Neuroinvasion in sheep transmissible spongiform encephalopathies: the role of the haematogenous route

Background: It is generally believed that after oral exposure to transmissible spongiform encephalopathy (TSE) agents, neuroinvasion occurs via the enteric nervous system (ENS) and the autonomic nervous system. As a result, the dorsal motor nucleus of the vagus nerve is the initial point of disease-associated prion protein (PrP^d) accumulation in the brain. Hypothesis and aim: If direct ENS invasion following oral infection results in an early and specific brain targeting for PrP^d accumulation, such topographical distribution could be different when other routes of infection were used, highlighting distinct routes for neuroinvasion. Methods: An immunohistochemical study has been conducted on the brain of 67 preclinically infected sheep exposed to natural scrapie or to experimental TSE infection by various routes. Results: Initial PrP^d accumulation consistently occurred in the dorsal motor nucleus of the vagus nerve followed by the hypothalamus, regardless of the breed of sheep, PrP genotype, TSE source and, notably, route of infection; these factors did not appear to affect the topographical progression of PrP^d deposition in the brain either. Moreover, the early and consistent appearance of PrP^d aggregates in the circumventricular organs, where the blood–brain barrier is absent, suggests that these organs can provide a portal for entry of prions when infectivity is present in blood. Conclusions: The haematogenous route, therefore, can represent a parallel or alternative pathway of neuroinvasion to ascending infection via the ENS/autonomic nervous system.     

CSF analysis in patients with sporadic CJD and other transmissible spongiform encephalopathies

Patients with suspected Creutzfeldt–Jakob disease (CJD) often have routine cerebrospinal fluid (CSF) analysis performed to exclude treatable inflammatory conditions; however, little information is available about the range of results obtained for CSF tests in patients with sporadic CJD and other transmissible spongiform encephalopathies (TSE). Data from 450 patients with sporadic CJD and 47 patients with other TSEs were collected as part of an EC-supported multinational study. Raised white cell counts of >5 cells/ μ l were found in three of 298 patients with sporadic CJD, with two cell counts of 7 cells/ μ l and one of 20 cells/ μ l. Total protein concentrations of >0.9 g/l were found in five of 438 patients with sporadic CJD, although none had a concentration of >1 g/l. CSF oligoclonal IgG was detected in eight of 182 sporadic CJD patients. Of the patients with other TSEs, six had elevated cell counts ranging from 6 to 14 cells/ μ l but none had total protein concentrations of >0.9 g/l and one patient had detectable oligoclonal IgG. None of the patients with sporadic CJD or other TSEs had abnormalities in all three tests.     

Synapse loss associated with abnormal PrP precedes neuronal degeneration in the scrapie-infected murine hippocampus

Numbers of neurones, synapses and axon terminals were quantified in a murine scrapie model with severe hippocampal pyramidal cell loss, in which definite clinical scrapie is evident from 226 days post-infection (dpi) and death occurs around 250 dpi. Disease-specific PrP accumulations were first seen at 70 dpi (28% of the incubation period (IP)) in thalamus and as sparse foci within the stratum pyramidale of CA1. By 98 dpi (39% IP), PrP was seen in the stratum radiatum and was found at later stages throughout all levels of the hippocampus. At the ultrastructural level in the stratum radiatum of CA1, a decrease in the numbers of simple synapses from 84 dpi (34% IP) and in perforated synapses from 98 dpi (42% IP) was found using an unbiased stereological method, the disector analysis. Degeneration of axon terminals was found from 98 dpi (39% IP) onwards. Neuronal loss was detected in CA1 from 180 dpi (72% IP). The results suggest that the fundamental lesion in the hippocampus of ME7-infected mice is associated with PrP release from CA1 pyramidal neurones, which perturbs synaptic function and leads to degeneration of preterminal axons, and that subsequent pathological changes including neurone loss are sequelae to this initial insult.     

How do neurons degenerate in transmissible spongiform encephalopathies?

Neuroaxonal dystrophy is a feature of neuronal degeneration encountered in all subacute spongiform virus encephalopathies including scrapie and Creutzfeldt-Jakob disease (CJD). By immunohistochemical techniques, the accumulation of 200 kDa neurofilament protein was demonstrated in affected neurites in human CJD. These neurites exhibited the ultrastructural features of dystrophic neurites encountered in other neurodegenerative disorders, particularly Alzheimer's disease. These findings support the hypothesis that impairment of slow axoplasmic transport is a common pathogenetic mechanism for CJD and many other neurodegenerative conditions.     

Review: Membrane‐associated misfolded protein propagation in natural transmissible spongiform encephalopathies (TSEs), synthetic prion diseases and Alzheimer's disease

Protein misfolding has long been recognized as a primary cause of systemic amyloidosis and, increasingly, template‐mediated misfolding of native host proteins is now also considered to be central pathogenetic events in some neurodegenerative diseases. Alzheimer's disease, naturally occurring transmissible spongiform encephalopathies (TSEs) and experimental disorders caused by misfolded prion protein (PrP) generated in vitro all share an imbalance of protein synthesis, aggregation and clearance that leads to protein aggregation, prompting some to suggest that Alzheimer's disease is caused by a prion‐like mechanism. In TSEs, the host‐coded, glycosyl‐phosphoinositol (GPI) membrane‐anchored prion protein (PrP^c) is misfolded into disease‐associated, putatively infectious aggregates known as prions. In Alzheimer's disease the membrane‐spanning Alzheimer's precursor protein (APP) is progressively cleaved within the plasmalemma to form Aβ peptide fragments that can form pathogenic extracellular aggregates while microtubule‐associated tau proteins may also aggregate within neurones. Oligomeric Aβ peptides and full‐length misfolded PrP show a common potential to convert native protein and aggregate on plasma membranes before subsequent release to form amyloid fibrils in the extracellular space. However, the nature, membrane topography and processing of the precursor and propagated proteins in prion and Alzheimer's disease all differ, and each group of diseases has distinctive spectra of additional pathological changes and clinical signs suggesting that fundamentally different disease mechanisms are involved.     

Brain lithium, N-acetyl aspartate and myo-inositol levels in older adults with bipolar disorder treated with lithium: a lithium-7 and proton magnetic resonance spectroscopy study

Objectives:  We investigated the relationship between brain lithium levels and the metabolites N -acetyl aspartate (NAA) and myo -inositol ( myo -Ino) in the anterior cingulate cortex of a group of older adults with bipolar disorder (BD).
Methods:  This cross-sectional assessment included nine subjects (six males and three females) with bipolar I disorder and currently treated with lithium, who were examined at McLean Hospital's Geriatric Psychiatry Research Program and Brain Imaging Center. The subjects' ages ranged from 56 to 85 years (66.0 ± 9.7 years) and all subjects had measurements of serum and brain lithium levels. Brain lithium levels were assessed using lithium magnetic resonance spectroscopy. All subjects also had proton magnetic resonance spectroscopy to obtain measurements of NAA and myo -Ino.
Results:  Brain lithium levels were associated with higher NAA levels [df = (1, 8), Β = 12.53, t  =   4.09, p < 0.005] and higher myo -Ino levels [df = (1, 7), F  =   16.81, p < 0.006]. There were no significant effects of serum lithium levels on any of the metabolites.
Conclusion:  Our findings of a relationship between higher brain lithium levels and elevated NAA levels in older adult subjects with BD may support previous evidence of lithium's neuroprotective, neurotrophic, and mitochondrial function-enhancing effects. Elevated myo -Ino related to elevated brain lithium levels may reflect increased inositol monophosphatase (IMPase) activity, which would lead to an increase in myo -Ino levels. This is the first study to demonstrate alterations in NAA and myo -Ino in a sample of older adults with BD treated with lithium.     

Association between dorsolateral prefrontal N-acetyl aspartate and depression in chronic back pain: an in vivo proton magnetic resonance spectroscopy study

Most studies of pain, including chronic pain, agree that depression and pain are interrelated, although the neurobiology of this relationship remains unknown. Neuroimaging studies suggest a specific role of the prefrontal brain regions in the mechanisms of mood disorders and chronic pain. The present study examines the interrelationships between regional brain N-Acetyl aspartate (NAA) levels (as identified by in vivo proton magnetic resonance spectroscopy in the right and left dorsolateral prefrontal cortex [DLPFC], orbitofrontal cortex, cingulate and thalamus), depression (as measured by the Beck Depression Inventory), and pain (as measured by short form of the McGill Pain Questionnaire) in 10 chronic back pain (CBP) patients with depression, and compared to the relationship between regional brain NAA levels and depression in 10 normal subjects (sex and age-matched). Reduction of NAA levels was demonstrated in the right DLPFC of CBP patients with depression, as compared to the normal controls (p < 0.02, two-tailed t-test). The depression levels in CBP patients were highly correlated with NAA levels in the right DLPFC (r = -0.99, p < 0.0001), and were unrelated to the other studied regional NAA in both groups, including the right DLPFC in normal subjects (p < 10(-6); comparing the difference between r values in the right DLPFC between the two groups). The pain levels in CBP patients were also associated with the right DLPFC (r = -0.62, p < 0.05), although these relationships were much weaker as compared to depression-NAA correlations (p < 0.0001; comparing the difference between r values). The interrelationships between NAA across brain regions were examined using correlation analysis, which detected different connectivity patterns between CBP patients with depression and normal subjects. These findings provide evidence for a stronger association of prefrontal NAA to depression than to pain in CBP, which may reflect the common neurobiological substrate underlying these conditions in CBP patients. Spectroscopic brain mapping of NAA, the marker of neuronal density and function, to the depression and pain measures might be used for segregation of their circuitries in the chronic pain brain.     

Weight loss,behavioral change,and structural neuroplasticity in children with obesity through a multidisciplinary treatment program

This study evaluated the effect of a multidisciplinary treatment program for children with obesity (OB) on motor competence, executive functioning (EF), and brain structure. Nineteen children with OB (7–11 years), who attended a multidisciplinary treatment program consisting of diet restriction, cognitive behavioral therapy, and physical activity, were compared with an age‐matched control group of 24 children with a healthy weight (HW), who did not follow any treatment. For both groups, anthropometric measurements and tests of motor competence and EF were administered twice, with 5 months between pretest and posttest. Additionally, children’s brain structure was assessed by performing a magnetic resonance imaging (MRI) scan at the pretest and posttest, which included a T1 anatomical scan, diffusion MRI scan, and magnetization transfer imaging scan. Compared to HW controls, children with OB lost a considerable amount of their body mass (p ≤ .001) and significantly improved their balance skills (p ≤ .001), while no transfer effects of the program were observed for EF. Furthermore, the program resulted in a significant increase in total (p ≤ .001) and cerebellar (p ≤ .001) gray matter volume in children with OB, while no change was observed in the HW controls. Finally, only weak to moderate (nonsignificant) correlations could be observed between structural brain alterations, weight‐related changes, and behavioral improvements. Altogether, this is the first longitudinal study showing behavioral and structural brain alterations in response to a multidisciplinary weight loss program for children with OB. Our findings support the need for multidimensional intervention (and prevention) measures for children with OB to deal with this multifactorial health problem.     

Proton magnetic resonance spectroscopy detects a relative decrease of N-acetylaspartate in the hippocampus of patients with dementia with Lewy bodies.

BACKGROUND AND PURPOSE: To characterize the cerebral metabolic changes in dementia with Lewy bodies patients. METHODS: The metabolic ratios of NAA/Cr and Cho/Cr in bilateral hippocampus were determined by proton magnetic resonance spectroscopy in 8 patients and 8 age-matched healthy controls. RESULTS: Dementia with Lewy bodies patients showed significantly lower NAA/Cr ratios in bilateral hippocampus, while the Cho/Cr ratio did not differ from the control group. CONCLUSIONS: Our data show relatively decrease of N-acetylaspartate in the hippocampus of patients with early or intermediate stage DLB. Hence, damage of neurons seems to be an early alteration in DLB.     

Overweight and obesity are associated with neuronal injury in the human cerebellum and hippocampus in young adults: a combined MRI,serum marker and gene expression study

There is growing evidence that obesity represents a risk for enhanced gray matter (GM) density changes comparable to those demonstrated for mild cognitive impairment in the elderly. However, it is not clear what mechanisms underlie this apparent alteration in brain structure of overweight subjects and to what extent these changes can already occur in the adolescent human brain. In the present volumetric magnetic resonance imaging study, we investigated GM changes and serum levels of neuron-specific enolase (NSE), a marker for neuronal injury, in a set of overweight/obese subjects and controls. We report a negative correlation for overweight and obese subjects between serum NSE and GM density in hippocampal and cerebellar regions. To validate our neuroimaging findings, we complement these data with NSE gene expression information obtained from the Allen Brain atlas. GM density changes were localized in brain areas that mediate cognitive function—the hippocampus associated with memory performance, and the cognitive cerebellum (lateral posterior lobes) associated with executive, spatial and linguistic processing. The data of our present study highlight the importance of extending current research on cognitive function and brain plasticity in the elderly in the context of obesity to young adult subjects and include serum biomarkers to validate imaging findings generally.     

Reduced anterior cingulate glutamate in pediatric major depression: a magnetic resonance spectroscopy study.

BACKGROUND: Anterior cingulate cortex has been implicated in the pathogenesis of major depressive disorder (MDD). With single voxel proton magnetic resonance spectroscopy, we reported reductions in anterior cingulate glutamatergic concentrations (grouped value of glutamate and glutamine) in 14 pediatric MDD patients versus 14 case-matched healthy control subjects. These changes might reflect a change in glutamate, glutamine, or their combination. METHODS: Fitting to individually quantify anterior cingulate glutamate and glutamine was performed in these subjects with a new basis set created from data acquired on a 1.5 Tesla General Electric Signa (GE Healthcare, Waukesha, Wisconsin) magnetic resonance imaging scanner with LCModel (Version 6.1-0; Max-Planck-Institute, Gottingen, Germany). RESULTS: Reduced anterior cingulate glutamate was observed in MDD patients versus control subjects (8.79 +/- 1.68 vs. 11.46 +/- 1.55, respectively, p = .0002; 23% decrease). Anterior cingulate glutamine did not differ significantly between patients with MDD and control subjects. CONCLUSIONS: These findings provide confirmatory evidence of anterior cingulate glutamate alterations in pediatric MDD.     

Glutamate/glutamine and neuronal integrity in adults with ADHD: a proton MRS study

There is increasing evidence that abnormalities in glutamate signalling may contribute to the pathophysiology of attention-deficit hyperactivity disorder (ADHD). Proton magnetic resonance spectroscopy ([1H]MRS) can be used to measure glutamate, and also its metabolite glutamine, in vivo. However, few studies have investigated glutamate in the brain of adults with ADHD naive to stimulant medication. Therefore, we used [1H]MRS to measure the combined signal of glutamate and glutamine (Glu+Gln; abbreviated as Glx) along with other neurometabolites such as creatine (Cr), N-acetylaspartate (NAA) and choline. Data were acquired from three brain regions, including two implicated in ADHD—the basal ganglia (caudate/striatum) and the dorsolateral prefrontal cortex (DLPFC)—and one ‘control'' region—the medial parietal cortex. We compared 40 adults with ADHD, of whom 24 were naive for ADHD medication, whereas 16 were currently on stimulants, against 20 age, sex and IQ-matched healthy controls. We found that compared with controls, adult ADHD participants had a significantly lower concentration of Glx, Cr and NAA in the basal ganglia and Cr in the DLPFC, after correction for multiple comparisons. There were no differences between stimulant-treated and treatment-naive ADHD participants. In people with untreated ADHD, lower basal ganglia Glx was significantly associated with more severe symptoms of inattention. There were no significant differences in the parietal ‘control'' region. We suggest that subcortical glutamate and glutamine have a modulatory role in ADHD adults; and that differences in glutamate–glutamine levels are not explained by use of stimulant medication.     

Preliminary evidence for neuronal damage in cortical grey matter and normal appearing white matter in short duration relapsing-remitting multiple sclerosis: a quantitative MR spectroscopic imaging study

Neuronal damage and loss is likely to underlie irreversible disability in multiple sclerosis (MS). The time of onset, location and extent of neuronal damage in early disease are all uncertain. To explore this issue 16 patients with short duration, mild relapsing-remitting disease (mean disease duration 1.8 years, median EDSS 1) were studied using short echo time proton magnetic resonance spectroscopic imaging (¹H-MRSI) to quantify the concentration of the neuronal marker N-acetyl-aspartate (NAA). The data were compared with those from 12 age-matched controls. ¹H-MRSI was obtained from a 1.5-cm-thick slice just above the lateral ventricles. The Linear Combination (LC) Model combined with locally developed software allowed automated measurement of absolute metabolite concentrations from lesions, normal-appearing white matter (NAWM) and cortical grey matter (CGM). MS CGM exhibited significantly lower NAA (P=0.01) and myo-inositol (P=0.04) than control CGM. MS NAWM exhibited a lower concentration of NAA (P=0.01) and increased myo-inositol (P=0.03) than control white matter. More marked reductions in NAA and increases in myo-inositol were seen in lesions. The reduced NAA in MS CGM and NAWM suggest that mild but widespread neuronal dysfunction or loss occurs early in the course of relapsing-remitting MS. This preliminary finding should be confirmed in a larger cohort, and follow-up studies are also needed to determine the prognostic and pathophysiological significance of these early changes Received: 23 May 2000 / Received in revised form: 9 August 2000 / Accepted: 25 August 2000     

Increased medial thalamic choline found in pediatric patients with obsessive-compulsive disorder versus major depression or healthy control subjects: a magnetic resonance spectroscopy study.

BACKGROUND: Neurobiologic abnormalities in medial thalamus have been implicated in the pathogenesis of obsessive-compulsive disorder (OCD). We previously used multislice proton magnetic resonance spectroscopic imaging (1-H MRSI) to identify localized functional neurochemical marker alterations in choline (Cho) in medial but not lateral thalamus in treatment-na?ve pediatric patients with OCD compared with matched control subjects. Altered brain Cho levels have also been implicated in the pathogenesis of mood disorders. METHODS: We used 1-H MRSI to study absolute Cho concentrations in 18 psychotropic-na?ve pediatric patients with major depressive disorder (MDD) not suffering from OCD, 9-17 years of age, 18 case-matched healthy control subjects, and 27 nondepressed, psychotropic-na?ve pediatric patients with OCD, 7-16 years of age. RESULTS: Significantly increased left and right medial thalamic Cho concentrations were observed in OCD patients compared with both healthy control subjects and patients with MDD. Medial thalamic Cho concentrations did not differ significantly between patients with MDD and control subjects. CONCLUSIONS: These results suggest that localized functional neurochemical marker alterations in medial thalamic Cho differentiate patients with OCD from healthy control subjects and patients with MDD. Although these results must be considered preliminary, further study of the diagnostic specificity of Cho as a relevant biomarker in OCD is clearly warranted.     

Multi-chemical networking profile of the living human brain: potential relevance to molecular studies of cognition and behavior in normal and diseased brain

Summary. Anatomical, electrophysiological and functional neuroimaging studies show that the human brain is a complex network, where cortico-cortical and thalamo-cortical connections are organized in a specific pattern giving rise to brain function. In our recent studies we found that chemical connectivity between brain regions might be changed in different conditions (e.g. aging, chronic pain, cognitive interference). The elucidation of properties of the human brain multi-chemical networking profile is the subject of this study. In vivo proton magnetic resonance spectroscopy was used to determine relative concentrations of multiple chemicals (N-Acetyl aspartate, choline, glutamate, glutamine, GABA, inositol, glucose, and lactate in relation to creatine/phosphocreatine complex) in 6 brain regions: thalamus, and cingulate, insula, sensorimotor, orbital frontal, and dorsolateral prefrontal cortices. The properties of the brain multi-chemical networking profile within and across the studied regions were examined using correlation analysis. Strong positive correlations were seen between chemicals within brain regions. Negative correlations were primarily seen across brain regions. The cortical connectivity for both neurotransmitters (GABA and glutamate) was stronger than for the other chemicals, and was stronger than for the same neurotransmitters in the thalamus. Factor analysis indicated that the natural clustering of regional chemical concentrations is by brain region and not by chemicals. These findings support the idea for the existence of a specific pattern of multi-chemical networking profile in the brain where the major excitatory and inhibitory neurotransmitters in neocortex perform a regulatory function. Received July 18, 2001; accepted September 6, 2001     

Evidence for cortical dysfunction in autism: a proton magnetic resonance spectroscopic imaging study.

BACKGROUND: Although brain imaging studies have reported neurobiological abnormalities in autism, the nature and distribution of the underlying neurochemical irregularities are unknown. The purpose of this study was to examine cerebral gray and white matter cellular neurochemistry in autism with proton magnetic resonance spectroscopic imaging (MRSI). METHODS: Proton MRSI examinations were conducted in 26 males with autism (age 9.8 +/- 3.2 years) and 29 male comparison subjects (age 11.1 +/- 2.4 years). Estimates of cerebral gray and white matter concentrations of N-acetylaspartate (NAA), creatine + phosphocreatine, choline-containing compounds, myo-inositol, and glutamate + glutamine (Glx) were made by linear regression analysis of multi-slice MRSI data and compared between groups. Regional estimates of metabolite concentration were also made with multivariate linear regression, allowing for comparisons of frontal, temporal, and occipital gray matter, cerebral white matter, and the cerebellum. RESULTS: Patients with autism exhibited significantly lower levels of gray matter NAA and Glx than control subjects. Deficits were widespread, affecting most cerebral lobes and the cerebellum. No significant differences were detected in cerebral white matter or cerebellar metabolite levels. CONCLUSIONS: These results suggest widespread reductions in gray matter neuronal integrity and dysfunction of cortical and cerebellar glutamatergic neurons in patients with autism.     

Proton magnetic resonance spectroscopy of the inferior frontal gyrus and thalamus and its relationship to verbal learning task performance in patients with schizophrenia: a preliminary report

Previous research has found frontal lobe involvement in memory impairment in schizophrenia. In the present study, proton magnetic resonance spectroscopy was performed in 13 young patients with schizophrenia and 13 normal control subjects. Spectra were obtained from a voxel of 2 x 2 x 1.5 cm(3) in the bilateral inferior frontal gyrus and thalamus. Subjects were given a verbal learning task and stimulus category repetition (SCR) was calculated from the performance of the task. Significantly reduced N-acetylaspartate (NAA)/choline-containing compounds ratios were found in the left inferior frontal cortex of patients compared with controls. The total number of words recalled by patients was significantly lower than that recalled by controls. In all subjects, SCR scores were positively correlated with NAA/phosphocreatine ratios of the left inferior frontal cortex, which showed a trend towards a decrease in patients. These results support the notion of metabolic abnormalities in the left inferior frontal region related to verbal memory deficits in patients with schizophrenia.     

Brainstem function in rapid eye movement sleep behavior disorder: the evaluation of brainstem function by proton MR spectroscopy (1H-MRS)

Brainstem function was evaluated by proton magnetic resonance (MR) spectroscopy (1H-MRS) in a 69-year-old man with idiopathic rapid eye movement (REM) sleep behavior disorder. An analysis of spectral peak area ratios revealed an increase in the choline/creatine ratio. This change suggests that brainstem neurons have functional impairment at the cell membrane level. Further, our results suggest that 1H-MRS may provide for non-invasive, metabolic evaluation of brainstem neuronal function in REM sleep behavior disorder and find application in the differentiation of secondary REM sleep behavior disorders with neurodegenerative disorders from idiopathic disorders.     

Neuronal loss in lumbar dorsal root ganglia after proximal compared to distal sciatic nerve resection: a quantitative study in the rat

The effects of unilateral sciatic nerve resections at proximal (thigh) or distal (proximal calf) locations on L4-L6 dorsal root ganglion (DRG) neuronal numbers have been studied in adult rats. Proximal nerve resection gave rise to a mean DRG neuronal loss of 27%, whereas in distal lesions a mean cell loss of 7% was found. This difference in cell loss between proximal and distal sciatic nerve resections is highly significant (P less than 0.001).