Genetic Background Influences Acute Response to TBI in Kindling-Susceptible, Kindling-Resistant, and Outbred Rats

Single Nucleotide Polymorphism in Cell Adhesion Molecule L1 Affects Learning and Memory in a Mouse Model of Traumatic Brain Injury

The L1 cell adhesion molecule (L1) has demonstrated a range of beneficial effects in animal models of spinal cord injury, neurodegenerative disease, and ischemia; however, the role of L1 in TBI has not been fully examined. Mutations in the L1 gene affecting the extracellular domain of this type 1 transmembrane glycoprotein have been identified in patients with L1 syndrome. These patients suffer from hydrocephalus, MASA (mental retardation, adducted thumbs, shuffling gait, aphasia) symptoms, and corpus callosum agenesis. Clinicians have observed that recovery post-traumatic brain injury (TBI) varies among the population. This variability may be explained by the genetic differences present in the general population. In this study, we utilized a novel mouse model of L1 syndrome with a mutation at aspartic acid position 201 in the extracellular domain of L1 (L1-201). We assessed the impact of this specific single nucleotide polymorphism (SNP) localized to the X-chromosome L1 gene on recovery outcomes following TBI by comparing the L1-201 mouse mutants with their wild-type littermates. We demonstrate that male L1-201 mice exhibit significantly worse learning and memory outcomes in the Morris water maze after lateral fluid percussion (LFP) injury compared to male wild-type mice and a trend to worse motor function on the rotarod. However, no significant changes were observed in markers for inflammatory responses or apoptosis after TBI.

Tau Phosphorylation Patterns in the Rat Cerebral Cortex After Traumatic Brain Injury and Sodium Selenate Effects: An Epibios4rx Project 2 Study

Sodium selenate (SS) activates protein phosphatase 2 (PP2A) and reduces phosphorylated tau (pTAU) and late post-traumatic seizures after lateral fluid percussion injury (LFPI). In EpiBioS4Rx Project 2, a multi-center international study for post-traumatic targets, biomarkers, and treatments, we tested the target relevance and modification by SS of pTAU forms and PP2A and in the LFPI model, at two sites: Einstein and Melbourne. In Experiment 1, adult male rats were assigned to LFPI and sham (both sites) and naïve controls (Einstein). Motor function was monitored by neuroscores. Brains were studied with immunohistochemistry (IHC), Western blots (WBs), or PP2A activity assay, from 2 days to 8 weeks post-operatively. In Experiment 2, LFPI rats received SS for 7 days (SS0.33: 0.33 mg/kg/day; SS1: 1 mg/kg/day, subcutaneously) or vehicle (Veh) post-LFPI and pTAU, PR55 expression, or PP2A activity were studied at 2 days and 1 week (on treatment), or 2 weeks (1 week off treatment). Plasma selenium and SS levels were measured. In Experiment 1 IHC, LFPI rats had higher cortical pTAU-Ser202/Thr205-immunoreactivity (AT8-ir) and pTAU-Ser199/202-ir at 2 days, and pTAU-Thr231-ir (AT180-ir) at 2 days, 2 weeks, and 8 weeks, ipsilaterally to LFPI, than controls. LFPI-2d rats also had higher AT8/total-TAU5-ir in cortical extracts ipsilateral to the lesion (WB). PP2A (PR55-ir) showed time- and region-dependent changes in IHC, but not in WB. PP2A activity was lower in LFPI-1wk than in sham rats. In Experiment 2, SS did not affect neuroscores or cellular AT8-ir, AT180-ir, or PR55-ir in IHC. In WB, total cortical AT8/total-TAU-ir was lower in SS0.33 and SS1 LFPI rats than in Veh rats (2 days, 1 week); total cortical PR55-ir (WB) and PP2A activity were higher in SS1 than Veh rats (2 days). SS dose dependently increased plasma selenium and SS levels. Concordant across-sites data confirm time and pTAU form-specific cortical increases ipsilateral to LFPI. The discordant SS effects may either suggest SS-induced reduction in the numbers of cells with increased pTAU-ir, need for longer treatment, or the involvement of other mechanisms of action.

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.

Diversity of kindling of limbic seizures after lateral fluid percussion injury in the rat

Lateral fluid percussion injury (LFPI) in rats is used to model post-traumatic epilepsy (PTE), with spontaneous seizures occurring in up to ½ of the subjects. Using the kindling paradigm, we examined whether animals without detectable seizures had an altered seizure susceptibility. Male Sprague Dawley rats were subjected to LFPI. Seven-nine months later, spontaneous seizures were monitored for two weeks. Afterward, the animals underwent kindling of basolateral amygdala. For kindling outcomes, the animals were categorized based on the 95% confidence intervals of mean number trials to kindling (ie 3 consecutive stage 4-5 seizures). Spontaneous seizures were detected in 7 out of 24 rats. There was no correlation between the severity of LFPI and either baseline afterdischarge properties, or kindling rates. Six LFPI rats kindled at a rate comparable to those in sham-LFPI (n = 10) and in naïve (n = 7) subjects. Ten LFPI rats kindled faster and 8-slower than controls. None of slow-kindling rats had spontaneous seizures during the prekindling monitoring. During the same period, six fast-kindling and three normal-kindling rats had been seizure-free. Thus, kindling reveals a diversity to seizure susceptibility after LFPI beyond an overt seizure symptomatology, ranging from the increased susceptibility to the increased resistance.