Inherent Susceptibility to Acquired Epilepsy in Selectively Bred Rats Influences the Acute Response to Traumatic Brain Injury

Traumatic brain injury (TBI) often causes seizures associated with a neuroinflammatory response and neurodegeneration. TBI responses may be influenced by differences between individuals at a genetic level, yet this concept remains understudied. Here, we asked whether inherent differences in one's vulnerability to acquired epilepsy would determine acute physiological and neuroinflammatory responses acutely after experimental TBI, by comparing selectively bred "seizure-prone" (FAST) rats with "seizure-resistant" (SLOW) rats, as well as control parental strains (Long Evans and Wistar rats). Eleven-week-old male rats received a moderate-to-severe lateral fluid percussion injury (LFPI) or sham surgery. Rats were assessed for acute injury indicators and neuromotor performance, and blood was serially collected. At 7 days post-injury, brains were collected for quantification of tissue atrophy by cresyl violet (CV) histology, and immunofluorescent staining of activated inflammatory cells. FAST rats showed an exacerbated physiological response acutely post-injury, with a 100% seizure rate and mortality within 24 h. Conversely, SLOW rats showed no acute seizures and a more rapid neuromotor recovery compared with controls. Brains from SLOW rats also showed only modest immunoreactivity for microglia/macrophages and astrocytes in the injured hemisphere compared with controls. Further, group differences were apparent between the control strains, with greater neuromotor deficits observed in Long Evans rats compared with Wistars post-TBI. Brain-injured Long Evans rats also showed the most pronounced inflammatory response to TBI across multiple brain regions, whereas Wistar rats showed the greatest extent of regional brain atrophy. These findings indicate that differential genetic predisposition to develop acquired epilepsy (i.e., FAST vs. SLOW rat strains) determines acute responses after experimental TBI. Differences in the neuropathological response to TBI between commonly used control rat strains is also a novel finding, and an important consideration for future study design. Our results support further investigation into whether genetic predisposition to acute seizures predicts the chronic outcomes after TBI, including the development of post-traumatic epilepsy.

Potential Neuroprotective Mechanisms of Methamphetamine Treatment in Traumatic Brain Injury Defined by Large-Scale IonStar-Based Quantitative Proteomics

Although traumatic brain injury (TBI) causes hospitalizations and mortality worldwide, there are no approved neuroprotective treatments, partly due to a poor understanding of the molecular mechanisms underlying TBI neuropathology and neuroprotection. We previously reported that the administration of low-dose methamphetamine (MA) induced significant functional/cognitive improvements following severe TBI in rats. We further demonstrated that MA mediates neuroprotection in part, via dopamine-dependent activation of the PI3K-AKT pathway. Here, we further investigated the proteomic changes within the rat cortex and hippocampus following mild TBI (TM), severe TBI (TS), or severe TBI plus MA treatment (TSm) compared to sham operated controls. We identified 402 and 801 altered proteins (APs) with high confidence in cortical and hippocampal tissues, respectively. The overall profile of APs observed in TSm rats more closely resembled those seen in TM rather than TS rats. Pathway analysis suggested beneficial roles for acute signaling through IL-6, TGFβ, and IL-1β. Moreover, changes in fibrinogen levels observed in TSm rats suggested a potential role for these proteins in reducing/preventing TBI-induced coagulopathies. These data facilitate further investigations to identify specific pathways and proteins that may serve as key targets for the development of neuroprotective therapies.

Initiators of Classical and Lectin Complement Pathways Are Differently Engaged after Traumatic Brain Injury-Time-Dependent Changes in the Cortex, Striatum, Thalamus and Hippocampus in a Mouse Model

The complement system is involved in promoting secondary injury after traumatic brain injury (TBI), but the roles of the classical and lectin pathways leading to complement activation need to be clarified. To this end, we aimed to determine the ability of the brain to activate the synthesis of classical and lectin pathway initiators in response to TBI and to examine their expression in primary microglial cell cultures. We have modeled TBI in mice by controlled cortical impact (CCI), a clinically relevant experimental model. Using Real-time quantitative polymerase chain reaction (RT-qPCR) we analyzed the expression of initiators of classical the complement component 1q, 1r and 1s (C1q, C1r, and C1s) and lectin (mannose binding lectin A, mannose binding lectin C, collectin 11, ficolin A, and ficolin B) complement pathways and other cellular markers in four brain areas (cortex, striatum, thalamus and hippocampus) of mice exposed to CCI from 24 h and up to 5 weeks. In all murine ipsilateral brain structures assessed, we detected long-lasting, time- and area-dependent significant increases in the mRNA levels of all classical (C1q, C1s, C1r) and some lectin (collectin 11, ficolin A, ficolin B) initiator molecules after TBI. In parallel, we observed significantly enhanced expression of cellular markers for neutrophils (Cd177), T cells (Cd8), astrocytes (glial fibrillary acidic protein—GFAP), microglia/macrophages (allograft inflammatory factor 1—IBA-1), and microglia (transmembrane protein 119—TMEM119); moreover, we detected astrocytes (GFAP) and microglia/macrophages (IBA-1) protein level strong upregulation in all analyzed brain areas. Further, the results obtained in primary microglial cell cultures suggested that these cells may be largely responsible for the biosynthesis of classical pathway initiators. However, microglia are unlikely to be responsible for the production of the lectin pathway initiators. Immunofluorescence analysis confirmed that at the site of brain injury, the C1q is localized in microglia/macrophages and neurons but not in astroglial cells. In sum, the brain strongly reacts to TBI by activating the local synthesis of classical and lectin complement pathway activators. Thus, the brain responds to TBI with a strong, widespread and persistent upregulation of complement components, the targeting of which may provide protection in TBI.

Rod microglia and their role in neurological diseases

The striking morphology of microglia is one of their most prominent characteristics, with many studies categorising microglial function based on morphology e.g. ramified, hyper-ramified, activated, or amoeboid. Communications regarding rod microglia in neurological disease are scant, and where reported, these cells are rarely the focus of discussion. These factors make it difficult to determine how widespread these cells are not only through the brain but also across diseases. Studies in experimental diffuse brain injury are the first reports of not only significant numbers of rod microglia, but distinct arrangements of these cells, reminiscent of carriages of a train. This review summarises the available reports of rod microglia in vivo and rod-like microglia in vitro and eludes to possible functions and signalling cascades that may evoke this distinct morphology. More investigations are required to fully elucidate the function that rod microglia play in neurological diseases.