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Orr TJ, Lesha E, Kramer AH, Cecia A, Dugan JE, Schwartz B, Einhaus SL. Traumatic Brain Injury: A Comprehensive Review of Biomechanics and Molecular Pathophysiology. World Neurosurg 2024; 185:74-88. [PMID: 38272305 DOI: 10.1016/j.wneu.2024.01.084] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2023] [Revised: 01/14/2024] [Accepted: 01/16/2024] [Indexed: 01/27/2024]
Abstract
Traumatic brain injury (TBI) is a critical public health concern with profound consequences for affected individuals. This comprehensive literature review delves into TBI intricacies, encompassing primary injury biomechanics and the molecular pathophysiology of the secondary injury cascade. Primary TBI involves a complex interplay of forces, including impact loading, blast overpressure, and impulsive loading, leading to diverse injury patterns. These forces can be categorized into inertial (e.g., rotational acceleration causing focal and diffuse injuries) and contact forces (primarily causing focal injuries like skull fractures). Understanding their interactions is crucial for effective injury management. The secondary injury cascade in TBI comprises multifaceted molecular and cellular responses, including altered ion concentrations, dysfunctional neurotransmitter networks, oxidative stress, and cellular energy disturbances. These disruptions impair synaptic function, neurotransmission, and neuroplasticity, resulting in cognitive and behavioral deficits. Moreover, neuroinflammatory responses play a pivotal role in exacerbating damage. As we endeavor to bridge the knowledge gap between biomechanics and molecular pathophysiology, further research is imperative to unravel the nuanced interplay between mechanical forces and their consequences at the molecular and cellular levels, ultimately guiding the development of targeted therapeutic strategies to mitigate the debilitating effects of TBI. In this study, we aim to provide a concise review of the bridge between biomechanical processes causing primary injury and the ensuing molecular pathophysiology of secondary injury, while detailing the subsequent clinical course for this patient population. This knowledge is crucial for advancing our understanding of TBI and developing effective interventions to improve outcomes for those affected.
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Affiliation(s)
- Taylor J Orr
- College of Medicine, University of Tennessee Health Science Center, Memphis, Tennessee.
| | - Emal Lesha
- Department of Neurological Surgery, University of Tennessee Health Science Center, Memphis, Tennessee; Semmes Murphey Clinic, Memphis, Tennessee
| | - Alexandra H Kramer
- College of Medicine, University of Tennessee Health Science Center, Memphis, Tennessee
| | - Arba Cecia
- School of Medicine, Loyola University Chicago, Chicago, Illinois
| | - John E Dugan
- College of Medicine, University of Tennessee Health Science Center, Memphis, Tennessee
| | - Barrett Schwartz
- Department of Neurological Surgery, University of Tennessee Health Science Center, Memphis, Tennessee; Semmes Murphey Clinic, Memphis, Tennessee
| | - Stephanie L Einhaus
- Department of Neurological Surgery, University of Tennessee Health Science Center, Memphis, Tennessee; Semmes Murphey Clinic, Memphis, Tennessee
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2
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Yeh TY, Liu PH. Removal of a compressive mass causes a transient disruption of blood-brain barrier but a long-term recovery of spiny stellate neurons in the rat somatosensory cortex. Restor Neurol Neurosci 2021; 39:111-127. [PMID: 34024792 DOI: 10.3233/rnn-201085] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
BACKGROUND In the cranial cavity, a space-occupying mass such as epidural hematoma usually leads to compression of brain. Removal of a large compressive mass under the cranial vault is critical to the patients. OBJECTIVE The purpose of this study was to examine whether and to what extent epidural decompression of the rat primary somatosensory cortex affects the underlying microvessels, spiny stellate neurons and their afferent fibers. METHODS Rats received epidural decompression with preceding 1-week compression by implantation of a bead. The thickness of cortex was measured using brain coronal sections. The permeability of blood-brain barrier (BBB) was assessed by Evans Blue and immunoglobulin G extravasation. The dendrites and dendritic spines of the spiny stellate neurons were revealed by Golgi-Cox staining and analyzed. In addition, the thalamocortical afferent (TCA) fibers in the cortex were illustrated using anterograde tracing and examined. RESULTS The cortex gradually regained its thickness over time and became comparable to the sham group at 3 days after decompression. Although the diameter of cortical microvessels were unaltered, a transient disruption of the BBB was observed at 6 hours and 1 day after decompression. Nevertheless, no brain edema was detected. In contrast, the dendrites and dendritic spines of the spiny stellate neurons and the TCA fibers were markedly restored from 2 weeks to 3 months after decompression. CONCLUSIONS Epidural decompression caused a breakdown of the BBB, which was early-occurring and short-lasting. In contrast, epidural decompression facilitated a late-onset and prolonged recovery of the spiny stellate neurons and their afferent fibers.
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Affiliation(s)
- Tzu-Yin Yeh
- Department of Anatomy, Tzu Chi University, Hualien, Taiwan
| | - Pei-Hsin Liu
- Department of Anatomy, Tzu Chi University, Hualien, Taiwan.,Medical Physiology, Tzu Chi University, Hualien, Taiwan
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3
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Selvakumar GP, Ahmed ME, Iyer SS, Thangavel R, Kempuraj D, Raikwar SP, Bazley K, Wu K, Khan A, Kukulka K, Bussinger B, Zaheer S, Burton C, James D, Zaheer A. Absence of Glia Maturation Factor Protects from Axonal Injury and Motor Behavioral Impairments after Traumatic Brain Injury. Exp Neurobiol 2020; 29:230-248. [PMID: 32565489 PMCID: PMC7344375 DOI: 10.5607/en20017] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2020] [Revised: 06/09/2020] [Accepted: 06/09/2020] [Indexed: 12/11/2022] Open
Abstract
Traumatic brain injury (TBI) causes disability and death, accelerating the progression towards Alzheimer's disease and Parkinson's disease (PD). TBI causes serious motor and cognitive impairments, as seen in PD that arise during the period of the initial insult. However, this has been understudied relative to TBI induced neuroinflammation, motor and cognitive decline that progress towards PD. Neuronal ubiquitin-C-terminal hydrolase- L1 (UCHL1) is a thiol protease that breaks down ubiquitinated proteins and its level represents the severity of TBI. Previously, we demonstrated the molecular action of glia maturation factor (GMF); a proinflammatory protein in mediating neuroinflammation and neuronal loss. Here, we show that the weight drop method induced TBI neuropathology using behavioral tests, western blotting, and immunofluorescence techniques on sections from wild type (WT) and GMF-deficient (GMF-KO) mice. Results reveal a significant improvement in substantia nigral tyrosine hydroxylase and dopamine transporter expression with motor behavioral performance in GMF-KO mice following TBI. In addition, a significant reduction in neuroinflammation was manifested, as shown by activation of nuclear factor-kB, reduced levels of inducible nitric oxide synthase, and cyclooxygenase- 2 expressions. Likewise, neurotrophins including brain-derived neurotrophic factor and glial-derived neurotrophic factor were significantly improved in GMF-KO mice than WT 72 h post-TBI. Consistently, we found that TBI enhances GFAP and UCHL-1 expression and reduces the number of dopaminergic TH-positive neurons in WT compared to GMF-KO mice 72 h post-TBI. Interestingly, we observed a reduction of THpositive tanycytes in the median eminence of WT than GMF-KO mice. Overall, we found that absence of GMF significantly reversed these neuropathological events and improved behavioral outcome. This study provides evidence that PD-associated pathology progression can be initiated upon induction of TBI.
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Affiliation(s)
- Govindhasamy Pushpavathi Selvakumar
- Harry S. Truman Memorial Veterans Hospital, Columbia, Missouri 65211, USA.,Department of Neurology, School of Medicine, University of Missouri, Columbia, Missouri 65211, USA.,Center for Translational Neuroscience, School of Medicine, University of Missouri, Columbia, Missouri 65211, USA
| | - Mohammad Ejaz Ahmed
- Harry S. Truman Memorial Veterans Hospital, Columbia, Missouri 65211, USA.,Department of Neurology, School of Medicine, University of Missouri, Columbia, Missouri 65211, USA.,Center for Translational Neuroscience, School of Medicine, University of Missouri, Columbia, Missouri 65211, USA
| | - Shankar S Iyer
- Harry S. Truman Memorial Veterans Hospital, Columbia, Missouri 65211, USA.,Department of Neurology, School of Medicine, University of Missouri, Columbia, Missouri 65211, USA.,Center for Translational Neuroscience, School of Medicine, University of Missouri, Columbia, Missouri 65211, USA
| | - Ramasamy Thangavel
- Harry S. Truman Memorial Veterans Hospital, Columbia, Missouri 65211, USA.,Department of Neurology, School of Medicine, University of Missouri, Columbia, Missouri 65211, USA.,Center for Translational Neuroscience, School of Medicine, University of Missouri, Columbia, Missouri 65211, USA
| | - Duraisamy Kempuraj
- Harry S. Truman Memorial Veterans Hospital, Columbia, Missouri 65211, USA.,Department of Neurology, School of Medicine, University of Missouri, Columbia, Missouri 65211, USA.,Center for Translational Neuroscience, School of Medicine, University of Missouri, Columbia, Missouri 65211, USA
| | - Sudhanshu P Raikwar
- Harry S. Truman Memorial Veterans Hospital, Columbia, Missouri 65211, USA.,Department of Neurology, School of Medicine, University of Missouri, Columbia, Missouri 65211, USA.,Center for Translational Neuroscience, School of Medicine, University of Missouri, Columbia, Missouri 65211, USA
| | - Kieran Bazley
- Department of Neurology, School of Medicine, University of Missouri, Columbia, Missouri 65211, USA.,Center for Translational Neuroscience, School of Medicine, University of Missouri, Columbia, Missouri 65211, USA
| | - Kristopher Wu
- Department of Neurology, School of Medicine, University of Missouri, Columbia, Missouri 65211, USA.,Center for Translational Neuroscience, School of Medicine, University of Missouri, Columbia, Missouri 65211, USA
| | - Asher Khan
- Department of Neurology, School of Medicine, University of Missouri, Columbia, Missouri 65211, USA.,Center for Translational Neuroscience, School of Medicine, University of Missouri, Columbia, Missouri 65211, USA
| | - Klaudia Kukulka
- Department of Neurology, School of Medicine, University of Missouri, Columbia, Missouri 65211, USA.,Center for Translational Neuroscience, School of Medicine, University of Missouri, Columbia, Missouri 65211, USA
| | - Bret Bussinger
- Department of Neurology, School of Medicine, University of Missouri, Columbia, Missouri 65211, USA.,Center for Translational Neuroscience, School of Medicine, University of Missouri, Columbia, Missouri 65211, USA
| | - Smita Zaheer
- Department of Neurology, School of Medicine, University of Missouri, Columbia, Missouri 65211, USA.,Center for Translational Neuroscience, School of Medicine, University of Missouri, Columbia, Missouri 65211, USA
| | | | | | - Asgar Zaheer
- Harry S. Truman Memorial Veterans Hospital, Columbia, Missouri 65211, USA.,Department of Neurology, School of Medicine, University of Missouri, Columbia, Missouri 65211, USA.,Center for Translational Neuroscience, School of Medicine, University of Missouri, Columbia, Missouri 65211, USA
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4
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McGuire JL, Ngwenya LB, McCullumsmith RE. Neurotransmitter changes after traumatic brain injury: an update for new treatment strategies. Mol Psychiatry 2019; 24:995-1012. [PMID: 30214042 DOI: 10.1038/s41380-018-0239-6] [Citation(s) in RCA: 44] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/08/2017] [Revised: 08/15/2018] [Accepted: 08/20/2018] [Indexed: 12/12/2022]
Abstract
Traumatic brain injury (TBI) is a pervasive problem in the United States and worldwide, as the number of diagnosed individuals is increasing yearly and there are no efficacious therapeutic interventions. A large number of patients suffer with cognitive disabilities and psychiatric conditions after TBI, especially anxiety and depression. The constellation of post-injury cognitive and behavioral symptoms suggest permanent effects of injury on neurotransmission. Guided in part by preclinical studies, clinical trials have focused on high-yield pathophysiologic mechanisms, including protein aggregation, inflammation, metabolic disruption, cell generation, physiology, and alterations in neurotransmitter signaling. Despite successful treatment of experimental TBI in animal models, clinical studies based on these findings have failed to translate to humans. The current international effort to reshape TBI research is focusing on redefining the taxonomy and characterization of TBI. In addition, as the next round of clinical trials is pending, there is a pressing need to consider what the field has learned over the past two decades of research, and how we can best capitalize on this knowledge to inform the hypotheses for future innovations. Thus, it is critically important to extend our understanding of the pathophysiology of TBI, particularly to mechanisms that are associated with recovery versus development of chronic symptoms. In this review, we focus on the pathology of neurotransmission after TBI, reflecting on what has been learned from both the preclinical and clinical studies, and we discuss new directions and opportunities for future work.
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Affiliation(s)
- Jennifer L McGuire
- Department of Neurosurgery, University of Cincinnati, Cincinnati, OH, USA.
| | - Laura B Ngwenya
- Department of Neurosurgery, University of Cincinnati, Cincinnati, OH, USA.,Department of Neurology and Rehabilitation Medicine, University of Cincinnati, Cincinnati, OH, USA.,Neurotrauma Center, University of Cincinnati Gardner Neuroscience Institute, Cincinnati, OH, 45219, USA
| | - Robert E McCullumsmith
- Department of Psychiatry and Behavioral Neuroscience, University of Cincinnati, Cincinnati, OH, USA.,Department of Psychiatry, Cincinnati Veterans Administration Medical Center, Cincinnati, OH, USA
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5
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Electrophysiological Correlates of Blast-Wave Induced Cerebellar Injury. Sci Rep 2018; 8:13633. [PMID: 30206255 PMCID: PMC6134123 DOI: 10.1038/s41598-018-31728-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2017] [Accepted: 08/24/2018] [Indexed: 12/17/2022] Open
Abstract
Understanding the mechanisms underlying traumatic neural injury and the sequelae of events in the acute phase is important for deciding on the best window of therapeutic intervention. We hypothesized that evoked potentials (EP) recorded from the cerebellar cortex can detect mild levels of neural trauma and provide a qualitative assessment tool for progression of cerebellar injury in time. The cerebellar local field potentials evoked by a mechanical tap on the hand and collected with chronically implanted micro-ECoG arrays on the rat cerebellar cortex demonstrated substantial changes both in amplitude and timing as a result of blast-wave induced injury. The results revealed that the largest EP changes occurred within the first day of injury, and partial recoveries were observed from day-1 to day-3, followed by a period of gradual improvements (day-7 to day-14). The mossy fiber (MF) and climbing fiber (CF) mediated components of the EPs were affected differentially. The behavioral tests (ladder rung walking) and immunohistological analysis (calbindin and caspase-3) did not reveal any detectable changes at these blast pressures that are typically considered as mild (100-130 kPa). The results demonstrate the sensitivity of the electrophysiological method and its use as a tool to monitor the progression of cerebellar injuries in longitudinal animal studies.
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Thomas TC, Stockhausen EM, Law LM, Khodadad A, Lifshitz J. Rehabilitation modality and onset differentially influence whisker sensory hypersensitivity after diffuse traumatic brain injury in the rat. Restor Neurol Neurosci 2018; 35:611-629. [PMID: 29036852 DOI: 10.3233/rnn-170753] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
BACKGROUND As rehabilitation strategies advance as therapeutic interventions, the modality and onset of rehabilitation after traumatic brain injury (TBI) are critical to optimize treatment. Our laboratory has detected and characterized a late-onset, long-lasting sensory hypersensitivity to whisker stimulation in diffuse brain-injured rats; a deficit that is comparable to visual or auditory sensory hypersensitivity in humans with an acquired brain injury. OBJECTIVE We hypothesize that the modality and onset of rehabilitation therapies will differentially influence sensory hypersensitivity in response to the Whisker Nuisance Task (WNT) as well as WNT-induced corticosterone (CORT) stress response in diffuse brain-injured rats and shams. METHODS After midline fluid percussion brain injury (FPI) or sham surgery, rats were assigned to one of four rehabilitative interventions: (1) whisker sensory deprivation during week one or (2) week two or (3) whisker stimulation during week one or (4) week two. At 28 days following FPI and sham procedures, sensory hypersensitivity was assessed using the WNT. Plasma CORT was evaluated immediately following the WNT (aggravated levels) and prior to the pre-determined endpoint 24 hours later (non-aggravated levels). RESULTS Deprivation therapy during week two elicited significantly greater sensory hypersensitivity to the WNT compared to week one (p < 0.05), and aggravated CORT levels in FPI rats were significantly lower than sham levels. Stimulation therapy during week one resulted in low levels of sensory hypersensitivity to the WNT, similar to deprivation therapy and naïve controls, however, non-aggravated CORT levels in FPI rats were significantly higher than sham. CONCLUSION These data indicate that modality and onset of sensory rehabilitation can differentially influence FPI and sham rats, having a lasting impact on behavioral and stress responses to the WNT, emphasizing the necessity for continued evaluation of modality and onset of rehabilitation after TBI.
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Affiliation(s)
- Theresa Currier Thomas
- Barrow Neurological Institute at Phoenix Children's Hospital - Phoenix, AZ, USA.,Department of Child Health, University of Arizona College of Medicine - Phoenix, AZ, USA.,Phoenix VA Healthcare System - Phoenix, AZ, USA.,Spinal Cord and Brain Injury Research Center, University of Kentucky Chandler Medical Center - Lexington, KY, USA
| | - Ellen Magee Stockhausen
- Core Medical Group, Manchester, NH, USA.,Spinal Cord and Brain Injury Research Center, University of Kentucky Chandler Medical Center - Lexington, KY, USA
| | - L Matthew Law
- Barrow Neurological Institute at Phoenix Children's Hospital - Phoenix, AZ, USA.,Department of Child Health, University of Arizona College of Medicine - Phoenix, AZ, USA
| | - Aida Khodadad
- Barrow Neurological Institute at Phoenix Children's Hospital - Phoenix, AZ, USA.,Department of Child Health, University of Arizona College of Medicine - Phoenix, AZ, USA
| | - Jonathan Lifshitz
- Barrow Neurological Institute at Phoenix Children's Hospital - Phoenix, AZ, USA.,Department of Child Health, University of Arizona College of Medicine - Phoenix, AZ, USA.,Phoenix VA Healthcare System - Phoenix, AZ, USA.,Neuroscience Program, Arizona State University - Tempe, AZ, USA.,Spinal Cord and Brain Injury Research Center, University of Kentucky Chandler Medical Center - Lexington, KY, USA
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7
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Chen YH, Huang EYK, Kuo TT, Miller J, Chiang YH, Hoffer BJ. Impact of Traumatic Brain Injury on Dopaminergic Transmission. Cell Transplant 2018; 26:1156-1168. [PMID: 28933212 PMCID: PMC5657731 DOI: 10.1177/0963689717714105] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Brain trauma is often associated with severe morbidity and is a major public health concern. Even when injury is mild and no obvious anatomic disruption is seen, many individuals suffer disabling neuropsychological impairments such as memory loss, mood dysfunction, substance abuse, and adjustment disorder. These changes may be related to subtle disruption of neural circuits as well as functional changes at the neurotransmitter level. In particular, there is considerable evidence that dopamine (DA) physiology in the nigrostriatal and mesocorticolimbic pathways might be impaired after traumatic brain injury (TBI). Alterations in DA levels can lead to oxidative stress and cellular dysfunction, and DA plays an important role in central nervous system inflammation. Therapeutic targeting of DA pathways may offer benefits for both neuronal survival and functional outcome after TBI. The purpose of this review is to discuss the role of DA pathology in acute TBI and the potential impact of therapies that target these systems for the treatment of TBI.
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Affiliation(s)
- Yuan-Hao Chen
- Department of Neurological Surgery, Tri-Service General Hospital, National Defense Medical Center, Taipei, Taiwan, Republic of China
- Yuan-Hao Chen, Department of Neurological Surgery, Tri-Service General Hospital, National Defense Medical Center, 4F, No. 325, 2nd Sec., Cheng-Kung Road, Nei-Hu District, Taipei City, 114 Taiwan, Republic of China.
| | - Eagle Yi-Kung Huang
- Department of Pharmacology, National Defense Medical Center, Taipei, Taiwan, Republic of China
| | - Tung-Tai Kuo
- Graduate Institute of Computer and Communication Engineering, National Taipei University of Technology, Taipei, Taiwan, Republic of China
| | - Jonathan Miller
- Department of Neurosurgery, Case Western Reserve University School of Medicine, Cleveland, OH, USA
| | - Yung-Hsiao Chiang
- Section of Neurosurgery, Department of Surgery, Taipei Medical University Hospital, Taipei Medical University, Taipei, Taiwan, Republic of China
| | - Barry J. Hoffer
- Department of Neurosurgery, Case Western Reserve University School of Medicine, Cleveland, OH, USA
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8
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Johnstone VP, Shultz SR, Yan EB, O'Brien TJ, Rajan R. The acute phase of mild traumatic brain injury is characterized by a distance-dependent neuronal hypoactivity. J Neurotrauma 2014; 31:1881-95. [PMID: 24927383 PMCID: PMC4224042 DOI: 10.1089/neu.2014.3343] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
The consequences of mild traumatic brain injury (TBI) on neuronal functionality are only now being elucidated. We have now examined the changes in sensory encoding in the whisker-recipient barrel cortex and the brain tissue damage in the acute phase (24 h) after induction of TBI (n=9), with sham controls receiving surgery only (n=5). Injury was induced using the lateral fluid percussion injury method, which causes a mixture of focal and diffuse brain injury. Both population and single cell neuronal responses evoked by both simple and complex whisker stimuli revealed a suppression of activity that decreased with distance from the locus of injury both within a hemisphere and across hemispheres, with a greater extent of hypoactivity in ipsilateral barrel cortex compared with contralateral cortex. This was coupled with an increase in spontaneous output in Layer 5a, but only ipsilateral to the injury site. There was also disruption of axonal integrity in various regions in the ipsilateral but not contralateral hemisphere. These results complement our previous findings after mild diffuse-only TBI induced by the weight-drop impact acceleration method where, in the same acute post-injury phase, we found a similar depth-dependent hypoactivity in sensory cortex. This suggests a common sequelae of events in both diffuse TBI and mixed focal/diffuse TBI in the immediate post-injury period that then evolve over time to produce different long-term functional outcomes.
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Affiliation(s)
| | - Sandy R. Shultz
- Department of Medicine, The Royal Melbourne Hospital, The Melbourne Brain Centre, The University of Melbourne, Parkville, Victoria, Australia
| | - Edwin B. Yan
- Department of Physiology, Monash University, Clayton, Victoria, Australia
| | - Terence J. O'Brien
- Department of Medicine, The Royal Melbourne Hospital, The Melbourne Brain Centre, The University of Melbourne, Parkville, Victoria, Australia
| | - Ramesh Rajan
- Department of Physiology, Monash University, Clayton, Victoria, Australia
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9
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Alwis DS, Johnstone V, Yan E, Rajan R. Diffuse traumatic brain injury and the sensory brain. Clin Exp Pharmacol Physiol 2014; 40:473-83. [PMID: 23611812 DOI: 10.1111/1440-1681.12100] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2012] [Accepted: 04/17/2013] [Indexed: 01/06/2023]
Abstract
In this review we discuss the consequences to the brain's cortex, specifically to the sensory cortex, of traumatic brain injury. The thesis underlying this approach is that long-term deficits in cognition seen after brain damage in humans are likely underpinned by an impaired cortical processing of the sensory information needed to drive cognition or to be used by cognitive processes to produce a response. We take it here that the impairment to sensory processing does not arise from damage to peripheral sensory systems, but from disordered brain processing of sensory input.
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Affiliation(s)
- Dasuni S Alwis
- Department of Physiology, Monash University, Melbourne, Vic., Australia
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10
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Tweedie D, Rachmany L, Rubovitch V, Zhang Y, Becker KG, Perez E, Hoffer BJ, Pick CG, Greig NH. Changes in mouse cognition and hippocampal gene expression observed in a mild physical- and blast-traumatic brain injury. Neurobiol Dis 2013; 54:1-11. [PMID: 23454194 PMCID: PMC3628969 DOI: 10.1016/j.nbd.2013.02.006] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2012] [Revised: 01/23/2013] [Accepted: 02/19/2013] [Indexed: 12/25/2022] Open
Abstract
Warfare has long been associated with traumatic brain injury (TBI) in militarized zones. Common forms of TBI can be caused by a physical insult to the head-brain or by the effects of a high velocity blast shock wave generated by the detonation of an explosive device. While both forms of trauma are distinctly different regarding the mechanism of trauma induction, there are striking similarities in the cognitive and emotional status of survivors. Presently, proven effective therapeutics for the treatment of either form of TBI are unavailable. To be able to develop efficacious therapies, studies involving animal models of physical- and blast-TBI are required to identify possible novel or existing medicines that may be of value in the management of clinical events. We examined indices of cognition and anxiety-like behavior and the hippocampal gene transcriptome of mice subjected to both forms of TBI. We identified common behavioral deficits and gene expression regulations, in addition to unique injury-specific forms of gene regulation. Molecular pathways presented a pattern similar to that seen in gene expression. Interestingly, pathways connected to Alzheimer's disease displayed a markedly different form of regulation depending on the type of TBI. While these data highlight similarities in behavioral outcomes after trauma, the divergence in hippocampal transcriptome observed between models suggests that, at the molecular level, the TBIs are quite different. These models may provide tools to help define therapeutic approaches for the treatment of physical- and blast-TBIs. Based upon observations of increasing numbers of personnel displaying TBI related emotional and behavioral changes in militarized zones, the development of efficacious therapies will become a national if not a global priority.
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Affiliation(s)
- David Tweedie
- Drug Design & Development Section, Translational Gerontology Branch, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA
| | - Lital Rachmany
- Department of Anatomy and Anthropology, Sackler School of Medicine, Tel-Aviv University, Tel-Aviv, 69978 Israel
| | - Vardit Rubovitch
- Department of Anatomy and Anthropology, Sackler School of Medicine, Tel-Aviv University, Tel-Aviv, 69978 Israel
| | - Yongqing Zhang
- Gene Expression and Genomics Unit, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA
| | - Kevin G. Becker
- Gene Expression and Genomics Unit, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA
| | - Evelyn Perez
- Laboratory of Experimental Gerontology, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA
| | - Barry J. Hoffer
- Department of Neurosurgery, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA
| | - Chaim G. Pick
- Department of Anatomy and Anthropology, Sackler School of Medicine, Tel-Aviv University, Tel-Aviv, 69978 Israel
| | - Nigel H. Greig
- Drug Design & Development Section, Translational Gerontology Branch, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA
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Johnstone VPA, Yan EB, Alwis DS, Rajan R. Cortical hypoexcitation defines neuronal responses in the immediate aftermath of traumatic brain injury. PLoS One 2013; 8:e63454. [PMID: 23667624 PMCID: PMC3646737 DOI: 10.1371/journal.pone.0063454] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2013] [Accepted: 04/03/2013] [Indexed: 11/19/2022] Open
Abstract
Traumatic brain injury (TBI) from a blow to the head is often associated with complex patterns of brain abnormalities that accompany deficits in cognitive and motor function. Previously we reported that a long-term consequence of TBI, induced with a closed-head injury method modelling human car and sporting accidents, is neuronal hyper-excitation in the rat sensory barrel cortex that receives tactile input from the face whiskers. Hyper-excitation occurred only in supra-granular layers and was stronger to complex than simple stimuli. We now examine changes in the immediate aftermath of TBI induced with same injury method. At 24 hours post-trauma significant sensorimotor deficits were observed and characterisation of the cortical population neuronal responses at that time revealed a depth-dependent suppression of neuronal responses, with reduced responses from supragranular layers through to input layer IV, but not in infragranular layers. In addition, increased spontaneous firing rate was recorded in cortical layers IV and V. We postulate that this early post-injury suppression of cortical processing of sensory input accounts for immediate post-trauma sensory morbidity and sets into train events that resolve into long-term cortical hyper-excitability in upper sensory cortex layers that may account for long-term sensory hyper-sensitivity in humans with TBI.
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Affiliation(s)
| | | | | | - Ramesh Rajan
- Department of Physiology, Monash University, Monash, VIC, Australia
- * E-mail:
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12
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Titus DJ, Furones C, Kang Y, Atkins CM. Age-dependent alterations in cAMP signaling contribute to synaptic plasticity deficits following traumatic brain injury. Neuroscience 2012; 231:182-94. [PMID: 23238576 DOI: 10.1016/j.neuroscience.2012.12.002] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2012] [Revised: 11/19/2012] [Accepted: 12/03/2012] [Indexed: 12/28/2022]
Abstract
The elderly have comparatively worse cognitive impairments from traumatic brain injury (TBI) relative to younger adults, but the molecular mechanisms that underlie this exacerbation of cognitive deficits are unknown. Experimental models of TBI have demonstrated that the cyclic AMP-protein kinase A (cAMP-PKA) signaling pathway is downregulated after brain trauma. Since the cAMP-PKA signaling pathway is a key mediator of long-term memory formation, we investigated whether the TBI-induced decrease in cAMP levels is exacerbated in aged animals. Aged (19 months) and young adult (3 months) male Fischer 344 rats received sham surgery or mild (1.4-1.6 atmospheres, atm) or moderate (1.7-2.1 atm) parasagittal fluid-percussion brain injury. At various time points after surgery, the ipsilateral parietal cortex, hippocampus, and thalamus were assayed for cAMP levels. Mild TBI lowered cAMP levels in the hippocampus of aged, but not young adult animals. Moderate TBI lowered cAMP levels in the hippocampus and parietal cortex of both age groups. In the thalamus, cAMP levels were significantly lowered after moderate, but not mild TBI. To determine if the TBI-induced decreases in cAMP had physiological consequences in aged animals, hippocampal long-term potentiation (LTP) in the Schaffer collateral pathway of the CA1 region was assessed. LTP was significantly decreased in both young adult and aged animals after mild and moderate TBI as compared to sham surgery animals. Rolipram rescued the LTP deficits after mild TBI for young adult animals and caused a partial recovery for aged animals. However, rolipram did not rescue LTP deficits after moderate TBI in either young adult or aged animals. These results indicate that the exacerbation of cognitive impairments in aged animals with TBI may be due to decreased cAMP levels and deficits in hippocampal LTP.
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Affiliation(s)
- D J Titus
- The Miami Project to Cure Paralysis and Department of Neurological Surgery, University of Miami Miller School of Medicine, Miami, FL 33136, USA
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14
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Abstract
Cortical compression can be a significant problem in many types of brain injuries, such as brain trauma, localized brain edema, hematoma, focal cerebral ischemia, or brain tumors. Mechanical and cellular alterations can result in global changes in excitation and inhibition on the neuronal network level even in the absence of histologically significant cell injury, often manifesting clinically as seizures. Despite the importance and prevalence of this problem, however, the precise electrophysiological effects of brain injury have not been well characterized. In this study, the changes in electrophysiology were characterized following sustained cortical compression using large-scale, multielectrode measurement of multiunit activity in primary somatosensory cortex in a sensory-evoked, in vivo animal model. Immediately following the initiation of injury at a distal site, there was a period of suppression of the evoked response in the rat somatosensory cortex, followed by hyper-excitability that was accompanied by an increase in the spatial extent of cortical activation. Paired-pulse tactile stimulation revealed a dramatic shift in the excitatory/inhibitory dynamics, suggesting a longer term hyperexcitability of the cortical circuit following the initial suppression that could be linked to the disruption of one or more inhibitory mechanisms of the thalamocortical circuit. Together, our results showed that the use of a sensory-evoked response provided a robust and repeatable functional marker of the evolution of the consequences of mild injury, serving as an important step toward in vivo quantification of alterations in excitation and inhibition in the cortex in the setting of traumatic brain injury.
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Abstract
Rich evidence indicates that monoamine oxidase (MAO) A, the major enzyme catalysing the degradation of monoamine neurotransmitters, plays a key role in emotional regulation. Although MAOA deficiency is associated with reactive aggression in humans and mice, the involvement of this enzyme in defensive behaviour remains controversial and poorly understood. To address this issue, we tested MAOA knockout (KO) mice in a spectrum of paradigms and settings associated with variable degrees of threat. The presentation of novel inanimate objects induced a significant reduction in exploratory approaches and increase in defensive behaviours, such as tail-rattling, biting and digging. These neophobic responses were context-dependent and particularly marked in the home cage. In the elevated plus- and T-mazes, MAOA KO mice and wild-type (WT) littermates displayed equivalent locomotor activity and time in closed and open arms; however, MAOA KO mice featured significant reductions in risk assessment, as well as unconditioned avoidance and escape. No differences between genotypes were observed in the defensive withdrawal and emergence test. Conversely, MAOA KO mice exhibited a dramatic reduction of defensive and fear-related behaviours in the presence of predator-related cues, such as predator urine or an anaesthetized rat, in comparison with those observed in their WT littermates. The behavioural abnormalities in MAOA KO mice were not paralleled by overt alterations in sensory and microvibrissal functions. Collectively, these results suggest that MAOA deficiency leads to a general inability to appropriately assess contextual risk and attune defensive and emotional responses to environmental cues.
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Bortolato M, Shih JC. Behavioral outcomes of monoamine oxidase deficiency: preclinical and clinical evidence. INTERNATIONAL REVIEW OF NEUROBIOLOGY 2011; 100:13-42. [PMID: 21971001 DOI: 10.1016/b978-0-12-386467-3.00002-9] [Citation(s) in RCA: 95] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/04/2022]
Abstract
Monoamine oxidase (MAO) isoenzymes A and B are mitochondrial-bound proteins, catalyzing the oxidative deamination of monoamine neurotransmitters as well as xenobiotic amines. Although they derive from a common ancestral progenitor gene, are located at X-chromosome and display 70% structural identity, their substrate preference, regional distribution, and physiological role are divergent. In fact, while MAO-A has high affinity for serotonin and norepinephrine, MAO-B primarily serves the catabolism of 2-phenylethylamine (PEA) and contributes to the degradation of other trace amines and dopamine. Convergent lines of preclinical and clinical evidence indicate that variations in MAO enzymatic activity--due to either genetic or environmental factors--can exert a profound influence on behavioral regulation and play a role in the pathophysiology of a large spectrum of mental and neurodegenerative disorders, ranging from antisocial personality disorder to Parkinson's disease. Over the past few years, numerous advances have been made in our understanding of the phenotypical variations associated with genetic polymorphisms and mutations of the genes encoding for both isoenzymes. In particular, novel findings on the phenotypes of MAO-deficient mice are highlighting novel potential implications of both isoenzymes in a broad spectrum of mental disorders, ranging from autism and anxiety to impulse-control disorders and ADHD. These studies will lay the foundation for future research on the neurobiological and neurochemical bases of these pathological conditions, as well as the role of gene × environment interactions in the vulnerability to several mental disorders.
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Affiliation(s)
- Marco Bortolato
- Department of Pharmacology and Pharmaceutical Sciences, School of Pharmacy, University of Southern California, Los Angeles, California, USA
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McNamara KCS, Lisembee AM, Lifshitz J. The whisker nuisance task identifies a late-onset, persistent sensory sensitivity in diffuse brain-injured rats. J Neurotrauma 2010; 27:695-706. [PMID: 20067394 DOI: 10.1089/neu.2009.1237] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Post-traumatic morbidity reduces the quality of life for traumatic brain injury (TBI) survivors by altering neuropsychological function. After midline fluid percussion injury (FPI), diffuse pathology in the ventral posterior thalamus suggests that somatosensory whisker function may be impaired post-injury. The goals of the present study were to design and validate a task to detect injury-induced somatosensory morbidity (Experiment 1), and to evaluate preliminary applications of the task (Experiment 2). In Experiment 1, male Sprague-Dawley rats were subjected to moderate FPI (approximately 1.9 atm) or sham injury. Over an 8-week time course, the whiskers on both mystacial pads were stimulated manually with an applicator stick in an open field for three 5-min periods. Behavioral responses in this whisker nuisance task were recorded using objective criteria (max score = 16). Sham animals were ambivalent or soothed by whisker stimulation (4.0 +/- 0.8), whereas brain-injured rats showed aggravated responses at 1 week (6.7 +/- 0.9), which became significant at 4 weeks (9.5 +/- 0.5) and 8 weeks (8.4 +/- 1.1) compared to sham injury, indicating chronic injury-induced sensory sensitivity. Total free serum corticosterone levels indicated a significant stress response in brain-injured (125.0 +/- 17.7 ng/mL), but not uninjured animals (74.2 +/- 12.2 ng/mL) in response to whisker stimulation. In Experiment 2, to evaluate applications of the whisker nuisance task, four additional uninjured and brain-injured groups were subjected to mild brain injury only, shaved whiskers after moderate brain injury, repeated whisker nuisance task stimulation after moderate brain injury, or regular opportunities for tactile exploration of an enriched environment after moderate brain injury over 4 weeks post-injury. The whisker nuisance task has the sensitivity to detect mild brain injury (7.7 +/- 1.0), but morbidity was not mitigated by any of the neurorehabilitative interventions. Following diffuse brain injury, the whisker nuisance task is a promising tool to detect post-traumatic morbidity and the efficacy of therapeutic interventions that may restore discrete circuit function in brain-injured patients.
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Affiliation(s)
- Katelyn C S McNamara
- Spinal Cord and Brain Injury Research Center, University of Kentucky College of Medicine, Lexington, Kentucky 40536-0509, USA
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Bales JW, Wagner AK, Kline AE, Dixon CE. Persistent cognitive dysfunction after traumatic brain injury: A dopamine hypothesis. Neurosci Biobehav Rev 2009; 33:981-1003. [PMID: 19580914 DOI: 10.1016/j.neubiorev.2009.03.011] [Citation(s) in RCA: 187] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2009] [Revised: 03/10/2009] [Accepted: 03/23/2009] [Indexed: 12/12/2022]
Abstract
Traumatic brain injury (TBI) represents a significant cause of death and disability in industrialized countries. Of particular importance to patients the chronic effect that TBI has on cognitive function. Therapeutic strategies have been difficult to evaluate because of the complexity of injuries and variety of patient presentations within a TBI population. However, pharmacotherapies targeting dopamine (DA) have consistently shown benefits in attention, behavioral outcome, executive function, and memory. Still it remains unclear what aspect of TBI pathology is targeted by DA therapies and what time-course of treatment is most beneficial for patient outcomes. Fortunately, ongoing research in animal models has begun to elucidate the pathophysiology of DA alterations after TBI. The purpose of this review is to discuss clinical and experimental research examining DAergic therapies after TBI, which will in turn elucidate the importance of DA for cognitive function/dysfunction after TBI as well as highlight the areas that require further study.
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Affiliation(s)
- James W Bales
- Brain Trauma Research Center, University of Pittsburgh, PA 15260, USA
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Pillay NS, Kellaway LA, Kotwal GJ. Vaccinia virus complement control protein significantly improves sensorimotor function recovery after severe head trauma. Brain Res 2007; 1153:158-65. [PMID: 17467672 DOI: 10.1016/j.brainres.2007.03.056] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2007] [Revised: 03/19/2007] [Accepted: 03/19/2007] [Indexed: 11/17/2022]
Abstract
Vaccinia virus complement control protein (VCP) is an immunomodulator that inhibits both the classical and alternate pathways of the complement system, therefore preventing cell death and inflammation. VCP has previously been shown to be therapeutically effective in mild and moderate traumatic brain injury models. In this study the efficacy of VCP in a severe head injury model is investigated in Wistar rats. Training in a Morris Water Maze (MWM) commenced 2 days prior stereotaxic surgery. Rats were anesthetized before being subjected to a severe (2.7-3.0 atm) lateral fluid percussion injury (FPI) 3.0 mm lateral to the sagittal suture and 4.5 mm posterior to bregma. Ten microliters of VCP (1.7 microg/microl) was injected into the injury site immediately after FPI. Fourteen days post-FPI, rats were tested for spatial learning and memory using the Morris Water Maze, followed by a battery of sensorimotor tests. The latter tests showed statistically significant differences between saline-treated and VCP-treated rats in lateral left pulsion (p=0.001) and tactile placing (p=0.002) on the first 5 days of testing. In addition, significant differences in right lateral pulsion in the first 4 days (p=0.007) of testing was evident. The results suggest that in a severe head injury model, VCP at this dosage favorably influences sensorimotor outcome.
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Affiliation(s)
- Nirvana S Pillay
- Division of Medical Virology, Faculty of Health Sciences, University of Cape Town, South Africa
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Gurkoff GG, Giza CC, Hovda DA. Lateral fluid percussion injury in the developing rat causes an acute, mild behavioral dysfunction in the absence of significant cell death. Brain Res 2006; 1077:24-36. [PMID: 16490184 DOI: 10.1016/j.brainres.2006.01.011] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2005] [Revised: 12/21/2005] [Accepted: 01/04/2006] [Indexed: 11/29/2022]
Abstract
Lateral fluid percussion injury (LFP), a model of mild-moderate concussion, leads to the temporary loss of the capacity for experience-dependent plasticity in developing rats. To determine if this injury-induced loss in capacity for plasticity is due to cell death, we conducted stereological measurements within the cerebral cortex and CA3 of the hippocampus 2 weeks following mild, moderate or severe LFP in the post-natal day 19 (P19) rat. Results indicated that there was no significant change in the absolute number of neurons, regardless of injury severity, in either the ipsilateral cortex (sham = 10.6 +/- 1.7, mild = 11.5 +/- 2.1, moderate = 10.0 +/- 1.0, severe = 10.9 +/- 1.3 million neurons) or CA3 region of the hippocampus (sham = 251 +/- 38, mild = 289 +/- 2, moderate = 245 +/- 48, severe = 255 +/- 62 thousand neurons). Even though there was no evidence of a significant degree of injury-induced cell death, animals exhibited cognitive deficits as revealed in a Morris water maze task (MWM). The MWM results indicated that regardless of injury severity, P19-injured rats exhibited a significant increase in escape latency compared to age-matched shams (injury by day; P < 0.001) and a significant increase in the number of trials needed to reach criterion (P < 0.05). Analysis of a probe trial one week post-MWM training, however, indicated that there was no deficit in storage or recall of the learned behavior as analyzed by platform hits (sham = 2.9 +/- 0.37, mild = 2.0 +/- 0.40, moderate = 1 +/- 0, severe = 2.8 +/- 0.62) or percent time spent in, or immediately surrounding, the platform area (sham = 13.5 +/- 1.71, mild = 10.8 +/- 2.32, moderate = 12.7 +/- 0, severe = 13.5 +/- 1.69). Taken together, these results indicate that while LFP in P19-injured animals does not lead to significant cell death, it does generate acute, mild deficits in MWM performance.
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Affiliation(s)
- Gene G Gurkoff
- Division of Neurosurgery, Department of Surgery, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095-7039, USA.
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Dean JB, Mulkey DK, Garcia AJ, Putnam RW, Henderson RA. Neuronal sensitivity to hyperoxia, hypercapnia, and inert gases at hyperbaric pressures. J Appl Physiol (1985) 2003; 95:883-909. [PMID: 12909594 DOI: 10.1152/japplphysiol.00920.2002] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
As ambient pressure increases, hydrostatic compression of the central nervous system, combined with increasing levels of inspired Po2, Pco2, and N2 partial pressure, has deleterious effects on neuronal function, resulting in O2 toxicity, CO2 toxicity, N2 narcosis, and high-pressure nervous syndrome. The cellular mechanisms responsible for each disorder have been difficult to study by using classic in vitro electrophysiological methods, due to the physical barrier imposed by the sealed pressure chamber and mechanical disturbances during tissue compression. Improved chamber designs and methods have made such experiments feasible in mammalian neurons, especially at ambient pressures <5 atmospheres absolute (ATA). Here we summarize these methods, the physiologically relevant test pressures, potential research applications, and results of previous research, focusing on the significance of electrophysiological studies at <5 ATA. Intracellular recordings and tissue Po2 measurements in slices of rat brain demonstrate how to differentiate the neuronal effects of increased gas pressures from pressure per se. Examples also highlight the use of hyperoxia (<or=3 ATA O2) as a model for studying the cellular mechanisms of oxidative stress in the mammalian central nervous system.
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Affiliation(s)
- Jay B Dean
- Department of Anatomy and Physiology, Wright State University, Dayton, OH 45435, USA.
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Mulkey DK, Henderson RA, Putnam RW, Dean JB. Pressure (< or=4 ATA) increases membrane conductance and firing rate in the rat solitary complex. J Appl Physiol (1985) 2003; 95:922-30. [PMID: 12704095 DOI: 10.1152/japplphysiol.00865.2002] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Neuronal sensitivity to pressure, barosensitivity, is illustrated by high-pressure nervous syndrome, which manifests as increased central nervous system excitability when heliox or trimix is breathed at >15 atmospheres absolute (ATA). We have tested the hypothesis that smaller levels of pressure (<or=4 ATA) also increase neuronal excitability. The effect of hyperbaric helium, which mimics increased hydrostatic pressure, was determined on putative CO2/H+-chemoreceptor neurons in the solitary complex in rat brain stem slices by intracellular recording. Pressure stimulated firing rate in 31% of neurons (barosensitivity) and decreased input resistance. Barosensitivity was retained during synaptic blockade and was unaffected by antioxidants. Barosensitivity was distributed among CO2/H+-chemosensitive and -insensitive neurons; in CO2/H+-chemosensitive neurons, pressure did not significantly reduce neuronal chemosensitivity. We conclude that moderate pressure stimulates certain solitary complex neurons by a mechanism that possibly involves an increased cation conductance, but that does not involve free radicals. Neuronal barosensitivity to <or=4 ATA may represent a physiological adaptive response to increased pressure or a pathophysiological response that is the early manifestation of high-pressure nervous syndrome.
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Affiliation(s)
- Daniel K Mulkey
- Department of Anatomy and Physiology, Wright State University, Dayton, OH 45435, USA
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