Cognitive deficits following traumatic brain injury produced by controlled cortical impact

Quetiapine attenuates spatial memory impairment and hippocampal neurodegeneration induced by bilateral common carotid artery occlusion in mice

Quetiapine, a new atypical antipsychotic drug, has beneficial effects on cognitive impairment and neuropathological changes in treating chronic neurodegenerative diseases. Our previous studies have demonstrated that quetiapine may have neuroprotective properties. In the present study, we investigated the effects of a 2-week pre-administration of quetiapine (10 mg/kg/day, i.p.) on spatial memory impairment and hippocampal neurodegeneration induced by 60-minute bilateral common carotid artery occlusion (CCAO). Following a 7-day recovery phase from CCAO, the spatial memory of the mice was tested using a modified water maze test. After the behavioural test, the mice were sacrificed and brain sections were stained with NeuN (a neuron-specific soluble nuclear antigen), cresyl violet (Nissl), and Fluoro-Jade B. CCAO significantly induced spatial memory impairment and caused neurodegeneration in the hilus of hippocampus, while quetiapine significantly attenuated these changes. This is the first study showing that quetiapine significantly attenuates CCAO-induced spatial memory impairment and this improvement parallels the alleviative effects of quetiapine on CCAO-induced neurodegeneration in the hilus of hippocampus. The results suggest that quetiapine may have defending effects on the impairments induced by cerebral ischemia, which enhances our understanding about the mechanisms of quetiapine.

Differential effects of single versus multiple administrations of haloperidol and risperidone on functional outcome after experimental brain trauma

OBJECTIVES

Antipsychotics are routinely administered to patients with traumatic brain injury, even though the benefits vs. risks of this approach on behavioral recovery are unclear. To clarify the issue, the present study evaluated the effect of single and multiple administrations of haloperidol and risperidone on functional outcome after traumatic brain injury.

DESIGN

Prospective and randomized study in rodents.

SETTING

Experimental research laboratory at the University of Pittsburgh.

SUBJECTS

A total of 60 adult male Sprague-Dawley rats weighing 300-325 g.

INTERVENTIONS

Anesthetized rats received either a cortical impact or sham injury and then were randomly assigned to five traumatic brain injury groups (0.045 mg/kg, 0.45 mg/kg, or 4.5 mg/kg risperidone; 0.5 mg/kg haloperidol; or 1 mL/kg vehicle) or three sham groups (4.5 mg/kg risperidone, 0.5 mg/kg haloperidol, or 1 mL/kg vehicle). The experiment consisted of three phases. In the first phase, a single treatment was provided (intraperitoneally) 24 hrs after surgery, and motor and cognitive function was assessed on postoperative days 1-5 and 14-18, respectively. During the second phase, after completion of the initial behavioral tasks, the same rats were treated once daily for 5 days and behavior was reevaluated. During the third phase, treatments were discontinued, and 3 days later, the rats were assessed one final time.

MEASUREMENTS AND MAIN RESULTS

Time (seconds) to maintain beam balance, traverse an elevated beam, and to locate a submerged platform in a Morris water maze was recorded. Neither motor nor cognitive performance was affected after a single treatment, regardless of group assignment (p > .05). In contrast, both behavioral deficits reoccurred after daily treatments of risperidone (4.5 mg/kg) and haloperidol (p < .05). The cognitive deficits persisted even after a 3-day washout period during the third phase.

CONCLUSIONS

These data suggest that although single or multiple low doses of risperidone and haloperidol may be innocuous to subsequent recovery after traumatic brain injury, chronic high-dose treatments are detrimental.

Gender associations with chronic methylphenidate treatment and behavioral performance following experimental traumatic brain injury

Evidence suggests that dopamine (DA) agonists improve cognition after traumatic brain injury (TBI). Methylphenidate (MPH) is a DA agonist that blocks the dopamine transporter (DAT). Moreover, female sex hormones modulate DAT expression. Therefore, the purpose of this study was to evaluate how MPH affects behavioral performance in male and female rats. Under anesthesia, rats underwent either controlled cortical impact (CCI) or sham injury operations. Beginning post-operative day 1, rats received daily intraperitoneal injections of MPH (5mg/kg) or saline. Beam balance (BB) and beam-walking (BW) were assessed on post-operative days 1-5. Exploratory behavior was assessed using an open field free choice novelty (FCN) task on day 13. Spatial memory was assessed with a Morris water maze (MWM) task on days 14-20. Multivariate analyses showed TBI females performed better than TBI males on both motor tasks (P<0.05 both comparisons), and MPH improved BB performance for both male and female injury groups (P=0.05) compared to their respective vehicle treated injury groups. Multivariate analysis showed that MPH enhanced MWM performance (spatial learning and retention) after TBI. Significant improvements were noted only in injured males treated with MPH compared to their vehicle control (P<0.05) with respect to improvements in memory acquisition and retention. Further, injured females treated with MPH had faster swimming speeds than all other groups (P<0.05 all comparisons), and MPH increased activity in TBI females but not males in the FCN task (P<0.05). These results suggest that MPH is beneficial after TBI. However there are gender specific drug differences in behavioral performance and sensitivity to treatment with MPH that may have implications for treatment efficacy and dosing clinically after TBI.

The neurobehavioral benefit conferred by a single systemic administration of 8-OH-DPAT after brain trauma is confined to a narrow therapeutic window

The 5-HT(1A) receptor agonist 8-OH-DPAT (0.5mg/kg) enhances behavioral recovery when administered 15min after experimental traumatic brain injury (TBI). To determine if benefits are still attainable at clinically relevant times, treatment was delayed 1 and 2h post-TBI and motor/cognitive performance was compared to early (i.e., 15min) administration. No differences were observed among the vehicle and 8-OH-DPAT groups treated at 1 and 2h, but all three were significantly impaired versus early 8-OH-DPAT. The data suggest that an early and narrow critical period exists for the behavioral recovery afforded by a single 8-OH-DPAT treatment paradigm. The critical window corresponds to the well documented TBI-induced glutamate increase, suggesting that 8-OH-DPAT may be conferring neuroprotection by attenuating this acute deleterious surge.

boc-Aspartyl(OMe)-fluoromethylketone attenuates mitochondrial release of cytochrome c and delays brain tissue loss after traumatic brain injury in rats

The pathobiology of traumatic brain injury (TBI) includes activation of multiple caspases followed by cell death with a spectrum of apoptotic phenotypes. There are initiator (e.g. caspase-2, -8, and -9) and effector (e.g. caspase-3 and -7) caspases. Recently, caspase-2 and -8 have been shown to regulate cell death via provoking cytochrome c release from the mitochondria upstream of caspase-9. Here, we show that an intracerebral injection of the pan-caspase inhibitor boc-Aspartyl(OMe)-fluoromethylketone (BAF; 1 micromol) 1 min after TBI in rats reduces caspase-3-like activity, terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) and tissue damage, and cytochrome c release in ipsilateral cortex at 24 h versus vehicle. To investigate whether either caspase-2 and/or caspase-8 activation may contribute to cytochrome release, the effect of BAF treatment on caspase-2 and caspase-8 proteolysis was also examined. boc-aspartyl(OMe)-fluoromethylketone treatment inhibited proteolysis of caspase-2 but not caspase-8 24 h after TBI in rats versus vehicle. However, BAF with or without nerve growth factor (12.5 ng/h x 14 days intracerebrally via osmotic pump) did not result in differences in motor function, Morris water maze performance, hippocampal neuron survival, nor contusion volume at 14 days. These data suggest that BAF treatment reduces acute cell death after TBI by inhibiting mitochondrial release of cytochrome c, possibly via a mechanism involving initiator caspases; however, BAF appears to delay cell death, rather than result in permanent protection.

Acute treatment with the 5-HT(1A) receptor agonist 8-OH-DPAT and chronic environmental enrichment confer neurobehavioral benefit after experimental brain trauma

Acute treatment with the 5-HT(1A) receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) or chronic environmental enrichment (EE) hasten behavioral recovery after experimental traumatic brain injury (TBI). The aim of this study was to determine if combining these interventions would confer additional benefit. Anesthetized adult male rats received either a cortical impact or sham injury followed 15min later by a single intraperitoneal injection of 8-OH-DPAT (0.5mg/kg) or saline vehicle (1.0mL/kg) and then randomly assigned to either enriched or standard (STD) housing. Behavioral assessments were conducted utilizing established motor and cognitive tests on post-injury days 1-5 and 14-18, respectively. Hippocampal CA(1)/CA(3) neurons were quantified at 3 weeks. Both 8-OH-DPAT and EE attenuated CA(3) cell loss. 8-OH-DPAT enhanced spatial learning in a Morris water maze (MWM) as revealed by differences between the TBI+8-OH-DPAT+STD and TBI+VEHICLE+STD groups (P=0.0014). EE improved motor function as demonstrated by reduced time to traverse an elevated narrow beam in both the TBI+8-OH-DPAT+EE and TBI+VEHICLE+EE groups versus the TBI+VEHICLE+STD group (P=0.0007 and 0.0016, respectively). EE also facilitated MWM learning as evidenced by both the TBI+8-OH-DPAT+EE and TBI+VEHICLE+EE groups locating the escape platform quicker than the TBI+VEHICLE+STD group (P's<0.0001). MWM differences were also observed between the TBI+8-OH-DPAT+EE and TBI+8-OH-DPAT+STD groups (P=0.0004) suggesting that EE enhanced the effect of 8-OH-DPAT. However, there was no difference between the TBI+8-OH-DPAT+EE and TBI+VEHICLE+EE groups. These data replicate previous results from our laboratory showing that both a single systemic administration of 8-OH-DPAT and EE improve recovery after TBI and extend those findings by elucidating that the combination of treatments in this particular paradigm did not confer additional benefit. One explanation for the lack of an additive effect is that EE is a very effective treatment and thus there is very little room for 8-OH-DPAT to confer additional statistically significant improvement.

Differential behavioral and histopathological responses to graded cortical impact injury in mice

Controlled cortical impact (CCI) injury, a model of contusive brain injury in humans, is being used with increasing frequency in mice to investigate post-traumatic cell damage and death and to evaluate treatment strategies. Because cellular injury mechanisms and therapeutic approaches may depend on the severity of the initial insult, it is important to utilize a model in which outcomes are sensitive to injury severity. Adult male C57Bl/6 mice were anesthetized and subjected to sham injury (n = 23) or CCI injury at either 0.5 mm (n = 22) or 1.0 mm (n = 22) depth of impact at a velocity of 5 m/sec. At 2 days, brain-injured mice exhibited significant memory (p < 0.05) and motor function (p < 0.001) deficits compared to sham-injured mice; furthermore, mice subjected to an impact of 1.0 mm were significantly more impaired in both outcome measures than those injured at 0.5 mm (p < 0.05). The cortical lesion increased in size between 24 h and 7 days in both injury groups, but was significantly larger in the 1.0 mm group. Hippocampal cell loss was observed in the hilar and CA3 regions in both groups, and in the CA1 and dentate granule cell layers in the 1.0 mm group. Regional patterns of IgG extravasation and reactive astrocytosis were similar in the two injured groups, but changes were more persistent in the 1.0 mm group. Both levels of injury resulted in acute loss of neuronal MAP-2 immunoreactivity in the cortex and sub-region specific changes in the hippocampus. Thus, increasing the depth of impact led to similar structural alterations in neurons, astrocytes and the vasculature, but resulted in greater behavioral deficits and cortical and hippocampal cell death.

Injury severity determines Purkinje cell loss and microglial activation in the cerebellum after cortical contusion injury

Clinical evidence suggests that the cerebellum is damaged after traumatic brain injury (TBI) and experimental studies have validated these observations. We have previously shown cerebellar vulnerability, as demonstrated by Purkinje cell loss and microglial activation, after fluid percussion brain injury. In this study, we examine the effect of graded controlled cortical impact (CCI) injury on the cerebellum in the context of physiologic and anatomical parameters that have been shown by others to be sensitive to injury severity. Adult male rats received mild, moderate, or severe CCI and were euthanized 7 days later. We first validated the severity of the initial injury using physiologic criteria, including apnea and blood pressure, during the immediate postinjury period. Increasing injury severity was associated with an increased incidence of apnea and higher mortality. Severe injury also induced transient hypertension followed by hypotension, while lower grade injuries produced an immediate and sustained hypotension. We next evaluated the pattern of subcortical neuronal loss in response to graded injuries. There was significant neuronal loss in the ipsilateral cortex, hippocampal CA2/CA3, and laterodorsal thalamus that was injury severity-dependent and that paralleled microglial activation. Similarly, there was a distinctive pattern of Purkinje cell loss and microglial activation in the cerebellar vermis that varied with injury severity. Together, these findings emphasize the vulnerability of the cerebellum to TBI. That a selective pattern of Purkinje cell loss occurs regardless of the type of injury suggests a generalized response that is a likely determinant of recovery and a target for therapeutic intervention.

Hippocampal vulnerability following traumatic brain injury: a potential role for neurotrophin-4/5 in pyramidal cell neuroprotection

Traumatic brain injury (TBI) causes selective hippocampal cell death, which is believed to be associated with cognitive impairment observed both in clinical and experimental settings. Although neurotrophin administration has been tested as a strategy to prevent cell death following TBI, the potential neuroprotective role of neurotrophin-4/5 (NT-4/5) in TBI remains unknown. We hypothesized that NT-4/5 would offer neuroprotection for selectively vulnerable hippocampal neurons following TBI. Measurements of NT-4/5 in rats subjected to lateral fluid percussion (LFP) TBI revealed two-threefold increases in the injured cortex and hippocampus in the acute period (1-3 days) following brain injury. Subsequently, the response of NT-4/5 knockout (NT-4/5(-/-)) mice to controlled-cortical impact TBI was investigated. NT-4/5(-/-) mice were more susceptible to selective pyramidal cell loss in Ahmon's corn (CA) subfields of the hippocampus following TBI, and showed impaired motor recovery when compared with their brain-injured wild-type controls (NT-4/5(wt)). Additionally, we show that acute, prolonged administration of recombinant NT-4/5 (5 microg/kg/day) prevented up to 50% of the hippocampal CA pyramidal cell death following LFP TBI in rats. These results suggest that post-traumatic increases in endogenous NT-4/5 may be part of an adaptive neuroprotective response in the injured brain, and that administration of this neurotrophic factor may be useful as a therapeutic strategy following TBI.

Enhanced catecholamine synthesis in the prefrontal cortex after traumatic brain injury: implications for prefrontal dysfunction

Traumatic brain injury (TBI)--induced dysfunction of the prefrontal cortex causes many high-level cognitive deficits, including working memory (WM) dysfunction. WM lies at the core of many high-level functions, yet the cellular and molecular mechanisms underlying its dysfunction are poorly understood. Lesion and pharmacological studies in rodents have implicated the medial prefrontal cortex (mPFC), which includes the prelimbic/infralimbic (PL/IL) cortices, in WM tasks. These studies have shown that optimal levels of catecholamine neurotransmission are critical for normalcy of WM function, suggesting that alterations in their synthesis may play a role in WM dysfunction. Using the cortical impact injury model of traumatic brain injury which reproducibly causes working memory deficits in rodents, we have measured the protein levels and activity of tyrosine hydroxylase (TH), the rate-limiting enzyme for catecholamine biosynthesis, and tissue dopamine (DA) and norepinephrine (NE) levels in microdissected PL/IL tissues. Our results show that TBI increases TH protein levels, its activity and tissue DA and NE content in the PL/IL. These findings suggest that altered catecholamine signaling within the PL/IL may contribute to impaired PFC function, and may have implications in the design and implementation of strategies to alleviate prefrontal dysfunction in brain injury patients.

Relationship of calpain-mediated proteolysis to the expression of axonal and synaptic plasticity markers following traumatic brain injury in mice

The role of neuronal plasticity and repair on the final functional outcome following traumatic brain injury (TBI) remains poorly understood. Moreover, the relationship of the magnitude of post-traumatic secondary injury and neurodegeneration to the potential for neuronal repair has not been explored. To address these questions, we employed Western immunoblotting techniques to examine how injury severity affects the spatial and temporal expression of markers of axonal growth (growth-associated protein GAP-43) and synaptogenesis (pre-synaptic vesicular protein synaptophysin) following either moderate (0.5 mm, 3.5 M/s) or severe (1.0 mm, 3.5 M/s) lateral controlled cortical impact traumatic brain injury (CCI-TBI) in young adult male CF-1 mice. Moderate CCI increased GAP-43 levels at 24 and 48 h post-insult in the ipsilateral hippocampus relative to sham, non-injured animals. This increase in axonal plasticity occurred prior to maximal hippocampal neurodegeneration, as revealed by de Olmos silver staining, at 72 h. However, moderate CCI-TBI did not elevate GAP-43 expression in the ipsilateral cortex where neurodegeneration was extensive by 6 h post-TBI. In contrast to moderate injury, severe CCI-TBI failed to increase hippocampal GAP-43 levels and instead resulted in depressed GAP-43 expression in the ipsilateral hippocampus and cortex at 48 h post-insult. In regards to injury-induced changes in synaptogenesis, we found that moderate CCI-TBI elevated synaptophysin levels in the ipsilateral hippocampus at 24, 48, 72 h and 21 days, but this effect was not present after severe injury. Together, these data highlights the adult brain's ability for axonal and synaptic plasticity following a focal cortical injury, but that severe injuries may diminish these endogenous repair mechanisms. The differential effects of moderate versus severe TBI on the post-traumatic plasticity response may be related to the calpain-mediated proteolytic activity occurring after a severe injury preventing increased expression of proteins required for plasticity. Supporting this hypothesis is the fact that GAP-43 is a substrate for calpain along with our data demonstrating that calpain-mediated degradation of the cytoskeletal protein, alpha-spectrin, is approximately 10 times greater in ipsilateral hippocampal tissue following severe compared to moderate CCI-TBI. Thus, TBI severity has a differential effect on the injury-induced neurorestorative response with calpain activation being one putative factor contributing to neuroregenerative failure following severe CCI-TBI. If true, then calpain inhibition may lead to both neuroprotective effects and an enhancement of neuronal plasticity/repair mechanisms post-TBI.

Sulforaphane enhances aquaporin-4 expression and decreases cerebral edema following traumatic brain injury

Brain edema, the infiltration and accumulation of excess fluid causing an increase in brain tissue volume, often leads to a rise in intracranial pressure and is a key contributor to the morbidity and mortality associated with traumatic brain injury (TBI). The cellular and molecular mechanisms contributing to the development/resolution of TBI-associated brain edema are poorly understood. Aquaporin-4 (AQP4) water channel is expressed at high levels in brain astrocytes, and the bidirectional transport of water through these channels is critical for the maintenance of brain water homeostasis. By using a rodent injury model, we show that TBI decreased AQP4 level in the injury core and modestly increased it in the penumbra region surrounding the core. Postinjury administration of sulforaphane (SUL), an isothiocyanate present in abundance in cruciferous vegetables such as broccoli, attenuated AQP4 loss in the injury core and further increased AQP4 levels in the penumbra region compared with injured animals receiving vehicle. These increases in AQP4 levels were accompanied by a significant reduction in brain edema (assessed by percentage water content) at 3 days postinjury. These findings suggest that the reduction of brain edema in response to SUL administration could be due, in part, to water clearance by AQP4 from the injured brain.

Plastic reorganization of hippocampal and neocortical circuitry in experimental traumatic brain injury in the immature rat

The reorganization of circuitry in the immature forebrain resulting from controlled cortical impact was examined with viral transneuronal tracing. Animals injured on postnatal day (PND) 17 and sham controls from the same litters received an intracerebral injection of a recombinant strain of pseudorabies virus (PRV) into the entorhinal cortex on PND 45. Fifty hours following injection of virus the animals were perfused and infected neurons were localized immunohistochemically with antisera specific for PRV. Prior studies have demonstrated that the PRV recombinant used in this analysis moves exclusively in the retrograde direction through synaptically linked neurons. CCI induced a necrotic loss of cortex at the site of impact and variable damage to the underlying corpus callosum and rostral (dorsal) hippocampus that was not present in sham controls. Analysis of viral transport in sham controls revealed retrograde transport of virus through hippocampal and neocortical circuitry in a pattern consistent with established patterns of connectivity and topography. Injured animals exhibited preservation of topographically organized connections in both the hippocampus and neocortex. However, the magnitude of labeling in the injured hemisphere was significantly increased relative to control animals and correlated with the magnitude of the injury. The distribution of infected neurons in the contralateral uninjured hemisphere also conformed to known connections. However differences in the involvement of the corpus callosum in the injury resulted in greater variability in the number of infected neurons among cases. These data provide novel insights into trauma induced reorganization of the developing brain and add to the experimental tools that can be used to assess the basis for functional recovery in animal models of developmental traumatic brain injury.

A persistent change in subcellular distribution of calcineurin following fluid percussion injury in the rat

Calcineurin, a neuronally enriched, calcium-stimulated phosphatase, is an important modulator of many neuronal processes, including several that are physiologically related to the pathology of traumatic brain injury. The effect of moderate, central fluid percussion injury on the subcellular distribution of this important neuronal enzyme was examined. Animals were sacrificed at several time points post-injury and calcineurin distribution in subcellular fractions was assayed by Western blot analysis and immunohistochemistry. A persistent increase in calcineurin concentration was observed in crude synaptoplasmic membrane-containing fractions. In cortical fractions, calcineurin immunoreactivity remained persistently increased for 2 weeks post-injury. In hippocampal homogenates, calcineurin immunoreactivity remained increased for up to 4 weeks. Finally, immunohistochemical analysis of hippocampal slices revealed increased staining in the apical dendrites of CA1 neurons. The increased staining was greatest in magnitude 24 h post-injury; however, staining was still more intense than control 4 weeks post-injury. The data support the conclusion that fluid percussion injury results in redistribution of the enzyme in the rat forebrain. These changes have broad physiological implications, possibly resulting in altered cellular excitability or a greater likelihood of neuronal cell death.

Synaptogenesis in the Hippocampal CA1 Field following Traumatic Brain Injury

Traumatic brain injury (TBI) results in both acute and chronic disruption of cognitive ability that may be mediated through a disruption of hippocampal circuitry. Experimental models of TBI have demonstrated that cortical contusion injuries can result in the loss of specific neurons in the CA3 subfield of the ipsilateral hippocampus, resulting in partial loss of afferents to the CA1 subfield. Numerous studies have documented the ability of the central nervous system to compensate for deafferentation by initiating a plasticity response capable of restoring lost synaptic contacts. The present study was designed to examine the time course of loss and replacement of synaptic contacts in stratum radiatum dendritic field of CA1. Young adult rats were subjected to a lateral cortical contusion injury and assayed for total synaptic numbers using unbiased stereology coupled with transmission electron microscopy. Injured animals demonstrated a 60% loss of synapses in CA1 at 2 days post-injury, followed by a reinnervation process that was apparent as early as 10 days post-injury. By 60 days post-injury, total synaptic numbers had approached pre-injury levels but were still significantly lower. Some animals were behaviorally tested for spatial memory in a Morris Water Maze at 15 and 30 days post-injury. While there was some improvement in spatial memory, injured animals continued to demonstrate a significant deficit in acquisition. These results show that the hippocampus ipsilateral to the cortical contusion is capable of a significant plasticity response but that synapse replacement in this area does not necessarily result in significant improvement in spatial learning.

Synaptosomal dopamine uptake in rat striatum following controlled cortical impact

Functional deficits following traumatic brain injury (TBI) are associated with alterations in markers of dopaminergic neurotransmission. To assess the effects of TBI on the expression and functional integrity of dopamine transporters, we measured transporter protein levels and investigated synaptosomal dopamine uptake in the rat striatum. Two or four weeks after lateral controlled cortical impact or sham injury, Western blotting revealed a decrease in transporter protein in the ipsilateral striatum of injured rats relative to shams (P < 0.05). However, no significant difference in synaptosomal uptake (K(m), V(max)) was found between injured and sham-injured animals. Our data suggest that striatal dopamine transporters are capable of normal function at 2 weeks and 4 weeks after injury. However, it is unclear whether neurons in the injured striatum can properly regulate the activity of dopamine transporters in vivo.

Cyclooxygenase-2-specific inhibitor improves functional outcomes, provides neuroprotection, and reduces inflammation in a rat model of traumatic brain injury

OBJECTIVE

Increases in brain cyclooxygenase-2 (COX2) are associated with the central inflammatory response and with delayed neuronal death, events that cause secondary insults after traumatic brain injury. A growing literature supports the benefit of COX2-specific inhibitors in treating brain injuries.

METHODS

DFU [5,5-dimethyl-3(3-fluorophenyl)-4(4-methylsulfonyl)phenyl-2(5)H)-furanone] is a third-generation, highly specific COX2 enzyme inhibitor. DFU treatments (1 or 10 mg/kg intraperitoneally, twice daily for 3 d) were initiated either before or after traumatic brain injury in a lateral cortical contusion rat model.

RESULTS

DFU treatments initiated 10 minutes before injury or up to 6 hours after injury enhanced functional recovery at 3 days compared with vehicle-treated controls. Significant improvements in neurological reflexes and memory were observed. DFU initiated 10 minutes before injury improved histopathology and altered eicosanoid profiles in the brain. DFU 1 mg/kg reduced the rise in prostaglandin E2 in the brain at 24 hours after injury. DFU 10 mg/kg attenuated injury-induced COX2 immunoreactivity in the cortex (24 and 72 h) and hippocampus (6 and 72 h). This treatment also decreased the total number of activated caspase-3-immunoreactive cells in the injured cortex and hippocampus, significantly reducing the number of activated caspase-3-immunoreactive neurons at 72 hours after injury. DFU 1 mg/kg amplified potentially anti-inflammatory epoxyeicosatrienoic acid levels by more than fourfold in the injured brain. DFU 10 mg/kg protected the levels of 2-arachidonoyl glycerol, a neuroprotective endocannabinoid, in the injured brain.

CONCLUSION

These improvements, particularly when treatment began up to 6 hours after injury, suggest exciting neuroprotective potential for COX2 inhibitors in the treatment of traumatic brain injury and support the consideration of Phase I/II clinical trials.

Regional distribution of Fluoro-Jade B staining in the hippocampus following traumatic brain injury

Fluoro-Jade B (FJB) is an anionic fluorescein derivative that has been reported to specifically stain degenerating neurons. We were interested in applying FJB staining in a well-characterized model of traumatic brain injury (TBI) in order to estimate the total number of neurons in different regions of the hippocampus that die after a mild or moderate injury. Rats were subjected to a mild or moderate unilateral cortical contusion (1.0- or 1.5-mm displacement from the cortical surface) with a controlled cortical impacting device. Animals were allowed to survive for 1, 2, or 7 days and the total number of FJB-positive neurons in hippocampal areas CA1, CA3, and the dentate gyrus granule layer was estimated using sterological methods. The region that had the highest number of FJP-positive neurons after TBI was the dentate gyrus. In both 1- and 1.5-mm injuries, FJB-positive granule cells were observed throughout the rostro-caudal extent of the dentate. In contrast, labeled pyramidal neurons of area CA3 were most numerous after the 1.5-mm injury. The area that had the fewest number of FJB-labeled cells was area CA1 with only scattered neurons seen in the 1.5-mm group. In both injury groups and in all hippocampal regions, more FJB-positive neurons were seen at the earlier times post injury (1 and 2 days) than at 7 days. FJB appears to be a reliable marker for neuronal vulnerability following TBI.

Bromocriptine reduces lipid peroxidation and enhances spatial learning and hippocampal neuron survival in a rodent model of focal brain trauma

Oxidative stress is a significant contributor to the secondary sequelae of traumatic brain injury (TBI), and may mediate subsequent neurobehavioral deficits and histopathology. The present study examined the neuroprotective effects of bromocriptine (BRO), a dopamine D2 receptor agonist with significant antioxidant properties, on cognition, histopathology, and lipid peroxidation in a rodent model of focal brain trauma. BRO (5 mg/kg) or a comparable volume of vehicle (VEH) was administered intraperitoneally 15 min prior to cortical impact or sham injury. In experiment 1, spatial learning was assessed in an established water maze task on post-surgery days 14-18, followed by quantification of hippocampal cell survival and cortical lesion volume at 4 weeks. In experiment 2, rats were sacrificed 1 hr post-surgery, and malondialdehyde (MDA), the end product of lipid peroxidation, was measured in the frontal cortex, striatum, and substantia nigra using a thiobarbituric acid reactive substances assay. The TBI+BRO group was significantly more adept at locating a hidden platform in the water maze compared to the TBI+VEH group and also exhibited a greater percentage of surviving CA3 hippocampal neurons. TBI increased MDA in all examined regions of the VEH-treated, but not BRO-treated group versus SHAMs. MDA was significantly decreased in both the striatum (4.22 +/- 0.52 versus 5.60 +/- 0.44 nmol per mg/tissue +/- SEM) and substantia nigra (4.18 +/- 0.35 versus 7.76 +/- 2.05) of the TBI+BRO versus TBI+VEH groups, respectively, while only a trend toward decreased MDA was observed in the frontal cortex (5.44 +/- 0.44 versus 6.96 +/- 0.77). These findings suggest that TBI-induced oxidative stress is attenuated by acute BRO treatment, which may, in part, explain the benefit in cognitive and histological outcome.

Post-Trauma Administration of Caffeine Plus Ethanol Reduces Contusion Volume and Improves Working Memory in Rats

It has been demonstrated that ethanol exerts dose-dependent effects, both beneficial and detrimental, on the outcome of traumatic brain injury (TBI). Recently, it has been reported that co-administration of caffeine (10 mg/kg) and a low amount of alcohol (0.65 g/kg; caffeinol) reduces cortical infarct volume up to 80%, and improves motor coordination, following a rodent model of reversible common carotid/middle cerebral artery occlusion. However, the protective effects of caffeinol following other CNS insults, nor its influence on cognitive function, have been examined. Using a controlled cortical impact model of brain injury, the effect of caffeinol administration on TBI-associated motor and cognitive deficits was assessed. When given 15 min following injury, caffeinol reduced cortical tissue loss and improved working memory. However, no influence on motor skills, Morris water maze performance or associative learning and memory was observed. Delayed administration (6 h post-injury) of caffeinol containing a dose of ethanol (1 g/kg) previously demonstrated to improve motor performance eliminated the working memory benefit and cortical protection. These results indicate that early administration of caffeinol may be beneficial in lessening some of the deficits and cortical tissue loss associated with brain trauma.

A Review and Rationale for the Use of Cellular Transplantation as a Therapeutic Strategy for Traumatic Brain Injury

Experimental research during the past decade has greatly increased our understanding of the pathophysiology of traumatic brain injury (TBI) and allowed us to develop neuroprotective pharmacological therapies. Encouraging results of experimental pharmacological interventions, however, have not been translated into successful clinical trials, to date. Traumatic brain injury is now believed to be a progressive degenerative disease characterized by cell loss. The limited capacity for self-repair of the brain suggests that functional recovery following TBI is likely to require cellular transplantation of exogenous cells to replace those lost to trauma. Recent advances in central nervous system transplantation techniques involve technical and experimental refinements and the analysis of the feasibility and efficacy of transplantation of a range of stem cells, progenitor cells and postmitotic cells. Cellular transplantation has begun to be evaluated in several models of experimental TBI, with promising results. The following is a compendium of these new and exciting studies, including a critical discussion of the rationale and caveats associated with cellular transplantation techniques in experimental TBI research. Further refinements in future research are likely to improve results from transplantation-based treatments for TBI.

Motor and cognitive function evaluation following experimental traumatic brain injury

Traumatic brain injury (TBI) in humans may cause extensive sensorimotor and cognitive dysfunction. As a result, many TBI researchers are beginning to assess behavioral correlates of histologically determined damage in animal models. Although this is an important step in TBI research, there is a need for standardization between laboratories. The ability to reliably test treatments across laboratories and multiple injury models will close the gap between treatment success in the lab and success in the clinic. The goal of this review is to describe and evaluate the tests employed to assess functional outcome after TBI and to overview aspects of cognitive, sensory, and motor function that may be suitable targets for therapeutic intervention.

The therapeutic efficacy conferred by the 5-HT(1A) receptor agonist 8-Hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) after experimental traumatic brain injury is not mediated by concomitant hypothermia

We recently reported that the 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) attenuated traumatic brain injury (TBI)-induced cognitive deficits and histopathology. However, 8-OH-DPAT also produced mild hypothermia (Hypo), which may have contributed to the benefit. To clarify this issue, we conducted an experiment similar to the previous, but included an 8-OH-DPAT group that was maintained at 37 +/- 0.5 degrees C (normothermia; Normo). Isoflurane-anesthetized rats received either a cortical impact (2.7-mm deformation at 4 m/sec) or sham injury and then were randomly assigned to two saline (Sham/Vehicle, n = 5; Injury/Vehicle, n = 10) or three 8-OH-DPAT (Sham/DPAT, n = 5; Injury/DPAT + Normo, n = 10; Injury/DPAT + Hypo, n = 10) groups. 8-OH-DPAT (0.5 mg/kg) or a comparable volume of saline was administered intraperitoneally 15 min after cortical impact or sham injury. Core temperatures were taken prior to treatment and every 15 min thereafter for 2 h. Function was assessed by established motor and cognitive tasks on post-operative days 1-5 and 14-20, respectively. Hippocampal CA1/CA3 cell survival and cortical lesion volume were quantified at 4 weeks. Both the Injury/DPAT + Normo and Injury/DPAT + Hypo groups exhibited enhanced cognitive performance (spatial acquisition and retention) and reduced histopathology (CA3 cell loss and cortical lesion volume) versus the Injury/ Vehicle group (P < 0.05), but did not differ from one another despite a rapid (15 min), mild (34.4-34.9 degrees C), and transient (~1 h) hypothermic effect in the latter. These data confirm that a single systemic administration of 8-OH-DPAT confers neurological protection after TBI, and demonstrate that the beneficial effect is not mediated by concomitant hypothermia. The mechanisms for the protective effects of 8-OH-DPAT after TBI require further inquiry.

Evaluation of estrous cycle stage and gender on behavioral outcome after experimental traumatic brain injury

Female sex hormones are acutely neuroprotective in experimental models of traumatic brain injury (TBI). Because hormonal profiles are known to vary with estrous cycle stage, the purpose of this study was to evaluate how pre-injury estrous stage affects motor and cognitive performance after experimental TBI. We also sought to compare post-injury behavioral performance in males vs. females. Under anesthesia, male (n=18) and female (n=35) Sprague-Dawley rats underwent either controlled cortical impact (CCI) injury (2.7 mm; 4 m/s) or sham operations. Females were grouped according to estrous stage (proestrous or non-proestrous) at the time of surgery. Motor function was assessed pre-injury and for the first 5 days after surgery using beam balance and walking tasks. Spatial memory was assessed beginning 14 days post-injury utilizing the Morris water maze (MWM) task. No significant differences were found on any task between injured females regardless of estrous cycle stage. Females performed significantly better than males on both motor tasks, but gender did not influence MWM performance. Mixed effects multivariate analysis corroborated these results by showing that pre-injury serum hormone levels had little affect on behavioral performance. The results suggest that the presence of endogenous circulating hormones, rather than hormonal status at time of injury, may confer early neuroprotection in females after TBI. The impact of early neuroprotection on later behavioral outcome and the anatomic structural specificity of hormonal neuroprotection require further study.

Neuronal and glial cell number in the hippocampus after experimental traumatic brain injury: analysis by stereological estimation

Fluid percussion (FP) brain injury causes spatial memory dysfunction in rats regardless of injury location (midline vs. lateral). Standard histological analysis of the injured brains shows hippocampal neuronal loss after lateral, but not midline FP injury. We have used the optical volume fractionator (OVF) stereological procedure to quantify neuronal loss and glial proliferation within specific subregions of the hippocampus after midline or lateral FP injury. The OVF method is a design-based cell counting procedure, which combines cellular numerical density estimates (from the optical disector) with volume estimates (generated by point counting and the fractionator stereology method) to produce an estimate of the absolute cell number. Fifteen adult male Sprague-Dawley rats were randomly divided into 3 groups (n = 5/group): midline injury, lateral injury and naive. A single fluid percussion pulse was delivered to anesthetized rats in the injured groups. At 14 days post-injury, strict morphological criteria enabled the estimation of neurons, astrocytes, oligodendrocytes, and microglia in defined hippocampal subregions. The results confirm that hippocampal neurons are selectively vulnerable to brain injury, particularly observed as a significant loss in the hilus following both types of injury and in area CA3 after lateral injury. In contrast, the number of astrocytes and oligodendrocytes remains unaffected by brain injury, regardless of subregion. However, the significant increase in microglia number (bilaterally after midline and ipsilateral following lateral injury) suggests that underlying cellular processes continue weeks following injury. The implications of the observed cell population changes are discussed in relation to the reported cognitive deficits associated with both lateral and midline FP brain injury.

Common patterns of bcl-2 family gene expression in two traumatic brain injury models

Cell death/survival following traumatic brain injury (TBI) may be a result of alterations in the intracellular ratio of death and survival factors. Bcl-2 family genes mediate both cell survival and the initiation of cell death. Using lysate RNase protection assays, mRNA expression of the anti-cell death genes Bcl-2 and Bcl-xL, and the pro-cell death gene Bax, was evaluated following experimental brain injuries in adult male Sprague-Dawley rats. Both the lateral fluid-percussion (LFP) and the lateral controlled cortical impact (LCI) models of TBI showed similar patterns of gene expression. Anti-cell death bcl-2 and bcl-xL mRNAs were attenuated early and tended to remain depressed for at least 3 days after injury in the cortex and hippocampus ipsilateral to injury. Pro-cell death bax mRNA was elevated in these areas, usually following the decrease in anti-cell death genes. These common patterns of gene expression suggest an important role for Bcl-2 genes in cell death and survival in the injured brain. Understanding the regulation of these genes may facilitate the development of new therapeutic strategies for a condition that currently has no proven pharmacologic treatments.

Acute etomidate treatment reduces cognitive deficits and histopathology in rats with traumatic brain injury

OBJECTIVE

To test the hypothesis that etomidate treatment improves functional, cognitive, and histologic outcome after experimental traumatic brain injury.

DESIGN

Controlled animal study.

SETTING

University research laboratory.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Traumatic brain injury was produced by controlled cortical impact injury (4 m/sec, 2.6 mm of tissue deformation). Etomidate (2 mg/kg) was administered intravenously immediately before injury (n = 13) or 5 mins after injury (n = 12). Additional rats received saline treatment 5 mins after injury (n = 12) or served as sham controls (n = 10).

MEASUREMENTS AND MAIN RESULTS

Rats were evaluated on beam balance and beam walk tasks on postoperative days 1-5 and then trained in the Morris water maze on postoperative days 14-18. On day 28, the rats were killed, and hippocampal CA1 and CA3 neuron counts and cortical lesion volume were measured in histologic brain sections. Preinjury etomidate attenuated beam balance deficits, water maze deficits, hippocampal CA3 neuronal loss, and cortical tissue loss but did not attenuate beam walk deficits or hippocampal CA1 neuronal loss. Postinjury etomidate attenuated water maze deficits, but it did not affect any other outcome measure.

CONCLUSIONS

Administration of etomidate both before and after injury attenuates secondary injury resulting from traumatic brain injury, but the effect is more pronounced with pretreatment. The ineffectiveness of postinjury etomidate on motor and histologic tasks suggests a brief therapeutic treatment window in rats. However, the treatment window in humans is unknown. Lastly, postinjury etomidate did not exacerbate neurologic or histologic outcome.

Basic science of closed head injuries and spinal cord injuries

Traumatic CNS injury is one of the most important health issues in our society and is a risk to all athletes, both in competitive and recreational sports. Our understanding of the pathophysiology has improved tremendously in the last 20 years. This progress has led to the identification of several possible treatments for improving outcome following spinal cord injury and traumatic brain injury. As no panacea exists, improvements in experimental models have empowered researchers in their search for novel therapeutic strategies.

Moderate hypothermia improves neurobehavioral deficits after an epidural focal mass lesion in rodents

The objective of this study was to evaluate the effects of a moderate, intraischemic hypothermia on the behavorial deficits up to 4 weeks after induction of a focal mass lesion. A focal epidural mass lesion was induced by an epidural balloon. The severity of the trauma was defined by the balloon volume and flattening of electroencephalography. Hypothermia (32 degrees C) was induced as soon as maximum balloon infIation was reached. Ischemia was extended over 30 min. After reperfusion, normothermic (n = 24) and hypothermic animals (n = 25) were monitored for 3 h followed by a rewarming of the cooled animals. Results were compared to sham-operated animals (n = 10). Behavioral deficits were assessed by postural reflex (PR), open field (OF), beam balance (BB), beam walking (BW), and water maze tests (WMT). MRI follow-up and histology was evaluated. Sham-operated rats showed normal test results. Rats with normothermia showed worsening of test performance (PR, p < 0.05; OF, p < 0.05; BB, p < 0.05; BW, p < 0.05; WMT, p < 0.05) compared to controls over the whole observation period. A significantly better behavioral outcome was observed in animals treated with hypothermia which showed no differences from controls 3-4 days after injury (PR, OF, BB, BW, WMT, p > 0.05). Lesion induced mortality was reduced in cooled animals but overall mortality rates were not influenced by this therapeutic measure. Neuronal cell loss in the CA1-CA4 region (p < 0.05) was reduced and the lesion size smaller (21%/p > 0.05) in hypothermic animals. Magnetic resonance imaging revealed that the lesion was more pronounced in the cortical grey matter after normothermia, whereas hypothermic animals showed more subcortical brain lacerations. In conclusion, intraischemic hypothermia significantly improved the behavioral outcome, and decreased lesion-induced mortality and the size of the lesion after an epidural focal mass lesion.

A novel dehydroepiandrosterone analog improves functional recovery in a rat traumatic brain injury model

The purpose of this study was to investigate the efficacy of a novel steroid, fluasterone (DHEF, a dehydroepiandrosterone (DHEA) analog), at improving functional recovery in a rat model of traumatic brain injury (TBI). The lateral cortical impact model was utilized in two studies of efficacy and therapeutic window. DHEF was given (25 mg/kg, intraperitoneally) at the initial time point and once a day for 2 more days. Study A included four groups: sham injury, vehicle treated (n = 22); injured, vehicle treated (n = 30); injured, pretreated (5-10 min prior to injury, n = 24); and injured, posttreated (initial dose 30 min postinjury, n = 15). Study B (therapeutic window) included five groups: sham injury, vehicle treated (n = 17); injured, vehicle treated (n = 26); and three posttreatment groups: initial dose at 30 min (n = 18), 2 h (n = 23), or 12 h (n = 16) postinjury. Three criteria were used to grade functional recovery. In study A, DHEF improved beam walk performance both with pretreatment (79%) and 30-min posttreatment group (54%; p < 0.01, Dunnett vs. injured vehicle). In study B, the 12-h posttreatment group showed a 97% improvement in beam walk performance (p < 0.01, Dunnett). The 30-min and 12-h posttreatment groups showed a decreased incidence of falls from the beam, which reached statistical significance (p < 0.05, Dunnett). Tests of memory (Morris water maze) and neurological reflexes both revealed significant improvements in all DHEF treatment groups. In cultured rat mesangial cells, DHEF (and DHEA) potently inhibited interleukin-1beta-induced cyclooxygenase-2 (COX2) mRNA and prostaglandin (PGE2) production. In contrast, DHEF treatment did not alter injury-induced COX2 mRNA levels in the cortex or hippocampus. However, DHEF (and DHEA) relaxed ex vivo bovine middle cerebral artery preparations by about 30%, with an IC(50) approximately 40 microM. This was a direct effect on the vascular smooth muscle, independent of the endothelial cell layer. Fluasterone (DHEF) treatments improved functional recovery in a rat TBI model. Possible mechanisms of action for this novel DHEA analog are discussed. These findings suggest an exciting potential use for this agent in the clinical treatment of traumatic brain injury.

Comparative analysis of mRNA levels in the frontal cortex and the hippocampus in the basal state and in response to experimental brain injury

Damage to the frontal cortex and to the hippocampus, both in terms of cell loss and neuronal dysfunction, is thought to underlie many of the neurological and behavioural consequences of traumatic brain injury (TBI). Several studies have indicated that the hippocampus is particularly susceptible to central nervous system insults, whereas the frontal cortex possesses relatively higher capacities for regeneration and plasticity. It has been postulated that dissimilarities in the gene expression profiles in these structures, both in the normal and the postinjury states, may underlie these differences. In order to explore this issue, mRNA samples taken from the frontal cortex and the hippocampus of uninjured animals were subjected to high-density microarray analysis. The analysis indicated that the mRNA levels of 65 genes were differentially expressed between these two brain regions. Among these, genes involved in intracellular signalling, neurotransmitter release, and genes encoding for channels and receptors were identified. Samples taken from animals injured using controlled cortical impact (a model of TBI) showed altered mRNA levels for 341 frontal cortex genes 24 h following injury. These genes can be broadly classified into one of 12 functional classes: cell cycle, metabolism, reactive oxygen metabolism, inflammation, receptors, channels and transporters, signal transduction, cytoskeleton, membrane proteins, neuropeptides, growth factors, and proteins involved in transcription/translation. The expression profile of these genes is compared to the expression profile of 241 genes in the hippocampus 24 h following cortical impact injury as previously reported by our laboratory. In addition to genes previously reported in the literature, this study found several genes that have not been associated with TBI. The functional implications of changes in the expression of some of these genes are discussed.

Novel diketopiperazine enhances motor and cognitive recovery after traumatic brain injury in rats and shows neuroprotection in vitro and in vivo

The authors developed a novel diketopiperazine that shows neuroprotective activity in a variety of in vitro models, as well as in a clinically relevant experimental model of traumatic brain injury (TBI) in rats. Treatment with 1-ARA-35b (35b), a cyclized dipeptide derived from a modified thyrotropin-releasing hormone (TRH) analog, significantly reduced cell death associated with necrosis (maitotoxin), apoptosis (staurosporine), or mechanical injury in neuronal-glial cocultures. Rats subjected to lateral fluid percussion-induced TBI and then treated with 1 mg/kg intravenous 35b thirty minutes after trauma showed significantly improved motor recovery and spatial learning compared with vehicle-treated controls. Treatment also significantly reduced lesion volumes as shown by magnetic resonance imaging, and decreased the number of TUNEL-positive neurons observed in ipsilateral hippocampus. Unlike TRH or traditional TRH analogs, 35b treatment did not change mean arterial pressure, body temperature, or thyroid-stimulating hormone release, and did not have analeptic activity. Moreover, in contrast to TRH or typical TRH analogs, 35b administration after TBI did not alter free-magnesium concentration or cellular bioenergetic state. Receptor-binding studies showed that 35b did not act with high affinity at 50 classical receptors, channels, or transporters. Thus, 35b shows none of the typical physiologic actions associated with TRH, but possesses neuroprotective actions in vivo and in vitro, and appears to attenuate both necrotic and apoptotic cell death.

Expression of the prodynorphin gene after experimental brain injury and its role in behavioral dysfunction

Traumatic brain injury (TBI) causes excess release of neurotransmitters, such as glutamate, and increases intracellular calcium levels. Elevated levels of calcium, and perhaps other intracellular second messengers, as a result of TBI can alter the expression of many genes. The protein products of some of these genes may be signals for TBI-associated memory dysfunction. Therefore, identification of genes whose expression is altered after TBI in the hippocampus, a structure in the medial temporal lobe that plays a critical role in memory formation and storage, and elucidation of the role(s) of their protein products may shed light on the molecular mechanisms underlying TBI-elicited memory dysfunction. The prodynorphin gene is expressed in hippocampal granule cells, and its expression has been reported to be enhanced as a result of elevated intracellular calcium. The prodynorphin protein is proteolytically cleaved to generate multiple dynorphin peptides, which can modulate neurotransmitter release through the activation of presynaptic kappa opioid receptors. In this study, we report that 1) TBI transiently increases prodynorphin mRNA in the hippocampus, 2) dynorphin peptide immunoreactivity is enhanced for up to 24 hr after TBI and 3) intracerebroventricular infusion of the kappa receptor antagonist nor-binaltorphimine (nor-BNI) impairs subsequent performance in a spatial memory task. These results suggest that dynorphin action may serve a beneficial role after TBI.

Functional recovery of cholinergic basal forebrain neurons under disease conditions: old problems, new solutions?

Recognition of the involvement of cholinergic neurons in the modulation of cognitive functions and their severe dysfunction in neurodegenerative disorders, such as Alzheimer's disease, initiated immense research efforts aimed at unveiling the anatomical organization and cellular characteristics of the basal forebrain (BFB) cholinergic system. Concomitant with our unfolding knowledge about the structural and functional complexity of the BFB cholinergic projection system, multiple pharmacological strategies were introduced to rescue cholinergic nerve cells from noxious attacks; however, a therapeutic breakthrough is still awaited. In this review, we collected recent findings that significantly contributed to our better understanding of cholinergic functions under disease conditions, and to the design of effective means to restore lost or damaged cholinergic functions. To this end, we first provide a brief survey of the neuroanatomical organization of BFB nuclei with emphasis on major evolutionary differences among mammalian species, in particular rodents and primates, and discuss limitations of the translation of experimental data to human therapeutic applications. Subsequently, we summarize the involvement of cholinergic dysfunction in the pathogenesis of severe neurological conditions, including stroke, traumatic brain injury, virus encephalitis and Alzheimer's disease, and emphasize the critical role of pro-inflammatory cytokines as common mediators of cholinergic neuronal damage. Moreover, we review leading functional concepts on the limited recovery of cholinergic neurons and their impaired plastic re-modeling, as well as on the hampered interplay of the ascending cholinergic and monoaminergic projection systems under neurodegenerative conditions. In addition, recent advances in the dynamic labeling of living cholinergic neurons by fluorochromated antibodies, referred to as in vivo labeling, and novel neuroimaging approaches as potential diagnostic tools of progressive cholinergic decline are surveyed. Finally, the potential of cell replacement strategies using embryonic and adult stem cells, and multipotent neural progenitors, as a means to recover damaged cholinergic functions, is discussed.

The role of extracellular signal-regulated kinase in cognitive and motor deficits following experimental traumatic brain injury

Traumatic brain injury (TBI) causes neuronal death and alters the plasticity (e.g. morphology) of surviving neurons. Both of these events contribute to TBI-associated neurological deficits, such as memory dysfunction. Although a majority of current research is directed towards identifying biochemical cascades responsible for cell death, little is known about mechanisms of altered neuronal plasticity following TBI. Extracellular signal-regulated kinases (Erk1 and 2) play a critical role in growth and have been implicated in long-lasting neuronal plasticity and memory storage. The activation of Erk following TBI was investigated utilizing an antibody that specifically binds to dually phosphorylated Erk. Using this antibody, we report that lateral cortical impact injury in rats increases Erk phosphorylation both in the cortex and the hippocampus as early as 10 min post-injury. Double immunostaining experiments using either a neuron-specific or an astroglial-specific marker show that the active Erk is localized almost exclusively in neuronal cells. Furthermore, the increase in phospho-Erk immunoreactivity was initially localized to axons and at later time points was observed to be predominantly in the cell soma. This suggests that Erk redistributed over time and may play a role in retrograde signaling. Administration of inhibitors of the Erk cascade worsened retrograde amnesia, impaired performances in hippocampus- and amygdala-dependent memory tasks, and exacerbated motor deficits following TBI. Furthermore, inhibition of this cascade did not have any overt effects on cell survival, but altered neuronal morphology as detected by a dendritic-specific marker. These findings suggest that the Erk cascade plays an essential role for the maintenance of neuronal function and plasticity following TBI.

Administration of adenosine receptor agonists or antagonists after controlled cortical impact in mice: effects on function and histopathology

Adenosine is an endogenous neuroprotectant via anti-excitotoxic effects at A(1) receptors, and blood flow promoting and anti-inflammatory effects at A(2a) receptors. Previous studies showed improved motor function after fluid percussion injury (FPI) in rats treated with the broad-spectrum adenosine receptor agonist 2-chloroadenosine (2-CA). We studied the effects of 2-CA, a specific A(1) agonist (2-chloro-N(6)-cyclopentyladenosine, CCPA), and a specific A(1) antagonist (8-cyclopentyl-1,3-dipropylxanthine, DPCPX) on motor task and Morris water maze (MWM) performance, and histopathology (contusion volume, hippocampal cell counts) after controlled cortical impact (CCI) in mice. Each agent (12 nmol), or respective vehicle (saline or DMSO) was injected into dorsal hippocampus beneath the contusion immediately after CCI or craniotomy (sham). 2-CA treatment attenuated wire grip deficits after CCI (P<0.05 versus other treatments). DPCPX treatment exacerbated deficits on beam balance (P<0.05 versus sham). No treatment effect was seen on MWM performance, although there was a deleterious effect of the DMSO vehicle used for DPCPX. Contusion volume tended to be attenuated by 2-CA (P=0.08 versus saline) and increased after either DMSO or DPCPX (P<0.05 versus all groups). CA1 and CA3 counts were decreased in all groups versus sham. However, treatment with the selective A(1) agonist CCPA attenuated the CA3 cell loss (P<0.05 versus other treatment). We suggest that the beneficial effect of the broad spectrum adenosine receptor agonist 2-CA on motor function after CCI is not mediated solely by effects at the A(1) receptor.

Effects of underwater sound exposure on neurological function and brain histology

To evaluate the safety of sonar exposure from a neurological perspective, the vulnerability of the central nervous system to underwater exposure with high-intensity, low-frequency sound (HI-LFS) was experimentally examined. Physiological, behavioral and histological parameters were measured in anesthetized, ventilated rats exposed to brief (5 min), underwater HI-LFS. Exposure to 180 dB sound pressure level (SPL) re 1 microPa at 150 Hz (n = 9) did not alter acute cardiovascular physiology (arterial blood pH, pO(2), pCO(2), heart rate, or mean arterial blood pressure) from that found in controls (n = 11). Rats exposed to either 180 dB SPL re 1 microPa at 150 Hz (n = 12) or 194 dB SPL re 1 microPa at 250 Hz (n = 12) exhibited normal cognitive function at 8 and 9 days after sound exposure. Evaluation of neurological motor function revealed a minor deficit 7 days after 180 dB SPL/150 Hz exposure that resolved by 14 days, and no deficits after 194 dB SPL/250 Hz exposure. No overt histological damage was detected in any group. These data suggest that underwater HI-LFS exposure may cause transient, mild motor dysfunction.

Acute systemic administration of interleukin-10 suppresses the beneficial effects of moderate hypothermia following traumatic brain injury in rats

Traumatic injury to the central nervous system initiates inflammatory processes such as the synthesis of proinflammatory mediators that contribute to secondary tissue damage. Hence, administration of anti-inflammatory cytokines, such as interleukin-10 (IL-10) may be neuroprotective. Moderate hypothermia (30-32 degrees C) also decreases the pro-inflammatory response to traumatic brain injury (TBI). Thus, we hypothesized that the combination of IL-10 and hypothermia would provide synergistic neuroprotective effects after TBI. To test this hypothesis, fifty isoflurane-anesthetized rats underwent a controlled cortical impact (2.7 mm tissue deformation at 4 m/s) or sham injury and then were randomly assigned to one of five conditions (TBI/VEH Normothermia (37 degrees C), TBI/VEH Hypothermia (32 degrees C for 3 h), TBI/IL-10 Normothermia, TBI/IL-10 Hypothermia, and Sham/VEH Normothermia). Human IL-10 (5 microg) or VEH was administered (i.p.) 30 min after surgery. Function was assessed by established motor and cognitive tests on post-operative days 1-5 and 14-18, respectively. Cortical lesion volume and hippocampal CA(1)/CA(3) cell survival were quantified at 4 weeks. Brain sections from 15 additional rats were immunohistochemically assessed (MoAB RP-3) to determine neutrophil accumulation at 5 h after TBI. The administration of IL-10 after TBI produced an approximately 75% reduction in the number of RP-3-positive cells in both the normothermic and hypothermic groups vs. the normothermic vehicle-treated group (P<0.05), but did not improve functional outcome. In contrast, hypothermia alone enhanced both motor and cognitive function and increased CA(3) neuronal survival after TBI. Contrary to our hypothesis, systemic administration of IL-10 combined with hypothermia did not provide synergistic neuroprotective effects after TBI. Rather, IL-10 administration suppressed the beneficial effects produced by hypothermia alone after TBI. The mechanism(s) for the negative effects of IL-10 combined with hypothermia after TBI remain to be determined.

Attenuation of working memory and spatial acquisition deficits after a delayed and chronic bromocriptine treatment regimen in rats subjected to traumatic brain injury by controlled cortical impact

Cognitive impairments are pervasive and persistent sequelae of human traumatic brain injury (TBI). In vivo models of TBI, such as the controlled cortical impact (CCI) and fluid percussion (FP), are utilized extensively to produce deficits reminiscent of those seen clinically with the hope that empirical study will lead to viable therapeutic interventions. Both CCI and FP produce spatial learning acquisition deficits, but only the latter has been reported to impair working memory in rats tested in the Morris water maze (MWM). We hypothesized that a CCI injury would impair working memory similarly to that produced by FP, and that delayed and chronic treatment with the D2 receptor agonist bromocriptine would attenuate both working memory and spatial learning acquisition deficits. To test these hypotheses, isoflurane-anesthetized adult male rats received either a CCI (2.7 mm deformation, 4 m/sec) or sham injury, and 24 h later were administered bromocriptine (5 mg/kg, i.p.) or vehicle, with continued daily injections until all behavioral assessments were completed. Motor function was assessed on beam balance and beam walking tasks on postoperative days 1-5 and cognitive function was evaluated in the MWM on days 11-15 for working memory (experiment 1) and on days 14-18 for spatial learning acquisition (experiment 2). Histological examination (hippocampal CA1 and CA3 cell loss/survival and cortical lesion volume) was conducted 4 weeks after surgery. All injured groups exhibited initial impairments in motor function, working memory, and spatial learning acquisition. Bromocriptine did not affect motor function, but did ameliorate working memory and significantly attenuated spatial acquisition deficits relative to the injured vehicle-treated controls. Additionally, the injured bromocriptine-treated group exhibited significantly more morphologically intact CA3 neurons than the injured vehicle-treated group (55.60 +/- 3.10% vs. 38.34 +/- 7.78% [p = 0.03]). No significant differences were observed among TBI groups in CA1 cell survival (bromocriptine, 40.26 +/- 4.74% vs. vehicle, 29.13 +/- 6.63% [p = 0.14]) or cortical lesion volume (bromocriptine, 17.78 +/- 0.62 mm3 vs. vehicle, 19.01 +/- 1.49 mm3 [p > 0.05]). These data reveal that CCI produces working memory deficits in rats that are similar to those observed following FP, and that the delayed and chronic bromocriptine treatment regimen conferred cognitive and neural protection after TBI.

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.

Acute ethanol intake attenuates inflammatory cytokines after brain injury in rats: a possible role for corticosterone

It has been reported that acute ethanol intoxication exerts dose-dependent effects, both beneficial and detrimental, on the outcome of traumatic brain injury (TBI), although the mechanism(s) has not been determined. Given that pro-inflammatory cytokines are either neuroprotective or neurotoxic, depending on their tissue levels, ethanol-induced alterations in brain cytokine production may be involved in determining the recovery after TBI. The present study was undertaken to examine the effect of acute ethanol pretreatments (producing blood alcohol concentrations of 100+/-16 mg/dL, and 220+/-10 mg/dL, considered low and intoxicating doses, respectively) on interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) levels in discrete brain regions. In addition, serum corticosterone levels were also examined because the hormone is a modulator of cytokine production, its secretion is stimulated by ethanol, and it has been associated with the severity of post-injury neurologic dysfunction. The data presented in this report demonstrate that moderate cortical impact brain injury elicits a marked increase in IL-1beta and TNF-alpha in the injured cortex as well as in the hippocampus ipsilateral to the injury. Ethanol pretreatment lowered cytokine levels in the cortex, hippocampus and hypothalamus in a dose-dependent manner after TBI compared to the untreated injured rats. Serum corticosterone levels were markedly increased in the injured rats, and were further augmented in the ethanol-pretreated injured animals in a dose-dependent manner. Our findings suggest that ethanol-induced decrease in pro-inflammatory cytokine production may be linked to increased circulating corticosterone, both of which may contribute to the outcome of brain injury.

Spatial learning deficits without hippocampal neuronal loss in a model of early-onset epilepsy

Studies were undertaken to examine the effects recurrent early-life seizures have on the ability of rats to acquire spatial memories in adulthood. A minute quantity of tetanus toxin was injected unilaterally into the hippocampus on postnatal day 10. Within 48 h, rats developed recurrent seizures that persisted for 1 week. Between postnatal days 57 and 61, rats were trained in a Morris water maze. Toxin-injected rats were markedly deficient in learning this task. While these rats showed gradual improvement in escape latencies over 20 trials, their performance always lagged behind that of controls. Poor performance could not be explained by motor impairments or motivational difficulties since swimming speed was similar for the groups. Only eight of 16 toxin-injected animals showed focal interictal spikes in the hippocampus during electroencephalographic recordings. This suggests that learning deficiencies and chronic epilepsy may be independent products of recurrent early-life seizures. A quantitative analysis of hippocampus revealed a significant decrease in neuronal density in stratum pyramidale of experimental rats. However, the differences were largely explained by a concomitant increase in the area of stratum pyramidale. Studies of glial fibrillary acidic protein expression and spread of horseradish peroxidase-conjugated tetanus toxin in the hippocampus suggest that the dispersion of cell bodies in stratum pyramidale can neither be explained by a reactive gliosis nor the direct action of the toxin itself. Taken together, we suggest that recurrent seizures beginning in early life can lead to a significant deficiency in spatial learning without ongoing hippocampal synchronized network discharging or a substantial loss of hippocampal pyramidal cells.

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.

Assessment of sensorimotor and cognitive deficits induced by a moderate traumatic injury in the right parietal cortex of the rat

The purpose of this study was to set-up a battery of behavioral tests to assess sensorimotor and cognitive deficits following a moderate traumatic brain injury (TBI) in rats. Coordinated walking ability was evaluated in an accelerated rotarod test. Vestibulomotor function and fine motor coordination were assessed by using a beam-walking task. Rotarod and beam-walking performances were both altered in injured rats compared to sham-operated and control rats. A more pronounced and longer-lasting deficit was measured in the beam-walking test. Cognitive function was studied by using the Lashley maze paradigm. A spatial localization deficit was significant for 4 weeks posttrauma in TBI rats. The beam-walking task and the Lashley maze are robust and sensitive methods in detecting sensorimotor and cognitive impairment after TBI in rats, respectively. These tests are proposed for evaluating the ability of new pharmacological agents to improve the functional recovery after a TBI in rats.

Mild head injury increasing the brain's vulnerability to a second concussive impact

OBJECT

Mild, traumatic repetitive head injury (RHI) leads to neurobehavioral impairment and is associated with the early onset of neurodegenerative disease. The authors developed an animal model to investigate the behavioral and pathological changes associated with RHI.

METHODS

Adult male C57BL/6 mice were subjected to a single injury (43 mice), repetitive injury (two injuries 24 hours apart; 49 mice), or no impact (36 mice). Cognitive function was assessed using the Morris water maze test, and neurological motor function was evaluated using a battery of neuroscore, rotarod, and rotating pole tests. The animals were also evaluated for cardiovascular changes, blood-brain barrier (BBB) breakdown, traumatic axonal injury, and neurodegenerative and histopathological changes between 1 day and 56 days after brain trauma. No cognitive dysfunction was detected in any group. The single-impact group showed mild impairment according to the neuroscore test at only 3 days postinjury, whereas RHI caused pronounced deficits at 3 days and 7 days following the second injury. Moreover, RHI led to functional impairment during the rotarod and rotating pole tests that was not observed in any animal after a single impact. Small areas of cortical BBB breakdown and axonal injury. observed after a single brain injury, were profoundly exacerbated after RHI. Immunohistochemical staining for microtubule-associated protein-2 revealed marked regional loss of immunoreactivity only in animals subjected to RHI. No deposits of beta-amyloid or tau were observed in any brain-injured animal.

CONCLUSIONS

On the basis of their results, the authors suggest that the brain has an increased vulnerability to a second traumatic insult for at least 24 hours following an initial episode of mild brain trauma.

Traumatic brain injury in mice deficient in poly-ADP(ribose) polymerase: a preliminary report

Poly (ADP-ribose) polymerase (PARP) is a ubiquitous nuclear enzyme that, when activated by free-radical induced DNA damage, contributes to energy failure and cell death in models of central nervous system ischemia and reperfusion. PARP contributes to neuronal cell death in vivo after cerebral ischemia/reperfusion, however, the role of PARP in the pathogenesis of traumatic brain injury (TBI) is unknown. We hypothesized that, compared to wild type mice (+/+), mice deficient in PARP (-/-) would have reduced motor and cognitive deficits after TBI. Mice underwent controlled cortical impact (CCI) (6 m/s, 1.2 mm depth) and were tested for motor (d 1-5) and cognitive (d 14-18) function after CCI. PARP -/- mice demonstrated improved motor performance and improved cognitive function after CCI (both p < 0.05 compared to +/+). This is the first study to evaluate a role for PARP in functional outcome after TBI. The results suggest a detrimental role for PARP in the pathogenesis of TBI.

Small shifts in craniotomy position in the lateral fluid percussion injury model are associated with differential lesion development

Previous studies have shown that location and direction of injury may affect outcome in experimental models of traumatic brain injury. Significant variability in outcome data has also been noted in studies using the lateral fluid percussion brain injury model (FPI) in rats. In recent studies from our laboratory, we observed considerable variability in localization and severity of tissue damage as a function of small changes in craniotomy position. To further address this issue, we examined the relationship between craniotomy position and brain lesion size/location in rats subjected to moderate FPI (2.28 +/- 0.18 atmospheres). With placement of a 5-mm craniotomy adjacent to the sagittal suture, there was both ipsilateral and contralateral damage as detected at 3 weeks posttrauma using T2-weighted magnetic resonance imaging (MRI). The MRI lesions were generally restricted to the hippocampus and subcortical layers. Shifting of the craniotomy site laterally was associated with increased ipsilateral tissue damage and a greater cortical component that correlated with distance from the sagittal suture. In contrast, the contralateral MRI lesion did not change significantly in size or location unless the center of the craniotomy was placed more than 3.5 mm from the sagittal suture, under which condition contralateral damage could no longer be detected. Ipsilateral tissue damage as determined from the MRI scans was linearly correlated to motor outcome but not with cognitive outcome as assessed by the Morris Water Maze. We conclude that craniotomy position is critical in determining extent and location of tissue injury produced during the lateral FPI model in rats. Addressing such potential variability is essential for studies that address either injury mechanisms or therapeutic treatments.

Behavioral, electrophysiological, and histopathological consequences of mild fluid-percussion injury in the rat

Metabolic dysfunction in the relay nuclei of the rat vibrissa circuit follows traumatic brain injury (TBI). This study examined the effects of mild (1.4-1.5 atm) parasagittal fluid-percussion injury on the electrophysiology of this circuit. TBI caused significant reductions in slope and increases in latency of vibrissa-evoked field potentials 3 days after injury. Assessment of open-field swimming revealed an increase in thigmotaxis 2 days after injury. TBI caused mild selective cortical damage and limited axonal swelling at the injury site. Thus mild injury disrupts somatosensory electrophysiology and exploratory behavior.

Impaired motor learning and diffuse axonal damage in motor and visual systems of the rat following traumatic brain injury

Cognitive-motor functioning or motor skill learning is impaired in humans following traumatic brain injury. A more complete understanding of the mechanisms involved in disorders of motor skill learning is essential for any effective rehabilitation. The specific goals of this study were to examine motor learning disorders, and their relationship to pathological changes in adult rats with mild to moderate closed head injury. Motor learning deficits were determined by comparing the ability to complete a series of complex motor learning tasks with simple motor activity. The extent of neuronal damage was determined using silver impregnation. At all post-injury time points (day 1 to day 14), statistically significant deficits were observed in parallel bar traversing, foot placing, ladder climbing, and rope climbing. Performance improved with time, but never reached control levels. In contrast, no deficits were found in simple motor activity skills tested with beam balance and runway traverse. Histologically, axonal degeneration was widely distributed in several brain areas that relate to motor learning, including the white matter of sensorimotor cortex, corpus callosum, striatum, thalamus and cerebellum. Additionally, severely damaged axons were observed in the primary visual pathway, including the optic chiasm, optic tract, lateral geniculate nuclei, and superior colliculus. These findings suggest that motor learning deficits could be detected in mild or moderate brain injury, and this deficit could be attributed to a diffuse axonal injury distributed both in the motor and the visual systems.