The neuroinflammatory response in humans after traumatic brain injury.

AIMS: Traumatic brain injury is a significant cause of morbidity and mortality worldwide. An epidemiological association between head injury and long-term cognitive decline has been described for many years and recent clinical studies have highlighted functional impairment within 12 months of a mild head injury. In addition chronic traumatic encephalopathy is a recently described condition in cases of repetitive head injury. There are shared mechanisms between traumatic brain injury and Alzheimer's disease, and it has been hypothesized that neuroinflammation, in the form of microglial activation, may be a mechanism underlying chronic neurodegenerative processes after traumatic brain injury. METHODS: This study assessed the microglial reaction after head injury in a range of ages and survival periods, from <24-h survival through to 47-year survival. Immunohistochemistry for reactive microglia (CD68 and CR3/43) was performed on human autopsy brain tissue and assessed 'blind' by quantitative image analysis. Head injury cases were compared with age matched controls, and within the traumatic brain injury group cases with diffuse traumatic axonal injury were compared with cases without diffuse traumatic axonal injury. RESULTS: A major finding was a neuroinflammatory response that develops within the first week and persists for several months after traumatic brain injury, but has returned to control levels after several years. In cases with diffuse traumatic axonal injury the microglial reaction is particularly pronounced in the white matter. CONCLUSIONS: These results demonstrate that prolonged microglial activation is a feature of traumatic brain injury, but that the neuroinflammatory response returns to control levels after several years.

Glial expression of cannabinoid CB(2) receptors and fatty acid amide hydrolase are beta amyloid-linked events in Down's syndrome.

Recent data suggest that the endocannabinoid system (ECS) may be involved in the glial response in different types of brain injury. Both acute and chronic insults seem to trigger a shift in the pattern of expression of some elements of this system from neuronal to glial. Specifically, data obtained in human brain tissue sections from Alzheimer's disease patients showed that the expression of cannabinoid receptors of the CB(2) type is induced in activated microglial cells while fatty acid amide hydrolase (FAAH) expression is increased in reactive astrocytes. The present study was designed to determine the time-course of the shift from neuronal to glial induction in the expression of these proteins in Down's syndrome, sometimes referred to as a human model of Alzheimer-like beta-amyloid (Abeta) deposition. Here we present immunohistochemical evidence that both CB(2) receptors and FAAH enzyme are induced in Abeta plaque-associated microglia and astroglia, respectively, in Down's syndrome. These results suggest that the induction of these elements of the ECS contributes to, or is a result of, amyloid deposition and subsequent plaque formation. In addition, they confirm a striking differential pattern of distribution of FAAH and CB(2) receptors.

The impact of argyrophilic grain disease on the development of dementia and its relationship to concurrent Alzheimer's disease-related pathology.

Argyrophilic grain disease (AGD) constitutes a neurodegenerative disorder that occurs in the brains of the elderly and affects 5% of all patients with dementia. Tau protein-containing lesions known as argyrophilic grains and located predominantly in limbic regions of the brain characterize this disease. Dementia is encountered in only a subset of cases that display the morphological pattern of AGD. The aim of this study is to determine the role of concurrent Alzheimer's disease (AD)-related pathology for the development of dementia in AGD patients. A total of 204 post-mortem brains from 30 demented and 49 nondemented AGD patients, 39 AD patients, and from 86 nondemented controls without AGD were staged for AD-related neurofibrillary tangles (NFTs) as well as amyloid beta-protein (Abeta) deposition. To identify differences in AD-related pathology between demented and nondemented AGD cases, and to differentiate the pattern of AD-related changes in demented and nondemented AGD cases from that seen in AD and nondemented controls, we statistically compared the stages of Abeta and NFT distribution among these groups. Using a logistic regression model, we showed that AGD has a significant effect on the development of dementia beyond that attributable to AD-related pathology (P < 0.005). Demented AGD cases showed lower stages of AD-related pathology than did pure AD cases but higher stages than nondemented AGD patients. AGD associated dementia was seen in the presence of NFT (Braak)-stages II-IV and Abeta-phases 2-3, whereas those stages were not associated with dementia in the absence of AGD. In conclusion, AGD is a clinically relevant neurodegenerative entity that significantly contributes to the development of dementia by lowering the threshold for cognitive deficits in the presence of moderate amounts of AD-related pathology.

Neuropsychiatric associations of apolipoprotein E alleles in subjects with combat-related posttraumatic stress disorder.

Previous studies have reported associations between apolipoprotein E (APOE) genotype, cognitive function, and psychopathology in psychiatric populations. The authors investigated the associations between APOE allele status, memory function, and posttraumatic stress disorder (PTSD) symptom severity in PTSD subjects. Presence of the APOE 2 allele was associated with significantly worse reexperiencing symptoms and impaired memory function in this population.

Long-term intracerebral inflammatory response after traumatic brain injury.

Epidemiological and pathological studies suggest that head injury is a significant risk factor for subsequent neurodegeneration and cognitive decline in later life. The precise mechanisms for the development of post-traumatic neurodegenerative change are unclear but we hypothesize that persistence of inflammatory processes in the brain may play a key role and that some individuals are more susceptible to such changes based on their genetic make-up. In support of this hypothesis we present evidence of persistent elevated microglial activity in long-term survivors of head injury and the suggestion of an association between the extent of this activity and interleukin-1 genotype.