Diffusion tensor imaging reveals microstructural alterations in corpus callosum and associated transcallosal fiber tracts in adult macaques with neonatal hippocampal lesions

Abstract

To investigate the effects of neonatal hippocampal lesions on the microstructural integrity of the corpus callosum (CC) in adulthood, macaque monkeys (n = 5) with neonatal bilateral neurotoxic hippocampal lesion (Neo-Hibo) and sham-operated controls (Neo-C, n = 5) were scanned using magnetic resonance diffusion tensor imaging (DTI) technique at 8-10 years old. CC was segmented into seven regionsgrouped into anterior CC (rostrum, genu, rostral body and anterior midbody) and posterior CC (posterior midbody, isthmus and splenium) for data analysis. Associated transcallosal fiber tracts were delineated using probabilistic tractography and evaluated with tract-based spatial statistics (TBSS). Neo-Hibo lesions resulted in significant increased diffusivity indices (mean, axial and radial diffusivity) in CC posterior segments. Also, significant decreased fractional anisotropy (FA) and increased diffusivity indices were seen in the associated transcallosal fiber tracts proximal to motor, posterior parietal and retrosplenial cortices. In Neo-Hibo animals, increased mean diffusivity (MD) in posterior midbody negatively correlated with reduction of CC surface areaand the magnitude of their memory impairments was significantly correlated with FA in transcallosal fiber tracts across splenium. Although no microstructural changes were observed in CC anterior segments, changes in FA values and diffusivity indices were observed in the white matter fibers of the ventromedial prefrontal cortex. Thus, Neo-H lesions resulted in enduring degradation in transcallosal fibers proximal to parietal and retrosplenial cortices, and hemispheric connections through posterior CC. The findings may provide complementary information for understanding the neural substrate of behavioral and cognitive deficits observed in patients with early insult to the hippocampus.

Combining Brain Perturbation and Neuroimaging in Non-human Primates

“…strokes, accidental injury, neurosurgery, traumatic brain injury etc). Studies to date have focused on changes in resting-state correlated activity (i.e., 'functional connectivity') following lesions, which can correlate with behavioral recovery following stroke lesions (He et al, 2007) or with structural connectivity changes in white matter tracts (Meng et al, 2018;Shamy et al, 2010). Clinical studies are now also documenting brain changes over time following permanent injury resulting in neglect or aphasia (Saur et al, 2006;Berthier et al, 2011;Hartwigsen et al, 2019;Stockert et al, 2020;Umarova et al, 2016).…”

Ultra-high field (10.5T) diffusion-weighted MRI of the macaque brain

“…In vivo macaque dMRI with 1–1.5 mm isotropic resolution has been widely reported and easily attainable with most 3T scanners and commercially available coils (Feng et al, 2017; Liu et al, 2016 ; Meng et al, 2018 ; Rane and Duong, 2011 ; Shen et al, 2019 ; Shimony et al, 2018; Weiss et al, 2022 ). 1.1 mm isotropic dMRI data has been acquired with a knee coil (Shimony et al, 2018).…”

Diffusion Tensor Imaging-Based Studies at the Group-Level Applied to Animal Models of Neurodegenerative Diseases

“…Initial studies of the application of DTI in non-human primates for the investigation of TBI are ongoing. Seminal work has shown that DTI can provide outcome measures in non-human primates models of traumatic spinal cord injury (Ma et al, 2016 ) and the remodeling of brain circuits upon hippocampal damage (Meng et al, 2018 ). Although non-human primate models of TBI has been established (e.g., King et al, 2010 ), the logistics and the ethics of non-human primates have so far limited the availability for DTI investigations.…”