Depletion of choline acetyltransferase activity but preservation of M1 and M2 muscarinic receptor binding sites in temporal cortex following head injury: a preliminary human postmortem study

Enhancing cognitive recovery in chronic traumatic brain injury through simultaneous allosteric modulation of α7 nicotinic acetylcholine and α5 GABAA receptors

Traumatic brain injury (TBI) leads to changes in the neural circuitry of the hippocampus that result in chronic learning and memory deficits. However, effective therapeutic strategies to ameliorate these chronic learning and memory impairments after TBI are limited. Two pharmacological targets for enhancing cognition are nicotinic acetylcholine receptors (nAChRs) and GABAA receptors (GABAARs), both of which regulate hippocampal network activity to form declarative memories. A promising compound, 522-054, both allosterically enhances α7 nAChRs and inhibits α5 subunit-containing GABAARs. Administration of 522-054 enhances long-term potentiation (LTP) and cognitive functioning in non-injured animals. In this study, we assessed the effects of 522-054 on hippocampal synaptic plasticity and learning and memory deficits in the chronic post-TBI recovery period. Adult male Sprague Dawley rats received moderate parasagittal fluid-percussion brain injury or sham surgery. At 12 wk after injury, we assessed basal synaptic transmission and LTP at the Schaffer collateral-CA1 synapse of the hippocampus. Bath application of 522-054 to hippocampal slices reduced deficits in basal synaptic transmission and recovered TBI-induced impairments in LTP. Moreover, treatment of animals with 522-054 at 12 wk post-TBI improved cue and contextual fear memory and water maze acquisition and retention without a measurable effect on cortical or hippocampal atrophy. These results suggest that dual allosteric modulation of α7 nAChR and α5 GABAAR signaling may be a potential therapy for treating cognitive deficits during chronic recovery from TBI.

Evaluating the Efficacy of Chronic Galantamine on Sustained Attention and Cholinergic Neurotransmission in A Pre-Clinical Model of Traumatic Brain Injury

Cholinergic disruptions underlie attentional deficits following traumatic brain injury (TBI). Yet, drugs specifically targeting acetylcholinesterase (AChE) inhibition have yielded mixed outcomes. Therefore, we hypothesized that galantamine (GAL), a dual-action competitive AChE inhibitor and α7 nicotinic acetylcholine receptor (nAChR) positive allosteric modulator, provided chronically after injury, will attenuate TBI-induced deficits of sustained attention and enhance ACh efflux in the medial prefrontal cortex (mPFC), as assessed by in vivo microdialysis. In Experiment 1, adult male rats (n = 10-15/group) trained in the 3-choice serial reaction time (3-CSRT) test were randomly assigned to controlled cortical impact (CCI) or sham surgery and administered GAL (0.5, 2.0, or 5.0 mg/kg; i.p.) or saline vehicle (VEH; 1 mL/kg; i.p) beginning 24-h post-surgery and once daily thereafter for 27 days. Measures of sustained attention and distractibility were assessed on post-operative days 21-25 in the 3-CSRT, following which cortical lesion volume and basal forebrain cholinergic cells were quantified on day 27. In Experiment 2, adult male rats (n = 3-4/group) received a CCI and 24 h later administered (i.p.) one of the three doses of GAL or VEH for 21 days to quantify the dose-dependent effect of GAL on in vivo ACh efflux in the mPFC. Two weeks after the CCI, a guide cannula was implanted in the right mPFC. On post-surgery day 21, baseline and post-injection dialysate samples were collected in a temporally matched manner with the cohort undergoing behavior. ACh levels were analyzed using reverse phase high-performance liquid chromatography (HPLC) coupled to an electrochemical detector. Cortical lesion volume was quantified on day 22. The data were subjected to ANOVA, with repeated measures where appropriate, followed by Newman-Keuls post hoc analyses. All TBI groups displayed impaired sustained attention versus the pooled SHAM controls (p's < 0.05). Moreover, the highest dose of GAL (5.0 mg/kg) exacerbated attentional deficits relative to VEH and the two lower doses of GAL (p's < 0.05). TBI significantly reduced cholinergic cells in the right basal forebrain, regardless of treatment condition, versus SHAM (p < 0.05). In vivo microdialysis revealed no differences in basal ACh in the mPFC; however, GAL (5.0 mg/kg) significantly increased ACh efflux 30 min following injection compared to the VEH and the other GAL (0.5 and 2.0 mg/kg) treated groups (p's < 0.05). In both experiments, there were no differences in cortical lesion volume across treatment groups (p's > 0.05). In summary, albeit the higher dose of GAL increased ACh release, it did not improve measures of sustained attention or histopathological markers, thereby partially supporting the hypothesis and providing the impetus for further investigations into alternative cholinergic pharmacotherapies such as nAChR positive allosteric modulators.

Intranasal human-recombinant NGF administration improves outcome in children with post-traumatic unresponsive wakefulness syndrome

BACKGROUND

Severe traumatic brain injury (TBI) is one of the most dramatic events in pediatric age and, despite advanced neuro-intensive care, the survival rate of these patients remains low. Children suffering from severe TBI show long-term sequelae, more pronounced in behavioral, neurological and neuropsychological functions leading to, in the most severe cases, an unresponsive wakefulness syndrome (UWS). Currently, no effective treatments can restore neuronal loss or produce significant improvement in these patients. In experimental animal models, human- recombinant Nerve Growth Factor (hr-NGF) promotes neural recovery supporting neuronal growth, differentiation and survival of brain cells and up-regulating the neurogenesis-associated processes. Only a few studies reported the efficacy of intranasal hr-NGF administration in children with post- traumatic UWS.

METHODS

Children with the diagnosis of post-traumatic UWS were enrolled. These patients underwent a treatment with intranasal hr-NGF administration, at a total dose of 50 gamma/kg, three times a day for 7 consecutive days. The treatment schedule was performed for 4 cycles, at one month distance each. Neuroradiogical evaluation by Positron Emission Tomography scan (PET), Single Photon Emission Computed Tomography (SPECT), Electroencephalography (EEG), and Power Spectral Density (PSD) was determined before the treatment and one month after the end. Neurological assessment was also deepened by using modified Ashworth Scale, Gross Motor Function Measure, and Disability Rating Scale.

RESULTS

Three children with post-traumatic UWS were treated. hr-NGF administration improved functional (PET and SPECT) and electrophysiological (EEG and PSD) assessment. Also clinical conditions improved, mainly for the reduction of spasticity and with the acquisition of voluntary movements, facial mimicry, attention and verbal comprehension, ability to cry, cough reflex, oral motility, and feeding capacity, with a significant improvement of their neurological scores. No side effects were reported.

CONCLUSION

These promising results and the ease of administration of this treatment make it worthwhile to be investigated further, mainly in the early stages from severe TBI and in patients with better baseline neurological conditions, to explore more thoroughly the benefits of this new approach on neuronal function recovery after traumatic brain damage.

Dynamics of Choline-Containing Phospholipids in Traumatic Brain Injury and Associated Comorbidities

The incidences of traumatic brain injuries (TBIs) are increasing globally because of expanding population and increased dependencies on motorized vehicles and machines. This has resulted in increased socio-economic burden on the healthcare system, as TBIs are often associated with mental and physical morbidities with lifelong dependencies, and have severely limited therapeutic options. There is an emerging need to identify the molecular mechanisms orchestrating these injuries to life-long neurodegenerative disease and a therapeutic strategy to counter them. This review highlights the dynamics and role of choline-containing phospholipids during TBIs and how they can be used to evaluate the severity of injuries and later targeted to mitigate neuro-degradation, based on clinical and preclinical studies. Choline-based phospholipids are involved in maintaining the structural integrity of the neuronal/glial cell membranes and are simultaneously the essential component of various biochemical pathways, such as cholinergic neuronal transmission in the brain. Choline or its metabolite levels increase during acute and chronic phases of TBI because of excitotoxicity, ischemia and oxidative stress; this can serve as useful biomarker to predict the severity and prognosis of TBIs. Moreover, the effect of choline-replenishing agents as a post-TBI management strategy has been reviewed in clinical and preclinical studies. Overall, this review determines the theranostic potential of choline phospholipids and provides new insights in the management of TBI.

Blockade of TRPC Channels Limits Cholinergic-Driven Hyperexcitability and Seizure Susceptibility After Traumatic Brain Injury

We investigated the contribution of excitatory transient receptor potential canonical (TRPC) cation channels to posttraumatic hyperexcitability in the brain 7 days following controlled cortical impact model of traumatic brain injury (TBI) to the parietal cortex in male adult mice. We investigated if TRPC1/TRPC4/TRPC5 channel expression is upregulated in excitatory neurons after TBI in contribution to epileptogenic hyperexcitability in key hippocampal and cortical circuits that have substantial cholinergic innervation. This was tested by measuring TRPC1/TRPC4/TRPC5 protein and messenger RNA (mRNA) expression, assays of cholinergic function, neuronal Ca²⁺ imaging in brain slices, and seizure susceptibility after TBI. We found region-specific increases in expression of TRPC1, TRPC4, and TRPC5 subunits in the hippocampus and cortex following TBI. The dentate gyrus, CA3 region, and cortex all exhibited robust upregulation of TRPC4 mRNA and protein. TBI increased cFos activity in dentate gyrus granule cells (DGGCs) and layer 5 pyramidal neurons both at the time of TBI and 7 days post-TBI. DGGCs displayed greater magnitude and duration of acetylcholine-induced rises in intracellular Ca²⁺ in brain slices from mice subjected to TBI. The TBI mice also exhibited greater seizure susceptibility in response to pentylenetetrazol-induced kindling. Blockade of TRPC4/TRPC5 channels with M084 reduced neuronal hyperexcitation and impeded epileptogenic progression of kindling. We observed that the time-dependent upregulation of TRPC4/TRPC5-containing channels alters cholinergic responses and activity of principal neurons acting to increase proexcitatory sensitivity. The underlying mechanism includes acutely decreased acetylcholinesterase function, resulting in greater G_q/11-coupled muscarinic receptor activation of TRPC channels. Overall, our evidence suggests that TBI-induced plasticity of TRPC channels strongly contributes to overt hyperexcitability and primes the hippocampus and cortex for seizures.

Chronic traumatic encephalopathy and the nucleus basalis of Meynert

Due to the growing number of chronic traumatic encephalopathy (CTE) cases in the military and contact sports, defining the cellular and molecular substrate of this disorder is crucial. Most classic neuropathological investigations describe cortical tau and, to a lesser extent, amyloid lesions, which may underlie the clinical sequela associated with CTE. The application of modern molecular biologic technology to postmortem human brain tissue has made it possible to evaluate the genetic signature of specific neuronal phenotypes at different stages of CTE pathology. Most recently, molecular pathobiology has been used in the field of CTE, with an emphasis on the cholinergic neurons located within the nucleus basalis of Meynert, which develop tau pathology and are associated with cognitive dysfunction similar to that found in Alzheimer's disease (AD). Quantitative findings derived from single-cell transcript investigations provide clues to our understanding of the selective vulnerability of neurons containing AD-like tau pathology at different stages of CTE. Since human tissue-based studies provide a gold standard for the field of CTE, continued molecular pathological studies are needed to reveal novel drug targets for the treatment of this disorder.

Disruption of basal forebrain cholinergic neurons after traumatic brain injury does not compromise environmental enrichment-mediated cognitive benefits

Environmental enrichment (EE) attenuates traumatic brain injury (TBI)-induced loss of medial septal (MS) choline acetyltransferase (ChAT)-cells and enhances spatial learning and memory vs. standard (STD) housing. Whether basal forebrain cholinergic neurons (BFCNs) are important mediators of EE-induced benefits after TBI requires further investigation. Anesthetized female rats were randomly assigned to intraseptal infusions of the immunotoxin 192-IgG-saporin (SAP; 0.22 μg in 1.0 μL) or vehicle (VEH; 1.0 μL IgG) followed immediately by a cortical impact (2.8 mm deformation depth at 4 m/s) or sham injury and divided into EE and STD housing. Spatial learning and memory retention were assessed on post-operative days 14-19. MS ChAT⁺ cells were quantified at 3 weeks. SAP significantly reduced ChAT⁺ cells in both the EE and STD groups. Cognitive performance was improved in the EE groups, regardless of VEH or SAP infusion, vs. the STD-housed groups (p's < 0.05). No cognitive differences were revealed between the TBI + EE + SAP and TBI + EE + VEH groups (p > 0.05) or between the TBI + STD + SAP and TBI + STD + VEH groups (p > 0.05). These data show that despite significant MS ChAT⁺ cell loss, the EE-mediated benefit in cognitive recovery is not compromised.

Approaches to Monitor Circuit Disruption after Traumatic Brain Injury: Frontiers in Preclinical Research

Mild traumatic brain injury (TBI) often results in pathophysiological damage that can manifest as both acute and chronic neurological deficits. In an attempt to repair and reconnect disrupted circuits to compensate for loss of afferent and efferent connections, maladaptive circuitry is created and contributes to neurological deficits, including post-concussive symptoms. The TBI-induced pathology physically and metabolically changes the structure and function of neurons associated with behaviorally relevant circuit function. Complex neurological processing is governed, in part, by circuitry mediated by primary and modulatory neurotransmitter systems, where signaling is disrupted acutely and chronically after injury, and therefore serves as a primary target for treatment. Monitoring of neurotransmitter signaling in experimental models with technology empowered with improved temporal and spatial resolution is capable of recording in vivo extracellular neurotransmitter signaling in behaviorally relevant circuits. Here, we review preclinical evidence in TBI literature that implicates the role of neurotransmitter changes mediating circuit function that contributes to neurological deficits in the post-acute and chronic phases and methods developed for in vivo neurochemical monitoring. Coupling TBI models demonstrating chronic behavioral deficits with in vivo technologies capable of real-time monitoring of neurotransmitters provides an innovative approach to directly quantify and characterize neurotransmitter signaling as a universal consequence of TBI and the direct influence of pharmacological approaches on both behavior and signaling.

Repositioning drugs for traumatic brain injury - N-acetyl cysteine and Phenserine

Traumatic brain injury (TBI) is one of the most common causes of morbidity and mortality of both young adults of less than 45 years of age and the elderly, and contributes to about 30% of all injury deaths in the United States of America. Whereas there has been a significant improvement in our understanding of the mechanism that underpin the primary and secondary stages of damage associated with a TBI incident, to date however, this knowledge has not translated into the development of effective new pharmacological TBI treatment strategies. Prior experimental and clinical studies of drugs working via a single mechanism only may have failed to address the full range of pathologies that lead to the neuronal loss and cognitive impairment evident in TBI and other disorders. The present review focuses on two drugs with the potential to benefit multiple pathways considered important in TBI. Notably, both agents have already been developed into human studies for other conditions, and thus have the potential to be rapidly repositioned as TBI therapies. The first is N-acetyl cysteine (NAC) that is currently used in over the counter medications for its anti-inflammatory properties. The second is (-)-phenserine ((-)-Phen) that was originally developed as an experimental Alzheimer's disease (AD) drug. We briefly review background information about TBI and subsequently review literature suggesting that NAC and (-)-Phen may be useful therapeutic approaches for TBI, for which there are no currently approved drugs.

Traumatic Brain Injury and Neuropsychiatric Complications

Traumatic brain injury (TBI) occurs when a blow or jolt to the head or a penetrating injury results in damage to the brain. It is the most frequent cause of hospitalization in young people with a higher prevalence in men. TBI is the leading cause of disability and mortality between the ages 1 and 45. TBI can be caused either by the direct result of trauma or due to a complication of the primary injury. The most common etiological factors for TBI are falls, road traffic accidents, violent physical assaults, and injuries associated with athletic activities. Following TBI, significant neurologic complications may occur which include seizures, dementia, Alzheimer's disease, and cranial nerve injuries. In addition, people may suffer from various psychiatric complications such as depression, posttraumatic stress disorder, generalized anxiety disorder, obsessive-compulsive disorder, and other cognitive and behavioral sequel that might significantly increase the comorbidity of the victims. Considering all of the above complications, TBI is one of the significant public health burdens. Literature has shown that only about 25% of people achieve long-term functional independence following TBI. In this paper, we focused not only on the epidemiology but also the etiology, complications following TBI and understanding their underlying pathogenesis. Further, we focused on analyzing the options to improve the treatment and rehabilitation following TBI in future.

Galantamine and Environmental Enrichment Enhance Cognitive Recovery after Experimental Traumatic Brain Injury But Do Not Confer Additional Benefits When Combined

Environmental enrichment (EE) enhances cognition after traumatic brain injury (TBI). Galantamine (GAL) is an acetylcholinesterase inhibitor that also may promote benefits. Hence, the aims of this study were to assess the efficacy of GAL alone (standard [STD] housing) and in combination with EE in adult male rats after TBI. The hypothesis was that both therapies would confer motor, cognitive, and histological benefits when provided singly, but that their combination would be more efficacious. Anesthetized rats received a controlled cortical impact or sham injury, then were randomly assigned to receive GAL (1, 2, or 3 mg/kg; intraperitoneally [i.p.]) or saline vehicle (VEH; 1 mL/kg; i.p.) beginning 24 h after surgery and once daily for 21 days (experiment 1). Motor (beam-balance/walk) and cognitive (Morris water maze [MWM]) assessments were conducted on post-operative Days 1-5 and 14-19, respectively. Cortical lesion volumes were quantified on Day 21. Sham controls were better versus all TBI groups. No differences in motor function or lesion volumes were observed among the TBI groups (p > 0.05). In contrast, GAL (2 mg/kg) enhanced MWM performance versus VEH and GAL (1 and 3 mg/kg; p < 0.05). In experiment 2, GAL (2 mg/kg) or VEH was combined with EE and the data were compared with the STD-housed groups from experiment 1. EE alone enhanced motor performance over the VEH-treated and GAL-treated (2 mg/kg) STD-housed groups (p < 0.05). Moreover, both EE groups (VEH or GAL) facilitated spatial learning and reduced lesion size versus STD + VEH controls (p < 0.05). No additional benefits were observed with the combination paradigm, which does not support the hypothesis. Overall, the data demonstrate that EE and once daily GAL (2 mg/kg) promote cognitive recovery after TBI. Importantly, the combined therapies did not negatively affect outcome and thus this therapeutic protocol may have clinical utility.

Cognitive Impairments Induced by Concussive Mild Traumatic Brain Injury in Mouse Are Ameliorated by Treatment with Phenserine via Multiple Non-Cholinergic and Cholinergic Mechanisms

Traumatic brain injury (TBI), often caused by a concussive impact to the head, affects an estimated 1.7 million Americans annually. With no approved drugs, its pharmacological treatment represents a significant and currently unmet medical need. In our prior development of the anti-cholinesterase compound phenserine for the treatment of neurodegenerative disorders, we recognized that it also possesses non-cholinergic actions with clinical potential. Here, we demonstrate neuroprotective actions of phenserine in neuronal cultures challenged with oxidative stress and glutamate excitotoxicity, two insults of relevance to TBI. These actions translated into amelioration of spatial and visual memory impairments in a mouse model of closed head mild TBI (mTBI) two days following cessation of clinically translatable dosing with phenserine (2.5 and 5.0 mg/kg BID x 5 days initiated post mTBI) in the absence of anti-cholinesterase activity. mTBI elevated levels of thiobarbituric acid reactive substances (TBARS), a marker of oxidative stress. Phenserine counteracted this by augmenting homeostatic mechanisms to mitigate oxidative stress, including superoxide dismutase [SOD] 1 and 2, and glutathione peroxidase [GPx], the activity and protein levels of which were measured by specific assays. Microarray analysis of hippocampal gene expression established that large numbers of genes were exclusively regulated by each individual treatment with a substantial number of them co-regulated between groups. Molecular pathways associated with lipid peroxidation were found to be regulated by mTBI, and treatment of mTBI animals with phenserine effectively reversed injury-induced regulations in the ‘Blalock Alzheimer’s Disease Up’ pathway. Together these data suggest that multiple phenserine-associated actions underpin this compound’s ability to ameliorate cognitive deficits caused by mTBI, and support the further evaluation of the compound as a therapeutic for TBI.

Hypocretinergic and cholinergic contributions to sleep-wake disturbances in a mouse model of traumatic brain injury

Disorders of sleep and wakefulness occur in the majority of individuals who have experienced traumatic brain injury (TBI), with increased sleep need and excessive daytime sleepiness often reported. Behavioral and pharmacological therapies have limited efficacy, in part, because the etiology of post-TBI sleep disturbances is not well understood. Severity of injuries resulting from head trauma in humans is highly variable, and as a consequence so are their sequelae. Here, we use a controlled laboratory model to investigate the effects of TBI on sleep-wake behavior and on candidate neurotransmitter systems as potential mediators. We focus on hypocretin and melanin-concentrating hormone (MCH), hypothalamic neuropeptides important for regulating sleep and wakefulness, and two potential downstream effectors of hypocretin actions, histamine and acetylcholine. Adult male C57BL/6 mice (n=6-10/group) were implanted with EEG recording electrodes and baseline recordings were obtained. After baseline recordings, controlled cortical impact was used to induce mild or moderate TBI. EEG recordings were obtained from the same animals at 7 and 15 days post-surgery. Separate groups of animals (n=6-8/group) were used to determine effects of TBI on the numbers of hypocretin and MCH-producing neurons in the hypothalamus, histaminergic neurons in the tuberomammillary nucleus, and cholinergic neurons in the basal forebrain. At 15 days post-TBI, wakefulness was decreased and NREM sleep was increased during the dark period in moderately injured animals. There were no differences between groups in REM sleep time, nor were there differences between groups in sleep during the light period. TBI effects on hypocretin and cholinergic neurons were such that more severe injury resulted in fewer cells. Numbers of MCH neurons and histaminergic neurons were not altered under the conditions of this study. Thus, we conclude that moderate TBI in mice reduces wakefulness and increases NREM sleep during the dark period, effects that may be mediated by hypocretin-producing neurons and/or downstream cholinergic effectors in the basal forebrain.

Progression of tau pathology within cholinergic nucleus basalis neurons in chronic traumatic encephalopathy: A chronic effects of neurotrauma consortium study

OBJECTIVE

To test the hypothesis that the nucleus basalis of Meynert (nbM), a cholinergic basal forebrain (CBF) cortical projection system, develops neurofibrillary tangles (NFTs) during the progressive pathological stages of chronic traumatic encephalopathy (CTE) in the brain of athletes.

METHOD

To characterize NFT pathology, tau-antibodies marking early, intermediate and late stages of NFT development in CBF tissue obtained at autopsy from eighteen former athletes and veterans with a history of repetitive mild traumatic brain injury (TBI) were used.

RESULTS

Analysis revealed that cholinergic nbM neurons develop intracellular tau-immunoreactive changes progressively across the pathological stages of CTE. In particular, there was an increase in pre-tangle (phosphorylated pS422) and oligomeric (TOC1 and TNT1) forms of tau in stage IV compared to stage II CTE cases. The nbM neurons also displayed pathologic TDP-43 inclusions and diffuse extracellular and vascular amyloid-β (Aβ) deposits in CTE. A higher percentage of pS422/p75NTR, pS422 and TNT1 labelled neurons were significantly correlated with age at symptom onset, interval between symptom onset and death and age at death.

CONCLUSION

The development of NFTs within the cholinergic nbM neurons could contribute to an axonal disconnection in CTE. Further studies are needed to determine the mechanism driving NFT formation in the nbM neurons and its relation to chronic cognitive dysfunction in CTE.

[Clinical syndromes of neurotransmitter system dysfunction in severe brain injury]

AIM

To explore neurotransmitter system dysfunctions involved in maintaining of consciousness and motor functions in patients with severe traumatic brain injury (TBI) and to assess their severity and predictive value.

MATERIAL AND METHODS

Authors examined 100 patients (34 women and 66 men), aged 32.0 ± 13.0 years, with severe TBI. Eighty-eight patients (31 women and 57 men) were studied in the acute stage (1-15 days, mean 5.8 ± 3.7 days) and 70 patients (24 women and 46 men) in the subacute stage (18-70 days, mean 30.4 ± 12.7 days). Inclusion criteria were: severe TBI with depression of consciousness (≤ 7 scores on the Glasgow Coma Scale), admission to the hospital in acute and subacute stages. Outcome of TBI was evaluated using the Glasgow Outcome Scale.

RESULTS AND CONCLUSION

The following clinical syndromes of neurotransmitter system dysfunction were singled out: excess or insufficiency of glutamate, cholinergic deficit, excess or insufficiency of dopamine. Their transformation during disease was identified. Predictive value of neurotransmitter dysfunctions for TBI is emphasized.

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.

Amyloid imaging with carbon 11-labeled Pittsburgh compound B for traumatic brain injury

OBJECTIVES

To image amyloid deposition in patients with traumatic brain injury (TBI) using carbon 11-labeled Pittsburgh Compound B ([11C]PiB) positron emission tomography (PET) and to validate these findings using tritium-labeled PiB ([3H]PiB) autoradiography and immunocytochemistry in autopsy-acquired tissue.

DESIGN, SETTING, AND PARTICIPANTS

In vivo PET at tertiary neuroscience referral center and ex vivo immunocytochemistry of autopsy-acquired brain tissue from a neuropathology archive. [11C]PiB PET was used to image amyloid deposition in 11 controls (median [range] age, 35 [24-60] years) and in 15 patients (median [range] age, 33 [21-50] years) between 1 and 361 days after a TBI. [3H]PiB autoradiography and immunocytochemistry for β-amyloid (Aβ) and β-amyloid precursor protein in brain tissue were obtained from separate cohorts of 16 patients (median [range] age, 46 [21-70] years) who died between 3 hours and 56 days after a TBI and 7 controls (median [range] age, 61 [29-71] years) who died of other causes.

MAIN OUTCOMES AND MEASURES

We quantified the [11C]PiB distribution volume ratio and standardized uptake value ratio in PET images. The distribution volume ratio and the standardized uptake value ratio were measured in cortical gray matter, white matter, and multiple cortical and white matter regions of interest, as well as in striatal and thalamic regions of interest. We examined [3H]PiB binding and Aβ and β-amyloid precursor protein immunocytochemistry in autopsy-acquired brain tissue.

RESULTS

Compared with the controls, the patients with TBI showed significantly increased [11C]PiB distribution volume ratios in cortical gray matter and the striatum (corrected P < .05 for both), but not in the thalamus or white matter. Increases in [11C]PiB distribution volume ratios in patients with TBI were seen across most cortical subregions, were replicated using comparisons of standardized uptake value ratios, and could not be accounted for by methodological confounders. Autoradiography revealed [3H]PiB binding in neocortical gray matter, in regions where amyloid deposition was demonstrated by immunocytochemistry; white matter showed Aβ and β-amyloid precursor protein by immunocytochemistry, but no [3H]PiB binding. No plaque-associated amyloid immunoreactivity or [3H]PiB binding was seen in cerebellar gray matter in autopsy-acquired tissue from either controls or patients with TBI, although 1 sample of cerebellar tissue from a patient with TBI showed amyloid angiopathy in meningeal vessels.

CONCLUSIONS AND RELEVANCE

[11C]PiB shows increased binding following TBI. The specificity of this binding is supported by neocortical [3H]PiB binding in regions of amyloid deposition in the postmortem tissue of patients with TBI. [11C]PiB PET could be valuable in imaging amyloid deposition following TBI.

Donepezil is ineffective in promoting motor and cognitive benefits after controlled cortical impact injury in male rats

The acetylcholinesterase (AChE) inhibitor donepezil is used as a therapy for Alzheimer's disease and has been recommended as a treatment for enhancing attention and memory after traumatic brain injury (TBI). Although select clinical case studies support the use of donepezil for enhancing cognition, there is a paucity of experimental TBI studies assessing the potential efficacy of this pharmacotherapy. Hence, the aim of this pre-clinical study was to evaluate several doses of donepezil to determine its effect on functional outcome after TBI. Ninety anesthetized adult male rats received a controlled cortical impact (CCI; 2.8 mm cortical depth at 4 m/sec) or sham injury, and then were randomly assigned to six TBI and six sham groups (donepezil 0.25, 0.5, 1.0, 2.0, or 3.0 mg/kg, and saline vehicle 1.0 mL/kg). Treatments began 24 h after surgery and were administered i.p. once daily for 19 days. Function was assessed by motor (beam balance/walk) and cognitive (Morris water maze) tests on days 1-5 and 14-19, respectively. No significant differences were observed among the sham control groups in any evaluation, regardless of dose, and therefore the data were pooled. Furthermore, no significant differences were revealed among the TBI groups in acute neurological assessments (e.g., righting reflex), suggesting that all groups received the same level of injury severity. None of the five doses of donepezil improved motor or cognitive function relative to vehicle-treated controls. Moreover, the two highest doses significantly impaired beam-balance (3.0 mg/kg), beam-walk (2.0 mg/kg and 3.0 mg/kg), and cognitive performance (3.0 mg/kg) versus vehicle. These data indicate that chronic administration of donepezil is not only ineffective in promoting functional improvement after moderate CCI injury, but depending on the dose is actually detrimental to the recovery process. Further work is necessary to determine if other AChE inhibitors exert similar effects after TBI.

Biologic and plastic effects of experimental traumatic brain injury treatment paradigms and their relevance to clinical rehabilitation

Neuroplastic changes, whether induced by traumatic brain injury (TBI) or therapeutic interventions, alter neurobehavioral outcome. Here we present several treatment strategies that have been evaluated by using experimental TBI models and discuss potential mechanisms of action (ie, plasticity) and how such changes affect function.

Neurobiological consequences of traumatic brain injury

Traumatic brain injury (TBI) is a worldwide public health problem typically caused by contact and inertial forces acting on the brain. Recent attention has also focused on the mechanisms of injury associated with exposure to blast events or explosions. Advances in the understanding of the neuropathophysiology of TBI suggest that these forces initiate an elaborate and complex array of cellular and subcellular events related to alterations in Ca⁺⁺ homeostasis and signaling. Furthermore, there is a fairly predictable profile of brain regions that are impacted by neurotrauma and the related events. This profile of brain damage accurately predicts the acute and chronic sequelae that TBI survivors suffer from, although there is enough variation to suggest that individual differences such as genetic polymorphisms and factors governing resiliency play a role in modulating outcome. This paper reviews our current understanding of the neuropathophysiology of TBI and how this relates to the common clinical presentation of neurobehavioral difficulties seen after an injury.

Functional imaging of hippocampal dysfunction among persons with Alzheimer's disease: a proof-of-concept study

Cholinergic deficits are an early and functionally significant manifestation of Alzheimer's disease (AD). These deficits contribute to impairment of hippocampally mediated information processing, including declarative memory impairments and abnormal auditory sensory gating. A functional imaging technique that facilitates identification of changes in cholinergically dependent hippocampal information processing would be of considerable use in the study and clinical evaluation of persons with this condition. Techniques that interrogate hippocampal function passively, ie, in a manner requiring no cognitive effort or novel task learning during the neuroimaging procedure, would also be especially useful in this cognitively impaired population. The functional magnetic resonance imaging sensory gating paradigm developed at the University of Colorado, CO, USA, is a functional neuroimaging technique that possesses both of these characteristics. We developed a demonstration project using this paradigm in which we passively interrogated hippocampal function in two subjects with probable AD of mild severity. Imaging data were quick and easy in these subjects and served usefully as an initial demonstration of the feasibility of using this neuroimaging method in this population. Preliminary analyses of the data obtained from these subjects identified abnormal blood oxygen level-dependent responses when compared with four healthy comparators, and the pattern of these responses was consistent with impaired function of the auditory sensory gating network. The strengths and limitations of this neuroimaging paradigm and the additional issues that require investigation in order to continue its development into a research and clinical technique for use in this population are discussed.

Long-term effects of rivastigmine capsules in patients with traumatic brain injury

OBJECTIVE

To investigate the safety, tolerability and efficacy of rivastigmine capsules (3-12 mg/day) in a 26-week, multi-centre, open-label extension of a double-blind study.

METHODS

Patients with traumatic brain injury (TBI) and persistent cognitive impairment who had received rivastigmine (3-6 mg/day) or placebo for 12 weeks could enter the extension study and receive rivastigmine (< or =12 mg/day). Patients were assessed using a range of cognitive tests including the Hopkins Verbal Learning Test (HVLT) and the Cambridge Neuropsychological Test Automated Battery Rapid Visual Information Processing (CANTAB RVIP) A' sub-test. Safety measures included monitoring of adverse events.

RESULTS

In the extension study (n = 127), the mean duration of rivastigmine treatment was 23.8 weeks and the mean final dosage was 7.9 mg/day. Approximately 40% of patients were responders (> or =1.0 SD improvement from baseline) on CANTAB RVIP A' or HVLT total score at week 38 or endpoint. Statistically significant changes from week 12 at week 38 were observed for CANTAB-RVIP A' and HVLT-total word recall for the sub-group of ex-placebo patients with greater severity of initial impairment. The safety profile of rivastigmine capsules was consistent with the label.

CONCLUSIONS

Treatment with rivastigmine for up to 38 weeks was safe in patients with TBI and cognitive impairment.

Neurobehavioral management of traumatic brain injury in the critical care setting

Traumatic brain injury (TBI) results in approximately 230,000 hospitalizations annually in the United States. Advances in the acute management of TBI have improved survival after TBI. Many TBI survivors develop neurobehavioral disturbances in the acute post-injury period. Neurobehavioral sequelae present clinical management challenges for critical care professionals. This article defines and describes TBI and reviews its common neuroanatomic and neurobehavioral consequences. These disturbances are organized under the framework of posttraumatic encephalopathy, and the characteristic forms and stages of recovery of this condition are discussed. Recommendations regarding evaluation and management of posttraumatic neurobehavioral problems in the critical care setting are offered.

Interleukin-6 and nerve growth factor upregulation correlates with improved outcome in children with severe traumatic brain injury

Secondary brain damage after traumatic brain injury (TBI) involves neuro-inflammatory mechanisms that are mainly dependent on the intracerebral production of cytokines. Interleukin-6 (IL-6) may have a role both in the pathogenesis of neuronal damage and in the recovery mechanisms of injured neurons through the modulation of nerve growth factor (NGF) biosynthesis. However, the relationship between IL-6 and NGF expression and the severity and outcome of TBI remains controversial. We have conducted a prospective observational clinical study to determine whether the concentration of IL-6 and NGF in the cerebrospinal fluid (CSF) of children with TBI correlates with the severity of the injury and neurologic outcome of patients. CSF samples were collected from 29 children at 2 h (time T1) and 48 h (time T2) after severe TBI, and from 31 matched controls. TBI severity was evaluated by Glasgow Coma Scale (GCS) and neurologic outcome by Glasgow Outcome Score (GOS). CSF concentrations of IL-6 and NGF were measured by immunoenzymatic assays. Early NGF concentrations (T1) correlated significantly with head injury severity, whereas no correlation was found between GCS and IL-6. Furthermore, IL-6 and NGF upregulation after injury was associated with better neurologic outcomes. Based on these findings, we posit that NGF expression is a useful marker of brain damage following severe TBI. Moreover, the early upregulation of both IL-6 and NGF, which correlates with a favorable neurologic outcome, may reflect an endogenous attempt at neuroprotection in response to the damaging biochemical and molecular cascades triggered by traumatic insult.

Nerve growth factor expression correlates with severity and outcome of traumatic brain injury in children

BACKGROUND

Secondary brain damage after traumatic brain injury (TBI) involves neuro-inflammatory mechanisms, mainly dependent on the intracerebral production of cytokines. In particular, interleukin 1beta (IL-1beta) is associated with neuronal damage, while interleukin 6 (IL-6) exerts a neuroprotective role due to its ability to modulate neurotrophins biosynthesis. However, the relationship between these cytokines and neurotrophins with the severity and outcome of TBI remains still controversial.

AIMS

To determine whether the concentration of IL-1beta and IL-6 and neurotrophins (nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), glial-derived neurotrophic factor (GDNF)) in the cerebrospinal fluid (CSF) of children with TBI correlates with the severity of the injury and its neurologic outcome.

METHODS

Prospective observational clinical study in a university hospital. CSF samples were collected from 27 children at 2h (Time T1) and 48 h (Time T2) after severe TBI, and from 21 matched controls. Severity of TBI was evaluated by GCS and neurologic outcome by GOS. CSF concentrations of cytokines and neurotrophins were measured by immunoenzymatic assays.

RESULTS

Early NGF and IL-1beta concentrations (T1) correlated significantly with the severity of head injury, whereas no correlation was found for IL-6, BDNF, and GDNF. Furthermore, higher NGF and IL-6 and lower IL-1beta expression at T2 were associated with better neurologic outcomes. No significant association was found between BDNF or GDNF expression and neurologic outcome.

CONCLUSIONS

NGF concentration in CSF is a useful marker of brain damage following severe TBI and its up-regulation, in the first 48 h after head injury together with lower IL-1beta expression, correlates with a favorable neurologic outcome. Clinical and prognostic information may also be obtained from IL-6 expression.

[Cholinergic hypothesis in psychosis following traumatic brain injury and cholinergic hypothesis in schizophrenia: a link?]

INTRODUCTION

While traumatic brain injury is a major public health issue, schizophrenia-like psychosis following traumatic brain injury is relatively rare and poorly studied. Yet the risk of developing schizophrenia-like psychosis after traumatic brain injury is 3 times more important than in the general population.

LITERATURE FINDINGS

Risk factors associated with onset of psychosis after traumatic brain injury include: left hemispheric lesions, closed head injury and coma of duration superior to 24 hours. Most patients develop symptoms of psychosis after a moderate to severe traumatic brain injury and often have lesions of the frontal and temporal lobes. CHOLINERGIC HYPOTHESIS:

ARGUMENTS

Neuropathologic, electrophysiological and pharmacologic evidence show that cognitive impairment including attention, memory and executive functioning impairment may be related with cholinergic dysfunction in patients with traumatic brain injury. The cholinergic hypothesis is also incriminated in the genesis of schizophrenia. The same biochemical disorders found in schizophrenia which imply many neurotransmitters are often present immediately after traumatic brain injury. However in chronic cognitive disorders secondary to traumatic brain injury, the cholinergic system alone seems to be specifically implied. This is due to the fragility of the cholinergic fibres and a chronic yet reversible reduction of the cholinergic reserves after traumatic brain injury. Cholinergic function can be studied by the P50 evoked response to paired auditory stimuli.While this is disturbed in patients presenting with cognitive impairment after traumatic brain injury its normalisation can be obtained after administration of an acetylcholine esterase inhibitor. In schizophrenic patients there is also an abnormal P50 evoked response due in part to a low number of alpha 7 nicotinic receptors which are implicated in sensory filtering in the frontal lobe. Moreover in schizophrenia, post-mortem studies show a negative correlation between the activity of acetylcholine transferase in the parietal cortex and the severity of the cognitive deficits, as well as a lesser density of the muscarinic M1 and M4 receptors in the frontal lobe. The lower concentration of M1 receptors in the frontal cortex is correlated with the severity of the positive symptoms. THERAPEUTICAL PERSPECTIVES: Antipsychotics have emerged as the first line treatment of psychotic disorders. In research, their ability for enhancing cognitive function could result in the increase of acetylcholine in the medial prefrontal cortex. Acetylcholinesterase inhibitors have been widely used for treatment of cognitive impairment in Alzheimer's disease. Galantamine could be interesting in schizophrenia and psychosis following traumatic brain injury because it has a dual mechanism of action: selective competitive inhibition of acetylcholinesterase and allosteric potentialisation of nicotinic receptor response. Therefore Galantamine remains active in nicotine addicted schizophrenic patients who may smoke as an auto treatment. Galantamine has shown efficacy in adjunction to Risperidone in one patient presenting with psychosis following traumatic brain injury and in 3 case reports of schizophrenic patients.

CONCLUSION

Further systematic studies are needed to confirm this hypothesis.

Neurobehavioral sequelae of traumatic brain injury: evaluation and management

Traumatic brain injury (TBI) is a worldwide public health problem. Over the last several decades, improvements in acute care have resulted in higher survival rates. Unfortunately, the majority of survivors of moderate and severe TBI have chronic neurobehavioral sequelae, including cognitive deficits, changes in personality and increased rates of psychiatric illness. These neurobehavioral problems are understandable in the context of the typical profile of regional brain damage associated with trauma. This paper presents an overview of the neurobehavioral sequelae of TBI and outlines issues to consider in the evaluation and management of these challenges.

Changes over time in cognitive and structural profiles of head injury survivors

Survivors of traumatic head injury often suffer chronic cognitive deficits. Considerable evidence implicates the cholinergic system in these deficits. Recently, we reported cognitive and structural abnormalities in a cohort of head injured survivors consistent with this hypothesis [see Salmond, C. H., Chatfield, D. A., Menon, D. K., Pickard, J. D., & Sahakian, B. J. (2005). Cognitive Sequelae of Head Injury: Involvement of Basal Forebrain and associated structures. Brain, 128(1), 189-200]. The stability of the cognitive and structural MRI profiles was investigated in a longitudinal study. Twenty-one survivors of moderate-severe head injury completed two comprehensive neuropsychological assessments and two structural MRI scans at least six months apart. A cohort of controls also completed these investigations. The results revealed that the cognitive and structural profiles are relatively stable from six months post-injury forward up to 3 years post-injury. Deficits in memory, attention and reaction time were found, with relative preservation of working memory, consistent with abnormalities in the cholinergic system. These findings suggest that cholinergic enhancers may be an effective treatment for cognitive deficits post-head injury in survivors up to three years post-injury.

Diffusion tensor imaging in chronic head injury survivors: correlations with learning and memory indices

Diffusion tensor imaging (DTI) provides a unique insight into the cellular integrity of the brain. While conventional magnetic resonance imaging underestimates the extent of pathology following closed head injury, diffusion-weighted imaging has been shown to more accurately delineate the extent of cerebral damage. There have only been a few case studies of DTI in chronic head injury survivors. This study used DTI to investigate changes in anisotropy and diffusivity in survivors of head injury at least 6 months after their injury. The relationship between cognition and diffusion abnormality was also investigated. The voxel-based analysis revealed significant bilateral decreases in anisotropy, in major white matter tracts and association fibers in the temporal, frontal, parietal and occipital lobes. Statistically significant increases in diffusivity were also found in widespread areas of the cortex. A significant positive correlation was found between diffusivity and impairment of learning and memory in the left posterior cingulate, left hippocampal formation and left temporal, frontal and occipital cortex. The common pattern of abnormality despite heterogeneous injury mechanism and lesion location in the group suggests that these cellular changes reflect secondary insults. The importance of diffusion abnormalities in head injury outcome is emphasized by the significant correlation between a learning and memory index and diffusivity in areas known to subserve this cognitive function.

Ex VivoGene Therapy Using Targeted Engraftment of NGF-Expressing Human NT2N Neurons Attenuates Cognitive Deficits Following Traumatic Brain Injury in Mice

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

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 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.

Nucleus basalis of Meynert pathology in the human brain after fatal head injury

Dysfunction of the basal forebrain cholinergic system has been hypothesized to contribute to deficits of memory and cognition after head injury. We have previously reported reduced levels of choline acetyltransferase activity in the cerebral cortex of patients who died after a head injury, demonstrating that there is a loss of cortical cholinergic innervation. In the present study, we examined the nucleus basalis of Meynert (NBM), which provides cortical cholinergic innervation, in fatally head-injured patients and in controls. The majority of head-injured patients had histological evidence of neuronal damage in the NBM, which was due to mechanical distortion of the tissue and/or ischemic damage. The findings demonstrate that the NBM is vulnerable after severe head injury and that secondary insults play an important role in the damage. Thus, both neuronal perikarya and terminals of the basal forebrain cholinergic system are damaged after human fatal head injury. This damage may contribute to persisting dysfunction of memory and cognition in head-injured patients who survive.

Cognitive Impairment Following Traumatic Brain Injury

Cognitive impairments due to traumatic brain injury (TBI) are substantial sources of morbidity for affected individuals, their family members, and society. Disturbances of attention, memory, and executive functioning are the most common neurocognitive consequences of TBI at all levels of severity. Disturbances of attention and memory are particularly problematic, as disruption of these relatively basic cognitive functions may cause or exacerbate additional disturbances in executive function, communication, and other relatively more complex cognitive functions. Because of the high rate of other physical, neurologic, and psychiatric syndromes following TBI, a thorough neuropsychiatric assessment of the patient is a prerequisite to the prescription of any treatment for impaired cognition. Psychostimulants and other dopaminergically active agents (eg, methylphenidate, dextroamphetamine, amantadine, levodopa/carbidopa, bromocriptine) may modestly improve arousal and speed of information processing, reduce distractibility, and improve some aspects of executive function. Cautious dosing (start-low and go-slow), frequent standardized assessment of effects and side effects, and monitoring for drug-drug interactions are recommended. Cognitive rehabilitation is useful for the treatment of memory impairments following TBI. Cognitive rehabilitation may also be useful for the treatment of impaired attention, interpersonal communication skills, and executive function following TBI. This form of treatment is most useful for patients with mild to moderate cognitive impairments, and may be particularly useful for those who are still relatively functionally independent and motivated to engage in and rehearse these strategies. Psychotherapy (eg, supportive, individual, cognitive-behavioral, group, and family) is an important component of treatment. For patients with medication- and rehabilitation-refractory cognitive impairments, psychotherapy may be needed to assist both patients and families with adjustment to permanent disability.

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.

Traumatic brain injury reduces hippocampal alpha7 nicotinic cholinergic receptor binding

Changes in the expression of central nervous system (CNS) neurotransmitter receptors may contribute to behavioral and physiological deficits that occur following traumatic brain injury (TBI). Studies investigating the neurochemical basis for the protracted cognitive dysfunction that follows TBI have focused in part on cholinergic mechanisms. The present study compared the effects of mild and moderate cortical contusion injury (CCI) on the density of cholinergic receptor subtypes, NMDA-type glutamate receptors, and calcium channel expression. Quantitative autoradiography was used to determine the effects of CCI on receptor expression, 48 h following injury. The most robust and consistent change in receptor binding was in the density of alpha7 nicotinic receptors as determined by alpha-[125I]-bungarotoxin (BTX) binding. Bilateral deficits in BTX binding were present following both mild and moderate levels of injury. In contrast, changes in the density of alpha3/alpha4 nAChr's, muscarinic AChr's, NMDA-type glutamate receptors, and L-type calcium channel expression were more regionally restricted and lower in magnitude, as compared to changes in BTX binding. The high calcium permeability of the alpha7 nAChr may be related to the extensive decrease in BTX binding that occurs following TBI.

Neurotrauma care in the new millennium

The next millennium will see an explosion of neuromonitoring technology that will provide a more detailed understanding of brain-injured patients. This understanding will allow an individualized and intelligent application of the wide range of therapies that will become available. The measure of success for all of these endeavors will be individual patients and physicians' ability to return them to their normal lives.

Calpain activation and cytoskeletal protein breakdown in the corpus callosum of head-injured patients

Calpain-mediated breakdown of the cytoskeleton has been proposed to contribute to brain damage resulting from head injury. We examined the corpus callosum from patients who died after a blunt head injury in order to determine if there was evidence of these pathophysiological events in a midline myelinated commissure that is susceptible to damage after human head injury. Western blotting revealed marked reductions in the levels of neurofilament triplet proteins 200 and 68kDa in the corpus callosum of head-injured patients compared with control subjects. Neurofilament 200kDa levels were significantly reduced as detected by either phosphorylation-dependent or -independent antibodies. In contrast, there were minimal changes in the levels of beta-tubulin or the microtubule-associated protein, tau, in the head-injured patients, although amyloid precursor protein immunostaining demonstrated axonal damage in 9 of the 10 patients. The inactive 800kDa and active 76kDa subunits of mu-calpain were present in control subjects and head-injured patients. However, there was a significant increase in the levels of calpain-mediated spectrin breakdown products in head-injured patients compared with the control subjects. The results demonstrate that following human blunt head injury, there is a significant degradation of neurofilament proteins and increased levels of calpain-mediated spectrin breakdown products within the corpus callosum. Therefore, our data support the hypothesis that calpain-mediated breakdown of the cytoskeleton may contribute to axonal damage after head injury.

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.

One-year study of spatial memory performance, brain morphology, and cholinergic markers after moderate controlled cortical impact in rats

Persistent cognitive deficits are one of the most important sequelae of head injury in humans. In an effort to model some of the structural and neuropharmacological changes that occur in chronic postinjury brains, we examined the longitudinal effects of moderate vertical controlled cortical impact (CCI) on place learning and memory using the Morris water maze (MWM) test, morphology, and vesicular acetylcholine (ACh) transporter (VAChT) and muscarinic receptor subtype 2 (M2) immunohistochemistry. Vertical CCI (left parietal cortex, 4 m/sec, 2.5 mm; n = 10) or craniotomy (sham) was produced in male Sprague-Dawley rats (n = 10). Place learning was tested at 2 weeks, 4 weeks, 3 months, 6 months, and 12 months postinjury with the escape platform in a different maze quadrant for each time point. At each interval, rats received 5 days of water maze acquisition (latency to find hidden platform), a probe trial to measure place memory, and 2 days of visible platform trials to control for nonspecific deficits. At 3 weeks, half the animals were sacrificed for histology. At these injury parameters, CCI produced no significant differences in place learning between injured and sham rats at 2 weeks, 4 weeks, or 6 months after injury. However, at 3 and 12 months, the injured rats took significantly longer to find the hidden platform than the sham rats. Probe trial performance differed only at 12 months postinjury between injured (25.73+/-2.1%, standard error of the mean) and sham rats (44.09+/-7.0%, p < 0.05). The maze deficits at 1 year were not due to a worsening of performance, but may have resulted from a reduced ability of injured rats to benefit from previous water maze experience. Hemispheric loss of 30.4+/-5.5 mm3 was seen at 3 weeks after injury (versus respective sham). However, hemispheric loss almost doubled by 1 year after injury (51.5+/-8.5 mm3, p < 0.05 versus all other groups). Progressive tissue loss was also reflected by a three- to fourfold increase in ipsilateral ventricular volume between 3 weeks and 1 year after injury. At 1 year after injury, immunostaining for VAChT was dramatically increased in all sectors of the hippocampus and cortex after injury. Muscarinic receptor subtype 2 (M2) immunoreactivity was dramatically decreased in the ipsilateral hippocampus. This suggests a compensatory response of cholinergic neurons to increase the efficiency of ACh neurotransmission. Moderate CCI in rats produces subtle MWM performance deficits accompanied by persistent alteration in M2 and VAChT immunohistochemistry and progressive tissue atrophy. The inability of injured rats to benefit from repeated exposures to the MWM may represent a deficit in procedural memory that is independent of changes in hippocampal cholinergic systems.

Novel pharmacologic strategies in the treatment of experimental traumatic brain injury: 1998

The mechanisms underlying secondary or delayed cell death following traumatic brain injury are poorly understood. Recent evidence from experimental models suggests that widespread neuronal loss is progressive and continues in selectively vulnerable brain regions for months to years after the initial insult. The mechanisms underlying delayed cell death are believed to result, in part, from the release or activation of endogenous "autodestructive" pathways induced by the traumatic injury. The development of sophisticated neurochemical, histopathological and molecular techniques to study animal models of TBI have enabled researchers to begin to explore the cellular and genomic pathways that mediate cell damage and death. This new knowledge has stimulated the development of novel therapeutic agents designed to modify gene expression, synthesis, release, receptor or functional activity of these pathological factors with subsequent attenuation of cellular damage and improvement in behavioral function. This article represents a compendium of recent studies suggesting that modification of post-traumatic neurochemical and cellular events with targeted pharmacotherapy can promote functional recovery following traumatic injury to the central nervous system.

Craniocerebral trauma: protection and retrieval of the neuronal population after injury

OBJECTIVE

To review the consequences of mechanical injury to the brain with an emphasis on factors that may explain the variability of outcomes and how this might be influenced.

METHODS

Information regarding the pathophysiology of traumatic brain damage contained in original scientific reports and in review articles published in recent years was reviewed from the perspective of a clinical neurosurgeon and a neuropathologist, each with major research interests in traumatic brain damage. The information was compiled on the basis of the knowledge of and personal selection of articles that were identified through selective literature searches and current awareness profiles. A systematic literature review was not conducted.

RESULTS

Mechanical input affects neuronal and vascular elements and is translated into biological effects on the brain through a complex series of interacting cellular and molecular events. Whether these lead to permanent structural damage or to resolution and recovery is determined by the balance between processes that, on the one hand, mediate the effects of initial injury and subsequent secondary insults and, on the other, are manifestations of the brain's protective, reparative response. Experimental and clinical research has identified opportunities for altering the balance in a way that might promote recovery, but data demonstrating that this can lead to substantial clinical benefit are lacking. Recent evidence of genetically determined, individual susceptibility to the effects of injury may explain some of the puzzling variability in outcome after apparently similar insults and may also provide new opportunities for treatment.

CONCLUSION

The understanding of traumatic brain damage that is being gained from recent research is widening and broadening perspectives from the traditional focus on mechanical, vascular, and metabolic effects to encompass wider, neurobiological issues, drawn from the fields of neurodevelopment, neuroplasticity, neurodegeneration, and neurogenetics. Neurotrauma is a fascinating area of neuroscience research, with promise for the translation of knowledge to improved clinical management and outcome.

Cortical cholinergic dysfunction after human head injury

Loss of cholinergic neurotransmission is implicated in memory impairment and cognitive dysfunction after head injury. The aim of the present study was to investigate presynaptic markers, particularly in relation to cholinergic neurotransmission in human postmortem brain from patients who died following a head injury and age-matched controls. Choline acetyltransferase activity and high-affinity nicotinic receptor binding sites were assayed in the inferior temporal gyrus, cingulate gyrus, and superior parietal cortex of 16 head-injured patients and 8 controls. Synaptophysin immunoreactivity was determined in the left cingulate gyrus from the same patient groups. In the head-injured group, choline acetyltransferase activity was consistently reduced in each cortical region compared to control subjects. The presence of a subdural haematoma and a prolonged survival period after head injury tended to be associated with lower choline acetyltransferase activity. In contrast to the marked reduction in choline acetyltransferase activity, nicotine receptor binding was unchanged in head-injured compared to control patients. Synaptophysin immunoreactivity in the cingulate gyrus was reduced by approximately 30% (p < 0.05) in the head-injured group compared to controls. Correlation of choline acetyltransferase activity with synaptophysin immunoreactivity indicated there is a deficit of cholinergic presynaptic terminals in postmortem human brain following head injury.

Chronic administration of a partial muscarinic M1 receptor agonist attenuates decreases in forebrain choline acetyltransferase immunoreactivity following experimental brain trauma

Lu 25-109-T is a partial muscarinic M1 receptor agonist with antagonistic effects at presynaptic M2 autoreceptors and has been shown to improve cognitive function following traumatic brain injury (TBI) in rats. This investigation examined the effects of TBI on basal forebrain choline acetyltransferase immunoreactivity (ChAT-IR) following daily administration of saline or 15 mumol/kg Lu 25-109-T. Rats received a moderate (2.1 +/- 0.1 atm) level of central fluid percussion TBI or were surgically prepared but not injured and were injected (sc) with saline or drug on Days 1-15 postinjury. Rats were sacrificed following the last daily injection, and sections were collected through the basal forebrain and processed for ChAT-IR. TBI caused a significant reduction in ChAT-IR neuronal density in saline- and Lu 25-109-T-treated rats with a 13% and 5% decrease in the medial septal nucleus (MSN), a 48 and 23% decrease in the vertical limb nucleus of the diagonal band (VDB), and a 51 and 28% decrease in the nucleus basalis magnocellularis (NBM), respectively. However, Lu 25-109-T significantly attenuated the injury-induced reductions in ChAT-IR. Loss in ChAT-IR neuronal density is not thought to result from cell death as parallel cresyl violet-stained sections indicated no decrease in neuronal cell density in the MSN, VDB, or NBM. These results support the hypothesis that increasing cholinergic tone during the recovery period after TBI will restore cholinergic function impaired by brain trauma.

Reduced evoked release of acetylcholine in the rodent neocortex following traumatic brain injury

Neocortical acetylcholine (ACh) release was examined in awake, freely-moving rats at 14 days following lateral controlled cortical impact. Extracellular ACh was measured prior to and after an intraperitoneal administration of scopolamine, which evokes ACh release by blocking autoreceptors. At 14 days post-injury there was a significant reduction in scopolamine-evoked ACh release. The data suggest that neocortical cholinergic neurotransmission is chronically compromised, and may contribute to post-traumatic memory deficits.