Professor, Dept. Neurobiology and Anatomy, Drexel University College of Medicine
Cellular Neurobiology of Brain Injury:
Mechanisms of Cell Dysfunction/Death and Plasticity
Research and Interest
The spectrum of traumatic brain injuries ranges from mild concussions that are treated in the emergency room, to severe head injuries that require acute critical and neurosurgical care. Improved critical and advanced radiological and neurosurgical techniques have led to decreases in mortality rates over the past 2 decades. However, survivors of brain injuries suffer long-term behavioral problems such as learning deficits, memory dysfunction, psychological and emotional disturbances – functional aspects that affect the quality of life and currently have no therapies. The economic costs of traumatic brain injuries, which include hospitalization, health care and lost work hours, is estimated at almost 35 billion dollars. This problem has become particularly relevant in the past 4 years, with the Iraq war veterans returning home having suffered blast-related concussions, an injury that is poorly understood. It is estimated that over 2500 soldiers have suffered head injuries since March 2003.
The damage observed after TBI comprises both primary disruption of neural tissue related to the impact, and secondary mechanisms that develop over the weeks to months after the traumatic event. The spectrum of pathologies observed after TBI include focal contusions in the gray matter and diffuse injuries to axons in the white matter. It has been suggested that these pathologies are a consequence of the biomechanics of the impact, i.e., focal injuries occur due to contact forces to the head, while diffuse injuries are a result of non-contact, rotational forces to the brain. While aspects of focal pathology can be superimposed on diffuse brain injury (and vice versa), it is our belief that significant differences exist between the pathobiology of these two types of injuries that warrant the separate evaluation of mechanisms of damage in the cell body (soma) and the axon. Secondary mechanisms of neural damage are initiated immediately after impact and result in a number of cascades that affect both the neural tissue and the vasculature. In response to the impact, the brain becomes edematous leading to increases in intracranial pressure and subsequent neuronal death, which may be an underlying cause for the neurologic impairment. In turn, injured neurons are faced with imbalances in ionic homeostasis, over-activation of excitatory amino acid receptors, increases in intracellular calcium, increased free radical generation, and mitochondrial dysfunction that may underlie the eventual death of injured neurons. Concomitant with neuronal death and damage, axons are also subjected to mechanical forces that lead to traumatic axonal injury. Injury to axons is characterized by focal accumulations cytoskeletal proteins resulting in a swollen phenotype in the acute post-traumatic period. Over time these swollen axons undergo complete axotomy (Wallerian degeneration), a process that is associated with death of oligodendrocytes.
Our studies of traumatic brain injury (TBI) have led to the following accomplishments:
- Documenting programmed cell death after brain injury in rats and in humans
- Demonstrating that strategies aimed at reduced the extent of programmed cell death can attenuate cognitive and motor deficits
- Development of injury-specific and clinically-relevant animal models of TBI (concussive to repetitive to severe brain injuries)
- Identification of specific intracellular pathways that underlie grey matter injuries (neuronal death) and white matter injuries (axonal damage).
The ongoing research efforts, funded in part by the National Institutes of Health and the Division of Veteran’s Affairs, are aimed at addressing the feasibility of cellular and pharmacologic strategies to attenuate and reverse TBI pathology. The focus of the research in this group of investigators extend from the basic cell biology of neuronal death and axonal injury to inhibition of seizure induction to the behavioral and rehabilitative strategies (including neuro-robotics and prosthetic use) that may be applied in the chronic post-traumatic phase. The mission of the Raghupathi laboratory is to develop pharmacological treatment and behaviorally therapeutic strategies to respectively, reduce acute post-traumatic neural damage and augment behavioral recovery in the chronic phase. Our research efforts offer some unique capabilities such as comparisons of acute and chronic pharmacologic treatments in multiple models of TBI, in both mice and rats, and, combination treatment strategies that encompass acute pharmacologic treatments with chronic phase behavioral modifications and/or stem cell transplants.We currently use models of focal or diffuse brain trauma in rodents, and have the capability to expand any of these injuries to poly-trauma, particularly focused on controlled hemorrhage and/or controlled hypoxia. Behavioral measures used in the group include (see list of publications): Cognitive function using the Morris water maze, the T-maze and the conditioned fear response test; motor function using the Schallert cylinder test of limb placement and the Feeney beam walk test. In addition, standard outcome measures include measurement of compound action potentials in the corpus callosum using ex vivo preparations of uninjured and injured coronal brain slices. Histological techniques include gross alterations using Nissl-Luxol Fast Blue stained sections followed by quantification of lesions; microscopic evidence of cell survival using unbiased stereology with the optical fractionator; stereologic approaches to counting double-labeled axonal profiles with confocal microscopy; optical imaging in live animals; cryoplane microscopy for imaging from the micro- to the macro-scale. We use a combination of in vivo and in vitro models of mechanical injury to delineate cellular mechanisms leading to neuronal and glial death and dysfunction. Using rodent models of focal or diffuse brain trauma (including repetitive injury), we ask fundamental questions whether inhibiting neural injury phenotypes (apoptosis, necrosis, axonal injury) will lead to better functional recovery. The working hypothesis in this project is that the choice of an appropriate treatment paradigm for head-injured patients will depend on the severity of the injury.
Ramesh Raghupathi graduated from Virginia Commonwealth University with a Ph.D. in Biochemistry and Molecular Biophysics. He did post-doctoral fellowships at the University of Connecticut Health Science Center and the University of Pennsylvania. He served on the faculty in the Department of Neurosurgery at the University of Pennsylvania School of Medicine. He was appointed to the faculty in the Department of Neurobiology and Anatomy at Drexel University College of Medicine in 2003.
1. Injury specific treatment strategies for traumatic brain injury (funded by the Veteran’s Administration, 2007-2011).
2. Pathology-directed combination therapies for pediatric brain trauma (funded by the Eunice Kennedy Shriver National Institutes of Child Health and Human Development, 2009-2014)
3. Mechanisms of injury and acute repair of axons in traumatic brain injury (funded by the National Institute of Neurological Disease and Stroke, 2010-2013)
4. Growth factor treatment for pediatric brain trauma (funded by the National Institute of Neurological Disease and Stroke, 2006-2011)
Ann Mae DiLeonardi, PhD candidate (Neuroscience) “Mechanisms and functional consequences of axonal injury following pediatric brain trauma”
Jenny Creed, MD/PhD candidate (Neuroscience) “Role of ionotropic glutamate receptors in neuronal and glial injury following mechanical trauma”
Robert Laskowski, MD/PhD candidate (Neuroscience) “Dopaminergic signaling in the prefrontal cortex following concussive brain trauma”
Rupal Prasad, Research technician
Douglas Fox, Research technician
Collaborators & Colleagues
Jimmy Huh, MD, Department of Anesthesiology and Critical Care, Children's Hospital of Philadelphia.
Gianluca Gallo, PhD, Department of Neurobiology and Anatomy, Drexel University College of Medicine
Ken Barbee, PhD, School of Biomedical Engineering, Science & Health Systems, Drexel University
Alan Tessler, MD, Philadelphia Veteran’s Administration Medical Center
Reviews and Book Chapters
- Raghupathi, R., McIntosh, T.K. Drugs in the Management of Acute TBI. Physical Medicine and Rehabilitation Clinics of North America 8:629-649, 1997.
- Raghupathi, R. Apoptosis and DNA Damage in Head Trauma, in Head Trauma: Basic, Preclinical and Clinical Aspects (Miller, L.P. and Hayes, R.L., eds.), John Wiley & Sons, Inc., New York, NY, pp 239-255, 2001.
- Raghupathi, R. Cell death mechanisms following traumatic brain injury. Brain Pathol. 14:215-222, 2004.
- Martin H.A., Woodson A., Christian C.W., Helfaer M.A., Raghupathi R., Huh J.W. Shaken Baby Syndrome, in Critical Care Nursing Clinics of North America (Violence, Injury and Trauma) (Thompson H.J. and Alexy E.M., Eds.), 18:279-286, 2006.
- Su F., Huh J.W., Raghupathi R. Neurointensive care for traumatic brain injury in children. http://www.emedicine.com/ped/topic3082.htm, updated July 2009.
- Huh J.W. and Raghupathi R. New concepts in treatment of pediatric traumatic brain injury. Anesthesiol. Clin. 27:213-40, 2009.
- Saatman K.E., Creed J. and Raghupathi R. Calpain as a therapeutic target for traumatic brain injury. Neurotherapeutics 7:31-42, 2010.
- Raghupathi, R., Muir, J.K., Fulp, C.T., Pittman, R.N., McIntosh, T.K. Acute alterations in mitogen-activated protein kinases following traumatic brain in the rat: implications for post-traumatic cell death. Exp. Neurol. 183:438-448, 2003.
- Gefen, A., Gefen, N., Zhu, Q., Raghupathi, R., Margulies, S.S. Age-dependent changes in material properties of the brain and braincase of the rat. J. Neurotrauma 20:1163-1177, 2003.
- Raghupathi, R., Mehr, M., Helfaer, M.A., Margulies, S.S. Traumatic axonal injury is exacerbated following repetitive closed head injury in the neonatal pig. J. Neurotrauma 21:307-316, 2004.
- Strauss K.I., Narayan R.K., Raghupathi R. Common patterns of Bcl-2 family gene expression in two traumatic brain injury models. Neurotox Res. 6:333-42, 2004.
- DeRidder M.N., Simon M.J., Siman R., Auberson Y.P., Raghupathi R., Meaney D.F. Mechanical injury to the hippocampus in vitro causes regional caspase-3 and calpain activation that is influenced by NMDA receptor subunit composition. Neurobiol Dis 22:165-176, 2006.
- Saatman K.E., Feeko K.J., Pape R.L., Raghupathi R. Differential behavioral and histological responses to the graded cortical impact injury in mice. J. Neurotrauma 23:1241-1253, 2006.
- Huh J.W., Widing A.G., Raghupathi R. Repetitive mild non-contusive brain trauma in immature rats exacerbates traumatic axonal injury and axonal calpain activation. J. Neurotrauma 24:15-27, 2007.
- Huh J.W. and Raghupathi R. Chronic cognitive deficits and long-term histopathological alterations following contusive brain injury in the immature rat. J. Neurotrauma 24:1460-1476, 2007.
- Raghupathi R. and Huh J.W. Diffuse brain injury in the immature rat: Evidence for an age-at-injury effect on cognitive function and histopathologic damage. J. Neurotrauma 24: 1596-1608, 2007.
- Serbest G., Burkhardt M.F., Siman R., Raghupathi R. and Saatman K.E. Temporal profiles of cytoskeletal protein loss following traumatic axonal injury in mice. Neurochem. Res. 32: 2006-14, 2007.
- Huh J.W., Widing A.G. and Raghupathi R. Midline brain injury in the immature rat induces sustained cognitive deficits, bihemispheric axonal injury and neurodegeneration. Exp. Neurol. 213: 84-92, 2008.
- DiLeonardi A.M., Huh J.W. and Raghupathi R. Impaired axonal transport and neurofilament compaction occur in separate populations of injured axons following diffuse brain injury in the immature rat. Brain Res. 1263:174-182, 2009.
Patent No. US 6,326,146: O'Dell, D.M., Raghupathi, R., McIntosh, T.K., Crino, P., Eberwine, J. Method of determining multiple mRNAs in dying cells. 2001.