Differential Modulation of Corticospinal Excitability by Different Current Densities of Anodal Transcranial Direct Current Stimulation

Background

Novel non-invasive brain stimulation techniques such as transcranial direct current stimulation (tDCS) have been developed in recent years. TDCS-induced corticospinal excitability changes depend on two important factors current intensity and stimulation duration. Despite clinical success with existing tDCS parameters, optimal protocols are still not entirely set.

Objective/hypothesis

The current study aimed to investigate the effects of four different anodal tDCS (a-tDCS) current densities on corticospinal excitability.

Methods

Four current intensities of 0.3, 0.7, 1.4 and 2 mA resulting in current densities (CDs) of 0.013, 0.029, 0.058 and 0.083 mA/cm² were applied on twelve right-handed (mean age 34.5±10.32 yrs) healthy individuals in different sessions at least 48 hours apart. a-tDCS was applied continuously for 10 minute, with constant active and reference electrode sizes of 24 and 35 cm² respectively. The corticospinal excitability of the extensor carpi radialis muscle (ECR) was measured before and immediately after the intervention and at 10, 20 and 30 minutes thereafter.

Results

Post hoc comparisons showed significant differences in corticospinal excitability changes for CDs of 0.013 mA/cm² and 0.029 mA/cm² (P = 0.003). There were no significant differences between excitability changes for the 0.013 mA/cm² and 0.058 mA/cm² (P = 0.080) or 0.013 mA/cm² and 0.083 mA/cm² (P = 0.484) conditions.

Conclusion

This study found that a-tDCS with a current density of 0.013 mA/cm² induces significantly larger corticospinal excitability changes than CDs of 0.029 mA/cm². The implication is that might help to avoid applying unwanted amount of current to the cortical areas.     

Destabilization of human IAPP amyloid fibrils by proline mutations outside of the putative amyloidogenic domain: is there a critical amyloidogenic domain in human IAPP?

Islet amyloid polypeptide (IAPP; amylin) is responsible for amyloid formation in type-2 diabetes. Not all organisms form islet amyloid, and amyloid formation correlates strongly with variations in primary sequence. Studies of human and rodent IAPP have pointed to the amino acid residues 20-29 region as the important amyloid-modulating sequence. The rat 20-29 sequence contains three proline residues and does not form amyloid, while the human sequence contains no proline and readily forms amyloid. This has led to the view that the 20-29 region constitutes a critical amyloidogenic domain that dictates the properties of the entire sequence. The different behavior of human and rat IAPP could be due to differences in the 20-29 region or due simply to the fact that multiple proline residues destabilize amyloid fibrils. We tested how critical the 20-29 region is by studying a variant identical with the human peptide in this segment but with three proline residues outside this region. We designed a variant of the amyloidogenic 8-37 region of human IAPP (hIAPP(8-37) 3xP) with proline substitutions at positions 17, 19 and 30. Compared to the wild-type, the 3xP variant was much easier to synthesize and had dramatically greater solubility. Fourier transform infra red spectroscopy, transmission electron microscopy, Congo red staining and thioflavin-T binding indicate that this variant has a reduced tendency to form beta-sheet structure and forms deposits with much less structural order than the wild-type. Far-UV CD studies show that the small amount of beta-sheet structure developed by hIAPP(8-37) 3xP after long periods of incubation dissociates readily into random-coil structure upon dilution into Tris buffer. The observation that proline substitutions outside the putative core domain effectively abolish amyloid formation indicates that models of IAPP aggregation must consider contributions from other regions.     

Guard cell photosynthesis is critical for stomatal turgor production,yet does not directly mediate CO2‐ and ABA‐induced stomatal closing

Stomata mediate gas exchange between the inter‐cellular spaces of leaves and the atmosphere. CO₂ levels in leaves (Ci) are determined by respiration, photosynthesis, stomatal conductance and atmospheric [CO₂]. [CO₂] in leaves mediates stomatal movements. The role of guard cell photosynthesis in stomatal conductance responses is a matter of debate, and genetic approaches are needed. We have generated transgenic Arabidopsis plants that are chlorophyll‐deficient in guard cells only, expressing a constitutively active chlorophyllase in a guard cell specific enhancer trap line. Our data show that more than 90% of guard cells were chlorophyll‐deficient. Interestingly, approximately 45% of stomata had an unusual, previously not‐described, morphology of thin‐shaped chlorophyll‐less stomata. Nevertheless, stomatal size, stomatal index, plant morphology, and whole‐leaf photosynthetic parameters (PSII, qP, qN, F_V′/F_M′) were comparable with wild‐type plants. Time‐resolved intact leaf gas‐exchange analyses showed a reduction in stomatal conductance and CO₂‐assimilation rates of the transgenic plants. Normalization of CO₂ responses showed that stomata of transgenic plants respond to [CO₂] shifts. Detailed stomatal aperture measurements of normal kidney‐shaped stomata, which lack chlorophyll, showed stomatal closing responses to [CO₂] elevation and abscisic acid (ABA), while thin‐shaped stomata were continuously closed. Our present findings show that stomatal movement responses to [CO₂] and ABA are functional in guard cells that lack chlorophyll. These data suggest that guard cell CO₂ and ABA signal transduction are not directly modulated by guard cell photosynthesis/electron transport. Moreover, the finding that chlorophyll‐less stomata cause a ‘deflated’ thin‐shaped phenotype, suggests that photosynthesis in guard cells is critical for energization and guard cell turgor production.     

Plant dehydrins: shedding light on structure and expression patterns of dehydrin gene family in barley

Dehydrins, an important group of late embryogenesis abundant proteins, accumulate in response to dehydration stresses and play protective roles under stress conditions. Herein, phylogenetic analysis of the dehydrin family was performed using the protein sequences of 108 dehydrins obtained from 14 plant species based on plant taxonomy and protein subclasses. Sub-cellular localization and phosphorylation sites of these proteins were also predicted. The protein features distinguishing these dehydrins categories were identified using various attribute weighting and decision tree analyses. The results revealed that the presence of the S motif preceding the K motif (Y_nSK_n, SK_n, and S_nKS) was more evident and the Y_nSK_n subclass was more frequent in monocots. In barley, as one of the most drought-tolerant crops, there are ten members of Y_nSK_n out of 13 HvDhns. In promoter regions, six types of abiotic stress-responsive elements were identified. Regulatory elements in UTR sequences of HvDhns were infrequent while only four miRNA targets were found. Furthermore, physiological parameters and gene expression levels of HvDhns were studied in tolerant (HV1) and susceptible (HV2) cultivars, and in an Iranian tolerant wild barley genotype (Spontaneum; HS) subjected to gradual water stress and after recovery duration at the vegetative stage. The results showed the significant impact of dehydration on dry matter, relative leaf water, chlorophyll contents, and oxidative damages in HV2 compared with the other studied genotypes, suggesting a poor dehydration tolerance, and incapability of recovering after re-watering in HV2. Under severe drought stress, among the 13 HvDhns genes, 5 and 10 were exclusively induced in HV1 and HS, respectively. The gene and protein structures and the expression patterns of HvDhns as well as the physiological data consistently support the role of dehydrins in survival and recovery of barley plants from drought particularly in HS. Overall, this information would be helpful for functional characterization of the Dhn family in plants.     

A Higher Number of TMS-Elicited MEP from a Combined Hotspot Improves Intra- and Inter-Session Reliability of the Upper Limb Muscles in Healthy Individuals

We aimed to determine, using transcranial magnetic stimulation (TMS), the number of elicited motor evoked potentials (MEPs) that induces the highest intra- and inter-sessions reliability for the extensor carpi radialis (ECR) and first dorsal interosseus (FDI) muscles. Twelve healthy subjects participated in this study on two separate days. Single pulse magnetic stimuli were triggered with Magstim 200² to obtain MEPs from the muscles of interest, with the subjects in a relaxed position. Reliability of MEP responses was investigated in three blocks of 5, 10 and 15 trials. The intra- and inter-session reliability of the MEPs'' amplitudes and latencies were assessed using intraclass correlation coefficients (ICCs). Repeated measures ANOVA and paired t-tests revealed no significant time effect in the MEP amplitude and latency measurements (P>0.05). The ICCs indicated high intra-session reliability in the MEPs'' amplitudes for the ECR and FDI muscles (0.77 to 0.99, 0.90 to 0.99, respectively) and latency (0.80 to 1.00, 0.75 to 0.97, respectively). The MEPs'' amplitudes also had high inter-session reliability (0.84 to 0.97, 0.88 to 0.93, respectively), as did their latency (0.80 to 0.90, 0.75 to 0.97, respectively). Highest intra- and inter-session reliability was achieved for blocks of 10 and 15 trials. Our data suggest that intra- and inter-session comparisons should be performed using at least 10 MEPs in “combined hotspot” stimulation technique to ensure highest reliability.     

Crocin and Metformin suppress metastatic breast cancer progression via VEGF and MMP9 downregulations: in vitro and in vivo studies

Metastatic breast cancer remains a serious health concern and numerous investigations recommended medicinal plants as a complementary therapy. Crocin is one of the known anticancer bio-component. Recently, the inhibitory effect of metformin has been studied on the various aspects of cancer. However, no study reported their combination effects on metastatic breast cancer. In the present study, we have assessed their anti-metastatic effects on in vitro and in vivo breast cancer models. Using MTT assay, scratch, and adhesion tests, we have evaluated the cytotoxic, anti-invasive and anti-adhesion effects of crocin and metformin on 4T1 cell line, respectively. Their protective effects and MMP9 as well as VEGF protein expression levels (Western blotting) investigated in the 4T1 murine breast cancer model. Our results showed that both crocin and metformin reduced cell viability, delayed scratch healing and inhibited the cell adhesion, in vitro. While crocin alone restored the mice’s weight reduction, crocin, metformin, and their combination significantly reduced the tumor volume size and enhanced animal survival rate in murine breast cancer model, responses that were associated with VEGF and MMP9 down-regulation. These findings suggest that a combination of crocin and metformin could serve as a novel therapeutic approach to enhance the effectiveness of metastatic breast cancer therapy.

     

SNP array-based homozygosity mapping reveals MCPH1 deletion in family with autosomal recessive mental retardation and mild microcephaly

Very little is known about the molecular basis of autosomal recessive MR (ARMR) because in developed countries, small family sizes preclude mapping and identification of the relevant gene defects. We therefore chose to investigate genetic causes of ARMR in large consanguineous Iranian families. This study reports on a family with six mentally retarded members. Array-based homozygosity mapping and high-resolution microarray-based comparative genomic hybridization (array CGH) revealed a deletion of approximately 150–200 kb, encompassing the promoter and the first six exons of the MCPH1 gene, one out of four genes that have been previously implicated in ARMR with microcephaly. Reexamination of affected individuals revealed a high proportion of prematurely condensed chromosomes, which is a hallmark of this condition, but in spite of the severity of the mutation, all patients showed only borderline to mild microcephaly. Therefore the phenotypic spectrum of MCPH1 mutations may be wider than previously assumed, with ARMR being the only consistent clinical finding.