Longitudinal Biochemical and Behavioral Alterations in a Gyrencephalic Model of Blast-Related Mild Traumatic Brain Injury

Abstract

Blast-related traumatic brain injury (bTBI) is a major cause of neurological disorders in the U.S. military that can adversely impact some civilian populations as well and can lead to lifelong deficits and diminished quality of life. Among these types of injuries, the long-term sequelae are poorly understood because of variability in intensity and number of the blast exposure, as well as the range of subsequent symptoms that can overlap with those resulting from other traumatic events (e.g., post-traumatic stress disorder). Despite the valuable insights that rodent models have provided, there is a growing interest in using injury models using species with neuroanatomical features that more closely resemble the human brain. With this purpose, we established a gyrencephalic model of blast injury in ferrets, which underwent blast exposure applying conditions that closely mimic those associated with primary blast injuries to warfighters. In this study, we evaluated brain biochemical, microstructural, and behavioral profiles after blast exposure using in vivo longitudinal magnetic resonance imaging, histology, and behavioral assessments. In ferrets subjected to blast, the following alterations were found: 1) heightened impulsivity in decision making associated with pre-frontal cortex/amygdalar axis dysfunction; 2) transiently increased glutamate levels that are consistent with earlier findings during subacute stages post-TBI and may be involved in concomitant behavioral deficits; 3) abnormally high brain N-acetylaspartate levels that potentially reveal disrupted lipid synthesis and/or energy metabolism; and 4) dysfunction of pre-frontal cortex/auditory cortex signaling cascades that may reflect similar perturbations underlying secondary psychiatric disorders observed in warfighters after blast exposure.

Keywords: biochemical and behavioral alterations; ferret; in vivo magnetic resonance spectroscopy; mild TBI; primary blast.

FIG. 1.

Demonstration of the MRS voxel in hippocampal (A) and pre-frontal cortex (B) and spectrums of a blast and sham ferret at 3 days post-blast. NAA, N-acetyl-aspartate; Glu, glutamate; Gln, glutamine; GABA, gamma-aminobutyric acid; GSH, glutathione; PCr, phosphocreatine; Cr, creatine; Cho, choline; Ins, myo-inositol; Tau, taurine; Glx, glutamate/glutamine complex; NAAG, N-acetylaspartylglutamate; MM, macro molecules; MRS, magnetic resonance spectroscopy.

FIG. 2.

(A) In-house trap test for the ferret. (B) Time required to walk out from the trap of the sham and blast-exposed ferrets at 1, 3, and 6 months post-blast. *p < 0.05, **p < 0.01, differences between sham and blast animals.

FIG. 3.

(A) Ferret anatomical MRI. (B) ROIs for DKI and DTI parameters extraction from FA maps. mPFC, medial pre-frontal cortex; S1, primary somatosensory cortex; Str, striatum; HP, hippocampus; Tha, thalamus; CC, corpus callosum; IC, internal capsule; AC, auditory cortex; MRI, magnetic resonance imaging; ROIs, regions of interest; DKI, diffusion kurtosis imaging; DTI, diffusion tensor imaging.

FIG. 4.

Effect of blast on cerebral metabolomics profiles in pre-frontal cortex. *p < 0.05, **p < 0.01, between group or time differences.

FIG. 5.

Effect of blast on cerebral metabolomics profiles in hippocampus. *p < 0.05, **p < 0.01, between group or time differences.

FIG. 6.

Effect of blast on argyrophilic inclusions in the auditory cortex. Note a significant increase in the density of silver-stained inclusions at 6 months post-blast. *p < 0.05. Scale bar = 100 μm.