M1 Region Research Articles

Functional Roles of a Conserved Tryptophan at Subunit-Subunit Interfaces in NMDA Receptor Membrane Regions

NMDA receptors (NMDARs) are ionotropic glutamate receptors (iGluRs) characterized by channel block by extracellular magnesium (Mg2+o) and slow deactivation kinetics. NMDARs are typically composed of two GluN1 and two GluN2 (GluN2A-GluN2D) subunits. The transmembrane domain (TMD) of each subunit contains three membrane-spanning regions (M1, M3, and M4) and a pore lining re-entrant loop (M2). The M2 region of each NMDAR subunit contains a tryptophan (W) that is highly conserved: nearly all known mammalian iGluR subunits, several potassium channels, and iGluR-like proteins in phylogenetically distant organisms contain W at the homologous site. This highly conserved W is located in NMDARs at the interface between the M2 region and the adjacent M3 region. Previous work demonstrated that mutation of this highly-conserved W in the GluN2B subunit (W607) drastically decreased block by Mg2+o, while mutation of the homologous residue in the GluN2A subunit (W606) had a relatively minor effect (Williams et al., 1998 Mol Pharmacol 53, 933). Interestingly, mutating the homologous residue in GluN1 subunits (W608) also has little effect on Mg2+o block (Siegler Retchless et al., 2012 Nat Neurosci 15, 406). To further explore the function of the conserved W at subunit-subunit interfaces we used whole-cell recordings from recombinant receptors expressed in tsA201 cells. We examined GluN2A(W606) and GluN2B(W607) mutants expressed with wild-type GluN1 subunits or GluN1 subunits with mutations of M3 residues at the M2-M3 interface. We found that receptors containing mutations at both GluN2A(W606) and a residue in the adjacent interface-lining GluN1 M3 region dramatically decreased block by Mg2+o. We also examined GluN1(W608) mutants and observed profoundly slowed deactivation kinetics. Overall, these results suggest that the conserved W is broadly involved in channel properties and gating of NMDARs.

Reduced functional connectivity within the primary motor cortex of patients with brachial plexus injury.

This study aims at the effects of traumatic brachial plexus lesion with root avulsions (BPA) upon the organization of the primary motor cortex (M1). Nine right-handed patients with a right BPA in whom an intercostal to musculocutaneous (ICN-MC) nerve transfer was performed had post-operative resting state fMRI scanning. The analysis of empirical functional correlations between neighboring voxels revealed faster correlation decay as a function of distance in the M1 region corresponding to the arm in BPA patients as compared to the control group. No differences between the two groups were found in the face area. We also investigated whether such larger decay in patients could be attributed to a gray matter diminution in M1. Structural imaging analysis showed no difference in gray matter density between groups. Our findings suggest that the faster decay in neighboring functional correlations without significant gray matter diminution in BPA patients could be related to a reduced activity in intrinsic horizontal connections in M1 responsible for upper limb motor synergies.

Abstract WMP16: Eloquence-Weighted Imaging Improves Clinical Outcomes Prediction in Endovascular Stroke Therapy

Background: Larger infarct size at presentation as determined by ASPECTS is associated with reduced likelihood of good outcome in acute ischemic stroke. However, infarct volume alone explains only a modest fraction (∼30%) of the variation in stroke outcome. Incorporating the relative eloquence of each ASPECTS region may improve the predictive power. Methods: In the combined database of the SWIFT and STAR trials, we identified patients treated with the Solitaire stent retriever. Using the 24hr CT scan, a multivariate linear regression was used to determine the relative contribution of each ASPECTS region, separately in each hemisphere, to freedom from disability (mRS 0-2) at 90 days. The coefficients from the regression were used to create an Eloquence-weighted ASPECTS score (EL-ASPECTS), which was compared against the original in predicting outcome based on the presentation CT scan. Results: Among 254 patients treated with ET, average age was 68, 64% were female, and NIHSS was mean 16 (SD +/- 5). Mean ASPECTS at presentation was 8.2 and 6.4 at 24 hrs. The most commonly involved ASPECTS regions were the lentiform nuclei (70%), insula (55%), and caudate (52%). In multivariate analysis, for the right hemisphere on 24hr CT, preservation of M1 (OR 1.6) and M4 (OR 1.2) regions were most strongly predictive of good outcome. For the left hemisphere on 24 hr CT, preservation of M3 (OR 2.6), and M5 (OR 2.5) and involvement of M2 (OR -1.9) were most predictive. Eloquence weights were assigned to all 20 R/L ASPECTS regions to create EL-ASPECTS. EL-ASPECTS, compared with original ASPECTS, demonstrated improved discrimination for independent functional outcome for right hemisphere (C-statistic 0.78 vs. 0.69), left hemisphere (0.78 vs. 0.72), and all stroke patients (0.76 vs. 0.70). On presentation CTs, multivariate analyses including age and presentation NIHSS demonstrated EL-ASPECTS but not original ASPECTS was predictive of good clinical outcome (OR 1.65, p<.01). Higher C-statistic values were seen with EL-ASPECTS in analysis of presentation CT scans. Conclusions: Incorporation of regional weighting into ASPECTS improves the ability to predict who will achieve independent functional outcomes with endovascular therapy in acute ischemic stroke.

Influence of repetitive transcranial magnetic stimulation on tibialis anterior activity during walking in humans

ObjectiveTo determine whether or not modulation of the excitability of the M1 region controlling the lower limb (using repetitive transcranial magnetic stimulation; TMS) would change the TA’s activity during gait and the effect of aging on this change. MethodsIn three separate sessions, participants underwent different repetitive TMS (rTMS) protocols (sham stimulation, intermittent theta-burst stimulation (TBS) and continuous TBS) delivered over the M1 region controlling the lower limb muscles, using a focal, figure-of-eight coil. Before and after rTMS, the TA’s activity was recorded using surface electrodes while participants walked at a freely chosen speed and at an imposed speed on a treadmill. Cortical excitability was assessed by characterizing input–output (IO) curves, after fitting the relationship between motor evoked potential amplitude and stimulus intensity with a Boltzmann sigmoidal equation. ResultsWe did not observe any effects of rTMS in terms of TA activation during locomotion, gait parameters or IO curves in either healthy young adults or elderly adults. Elderly patients presented lower excitability of cortical TA representation area. ConclusionModulation of TA activity by TBS was ineffective contrary to what is observed for upper limbs. Interindividual variability in the effects of rTMS on TA activation, activation of the TA before the rTMS and/or differences in the depth of the cortical representation of the TA could have influenced the results and should be taken into account for further studies.

Brain Region-Specific Histopathological Effects of Varying Trajectories of Controlled Cortical Impact Injury Model of Traumatic Brain Injury.

SummaryAimsTraumatic brain injury (TBI) occurs when the head is impacted by an external force causing either a closed or penetrating head injury through a direct or accelerating impact. In laboratory research, most of the TBI animal models focus on a specific region to cause brain injury, but traumatic injuries in patients do not always impact the same brain regions. The aim of this study was to examine the histopathological effects of different angles of mechanical injury by manipulating the trajectory of the controlled cortical impact injury (CCI) model in adult Sprague‐Dawley rats.MethodsThe CCI model was manipulated as follows: conventional targeting of the frontal cortex, farthest right angle targeting the frontal cortex, closest right angle targeting the frontal cortex, olfactory bulb injury, and cerebellar injury. Three days after TBI, brains were harvested to analyze cortical and hippocampal cell loss, neuroinflammatory response, and neurogenesis via immunohistochemistry.ResultsResults revealed cell death in the M1 region of the cortex across all groups, and in the CA3 area from olfactory bulb injury group. This observed cell death involved upregulation of inflammation as evidenced by rampant MHCII overexpression in cortex, but largely spared Ki‐67/nestin neurogenesis in the hippocampus during this acute phase of TBI.ConclusionThese results indicate a trajectory‐dependent injury characterized by exacerbation of inflammation and different levels of impaired cell proliferation and neurogenesis. Such multiple brain areas showing varying levels of cell death after region‐specific CCI model may closely mimic the clinical manifestations of TBI.

Mandibular bone mineral density variation in three West African Cercopithecoid monkey species: Associations with diet and feeding behavior

ObjectiveProcolobus badius, Colobus polykomos, and Cercocebus atys are three West African primate species known to have distinctive feeding behaviors. Our objectives were (1) to test whether intra-taxon variation in bone mineral content exists between anterior and posterior regions of the mandible and (2) to determine if interspecific differences are interpretable via feeding and dietary idiosyncracies among the three taxa. DesignTwenty-one mandibles from naturally deceased C. polykomos (n=7), P. badius (n=9), and C. atys (n=5) were scanned using cone beam computerized tomography. Alveolar bone (AB) and basal cortical bone (CB) of incisor (I1) and second molar (M2) regions were digitally isolated. Degree of bone mineralization (DBM) distribution was obtained using histograms of CT attenuation values. Mean, standard deviation (SD), the 5th (Low5) and the 95th (High5) percentiles of the DBM histogram were compared between the jaw regions in species. ResultsThe mean and Low5 of DBM were significantly lower for AB than CB of all species (p<0.001). The AB DBM parameters were not significantly different between I1 and M2 of all species (p>0.056) except the mean of C. polykomos (p<0.05). The mean, SD, High5 of CB DBM at M2 of C. atys was significantly higher than those of C. polykomos and P. badius (p<0.006). ConclusionsThe durophagous C. atys had higher CB DBM value at the M2 region than C. polykomos and P. badius, which supports the hypothesis that materially stiffer mandibular bone in C. atys can develop in response to the generation of high bite forces during hard object feeding.

Broflanilide: A meta-diamide insecticide with a novel mode of action

Broflanilide is a meta-diamide [3-benzamido-N-(4-(perfluoropropan-2-yl)phenyl)benzamide] that exhibits high larvicidal activity against Spodoptera litura. It has been suggested that broflanilide is metabolized to desmethyl-broflanilide and that it acts as a noncompetitive resistant-to-dieldrin (RDL) γ-aminobutyric acid (GABA) receptor antagonist. The binding site of desmethyl-broflanilide was demonstrated to be distinct from that of conventional noncompetitive antagonists such as fipronil. It has been proposed that the site of action for desmethyl-broflanilide is close to G336 in the M3 region of the Drosophila RDL GABA receptor. However, although the site of action for desmethyl-broflanilide appears to overlap with that of macrocyclic lactones, different modes of actions have been demonstrated for desmethyl-broflanilide and the macrocyclic lactones. The mechanisms underlying the high selectivity of meta-diamides are also discussed in this review. Broflanilide is expected to become a prominent insecticide because it is effective against pests with resistance to cyclodienes and fipronil.

Sequence variability is correlated with weak immunogenicity in Streptococcus pyogenes M protein.

The M protein of Streptococcus pyogenes, a major bacterial virulence factor, has an amino-terminal hypervariable region (HVR) that is a target for type-specific protective antibodies. Intriguingly, the HVR elicits a weak antibody response, indicating that it escapes host immunity by two mechanisms, sequence variability and weak immunogenicity. However, the properties influencing the immunogenicity of regions in an M protein remain poorly understood. Here, we studied the antibody response to different regions of the classical M1 and M5 proteins, in which not only the HVR but also the adjacent fibrinogen-binding B repeat region exhibits extensive sequence divergence. Analysis of antisera from S. pyogenes-infected patients, infected mice, and immunized mice showed that both the HVR and the B repeat region elicited weak antibody responses, while the conserved carboxy-terminal part was immunodominant. Thus, we identified a correlation between sequence variability and weak immunogenicity for M protein regions. A potential explanation for the weak immunogenicity was provided by the demonstration that protease digestion selectively eliminated the HVR-B part from whole M protein-expressing bacteria. These data support a coherent model, in which the entire variable HVR-B part evades antibody attack, not only by sequence variability but also by weak immunogenicity resulting from protease attack.

Intrinsic functional plasticity of the sensorimotor network in relapsing-remitting multiple sclerosis: evidence from a centrality analysis.

Background and PurposeAdvanced MRI studies have revealed regional alterations in the sensorimotor cortex of patients with relapsing-remitting multiple sclerosis (RRMS). However, the organizational features underlying the relapsing phase and the subsequent remitting phase have not been directly shown at the functional network or the connectome level. Therefore, this study aimed to characterize MS-related centrality disturbances of the sensorimotor network (SMN) and to assess network integrity and connectedness.MethodsThirty-four patients with clinically definite RRMS and well-matched healthy controls participated in the study. Twenty-three patients in the remitting phase underwent one resting-state functional MRI, and 11 patients in the relapsing-remitting phase underwent two different MRIs. We measured voxel-wise centrality metrics to determine direct (degree centrality, DC) and global (eigenvector centrality, EC) functional relationships across the entire SMN.ResultsIn the relapsing phase, DC was significantly decreased in the bilateral primary motor and somatosensory cortex (M1/S1), left dorsal premotor (PMd), and operculum-integrated regions. However, DC was increased in the peripheral SMN areas. The decrease in DC in the bilateral M1/S1 was associated with the expanded disability status scale (EDSS) and total white matter lesion loads (TWMLLs), suggesting that this adaptive response is related to the extent of brain damage in the rapid-onset attack stage. During the remission process, these alterations in centrality were restored in the bilateral M1/S1 and peripheral SMN areas. In the remitting phase, DC was reduced in the premotor, supplementary motor, and operculum-integrated regions, reflecting an adaptive response due to brain atrophy. However, DC was enhanced in the right M1 and left parietal-integrated regions, indicating chronic reorganization. In both the relapsing and remitting phases, the changes in EC and DC were similar.ConclusionsThe alterations in centrality within the SMN indicate rapid plasticity and chronic reorganization with a biased impairment of specific functional areas in RRMS patients.

Evolutionary transition in symbiotic syndromes enabled diversification of phytophagous insects on an imbalanced diet.

Evolutionary adaptations for the exploitation of nutritionally challenging or toxic host plants represent a major force driving the diversification of phytophagous insects. Although symbiotic bacteria are known to have essential nutritional roles for insects, examples of radiations into novel ecological niches following the acquisition of specific symbionts remain scarce. Here we characterized the microbiota across bugs of the family Pyrrhocoridae and investigated whether the acquisition of vitamin-supplementing symbionts enabled the hosts to diversify into the nutritionally imbalanced and chemically well-defended seeds of Malvales plants as a food source. Our results indicate that vitamin-provisioning Actinobacteria (Coriobacterium and Gordonibacter), as well as Firmicutes (Clostridium) and Proteobacteria (Klebsiella) are widespread across Pyrrhocoridae, but absent from the sister family Largidae and other outgroup taxa. Despite the consistent association with a specific microbiota, the Pyrrhocoridae phylogeny is neither congruent with a dendrogram based on the hosts' microbial community profiles nor phylogenies of individual symbiont strains, indicating frequent horizontal exchange of symbiotic partners. Phylogenetic dating analyses based on the fossil record reveal an origin of the Pyrrhocoridae core microbiota in the late Cretaceous (81.2-86.5 million years ago), following the transition from crypt-associated beta-proteobacterial symbionts to an anaerobic community localized in the M3 region of the midgut. The change in symbiotic syndromes (that is, symbiont identity and localization) and the acquisition of the pyrrhocorid core microbiota followed the evolution of their preferred host plants (Malvales), suggesting that the symbionts facilitated their hosts' adaptation to this imbalanced nutritional resource and enabled the subsequent diversification in a competition-poor ecological niche.

Googling Stroke ASPECTS to Determine Disability: Exploratory Analysis from VISTA-Acute Collaboration.

The summed Alberta Stroke Program Early CT Score (ASPECTS) is useful for predicting stroke outcome. The anatomical information in the CT template is rarely used for this purpose because traditional regression methods are not adept at handling collinearity (relatedness) among brain regions. While penalized logistic regression (PLR) can handle collinearity, it does not provide an intuitive understanding of the interaction among network structures in a way that eigenvector method such as PageRank can (used in Google search engine). In this exploratory analysis we applied graph theoretical analysis to explore the relationship among ASPECTS regions with respect to disability outcome. The Virtual International Stroke Trials Archive (VISTA) was searched for patients who had infarct in at least one ASPECTS region (ASPECTS ≤9, ASPECTS=10 were excluded), and disability (modified Rankin score/mRS). A directed graph was created from a cross correlation matrix (thresholded at false discovery rate of 0.01) of the ASPECTS regions and demographic variables and disability (mRS>2). We estimated the network-based importance of each ASPECTS region by comparing PageRank and node strength measures. These results were compared with those from PLR. There were 185 subjects, average age 67.5± 12.8 years (55% Males). Model 1: demographic variables having no direct connection with disability, the highest PageRank was M2 (0.225, bootstrap 95% CI 0.215-0.347). Model 2: demographic variables having direct connection with disability, the highest PageRank were M2 (0.205, bootstrap 95% CI 0.194-0.367) and M5 (0.125, bootstrap 95% CI 0.096-0.204). Both models illustrate the importance of M2 region to disability. The PageRank method reveals complex interaction among ASPECTS regions with respects to disability. This approach may help to understand the infarcted brain network involved in stroke disability.

Measurement of mucosal thickness in denture-bearing area of edentulous mandible.

Background:The thickness of the alveolar mucosa influences the probability of the occurrence of denture-induced irritations. Thick denture-supporting tissues offer relief from mucosal tenderness and ulcers; however, the uniformity of the thickness across the entire mandibular alveolar mucosa cannot be accurately determined in edentulous patients. This study aimed to assess the mucosal thickness of the denture-bearing area in the edentulous mandible.Methods:Twenty-seven edentulous patients underwent cone-beam computed tomography scanning, wherein the patients wore a record base to retract soft tissues away from the alveolar mucosa. The measured regions were the central incisor (IC), lateral incisor (IL), canine (Ca), first premolar (P1), second premolar (P2), first molar (M1), and second molar (M2) regions. The thickness was measured in the alveolar ridge crest (T), buccal (B1–B4), and lingual (L1–L4) alveolar ridge mucosa. The average thickness of the mucosa at buccal sides (B) and lingual sides (L) were also assessed.Results:The differences in the mucosal thickness between the left and right sides were not significant. In the Ca–M2 regions, T was the thickest, and L3 was the thinnest of all the measured points in the same regions. L was significantly less than B in posterior regions (P < 0.01). On the other hand, M2 at L4 was thinnest of all the measured regions from Ca to M2 (P < 0.01), and was thicker than IC, IL, P1, and P2 at B2.Conclusions:Since the mucosal thickness of denture-bearing area in the edentulous mandible is not uniform; the tissue surface of the denture base or custom tray should be selectively relieved, which may reduce the risk of denture-induced irritations.

Sequential activation of premotor, primary somatosensory and primary motor areas in humans during cued finger movements

ObjectiveHuman voluntary movements are a final product of complex interactions between multiple sensory, cognitive and motor areas of central nervous system. The objective was to investigate temporal sequence of activation of premotor (PM), primary motor (M1) and somatosensory (S1) areas during cued finger movements. MethodsElectrocorticography (ECoG) was used to measure activation timing in human PM, S1, and M1 neurons in preparation for finger movements in 5 subjects with subdural grids for seizure localization. Cortical activation was determined by the onset of high gamma (HG) oscillation (70–150Hz). The three cortical regions were mapped anatomically using a common brain atlas and confirmed independently with direct electrical cortical stimulation, somatosensory evoked potentials and detection of HG response to tactile stimulation. Subjects were given visual cues to flex each finger or pinch the thumb and index finger. Movements were captured with a dataglove and time-locked with ECoG. A windowed covariance metric was used to identify the rising slope of HG power between two electrodes and compute time lag. Statistical constraints were applied to the time estimates to combat the noise. Rank sum testing was used to verify the sequential activation of cortical regions across 5 subjects. ResultsIn all 5 subjects, HG activation in PM preceded S1 by an average of 53±13ms (P=0.03), PM preceded M1 by 180±40ms (P=0.001) and S1 activation preceded M1 by 136±40ms (P=0.04). ConclusionsSequential HG activation of PM, S1 and M1 regions in preparation for movements is reported. Activity in S1 prior to any overt body movements supports the notion that these neurons may encode sensory information in anticipation of movements, i.e., an efference copy. Our analysis suggests that S1 modulation likely originates from PM. SignificanceFirst electrophysiological evidence of efference copy in humans.

Chemoarchitecture of glial fibrillary acidic protein (GFAP) and glutamine synthetase in the rat optic nerve: an immunohistochemical study.

An immunohistochemical analysis of the chemoarchitecture of glial fibrillary acidic protein (GFAP) and glutamine synthetase (GS) was conducted in the rat optic nerve. The optic nerve has been divided into 3 regions: the intraretinal, unmyelinated, and myelinated regions. However, it currently remains unclear whether the chemoarchitecture of GFAP and GS is homogeneously organized, especially in the myelinated region. The intraretinal region was divided into intraretinal regions 1 (i1) and 2 (i2). GFAP immunoreactivity was very strong in the i2 and unmyelinated regions, and strong in the i1 region. GS immunoreactivity was moderate in the i1 and i2 regions, and weak in the unmyelinated region. The myelinated region was separated into myelinated regions 1 (m1) and 2 (m2). In the m1 region, GFAP immunoreactivity was strong and GS immunoreactivity was moderate; however, GFAP immunoreactivity was moderate and GS immunoreactivity was weak in the m2 region. Thus, the chemoarchitecture was heterogeneously organized in the myelinated region, with the i1, i2 and m1 regions being the main GS distribution sites. Moreover, most GS-immunoreactive glial cells were oligodendrocytes in the myelinated region. Since GS is a key enzyme in glutamate metabolism, these results may facilitate future investigations for a clearer understanding of glutamate metabolism.

Correlation between the Occlusion Site and Clinical Outcome after Acute Ischemic Stroke

The significance of early mild clinical improvement after intravenous tissue plasminogen activator (IVtPA) treatment is unclear. Therefore, we examined whether the timing of clinical improvement after IVtPA predicted the clinical outcome at 3 months. Consecutive patients with acute cerebral infarction in the anterior circulation who received IVtPA treatment within 3 hours of the onset of symptoms were enrolled in the study. Patients were classified according to the timing of clinical improvement [early responder (ER), National Institutes of Health Stroke Scale (NIHSS) score improved ≥4 points or who had a score of 0 within 2 hours after IVtPA; late responder (LR), a similar improvement between 2 and 24 hours; and non-responder (NR)] and according to the arterial occlusion site (P group, internal carotid artery and proximal middle cerebral artery M1 region; and D group, distal M1 and M2). Ninety-three patients [median age, 74 (67-79) years; 54 men (58%); median NIHSS score, 11 (7-16)] were enrolled in the study. The P group consisted of 48 (52%) patients and the D group consisted of 45 (48%) patients. Thirty-eight patients (41%) were classified as ERs, 20 (22%) as LRs, and 35 (38%) as NRs. On a multivariate regression analysis, the P group [odds ratio (OR), 3.24; 95% confidence interval (CI), 1.08-10.45; p=0.036] and NR (OR, 4.04; 95% CI, 1.29-14.27; p=0.016) were independent predictors of a poor outcome. ER (47%, p=0.01) and LR (45%, p=0.01) patients showed fewer poor outcomes than NR (77%) patients, but the rate did not differ significantly between the ER and LR patients. Early mild clinical recovery did not predict a good outcome. The occlusion site was a stronger predictor of clinical improvement after IVtPA administration.

Second Transmembrane Helix (M2) and Long Range Coupling in Ca2+-ATPase

The actuator (A) domain of sarco(endo)plasmic reticulum Ca(2+)-ATPase not only plays a catalytic role but also undergoes large rotational movements that influence the distant transport sites through connections with transmembrane helices M1 and M2. Here we explore the importance of long helix M2 and its junction with the A domain by disrupting the helix structure and elongating with insertions of five glycine residues. Insertions into the membrane region of M2 and the top junctional segment impair Ca(2+) transport despite reasonable ATPase activity, indicating that they are uncoupled. These mutants fail to occlude Ca(2+). Those at the top segment also exhibited accelerated phosphoenzyme isomerization E1P → E2P. Insertions into the middle of M2 markedly accelerate E2P hydrolysis and cause strong resistance to inhibition by luminal Ca(2+). Insertions along almost the entire M2 region inhibit the dephosphorylated enzyme transition E2 → E1. The results pinpoint which parts of M2 control cytoplasm gating and which are critical for luminal gating at each stage in the transport cycle and suggest that proper gate function requires appropriate interactions, tension, and/or rigidity in the M2 region at appropriate times for coupling with A domain movements and catalysis.

An atypical residue in the pore of Varroa destructor GABA-activated RDL receptors affects picrotoxin block and thymol modulation

GABA-activated RDL receptors are the insect equivalent of mammalian GABAA receptors, and play a vital role in neurotransmission and insecticide action. Here we clone the pore lining M2 region of the Varroa mite RDL receptor and show that it has 4 atypical residues when compared to M2 regions of most other insects, including bees, which are the major host of Varroa mites. We create mutant Drosophila RDL receptors containing these substitutions and characterise their effects on function. Using two electrode voltage clamp electrophysiology we show that one substitution (T6′M) ablates picrotoxin inhibition and increases the potency of GABA. This mutation also alters the effect of thymol, which enhances both insect and mammalian GABA responses, and is widely used as a miticide. Thymol decreases the GABA EC50 of WT receptors, enhancing responses, but in T6′M-containing receptors it is inhibitory. The other 3 atypical residues have no major effects on either the GABA EC50, the picrotoxin potency or the effect of thymol. In conclusion we show that the RDL 6′ residue is important for channel block, activation and modulation, and understanding its function also has the potential to prove useful in the design of Varroa-specific insecticidal agents.

The power of the mind: the cortex as a critical determinant of muscle strength/weakness.

We tested the hypothesis that the nervous system, and the cortex in particular, is a critical determinant of muscle strength/weakness and that a high level of corticospinal inhibition is an important neurophysiological factor regulating force generation. A group of healthy individuals underwent 4 wk of wrist-hand immobilization to induce weakness. Another group also underwent 4 wk of immobilization, but they also performed mental imagery of strong muscle contractions 5 days/wk. Mental imagery has been shown to activate several cortical areas that are involved with actual motor behaviors, including premotor and M1 regions. A control group, who underwent no interventions, also participated in this study. Before, immediately after, and 1 wk following immobilization, we measured wrist flexor strength, voluntary activation (VA), and the cortical silent period (SP; a measure that reflect corticospinal inhibition quantified via transcranial magnetic stimulation). Immobilization decreased strength 45.1 ± 5.0%, impaired VA 23.2 ± 5.8%, and prolonged the SP 13.5 ± 2.6%. Mental imagery training, however, attenuated the loss of strength and VA by ∼50% (23.8 ± 5.6% and 12.9 ± 3.2% reductions, respectively) and eliminated prolongation of the SP (4.8 ± 2.8% reduction). Significant associations were observed between the changes in muscle strength and VA (r = 0.56) and SP (r = -0.39). These findings suggest neurological mechanisms, most likely at the cortical level, contribute significantly to disuse-induced weakness, and that regular activation of the cortical regions via imagery attenuates weakness and VA by maintaining normal levels of inhibition.

Transcranial direct current stimulation of the primary motor cortex improves word-retrieval in older adults.

Language facilitation by transcranial direct current stimulation (tDCS) in healthy individuals has generated hope that tDCS may also allow improving language impairment after stroke (aphasia). However, current stimulation protocols have yielded variable results and may require identification of residual language cortex using functional magnetic resonance imaging (fMRI), which complicates incorporation into clinical practice. Based on previous behavioral studies that demonstrated improved language processing by motor system pre-activation, the present study assessed whether tDCS administered to the primary motor cortex (M1) can enhance language functions. This proof-of-concept study employed a sham-tDCS controlled, cross-over, within-subject design and assessed the impact of unilateral excitatory (anodal) and bihemispheric (dual) tDCS in 18 healthy older adults during semantic word-retrieval and motor speech tasks. Simultaneous fMRI scrutinized the neural mechanisms underlying tDCS effects. Both active tDCS conditions significantly improved word-retrieval compared to sham-tDCS. The direct comparison of activity elicited by word-retrieval vs. motor-speech trials revealed bilateral frontal activity increases during both anodal- and dual-tDCS compared to sham-tDCS. This effect was driven by more pronounced deactivation of frontal regions during the motor-speech task, while activity during word-retrieval trials was unaffected by the stimulation. No effects were found in M1 and secondary motor regions. Our results show that tDCS administered to M1 can improve word-retrieval in healthy individuals, thereby providing a rationale to explore whether M1-tDCS may offer a novel approach to improve language functions in aphasia. Functional magnetic resonance imaging revealed neural facilitation specifically during motor speech trials, which may have reduced switching costs between the overlapping neural systems for lexical retrieval and speech processing, thereby resulting in improved performance.

Fractional anisotropy in corpus callosum is associated with facilitation of motor representation during ipsilateral hand movements.

BackgroundCoactivation of primary motor cortex ipsilateral to a unilateral movement (M1ipsilateral) has been observed, and the magnitude of activation is influenced by the contracting muscles. It has been suggested that the microstructural integrity of the callosal motor fibers (CMFs) connecting M1 regions may reflect the observed response. However, the association between the structural connectivity of CMFs and functional changes in M1ipsilateral remains unclear. The purpose of this study was to investigate the relationship between functional changes within M1ipsilateral during unilateral arm or leg movements and the microstructure of the CMFs connecting both homotopic representations (arm or leg).MethodsTranscranial magnetic stimulation was used to assess changes in motor evoked potentials (MEP) in an arm muscle during unilateral movements compared to rest in fifteen healthy adults. Functional magnetic resonance imaging was then used to identify regions of M1 associated with either arm or leg movements. Diffusion-weighted imaging data was acquired to generate CMFs for arm and leg areas using the areas of activation from the functional imaging as seed masks. Individual values of regional fractional anisotropy (FA) of arm and leg CMFs was then calculated by examining the overlap between CMFs and a standard atlas of corpus callosum.ResultsThe change in the MEP was significantly larger in the arm movement compared to the leg movement. Additionally, regression analysis revealed that FA in the arm CMFs was positively correlated with the change in MEP during arm movement, whereas a negative correlation was observed during the leg movement. However, there was no significant relationship between FA in the leg CMF and the change in MEP during the movements.ConclusionsThese findings suggest that individual differences in interhemispheric structural connectivity may be used to explain a homologous muscle-dominant effect within M1ipsilateral hand representation during unilateral movement with topographical specificity.