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Traumatic brain injury (TBI) in children younger than 4 years old results in cognitive and psychosocial deficits in adolescence and adulthood. At 4 weeks following closed head injury on postnatal day 11, male and female rats exhibited impairment in novel object recognition memory (NOR) along with an increase in open arm time in the elevated plus maze (EPM), suggestive of risk-taking behaviors. This was accompanied by an increase in intrinsic excitability and frequency of spontaneous excitatory post-synaptic currents (EPSCs), and a decrease in the frequency of spontaneous inhibitory post-synaptic currents in layer 2/3 neurons within the medial prefrontal cortex (PFC), a region that is implicated in both object recognition and risk-taking behaviors. Treatment with progesterone for the first week after brain injury improved NOR memory at the 4-week time point in both sham and brain-injured rats and additionally attenuated the injury-induced increase in the excitability of neurons and the frequency of spontaneous EPSCs. The effect of progesterone on cellular excitability changes after injury may be related to its ability to decrease the mRNA expression of the β3 subunit of the voltage-gated sodium channel and increase the expression of the neuronal excitatory amino acid transporter 3 in the medial PFC in sham- and brain-injured animals and also increase glutamic acid decarboxylase mRNA expression in sham- but not brain-injured animals. Progesterone treatment did not affect injury-induced changes in the EPM test. These results demonstrate that administration of progesterone immediately after TBI in 11-day-old rats reduces cognitive deficits in adolescence, which may be mediated by progesterone-mediated regulation of excitatory signaling mechanisms within the medial PFC., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Concussive brain injury (CBI) accounts for approximately 75% of all brain-injured people in the United States each year and is particularly prevalent in contact sports. Concussion is the mildest form of diffuse traumatic brain injury (TBI) and results in transient cognitive dysfunction, the neuropathologic basis for which is traumatic axonal injury (TAI). To evaluate the structural and functional changes associated with concussion-induced cognitive deficits, adult mice were subjected to an impact on the intact skull over the midline suture that resulted in a brief apneic period and loss of the righting reflex. Closed head injury also resulted in an increase in the wet weight:dry weight ratio in the cortex suggestive of edema in the first 24 h, and the appearance of Fluoro-Jade-B-labeled degenerating neurons in the cortex and dentate gyrus of the hippocampus within the first 3 days post-injury. Compared to sham-injured mice, brain-injured mice exhibited significant deficits in spatial acquisition and working memory as measured using the Morris water maze over the first 3 days (p<0.001), but not after the fourth day post-injury. At 1 and 3 days post-injury, intra-axonal accumulation of amyloid precursor protein in the corpus callosum and cingulum was accompanied by neurofilament dephosphorylation, impaired transport of Fluoro-Gold and synaptophysin, and deficits in axonal conductance. Importantly, deficits in retrograde transport and in action potential of myelinated axons continued to be observed until 14 days post-injury, at which time axonal degeneration was apparent. These data suggest that despite recovery from acute cognitive deficits, concussive brain trauma leads to axonal degeneration and a sustained perturbation of axonal function.

Deletion of the tumor suppressor gene p53 has been shown to improve the outcome in experimental models of focal cerebral ischemia and kainate-induced seizures. To evaluate the potential role of p53 in traumatic brain injury, genetically modified mice lacking a functional p53 gene (p53(-/-), n = 9) and their wild-type littermates (p53(+/+), n = 9) were anesthetized and subjected to controlled cortical impact (CCI) experimental brain trauma. After brain injury, neuromotor function was assessed by using composite neuroscore and rotarod tests. By 7 days posttrauma, p53(-/-) mice exhibited significantly improved neuromotor function, in the composite neuroscore (P = 0.002) as well as in two of three individual tests, when compared with brain-injured p53(+/+) animals. CCI resulted in the formation of a cortical cavity (mean volume = 6.1 mm(3)) 7 days postinjury in p53(+/+) as well as p53(-/-) mice. No difference in lesion volume was detected between the two genotypes (P = 0.95). Although significant cell loss was detected in the ipsilateral hippocampus and thalamus of brain-injured animals, no differences between p53(+/+) and p53(-/-) mice were detected. Although our results suggest that lack of the p53 gene results in augmented recovery of neuromotor function following experimental brain trauma, they do not support a role for p53 acting as a mediator of neuronal death in this context, underscoring the complexity of its role in the injured brain.

Purpose: The ability of brain-derived neurotrophic factor (BDNF) to attenuate secondary damage and influence behavioral outcome after experimental traumatic brain injury (TBI) remains controversial. Because TBI can result in decreased expression of the trkB receptor, thereby preventing BDNF from exerting potential neuroprotective effects, the contribution of both BDNF and its receptor trkB to hippocampal neuronal loss and cognitive dysfunction were evaluated., Methods: Full-length trkB was overexpressed in the left hippocampus of adult C57Bl/6 mice using recombinant adeno-associated virus serotype 2/5 (rAAV 2/5). EGFP (enhanced green fluorescent protein) expression was present at two weeks after AAV-EGFP injection and remained sustained up to four weeks after the injection. At 2 weeks following gene transduction, mice were subjected to parasagittal controlled cortical impact (CCI) brain injury, followed by either BDNF or PBS infusion into the hippocampus., Results: No differences were observed in learning ability at two weeks post-injury or in motor function from 48 hours to two weeks among treatment groups. The number of surviving pyramidal neurons in the CA2-CA3 region of the hippocampus was also not different among treatment groups., Conclusions: These data suggest that neither overexpression of trkB, BNDF infusion or their combination affects neuronal survival or behavioral outcome following experimental TBI in mice.

Infusion of nerve growth factor (NGF) has been shown to be neuroprotective following traumatic brain injury (TBI). In this study, we tested the hypothesis that NGF-expressing human NT2N neurons transplanted into the basal forebrain of brain-injured mice can attenuate long-term cognitive dysfunction associated with TBI. Undifferentiated NT2 cells were transduced in vitro with a lentiviral vector to release NGF, differentiated into NT2N neurons by exposure to retinoic acid and transplanted into the medial septum of mice 24 h following controlled cortical impact (CCI) brain injury or sham injury. Adult mice (n = 78) were randomly assigned to one of four groups: (1) sham-injured and vehicle (serum-free medium)-treated, (2) brain-injured and vehicle-treated, (3) brain-injured engrafted with untransduced NT2N neurons, and (4) brain-injured engrafted with transduced NGF-NT2N neurons. All groups were immunosuppressed daily with cyclosporin A (CsA) for 4 weeks. At 1 month post-transplantation, animals engrafted with NGF-expressing NT2N neurons showed significantly improved learning ability (evaluated with the Morris water maze) compared to brain-injured mice receiving either vehicle (p < 0.05) or untransduced NT2N neurons (p < 0.01). No effect of NGF-secreting NT2N cells on motor function deficits at 1-4 weeks post-transplantation was observed. These data suggest that NGF gene therapy using transduced NT2N neurons (as a source of delivery) may selectively improve cognitive function following TBI.

In an effort to understand the complexity of genomic responses within selectively vulnerable regions after experimental brain injury, we examined whether single apoptotic neurons from both the CA3 and dentate differed from those in an uninjured brain. The mRNA from individual active caspase 3(+)/terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling [TUNEL(-)] and active caspase 3(+)/TUNEL(+) pyramidal and granule neurons in brain-injured mice were amplified and compared with those from nonlabeled neurons in uninjured brains. Gene analysis revealed that overall expression of mRNAs increased with activation of caspase 3 and decreased to below uninjured levels with TUNEL reactivity. Cell type specificity of the apoptotic response was observed with both regionally distinct expression of mRNAs and differences in those mRNAs that were maximally regulated. Immunohistochemical analysis for two of the most highly differentially expressed genes (prion and Sos2) demonstrated a correlation between the observed differential gene expression after traumatic brain injury and corresponding protein translation.

Cell death/survival following CNS injury may be a result of alterations in the intracellular ratio of death and survival factors. Using immunohistochemistry, Western analysis and in situ hybridization, the expression of the anti-cell death protein, Bcl-2, and the pro-cell death protein, Bax, was evaluated following lateral fluid-percussion (FP) brain injury of moderate severity (2.3-2.6 atm) in adult male Sprague-Dawley rats. By 2 h post-injury, a marked reduction of cellular Bcl-2-immunoreactivity (IR) and a mild decrease in cellular Bax IR were observed in the temporal and occipital cortices, and in the hippocampal CA3 ipsilateral to the site of impact. These decreases in Bcl-2 and Bax IR appeared to precede the overt cell loss in these regions that was evident at 24 h. Immunoblot analysis supported the immunohistochemical data, with a modest but significant reduction in the intensities of both the Bcl-2 and Bax protein bands at 2 h (p < 0.05 compared to sham levels). However, the Bax:Bcl-2 ratio increased significantly at 2 h (2.28 +/- 0.13) and remained elevated up to 7 days (2.05 +/- 0.13) post-injury compared to sham-injured control tissue (1.62 +/- 0.10, p < 0.05). Furthermore, cortical, but not hippocampal, levels of Bax protein increased by 25% (p < 0.05 compared to sham-injured controls) at 24 h post-injury, and returned to control levels by 7 days. In situ hybridization analysis of Bax mRNA revealed increased cellular grain density in the injured cortex (p < 0.05 compared to sham-injured brains), but not in the CA3 region of the injured hippocampus. No injury-induced changes in the expression of Bcl-2 mRNA were observed in any brain region. Taken together, these data suggest that the association between regional post-traumatic cell death and alterations in the cellular ratio of Bcl-2 and Bax may be, in part, due to alterations in mRNA and/or protein expression of the Bcl-2 family of proteins.

Objective: Using the neural stem cell (NSC) clone C17.2, we evaluated the ability of transplanted murine NSCs to attenuate cognitive and neurological motor deficits after traumatic brain injury., Methods: Nonimmunosuppressed C57BL/6 mice (n = 65) were anesthetized and subjected to lateral controlled cortical impact brain injury (n = 52) or surgery without injury (sham operation group, n = 13). At 3 days postinjury, all brain-injured animals were reanesthetized and randomized to receive stereotactic injection of NSCs or control cells (human embryonic kidney cells) into the cortex-hippocampus interface in either the ipsilateral or the contralateral hemisphere. One group of animals (n = 7) was killed at either 1 or 3 weeks postinjury to assess NSC survival in the acute posttraumatic period. Motor function was evaluated at weekly intervals for 12 weeks in the remaining animals, and cognitive (i.e., learning) deficits were assessed at 3 and 12 weeks after transplantation., Results: Brain-injured animals that received either ipsilateral or contralateral NSC transplants showed significantly improved motor function in selected tests as compared with human embryonic kidney cell-transplanted animals during the 12-week observation period. Cognitive dysfunction was unaffected by transplantation at either 3 or 12 weeks postinjury. Histological analyses showed that NSCs survive for as long as 13 weeks after transplantation and were detected in the hippocampus and/or cortical areas adjacent to the injury cavity. At 13 weeks, the NSCs transplanted ipsilateral to the impact site expressed neuronal (NeuN) or astrocytic (glial fibrillary acidic protein) markers but not markers of oligodendrocytes (2'3'cyclic nucleotide 3'-phosphodiesterase), whereas the contralaterally transplanted NSCs expressed neuronal but not glial markers (double-labeled immunofluorescence and confocal microscopy)., Conclusion: These data suggest that transplanted NSCs can survive in the traumatically injured brain, differentiate into neurons and/or glia, and attenuate motor dysfunction after traumatic brain injury.

Using the terminal deoxynucleotidyl transferase-mediated biotinylated deoxyuridine triphosphate nick-end labelling (TUNEL) histochemical technique, evidence for DNA fragmentation was sought in the hippocampus, cingulate gyrus and insula from 18 patients who survived for up to 12 months after head injury, and 15 matched controls. Both conventional (haematoxylin and eosin and Luxol-fast blue/cresyl violet) and immunohistochemical (glial fibrillary acidic protein, CD68) staining techniques were used to identify the cellular response and its time course in the regions of interest. Only the occasional TUNEL-positive (+) cell/unit area was seen in any area of the control brains. In contrast there were more TUNEL+ cells/unit area in the injured brains. TUNEL+ cells were present in white matter and their average numbers ranged from three to five per unit area for up to 3 months survival in the extreme capsule and the parasagittal white matter, with similar numbers in the hippocampus, and between two and three per unit area in the parasagittal white matter and hippocampus of the cases surviving up to 12 months post injury. Between one and two TUNEL+ cells/unit area were also seen in grey matter, of which most appeared as neurones. About 5% of the TUNEL+ cells in white matter had the morphological features of apoptosis: the corresponding figure in grey matter was less than 1%. In many instances the TUNEL+ cells were also CD68+ and appeared by light microscopy to be macrophages. It was concluded that, as reflected by TUNEL histochemistry, long-term DNA fragmentation is present in white matter after traumatic brain injury in man. [ABSTRACT FROM AUTHOR]

Abstract: This study sought to determine the role of the transcription factor E2F1 in CXCR4-mediated neurotoxicity and HIV neuropathology. We studied the effect of the HIV envelope protein gp120 on the expression of E2F1-dependent apoptotic proteins in human and rodent neurons and examined the expression pattern of E2F1 in the brain of HIV-infected individuals. Our findings suggest that in cultured neurons gp120 increased E2F1 levels in the nucleus, stimulated its transcriptional activity and enhanced the expression of the E2F1 target proteins Cdc2 and Puma. Studies with neuronal cultures from E2F1 deficient mice demonstrated that the transcription factor is required for gp120-induced neurotoxicity and up-regulation of Cdc2 and Puma. Levels of E2F1 protein were greater in the nucleus of neurons in brains of HIV-infected patients exhibiting dementia when compared to HIV-negative subjects or HIV-positive neurologically normal patients. Overall, these studies indicate that E2F1 is primarily involved in CXCR4-mediated neurotoxicity and HIV neuropathogenesis. [Copyright &y& Elsevier]