Evaluation of Touchscreen Chambers To Assess Cognition in Adult Mice: Effect of Training and Mild Traumatic Brain Injury.

Cognitive impairments are often experienced after a mild traumatic brain injury (mTBI). In the clinical arena, neuropsychological assessments are used frequently to detect cognitive deficits. Animal models of mTBI, however, rely on an assortment of behavioral tasks to assess cognitive outcome. Computer-based touchscreen systems have been developed for rodents and are hypothesized to offer a translational approach to evaluate cognitive function because of the similarities of tasks performed in rodents to those implemented in humans. While these touchscreen systems have been used in pre-clinical models of neurodegenerative diseases and psychiatric disorders, their use in assessing cognitive impairment after mTBI has not been investigated. We hypothesized that mTBI would result in impaired cognitive performance on touchscreen tasks, particularly those with hippocampal-based learning components, including the paired associate learning (PAL) task and the location discrimination (LD) task. Adult male, C57BL/6 mice received a single impact-acceleration mTBI. We found that training mice before injury to perform to criteria is arduous and that performance is sensitive to many environmental variables. Despite extensive optimization and training, mice failed to perform better than chance in the PAL paradigm. Alternatively, mice demonstrated some capacity to learn in the LD paradigm, but only with the easier stages of the task. The mTBI did not affect performance in the LD paradigm, however. Thus, we concluded that under the conditions presented here, the PAL and LD touchscreen tasks are not robust outcome measures for the evaluation of cognitive performance in C57BL/6 mice after a single impact-acceleration mTBI.

Greater neurobehavioral deficits occur in adult mice after repeated, as compared to single, mild traumatic brain injury (mTBI).

Mild traumatic brain injury (mTBI) accounts for the majority of all brain injuries and affected individuals typically experience some extent of cognitive and/or neuropsychiatric deficits. Given that repeated mTBIs often result in worsened prognosis, the cumulative effect of repeated mTBIs is an area of clinical concern and on-going pre-clinical research. Animal models are critical in elucidating the underlying mechanisms of single and repeated mTBI-associated deficits, but the neurobehavioral sequelae produced by these models have not been well characterized. Thus, we sought to evaluate the behavioral changes incurred after single and repeated mTBIs in mice utilizing a modified impact-acceleration model. Mice in the mTBI group received 1 impact while the repeated mTBI group received 3 impacts with an inter-injury interval of 24h. Classic behavior evaluations included the Morris water maze (MWM) to assess learning and memory, elevated plus maze (EPM) for anxiety, and forced swim test (FST) for depression/helplessness. Additionally, species-typical behaviors were evaluated with the marble-burying and nestlet shredding tests to determine motivation and apathy. Non-invasive vibration platforms were used to examine sleep patterns post-mTBI. We found that the repeated mTBI mice demonstrated deficits in MWM testing and poorer performance on species-typical behaviors. While neither single nor repeated mTBI affected behavior in the EPM or FST, sleep disturbances were observed after both single and repeated mTBI. Here, we conclude that behavioral alterations shown after repeated mTBI resemble several of the deficits or disturbances reported by patients, thus demonstrating the relevance of this murine model to study repeated mTBIs.

NF-κB mediates Gadd45ß expression and DNA demethylation in the hippocampus during fear memory formation.

Gadd45-mediated DNA demethylation mechanisms have been implicated in the process of memory formation. However, the transcriptional mechanisms involved in the regulation of Gadd45 gene expression during memory formation remain unexplored. NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) controls transcription of genes in neurons and is a critical regulator of synaptic plasticity and memory formation. In silico analysis revealed several NF-κB (p65/RelA and cRel) consensus sequences within the Gadd45ß gene promoter. Whether NF-κB activity regulates Gadd45 expression and associated DNA demethylation in neurons during memory formation is unknown. Here, we found that learning in a fear conditioning paradigm increased Gadd45ß gene expression and brain-derivedneurotrophic factor (BDNF) DNA demethylation in area CA1 of the hippocampus, both of which were prevented with pharmacological inhibition of NF-κB activity. Further experiments found that conditional mutations in p65/RelA impaired fear memory formation but did not alter changes in Gadd45ß expression. The learning-induced increases in Gadd45ß mRNA levels, Gadd45ß binding at the BDNF gene and BDNF DNA demethylation were blocked in area CA1 of the c-rel knockout mice. Additionally, local siRNA-mediated knockdown of c-rel in area CA1 prevented fear conditioning-induced increases in Gadd45ß expression and BDNF DNA demethylation, suggesting that c-Rel containing NF-κB transcription factor complex is responsible for Gadd45ß regulation during memory formation. Together, these results support a novel transcriptional role for NF-κB in regulation of Gadd45ß expression and DNA demethylation in hippocampal neurons during fear memory.