Autistic Traits in Neurotypical Adults: Correlates of Graph Theoretical Functional Network Topology and White Matter Anisotropy Patterns

Attempts to explicate the neural abnormalities behind autism spectrum disorders frequently revealed impaired brain connectivity, yet our knowledge is limited about the alterations linked with autistic traits in the non-clinical population. In our study, we aimed at exploring the neural correlates of dimensional autistic traits using a dual approach of diffusion tensor imaging (DTI) and graph theoretical analysis of resting state functional MRI data. Subjects were sampled from a public neuroimaging dataset of healthy volunteers. Inclusion criteria were adult age (age: 18–65), availability of DTI and resting state functional acquisitions and psychological evaluation including the Social Responsiveness Scale (SRS) and Autistic Spectrum Screening Questionnaire (ASSQ). The final subject cohort consisted of 127 neurotypicals. Global brain network structure was described by graph theoretical parameters: global and average local efficiency. Regional topology was characterized by degree and efficiency. We provided measurements for diffusion anisotropy. The association between autistic traits and the neuroimaging findings was studied using a general linear model analysis, controlling for the effects of age, gender and IQ profile. Significant negative correlation was found between the degree and efficiency of the right posterior cingulate cortex and autistic traits, measured by the combination of ASSQ and SRS scores. Autistic phenotype was associated with the decrease of whole-brain local efficiency. Reduction of diffusion anisotropy was found bilaterally in the temporal fusiform and parahippocampal gyri. Numerous models describe the autistic brain connectome to be dominated by reduced long-range connections and excessive short-range fibers. Our finding of decreased efficiency supports this hypothesis although the only prominent effect was seen in the posterior limbic lobe, which is known to act as a connector hub. The neural correlates of the autistic trait in neurotypicals showed only limited similarities to the reported findings in clinical populations with low functioning autism.     

Ferroxidases and xanthine oxidase in plasma of healthy newborn infants

In the neonatal period, there is a high iron load, while both the level and molar oxidase activity of ceruloplasmin are low. On the other hand, the neonatal xanthine oxidase (XO) activity is higher than later in life and XO has a significant iron-oxidizing capacity. We therefore studied the physiological contribution of XO to the ferroxidase activity of the plasma in 20 full-term newborn infants. Ferroxidase activity was measured spectrophotometrically, with Fe⁺⁺ as substrate. The uric acid formed by XO was assayed by means of HPLC, with electrochemical detection.

The total ferroxidase activity in the plasma was about one-fourth of the adult level and rapidly increased doubling within 3 days after birth. About 90% of the plasma ferroxidase activity was due to ceruloplasmin, the remainder being accounted for by ferroxidase II. The XO activity underwent a 30% (statistically non-significant) elevation at 24 h, though ferroxidase activity attributable to XO was not detected at any time.

Accordingly, XO does not seem to add substantially to the total iron-oxidizing capacity of the plasma in the neonatal period. The high molar ferroxidase activity is probably of importance at the endothelial cell surface.     

Single-molecule atomic force microscopy force spectroscopy study of Aβ-40 interactions

Misfolding and aggregation of amyloid β-40 (Aβ-40) peptide play key roles in the development of Alzheimer's disease (AD). However, very little is known about the molecular mechanisms underlying these molecular processes. We developed a novel experimental approach that can directly probe aggregation-prone states of proteins and their interactions. In this approach, the proteins are anchored to the surface of the atomic force microscopy substrate (mica) and the probe, and the interaction between anchored molecules is measured in the approach-retraction cycles. We used dynamic force spectroscopy (DFS) to measure the stability of transiently formed dimers. One of the major findings from DFS analysis of α-synuclein (α-Syn) is that dimeric complexes formed by misfolded α-Syn protein are very stable and dissociate over a range of seconds. This differs markedly from the dynamics of monomers, which occurs on a microsecond to nanosecond time scale. Here we applied the same approach to quantitatively characterize interactions of Aβ-40 peptides over a broad range of pH values. These studies showed that misfolded dimers are characterized by lifetimes in the range of seconds. This value depends on pH and varies between 2.7 s for pH 2.7 and 0.1 s for pH 7, indicating that the aggregation properties of Aβ-40 are modulated by the environmental conditions. The analysis of the contour lengths revealed the existence of various pathways for dimer dissociation, suggesting that dimers with different conformations are formed. These structural variations result in different aggregation pathways, leading to different types of oligomers and higher-order aggregates, including fibrils.     

A study on the analytical sensitivity of 6 BSE tests used by the Canadian BSE reference laboratory

Bovine spongiform encephalopathy (BSE) surveillance programs have been employed in numerous countries to monitor BSE prevalence and to protect animal and human health. Since 1999, the European Commission (EC) authorized the evaluation and approval of 20 molecular based tests for the rapid detection of the pathological prion protein (PrP^sc) in BSE infection. The diagnostic sensitivity, convenience, and speed of these tests have made molecular diagnostics the preferred method for BSE surveillance. The aim of this study was to determine the analytical sensitivity of 4 commercially available BSE rapid-test kits, including the Prionics®-Check WESTERN, the Prionics® Check-PrioSTRIP™, the BioRad® TeSeE™ ELISA, and the IDEXX® HerdChek™ EIA. Performances of these tests were then compared to 2 confirmatory tests, including the BioRad® TeSeE™ Western Blot and the modified Scrapie Associated Fibrils (SAF)/OIE Immunoblot. One 50% w/v homogenate was made from experimentally generated C-type BSE brain tissues in ddH₂O. Homogenates were diluted through a background of BSE-negative brainstem homogenate. Masses of both positive and negative tissues in each dilution were calculated to maintain the appropriate tissue amounts for each test platform. Specific concentrated homogenization buffer was added accordingly to maintain the correct buffer condition for each test. ELISA-based tests were evaluated using their respective software/detection platforms. Blot-protocols were evaluated by manual measurements of blot signal density. Detection limitations were determined by fitted curves intersecting the manufacturers'' positive/negative criteria. The confirmatory SAF Immunoblot displayed the highest analytical sensitivity, followed by the IDEXX® HerdChek™ EIA, Bio-Rad® TeSeE™ Western Blot, the Bio-Rad® TeSeE™ ELISA, Prionics®-Check PrioSTRIP™, and Prionics®-Check WESTERN™, respectively. Although the tests performed at different levels of sensitivity, the most sensitive and least sensitive of the rapid tests were separated by 2 logs in analytical sensitivity, meeting European performance requirements. All rapid tests appear suitable for targeted BSE surveillance programs, as implemented in Canada.     

Minimal ensembles of side chain conformers for modeling protein–protein interactions

The goal of this article is to reduce the complexity of the side chain search within docking problems. We apply six methods of generating side chain conformers to unbound protein structures and determine their ability of obtaining the bound conformation in small ensembles of conformers. Methods are evaluated in terms of the positions of side chain end groups. Results for 68 protein complexes yield two important observations. First, the end‐group positions change less than 1 Å on association for over 60% of interface side chains. Thus, the unbound protein structure carries substantial information about the side chains in the bound state, and the inclusion of the unbound conformation into the ensemble of conformers is very beneficial. Second, considering each surface side chain separately in its protein environment, small ensembles of low‐energy states include the bound conformation for a large fraction of side chains. In particular, the ensemble consisting of the unbound conformation and the two highest probability predicted conformers includes the bound conformer with an accuracy of 1 Å for 78% of interface side chains. As more than 60% of the interface side chains have only one conformer and many others only a few, these ensembles of low‐energy states substantially reduce the complexity of side chain search in docking problems. This approach was already used for finding pockets in protein–protein interfaces that can bind small molecules to potentially disrupt protein–protein interactions. Side‐chain search with the reduced search space will also be incorporated into protein docking algorithms. Proteins 2012. © 2011 Wiley Periodicals, Inc.     

Computational mapping reveals dramatic effect of Hoogsteen breathing on duplex DNA reactivity with formaldehyde

Formaldehyde has long been recognized as a hazardous environmental agent highly reactive with DNA. Recently, it has been realized that due to the activity of histone demethylation enzymes within the cell nucleus, formaldehyde is produced endogenously, in direct vicinity of genomic DNA. Should it lead to extensive DNA damage? We address this question with the aid of a computational mapping method, analogous to X-ray and nuclear magnetic resonance techniques for observing weakly specific interactions of small organic compounds with a macromolecule in order to establish important functional sites. We concentrate on the leading reaction of formaldehyde with free bases: hydroxymethylation of cytosine amino groups. Our results show that in B-DNA, cytosine amino groups are totally inaccessible for the formaldehyde attack. Then, we explore the effect of recently discovered transient flipping of Watson–Crick (WC) pairs into Hoogsteen (HG) pairs (HG breathing). Our results show that the HG base pair formation dramatically affects the accessibility for formaldehyde of cytosine amino nitrogens within WC base pairs adjacent to HG base pairs. The extensive literature on DNA interaction with formaldehyde is analyzed in light of the new findings. The obtained data emphasize the significance of DNA HG breathing.     

Kainic acid-induced changes in the opioid/nociceptin system and the stress/toxicity pathways in the rat hippocampus

Excitotoxicity is a contributing factor to the pathogenesis of acute or chronic neurodegenerative disease states. Kainic acid (KA) is an excitotoxic substance and the administration of it to rodents induces seizure activity (status epilepticus, SE) and leads to neurodegeneration. In this study the effect of KA-induced excitotoxicity on the G-protein activations and the gene expression levels of the opioid/nociceptin system receptors as MOPr, KOPr, DOPr, ORL-1, and PNOC (N/OFQ) were investigated, and the regulator effect of naloxone (Nal) on the gene expressions of the opioid system receptors against KA-induced seizures in the rat hippocampus was tested. In addition, the expression levels of stress-toxicity genes were assessed in the hippocampus following KA-induced excitotoxicity in order to determine the potential genetic targets which can be helpful for neuroprotective interventions. Our results indicate that the KA-induced excitotoxicity increased the mRNA levels of MOPr, DOPr, KOPr, PNOC, and ORL-1. However, G-protein activations of MOPr, DOPr, and KOPr remained relatively unchanged while both the potency and efficacy of N/OFQ were significantly increased. The PCR array data showed that KA-induced excitotoxicity altered the expression levels of genes in the cellular stress or toxicity pathways. Our data suggests that the induction of the opioid/nociceptin system may be involved in the cellular stress response following a neurodegenerative insult and that the genes modulated by the KA-treatment in the stress-toxicity pathways may be evaluated as targets of potential neuroprotective interventions.     

Contractile parameters and occurrence of alternans in isolated rat myocardium at supra-physiological stimulation frequency

The cardiac refractory period prevents the heart from tetanic activation that is typically used in noncardiac striated muscle tissue. To what extent the refractory period prevents successive action potentials to activate the excitation-contraction coupling process and contractile machinery at supra-physiological rates, such as those present during ventricular fibrillation, is unknown. Using multicellular trabeculae isolated from rat hearts, we studied amplitude and kinetics of contraction at rates well above the normal in vivo rat heart range. We show that even at twice the maximal heart rate of the rat, little or no mechanical instability is observed; twitch contractions are at steady state, albeit with an elevated active diastolic force. Although the amplitude of contraction increased within in vivo heart rates (positive force-frequency response), at frequencies beyond the maximal heart rate (10-30 Hz) a steady decline of contractile amplitude is observed. Not until 30 Hz do the majority of the isolated muscle preparations show mechanical alternans, where strong and weak beats alternate. Interestingly, unlike striated limb skeletal muscle, fusing of twitch contractions did not cause a continuous increase in peak force: at frequencies of 10 Hz and above, systolic force declines with relatively little elevation in diastolic force. Contractile kinetics continued to accelerate, from 1 Hz up to 30 Hz, whereas the relative speed of contraction and relaxation remained closely coupled, reflected by a singular linear relationship between the maximal and minimal derivative of force (dF/dt). We conclude that cardiac muscle can produce mechanically stable steady-state contractions at supra-physiological pacing rates, while these contractions continue to decline in amplitude and increase in diastolic force past maximal heart rate.     

Higher muscle performance in adolescents compared with adults after a resistance training session with different rest intervals

The aim of the present study was to compare the effect of 3 different rest intervals between sets on the total training volume, number of repetitions, ratings of perceived exertion (RPE), and resistance to fatigue in adolescents and adults during a resistance training session in the isoinertial chest press exercise. Fifteen male adolescents (15.2 ± 1.2 years; 20.7 ± 2.0 kg·m(-2); Tanner -4; 61.5 ± 8.9, 10 repetition maximum [RM]) and 15 adults (22.2 ± 2.7 years; 23.3 ± 2.0 kg·m(-2); Tanner -5; 84.3 ± 13.5, 10RM) without previous experience with resistance training participated in the study. After 10RM test-retest on 3 different occasions, participants were randomly assigned to a resistance training protocol with 30-, 60-, and 120-second rest interval between sets. The protocol consisted of 3 sets with 10RM. In all studied variables, with exception to total training volume and RPE, adolescents presented superior results as compared with adults (p < 0.001). On the other hand, both adults and adolescents exhibited a higher resistance to fatigue, total training volume, and number of repetitions with a longer rest interval (120 > 60 > 30 seconds) (p < 0.01). Thus, these results indicate that adolescents present a higher recovery capacity between sets in a resistance training session than adults and a longer rest interval results in a higher number of repetitions completed, total training volume, and resistance to fatigue.