Diffusion tensor imaging of hippocampal network plasticity

Abstract

Diffusion tensor imaging (DTI) has become a valuable tool to investigate white matter integrity in the brain. DTI also gives contrast in gray matter, which has been relatively little explored in studies assessing post-injury structural abnormalities. The present study was designed to compare white and gray matter reorganization in the rat hippocampus after two epileptogenic brain injuries, status epilepticus (SE) and traumatic brain injury (TBI), using ex vivo high-resolution DTI. Imaging was performed at 6-12 months post-injury and findings were compared to histological analyses of Nissl, myelin, and Timm-stained preparations from the same animals. In agreement with the severity of histological damage, fractional anisotropy (FA), axial (D ||) and radial (D ⊥) diffusivities, and mean diffusivity (MD) measurements were altered in the order SE > TBI ipsilaterally > TBI contralaterally. After SE, the most severe abnormalities were found in the dentate gyrus and CA3b-c subfields, in which the mean FA was increased to 125 % (p < 0.001) and 143 % (p < 0.001) of that in controls, respectively. In both subfields, the change in FA was associated with an increase in D || (p < 0.01). In the stratum radiatum of the CA1, FA was decreased to 81 % of that in controls (p < 0.05) which was associated with an increase in D ⊥ (p < 0.01). After TBI, DTI did not reveal any major abnormalities in the dentate gyrus. In the ipsilateral CA3b-c, however, FA was increased to 126 % of that in controls (p < 0.01) and associated with a mild decrease in D ⊥ (p < 0.05). In the stratum radiatum of the ipsilateral CA1, FA was decreased to 88 % of that in controls (p < 0.05). Our data demonstrate that DTI reveals subfield-specific abnormalities in the hippocampus with remarkable qualitative and quantitative differences between the two epileptogenic etiologies, suggesting that DTI could be a valuable tool for follow-up of focal circuitry reorganization during the post-injury aftermath.

Imaging and serum biomarkers reflecting the functional efficacy of extended erythropoietin treatment in rats following infantile traumatic brain injury

“…Recently it was recognized that DTI can detect abnormalities in gray matter as well as in white matter. 91 Results from the present study demonstrated the feasibility of using DTI as a detailed biomarker to quantify the severity and regional extent of injury and repair after infant TBI. Additional detailed regional analyses to clarify the extent of microstructural abnormalities throughout the brain using this model are underway.…”

MRI uncovers disrupted hippocampal microstructure that underlies memory impairments after early‐life adversity

“…Thus, our ROI analysis of hippocampal gray matter using DTI is relatively new. Hippocampal plasticity via manual ROI delineation has been examined in rodents (Sierra et al ., ) and in humans (Goubran et al ., ). These studies did not focus on the dendritic regions but included all hippocampal structures.…”

Early tissue damage and microstructural reorganization predict disease severity in experimental epilepsy

“…In the epileptic hippocampus of several rodent epilepsy models DWI successfully identified changes of water diffusion, which is discussed to primarily relate to mossy fiber sprouting and reorganization of myelinated axons (Kharatishvili et al, 2007; Kuo et al, 2008; Laitinen et al, 2010; Sierra et al, 2015a, 2015b; Salo et al, 2017). However, it is important to note that the above mentioned epilepsy models do not fully reflect the histopathological hallmarks of pharmacoresistant mTLE (i.e., unilateral HS including GCD) complicating a translation to the human disease.…”