Diverse changes in microglia morphology and axonal pathology during the course of 1 year after mild traumatic brain injury in pigs

Abstract

Over 2.8 million people experience mild traumatic brain injury (TBI) in the United States each year, which may lead to long-term neurological dysfunction.The mechanical forces that are caused by TBI propagate through the brain to produce diffuse axonal injury (DAI) and trigger secondary neuroinflammatory cascades. The cascades may persist from acute to chronic time points after injury, altering the homeostasis of the brain. However, the relationship between the hallmark axonal pathology of diffuse TBI and potential changes in glial cell activation or morphology have not been established in a clinically relevant large animal model at chronic time points. In this study, we assessed the tissue from pigs subjected to rapid head rotation in the coronal plane to generate mild TBI. Neuropathological assessments for axonal pathology, microglial morphological changes, and astrocyte reactivity were conducted in specimens out to 1-year post-injury. We detected an increase in overall amyloid precursor protein pathology, as well as periventricular white matter and fimbria/fornix pathology after a single mild TBI. We did not detect the changes in corpus callosum integrity or astrocyte reactivity. However, detailed microglial skeletal analysis revealed changes in morphology, most notably increases in the number of microglial branches, junctions, and endpoints. These subtle changes were most evident in periventricular white matter and certain hippocampal subfields, and were observed out to 1-year post-injury in some cases. These ongoing morphological alterations suggest persistent change in neuroimmune homeostasis. Additional studies are needed to characterize the underlying molecular andThis is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

Hippocampal Interneuronal Dysfunction and Hyperexcitability in a Porcine Model of Concussion

“…A mild form of TBI or concussion was produced as previously described (Johnson, Stewart et al 2016, Johnson, Weber et al 2018, Grovola, Paleologos et al 2021). Briefly, the injury was performed under isoflurane anesthesia, while physiological parameters of the animals were being closely monitored.…”

“…The animal’s head was secured to a padded bite plate under anesthesia and attached to the HYGE device. We utilized a coronal plane of rotation that induces a modest delay in return-of-consciousness post-injury (compared to anesthetized sham animals) and minimal subdural bleeding, but produces patterns of diffuse axonal injury, such as swellings in the form of discrete axonal bulbs and axonal varicosities observed at the roots of the cortical gyri, at the interface of the grey and white matter, and within the deep white matter (Johnson, Stewart et al 2016, Johnson, Weber et al 2018, Grovola, Paleologos et al 2021, Wofford, Grovola et al 2021). To induce a mild injury phenotype (concussion), a single rapid head rotation was performed within a range of rotational velocities (168 – 269 rad/sec, n = 9), with the mean angular peak velocity being 226 ± 13 rad/sec.…”

“…For a subset of analyses, the injured animals were divided into two subgroups, those injured at ∼190 rad/sec (188 ± 11 rad/sec, n = 4) versus those injured at ∼260 rad/sec (256 ± 7 rad/sec, n = 5). The injury model has been extensively characterized in previously published studies (Grovola et al, 2021; Johnson et al, 2016; Johnson et al, 2018).…”

The Importance of Animal Models in Biomedical Research: Current Insights and Applications

“…Moreover, the replication of trauma may be greater in rodents since traumatisms in these animals tend to generate focal instead of diffuse lesions [ 127 ]. Grovola et al [ 128 ] used male Yucatán miniature pigs to analyze neurological dysfunction in animals with mild traumatism 1-year postevent. They found a persistent neuroimmune response in animals with morphological changes to the microglia, with increased branches and junctions per cell ( p = 0.026 and p = 0.045, respectively).…”

Porcine Astrocytes and Their Relevance for Translational Neurotrauma Research

“…The Cullen Lab then also conducted studies that included analysis of astrocyte response to head rotational acceleration injury. Grovola et al analyzed astrocyte reactivity via GFAP expression following two severities of mild injury in the coronal plane [ 84 ]. They scored GFAP+ cell size and the density of GFAP+ cells in the hippocampus, periventricular white matter, inferior temporal gyrus, and cingulate gyrus and averaged these scores to provide a single score of reactivity for each subject.…”