Cholinergic deficits and galaninergic hyperinnervation of the nucleus basalis of Meynert in Alzheimer's disease and Lewy body disorders

AIMS

Galanin is a highly inducible neuroprotective neuropeptide and in Alzheimer's disease (AD), a network of galaninergic fibres has been reported to hypertrophy and hyperinnervate the surviving cholinergic neurons in the basal forebrain. We aimed to determine (i) the extent of galanin hyperinnervation in patients with AD and Lewy body disease and (ii) whether galanin expression relates to the neuropathological burden and cholinergic losses.

METHODS

Galanin immunohistochemistry was carried out in the anterior nucleus basalis of Meynert of 27 Parkinson's disease (PD) cases without cognitive impairment (mild cognitive impairment [MCI]), 15 with PD with MCI, 42 with Parkinson's disease dementia (PDD), 12 with Dementia with Lewy bodies (DLB), 19 with AD, 12 mixed AD/DLB and 16 controls. Galaninergic innervation of cholinergic neurons was scored semiquantitatively. For a subgroup of cases (n = 60), cholinergic losses were determined from maximum densities of choline acetyltransferase positive (ChAT+ve) neurons and their projection fibres. Quantitative data for α-synuclein, amyloid beta and tau pathology were obtained from tissue microarrays covering cortical/subcortical regions.

RESULTS

Significant losses of cholinergic neurons and their projection fibres were observed across all diseases. Galaninergic hyperinnervation was infrequent and particularly uncommon in established AD and DLB. We found that hyperinnervation frequencies are significantly higher in the transition between PD without MCI to PDD and that higher burdens of co-existent AD pathology impair this galaninergic response.

CONCLUSIONS

Our results suggest that galanin upregulation represents an intrinsic response early in Lewy body diseases but which fails with increasing burdens of AD related pathology.

Review: Revisiting the human cholinergic nucleus of the diagonal band of Broca

Although the nucleus of the vertical limb of the diagonal band of Broca (nvlDBB) is the second largest cholinergic nucleus in the basal forebrain, after the nucleus basalis of Meynert, it has not generally been a focus for studies of neurodegenerative disorders. However, the nvlDBB has an important projection to the hippocampus and discrete lesions of the rostral basal forebrain have been shown to disrupt retrieval memory function, a major deficit seen in patients with Lewy body disorders. One reason for its neglect is that the anatomical boundaries of the nvlDBB are ill defined and this area of the brain is not part of routine diagnostic sampling protocols. We have reviewed the history and anatomy of the nvlDBB and now propose guidelines for distinguishing nvlDBB from other neighbouring cholinergic cell groups for standardizing future clinicopathological work. Thorough review of the literature regarding neurodegenerative conditions reveals inconsistent results in terms of cholinergic neuronal loss within the nvlDBB. This is likely to be due to the use of variable neuronal inclusion criteria and omission of cholinergic immunohistochemical markers. Extrapolating from those studies showing a significant nvlDBB neuronal loss in Lewy body dementia, we propose an anatomical and functional connection between the cholinergic component of the nvlDBB (Ch2) and the CA2 subfield in the hippocampus which may be especially vulnerable in Lewy body disorders.

A novel method to visualise the three-dimensional organisation of the human cerebral cortical vasculature

Current tissue-clearing protocols for imaging in three dimensions (3D) are typically applied to optimally fixed, small-volume rodent brain tissue - which is not representative of the tissue found in diagnostic neuropathology laboratories. We present a method to visualise the cerebral cortical vasculature in 3D in human post-mortem brain tissue which had been preserved in formalin for many years. Tissue blocks of cerebral cortex from two control cases, two Alzheimer's brains and two cases from Alzheimer's patients immunised against Aβ₄₂ were stained with fluorescent Lycopersicon esculentum agglutinin (Tomato lectin), dehydrated and cleared using an adapted three-dimensional imaging of solvent cleared organs (3DISCO) protocol to visualise the vascular endothelium. Tissue was imaged using light sheet and confocal microscopy and reconstructed in 3D using amira software. The method permits visualisation of the arrangement of the parallel penetrating cortical vasculature in the human brain. The presence of four vascular features including anastomosis, U-shaped vessels, spiralling and loops were revealed. In summary, we present a low cost and simple method to visualise the human cerebral vasculature in 3D compatible with prolonged fixation times (years), allowing study of vascular involvement in a range of normative and pathological states.

Bringing CLARITY to the human brain: visualization of Lewy pathology in three dimensions

AIMS

CLARITY is a novel technique which enables three-dimensional visualization of immunostained tissue for the study of circuitry and spatial interactions between cells and molecules in the brain. In this study, we aimed to compare methodological differences in the application of CLARITY between rodent and large human post mortem brain samples. In addition, we aimed to investigate if this technique could be used to visualize Lewy pathology in a post mortem Parkinson's brain.

METHODS

Rodent and human brain samples were clarified and immunostained using the passive version of the CLARITY technique. Samples were then immersed in different refractive index matching media before mounting and visualizing under a confocal microscope.

RESULTS

We found that tissue clearing speed using passive CLARITY differs according to species (human vs. rodents), brain region and degree of fixation (fresh vs. formalin-fixed tissues). Furthermore, there were advantages to using specific refractive index matching media. We have applied this technique and have successfully visualized Lewy body inclusions in three dimensions within the nucleus basalis of Meynert, and the spatial relationship between monoaminergic fibres and Lewy pathologies among nigrostriatal fibres in the midbrain without the need for physical serial sectioning of brain tissue.

CONCLUSIONS

The effective use of CLARITY on large samples of human tissue opens up many potential avenues for detailed pathological and morphological studies.

Neuropathological changes in the nucleus basalis in schizophrenia

The nucleus basalis has not been examined in detail in severe mental illness. Several studies have demonstrated decreases in glia and glial markers in the cerebral cortex in schizophrenia, familial bipolar disorder and recurrent depression. Changes in neocortical neuron size and shape have also been reported. The nucleus basalis is a collection of large cholinergic neurons in the basal forebrain receiving information from the midbrain and limbic system, projecting to the cortex and involved with attention, learning and memory, and receives regulation from serotonergic inputs. Forty-one cases aged 41-60 years with schizophrenia or major depressive disorder with age-matched controls were collected. Formalin-fixed paraffin-embedded coronal nucleus basalis sections were histologically stained for oligodendrocyte identification with cresyl-haematoxylin counterstain, for neuroarchitecture with differentiated cresyl violet stain and astrocytes were detected by glial fibrillary acid protein immunohistochemistry. Cell density and neuroarchitecture were measured using Image Pro Plus. There were larger NB oval neuron soma in the combined schizophrenia and major depression disorder groups (p = 0.038), with no significant change between controls and schizophrenia and major depression disorder separately. There is a significant reduction in oligodendrocyte density (p = 0.038) in the nucleus basalis in schizophrenia. The ratio of gemistocytic to fibrillary astrocytes showed a greater proportion of the former in schizophrenia (18.1 %) and major depressive disorder (39.9 %) than in controls (7.9 %). These results suggest glial cell abnormalities in the nucleus basalis in schizophrenia possibly leading to cortical-limbic disturbance and subcortical dysfunction.

Review: microglia in protein aggregation disorders: friend or foe?

Microglia cells have been implicated, to some extent, in the pathogenesis of all of the common neurodegenerative disorders involving protein aggregation such as Alzheimer's disease, Parkinson's disease and Amyotrophic Lateral Sclerosis. However, the precise role they play in the development of the pathologies remains unclear and it seems that they contribute to the pathological process in different ways depending on the specific disorder. A better understanding of their varied roles is essential if they are to be the target for novel therapeutic strategies.

Inflammatory risk factors and pathologies associated with Alzheimer's disease

The importance of inflammatory processes in Alzheimer's disease (AD) progression has been confirmed during the past decade by the intensive investigation of inflammatory mediators in the brain of AD patients as well as by the genetic and drug manipulation of animal models of AD. Imaging studies have revealed that the activation of microglia occurs in early stages of the disease, even before plaque and tangle formation, and is correlated with early cognitive deficits. In this review, we analyze how different risk factors, such as trauma, stroke, infection, and metabolic diseases can lead to an acceleration of the inflammatory response in the AD brain and to an increased risk of developing this disorder. The use of imaging techniques for early detection of glial activation which offer the advantage of investigating how potential anti-inflammatory therapies may influence disease progression and levels of cognition is also discussed.

Differential effects of amyloid-β peptide aggregation status on in vivo retinal neurotoxicity

The present study examined the relationship between amyloid beta (Aβ)-peptide aggregation state and neurotoxicity in vivo using the rat retinal-vitreal model. Following single unilateral intravitreal injection of either soluble Aβ1-42 or Aβ1-42 preaggregated for different periods, retinal pathology was evaluated at 24 hours, 48 hours, and 1-month postinjection. Injection of either soluble Aβ (sAβ) or preaggregated Aβ induced a rapid reduction in immunoreactivity (IR) for synaptophysin, suggesting that direct contact with neurons is not necessary to disrupt synapses. Acute neuronal ionic and metabolic dysfunction was demonstrated by widespread loss of IR to the calcium buffering protein parvalbumin (PV) and protein gene product 9.5, a component of the ubiquitin-proteosome system. Injection of sAβ appeared to have a more rapid impact on PV than the preaggregated treatments, producing a marked reduction in PV cell diameters at 48 hours, an effect that was only observed for preaggregated Aβ after 1-month survival. Extending the preaggregation period from 4 to 8 days to obtain highly fibrillar Aβ species significantly increased the loss of choline acteyltransferase IR, but had no effect on PV-IR. These findings prompt the conclusion that Aβ assembly state has a significant impact on in vivo neurotoxicity by triggering distinct molecular changes within the cell.

The dorsal motor nucleus of the vagus is not an obligatory trigger site of Parkinson's disease: a critical analysis of alpha-synuclein staging

AIMS

It has been proposed that alpha-synuclein (alpha Syn) pathology in Parkinson's disease (PD) spreads in a predictable caudo-rostral way with the earliest changes seen in the dorsal motor nucleus of the vagus nerve (DMV). However, the reliability of this stereotypical spread of alpha Syn pathology has been questioned. In addition, the comparative occurrence of alpha Syn pathology in the spinal cord and brain has not been closely studied.

METHODS

In order to address these issues, we have examined 71 cases of PD from the UK Parkinson's Disease Society Tissue Bank at Imperial College, London. The incidence and topographic distribution of alpha Syn pathology in several brain regions and the spinal cord were assessed.

RESULTS

The most affected regions were the substantia nigra (SN; in 100% of cases) followed by the Nucleus Basalis of Meynert (NBM) in 98.5%. Fifty-three per cent of cases showed a distribution pattern of alpha Syn compatible with a caudo-rostral spread of alpha Syn through the PD brain. However, 47% of the cases did not fit the predicted spread of alpha Syn pathology and in 7% the DMV was not affected even though alpha Syn inclusions were found in SN and cortical regions. We also observed a high incidence of alpha Syn in the spinal cord with concomitant affection of the DMV and in a few cases in the absence of DMV involvement.

CONCLUSIONS

Our results demonstrate a predominant involvement of the SN and NBM in PD but do not support the existence of a medullary induction site of alpha Syn pathology in all PD brains.

Amyloid beta peptide causes chronic glial cell activation and neuro-degeneration after intravitreal injection

We have previously demonstrated that amyloid beta (Abeta) peptide is acutely toxic to retinal neurones in vivo and that this toxicity is mediated by an indirect mechanism. We have now extended these studies to look at the chronic effect of intravitreal injection of Abeta peptides on retinal ganglion cells (RGC), the projection neurones of the retina and the glial cell response. 5 months after injection of Abeta1-42 or Abeta42-1 there was no significant reduction in RGC densities but there was a significant reduction in the retinal surface area after both peptides. Phosphate-buffered saline (PBS) injection had no effect on retinal size or RGC density. There was a pronounced reduction in the number of large RGCs with a concomitant significant increase in medium and small RGCs. There was no change in cell sizes 5 months after injection with PBS. At 5 months after injection of both peptides, there was marked activation of Muller glial cells and microglia. There was also expression of the major histocompatibility complex (MHC) class II molecule on some of the microglial cells but we saw no evidence of T-cell infiltration into the injected retinas. In order to elucidate potential toxic mechanisms, we have looked at levels of glutamine synthetase and nitric oxide synthase. As early as 2 days after injection we noted that activation of Muller glia was associated with a decrease in glutamine synthetase immuno-reactivity but there was no detectable expression of inducible nitric oxide synthase in any retinal cells. These results suggest that chronic activation of glial cells induced by Abeta peptides may result in chronic atrophy of projection neurones in the rat retina.

Cerebral amyloid angiopathy in traumatic brain injury: association with apolipoprotein E genotype

OBJECTIVE

In view of the association of the apolipoprotein E (APOE) epsilon 4 allele with poor outcome after traumatic brain injury we determined the frequency of cerebral amyloid angiopathy (CAA) and the extent of haemorrhagic pathology in relation to APOE genotype in an autopsy series of 88 head injured cases.

METHODS

Tissue sections from the frontal and temporal lobes were immunostained for amyloid-beta peptide (A beta) and stained for Congo red to identify vascular amyloid pathology. A semiquantitative assessment of contusions, the total contusion index, was used to estimate the severity of the haemorrhagic pathology. APOE genotypes were determined by polymerase chain reaction of genomic DNA extracted from paraffin embedded tissue sections.

RESULTS

CAA was present in 7/40 (18%) epsilon 4 carriers compared with 1/48 (2%) non-epsilon 4 carriers (p = 0.021, 95% confidence interval (CI) for difference in proportions with CAA 3% to 29%) with 6/40 (4 with CAA) epsilon 4 carriers being homozygotes. Thus the risk of having CAA for epsilon 4 carriers was 8.4 times that for the non-epsilon 4 carriers. However, there was no clear tendency for patients with CAA to have more severe or more numerous contusions (median contusion index 19 (CAA) v 14.5, p = 0.23, 95% CI for difference in medians -5 to 14).

CONCLUSIONS

Presence of CAA in head injured cases was significantly associated with possession of an APOE epsilon 4 allele but not with the severity of contusions.

Axonal injury is accentuated in the caudal corpus callosum of head-injured patients

Amyloid precursor protein (APP) accumulation is a sensitive marker for the axonal damage that is commonly seen in the brain as the result of head injury. This form of damage is particularly associated with midline structures such as the corpus callosum, although it is not clear whether some areas are more susceptible than others. The aim of this study was to determine if there was a differential distribution of axonal injury throughout the corpus callosum after head injury in an unselected group of cases. Coronal tissue sections from eight cases were taken at different levels through the corpus callosum, including the genu, body, and splenium. The sections were immunostained with an antibody to APP, and the amount of axonal damage at the different levels was quantified using computer image analysis to build up a rostro-caudal profile for each case. The profiles revealed a significantly higher APP load in caudal parts of the corpus callosum. This supports previous nonquantitative reports in the literature and has important implications in terms of choosing where tissue should be sampled to maximize the chance of detecting axonal injury post mortem.

beta-amyloid (Abeta)42(43), abeta42, abeta40 and apoE immunostaining of plaques in fatal head injury

beta-Amyloid (Abeta) deposits are found in the brains of approximately one-third of patients who die within days after a severe head injury; their presence correlating strongly with possession of an apolipoprotein E (apoE)-epsilon4 allele. The aim of the study was to investigate the relationship between Abeta42, Abeta40 and apoE immunostaining of Abeta plaques in the cerebral cortex and the relevance of apoE genotype in 23 fatally head-injured patients. These cases were known to have Abeta deposits from a previous study in which they were examined and semiquantified and related to apoE genotype. In the present study, the temporal cortex was probed using four different antibodies that recognize Abeta42(43), Abeta40 and an antibody to apoE. Abeta42(43)-positive plaques were observed in all of the 23 cases and Abeta40 immunoreactivity in only 11 of the 23 cases. In addition, semiquantitative analysis showed that relatively fewer plaques were detected with anti-Abeta40 than anti-Abeta42(43). ApoE-immunoreactive plaques were identified in 18 of the 23 cases. The number of plaques stained for apoE was relatively less than for Abeta42(43) but greater than for Abeta40. Furthermore, the density of Abeta plaques detected using either Abeta42(43), Abeta40 or apoE antibodies was associated with possession of apoE-epsilon4 in an allele dose-dependent manner. The results are consistent with Abeta42(43) as the initially deposited species in brain parenchyma and provide evidence that apoE is involved in the early stages of amyloid deposition. Further, the findings may be of relevance to the role of apoE genotype in influencing outcome after acute brain injury.

Increase in HLA-DR immunoreactive microglia in frontal and temporal cortex of chronic schizophrenics

Glia play a major role in neuronal migration, synapse formation, and control of neurotransmission in the developing and mature nervous system. This study investigated whether chronic schizophrenia is associated with glial changes in 3 regions of the cerebral cortex: dorsolateral prefrontal cortex (Brodmann's area 9), the superior temporal gyrus (area 22), and the anterior cingulate gyrus (area 24). In a blind study, astroglia and microglia were identified immunocytochemically in frozen sections from postmortem schizophrenic and control brains. Astroglia and microglia were identified using antibodies to glial fibrillary acidic protein (GFAP) and class II human leucocyte antigen (HLA-DR) respectively. They were then quantified for each cortical layer. Significant differences were found in HLA-DR+ microglial numerical density in 2 of the areas. A 28% increase (p < 0.05) was found in area 9 in 8 schizophrenics (115 +/- 9 cells/mm2) compared with 10 controls (89 +/- 5 cells/mm2), when combining all cortical layers and both cerebral hemispheres. For area 22, there was a 57% increase (p < 0.01) in microglia in 7 schizophrenics (139 +/- 6 cells/mm2) compared with 10 controls (88 +/- 5 cells/mm2). In area 24 the same trend was evident, but the results did not reach significance. Microglial number was further analyzed for each cortical layer, which confirmed the overall pattern. For all areas, numerical density of astroglia showed no significant differences between schizophrenics and controls. Cortical thickness was measured in all areas and total neuronal numerical density was estimated for area 22. Again, no significant differences were found between schizophrenics and controls. This study demonstrates a specific increase in the numerical density of HLA-DR+ microglia in temporal and frontal cortex of chronic schizophrenics, not related to aging, which might be implicated in possible changes in cortical neuropil architecture in schizophrenia.

Overexpression of s100beta in Down's syndrome: correlation with patient age and with beta-amyloid deposition

S100beta is an astrocyte-derived uritotrophic' cytokine which has been implicated in the pathogenesis of Alzheimer's disease. S100beta overexpression by plaque-associated astrocytes correlates with growth of abnormal (strophic') neurites in beta-amyloid plaques, one of the major neuropathological hallmarks of Alzheimer's disease. As the characteristic neuropathological changes of Alzheimer's disease are virtually universal in middle-aged Down's syndrome patients, studies of Down's syndrome patients provide a unique opportunity to investigate the pathophysiological processes underlying the development of Alzheimer-type neuropathological changes. Computerized morphometric analysis was used to quantify astrocyte activation and astrocytic expression of S100beta, and to correlate these with beta-amyloid deposition, in a clinically well-characterized cohort of Down's syndrome subjects, aged 13-65 years. There were significant positive correlations between S100beta expression and patient age, and between S100beta expression and cerebral cortical beta-amyloid deposition. Moreover, the numbers of activated (enlarged) astrocytes overexpressing S100beta showed a significant correlation with the numeric density of beta-amyloid plaques, from the youngest to the oldest ages and within age ranges where pathology is most florid, while no such relationship was found between the numbers of small, non-activated S100beta-immunoreactive cells and numerical density of beta-amyloid plaques. These correlations, together with established functions of S100beta, are consistent with the idea that S100beta overexpression promotes beta-amyloid plaque formation and progression in Down's syndrome.

Effects of bFGF and TGFbeta on the expression of amyloid precursor and B-cell lymphoma protooncogene proteins in the rat retina

The pattern of immunoreactivity for amyloid precursor (APP) and B-cell lymphoma protooncogene (Bcl-2) proteins in the rat retina was studied after intravitreal injection of basic fibroblast growth factor (bFGF) or transforming growth factor-beta (TGFbeta). In normal control retinas, intense immunostaining of APP and Bcl-2 was observed primarily in the endfeet and proximal part of radial processes of Müller glial cells. A dose-dependent reduction in immunostaining of APP and Bcl-2 in Müller cells was observed after injection of bFGF and TGFbeta. These results provide the first evidence that APP and Bcl-2 can be down-regulated by cytokines in vivo.

A comparison of manual and semi-automated methods in the assessment of axonal injury

Diffuse axonal injury (DAI) in the central nervous system is a common cause of post-traumatic coma and may result in varying degrees of disability up to and including the vegetative state. Experimental studies in man and animals have previously relied upon semi-quantitative grading systems for determining the relationship between the extent of DAI and the clinical features of patients. Using beta-amyloid precursor protein immunocytochemistry for the detection of DAI in sections of corpus callosum from 15 cases of fatal head injury, we have developed a quantitative image analysis technique for the assessment of axonal injury. This new method is objective and reproducible and should allow better correlation with biomechanical, radiological, and clinical parameters to increase our understanding of DAI.

Is there a genetic basis for the deposition of beta-amyloid after fatal head injury?

1. Alzheimer's disease is a heterogeneous disorder that may be caused by genetic or environmental factors or by a combination of both. Abnormalities in chromosomes 1, 14, and 21 have all been implicated in the pathogenesis of the early-onset form of the disease, while the epsilon 4 allele of the apolipoprotein E gene (on chromosome 19) is now recognized as a risk factor for early- and late-onset sporadic and familial Alzheimer's disease. 2. The best-established environmental trigger for the disease is a head injury, based on epidemiological and neuropathological evidence. Approximately 30% of patients who die after a single episode of severe head injury show intracerebral deposition of beta-amyloid protein (A beta), a protein that is thought to be central to the pathogenesis of Alzheimer's disease. 3. Recent studies have revealed an over-representation of the apoE epsilon 4 allele in those head-injured patients displaying A beta pathology, thus providing the first evidence for a link between a genetic susceptibility (apoE epsilon 4) and an environmental trigger (head injury) in the development of Alzheimer-type pathology.

Life-long overexpression of S100beta in Down's syndrome: implications for Alzheimer pathogenesis

Chronic overexpression of the neurite growth-promoting factor S100beta has been implicated in the pathogenesis of neuritic plaques in Alzheimer's disease. Such plaques are virtually universal in middle-aged Down's syndrome, making Down's a natural model of Alzheimer's disease. We determined numbers of astrocytes overexpressing S100beta, and of neurons overexpressing beta-amyloid precursor protein (beta-APP), and assayed for neurofibrillary tangles in neocortex of 20 Down's syndrome patients (17 weeks gestation to 68 years). Compared to controls, there were twice as many S100beta-immunoreactive (S100beta+) astrocytes in Down's patients at all ages: fetal, young, and adult (p = 0.01, or better, in each age group). These were activated (i.e., enlarged), and intensely immunoreactive, even in the fetal group. There were no neurofibrillary changes in fetal or young Down's patients. The numbers of S100beta+ astrocytes in young and adult Down's patients correlated with the numbers of neurons overexpressing beta-APP (p < 0.05). Our findings are consistent with the idea that conditions--including Down's syndrome--that promote chronic overexpression of S100beta may confer increased risk for later development of Alzheimer's disease.

Glial-neuronal interactions in Alzheimer's disease: the potential role of a 'cytokine cycle' in disease progression

The role of glial inflammatory processes in Alzheimer's disease has been highlighted by recent epidemiological work establishing head trauma as an important risk factor, and the use of anti-inflammatory agents as an important ameliorating factor, in this disease. This review advances the hypothesis that chronic activation of glial inflammatory processes, arising from genetic or environmental insults to neurons and accompanied by chronic elaboration of neuroactive glia-derived cytokines and other proteins, sets in motion a cytokine cycle of cellular and molecular events with neurodegenerative consequences. In this cycle, interleukin-1 is a key initiating and coordinating agent. Interleukin-1 promotes neuronal synthesis and processing of the beta-amyloid precursor protein, thus favoring continuing deposition of beta-amyloid, and activates astrocytes and promotes astrocytic synthesis and release of a number of inflammatory and neuroactive molecules. One of these, S100beta, is a neurite growth-promoting cytokine that stresses neurons through its trophic actions and fosters neuronal cell dysfunction and death by raising intraneuronal free calcium concentrations. Neuronal injury arising from these cytokine-induced neuronal insults can activate microglia with further overexpression of interleukin-1, thus producing feedback amplification and self-propagation of this cytokine cycle. Additional feedback amplification is provided through other elements of the cycle. Chronic propagation of this cytokine cycle represents a possible mechanism for progression of neurodegenerative changes culminating in Alzheimer's disease.

Nitric oxide synthase in developing retinas and after optic tract section

We compared the pattern of nitric oxide synthase (NOS) immunoreactivity in retinas of rats during normal development and after unilateral transection of the optic tract at postnatal day 7. NOS was first detected in the second postnatal week in the inner nuclear and inner plexiform layers. There was no detectable difference in the overall pattern of immunoreactivity between normal retinas and retinas with severe loss of ganglion cells due to the lesion. We suggest that NOS may have a role in synaptic and vascular development in the inner retina, but is unlikely to play a major role in normal physiological retinal ganglion cell death or axotomy-induced cell death.

A beta 42 is the predominant form of amyloid beta-protein in the brains of short-term survivors of head injury

Fatal head injury results in the formation of diffuse parenchymal deposits of amyloid beta-protein (A beta) in the brains of approximately 30% of individuals. We used carboxyl terminal-specific antisera to examine the exact nature of these deposits in paraffin sections of neocortex from seven head-injured patients. Immunostaining for A beta 42 was observed in all parenchymal deposits whereas staining for A beta 40, the form of the protein which predominates in serum and cerebrospinal fluid, was seen in only a small proportion of deposits. The relative paucity of A beta 40 suggests that post-traumatic deposits do not arise as a result of passive leakage from damaged cerebral blood vessels but are similar to the early A beta 42 parenchymal deposits seen in Down's syndrome and Alzheimer's disease.

Prion protein immunocytochemistry--UK five centre consensus report

Creutzfeldt-Jakob disease (CJD) and other prion diseases are associated with the deposition of insoluble prion protein (PrPCJD) in the central nervous system (CNS). Antibodies raised against PrPCJD also react with its precursor protein, a soluble form of PrP (PrPC), which is widely distributed in the normal CNS. This cross-reactivity has in the past raised doubts as to the specificity and diagnostic reliability of PrP immunolocalization, especially in familial cases which are atypical clinically and which lack characteristic pathology findings. Following an MRC-funded workshop which focused on this problem, a multicentre prospective study was set up to identify a reliable protocol for PrPCJD immunocytochemistry. Five UK centres took part in this study and demonstrated consistent staining of plaques, vacuolar deposits in severe spongiform change, and perineuronal deposits using a variety of antibodies and enhancement procedures. A protocol using formic acid, guanidine thiocyanate, and hydrated autoclaving pre-treatment in conjunction with a monoclonal PrPCJD antibody produced the clearest immunochemical results and is presented as the consensus UK recommendation for PrPCJD immunocytochemical procedures.

Is beta-APP a marker of axonal damage in short-surviving head injury?

beta-Amyloid precursor protein (beta-APP), a normal constituent of neurons which is conveyed by fast axonal transport, has been found to be a useful marker for axonal damage in cases of fatal head injury. Immunocytochemistry for beta-APP is a more sensitive technique for identifying axonal injury than conventional silver impregnation. This study was designed to determine how quickly evidence of axonal damage and bulb formation appears. Using this method a variety of brain areas were studied from 55 patients who died within 24 h of a head injury. Immunocytochemical evidence of axonal injury was first detected after 2 h survival, axonal bulbs were first identified after 3 h survival, and the amount of axonal damage and axonal bulb formation increased the longer the survival time.

Distribution of beta-amyloid precursor and B-cell lymphoma protooncogene proteins in the rat retina after optic nerve transection or vascular lesion

The expression of beta-amyloid precursor protein (APP) and B-cell lymphoma protooncogene protein (Bcl-2) in retinal cells in the rat was studied using immunocytochemistry at different times after intraorbital optic nerve transection or vascular lesion. Three hours to one month after transection of the optic nerve, a significant increase in APP and Bcl-2 immunostaining was observed in retinal Müller glia but not in retinal neurons. In contrast, injury to blood vessels that supply the eye without cutting the optic nerve resulted in a complete loss of APP and Bcl-2 immunostaining in Müller cells and an increase in immunoreactivity in distinct populations of retinal neurons. The overall pattern of APP immunostaining in Müller cells and neurons was essentially the same as that of Bcl-2 under identical experimental conditions. These results suggest that the expression of APP and Bcl-2 in retinal cells is dependent on the nature and severity of injury, and that rapid and common mechanisms are involved in regulating the expression of these molecules.

A quantitative comparison of plaque types in Alzheimer's disease and senile dementia of the Lewy body type

In a previous study we reported no difference in the overall beta-amyloid protein (beta AP) load between Alzheimer's disease (AD) and senile dementia of the Lewy body type (SDLT). However, it is possible that differences in the morphology of beta AP plaque types exist, analogous to the differences in cytoskeletal pathology found in these two disorders. We have carried out a quantitative image analysis of plaque subtypes in the temporal lobe of AD (n = 8), SDLT (n = 9) and control (n = 11) cases. Measurements of beta AP load and plaque density were consistently higher in AD and SDLT than in controls. When AD and SDLT cases were compared no differences were seen in either the density or relative proportions of classic and diffuse plaques. Based on these results we suggest that the variation in the clinical course of these diseases reflects differences in the cytoskeletal pathology, whereas the final stages of profound dementia common to both disorders is associated with the deposition of beta AP.

Altered beta-APP metabolism after head injury and its relationship to the aetiology of Alzheimer's disease

There is increasing evidence of a link between head injury and the subsequent onset of Alzheimer's disease. Deposits of amyloid beta-protein (A beta) are found not only in cases of dementia pugilistica but in some 30% of patients dying after a single episode of severe head injury. Detailed clinicopathological studies have shown that A beta deposition is most likely, but not exclusively, to occur, the older the patient at the time of injury, and if the injury is the result of a fall. Distribution studies have shown that the A beta is widely deposited in the neocortex and there is no apparent association with any of the multiple primary or secondary pathologies of traumatic brain injury. There is an increased expression of beta-APP particularly in the pre-alpha cells of the entorhinal cortex and in areas of axonal damage. Recent molecular genetic studies have shown that there is a strong association between deposits of A beta and the apolipoprotein E genotype of the individual.

Diagnosis and incidence of prion (Creutzfeldt-Jakob) disease: a retrospective archival survey with implications for future research

Reliable identification of Creutzfeldt-Jakob disease (CJD) in the UX has become essential following the suggestion that prion disease in cattle (BSE) might transmit, accidentally, to humans who eat contaminated beef. Recent data suggest that some cases of CJD may be clinically unrecognized; in order to examine this proposal we reviewed all cases of dementia (n = 1000+) collected in the Runwell Hospital Brain Archive between 1964 and 1990. We identified 19 cases of spongiform encephalopathy of which only 11 were diagnosed before death. These 11 individuals had a characteristic clinical history of CJD (relentless mental deterioration, prominent motor signs and death within a year). Their brains showed little or no external abnormality. In contrast, only two of the eight clinically unrecognized cases had characteristic symptoms. The remaining six presented atypically; their illness lasted 3 years or more, motor signs were much less evident, and simple dementia was the most prominent feature. The brains showed moderate or severe cerebral atrophy. Our data indicate that only about 60% of prion disease cases with pathologically typical spongiform encephalopathy were identified clinically during life. This suggests that human prion disease may be more common than previously supposed and that a further review of the epidemiology of the disease is required.

Quantification of beta APP immunoreactive pre-alpha cells in the entorhinal cortex using image analysis

The neuropathological diagnosis of Alzheimer's disease requires an assessment of the quantity of pathology present. Advances in molecular biology have highlighted the role of beta-amyloid precursor protein (beta APP) in the pathogenesis of the disease. This protein is found in neurons and other cells and many neuropathological studies would benefit from a method which generates reliable data on the numbers of cells containing significant amounts of the protein. Classically, generation of such data would have involved laborious manual counting. This particular approach carries low levels of inter- and intra-rater reliability and is much dependent on the skill and experience of the operator. We have used immunocytochemistry to specifically define a single cell population, pre-alpha cells, containing beta APP, and have developed a computerized cell counting programme that can reliably quantify these cells in human post-mortem brain samples. We have obtained a high level of accuracy (> 95%) and efficiency in identifying and quantifying target cells and have demonstrated that our protocol can be used effectively by both novice and expert. This method could be easily configured to provide quantitative data for a wide range of immunocytochemically defined cell populations.

Distribution of beta-amyloid protein in the brain following severe head injury

Deposits of beta-amyloid protein (beta AP) can be found in the brains of 30% of fatally head-injured patients; they have been found in children and after survival times of only 4 h. The principal aims of this study were to map the distribution of beta AP in 14 patients aged 65 years or less in whom it was known that the protein had been deposited, and to correlate its distribution with the pathologies of traumatic brain injury. The results show that beta AP is widely distributed, and that there is no correlation between its presence and cerebral contusions, intracranial haematoma, axonal injury, ischaemic brain damage, brain swelling or the pathology of raised intracranial pressure. These findings suggest that the deposition of beta AP is a consequence of the acute phase response of nerve cells to stress in susceptible individuals. Further studies will be required to establish the possible relationship between the deposition of beta AP following head injury and the molecular neuropathology of Alzheimer's disease.

Axonal injury: a universal consequence of fatal closed head injury?

beta-Amyloid precursor protein immunostaining has recently been shown to be a reliable method for detecting the damage to axons associated with fatal head injury. In an attempt to compare the efficacy of this technique with conventional histological detection of axonal damage, we have reanalysed sections from a large well-characterised series of head-injured and control patients. The results indicate that the frequency of axonal injury has been vastly underestimated using conventional silver techniques, and that axonal injury may in fact be an almost universal consequence of fatal head injury.

Increased numbers of beta APP-immunoreactive neurones in the entorhinal cortex after head injury

In a previous publication we hypothesized that Alzheimer's disease (AD) can be induced by the age-related increase in expression of beta-amyloid precursor protein (beta APP) in the medial temporal lobe. Head injury has also been identified as a risk factor for AD and as such, similarities should exist between the pathology found after head injury and the earliest stages of pathology in AD. In this study, we have quantified the number of beta APP-immunoreactive neurones in the medial temporal cortex (pre-alpha cells, layer II) of 13 head injured and 17 control patients. Significantly more beta APP immunoreactive neurones were observed in head injury cases (mean 18.4 per cluster) compared with controls (mean 13.4 per cluster, p < 0.05). These data provide a mechanism to explain how an environmental event such as head injury can generate the same molecular pathology (increased neuronal beta APP) as is found in the earliest stages of AD.

Microglial interleukin-1 alpha expression in human head injury: correlations with neuronal and neuritic beta-amyloid precursor protein expression

Activated microglia containing IL-1 alpha-immunoreactive (IL-1 alpha +) product were increased 3-fold in number in the acute phase following head injury, a risk factor for later development of Alzheimer's disease, and this increase was correlated with a 7-fold increase in the number of neurons with elevated beta-amyloid precursor protein (beta-APP) levels (R = 0.78; P < 0.05). Furthermore, clusters of beta-APP+ dystrophic neurites present in these patients were invariably associated with activated IL-1 alpha + microglia. These findings suggest that early overexpression of IL-1 alpha and beta-APP is a priming event for later neuropathological changes evident at end stages of Alzheimer's disease.

The distribution of nitric oxide synthase immunoreactivity in the human brain

Nitric oxide is a free radical which is produced in the brain and is thought to be the first of a new class of neural messenger molecules. It is postulated to act by inducing an increase in cyclic guanosine monophosphate levels in target cells. The neuronal isoform of nitric oxide synthase, the enzyme responsible for the calcium-dependent synthesis of nitric oxide from L-arginine, has been purified from brain homogenate. Using a specific polyclonal antibody, we have localized brain nitric oxide synthase to the cytosol of discrete neuronal subpopulations and glial elements. These include non-pyramidal cells in the cerebral cortex, pyramidal and non-pyramidal cells of the hippocampus, aspiny neurons of the corpus striatum, basket, Purkinje and granule cells in the cerebellum and neurons of various brain stem nuclei. The localization of nitric oxide-producing neurons in morphologically different and neurochemically diverse cell types suggests a widespread neuromodulatory role for nitric oxide in the central nervous system of man.

Beta amyloid protein deposition in the brain after severe head injury: implications for the pathogenesis of Alzheimer's disease

In a recent preliminary study it was reported that a severe head injury resulted in the deposition of beta amyloid protein (beta AP) in the cortical ribbon of 30% of patients who survived for less than two weeks. Multiple cortical areas have now been examined from 152 patients (age range 8 weeks-81 years) after a severe head injury with a survival time of between four hours and 2.5 years. This series was compared with a group of 44 neurologically normal controls (age range 51 to 80 years). Immunostaining with an antibody to beta AP confirmed the original findings that 30% of cases of head injury have beta AP deposits in one or more cortical areas. Increasing age seemed to accentuate the extent of beta AP deposition and potential correlations with other pathological changes associated with head injury were also investigated. In addition, beta amyloid precursor protein (beta APP) immunoreactivity was increased in the perikarya of neurons in the vicinity of beta AP deposits. The data from this study support proposals that increased expression of beta APP is part of an acute phase response to neuronal injury in the human brain, that extensive overexpression of beta APP can lead to deposition of beta AP and the initiation of an Alzheimer disease-type process within days, and that head injury may be an important aetiological factor in Alzheimer's disease.

Markers of axonal injury in post mortem human brain

beta-Amyloid precursor protein (beta APP) can be detected immunocytochemically at sites of axonal injury in the brain, and has recently been found to be a useful marker for injured axons in patients who survived for only 3 h after head trauma. It is transported by fast axonal transport and is thought to accumulate in detectable levels where the cytoskeleton breaks down. If this theory is correct, other substances should accumulate here in the same way, so we have used antibodies to other neuronal proteins to compare their efficacy as markers of axonal injury. SNAP-25, chromogranin A and cathepsin D also marked injured axons at all survival times studied (2.5 h-2 weeks), although they were not as sensitive or specific as beta APP. Immunolabelling for the 68-kDa neurofilament subunit (NF68) was present in most uninjured axons, and allowed axonal swellings to be seen in some cases. Synaptophysin, GAP-43, ubiquitin or tau did not label any normal or injured axons in this study. We, therefore, suggest that beta APP should be the immunocytochemical marker of choice for the detection of injured axons. This study also showed that microwave antigen retrieval significantly enhances the immunoreactivity of SNAP-25, chromogranin A, synaptophysin, GAP-43, ubiquitin and tau, in addition to that of beta APP, in formalin-fixed, paraffin-embedded tissue, and reveals NF68 antigenicity where it was not previously detectable.

Beta-amyloid precursor protein (beta APP) as a marker for axonal injury after head injury

It has been demonstrated recently that beta-amyloid protein (beta AP), generally associated with the plaques of Alzheimer's disease, can also be found in the brains of survivors of head injury. In this study the distribution of the beta AP precursor protein (beta APP) was examined immunohistochemically to determine if it is colocalized with beta AP in such cases. beta APP immunoreactivity was observed in neuronal perikarya in the neocortex and in dystrophic neurites surrounding beta AP immunoreactive plaques i.e. in a distribution similar to that seen in Alzheimer's disease. In addition, beta APP immunoreactivity was noted within white matter tracts where it marked damaged axons. However, no colocalisation of beta APP with beta AP was observed in any white matter region. These results indicate that processing of beta APP to produce beta AP occurs in the synaptic terminal field of axons and illustrate the utility of beta APP immunoreactivity as a general marker for axonal injury.

Differential pattern of beta-amyloid protein deposition within cortical sulci and gyri in Alzheimer's disease

We have quantified the pattern of beta-amyloid protein (beta AP) deposition in the sulci and gyri of the frontal cortex in Alzheimer's disease. The distribution pattern in the frontal cortex gyri is unequivocally different from the pattern found in the frontal sulci. These findings, in conjunction with our previous studies, reflect a differential vulnerability between the sulci and the gyri with respect to Alzheimer's disease pathology, sulci being affected to a greater extent. It is probable that the different patterns of deposition relate to the underlying cytoarchitecture of the cortex.