Assessment of Temporal and Spatial Alterations in Spinal Glial Reactivity and the Extent of Cervical Spinal Axonal Injury in the Rat After Blast Overpressure Exposure

Links

Abstract

Blast induced neurotrauma (BINT) is the signature wound of veterans returning from various military operations. A substantial percentage of Operations Enduring Freedom (OEF) and Iraqi Freedom (OIF) veterans have reported to experience ongoing or new pain following their military service. Head (58%) and back (55%) have been the high prevailing locations of pain in these returning OIF and OEF veterans and the underlying pathomechanism of these conditions is yet to be understood. In the context of blast overpressure induced pathological changes, the fundamental question that still needs to be addressed is whether there are any underlying cellular injury changes the spinal cord following blast. If proven, it is postulated that cellular injury changes in the form of glial activation may contribute to neuronal sensitization and altered sensation through the release of various inflammatory mediators. Much of the previous and ongoing research studies have been directed at understanding blast induced changes in the brain alone with changes in the spinal cord still remaining an enigma. Accordingly, as a first step, we attempted to investigate spatial and temporal alterations in glial activation in the spinal cord following blast exposure. In addition, we also attempted to study the presence of axonal injury in the cervical spinal cord following blast overpressure.

As part of this investigation, anaesthetized male Sprague Dawley rats were subjected to a single insult of blast overpressure (22psi)using a helium driven shock tube. The rats were divided into two groups; Sham and Blast with acute and sub-acute survival periods; 6hrs, 24hrs, 3days and 7days respectively. Glial activation was assessed by GFAP (Glial Fibrillary Acidic Protein) and IBA1 (Ionized Calcium Binding Molecule 1) immunohistochemistry. GFAP and Iba1 are routinely used to investigate astrocytic and microglial activation in the brain and spinal cord. Axonal injury in the cervical spinal cord was assessed by β-APP (Beta Amyloid Precursor Protein) immunohistochemistry. βAPP is a commonly used marker to detect the presence of diffuse axonal injury in the brain.

Behaviorally, blast exposed rats exhibited significantly increased surface righting duration compared to sham rats. Our immunohistochemistry results indicate differential activation of astrocytes and microglia in various spinal cord regions in blast exposed group compared to sham. Rats subjected to blast overpressure showed increased expression of astrocytes and microglia at acute and sub-acute periods. Evidence of diffuse axonal injury also observed in the cervical spinal cord following the blast overpressure. Taken together, our results suggest that blast exposure in a craniocephalic orientation in rats resulted an enhanced spinal glial reactivity as well as cervical spinal axonal injury. We postulate that injury changes in the form of activation of astrocytes and microglia with diffuse axonal injury may contribute to the release of various inflammatory mediators which may in turn be related to the ensuing sensory changes. These results lay foundation to further studies on blast related injury changes in the spinal cord.

Cited Works (11)

Year	Entry
2007	Chavko M, Koller WA, Prusaczyk WK, McCarron RM. Measurement of blast wave by a miniature fiber optic pressure transducer in the rat brain. J Neurosci Meth. January 30, 2007;159(2):277-281.
2012	Rafaels KA, Bass CRD, Panzer MB, Salzar RS, Woods WA, Feldman SH, Walilko T, Kent RW, Capehart BP, Foster JB, Derkunt B, Toman A. Brain injury risk from primary blast. J Trauma Acute Care Surg. October 2012;73(4):895-901.
1989	McIntosh TK, Vink R, Noble L, Yamakami I, Fernyak S, Soares H, Faden AL. Traumatic brain injury in the rat: characterization of a lateral fluid-percussion model. Neuroscience. 1989;28(1):233-244.
2011	Li Y, Zhang L, Kallakuri S, Zhou R, Cavanaugh JM. Injury predictors for traumatic axonal injury in a rodent head impact acceleration model. Stapp Car Crash J. 2011;55:25-47.
2010	Svetlov SI, Prima V, Kirk DR, Gutierrez H, Curley KC, Hayes RL, Wang KKW. Morphologic and biochemical characterization of brain injury in a model of controlled blast overpressure exposure. J Trauma-Inj Infect Crit Care. October 2010;69(4):795-804.
2012	Bolander R. A Multi-Species Analysis of Biomechanical Responses of the Head to a Shock Wave [PhD thesis]. Detroit, MI: Wayne State University; May 2012.
2009	Bauman RA, Ling G, Tong L, Januszkiewicz A, Agoston D, Delanerolle N, Kim Y, Ritzel D, Bell R, Ecklund J, Armonda R, Bandak F, Parks S. An introductory characterization of a combat-casualty-care relevant swine model of closed head injury resulting from exposure to explosive blast. J Neurotrauma. June 2009;26(6):841-860.
2012	VandeVord PJ, Bolander R, Sajja VSSS, Hay K, Bir CA. Mild neurotrauma indicates a range-specific pressure response to low level shock wave exposure. Ann Biomed Eng. January 2012;40(1):227-236.
1994	Marmarou A, Foda MAA-E, van den Brink W, Campbell J, Kita H, Demetriadou K. A new model of diffuse brain injury in rats, I: pathophysiology and biomechanics. J Neurosurg. February 1994;80(2):291-300.
2001	Cernak I, Wang Z, Jiang J, Bian X, Savic J. Ultrastructural and functional characteristics of blast injury-induced neurotrauma. J Trauma. April 2001;50(4):695-706.
1981	Feeney DM, Boyeson MG, Linn RT, Murray HM, Dail WG. Responses to cortical injury, I: methodology and local effects of contusions in the rat. Brain Res. April 27, 1981;211(1):67-77.