Brain-derived neurotrophic factor administration after traumatic brain injury in the rat does not protect against behavioral or histological deficits

A molecular description of brain trauma pathophysiology using microarray technology: an overview

It has been estimated that 50% of human transcriptome, the collection of mRNA in a cell, is expressed in the brain, making it one of the most complex organs to understand in terms of genomic responses to injury. The availability of genome sequences for several organisms coupled with the increasing affordability of microarray technologies makes it feasible to monitor the mRNA levels of thousands of genes simultaneously. In this paper, we provide an overview of findings using both cDNA- and oligonucleotide-based microarray analyses after experimental traumatic brain injury (TBI). Specifically, the utility of this methodology as a means of cataloging the biochemical sequelae of brain trauma and elucidating novel genes or pathways for further study is discussed. Furthermore, we offer future directions for the continued evaluation of microarray results and discuss the usefulness of microarray techniques as a testing format for determining the efficacy of mechanism-based therapies.

Intravenous Administration of Marrow Stromal Cells (MSCs) Increases the Expression of Growth Factors in Rat Brain after Traumatic Brain Injury

This study was designed to investigate the effects of intravenous administration of marrow stromal cells (MSCs) on the expression of growth factors in rat brain after traumatic brain injury (TBI). The fate of transplanted MSCs and expression of growth factors was examined by immunohistochemistry. In addition, the level of growth factors was measured quantitatively using enzyme linked immunosorbent assay (ELISA). Growth factors that were studied included nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and basic fibroblast growth factor (bFGF). For immunohistochemical studies, 12 male Wistar rats were subjected to TBI and then divided into three groups with the first group receiving no treatment, the second group receiving saline (placebo) and the third group receiving MSCs intravenously 1 day after TBI. The neurological function of rats was studied by using Rotarod motor test and modified neurological severity scores. The animals were sacrificed 15 days after TBI and brain sections stained by immunohistochemistry to study the distribution of MSCs as well as expression of growth factors NGF, BDNF, and bFGF. For quantitative analysis, a second set of male Wistar rats (n = 18) was subjected to TBI and then injected with either saline (n = 9) or MSCs (n = 9) 1 day after injury. These rats were sacrificed on days 2, 5, and 8 after TBI and brain extracts used to measure NGF, BDNF, and bFGF. We found that after transplantation, MSCs preferentially migrated into the injured hemisphere and there was a statistically significant improvement in the functional outcome of MSC-treated rats compared to control rats. NGF, BDNF, and bFGF were expressed in the injured brain of both treated as well as control rats; however, quantitative ELISA studies showed that expression of NGF and BDNF was significantly increased (p < 0.05) in the treated group. This study shows that intravenous administration of MSCs after TBI increases the expression of growth factors (NGF, BDNF), which possibly contributes to the improvement in functional outcome seen in these rats.

Voluntary exercise following traumatic brain injury: brain-derived neurotrophic factor upregulation and recovery of function

Voluntary exercise leads to an upregulation of brain-derived neurotrophic factor (BDNF) and associated proteins involved in synaptic function. Activity-induced enhancement of neuroplasticity may be considered for the treatment of traumatic brain injury (TBI). Given that during the first postinjury week the brain is undergoing dynamic restorative processes and energetic changes that may influence the outcome of exercise, we evaluated the effects of acute and delayed exercise following experimental TBI. Male Sprague-Dawley rats underwent either sham or lateral fluid-percussion injury (FPI) and were housed with or without access to a running wheel (RW) from postinjury days 0-6 (acute) or 14-20 (delayed). FPI alone resulted in significantly elevated levels of hippocampal phosphorylated synapsin I and phosphorylated cyclic AMP response element-binding-protein (CREB) at postinjury day 7, of which phosphorylated CREB remained elevated at postinjury day 21. Sham and delayed FPI-RW rats showed increased levels of BDNF, following exercise. Exercise also increased phosphorylated synapsin I and CREB in sham rats. In contrast to shams, the acutely exercised FPI rats failed to show activity-dependent BDNF upregulation and had significant decreases of phosphorylated synapsin I and total CREB. Additional rats were cognitively assessed (learning acquisition and memory) by utilizing the Morris water maze after acute or delayed RW exposure. Shams and delayed FPI-RW animals benefited from exercise, as indicated by a significant decrease in the number of trials to criterion (ability to locate the platform in 7 s or less for four consecutive trials), compared with the delayed FPI-sedentary rats. In contrast, cognitive performance in the acute FPI-RW rats was significantly impaired compared with all the other groups. These results suggest that voluntary exercise can endogenously upregulate BDNF and enhance recovery when it is delayed after TBI. However, when exercise is administered to soon after TBI, the molecular response to exercise is disrupted and recovery may be delayed.

Elevated GDNF levels following viral vector-mediated gene transfer can increase neuronal death after stroke in rats

Previous studies have indicated that administration of glial cell line-derived neurotrophic factor (GDNF) counteracts neuronal death after stroke. However, in these studies damage was evaluated at most a few days after the insult. Here, we have explored the long-term consequences of two routes of GDNF delivery to the rat striatum prior to stroke induced by 30 min of middle cerebral artery occlusion (MCAO): striatal transduction with a recombinant lentiviral vector or transduction of the substantia nigra with a recombinant adeno-associated viral vector and subsequent anterograde transport of GDNF to striatum. Despite high GDNF levels, stereological quantification of striatal neuron numbers revealed no protection at 5 or 8 weeks after MCAO. In fact, anterograde GDNF delivery exacerbated neuronal loss. Moreover, supply of GDNF did not alleviate the striatum-related behavioral deficits. Thus, we demonstrate that the actions of GDNF after stroke are more complex than previously believed and that high levels of this factor, which are neuroprotective in models of Parkinson's disease, can increase ischemic damage. Our findings also underscore the need for quantitative assessment of long-term neuronal survival and behavioral changes to evaluate the therapeutic potential of factors such as GDNF.

Continuous low-dose treatment with brain-derived neurotrophic factor or neurotrophin-3 protects striatal medium spiny neurons from mild neonatal hypoxia/ischemia: a stereological study

This study aimed to investigate whether continuous, low-dose, intracerebral infusion of either brain-derived neurotrophic factor (BDNF) or neurotrophin-3 (NT-3) could protect against striatal neuronal loss in mild neonatal hypoxic/ischaemic brain injury. Continuous, low-dose, intracerebral treatment is likely to minimise unwanted side effects of a single high dose and lengthen the time window for neuroprotection. A milder, albeit brain damage-inducing, hypoxic/ischaemic injury paradigm was used since this situation is likely to produce the highest survival rates and thus the greatest prevalence. Anaesthetised postnatal day 7 rats were each stereotaxically implanted with a brain infusion kit connected to a micro-osmotic pump. The pump continuously infused either BDNF (4.5 microg/day), NT-3 (12 microg/day), or vehicle solution into the right striatum for 3 days from postnatal day 7. The intrastriatal presence of BDNF or NT-3 was verified immunohistochemically. On postnatal day 8, the rats underwent right common carotid artery ligation followed by hypoxic exposure for 1.5 h. Animals were weighed daily thereafter and killed 1 week later on postnatal day 14. The total number of medium spiny neurons within the right striatum was stereologically determined using an optical disector/Cavalieri combination. Other measures of neuroprotection such as brain weight and striatal infarct volume were also undertaken. BDNF or NT-3 significantly increased the total number of surviving medium spiny neurons by 43% and 33% respectively. This significant neuroprotection was not evident when brain weight, striatal volume, striatal infarct volume, and neuronal density measures for NT-3, were compared. These measures therefore missed the protective effect demonstrated by the total neuronal count. This suggests that stereological measurement of total neuronal number is needed to detect neuroprotection at 1 week after low-dose, continuously infused, neurotrophin treatment and mild hypoxic/ischaemic injury. The results also suggest that lower treatment doses may be more useful than previously thought. BDNF may be particularly useful since it fostered both neuroprotection and normal weight gain. The ability to rescue striatal neurons from death may contribute toward a potential short-term, low-dose neurotrophin treatment for mild perinatal hypoxic/ischaemic brain injury in humans.

Fluoxetine's effects on cognitive performance in patients with traumatic brain injury

OBJECTIVE

There are preclinical data showing that fluoxetine stimulated expression of Brain Derived Neurotrophic Factor (BDNF) and its specific tyrosine kinase receptor, and caused neuritic elongation and increased dendritic branching density of CA3 hippocampal pyramidal cell neurons in rodents. The latter effect of fluoxetine has been referred to as neuronal remodeling. In view of this preclinical data, we wondered if specific cognitive measures could serve as novel therapeutic targets for fluoxetine in head-injured patients. Theoretically, fluoxetine-induced "neuronal remodeling" might improve cognition, independently of a primary effect on mood.

METHOD

In an open-label pilot investigation, fluoxetine hydrochloride (Prozac; 20-60 mg/day) was administered to a heterogeneous group of five head-injured patients with either no or moderate depression for a period of eight months. These patients had no histories of prior treatment with antidepressant medications. They were administered cognitive and memory tests at baseline and after eight months of treatment on fluoxetine.

RESULTS

The preliminary results showed that fluoxetine improved mood, in addition to improving performance on the Trail Making Test Part A, an attentional-motor speed task, and the letter-number sequencing subtest of the WAIS-III, a measure reflecting "working memory."

CONCLUSIONS

Although fluoxetine had beneficial effects on some measures of cognition, more work is needed to connect these improvements with neuronal remodeling.

Biologic Transplantation and Neurotrophin-Induced Neuroplasticity After Traumatic Brain Injury

OBJECTIVE

In this review, we analyze progress in the treatment of traumatic brain injury with neurotrophins, growth factors and cell and tissue neurotransplantation. The primary objective of these therapies is to reduce neurologic deficits associated with the trauma by inducing neuroplasticity. These therapies are restorative and not necessarily neuroprotective.

MAIN OUTCOME MEASURES

An extensive literature on administration of neurotrophics factors and cell and tissue cerebral transplantation is reviewed. The effects of these therapeutic approaches on brain biochemical, molecular, cellular, and tissue responses are summarized.

CONCLUSION

The cumulative data indicate that cell therapy shows substantial promise in the treatment of neural injury.

Environmental enrichment attenuates cognitive deficits, but does not alter neurotrophin gene expression in the hippocampus following lateral fluid percussion brain injury

Environmental enrichment attenuates neurological deficits associated with experimental brain injury. The molecular events that mediate these environmentally induced improvements in function after injury are largely unknown, but neurotrophins have been hypothesized to be a neural substrate because of their role in cell survival and neural plasticity. Furthermore, exposure to complex environments in normal animals increases neurotrophin gene expression. However, following an ischemic injury, environmental enrichment decreases neurotrophin mRNA levels. Whether these contrasting findings are attributable to differences between injured and uninjured animals or are dependent upon the specific type of brain injury has not been determined. We examined the effects of 14 days of environmental enrichment following a lateral fluid percussion brain injury on behavior and gene expression of brain-derived neurotrophic factor, its high-affinity receptor, TrkB, and neurotrophin-3 in the rat hippocampus. Environmental enrichment attenuated learning deficits in the injured animals, but neither the injury nor housing conditions influenced neurotrophin/receptor mRNA levels. From these data we suggest that following brain trauma, improvements in learning associated with environmental enrichment are not mediated by alterations in brain-derived neurotrophic factor, TrkB or neurotrophin-3 gene expression.

Vaccinia virus complement control protein enhances functional recovery after traumatic brain injury

Inflammation is a major contributor to the neuropathological consequences of traumatic brain injury (TBI). Previous studies have shown that proinflammatory complement activation fragments are present in the injured brain within the first 24 h after trauma. To investigate whether complement activation within the injured brain leads to the neuropathology and subsequent functional impairment associated with TBI, we examined what effect administration of a complement inhibitor, the vaccinia virus complement control protein (VCP), would have on spatial learning and memory in brain injured rats, as measured using the Morris Water Maze (MWM) procedure. Animals were subjected to a lateral fluid percussion brain injury of moderate severity and, 15 min later, received a 10-microL injection of either full-length VCP, a truncated version of VCP (VCPt), which lacks the complement inhibitory activity but retains the heparin binding activity of VCP, or saline directly into the cortex. Results of such intervention indicated that, at 2 weeks postinjury, both VCP and VCPt treatment attenuated impairments in spatial memory, but not neuropathological damage, as compared to the saline treated controls. These results were surprising and suggest that the neuroprotective effects following administration of VCP after acute brain injury are mediated by mechanisms other than complement inhibition. Potential mechanisms are discussed.

High-density microarray analysis of hippocampal gene expression following experimental brain injury

Behavioral, biophysical, and pharmacological studies have implicated the hippocampus in the formation and storage of spatial memory. Traumatic brain injury (TBI) often causes spatial memory deficits, which are thought to arise from the death as well as the dysfunction of hippocampal neurons. Cell death and dysfunction are commonly associated with and often caused by altered expression of specific genes. The identification of the genes involved in these processes, as well as those participating in postinjury cellular repair and plasticity, is important for the development of mechanism-based therapies. To monitor the expression levels of a large number of genes and to identify genes not previously implicated in TBI pathophysiology, a high-density oligonucleotide array containing 8,800 genes was interrogated. RNA samples were prepared from ipsilateral hippocampi 3 hr and 24 hr following lateral cortical impact injury and compared to samples from sham-operated controls. Cluster analysis was employed using statistical algorithms to arrange the genes according to similarity in patterns of expression. The study indicates that the genomic response to TBI is complex, affecting approximately 6% (at the time points examined) of the total number of genes examined. The identity of the genes revealed that TBI affects many aspects of cell physiology, including oxidative stress, metabolism, inflammation, structural changes, and cellular signaling. The analysis revealed genes whose expression levels have been reported to be altered in response to injury as well as several genes not previously implicated in TBI pathophysiology.

The selective 5-HT(1A) receptor agonist repinotan HCl attenuates histopathology and spatial learning deficits following traumatic brain injury in rats

The selective 5-HT(1A) receptor agonist Repinotan HCl (BAY x3702) has been reported to attenuate cortical damage and improve functional performance in experimental models of cerebral ischemia and acute subdural hematoma. Using a clinically relevant contusion model of traumatic brain injury, we tested the hypothesis that a 4-h continuous infusion of Repinotan HCl (10 microg/kg/h i.v.) commencing 5 min post-injury would ameliorate functional outcome and attenuate histopathology. Forty isoflurane-anesthetized male adult rats were randomly assigned to receive either a controlled cortical impact (2.7 mm tissue deformation, 4 m/s) or sham injury (Injury/Vehicle=10, Injury/MK-801=10, Injury/Repinotan HCl=10, Sham/Vehicle=10), then tested for vestibulomotor function on post-operative days 1-5 and for spatial learning on days 14-18. Neither Repinotan HCl nor the non-competitive N-methyl-D-aspartate receptor antagonist MK-801, which served as a positive control, improved vestibulomotor function on beam balance and beam walk tasks relative to the Injury/Vehicle group, but both did significantly attenuate spatial learning and memory deficits on a water maze task. Repinotan HCl also reduced hippocampal CA(1) and CA(3) neuronal loss, as well as cortical tissue damage, compared to the Injury/Vehicle group at 4 weeks post-trauma. No significant difference in histological outcome was revealed between the Repinotan HCl- and MK-801-treated groups.These findings extend the therapeutic efficacy of Repinotan HCl to a contusion model of experimental brain injury and demonstrate for the first time that 5-HT(1A) receptor agonists confer neuroprotection and attenuate spatial learning deficits following controlled cortical impact injury. This treatment strategy may be beneficial in a clinical context where memory impairments are common following human traumatic brain injury.

Traumatic brain injury alters the molecular fingerprint of TUNEL-positive cortical neurons In vivo: A single-cell analysis

The cerebral cortex is selectively vulnerable to cell death after traumatic brain injury (TBI). We hypothesized that the ratio of mRNAs encoding proteins important for cell survival and/or cell death is altered in individual damaged neurons after injury that may contribute to the cell's fate. To investigate this possibility, we used amplified antisense mRNA (aRNA) amplification to examine the relative abundance of 31 selected candidate mRNAs in individual cortical neurons with fragmented DNA at 12 or 24 hr after lateral fluid percussion brain injury in anesthetized rats. Only pyramidal neurons characterized by nuclear terminal deoxynucleotidyl transferase-mediated biotinylated dUTP nick end labeling (TUNEL) reactivity with little cytoplasmic staining were analyzed. For controls, non-TUNEL-positive neurons from the cortex of sham-injured animals were obtained and subjected to aRNA amplification. At 12 hr after injury, injured neurons exhibited a decrease in the relative abundance of specific mRNAs including those encoding for endogenous neuroprotective proteins. By 24 hr after injury, many of the mRNAs altered at 12 hr after injury had returned to baseline (sham-injured) levels except for increases in caspase-2 and bax mRNAs. These data suggest that TBI induces a temporal and selective alteration in the gene expression profiles or "molecular fingerprints" of TUNEL-positive neurons in the cerebral cortex. These patterns of gene expression may provide information about the molecular basis of cell death in this region after TBI and may suggest multiple avenues for therapeutic intervention.