Increased anticholinergic sensitivity following closed skull impact and controlled cortical impact traumatic brain injury in the rat

Altered amyloid precursor protein, tau-regulatory proteins, neuronal numbers and behaviour, but no tau pathology, synaptic and inflammatory changes or memory deficits, at 1 month following repetitive mild traumatic brain injury

Repetitive mild traumatic brain injury, commonly experienced following sports injuries, results in various secondary injury processes and is increasingly recognised as a risk factor for the development of neurodegenerative conditions such as chronic traumatic encephalopathy, which is characterised by tau pathology. We aimed to characterise the underlying pathological mechanisms that might contribute to the onset of neurodegeneration and behavioural changes in the less-explored subacute (1-month) period following single or repetitive controlled cortical impact injury (five impacts, 48 h apart) in 12-week-old male and female C57Bl6 mice. We conducted motor and cognitive testing, extensively characterised the status of tau and its regulatory proteins via western blot and quantified neuronal populations using stereology. We report that r-mTBI resulted in neurobehavioural deficits, gait impairments and anxiety-like behaviour at 1 month post-injury, effects not seen following a single injury. R-mTBI caused a significant increase in amyloid precursor protein, an increased trend towards tau phosphorylation and significant changes in kinase/phosphatase proteins that may promote a downstream increase in tau phosphorylation, but no changes in synaptic or neuroinflammatory markers. Lastly, we report neuronal loss in various brain regions following both single and repeat injuries. We demonstrate herein that repeated impacts are required to promote the initiation of a cascade of biochemical events that are consistent with the onset of neurodegeneration subacutely post-injury. Identifying the timeframe in which these changes occur and the pathological mechanisms involved will be crucial for the development of future therapeutics to prevent the onset or mitigate the progression of neurodegeneration following r-mTBI.

Poly(butyl cyanoacrylate) nanoparticles-deliveredβ-nerve growth factor promotes the neurite outgrowth and reduces the mortality in the rat after traumatic brain injury

Several transport vectors, including nanoparticles, have been reported to be used for the delivery of therapeutic medicines crossing the impermeable blood-brain barrier (BBB) to treat the diseases in the central nerve system (CNS), such as traumatic brain injury (TBI). Poly(n-butyl-2-cyanoacrylate) (PBCA) nanoparticles, made from biocompatible material, are regarded as a better potential delivery tool than others such as gold nanoparticles due to their degradabilityin vivo. However, little is known whether PBCA nanoparticles can be used to deliver neurotrophic factors into the brain to treat TBI. In this study, we first synthesized PBCA-carriedβ-nerve growth factor, a neurotrophic agent with a large molecular weight, and then intravenously injected the compound into TBI rats. We found that despite undergoing several synthesis steps and host circulation,β-NGF was able to be successfully delivered into the injured brain by PBCA nanoparticles, still maintain its neurotrophic activity for neurite outgrowth, and reduce the mortality of TBI rats. Our findings indicate that PBCA nanoparticles, with Tween 80, are an efficient delivery vector and a protective reservoir for large molecular therapeutic agents to treat TBI intravenously.

Anticholinergics: A potential option for preventing posttraumatic epilepsy

Interest in the use of anticholinergics to prevent the development of epilepsy after traumatic brain injury (TBI) has grown since recent basic studies have shown their effectiveness in modifying the epileptogenic process. These studies demonstrated that treatment with anticholinergics, in the acute phase after brain injury, decreases seizure frequency, and severity, and the number of spontaneous recurrent seizures (SRS). Therefore, anticholinergics may reduce the risk of developing posttraumatic epilepsy (PTE). In this brief review, we summarize the role of the cholinergic system in epilepsy and the key findings from using anticholinergic drugs to prevent PTE in animal models and new clinical trial protocols. Furthermore, we discuss why treatment with anticholinergics is more likely to prevent PTE than treatment for other epilepsies.

An experimental study on the early diagnosis of traumatic brain injury in rabbits based on a noncontact and portable system

Closed cerebral hemorrhage (CCH) is a common symptom in traumatic brain injury (TBI) patients who suffer intracranial hemorrhage with the dura mater remaining intact. The diagnosis of CCH patients prior to hospitalization and in the early stage of the disease can help patients get earlier treatments that improve outcomes. In this study, a noncontact, portable system for early TBI-induced CCH detection was constructed that measures the magnetic induction phase shift (MIPS), which is associated with the mean brain conductivity caused by the ratio between the liquid (blood/CSF and the intracranial tissues) change. To evaluate the performance of this system, a rabbit CCH model with two severity levels was established based on the horizontal biological impactor BIM-II, whose feasibility was verified by computed tomography images of three sections and three serial slices. There were two groups involved in the experiments (group 1 with 10 TBI rabbits were simulated by hammer hit with air pressure of 600 kPa by BIM-II and group 2 with 10 TBI rabbits were simulated with 650 kPa). The MIPS values of the two groups were obtained within 30 min before and after injury. In group 1, the MIPS values showed a constant downward trend with a minimum value of −11.17 ± 2.91° at the 30th min after 600 kPa impact by BIM-II. After the 650 kPa impact, the MIPS values in group 2 showed a constant downward trend until the 25th min, with a minimum value of −16.81 ± 2.10°. Unlike group 1, the MIPS values showed an upward trend after that point. Before the injury, the MIPS values in both group 1 and group 2 did not obviously change within the 30 min measurement. Using a support vector machine at the same time point after injury, the classification accuracy of the two types of severity was shown to be beyond 90%. Combined with CCH pathological mechanisms, this system can not only achieve the detection of early functional changes in CCH but can also distinguish different severities of CCH.

Repetitive mild concussion in subjects with a vulnerable cholinergic system: Lasting cholinergic-attentional impairments in CHT+/- mice

Previous research emphasized the impact of traumatic brain injury on cholinergic systems and associated cognitive functions. Here we addressed the converse question: Because of the available evidence indicating cognitive and neuronal vulnerabilities in humans expressing low-capacity cholinergic systems or with declining cholinergic systems, do injuries cause more severe cognitive decline in such subjects, and what cholinergic mechanisms contribute to such vulnerability? Using mice heterozygous for the choline transporter (CHT+/- mice) as a model for a limited cholinergic capacity, we investigated the cognitive and neuronal consequences of repeated, mild concussion injuries (rmCc). After five rmCc, and compared with wild type (WT) mice, CHT+/- mice exhibited severe and lasting impairments in sustained attention performance, consistent with effects of cholinergic losses on attention. However, rmCc did not affect the integrity of neuronal cell bodies and did not alter the density of cortical synapses. As a cellular mechanism potentially responsible for the attentional impairment in CHT+/- mice, we found that rmCc nearly completely attenuated performance-associated, CHT-mediated choline transport. These results predict that subjects with an already vulnerable cholinergic system will experience severe and lasting cognitive-cholinergic effects after even relatively mild injuries. If confirmed in humans, such subjects may be excluded from, or receive special protection against, activities involving injury risk. Moreover, the treatment and long-term outcome of traumatic brain injuries may benefit from determining the status of cholinergic systems and associated cognitive functions. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

The interplay between neuroendocrine and sleep alterations following traumatic brain injury

BACKGROUND

Sleep and endocrine disruptions are prevalent after traumatic brain injury (TBI) and are likely to contribute to morbidity.

OBJECTIVE

To describe the interaction between sleep and hormonal regulation following TBI and elucidate the impact that alterations of these systems have on cognitive responses during the posttraumatic chronic period.

METHODS

Review of preclinical and clinical literature describing long-lasting endocrine dysregulation and sleep alterations following TBI. The bidirectional relationship between sleep and hormones is described. Literature describing co-occurrence between sleep-wake disturbances and hormonal dysregulation will be presented. Review of literature describing cognitive effects of seep and hormones. The cognitive and functional impact of sleep disturbances and hormonal dysregulation is discussed within the context of TBI.

RESULTS/CONCLUSIONS

Sleep and hormonal alterations impact cognitive and functional outcome after TBI. Diagnosis and treatment of these disturbances will impact recovery following TBI and should be considered in the post-acute rehabilitative setting.

The Controlled Cortical Impact Model: Applications, Considerations for Researchers, and Future Directions

Controlled cortical impact (CCI) is a mechanical model of traumatic brain injury (TBI) that was developed nearly 30 years ago with the goal of creating a testing platform to determine the biomechanical properties of brain tissue exposed to direct mechanical deformation. Initially used to model TBIs produced by automotive crashes, the CCI model rapidly transformed into a standardized technique to study TBI mechanisms and evaluate therapies. CCI is most commonly produced using a device that rapidly accelerates a rod to impact the surgically exposed cortical dural surface. The tip of the rod can be varied in size and geometry to accommodate scalability to difference species. Typically, the rod is actuated by a pneumatic piston or electromagnetic actuator. With some limits, CCI devices can control the velocity, depth, duration, and site of impact. The CCI model produces morphologic and cerebrovascular injury responses that resemble certain aspects of human TBI. Commonly observed are graded histologic and axonal derangements, disruption of the blood-brain barrier, subdural and intra-parenchymal hematoma, edema, inflammation, and alterations in cerebral blood flow. The CCI model also produces neurobehavioral and cognitive impairments similar to those observed clinically. In contrast to other TBI models, the CCI device induces a significantly pronounced cortical contusion, but is limited in the extent to which it models the diffuse effects of TBI; a related limitation is that not all clinical TBI cases are characterized by a contusion. Another perceived limitation is that a non-clinically relevant craniotomy is performed. Biomechanically, this is irrelevant at the tissue level. However, craniotomies are not atraumatic and the effects of surgery should be controlled by including surgical sham control groups. CCI devices have also been successfully used to impact closed skulls to study mild and repetitive TBI. Future directions for CCI research surround continued refinements to the model through technical improvements in the devices (e.g., minimizing mechanical sources of variation). Like all TBI models, publications should report key injury parameters as outlined in the NIH common data elements (CDEs) for pre-clinical TBI.

The Controlled Cortical Impact Model of Experimental Brain Trauma: Overview, Research Applications, and Protocol

Controlled cortical impact (CCI) is a commonly used and highly regarded model of brain trauma that uses a pneumatically or electromagnetically controlled piston to induce reproducible and well-controlled injury. The CCI model was originally used in ferrets and it has since been scaled for use in many other species. This chapter will describe the historical development of the CCI model, compare and contrast the pneumatic and electromagnetic models, and summarize key short- and long-term consequences of TBI that have been gleaned using this model. In accordance with the recent efforts to promote high-quality evidence through the reporting of common data elements (CDEs), relevant study details-that should be reported in CCI studies-will be noted.

Chronic Histopathological and Behavioral Outcomes of Experimental Traumatic Brain Injury in Adult Male Animals

The purpose of this review is to survey the use of experimental animal models for studying the chronic histopathological and behavioral consequences of traumatic brain injury (TBI). The strategies employed to study the long-term consequences of TBI are described, along with a summary of the evidence available to date from common experimental TBI models: fluid percussion injury; controlled cortical impact; blast TBI; and closed-head injury. For each model, evidence is organized according to outcome. Histopathological outcomes included are gross changes in morphology/histology, ventricular enlargement, gray/white matter shrinkage, axonal injury, cerebrovascular histopathology, inflammation, and neurogenesis. Behavioral outcomes included are overall neurological function, motor function, cognitive function, frontal lobe function, and stress-related outcomes. A brief discussion is provided comparing the most common experimental models of TBI and highlighting the utility of each model in understanding specific aspects of TBI pathology. The majority of experimental TBI studies collect data in the acute postinjury period, but few continue into the chronic period. Available evidence from long-term studies suggests that many of the experimental TBI models can lead to progressive changes in histopathology and behavior. The studies described in this review contribute to our understanding of chronic TBI pathology.

Alterations in Cholinergic Pathways and Therapeutic Strategies Targeting Cholinergic System after Traumatic Brain Injury

Traumatic brain injury (TBI) results in varying degrees of disability in a significant number of persons annually. The mechanisms of cognitive dysfunction after TBI have been explored in both animal models and human clinical studies for decades. Dopaminergic, serotonergic, and noradrenergic dysfunction has been described in many previous reports. In addition, cholinergic dysfunction has also been a familiar topic among TBI researchers for many years. Although pharmacological agents that modulate cholinergic neurotransmission have been used with varying degrees of success in previous studies, improving their function and maximizing cognitive recovery is an ongoing process. In this article, we review the previous findings on the biological mechanism of cholinergic dysfunction after TBI. In addition, we describe studies that use both older agents and newly developed agents as candidates for targeting cholinergic neurotransmission in future studies.

Functional assessment of long-term deficits in rodent models of traumatic brain injury

Traumatic brain injury (TBI) ranks as the leading cause of mortality and disability in the young population worldwide. The annual US incidence of TBI in the general population is estimated at 1.7 million per year, with an estimated financial burden in excess of US$75 billion a year in the USA alone. Despite the prevalence and cost of TBI to individuals and society, no treatments have passed clinical trial to clinical implementation. The rapid expansion of stem cell research and technology offers an alternative to traditional pharmacological approaches targeting acute neuroprotection. However, preclinical testing of these approaches depends on the selection and characterization of appropriate animal models. In this article we consider the underlying pathophysiology for the focal and diffuse TBI subtypes, discuss the existing preclinical TBI models and functional outcome tasks used for assessment of injury and recovery, identify criteria particular to preclinical animal models of TBI in which stem cell therapies can be tested for safety and efficacy, and review these criteria in the context of the existing TBI literature. We suggest that 2 months post-TBI is the minimum period needed to evaluate human cell transplant efficacy and safety. Comprehensive review of the published TBI literature revealed that only 32% of rodent TBI papers evaluated functional outcome ≥1 month post-TBI, and only 10% evaluated functional outcomes ≥2 months post-TBI. Not all published papers that evaluated functional deficits at a minimum of 2 months post-TBI reported deficits; hence, only 8.6% of overall TBI papers captured in this review demonstrated functional deficits at 2 months or more postinjury. A 2-month survival and assessment period would allow sufficient time for differentiation and integration of human neural stem cells with the host. Critically, while trophic effects might be observed at earlier time points, it will also be important to demonstrate the sustainability of such an effect, supporting the importance of an extended period of in vivo observation. Furthermore, regulatory bodies will likely require at least 6 months survival post-transplantation for assessment of toxicology/safety, particularly in the context of assessing cell abnormalities.

A novel animal model of closed-head concussive-induced mild traumatic brain injury: development, implementation, and characterization

Closed-head concussive injury is one of the most common causes of traumatic brain injury (TBI). While single concussions result in short-term neurologic dysfunction, multiple concussions can result in cumulative damage and increased risk for neurodegenerative disease. Despite the prevalence of concussion, knowledge about what occurs in the brain following this injury is limited, in part due to the limited number of appropriate animal research models. To study clinically relevant concussion we recently developed a simple, non-invasive rodent model of closed-head projectile concussive impact (PCI) TBI. For this purpose, anesthetized rats were placed on a platform positioned above a torque-sealed microcentrifuge tube packed with fixed amounts of dry ice. Upon heating, rapid sublimation of the dry ice produced a build-up of compressed CO(2) that triggered an eruptive force causing the cap to launch as an intact projectile, resulting in a targeted PCI head injury. A stainless steel helmet was implemented to protect the head from bruising, yet allowing the brain to sustain a mild PCI event. Depending on the injury location and the application of the helmet, PCI-induced injuries ranged from severe (i.e., head injury with subdural hematomas, intracranial hemorrhage, and brain tissue damage), to mild (no head injury, intracranial hemorrhage, or gross morphological pathology). Although no gross pathology was evident in mild PCI-induced injury, the following protein changes and behavioral abnormalities were detected between 1 and 24 h after PCI injury: (1) upregulation of glial fibrillary acidic protein (GFAP) in hippocampal regions; (2) upregulation of ubiquitin carboxyl-terminal hydrolase L1 (UCHL-1) in cortical tissue; and (3) significant sensorimotor abnormalities. Overall, these results indicated that this PCI model was capable of replicating salient pathologies of a clinical concussion, and could generate reproducible and quantifiable outcome measures.

Hippocampal θ dysfunction after lateral fluid percussion injury

Chronic memory deficits are a major cause of morbidity following traumatic brain injury (TBI). In the rat, the hippocampal theta rhythm is a well-studied correlate of memory function. This study sought to investigate disturbances in hippocampal theta rhythm following lateral fluid percussion injury in the rat. A total of 13 control rats and 12 TBI rats were used. Electrodes were implanted in bilateral hippocampi and an electroencephalogram (EEG) was recorded while the rats explored a new environment, and also while navigating a modified version of the Barnes maze. Theta power and peak theta frequency were significantly attenuated in the injured animals. Further, injured rats were less likely to develop a spatial strategy for Barnes maze navigation compared to control rats. In conclusion, rats sustaining lateral fluid percussion injury demonstrated deficits in hippocampal theta activity. These deficits may contribute to the underlying memory problems seen in chronic TBI.

The combined effects of exercise and foods in preventing neurological and cognitive disorders

OBJECTIVE

Exercise and select diets have important influences on health and plasticity of the nervous system, and the molecular mechanisms involved with these actions are starting to be elucidated. New evidence indicates that exercise, in combination with dietary factors, exerts its effects by affecting molecular events related to the management of energy metabolism and synaptic plasticity.

METHODS

Published studies in animals and humans describing the effects of exercise and diets in brain plasticity and cognitive abilities are discussed.

RESULTS

New evidence indicates that exercise and select diets exert their effects by affecting molecular events related to the management of energy metabolism and synaptic plasticity. An important instigator in the molecular machinery stimulated by exercise is brain-derived neurotrophic factor (BDNF), which acts at the interface of metabolism and plasticity.

CONCLUSIONS

Recent studies show that selected dietary factors share similar mechanisms with exercise, and in some cases they can complement the action of exercise. Therefore, exercise and dietary management appear as a non-invasive and effective strategy to counteract neurological and cognitive disorders.

Resveratrol attenuates behavioral impairments and reduces cortical and hippocampal loss in a rat controlled cortical impact model of traumatic brain injury

Resveratrol (3,5,4'-trihydroxystilbene) is a plant-derived small molecule that is protective against multiple neurological and systemic insults. To date, no studies have explored the potential for resveratrol to provide behavioral protection in adult animals in the setting of traumatic brain injury (TBI). Using 50 male Sprague-Dawley rats, we employed the controlled cortical impact (CCI) model to ascertain whether post-injury administration of resveratrol would reduce the severity of the well-described cognitive and motor deficits associated with the model. Contusion volumes and hippocampal neuronal numbers were also measured to characterize the tissue and neuronal-sparing properties, respectively, of resveratrol. We found that 100 mg/kg, but not 10 mg/kg, of intraperitoneal resveratrol administered after injury provides significant behavioral protection in rats sustaining CCI. Specifically, rodents treated with 100 mg/kg of resveratrol showed improvements in motor performance (beam balance and beam walking) and testing of visuospatial memory (Morris water maze). Behavioral protection was correlated with significantly reduced contusion volumes, preservation of CA1 and CA3 hippocampal neurons, and protection from overt hippocampal loss as a result of incorporation into the overlying cortical contusion in resveratrol-treated animals. Although the mechanisms by which resveratrol mediates its neuroprotection is unclear, the current study adds to the growing literature identifying resveratrol as a potential therapy for human brain injury.

Flumazenil administration attenuates cognitive impairment in immature rats after controlled cortical impact

Evidence suggests that the gamma-aminobutyric acid (GABA)ergic system may be involved in cognitive dysfunction following traumatic brain injury (TBI). We investigated the effect of flumazenil treatment, a benzodiazepine antagonist approved by the U.S. Food and Drug Administration, on learning and memory in the immature rat following experimental brain injury. Post-natal day 17 rats were injured using controlled cortical impact. Systemic treatment with flumazenil at 1, 5, and 10 mg/kg was initiated on post-injury day 1 and administered for 13 days via daily intraperitoneal injections. Morris water maze (MWM) testing was used to measure latency to find a submerged platform and the results from experimental and control animals were compared. We demonstrated a significant dose-dependent improvement in MWM performance in drug-treated animals. This is the first study demonstrating the efficacy of flumazenil in reducing post-TBI cognitive deficits and we propose that these effects may be related to modulation of the GABA(A) receptor.

Acute neuroprotection to pilocarpine-induced seizures is not sustained after traumatic brain injury in the developing rat

Following CNS injury there is a period of vulnerability when cells will not easily tolerate a secondary insult. However recent studies have shown that following traumatic brain injury (TBI), as well as hypoxic-ischemic injuries, the CNS may experience a period of protection termed "preconditioning." While there is literature characterizing the properties of vulnerability and preconditioning in the adult rodent, there is an absence of comparable literature in the developing rat. To determine if there is a window of vulnerability in the developing rat, post-natal day 19 animals were subjected to a severe lateral fluid percussion injury followed by pilocarpine (Pc)-induced status epilepticus at 1, 6 or 24 h post TBI. During the first 24 h after TBI, the dorsal hippocampus exhibited less status epilepticus-induced cell death than that normally seen following Pc administration alone. Instead of producing a state of hippocampal vulnerability to activation, TBI produced a state of neuroprotection. However, in a second group of animals evaluated 20 weeks post injury, double-injured animals were statistically indistinguishable in terms of seizure threshold, mossy fiber sprouting and cell survival when compared to those treated with Pc alone. TBI, therefore, produced a temporary state of neuroprotection from seizure-induced cell death in the developing rat; however, this ultimately conferred no long-term protection from altered hippocampal circuit rearrangements, enhanced excitability or later convulsive seizures.

The effects of a ketogenic diet on behavioral outcome after controlled cortical impact injury in the juvenile and adult rat

The ketogenic diet has been shown to have unique properties that make it a more suitable cerebral fuel under various neuropathological conditions (e.g., starvation, ischemia, and traumatic brain injury (TBI). Recently, age-dependent ketogenic neuroprotection was shown among postnatal day 35 (PND35) and PND45 rats after TBI, but not in PND17 and PND65 animals (Prins et al., 2005). The present study addresses the therapeutic potential of a ketogenic diet on motor and cognitive deficits after TBI. PND35 and PND75 rats received sham or controlled cortical impact (CCI) surgery and were placed on either standard (Std) or ketogenic (KG) diet for 7 days. Beam walking and the Morris water maze (MWM) were used to assess sensory motor function and cognition, respectively. PND35 CCI Std animals showed significantly longer traverse times than sham and CCI KG animals at the beginning of motor training. Footslip analysis revealed better performance among the sham and the CCI KG animals compared to the CCI Std group. In the MWM PND35 CCI KG animals showed significantly shorter escape latencies compared to CCI Std-fed animals. During the same time period there was no significant difference between sham animals and CCI KG animals. The therapeutic effect of the ketogenic diet on beam walking and cognitive performance was not observed in PND75 animals. This finding supports our theory about age-dependent utilization and effectiveness of ketones as an alternative fuel after TBI.

The cognitive impact of anticholinergics: a clinical review

Context:

The cognitive side effects of medications with anticholinergic activity have been documented among older adults in a variety of clinical settings. However, there has been no systematic confirmation that acute or chronic prescribing of such medications lead to transient or permanent adverse cognitive outcomes.

Objective:

Evaluate the existing evidence regarding the effects of anticholinergic medications on cognition in older adults.

Data sources:

We searched the MEDLINE, OVID, and CINAHL databases from January, 1966 to January, 2008 for eligible studies.

Study selection:

Studies were included if the anticholinergic activity was systematically measured and correlated with standard measurements of cognitive performance. Studies were excluded if they reported case studies, case series, editorials, and review articles.

Data extraction:

We extracted the method used to determine anticholinergic activity of medications and its association with cognitive outcomes.

Results:

Twenty-seven studies met our inclusion criteria. Serum anticholinergic assay was the main method used to determine anticholinergic activity. All but two studies found an association between the anticholinergic activity of medications and either delirium, cognitive impairment or dementia.

Conclusions:

Medications with anticholinergic activity negatively affect the cognitive performance of older adults. Recognizing the anticholinergic activity of certain medications may represent a potential tool to improve cognition.

Cholinergic deficiency hypothesis in delirium: a synthesis of current evidence

Deficits in cholinergic function have been postulated to cause delirium and cognitive decline. This review examines current understanding of the cholinergic deficiency hypothesis in delirium by synthesizing evidence on potential pathophysiological pathways. Acetylcholine synthesis involves various precursors, enzymes, and receptors, and dysfunction in these components can lead to delirium. Insults to the brain, like ischemia and immunological stressors, can precipitously alter acetylcholine levels. Imbalances between cholinergic and other neurotransmitter pathways may result in delirium. Furthermore, genetic, enzymatic, and immunological overlaps exist between delirium and dementia related to the cholinergic pathway. Important areas for future research include identifying biomarkers, determining genetic contributions, and evaluating response to cholinergic drugs in delirium. Understanding how the cholinergic pathway relates to delirium may yield innovative approaches in the diagnosis, prevention, and treatment of this common, costly, and morbid condition.

A review of pharmacological treatments used in experimental models of traumatic brain injury

PRIMARY OBJECTIVE

We provide a review of recent chronic and delayed rehabilitative pharmacological treatments examined in experimental models of traumatic brain injury. There is a specific emphasis on studies aiming to enhance cognitive recovery.

MAIN OUTCOMES AND RESULTS

Decreased neuronal activity is believed to contribute to persistent cognitive disabilities. Neurotransmitter based rehabilitative treatments that increase neuronal activity may assist in the recovery of cognitive function. However, timing and dosage of drug treatment are influential in cognitive enhancement. Drug treatments that affect single and multiple neurotransmitter systems have the ability to significantly influence recovery of function following brain injury.

CONCLUSIONS

Understanding the relationship between neural disturbances and functional deficits following brain injury is challenging. Cognitive impairment may be the result of a single event or multiple events that occur after the initial insult. Increasing neuronal activity during the chronic phase of injury seems to be an effective treatment strategy for facilitating cognitive recovery. Pharmacological agents do not necessarily display the same effects in an injured brain as in a non-injured brain. Thus, further research is needed to establish the effectiveness of rehabilitative drug treatments.

Extracellular signal-regulated kinase 2 (ERK2) knockdown mice show deficits in long-term memory; ERK2 has a specific function in learning and memory

The extracellular signal-regulated kinase (ERK) 1 and 2 are important signaling components implicated in learning and memory. These isoforms display a high degree of sequence homology and share a similar substrate profile. However, recent findings suggest that these isoforms may have distinct roles: whereas ERK1 seems to be not so important for associative learning, ERK2 might be critically involved in learning and memory. Thus, the individual role of ERK2 has received considerable attention, although it is yet to be understood. Here, we have generated a series of mice in which ERK2 expression decreased in an allele dose-dependent manner. Null ERK2 knock-out mice were embryonic lethal, and the heterozygous mice were anatomically impaired. To gain a better understanding of the influence of ERK2 on learning and memory, we also generated knockdown mice in which ERK2 expression was partially (20-40%) reduced. These mutant mice were viable and fertile with normal appearance. The mutant mice showed a deficit in long-term memory in classical fear conditioning, whereas short-term memory was normal. The mice also showed learning deficit in the water maze and the eight-arm radial maze. The ERK1 expression level of the knockdown mice was comparable with the wild-type control. Together, our results indicate a noncompensable role of ERK2-dependent signal transduction in learning and memory.

Acetylcholine and choline dynamics provide early and late markers of traumatic brain injury

We assessed acetylcholine (ACh) and choline (Ch) dynamics 2.5 h, 1, 4 and 14 days after cerebral cortex impact injury or craniotomy only in adult male Sprague-Dawley rats. Cortical endogenous ACh (D0ACh), endogenous free Ch (D0Ch), deuterium-labeled Ch (D4Ch), and ACh synthesized from D4Ch (D4ACh) were measured by gas-chromatography mass-spectrometry after intravenous injection of D4Ch followed in 1 min by microwave fixation of the brain. D0Ch increased in and around the impact up to 700% of control within 1 day after trauma. Smaller D0Ch increases were found in the cortex contralateral to the impact and in both hemispheres after craniotomy only. D4Ch contents increased to 200% in the impact and surrounding regions 4-14 days post-trauma, with lower increases 2.5 h post-trauma. D0ACh decreased at all times post-trauma in the impact center, and initially in the periphery and adjacent regions with a recovery at 14 days. Similar D0ACh decreases, although of lesser extent and magnitude were present in the craniotomy only group. D4ACh showed a peak at one day post-trauma in all regions studied in the impact and craniotomy groups. In conclusion, D0Ch tissue level was an early marker of trauma, while 14 days after trauma Ch uptake from blood was enhanced in and around the traumatized cortex. Craniotomy by itself induced a generalized increase in ACh turnover 1 day after this minimal trauma. Choline acetyltransferase activity was reduced in the impact center region but not affected in the adjacent and contralateral regions or by craniotomy.

Delayed, post-injury treatment with aniracetam improves cognitive performance after traumatic brain injury in rats

Chronic cognitive impairment is an enduring aspect of traumatic brain injury (TBI) in both humans and animals. Treating cognitive impairment in the post-traumatic stages of injury often involves the delivery of pharmacologic agents aimed at specific neurotransmitter systems. The current investigation examined the effects of the nootropoic drug aniracetam on cognitive recovery following TBI in rats. Three experiments were performed to determine (1) the optimal dose of aniracetam for treating cognitive impairment, (2) the effect of delaying drug treatment for a period of days following TBI, and (3) the effect of terminating drug treatment before cognitive assessment. In experiment 1, rats were administered moderate fluid percussion injury and treated with vehicle, 25, or 50 mg/kg aniracetam for 15 days. Both doses of aniracetam effectively reduced injury-induced deficits in the Morris water maze (MWM) as measured on postinjury days 11-15. In experiment 2, injured rats were treated with 50 mg/kg aniracetam or vehicle beginning on day 11 postinjury and continuing for 15 days. MWM performance, assessed on days 26-30, indicates that aniracetam-treated animals performed as well as sham-injured controls. In experiment 3, animals were injured and treated with aniracetam for 15 days. Drug treatment was terminated during MWM testing on postinjury days 16-20. In this experiment, aniracetam-treated rats did not perform better than vehicle-treated rats. The results of these experiments indicate that aniracetam is an effective treatment for cognitive impairment induced by TBI, even when treatment is delayed for a period of days following injury.

Spatial memory formation and memory-enhancing effect of glucose involves activation of the tuberous sclerosis complex-Mammalian target of rapamycin pathway

The tuberous sclerosis complex-mammalian target of rapamycin (TSC-mTOR) cascade integrates growth factor and nutritional signals to regulate the synthesis of specific proteins. Because both growth factor signaling and glucose have been implicated in memory formation, we questioned whether mTOR activity is required for long-term spatial memory formation and whether this cascade is involved in the memory-augmenting effect of centrally applied glucose. To test our hypothesis, we directly administered rapamycin (an inhibitor of mTOR), glucose, 5-aminoimidazole-4-carboxamide-1beta-4-ribonucleoside (AICAR; an activator of AMP kinase), or glucose plus rapamycin into the dorsal hippocampus after we trained rats in the Morris water maze task. The results from these studies indicate that glucose enhances, whereas AICAR and rapamycin both impair, long-term spatial memory. Furthermore, the memory-impairing effect of targeted rapamycin administration could not be overcome by coadministration of glucose. Consistent with these behavioral results, biochemical analysis revealed that glucose and AICAR had opposing influences on the activation of the TSC-mTOR cascade, as indicated by the phosphorylation of ribosomal S6 kinase (S6K) and 4E binding protein 1 (4EBP1), targets of mTOR. Together, these findings suggest that memory formation requires the mTOR cascade and that the memory-enhancing effect of glucose involves its ability to activate this pathway.

Treatment of depression following traumatic brain injury

Depression is a common consequence of traumatic brain injury (TBI), and is a source of substantial distress and disability for persons with TBI and their families. This article offers a practical approach to the evaluation and treatment of this condition. Diagnostic and etiologic considerations relevant to this issue are reviewed first. Next, somatic therapies for posttraumatic depression, including antidepressant medications and electroconvulsive therapy, are discussed. Use of these therapies is also considered in the context of the common medical and neurological comorbidities among persons with TBI. Finally, psychosocial interventions relevant to the care of persons with posttraumatic depression are presented.

Blockade of γ-secretase activity within the hippocampus enhances long-term memory

The gamma-secretase complex, a membrane-bound aspartyl protease, hydrolyzes the transmembrane domains of several integral membrane proteins including the key signaling molecules amyloid precursor protein (APP), Notch, deleted in colorectal cancer (DCC), and N- and E-cadherins. The proteolysis processing of these proteins is critical for generation of signaling molecules that may participate in neuronal communication and plasticity. Using a potent gamma-secretase inhibitor, L-685,458, we examined if blockade of its activity in the hippocampus can influence contextual and spatial memory in rats. Surprisingly, we observed that post-training blockade of gamma-secretase activity leads to enhanced long-term memory in two hippocampus-dependent tasks. This suggests that a signaling molecule(s) generated by gamma-secretase activity may have a negative influence on long-term memory formation.

Methylphenidate treatment of attention-deficit/hyperactivity disorder secondary to traumatic brain injury: a critical appraisal of treatment studies

OBJECTIVE

Are stimulants effective in treating attention-deficit/hyperactivity disorder secondary to traumatic brain injury (ADHD/TBI)? The authors reviewed and examined the current knowledge on efficacy of stimulant treatment ADHD/TBI.

METHOD

A systematic review of the literature using a quality assessment scale to assess the quality of randomized clinical trials was undertaken. We identified all studies in which stimulants had been administered to individuals with ADHD/TBI. Information was extracted on study characteristics, interventions, and outcomes. A meta-analysis was not performed because of the limited number of studies with strict research design and the heterogeneity of outcome measures. Seven studies involving 118 subjects, 41 of whom were children and adolescents, were identified.

RESULTS

Of the seven identified studies, one was a chart review, one used a single-blind, placebo-controlled crossover design, and five were double-blind, placebo-controlled crossovers. These studies used >50 subjective and objective tests to measure behavioral and cognitive outcomes. Methylphenidate (MPH) effects on behavior (hyperactivity, impulsivity) were evident but were not as robust as those typically observed with MPH in primary ADHD. The effect of MPH on cognition was less apparent. More favorable outcome was associated with initiation of treatment soon after head injury, although this factor was not systematically studied, and trials with relatively long durations. Studies with negative MPH response reported neither improvement in behavioral nor cognitive symptoms.

CONCLUSION

There is only modest evidence to support the efficacy of MPH in the treatment of ADHD/TBI. While MPH might still be a promising treatment for ADHD/TBI, there is need for rigorous treatment outcome research among representative samples of ADHD/TBI individuals.

Applications of the P50 evoked response to the evaluation of cognitive impairments after traumatic brain injury

This article reviews the applications of the P50 evoked response to paired auditory stimuli (P50 ERP) in the study and evaluation of cognitive impairments after traumatic brain injury (TBI). The cholinergic hypothesis of cognitive impairment after TBI and the relationship of impaired auditory sensory gating to that hypothesis are presented. The neurobiology of impaired sensory gating, the relationship of that neurobiology to the P50 ERP, and the principles of P50 ERP recording are discussed. Studies of the P50 ERP among patients with persistent cognitive complaints after TBI are reviewed. Finally, possible clinical applications and limitations of the P50 ERP in the study, evaluation, and treatment of patients with cognitive impairments after TBI are offered.

The delayed administration of dehydroepiandrosterone sulfate improves recovery of function after traumatic brain injury in rats

The goal of the current study was to test the hypothesis that dehydroepiandrosterone-sulfate (DHEAS), a pro-excitatory neurosteroid, could facilitate recovery of function in male rats after delayed treatment following TBI. DHEAS has been found to play a major role in brain development and aging by influencing the migration of neurons, arborization of dendrites, and formation of new synapses. These characteristics make it suitable as a potential treatment to enhance neural repair in response to CNS injury. In our study, behavioral tests were conducted concurrently with DHEAS administration (0, 5, 10, or 20 mg/kg) starting seven days post-injury (PI). These assays included 10 days of Morris Water Maze testing (MWM; 7d PI), 10 days of Greek-Cross (GC; 21d PI), Tactile Adhesive Removal task (TAR; PI days: 6, 13, 20, 27, 34), and spontaneous motor behavior testing (SMB; PI days: 2, 4, 6, 12, 19, 26, 33). Brain-injured rats showed an improvement in performance in all tasks after 5, 10, or 20 mg/kg DHEAS. The most effective dose of DHEAS in the MWM was 10 mg/kg, while in the GC it was 20 mg/kg, in TAR 5 mg/kg, and all doses, except for vehicle, were effective at reducing injury-induced SMB hyperactivity. In no task did DHEAS-treated animals perform worse than the injured controls. In addition, DHEAS had no significant effects on behavioral performance in the sham-operates. These results can be interpreted to demonstrate that after a 7-day delay, the chronic administration of DHEAS to injured rats significantly improves behavioral recovery on both sensorimotor and cognitive tasks.

The cholinergic hypothesis of cognitive impairment caused by traumatic brain injury

Cognitive impairments are among the most common neuropsychiatric sequelae of traumatic brain injury at all levels of severity. Cerebral cholinergic neurons and their ascending projections are particularly vulnerable to acute and chronic traumatically mediated dysfunction. In light of the important role of acetylcholine in arousal, attention, memory, and other aspects of cognition, cerebral cholinergic systems contribute to and may also be a target for pharmacologic remediation among individuals with post-traumatic cognitive impairments. This article will review the evidence in support of this hypothesis. Evidence of relatively selective damage to cholinergic injury, the development of persistent anticholinergic sensitivity, and the effects of cholinergic augmentation on memory performance are presented first. Thereafter, neuropathologic, electrophysiologic, and pharmacologic evidence of cholinergic dysfunction after traumatic brain injury in humans is reviewed. Finally, future directions for investigation of the cholinergic hypothesis and possible clinical applications of this information are discussed.

Concepts of CNS Plasticity in the Context of Brain Damage and Repair

BACKGROUND

How effectively the brain can respond to injury and undergo structural repair has become one of the most exciting areas of contemporary basic and translational neuroscience research. Although there are no clinical treatments yet available to enhance repair of the damaged brain, there are a number of potential therapies being investigated. New drugs are designed to provide some degree of neuroprotection by preventing injured or vulnerable nerve cells from dying, or they are given in the hope of stimulating regenerative processes that could lead to the restoration or the formation of new connections that were lost because of the injury.

MAIN OUTCOME MEASURES

The developments in pharmacology are based primarily upon understanding the molecular mechanisms of drug actions at the level of the genome or with respect to cellular metabolism. Although there is a substantial interest in the pharmacology of brain repair, there seems to be less concern with the various theories of central nervous system plasticity, organization, and reorganization after an injury.

CONCLUSIONS

This review discusses some of the older and current ideas and theories that have been presented over the years to explain recovery of function. We then provide an overview of what is being done in the laboratory to develop new and safe drugs for the treatment of traumatic brain injuries.

Intrahippocampal wortmannin infusion enhances long-term spatial and contextual memories

The transition from short- to long-term memory involves several biochemical cascades, some of which act in an antagonistic manner. Post-training intrahippocampal administration of wortmannin, a pharmacological inhibitor of phosphatidylinositol 3-kinase, had no effect on memory tested 3 h later, but improved long-term memory tested 48 h following the completion of training. This effect was seen in two hippocampus-dependent tasks: the Morris water maze, using both massed and distributed training paradigms, and contextual fear conditioning. The improvement of long-term memory appears to be the result of enhanced consolidation, as wortmannin had no effect on memory recall. These results are consistent with the hypothesis that memory consolidation involves competing processes, and that blockade of an inhibitory constraint facilitates the consolidation process.

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 research: a review of clinical studies

There is a growing volume of research on trauma brain injury (TBI) as evidenced by a recent Medline search that reported over 6000 articles published on TBI in the past 5 years.

Traumatic injury of cultured astrocytes alters inositol (1,4,5)-trisphosphate-mediated signaling

Our previous studies using an in vitro model of traumatic injury have shown that stretch injury of astrocytes causes a rapid elevation in intracellular free calcium ([Ca2+]i), which returns to near normal by 15 min postinjury. We have also shown that after injury astrocyte intracellular calcium stores are no longer able to release Ca2+ in response to signal transduction events mediated by the second messenger inositol (1,4,5)-trisphosphate (IP3, Rzigalinski et al., 1998). Therefore, we tested the hypothesis that in vitro injury perturbs astrocyte IP3 levels. Astrocytes grown on Silastic membranes were labeled with [3H]-myo-inositol and stretch-injured. Cells and media were acid-extracted and inositol phosphates isolated using anion-exchange columns. After injury, inositol polyphosphate (IPx) levels increased up to 10-fold over uninjured controls. Significant injury-induced increases were seen at 5, 15, and 30 min and at 24 and 48 h postinjury. Injury-induced increases in IPx were equivalent to the maximal glutamate and trans-(1S,3R)-1-amino-1,3-cyclopentanedicarboxylic acid-stimulated IPx production, however injury-induced increases in IPx were sustained through 24 and 48 h postinjury. Injury-induced increases in IPx were attenuated by pretreatment with the phospholipase C inhibitors neomycin (100 microM) or U73122 (1.0 microM). Since we have previously shown that astrocyte [Ca2+]i returns to near basal levels by 15 min postinjury, the current results suggest that IP3-mediated signaling is uncoupled from its target, the intracellular Ca2+ store. Uncoupling of IP3-mediated signaling may contribute to the pathological alterations seen after traumatic brain injury.

Recovery of water maze performance in aged versus young rats after brain injury with the impact acceleration model

Clinically, elderly patients have a higher cognitive morbidity from head trauma than young patients. We have modeled injury in aged rats in an effort to elucidate the pathophysiology of this enhanced sensitivity and, in particular, to determine if there are susceptibility differences in forebrain cholinergic innervation in young versus aged rats. Aged (20-23 months) and young (2-3 months) rats were subjected to injury under halothane anesthesia using the Marmarou impact acceleration model. Injury parameters required adjustment downward for the aged rats (323 g at 1.61 m versus 494 g at 2.06 m) to provide equivalent mortality (30% versus 20%) and loss of righting-reflex times (10-12 min average). At 1 week following injury, the aged animals were markedly more impaired in water maze performance than were young rats, and this difference persisted at least up to 5 weeks following injury. The extent of improvement in performance from 1 to 5 weeks was markedly worse for aged animals compared to young animals. Forebrain synaptosomal choline uptake was decreased in aged injured rats by 8-14% at 1, 3, and 5 weeks postinjury, but not decreased in young injured rats. No differences were noted in entorhinal cortex or hippocampal choline uptake. This model effectively demonstrates the markedly increased susceptibility of older animals to head injury and their decreased capacity for recovery. The neurophysiological basis for this difference is presently unknown, but the differences in cognitive dysfunction between young and aged rats appears to be much greater than would seem to be explained by the small differences in forebrain cholinergic innervation.

Cognitive impairment and synaptosomal choline uptake in rats following impact acceleration injury

Traumatic brain injury is well known to cause deficits in learning and memory, which typically improve with time. Animal studies with fluid percussion or controlled cortical impact injury have identified transient disturbances in forebrain cholinergic innervation which may contribute to such cognitive problems. This study examines the extent to which water maze performance and forebrain synaptosomal choline uptake are affected one week after injury using the newly developed impact acceleration injury model. Injury or sham injury was delivered to adult male Sprague-Dawley rats under halothane anesthesia using a 500-g 2.1-m weight drop. Based on righting reflex, injured rats were divided into moderate (< or = 12 min) or severe (>12 min) groups. Water maze testing was performed on days 5-7 postinjury. On day 7, choline uptake was determined in synaptosomes from hippocampus, a parietal cortex, and entorhinal cortex. Maze learning was severely impaired in the severe injury group but not in the moderate injury group. Learning retention was slightly impaired in the moderate injury group and severely affected in the severe injury group. There was a very strong correlation between the severity of injury as determined by prolongation of righting times and disruption of maze learning at 1 week postinjury. There was no change in synaptosomal choline uptake in any of the forebrain regions in the severe injury group, but a slight (14%) decrease in the hippocampus and parietal cortex of the moderate injury group. Correlation analysis showed no relationship between synaptosomal choline uptake in any brain region and performance in either water maze learning or retention. This study shows that the impact acceleration model produces cognitive impairments equivalent to those seen with fluid percussion injury and controlled cortical impact. Compared with those models, the impact acceleration model does not produce a similar disruption of forebrain cholinergic nerve terminals.

Time course for recovery of water maze performance and central cholinergic innervation after fluid percussion injury

This study further investigates the possible connection between postconcussive cognitive impairment and damage to forebrain cholinergic innervation. Moderate parasagittal fluid percussion injury was delivered to adult male rats. Water maze performance and synaptosomal choline uptake was measured at various times following injury. Water maze learning was severely impaired between 1 and 5 weeks, but recovered to normal by 10 weeks. Synaptosomal choline uptake was significantly decreased by 15-27% in the ipsilateral hippocampus and parietal cortex 3 and 7 days following injury, but not by 3 weeks or thereafter. Choline acetyltransferase was also significantly decreased in the ipsilateral cortex at 3 and 7 days with subsequent recovery. This study shows that parasagittal fluid percussion injury causes significant impairment in water maze learning and ipsilateral forebrain cholinergic innervation. Both of these parameters recover spontaneously, but with different time courses.

Differential effects of traumatic brain injury on vesicular acetylcholine transporter and M2 muscarinic receptor mRNA and protein in rat

Experimental traumatic brain injury (TBI) produces cholinergic neurotransmission deficits that may contribute to chronic spatial memory deficits. Cholinergic neurotransmission deficits may result from presynaptic alterations in the storage and release of acetylcholine (ACh) or from changes in the receptors for ACh. The vesicular ACh transporter (VAChT) mediates accumulation of ACh into secretory vesicles, and the M2 muscarinic receptor subtype can modulate cholinergic neurotransmission via a presynaptic inhibitory feedback mechanism. We examined the effects of controlled cortical impact (CCI) injury on hippocampal VAChT and M2 muscarinic receptor subtype protein and medial septal mRNA levels at 4 weeks following injury. Rats were anesthetized and surgically prepared for CCI injury (4 m/sec, 2.5 to 2.9 mm in depth) and sham surgery. Animals were sacrificed, and coronal sections (35 microm thick) were cut through the dorsal hippocampus for VAChT and M2 immunohistochemistry. Semiquantitative measurements of VAChT and M2 protein in hippocampal homogenates from injured and sham rats were assessed with Western blot analysis. Changes in VAChT and M2 mRNA levels were evaluated by reverse transcriptase polymerase chain reaction (RT-PCR). At 4 weeks after injury, both immunohistochemical and Western blot methods demonstrated an increase in hippocampal VAChT protein. An increase in VAChT mRNA was also observed. Immunohistochemistry demonstrated a loss of M2; however, there was no significant change in M2 mRNA levels in comparison with sham controls. These changes may represent a compensatory response of cholinergic neurons to increase the efficiency of ACh neurotransmission chronically after TBI through differential transcriptional regulation.

Neuroprotective effect of hypothermia on neuronal injury in diffuse traumatic brain injury coupled with hypoxia and hypotension

It is well established in mechanical head trauma that posttraumatic secondary insults, such as hypoxia and hypotension exacerbate neuronal injury and lead to worse outcome. In this study, the neuroprotective effect of hypothermia on the reduction of supraventricular subcortical neuronal damage was evaluated using an impact-acceleration model of diffuse traumatic brain injury coupled with both moderate and severe periods of hypoxia and hypotension. A total of 135 adult male Sprague-Dawley rats (340-375 g) were divided into three experimental studies: (I) physiological evaluation (n = 36); (II) quantitative analysis of the effect of trauma coupled with moderate and severe hypotension on neuronal damage assessed at 4 (n = 39) and 24 h (n = 24); and (III) the neuroprotective effect of hypothermia following moderate secondary insult (n = 36). Induction of hypothermia occurred at 15 min postinjury, to a level of 30 degrees C for 60 min. At the designated time points (4 and 24 h), the animals were sacrificed via standard transcardial perfusion techniques for histological processing. Quantitative assessment of neuronal damage using routine H&E staining at 4 hours showed neuronal damage which correlated with the severity of secondary insult. Animals exposed to trauma alone had a mean number of damaged neurons of 7.61 +/- 3.08/high powered field (hpf) compared with a mean of 1.21 +/- 0.30/hpf in the sham operated group (p = 0.015). Animals exposed to trauma with 10 min of hypoxia and hypotension (THH-10) showed a statistically significant number of damaged neurons compared to the sham-operated animals (7.50 +/- 2.15 damaged neurons/hpf, p = 0.013), whereas, neuronal damage in animals undergoing trauma with a 30-min secondary insult of hypoxia and hypotension (THH-30) was markedly increased (100 +/- 30.20/hpf, p = 0.002). Statistical analysis showed no significant difference in neuronal damage in animals subjected to secondary insult alone. At 24 h, the evolution of neuronal damage in the trauma alone group (5.08 +/- 1.63/hpf) was relatively static; however, there was a remarkable increase in the neuronal damage of the THH-10 group (29.88 50 +/- 8.20/hpf). However, hypothermia provided nearly complete protection against secondary insults, and neuronal damage was equal to that of the trauma alone group (p = 0.42). The results of this study confirm that hypothermia provides remarkable protection against the adverse effects of neuronal damage exacerbated by secondary injury. This study also presents a new model of secondary insult, which can be used experimentally to further define the mechanism of increased vulnerability of the injured brain.

A mitogen-activated protein kinase cascade in the CA1/CA2 subfield of the dorsal hippocampus is essential for long-term spatial memory

Behavioral, biophysical, and pharmacological studies have implicated the hippocampus in the formation and storage of spatial memory. However, the molecular mechanisms underlying long-term spatial memory are poorly understood. In this study, we show that mitogen-activated protein kinase (MAPK, also called ERK) is activated in the dorsal, but not the ventral, hippocampus of rats after training in a spatial memory task, the Morris water maze. The activation was expressed as enhanced phosphorylation of MAPK in the pyramidal neurons of the CA1/CA2 subfield. In contrast, no increase in the percentage of phospho-MAPK-positive cells was detected in either the CA3 subfield or the dentate gyrus. The enhanced phosphorylation was observed only after multiple training trials but not after a single trial or after multiple trials in which the location of the target platform was randomly changed between each trial. Inhibition of the MAPK/ERK cascade in dorsal hippocampi did not impair acquisition, but blocked the formation of long-term spatial memory. In contrast, intrahippocampal infusion of SB203580, a specific inhibitor of the stress-activated MAPK (p38 MAPK), did not interfere with memory storage. These results demonstrate a MAPK-mediated cellular event in the CA1/CA2 subfields of the dorsal hippocampus that is critical for long-term spatial memory.