, J. W. Lighthall and T. E. Anderson, “Physi- ologic, Histopathologic, and Cineradiographic Charac- terization of a New Fluid-Percussion Model of Experi- mental Brain Injury in the Rat,” Journal of Neurotrauma, Vol. 5, No. 2, 1988, pp. 91-104. doi:10.1089/neu.1988.5.91
[11]	R. Hicks, H. Soares, D. Smith and T. McIntosh, “Tempo- ral and Spatial Characterization of Neuronal Injury Fo- llowing Lateral Fluid-Percussion Brain Injury in the Rat,” Acta Neuropathologica (Berl), Vol. 91, No. 3, 1996, pp. 236-246. doi:10.1007/s004010050421
[12]	S. C. Cortez, T. K. Mcintosh and L. J. Noble, “Exerimen- tal Fluid Percussion Brain Injury: Vascular Disruption and Neuronal and Glial Alterations,” Brain Research, Vol. 482, No. 2, 1989, pp. 271-282. doi:10.1016/0006-8993(89)91190-6
[13]	H. Nawashiro, K. Shima and H. Chigasaki, “Selective Vulnerability of Hippocampal CA3 Neurons to Hypoxia after Mild Concussion in the Rat,” Neurological Research, Vol. 17, No. 6, 1995, pp. 455-460.
[14]	R. J. Immonen, I. Kharatishvili, H. Gr?hn, A. Pitk?nen and O. H. Gr?hn, “Quantitative MRI Predicts Long-Term Structural and Functional Outcome after Experimental Traumatic Brain Injury,” Neuroimage, Vol. 45, No. 1, 2009, pp. 1-9.
[15]	H. Ooigawa, H. Nawashiro, S. Fukui, N. Otani, A. Osumi, T. Toyooka and K. Shima, “The Fate of Nissl-Stained Dark Neurons Following Traumatic Brain Injury in Rats: Difference between Neocortex and Hippocampus Re- garding Survival Rate,” Acta Neuropathologica, Vol. 112, No. 4, 2006, pp. 471-481. doi:10.1007/s00401-006-0108-2
[16]	D. H. Lowenstein, M. J. Thomas, D. H. Smith and T. K. McIntosh, “Selective Vulnerability of Dentate Hilar Neu- Rons Following Traumatic Brain Injury: A Potential Mechanistic Link between Head Trauma and Disorders of the Hippocampus,” The Journal of Neuroscience, Vol. 12, No. 12, 1992, pp. 4846-4853.
[17]	W. D. Dietrich, O. F. Alonso and M. Halley, “Early Mi- Crovascular and Neuronal Consequences of Traumatic Brain Injury: A Light Microscopic Study in Rats,” Journal of Neurotrauma, Vol. 13, 1994, pp. 289-301. doi:10.1089/neu.1994.11.289
[18]	D. H. Smith, X. H. Chen and J. E. Pierce, “Progressive Atrophy and Neuron Death for One Year Following Brain Trauma in the Rat,” Journal of Neurotrauma, Vol. 14, No. 7, 1997, pp. 715-727. doi:10.1089/neu.1997.14.715
[19]	A. C. Conti, R. Raghupathi, J. Q. Trojanowski and T. K. Mcintosh, “Experimental Brain Injury Induces Regionally Distinct Apoptosis during the Acute and Delayed Post- Traumatic Period,” Journal of Neuroscience, Vol. 18, No. 15, 1998, pp. 5663-5672.
[20]	X. Di, J. Gordon and R. Bullock, “Fluid Percussion Brain Injury Exacerbates Glutamate-Induced Focal Damage in the Rat,” Journal of Neurotrauma, Vol. 16, No. 3, 1999, pp. 195-201. http://dx.doi.org/10.1089/neu.1999.16.195
[21]	Y. Matsushita, K. Shima, H. Nawashiro and K. Wada, “Real-Time Monitoring Of Glutamate Following Fluid Percussion Brain Injury with Hypoxia in the Rat,” Jour- nal of Neurotrauma, Vol. 17, No. 2, 2000, pp. 143-153. doi:10.1089/neu.2000.17.143
[22]	C. L. Osteen, A. H. Moore, M. L. Prins and D. A. Hovda, “Age-Dependency of 45calcium Accumulation Following Lateral Fluid Percussion: Acute and Delayed Patterns,” Journal of Neurotrauma, Vol. 18, No. 2, 2001, pp. 141- 162. doi:10.1089/08977150150502587
[23]	Y. Katayama, D. P. Becker, T. Tamura and D. A. Hovda, “Massive Increases in Extracellular Potassium and the In- Discriminate Release of Glutamate Following Concussive Brain Injury,” Journal of Neurosurgery, Vol. 73, 1990, pp. 889-900. doi:10.3171/jns.1990.73.6.0889
[24]	S. Jander, M. Schroeter, O. Peters, O. W. Witte and G. Stoll, “Cortical Spreading Depression Induces Proinflam- Matory Cytokine Gene Expression in the Rat Brain,” Journal of Cerebral Blood Flow & Metabolism, Vol. 21, 2001, pp. 218-225. doi:10.1097/00004647-200103000-00005
[25]	J. Truettner, R. Schmidt-Kastner and R. Busto, “Expres- sion of Brain-Derived Neurotrophic Factor, Nerve Growth Factor, and Heat Shock Protein HSP70 Following Fluid Percussion Brain Injury in Rats,” Journal of Neuro- trauma, Vol. 16, No. 6, 1999, pp. 471-486. doi:10.1089/neu.1999.16.471
[26]	N. M. Oyesiku, C. O. Evans and S. Houston, “Regional Changes in the Expression of Neurotrophic Factors and Their Receptors Following Acute Traumatic Brain Injury in the Adult Rat Brain,” Brain Research, Vol. 833, No. 2, 1999, pp. 161-172. doi:10.1016/S0006-8993(99)01501-2
[27]	C. C. Giza, N. S. Maria and D. A. Hovda, “N-methyl-D- Aspartate Receptor Subunit Changes after Traumatic Injury to the Developing Brain,” Journal of Neurotrauma, Vol. 23, No. 6, 2006, pp. 950-961. doi:10.1089/neu.2006.23.950
[28]	A. Kumar, L. Zou, X. Yuan, Y. Long and K. Yang, “N- methyl-D-Aspartate Receptors: Transient Loss of NR1/ NR2A/NR2B Subunits after Traumatic Brain Injury in a Rodent Model,” Journal of Neuroscience Research, Vol. 67, No. 6, 2002, pp. 781-786. doi:10.1002/jnr.10181
[29]	R. Raghupathi, D. I. Graham and T. K. McIntosh, “Apoptosis after Traumatic Brain Injury,” Journal of Neurotrauma, Vol. 17, No. 10, 2000, pp. 927-938. doi:10.1089/neu.2000.17.927
[30]	H. Katoh, K. Shima, H. Nawashiro, K. Wada and H. Chi- gasaki, “The Effect of MK-801 on Extracellular Neuroac- Tive Amino Acids in Hippocampus after Closed Head Injury Followed by Hypoxia in Rats,” Brain Research, Vol. 758, No. 1-2, 1997, pp. 153-162. doi:10.1016/S0006-8993(97)00213-8
[31]	S. Jander, M. Schroeter, O. Peters, O. W. Witte and G. Stoll, “Cortical Spreading Depression Induces Proinflam- Matory Cytokine Gene Expression in the Rat Brain,” Journal of Cerebral Blood Flow & Metabolism, Vol. 21, 2001, pp. 218-225. doi:10.1097/00004647-200103000-00005
[32]	I. Mocchetti and J. R. Wrathall, “Neurotrophic Factors in Central Nervous System Trauma,” Journal of Neuro- trauma, Vol. 12, No. 5, 1995, pp. 853-870. doi:10.1089/neu.1995.12.853
[33]	L. F. Kromer, “Nerve Growth Factor Treatment after Brain Injury Prevents Neuronal Death,” Science, Vol. 235, No. 4785, 1987, pp. 214-216.
[34]	R. R. Hicks, V. B. Martin, L. Zhang and K. B. Seroogy, “Mild Experimental Brain Injury Differentially Alters the Expression of Neurotrophin and Neurotrophin Receptor mRNAs in the Hippocampus,” Experimental Neurology, Vol. 160, No. 2, 1999, pp. 469-478. doi:10.1006/exnr.1999.7216
[35]	R. J. Mckeon, J. Silver and T. H. Large, “Expression of Full-Length trkB Receptors by Reactive Astrocytes after Chronic CNS Injury,” Experimental Neurology, Vol. 148, No. 2, 1997, pp. 558-567. doi:10.1006/exnr.1997.6698
[36]	A. Bonni, A. Brunet, A. E. West, S. R. Datta, M. A. Ta- kasu and M. E. Greenberg, “Cell Survival Promoted by the Ras-MAPK Signaling Pathway by Transcription-De- Pendent and Independent Mechanisms,” Science, Vol. 286, No. 5543, 1999, pp. 1358-1362.
[37]	S. D. Skaper and F. S. Walsh, “Neurotrophic Molecules: Strategies for Designing Effective Therapeutic Molecules in neurodegeneration,” Molecular and Cellular Neuro- science, Vol. 12, No. 4-5, 1999, pp. 179-193.
[38]	T. G. Boulton, S. H. Nye and D. J. Robbins, “ERKs: A Family of Protein-Serine/Threonine Kinases that Are Ac- tivated and Tyrosine Phosphorylated in Response to Insu- lin and NGF,” Cell, Vol. 65, No. 4, 1991, pp. 663-675.
[39]	R. Aikawa, I. Komuro, T. Yamazaki, Y. Zou, S. Kudoh, M. Tanaka and I. Shiojima, “Oxidative Stress Activates Extracellular Signal-Regulated Kinases through Src and Ras in Cultured Cardiac Myocytes of Neonatal Rats,” The Journal of Clinical Investigation, Vol. 100, No. 7, 1997, pp. 1813-1821. doi:10.1172/JCI119709
[40]	M. Kurino, K. Fukunaga, Y. Ushio and E. Miyamoto, “Activation of Mitogen-Activated Protein Kinase in Cul- Tured Rat Hippocampal Neurons by Stimulation of Glu- tamate Receptors,” Journal of Neurochemistry, Vol. 65, 1995, pp. 1282-1289. doi:10.1046/j.1471-4159.1995.65031282.x
[41]	M. Stanciu and D. B. DeFranco, “Prolonged Nuclear Re- Tention of Activated Extracellular Signal-Regulated Pro- tein Kinase Promotes Cell Death Generated by Oxidative Toxicity or Proteasome Inhibition in a Neuronal Cell Line,” Journal of Biological Chemistry, Vol. 277, No. 6, 2002, pp. 4010-4017. doi:10.1074/jbc.M104479200
[42]	S. Subramaniam, U. Zirrgiebel, O. von Bohlen Und Hal- bach, J. Strelau, C. Laliberte, D. R. Kaplan and K. Un- sicker, “ERK1/2 Activation Promotes Neuronal Degen- eration Predominantly through Plasma Membrane Da- mage and Independently of Caspase-3,” Journal of Cell Biology, Vol. 165, 2004, pp. 357-369. doi:10.1083/jcb.200403028
[43]	S. Subramaniam and K. Unsicker, “Extracellular Sig- Nal-Regulated Kinase as an Inducer of Non-Apoptotic Neuronal Death,” Neuroscience, Vol. 138, No. 4, 2006, pp. 1055-1065.
[44]	R. Seger and E. G. Krebs, “The MAPK Signaling Cas- cade,” FASEB Journal, Vol. 9, No. 9, 1995, pp. 726-735.
[45]	J. E. Cavanaugh, “Role of Extracellular Signal Regulated Kinase 5 in Neuronal Survival,” European Journal of Biochemistry, Vol. 271, No. 11, 2004, pp. 2056-2059. doi:10.1111/j.1432-1033.2004.04131.x
[46]	R. M. Wang, Q. G. Zhang, C. H. Li and G. Y. Zhang, “Activation of Extracellular Signal-Regulated Kinase 5 May Play a Neuroprotective Role in Hippocampal CA3/ DG Region after Cerebral Ischemia,” Journal of Neuro- science Research, Vol. 80, No. 3, 2005, pp. 391- 399. doi:10.1002/jnr.20433
[47]	J. M. Kyriakis and J. Avruch, “Protein Kinase Cascades Activated by Stress and Inflammatory Cytokines,” Bio- Essays, Vol. 18, No. 7, 1996, pp. 567-577.
[48]	H. Kawasaki, T. Morooka, S. Shimohara, J. Kimura, T. Hirano, Y. Gotoh and E. Nishida, “Activation and In- Volvement of p38 Mitogen-Activated Protein Kinase in Glutamate-Induced Apoptosis in Rat Cerebellar Granule Cells,” Journal of Biological Chemistry, Vol. 272, No. 30, 1997, pp. 18518-18521. doi:10.1074/jbc.272.30.18518
[49]	Z. Xia, M. Dickens, J. Raingeaud, R. J. Davis and M. E. Greenberg, “Opposing Effects of ERK and JNK-p38 MAP Kinases on Apoptosis,” Science, Vol. 270, No. 5240, 1995, pp. 1326-1331.
[50]	D. C. Wu, W. Ye, X. M. Che and G. Y. Yang, “Activa- tion of Mitogen-Activated Protein Kinases after Perma- nent Cerebral Artery Occlusion in Mouse Brain,” Journal of Cerebral Blood Flow & Metabolism, Vol. 20, No. 9, 2000, pp. 1320-1330. doi:10.1097/00004647-200009000-00007
[51]	T. Hayashi, K. Sakai, C. Sasaki, W. R. Zhang, H. Warita and K. Abe, “c-Jun N-terminal Kinase (JNK) and JNK In- Teracting Protein Response in Rat Brain after Transient Middle Cerebral Artery Occlusion,” Neuroscience Letters, Vol. 284, No. 3, 2000, pp. 195-199. doi:10.1016/S0304-3940(00)01024-7
[52]	S. Nakahara, K. Yone, T. Sakou, S. Wada, T. Nagamine, T. Niiyama and H. Ichijo, “Induction of Apoptosis Signal Regulating Kinase 1 (ASK1) after Spinal Cord Injury In Rats: Possible Involvement of ASK1-JNK and -p38 Pathways in Neuronal Apoptosis,” Journal of Neuropa- thology & Experimental Neurology, Vol. 58, No. 5, 1990, pp. 442-450. doi:10.1097/00005072-199905000-00003
[53]	J. W. Mandell, N. C. Gocan and S. R. Vandenberg, “Me- chanical Trauma Induces Rapid Astroglial Activation of ERK/MAP Kinase: Evidence for a Paracrine Signal,” Glia, Vol. 34, 2001, pp. 283-295.
[54]	N. Otani, H. Nawashiro, S. Fukui, N. Nomura, A. Yano, T. Miyazawa and K. Shima, “Differential Activation of the Mitogen-Activated Protein Kinase Pathways Follow- ing Traumatic Brain Injury in the Rat Hippocampus,” Journal of Cerebral Blood Flow & Metabolism, Vol. 22, 2002, pp. 327-334. doi:10.1097/00004647-200203000-00010
[55]	T. Sugino, K. Nozaki, Y. Takagi, I. Hattori, N. Hashi- moto, T. Moriguchi and E. Nishida, “Activation of Mito- Gen-Activated Protein Kinases after Transient Forebrain Ischemia in Gerbil Hippocampus,” Journal of Neurosci- ence, Vol. 20, No. 12, 2000, pp. 4506-4515.
[56]	B. R. Hu, C. L. Liu and D. J. Park, “Alteration of MAP Kinase Pathways after Transient Forebrain Ischemia,” Journal of Cerebral Blood Flow & Metabolism, Vol. 20, No. 7, 2000, pp. 1089-1095. doi:10.1097/00004647-200007000-00008
[57]	R. Raghupathi, J. K. Muir, C. T. Fulp, R. N. Pittman and T. K. McIntosh, “Acute Activation of Mitogen-Activated Protein Kinases Following Traumatic Brain Injury in the Rat: Implications for Posttraumatic Cell Death,” Experi- mental Neurology, Vol. 183, No. 2, 2003, pp. 438-448.
[58]	S. S. Grewal, R. D. York and P. J. Stork, “Extracellular- Signal-Regulated Kinase Signaling in Neurons,” Current Opinion in Neurobiology, Vol. 9, 1999, pp. 544-553. doi:10.1016/S0959-4388(99)00010-0
[59]	J. D. Sweatt, “Mitogen-Activated Protein Kinases in Syn- Aptic Plasticity and Memory,” Current Opinion in Neu- robiology, Vol. 14, No. 3, 2004, pp. 311-317. doi:10.1016/j.conb.2004.04.001
[60]	T. Mori, X. Wang, J. C. Jung, S. Tumii, A. B. Singhal, M. E. Fini and C. E. Dixon, “Mitogen-Activated Protein Kinase Inhibition in Traumatic Brain Injury: In Vitro and in Vivo Effects,” Journal of Cerebral Blood Flow & Me- tabolism, Vol. 22, No. 4, 2002, pp. 444-452. doi:10.1097/00004647-200204000-00008
[61]	N. Otani, H. Nawashiro, S. Fukui, H. Ooigawa, A. Oh- sumi, T. Toyooka and K. Shima, “Role of the Activated Extracellular Signal-Regulated Kinase Pathway on His- tological and Behavioral Outcome after Traumatic Brain Injury In Rats,” Journal of Clinical Neuroscience, Vol. 14, No. 1, 2007, pp. 42-48. doi:10.1016/j.jocn.2005.11.044
[62]	A. Y. Zobkov, K. S. Rollins, A. D. Parent, J. Zhang and R. M. Bryan, “Mechanism of Endothelin-1 Induced Contrac- Tion in Rabbit Basilar Artery,” Stroke, Vol. 31, No. 2, 2000, pp. 526-533.
[63]	B. K. Lal, S. Varma, P. J. Pappas, R. W. Hobson and W. N. Duran, “VEGF Increases Permeability of the Endothe- Lial Cell Monolayer by Action of PKB/Akt, Endothelial Nitric-Oxide Synthase, and MAP Kinase Pathways,” Mi- crovascular Research, Vol. 62, 2001, pp. 252-262.
[64]	X. Wang, T. Mori, J. C. Jung, M. E. Fini and E. H. Lo, “Secretion of Matrix Metalloproteinase-2 and -9 after Mechanical Trauma Injury in Rat Cortical Cultures And Involvement of MAP kinase,” Journal of Neurotrauma, Vol. 19, No. 5, 2002, pp. 615-625. doi:10.1089/089771502753754082
[65]	E. H. Lo, X. Wang and M. L. Cuzner, “Extracellular Pro- Teolysis in Brain Injury and Inflammation: Role for Plas- minogen Activators and Matrix Metalloproteinases,” Journal of Neuroscience Research, Vol. 69, No. 1, 2002, pp. 1-9. doi:10.1002/jnr.10270
[66]	M. Asahi, X. Wang, T. Mori, T. Sumii, J. C. Jung, M. A. Moskowitz and M. E. Fini, “Effects of Matrix Metallo- Proteinase-9 Gene Knock-Out on the Proteolysis of Blood-Brain Barrier and White Matter Components after Cerebral Ischemia,” Journal of Neuroscience, Vol. 21, No. 19, 2001, pp. 7724-7732.
[67]	T. Mori, X. Wang, T. Aoki and E. H. Lo, “Downregula- tion of Matrix Metalloproteinase-9 and Attenuation of Edema via Inhibition of ERK Mitogen Activated Protein Kinase in Traumatic Brain Injury,” Journal of Neuro- trauma, Vol. 19, No. 11, 2002, pp. 1411-1419. doi:10.1089/089771502320914642
[68]	M. C. Morganti-Kossmann, M. Rancan, P. F. Stahel and T. Kossmann, “Inflammatory Response in Acute Trau- matic Brain Injury: A Double-Edged Sword,” Current Opinion in Critical Care, Vol. 8, No. 2, 2002, pp. 101- 105. doi:10.1097/00075198-200204000-00002
[69]	V. Taupin, S. Toulmond, A. Serrano, J. Benavides and F. Zavala, “Increase in IL-6, IL-1 and TNF Levels in Rat Brain Following Traumatic Lesion. Influence of Pre- and Post-Traumatic Treatment with Ro5 4864, a Periph- eral-Type (p site) Benzodiazepine Ligand,” Journal of Neuroimmunology, Vol. 42, 1993, pp. 177-185. doi:10.1016/0165-5728(93)90008-M
[70]	L. Fan, P. R. Young, F. C. Barone, G. Z. Feuerstein, D. H. Smith and T. K. McIntosh, “Experimental Brain Injury Induces Differential Expression of Tumor Necrosis Fac- Tor-Alpha mRNA in the CNS,” Brain Research. Mo- lecular Brain Research, Vol. 36, No. 2, 1996, pp. 287- 291. doi:10.1016/0169-328X(95)00274-V
[71]	V. Balasingam, T. Tejada-Berges, E. Wright, R. Bouck- ova and V. W. Yong, “Reactive Astrogliosis in the Neo- natal Mouse Brain and Its Modulation by Cytokines,” Journal of Neuroscience Vol. 14, No. 2, 1994, pp. 846- 856.
[72]	E. Shohami, M. Novikov, R. Bass, A. Yamin and R. Gal- lily, “Closed Head Injury Triggers Early Production of TNF α and IL-6 by Brain Tissue,” Journal of Cerebral Blood Flow & Metabolism, Vol. 14, 1994, pp. 615-619. doi:10.1038/jcbfm.1994.76
[73]	K. Kinoshita, K. Chatzipanteli, E, Vitarbo, J. S. Truettner, O. F. Alonso and W. D. Dietrich, “Interleukin-1βMessen- Ger Ribonucleic Acid and Protein Levels after Fluid- Percussion Brain Injury in Rats: Importance of Injury Severity and Brain Temperature,” Neurosurgery, Vol. 51, 2002, pp. 195-203.
[74]	E. A. Vitarbo, K. Chatzipanteli, K. Kinoshita, J. S. Truett- ner, O. F. Alonso and W. D. Dietrich, “Tumor Necrosis Factorα Expression and Protein Levels after Fluid Percus- Sion Injury in Rats: The Effect of Injury Severity and Brain Temperature,” Neurosurgery, Vol. 55, No. 2, 2004, pp. 416-424.
[75]	H. D. Soares, R. R. Hicks, D. Smith and T. K. McIntosh, “Inflammatory Leukocytic Recruitment and Diffuse Neu- Ronal Degeneration Are Separate Pathological Processes Resulting from Traumatic Brain Injury,” Journal of Neu- roscience, Vol. 15, No. 12, 1995, pp. 8223-8233.
[76]	L. Meda, M. A. Cassatella, G. I. Szendrei, L. Otvos, P. Baron, M. Villalba and D. Ferrari, “Activation of Micro- Glial Cells by β-Amyloid Protein and Interferon-γ,” Na- ture, Vol. 374, No. 6523, 1995, pp. 647–650.
[77]	L. Zhang, W. Zhao and B. Li, “TNF-Alpha Induced Over- Expression of GFAP is Associated with MAPKs,” Neu- roReport, Vol. 11, No. 2, 2000, pp. 409-412.
[78]	T. G. Bush, N. Puvanachandra and C. H. Horner, “Leu- kocyte Infiltration, Neuronal Degeneration, and Neurite Outgrowth after Ablation of Scar-Forming, Reactive As- trocytes in Adult Transgenic Mice,” Neuron, Vol. 23, No. 2, 1999, pp. 297-308.
[79]	N. Sang, J. Zhang and C. Chen, “PGE2-G, a COX-2 Oxi- Dative Metabolite of 2-Arachidonylglycerol, Modulates Inhibitory Synaptic Transmission in Mouse Hippocampal Neurons,” Journal of Physiology (London), Vol. 572, 2006, pp. 735-745.
[80]	N. Sang, J. Zhang and C. Chen, “COX-2 Oxidative Me- Tabolite of Endocannabinoid 2-AG Enhances Excitatory Glutamatergic Synaptic Transmission and Induces Neuro- Toxicity,” Journal of Neurochemistry, Vol. 102, 2007, pp. 1966-1977. doi:10.1111/j.1471-4159.2007.04668.x
[81]	H. Yang, J. Zhang, K. Andreasson and C. Chen, “COX-2 Oxidative Metabolism of Endocannabinoids Augments Hippocampal Synaptic Plasticity,” Molecular and Cellu- lar Neuroscience, Vol. 37, No. 4, 2008, pp. 682-695. doi:10.1016/j.mcn.2007.12.019
[82]	R. S. Fiore, V. E. Bayer, S. L. Pelech, J. Posada, J. A. Cooper and J. M. Baraban, “p42 Mitogen-Activated Pro- Tein Kinase in Brain: Prominent Localization in Neuronal Cell Bodies and Dendrites,” Neuroscience, Vol. 55, No. 2, 1993, pp. 463-472. doi:10.1016/0006-8993(95)00587-G
[83]	S. O. Johanson, M. F. Crouch and I. A. Hendry, “Retro- grade Axonal Transport of Signal Transduction Proteins in Rat Sciatic Nerve,” Brain Research, Vol. 690, No. 1, 1995, pp. 55-63.
[84]	B. Morrison, J. H. Eberwine, D. F. Meaney and T. K. McIntosh, “Traumatic Injury Induces Differential Expres- Sion of Cell Death Genes in Organotypic Brain Slice Cultures Determined by Complementary DNA Array Hybridization,” Neuroscience, Vol. 96, No. 1, 2000, pp. 131-139.
[85]	N. Otani, H. Nawashiro, S. Fukui, N. Nomura and K. Shima, “Temporal and Spatial Profile of Phosphorylated Mitogen-Activated Protein Kinase Pathways after Lateral Fluid Percussion Injury in the Cortex of the Rat Brain,” Journal of Neurotrauma Vol. 19, No. 12, 2002, pp. 1587- 1596. doi:10.1089/089771502762300247
[86]	J. W. Mandell, N. C. Gocan and S. R. Vandenberg, “Me- chanical Trauma Induces Rapid Astroglial Activation of ERK/MAP Kinase: Evidence for a Paracrine Signal,” Glia, Vol. 34, 2001, pp. 283-295.
[87]	T. G. Bush, N. Puvanachandra, C. H. Horner, A. Polito, T. Ostenfeld, C. N. Svendsen, L. Mucke, M. H. Johnson and M. V. Sofroniew, “Leukocyte Infiltration, Neuronal De- Generation, and Neurite Outgrowth after Ablation of Scar-Forming, Reactive Astrocytes in Adult Transgenic Mice,” Neuron, Vol. 23, No. 2, 1999, pp. 297-308.
[88]	W. D. Dietrich, J. Truettner, W. Zhan, O. F. Alonso, R. Busto and M. D. Ginsberg, “Sequential Changes in Glial Fibrillary Acidic Protein and Gene Expression Following Parasagittal Fluid-Percussion Brain Injury in Rats,” Journal of Neurotrauma, Vol. 16, No. 7, 1999, pp. 567- 581. doi:10.1089/neu.1999.16.567
[89]	A. P. Lieberman, P. M. Pitha and M. L. Shin, “Poly(A) Removal Is the Kinase-Regulated Step in Tumor Necrosis Factor mRNA Decay,” Journal of Biological Chemistry, Vol. 267, No. 4, 1992, pp. 2123-2126.
[90]	R. J. Mckeon, J. Silver and T. H. Large, “Expression of Full-Length trkB Receptors by Reactive Astrocytes after Chronic CNS Injury,” Experimental Neurology, Vol. 148, No. 2, 1997, pp. 558-567. doi:10.1006/exnr.1997.6698