genetic association study; disease genetics; immunogenetics; liver
To study magnetic resonance imaging (MRI) correlates of novel (new-onset) psychiatric disorders (NPD) following traumatic brain injury (TBI) and orthopedic injury (OI).
Participants were age 7–17 years at the time of hospitalization for either TBI or OI. The study used a prospective, longitudinal, controlled design with standardized psychiatric assessments conducted at baseline (reflecting pre-injury function) and 3 months post-injury. MRI assessments including diffusion tensor imaging (DTI)–derived fractional anisotropy (FA), volumetric measures of gray and white matter regions, volumetric measures of lesions, and cortical thickness were conducted. Injury severity was assessed by standard clinical scales. The outcome measure was the presence of an NPD identified during the first 3 months following injury.
There were 88 participants (TBI=44; OI=44). NPD occurred more frequently in the TBI (21/44; 48%) versus the OI (6/44; 14%) group (Fisher’s Exact p=.001). NPD in TBI participants was not related to injury severity. Multivariate analysis of covariance of the relationship between FA in hypothesized regions of interest (bilateral frontal and temporal lobes, bilateral centrum semiovale, bilateral uncinate fasciculi) and NPD and group (TBI versus OI) was significant, and both variables (NPD: p<.05; group: p<.001) were jointly significantly related to FA. NPD was not significantly related to volumetric measures of white or gray matter structures, volumetric measures of lesions, or to cortical thickness measures.
Lowered white matter integrity may be more important in the pathophysiology of NPD than indices of gray matter or white matter atrophic changes, macroscopic lesions, and injury severity.
TBI; pediatric; psychiatric disorders; prospective; diffusion tensor imaging
Epidemiological and molecular findings suggest a relationship between Alzheimer’s disease (AD) and dyslipidemia, although the nature of this association is not well understood.
Using linear mixed effects models, we investigated the relationship between CSF levels of heart fatty acid binding protein (HFABP), a lipid binding protein involved with fatty acid metabolism and lipid transport, amyloid-β (Aβ), phospho-tau, and longitudinal MRI-based measures of brain atrophy among 295 non-demented and demented older individuals. Across all participants, we found a significant association of CSF HFABP with longitudinal atrophy of the entorhinal cortex and other AD-vulnerable neuroanatomic regions. However, we found that the relationship between CSF HABP and brain atrophy was significant only among those with low CSF Aβ1–42 and occurred irrespective of phospho-tau181p status.
Our findings indicate that Aβ-associated volume loss occurs in the presence of elevated HFABP irrespective of phospho-tau. This implicates a potentially important role for fatty acid binding proteins in Alzheimer’s disease neurodegeneration.
Alzheimer’s disease; Fatty acids; Lipids; Amyloid; Tau; Brain atrophy
The absence of pathophysiologically relevant diagnostic markers of bipolar disorder (BD) leads to its frequent misdiagnosis as unipolar depression (UD). We aimed to determine whether whole brain white matter connectivity differentiated BD from UD depression.
We employed a three-way analysis of covariance, covarying for age, to examine whole brain fractional anisotropy (FA), and corresponding longitudinal and radial diffusivity, in currently depressed adults: 15 with BD-type I (mean age 36.3 years, SD 12.0 years), 16 with recurrent UD (mean age 32.3 years, SD 10.0 years), and 24 healthy control adults (HC) (mean age 29.5 years, SD 9.43 years). Depressed groups did not differ in depression severity, age of illness onset, and illness duration.
There was a main effect of group in left superior and inferior longitudinal fasciculi (SLF and ILF) (all F ≥ 9.8; p ≤ .05, corrected). Whole brain post hoc analyses (all t ≥ 4.2; p ≤ .05, corrected) revealed decreased FA in left SLF in BD, versus UD adults in inferior temporal cortex and, versus HC, in primary sensory cortex (associated with increased radial and decreased longitudinal diffusivity, respectively); and decreased FA in left ILF in UD adults versus HC. A main effect of group in right uncinate fasciculus (in orbitofrontal cortex) just failed to meet significance in all participants but was present in women. Post hoc analyses revealed decreased right uncinate fasciculus FA in all and in women, BD versus HC.
White matter FA in left occipitotemporal and primary sensory regions supporting visuospatial and sensory processing differentiates BD from UD depression. Abnormally reduced FA in right fronto-temporal regions supporting mood regulation, might underlie predisposition to depression in BD. These measures might help differentiate pathophysiologic processes of BD versus UD depression.
Depression; diffusion tensor imaging; inferior longitudinal fasciculus; mood disorders; superior longitudinal fasciculus; uncinate fasciculus
This study is a retrospective chart review comparing rural-dwelling Caucasian and Hispanic outpatients' attribution of depressive symptoms. Based on the data gathered at intake, Hispanics were more likely to attribute depression to curse/spell and supernatural causes, while Caucasians were more likely to attribute symptoms to hereditary factors or job stress. Among both groups, higher CESD score was associated with problems with significant others or how they got along with others. Among Hispanics, depression severity was additionally associated with problems related to job or finances. Our findings point to a consequential role for clinical inquiry into attributed causes of depressive symptoms.
Resilience is proposed as a significant component of successful aging. Young adult carriers of the Serotonin Transporter Polymorphism (5HTTLPR) short(s) allele appear to have reduced resilience to stress. We examined if presence of the short allele was associated with poorer emotional resilience in older adults.
In a cross-sectional study of 99 healthy, community-dwelling, older adults we determined 5HTTLPR genotype status and administered the Connor-Davidson Resilience Scale and self-reported measures of successful aging, cognition and health.
There was no significant association between the 5HTTLPR s allele and resilience. S allele carriers had worse cognition and self-report ratings of successful aging.
These findings suggest that the impact of the 5HTTLPR s allele on stress-related outcomes may attenuate with older age. However, s allele status appears to be a biomarker of poorer self-rated successful aging, and cognitive performance in older adults.
5-HTT; Serotonin transporter polymorphism; Resilience; Stress; Successful Aging; Cognition
Several lines of evidence suggest that genome-wide association studies (GWAS) have the potential to explain more of the “missing heritability” of common complex phenotypes. However, reliable methods to identify a larger proportion of single nucleotide polymorphisms (SNPs) that impact disease risk are currently lacking. Here, we use a genetic pleiotropy-informed conditional false discovery rate (FDR) method on GWAS summary statistics data to identify new loci associated with schizophrenia (SCZ) and bipolar disorders (BD), two highly heritable disorders with significant missing heritability. Epidemiological and clinical evidence suggest similar disease characteristics and overlapping genes between SCZ and BD. Here, we computed conditional Q–Q curves of data from the Psychiatric Genome Consortium (SCZ; n = 9,379 cases and n = 7,736 controls; BD: n = 6,990 cases and n = 4,820 controls) to show enrichment of SNPs associated with SCZ as a function of association with BD and vice versa with a corresponding reduction in FDR. Applying the conditional FDR method, we identified 58 loci associated with SCZ and 35 loci associated with BD below the conditional FDR level of 0.05. Of these, 14 loci were associated with both SCZ and BD (conjunction FDR). Together, these findings show the feasibility of genetic pleiotropy-informed methods to improve gene discovery in SCZ and BD and indicate overlapping genetic mechanisms between these two disorders.
Genome-wide association studies (GWAS) have thus far identified only a small fraction of the heritability of common complex disorders, such as severe mental disorders. We used a conditional false discovery rate approach for analysis of GWAS data, exploiting “genetic pleiotropy” to increase discovery of common gene variants associated with schizophrenia and bipolar disorders. Leveraging the increased power from combining GWAS of two associated phenotypes, we found a striking overlap in polygenic signals, allowing for the discovery of several new common gene variants associated with bipolar disorder and schizophrenia that were not identified in the original analysis using traditional GWAS methods. Some of the gene variants have been identified in other studies with large targeted replication samples, validating the present findings. Our pleiotropy-informed method may be of significant importance for detecting effects that are below the traditional genome-wide significance level in GWAS, particularly in highly polygenic, complex phenotypes, such as schizophrenia and bipolar disorder, where most of the genetic signal is missing (i.e., “missing heritability”). The findings also offer insights into mechanistic relationships between bipolar disorder and schizophrenia pathogenesis.
Schizophrenia is associated with executive dysfunction. Yet, the degree to which executive functions are impaired differentially, or above and beyond underlying basic cognitive processes is less clear. Participants included 145 matched pairs of individuals with schizophrenia (SCs) and normal comparison subjects (NCs). Executive functions were assessed with 10 tasks of the Delis-Kaplan Executive Function System (D-KEFS), in terms of “achievement scores” reflecting overall performance on the task. Five of these tasks (all measuring executive control) were further examined in terms of their basic component (e.g., processing speed) scores and contrast scores (reflecting residual higher order skills adjusted for basic component skills). Group differences were examined via multivariate analysis of variance. SCs had worse performance than NCs on all achievement scores, but the greatest SC-NC difference was that for the Trails Switching task. SCs also had worse performance than NCs on all basic component skills. Of the executive control tasks, only Trails Switching continued to be impaired after accounting for impairments in underlying basic component skills. Much of the impairment in executive functions in schizophrenia may reflect the underlying component skills rather than higher-order functions. However, the results from one task suggest that there might be additional impairment in some aspects of executive control.
Cognition; Executive function; Schizoaffective disorder; Psychotic disorders; Trail Making Test; D-KEFS
The reasons for the reportedly high use of TV watching among older adults despite its potential negative health consequences are not known.
To investigate age differences in time use and affective experience in TV use in a nationally representative sample
Using an innovative assessment of affective experience in a nationally representative sample, several putative reasons were examined for age-related increases in TV use. A sample of 3982 Americans aged 15–98 years who were assessed using a variant of the Day Reconstruction Method, a survey method for measuring how people experience their lives, was analyzed. To understand age increases in TV use, analyses examined whether older people (1) enjoy TV more, (2) watch TV because it is less stressful than alternatives, or whether (3) TV use related to age differences in demographics, being alone, or life satisfaction. Data were collected in 2006 and analyzed in 2008–2009.
Adults aged >65 years spent threefold more waking time watching TV than young adults. Despite this trend, older people enjoyed TV less, in contrast to stable enjoyment with other leisure activities. Older adults did not seem to experience the same stress buffering effects of watching TV as did young and middle-aged adults. This negative age-associated trend in how TV was experienced was not accounted for by demographic factors or in time spent alone. Greater TV use, but not time spent in other leisure activities, was related to lower life satisfaction.
Older adults watch more TV but enjoy it less than younger people. Awareness of this discrepancy could be useful for those developing interventions to promote reduced sedentary behaviors in older adults.
A substantial barrier to commercialization of lignocellulosic ethanol production is a lack of process specific sensors and associated control strategies that are essential for economic viability. Current sensors and analytical techniques require lengthy offline analysis or are easily fouled in situ. Raman spectroscopy has the potential to continuously monitor fermentation reactants and products, maximizing efficiency and allowing for improved process control.
In this paper we show that glucose and ethanol in a lignocellulosic fermentation can be accurately monitored by a 785 nm Raman spectroscopy instrument and novel immersion probe, even in the presence of an elevated background thought to be caused by lignin-derived compounds. Chemometric techniques were used to reduce the background before generating calibration models for glucose and ethanol concentration. The models show very good correlation between the real-time Raman spectra and the offline HPLC validation.
Our results show that the changing ethanol and glucose concentrations during lignocellulosic fermentation processes can be monitored in real-time, allowing for optimization and control of large scale bioconversion processes.
Frontoparietal connections underlie key executive cognitive functions. Abnormalities in the frontoparietal network have been observed in chronic alcoholics and associated with alcohol-related cognitive deficits. It remains unclear whether neurobiological differences in frontoparietal circuitry exist in substance-naïve youth who are at-risk for alcohol use disorders. This study used functional connectivity magnetic resonance imaging and diffusion tensor imaging to examine frontoparietal connectivity and underlying white matter microstructure in 20 substance-naïve youth with a family history of alcohol dependence and 20 well-matched controls without familial substance use disorders. Youth with a family history of alcohol dependence showed significantly less functional connectivity between posterior parietal and dorsolateral prefrontal seed regions (ps < .05), as compared to family history negative controls; however, they did not show differences in white matter architecture within tracts subserving frontoparietal circuitry (ps > .34). Substance-naïve youth with a family history of alcohol dependence show less frontoparietal functional connectivity in the absence of white matter microstructural abnormalities as compared to youth with no familial risk. This may suggest a potential neurobiological marker for the development of substance use disorders.
Alcohol; Functional connectivity; Adolescence; Frontoparietal; At-risk
This study examined differences in the frequency of leisure activity participation and relationships to depressive symptom burden and cognition in Latino and Caucasian women. Cross-sectional data were obtained from a demographically matched subsample of Latino and Caucasian (n = 113 each) post-menopausal women (age ≥60), interviewed in 2004–06 for a multi-ethnic cohort study of successful aging in San Diego County. Frequencies of engagement in 16 leisure activities and associations between objective cognitive performance and depressive symptom burden by ethnicity were identified using bivariate and linear regression, adjusted for physical functioning and demographic covariates. Compared to Caucasian women, Latinas were significantly more likely to be caregivers and used computers less often. Engaging in organized social activity was associated with fewer depressive symptoms in both groups. Listening to the radio was positively correlated with lower depressive symptom burden for Latinas, and better cognitive functioning in Caucasians. Cognitive functioning was better in Latinas who read and did puzzles. Housework was negatively associated with Latinas’ emotional health and Caucasians’ cognitive functioning. Latino and Caucasian women participate in different patterns of leisure activities. Additionally, ethnicity significantly affects the relationship between leisure activities and both emotional and cognitive health.
A series of reports have recently appeared using tensor based morphometry statistically-defined regions of interest, Stat-ROIs, to quantify longitudinal atrophy in structural MRIs from the Alzheimer’s Disease Neuroimaging Initiative (ADNI). This commentary focuses on one of these reports, Hua et al. (2010), but the issues raised here are relevant to the others as well. Specifically, we point out a temporal pattern of atrophy in subjects with Alzheimer’s disease and mild cognitive impairment whereby the majority of atrophy in two years occurs within the first 6 months, resulting in overall elevated estimated rates of change. Using publicly-available ADNI data, this temporal pattern is also found in a group of identically-processed healthy controls, strongly suggesting that methodological bias is corrupting the measures. The resulting bias seriously impacts the validity of conclusions reached using these measures; for example, sample size estimates reported by Hua et al. (2010) may be underestimated by a factor of five to sixteen.
Nonlinear image registration; Regional change quantification; MRI biomarkers; Clinical trials; Bias; Alzheimer’s disease
This study utilized a new cellular phone ecological momentary assessment approach to investigate daily emotional dynamics in 47 youth with Major Depressive Disorder (MDD) and 32 no psychopathology controls (CON), ages 7 – 17. Information about emotional experience in the natural environment was obtained using answer-only cellular phones while MDD youth received an 8 week course of cognitive behavioral therapy and/or psychopharmacological treatment. Compared to CON youth, MDD youth reported more intense and labile global negative affect, greater sadness, anger, and nervousness, and a lower ratio of positive to negative affect. These differences increased with pubertal maturation. MDD youth spent more time alone and less time with their families than CON youth. Although differences in emotional experiences were found across social contexts, MDD youth were more negative than CON youth in all contexts examined. As the MDD participants progressed through treatment, diagnostic group differences in the intensity and lability of negative affect decreased, but there were no changes in the ratio of positive to negative affect or measures of social context. We discuss methodological innovations and advantages of this approach, including improved ecological validity and access to information about variability in emotions, change in emotions over time, the balance of positive and negative emotions, and the social context of emotional experience.
ecological momentary assessment; experience sampling; depression; emotionality; emotion regulation; social context; psychotherapy
Cortical surface area measures appear to be functionally relevant and distinct in etiology, development, and behavioral correlates compared with other size characteristics, such as cortical thickness. Little is known about genetic and environmental influences on individual differences in regional surface area in humans. Using a large sample of adult twins, we determined relative contributions of genes and environment on variations in regional cortical surface area as measured by magnetic resonance imaging before and after adjustment for genetic and environmental influences shared with total cortical surface area. We found high heritability for total surface area and, before adjustment, moderate heritability for regional surface areas. Compared with other lobes, heritability was higher for frontal lobe and lower for medial temporal lobe. After adjustment for total surface area, regionally specific genetic influences were substantially reduced, although still significant in most regions. Unlike other lobes, left frontal heritability remained high after adjustment. Thus, global and regionally specific genetic factors both influence cortical surface areas. These findings are broadly consistent with results from animal studies regarding the evolution and development of cortical patterning and may guide future research into specific environmental and genetic determinants of variation among humans in the surface area of particular regions.
cortex; cortical thickness; heritability
To elucidate the relationship between the two hallmark proteins of Alzheimer's disease (AD), amyloid-β (Aβ) and tau, and clinical decline over time among cognitively normal older individuals.
A longitudinal cohort of clinically and cognitively normal older individuals assessed with baseline lumbar puncture and longitudinal clinical assessments.
Research centers across the United States and Canada.
We examined one hundred seven participants with a Clinical Dementia Rating (CDR) of 0 at baseline examination.
Main Outcome Measures
Using linear mixed effects models, we investigated the relationship between CSF p-tau181p, CSF Aβ1-42 and clinical decline as assessed using longitudinal change in global CDR, CDR-Sum of Boxes (CDR-SB), and the Alzheimer's Disease Assessment Scale-cognitive subscale (ADAS-cog).
We found a significant relationship between decreased CSF Aβ1-42 and longitudinal change in global CDR, CDR-SB, and ADAS-cog in individuals with elevated CSF p-tau181p. In the absence of CSF p-tau181p, the effect of CSF Aβ1-42 on longitudinal clinical decline was not significantly different from zero.
In cognitively normal older individuals, Aβ-associated clinical decline over a mean of three years may occur only in the presence of ongoing, “downstream” neurodegeneration.
A mouse model of the devastating human disease "spinal muscular atrophy" (SMA) was used to investigate the severe muscle weakness and spasticity that precedes the death of these animals near the end of the 2nd postnatal week. Counts of motor units to the soleus muscle as well as of axons in the soleus muscle nerve showed no loss of motor neurons. Similarly, neither immunostaining of neuromuscular junctions nor the measurement of the tension generated by nerve stimulation gave evidence of any significant impairment in neuromuscular transmission, even when animals were maintained up to 5 days longer via a supplementary diet. However, the muscles were clearly weaker, generating less than half their normal tension. Weakness in 3 muscles examined in the study appears due to a severe but uniform reduction in muscle fiber size. The size reduction results from a failure of muscle fibers to grow during early postnatal development and, in soleus, to a reduction in number of fibers generated. Neuromuscular development is severely delayed in these mutant animals: expression of myosin heavy chain isoforms, the elimination of polyneuronal innervation, the maturation in the shape of the AChR plaque, the arrival of SCs at the junctions and their coverage of the nerve terminal, the development of junctional folds. Thus, if SMA in this particular mouse is a disease of motor neurons, it can act in a manner that does not result in their death or disconnection from their targets but nonetheless alters many aspects of neuromuscular development.
Spinal muscular atrophy; neuromuscular junction; Schwann cells; skeletal muscle development; mouse model
To date, no cross-national RCT has addressed the mechanisms underlying the relative success of pharmacological and psychotherapeutic interventions for depression. A multi-site clinical trial that includes psychotherapy as one of the treatments presents numerous challenges related to cross-site consistency and communication.
This report describes how those challenges were met in the study “Depression: The Search for Treatment Relevant Phenotypes”, being carried out at the University of Pittsburgh and the University of Pisa, Italy.
Implementing the study required the investigators to address methodological and practical challenges related to the different requirements of the two Institutional Review Boards (IRBs), psychotherapy training, independent evaluator training, patient recruitment, development of common tools for data entry, quality control and generation of weekly reports of patient progress as well as establishing a similar clinical and research framework in two countries with substantially different health care systems.
By having bilingual investigators and staff members who spent time at one another’s sites, making use of frequent conference-call staff meetings and being flexible within the bounds of the sometimes contradictory requirements of the IRBs, the investigators were able to meet the human subjects protection requirements of both institutions, surmount language barriers to consistent therapist and evaluator training and develop common tools for study management. As a result, recruitment goals were met at both sites and retention rates were high. One instance of inconsistent implementation of the protocol was corrected within the first year.
This study was conducted in two Western cultures by researchers with long-standing collaboration. Our findings may not be generalizable to other countries or research settings.
The implementation of a cross-national protocol and the adoption and maintenance of common procedures is possible when investigators are aware of the challenges this may present and are proactive in trying to address them.
Intense efforts are underway to evaluate neuroimaging measures as biomarkers for neurodegeneration in premanifest Huntington’s disease (preHD). We used a completely automated longitudinal analysis method to compare structural scans in preHD and controls.
Using a one-year longitudinal design, we analyzedT1-weighted structural scans in 35 preHD individuals and 22 age-matched controls. We used the SIENA software tool (Structural Image Evaluation, using Normalization, of Atrophy) to yield overall Percentage Brain Volume Change (PBVC) and voxel-level changes in atrophy. We calculated sample sizes for a hypothetical disease modifying (neuroprotection) study.
We found significantly greater yearly atrophy in preHD vs. controls (Mean PBVC controls = −0.149%; preHD = −0.388%; p=.031, Cohen’s d=.617). For a preHD subgroup closest to disease onset, yearly atrophy was over three times that of controls (Mean PBVC close-to-onset preHD = −0.510%; p=.019, Cohen’s d=.920). This atrophy was evident at the voxel level in periventricular regions – consistent with well-established preHD basal ganglia atrophy. We estimated that a neuroprotection study using SIENA would only need 74close-to-onset individuals in each arm (treatment vs. placebo) to detect a 50% slowing in yearly atrophy with80% power.
Automated whole-brain analysis of structural MRI can reliably detect preHD disease progression over one year. These results were attained with a readily available imaging analysis tool – SIENA – which is observer-independent, automated, and robust with respect to image quality, slice thickness, and different pulse sequences. This MRI biomarker approach could be used to evaluate neuroprotection in preHD.
MRI biomarker; Premanifest HD; Longitudinal atrophy
To explore factors associated with the provision of diabetes-monitoring practices among older Latinos with type 2 diabetes.
Data from 547 Latinos (≥55 years) were analyzed from the 2007 California Health Interview Survey. Multivariate logistic regression modeled the relationship between health status and sociodemographic factors and the receipt of semiannual HbA1c tests, annual foot exams, and annual retinal exams.
The majority of older Latino diabetics received foot exams (87%) and retinal exams (77%), but the provision of semiannual HbA1c tests (30%) was low. Higher English-language proficiency and health insurance coverage were associated with the provision of HbA1c tests and foot exams, but not retinal exams. Insulin therapy was positively associated with semiannual HbA1c testing, but negatively associated with foot exams.
There are considerable missed opportunities in the provision of diabetes monitoring for older Latinos, particularly those with limited English proficiency, less comprehensive insurance, and noninsulin therapy.
type 2 diabetes; health services; Mexican American
We developed models of Specialized Care for Bipolar Disorder (SCBD) and a psychosocial treatment [Enhanced Clinical Intervention (ECI)] that is delivered in combination with SCBD. We investigated whether SCBD and ECI + SCBD are able to improve outcomes and reduce health disparities for young and elderly individuals, African Americans, and rural residents with bipolar disorder.
Subjects were 463 individuals with bipolar disorder, type I, II, or not otherwise specified, or schizoaffective disorder, bipolar type, randomly assigned to SCBD or ECI + SCBD and followed longitudinally for a period of one to three years at four clinical sites.
Both treatment groups significantly improved over time, with no significant differences based on age, race, or place of residence, except for significantly greater improvement among elderly versus adult subjects. Improvement in quality of life was greater in the ECI + SCBD group. Of the 299 participants who were symptomatic at study entry, 213 achieved recovery within 24 months, during which 86 of the 213 subjects developed a new episode. No significant difference was found for race, place of residence, or age between the participants who experienced a recurrence and those who did not. However, the adolescent patients were less likely than the adult and elderly patients to experience a recurrence.
This study demonstrated the effectiveness of SCBD and the additional benefit of ECI independent of age, race, or place of residence. It also demonstrated that new mood episodes are frequent in individuals with bipolar disorder who achieve recovery and are likely to occur in spite of specialized, guideline-based treatments.
bipolar disorder; health disparities; outcomes; randomized trial
Vertebrate neuromuscular junctions are highly stable synapses, retaining the morphology they achieve in early postnatal development throughout most of life. However, these synapses undergo dramatic change during aging. The acetylcholine receptors (AChRs) change from smooth gutters into fragmented islands and the nerve terminals change similarly to be varicosities apposed to these islands. These changes have been attributed to a slow deterioration in mechanisms maintaining the synapse. We have utilized repeated, vital imaging to investigate how these changes occur in the sternomastoid muscle of aging mice. We have found, contrary to expectation, that individual junctions change infrequently, but change, when it occurs, is sudden and dramatic. The change mimics that reported previously for cases in which muscle fibers are deliberately damaged: most of the AChR present disappear rapidly and are replaced by a new set of receptors that become fragmented. The fiber segment underneath the synapse has centrally located nuclei, showing that this segment has undergone necrosis, quickly regenerated, and been reinnervated with an altered synapse. We show that necrotic events are common in aged muscle and have likely been missed previously as a cause of the alterations in aging because central nuclei are a transient phenomenon and the necrotic events at the junction infrequent. However, the changes are permanent and accumulate over time. Interventions to reduce the neuromuscular changes during aging should likely focus on making muscle fibers resistant to injury.
Spatial competition between glial cells causes them to partition neuromuscular junctions into discrete domains within a synapse.
Schwann cells (SCs), the glial cells of the peripheral nervous system, cover synaptic terminals, allowing them to monitor and modulate neurotransmission. Disruption of glial coverage leads to axon degeneration and synapse loss. The cellular mechanisms that establish and maintain this coverage remain largely unknown. To address this, we labeled single SCs and performed time-lapse imaging experiments. Adult terminal SCs are arranged in static tile patterns, whereas young SCs dynamically intermingle. The mechanism of developmental glial segregation appears to be spatial competition, in which glial–glial and axonal–glial contacts constrain the territory of single SCs, as shown by four types of experiments: (1) laser ablation of single SCs, which led to immediate territory expansion of neighboring SCs; (2) axon removal by transection, resulting in adult SCs intermingling dynamically; (3) axotomy in mutant mice with blocked axon fragmentation in which intermingling was delayed; and (4) activity blockade, which had no immediate effects. In summary, we conclude that glial cells partition synapses by competing for perisynaptic space.
Muscle fibers degenerate and regenerate in response to contractile damage, during aging, and in various muscle diseases that weaken the fibers. It is known that degeneration and regeneration of the segment of the postsynaptic fiber produces dramatic alterations in the neuromuscular junction (NMJ) that forms on the regenerated fiber, but the mechanisms here are incompletely understood. We have used a laser microbeam to damage the postsynaptic fibers at individual NMJs in the sternomastoid muscle of living young adult mice and then followed the synapses vitally over time using fluorescent proteins expressed in motor neurons and glial cells and staining of postsynaptic acetylcholine receptors (AChR). We find, in contrast to previous reports, that the mouse nerve terminal retains contact with the synaptic basal lamina marked by cholinesterase staining even in the absence of the target, showing that this terminal does not require a continuous supply of target-derived molecules for its maintenance. Thus, remodeling of the nerve terminal during the period of target absence does not explain the subsequent changes in the new NMJ. Rather, we see that the synapse becomes altered as the new fiber segment regenerates. Mechanisms for remodeling the synapse include failure of the regenerating muscle fiber to contact the old basal lamina and nerve terminal, growth of the nerve terminal and its glia towards the regenerating fiber, and remodeling of the initial contact as the nerve terminal becomes varicose.
The presence of an ApoE ε4 allele (ε4+) increases the risk of developing Alzheimer’s disease (AD). Previous studies support an adverse relationship between ε4+ status and brain structure and function in mild cognitive impairment and AD; in contrast, the presence of an ε2 allele may be protective. Whether these findings reflect disease-related effects or pre-existing endophenotypes, however, remains unclear. The present study examined the influence of ApoE allele status on brain structure solely during middle-age in a large, national sample. Participants were 482 men, ages 51–59, from the Vietnam Era Twin Study of Aging (VETSA). T1-weighted images were used in volumetric segmentation and cortical surface reconstruction methods to measure regional volume and thickness. Primary linear mixed effects models predicted structural measures with ApoE status (ε3/3, ε2/3, ε3/4) and control variables for effects of site, non-independence of twin data, age, and average cranial vault or cortical thickness. Relative to the ε3/3 group, the ε3/4 group demonstrated significantly thinner cortex in superior frontal and left rostral and right caudal midfrontal regions; there were no significant effects of ε4 status on any temporal lobe measures. The ε2/3 group demonstrated significantly thicker right parahippocampal cortex relative to the ε3/3 group. The ApoE ε4 allele may influence cortical thickness in frontal areas, which are later developing regions thought to be more susceptible to the natural aging process. Previous conflicting findings for mesial temporal regions may be driven by the inclusion of older individuals, who may evidence preclinical manifestations of disease, and by unexamined moderators of ε4-related effects. The presence of the ε2 allele was related to thicker cortex, supporting a protective role. Ongoing follow-up of the VETSA sample may shed light on the potential for age- and disease-related mediation of the influence of ApoE allele status.
Magnetic Resonance Imaging; Cerebral Cortex; Brain; Frontal Lobe; Apolipoproteins E; Apolipoprotein E2; Apolipoprotein E3; Apolipoprotein E4; Genetic Association Studies; Aging