M1 Region Research Articles

Alpha band functional connectivity correlates with the performance of brain-machine interfaces to decode real and imagined movements.

Brain signals recorded from the primary motor cortex (M1) are known to serve a significant role in coding the information brain–machine interfaces (BMIs) need to perform real and imagined movements, and also to form several functional networks with motor association areas. However, whether functional networks between M1 and other brain regions, such as these motor association areas, are related to the performance of BMIs is unclear. To examine the relationship between functional connectivity and performance of BMIs, we analyzed the correlation coefficient between performance of neural decoding and functional connectivity over the whole brain using magnetoencephalography. Ten healthy participants were instructed to execute or imagine three simple right upper limb movements. To decode the movement type, we extracted 40 virtual channels in the left M1 via the beam forming approach, and used them as a decoding feature. In addition, seed-based functional connectivities of activities in the alpha band during real and imagined movements were calculated using imaginary coherence. Seed voxels were set as the same virtual channels in M1. After calculating the imaginary coherence in individuals, the correlation coefficient between decoding accuracy and strength of imaginary coherence was calculated over the whole brain. The significant correlations were distributed mainly to motor association areas for both real and imagined movements. These regions largely overlapped with brain regions that had significant connectivity to M1. Our results suggest that use of the strength of functional connectivity between M1 and motor association areas has the potential to improve the performance of BMIs to perform real and imagined movements.

E-057 Correlation between Angiographic Transit Times and Neurological Status in Patients with Aneurysmal Subarachnoid Haemorrhage

IntroductionThe use of digital subtraction angiography (DSA) for semi-quantitative cerebral blood flow (CBF) assessment is a new method. In this report we sought to correlate angiographic transit times (TT) in...

Dose-dependent effects of theta burst rTMS on cortical excitability and resting-state connectivity of the human motor system.

Theta burst stimulation (TBS), a specific protocol of repetitive transcranial magnetic stimulation (rTMS), induces changes in cortical excitability that last beyond stimulation. TBS-induced aftereffects, however, vary between subjects, and the mechanisms underlying these aftereffects to date remain poorly understood. Therefore, the purpose of this study was to investigate whether increasing the number of pulses of intermittent TBS (iTBS) (1) increases cortical excitability as measured by motor-evoked potentials (MEPs) and (2) alters functional connectivity measured using resting-state fMRI, in a dose-dependent manner. Sixteen healthy, human subjects received three serially applied iTBS blocks of 600 pulses over the primary motor cortex (M1 stimulation) and the parieto-occipital vertex (sham stimulation) to test for dose-dependent iTBS effects on cortical excitability and functional connectivity (four sessions in total). iTBS over M1 increased MEP amplitudes compared with sham stimulation after each stimulation block. Although the increase in MEP amplitudes did not differ between the first and second block of M1 stimulation, we observed a significant increase after three blocks (1800 pulses). Furthermore, iTBS enhanced resting-state functional connectivity between the stimulated M1 and premotor regions in both hemispheres. Functional connectivity between M1 and ipsilateral dorsal premotor cortex further increased dose-dependently after 1800 pulses of iTBS over M1. However, no correlation between changes in MEP amplitudes and functional connectivity was detected. In summary, our data show that increasing the number of iTBS stimulation blocks results in dose-dependent effects at the local level (cortical excitability) as well as at a systems level (functional connectivity) with a dose-dependent enhancement of dorsal premotor cortex-M1 connectivity.

Selective modulation of left primary motor cortex excitability after continuous theta burst stimulation to right primary motor cortex and bimanual training

Bimanual movement training (BMT) enhances the excitability of human preparatory premotor and primary motor (M1) cortices. We have shown that activity in M1 is enhanced after BMT involving simultaneous activation of homologous muscles (in-phase). Potential neural mechanisms underlying this effect could be input from premotor areas (i.e. dorsal premotor cortex (PMd)) and/or the homologous M1 representation. Recently, we showed that increasing PMd activity using theta burst stimulation (TBS) followed by BMT enhanced the corticospinal excitability of M1 compared to BMT alone. The purpose of this study was to investigate the effects of continuous TBS (cTBS) to right hemisphere M1 (rM1) on the homologous wrist extensor representation in left M1 (lM1), and its potential combined effects when followed by BMT. We used transcranial magnetic stimulation (TMS) to measure cortical excitability of extensor carpi radialis (ECR) representation at multiple time points in three conditions: (1) BMT, (2) cTBS to rM1 or (3) cTBS to rM1 and BMT. The combination of cTBS to rM1 and BMT resulted in an increased shift in the centre of gravity (CoG) compared to either intervention alone, along with an increased muscle topographical representation up to 60min when cTBS to rM1 was combined with BMT compared to cTBS to rM1 alone. These results suggest that modulation of M1 may reduce ongoing interhemispheric inhibition (or increase facilitation indirectly) to the opposite homologous M1 region in healthy individuals via transcallosal or subcortical connections. Critically, this work may guide rehabilitation training and stimulation techniques that modulate cortical plasticity after brain injury.

Structural Damage and Functional Reorganization in Ipsilesional M1 in Well-Recovered Patients With Subcortical Stroke

Both structural atrophy and functional reorganization of the primary motor cortex (M1) have been reported in patients with subcortical infarctions affecting the motor pathway. However, the relationship between structural impairment and functional reorganization in M1 remains unclear. Twenty-six patients exhibiting significant recovery after subcortical infarctions were investigated using multimodal MRI techniques. Structural impairment was assessed via cortical thickness, and functional reorganization was analyzed using task-evoked activation, amplitude of low-frequency fluctuation, and resting-state functional connectivity. Compared with healthy controls, patients with stroke exhibited reduced cortical thickness in the ipsilesional M1; however, this region exhibited increased task-evoked activation, amplitude of low-frequency fluctuation, and resting-state functional connectivity in these patients. Patients with stroke demonstrated increased task-evoked activation in another ipsilesional M1 region, in which increased amplitude of low-frequency fluctuation and resting-state functional connectivity were observed. The structural and functional changes in M1 were located selectively in the ipsilesional hemisphere. We provide convincing evidence that indicates extensive functional reorganization in the ipsilesional M1 of patients with chronic subcortical infarctions, including the structurally impaired M1 region.

P 189. The extent of perifocal edema in function associated motor fibers correlates to the primary motor deficit in patients with M1-adjacent intracerebral tumors. A volumetric analysis of presurgically acquired data based on MRI, FET-PET and navigated TMS on primary motor functions

Question Many patients with brain tumors adjacent to the primary motor (M1) region initially present with transient or permanent motor deficits. Factors like compression by tumor mass, tumor infiltration, as well as the extent of the perifocal edema might contribute to the motor deficit. In order to assess the relevance of these factors, we analyzed the spatial relationship between M1 cortical representation assessed with navigated transcranial magnetic stimulation (nTMS) and the anatomical and metabolic extension of tumors in the M1 region in patients prior to surgery. Methods To date, 21 patients with M1-adjacent tumors (glioblastoma ( n = 14), anaplastic astrocytoma ( n = 1), carcinoma metastasis ( n = 4), anaplastic ependymoma ( n = 1), lymphoma ( n = 1)) underwent an anatomical MRI protocol including a T2-weighted sequence, a gadolinium-contrast-enhanced sequence (GCE) and diffused tensor imaging as well as 18F-fluoroethyl-L-tyrosine (FET) PET for presurgical planning. Cortical M1 representations for the hand, foot and tongue were assessed by nTMS within 7 days. “Functional” fiber tracking of the corticospinal tract (CST) consisted of the following processing steps: (1) setting the seed points defined by the coordinate revealing the highest motor evoked potential (MEP) when stimulated by nTMS at 110% of the resting motor threshold and the surrounding 5 mm, according to the registration and E-field calculation mismatch and (2) a seed volume at the midbrain level. Total volumes and intersection volumes of the CST and the anatomically defined areas were expressed in cm 3 ±standard deviation (SD). Results 15 out of the 21 patients had a primary motor deficit recorded in either the upper or lower limb, the facial muscles or initially presented with a hemiparesis, 6 patients had not developed any deficit prior to or at admission to surgery. Neither the GCE ( p = .96) nor the FET ( p = .45) tumor volume statistically differed between the group of patients with a motor deficit (GCE: 19.7 ± 17.2 cm 3 ; FET: 9.6 ± 5.3 cm 3 , n = 15) compared to one without a motor deficit (GCE: 12.1 ± 16.8 cm 3 ; 6.4 ± 6.5 cm 3 , n = 6). The mean perifocal edema volume based on the T2-weighted MRI data was slightly greater in the motor deficit group (64.2 ± 38.1 cm 3 ) than in the group of patients without any motor deficit (43.4 ± 28.6 cm 3 ) but did again not pass the statistical threshold ( p = .37). However, the mean relative volume of functional fibers intersected by the T2-weighted edema volume was statistically greater in the primary motor deficit group (16.1 ± 13.1%) than in the one without motor deficits (0.1 ± 0.0%). By contrast, the mean relative volume of cortical M1 representation intersected by the edematous area did not statistically differ between the two groups ( p = .09). Nor the mean relative volume of functional fibers or functional motor cortex intersected by GCE or PET tumor volumes were statistically different between the two groups. Likewise, neither the mean absolute volume of supratentorial functional fibers nor of the cortical M1 representation volumes differed between the two groups. Conclusion The study implicates that neither direct tumor infiltration of the M1 region or the CST nor the tumor volume nor the extension of perifocal edema in total may be the main causes for the primary motor deficit of brain tumor patients at initial presentation. In contrast, the extent of the perifocal edema affecting CST fibers seems to be responsible for motor deficits prior to surgery.

P 108. Robotized-navigated low-frequency repetitive transcranial magnetic stimulation over the right motor and prefrontal cortex improved pain and fatigue in patients with macrophagic myofasciitis

Question Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive way to modulate brain neural activities, able to modify cortical functions for clinical and therapeutic purposes. Neuromodulation induced by rTMS notably depends on the frequency of stimulation, equal or less than 1 Hz (low-frequency (LF) rTMS) or equal or more than 5 Hz (high-frequency (HF) rTMS). In patients with unilateral or asymmetric chronic neuropathic pain, HF-rTMS is known to be able to produce analgesic effects when applied to the motor cortex (precentral gyrus) contralateral to pain side. Analgesic effects of HF-rTMS have been also reported when applied to the left dominant motor cortex (M1) in patients with generalized non-neuropathic pain (fibromyalgia). Conversely, motor cortex LF-rTMS was found to be inefficacious in the same conditions. A therapeutic impact on pain syndromes was also observed following HF-rTMS delivered to the left dorsolateral prefrontal cortex (DLPFC), but LF-rTMS of the right DLPFC showed a similar efficacy, according to the theory of interhemispheric balance. In contrast, the potential analgesic effect of LF-rTMS of the right M1 has never been investigated. Methods In a randomized placebo-controlled and double-blinded study, the effects of robotized-navigated LF-TMS applied for two weeks over a target grid of the non-dominant right M1 or DLPFC were assessed in 24 right-handed patients with macrophagic myofasciitis (MFM). Symptomatic MFM represents a rare generalized pain syndrome induced by aluminium oxyhydroxide from vaccine injections. Assessments included measures of pain, fibromyalgia symptoms, quality of life, depression, anxiety, fatigue and cortical excitability. Results LF-rTMS of the right M1 but not of the right DLPFC reduced pain level for at least 4 weeks. Both M1 and DLPFC stimulation yielded significant effects on fibromyalgia symptom severity scale as well as on the cognitive and social components of fatigue. Conclusion For the first time we showed that LF-rTMS may have therapeutic effects in generalized pain, when applied to the non-dominant cortex. We also demonstrated the eligibility of a robotized-navigated rTMS procedure, allowing a precise stimulation over M1 or DLPFC regions, based on individual anatomical targeting.

Distinct roles of M1 and M3 muscarinic acetylcholine receptors controlling oscillatory and non-oscillatory [Ca2+]i increase

We examined ACh-induced [Ca2+]i dynamics in pancreatic acinar cells prepared from mAChR subtype-specific knockout (KO) mice. ACh did not induce any [Ca2+]i increase in the cells isolated from M1/M3 double KO mice. In the cells from M3KO mice, ACh (0.3–3μM) caused a monotonic [Ca2+]i increase. However, we found characteristic oscillatory [Ca2+]i increases in cells from M1KO mice in lower concentrations of ACh (0.03–0.3μM).We investigated the receptor specific pattern of [Ca2+]i increase in COS-7 cells transfected with M1 or M3 receptors. ACh induced the oscillatory [Ca2+]i increase in M3 expressing cells, but not in cells expressing M1, which exhibited monotonic [Ca2+]i increases. IP3 production detected in fluorescent indicator co-transfected cells was higher in M1 than in M3 expressing cells. From the examination of four types of M1/M3 chimera receptors we found that the carboxyl-terminal region of M3 was responsible for the generation of Ca2+ oscillations.The present results suggest that the oscillatory Ca2+ increase in response to M3 stimulation is dependent upon a moderate IP3 increase, which is suitable for causing Ca2+-dependent IP3-induced Ca2+ release. The C-terminal domain of M3 may contribute as a regulator of the efficiency of Gq and PLC cooperation.

Functional Corticospinal Projections from Human Supplementary Motor Area Revealed by Corticomuscular Coherence during Precise Grip Force Control

The purpose of the present study was to investigate whether corticospinal projections from human supplementary motor area (SMA) are functional during precise force control with the precision grip (thumb-index opposition). Since beta band corticomuscular coherence (CMC) is well-accepted to reflect efferent corticospinal transmission, we analyzed the beta band CMC obtained with simultaneous recording of electroencephalographic (EEG) and electromyographic (EMG) signals. Subjects performed a bimanual precise visuomotor force tracking task by applying isometric low grip forces with their right hand precision grip on a custom device with strain gauges. Concurrently, they held the device with their left hand precision grip, producing similar grip forces but without any precision constraints, to relieve the right hand. Some subjects also participated in a unimanual control condition in which they performed the task with only the right hand precision grip while the device was held by a mechanical grip. We analyzed whole scalp topographies of beta band CMC between 64 EEG channels and 4 EMG intrinsic hand muscles, 2 for each hand. To compare the different topographies, we performed non-parametric statistical tests based on spatio-spectral clustering. For the right hand, we obtained significant beta band CMC over the contralateral M1 region as well as over the SMA region during static force contraction periods. For the left hand, however, beta band CMC was only found over the contralateral M1. By comparing unimanual and bimanual conditions for right hand muscles, no significant difference was found on beta band CMC over M1 and SMA. We conclude that the beta band CMC found over SMA for right hand muscles results from the precision constraints and not from the bimanual aspect of the task. The result of the present study strongly suggests that the corticospinal projections from human SMA become functional when high precision force control is required.

In silico Identification of IgE-Binding Epitopes of Osmotin Protein

The identification of B-cell epitopes is an important step to study the antigen- antibody interactions for diagnosis and therapy. The present study aimed to identify B- cell epitopes of osmotin using bioinformatic tools and further modify these regions to study the allergenic property. B-cell epitopes were predicted based on amino acid physicochemical properties. Three single point mutations M1, M2, and M3 and a multiple point mutant (M123) were selected to disrupt the IgE binding. These mutants were cloned, expressed and proteins purified to homogeneity. The IgE binding of the purified proteins was evaluated by ELISA and ELISA inhibition with patients' sera. Three regions of osmotin M1 (57–70 aa), M2 (72–85 aa) and M3 (147–165 aa) were identified as potential antibody recognition sites using in silico tools. The sequence similarity search of the predicted epitopes of osmotin using Structural Database of Allergenic proteins (SDAP) showed similarity with known allergens from tomato, kiwifruit, bell pepper, apple, mountain cedar and cypress. Mutants M1, M2 and M3 showed up to 72%, 60% and 76% reduction, respectively in IgE binding whereas M123 showed up to 90% reduction with patients' sera. The immunoblot of M123 mutant showed 40% reduction in spot density as compared to osmotin. All mutants showed decreased inhibition potency with M123 exhibiting lowest potency of 32% with osmotin positive pooled patients' sera. The three B- cell epitopes of osmotin predicted by in silico method correlated with the experimental approach. The mutant M123 showed a reduction of 90% in IgE binding. The present method may be employed for prediction of B- cell epitopes of allergenic proteins.

Probing the Trans-Membrane Domain of GLIC, a Prokaryotic Ligand-Gated Ion Channel

The Gloeobacter ligand-gated ion channel, GLIC, has up to 28% sequence identity with eukaryotic Cys-loop receptors, and many key residues are conserved, especially in the 2nd trans-membrane pore lining region, M2. The M2 region is responsible for ion selectivity, ion flux, and binding a wide range of non-competitive inhibitors (Alqazzaz et al., 2011). The aim of this work was to investigate the GLIC M2 region, especially His235 (or 11'), which has been proposed as essential in proton sensing linked to channel opening (Wang et al., 2012), and residues that are conserved across the Cys-loop receptor family. To probe the roles of specific amino acids in GLIC M2 trans-membrane domain, we substituted M2 residues lining the ion pore and M2 residues facing M3 trans-membrane domains. We generated over 40 mutations at various positions including those at Glu 222(-2'), Thr 226 (2'), Ser 230 (6'), Leu 232 (8'), Ile 233 (9'), Ala 234 (10'), Ile 236 (12'), Ala 237 (13') and Phe 238 (14') using site-directed mutagenesis, and tested their function using two-electrode voltage clamp as previously described (Alqazzaz et al., 2011). Our results showed that Ser6', Ile9' and His11' residues are very sensitive to subsitution with all substituents resulting in non-functional receptors. We conclude that His 11' has a role in channel opening/closing, and the residues Thr226, Ser230, and Ile233 also play an important role in receptor function.Alqazzaz M, Thompson AJ, Price KL, Breitinger HG, Lummis SC (2011). Cys-loop receptor channel blockers also block GLIC. Biophysical journal 101(12): 2912-2918.Wang HL, Cheng X, Sine SM (2012). Intramembrane proton binding site linked to activation of bacterial pentameric ion channel. The Journal of biological chemistry 287(9): 6482-6489.

Cell and neuron densities in the primary motor cortex of primates

Cell and neuron densities vary across the cortical sheet in a predictable manner across different primate species (Collins et al., 2010b). Primary motor cortex, M1, is characterized by lower neuron densities relative to other cortical areas. M1 contains a motor representation map of contralateral body parts from tail to tongue in a mediolateral sequence. Different functional movement representations within M1 likely require specialized microcircuitry for control of different body parts, and these differences in circuitry may be reflected by variation in cell and neuron densities. Here we determined cell and neuron densities for multiple sub-regions of M1 in six primate species, using the semi-automated flow fractionator method. The results verify previous reports of lower overall neuron densities in M1 compared to other parts of cortex in the six primate species examined. The most lateral regions of M1 that correspond to face and hand movement representations, are more neuron dense relative to medial locations in M1, which suggests differences in cortical circuitry within movement zones.

Actinobacteria as essential symbionts in firebugs and cotton stainers (Hemiptera, Pyrrhocoridae)

Actinobacteria engage in defensive symbioses with several insect taxa, but reports of nutritional contributions to their hosts have been exceptionally rare. Cotton stainers (Dysdercus fasciatus) and red firebugs (Pyrrhocoris apterus) (both Hemiptera, Pyrrhocoridae) harbour the actinobacterial symbionts Coriobacterium glomerans and Gordonibacter sp. as well as Firmicutes (Clostridium sp. and Lactococcus sp.) and Proteobacteria (Klebsiella sp. and a Rickettsiales bacterium) in the M3 region of their mid-gut. We combined experimental manipulation with community-level analyses to elucidate the function of the gut symbionts in both pyrrhocorid species. Elimination of symbionts by egg-surface sterilization resulted in significantly higher mortality and reduced growth rates, indicating that the microbial community plays an important role for host nutrition. Fitness of symbiont-deprived bugs could be completely restored by re-infection with the original microbiota, while reciprocal cross-infections of microbial communities across both pyrrhocorid species only partially rescued fitness, demonstrating a high degree of host-symbiont specificity. Community-level analyses by quantitative PCRs targeting the dominant bacterial strains allowed us to link the observed fitness effects to the abundance of the two actinobacterial symbionts. The nutritional mutualism with Actinobacteria may have enabled pyrrhocorid bugs to exploit Malvales seeds as a food source and thereby possibly allowed them to occupy and diversify in this ecological niche.

Geographical and ecological stability of the symbiotic mid‐gut microbiota in European firebugs, Pyrrhocoris apterus (Hemiptera, Pyrrhocoridae)

Symbiotic bacteria often play an essential nutritional role for insects, thereby allowing them to exploit novel food sources and expand into otherwise inaccessible ecological niches. Although many insects are inhabited by complex microbial communities, most studies on insect mutualists so far have focused on single endosymbionts and their interactions with the host. Here, we provide a comprehensive characterization of the gut microbiota of the red firebug (Pyrrhocoris apterus, Hemiptera, Pyrrhocoridae), a model organism for physiological and endocrinological research. A combination of several culture-independent techniques (454 pyrosequencing, quantitative PCR and cloning/sequencing) revealed a diverse community of likely transient bacterial taxa in the mid-gut regions M1, M2 and M4. However, the completely anoxic M3 region harboured a distinct microbiota consisting of facultative and obligate anaerobes including Actinobacteria (Coriobacterium glomerans and Gordonibacter sp.), Firmicutes (Clostri-dium sp. and Lactococcus lactis) and Proteobacteria (Klebsiella sp. and a previously undescribed Rickettsiales bacterium). Characterization of the M3 microbiota in different life stages of P.apterus indicated that the symbiotic bacterial community is vertically transmitted and becomes well defined between the second and third nymphal instar, which coincides with the initiation of feeding. Comparing the mid-gut M3 microbial communities of P.apterus individuals from five different populations and after feeding on three different diets revealed that the community composition is qualitatively and quantitatively very stable, with the six predominant taxa being consistently abundant. Our findings suggest that the firebug mid-gut microbiota constitutes a functionally important and possibly coevolved symbiotic community.

Is There Pathology Associated With Asymptomatic Third Molars?

The purpose of this article was to estimate the proportion of patients with asymptomatic third molars (M3s) and evidence of disease at baseline and to measure the health risks of retained M3s in the long term. A literature search was conducted using Google Scholar. Search terms included third molars and periodontitis, pericoronitis, caries, odontogenic cysts or tumors, and infections. To be included in this review, studies were limited to prospective studies with samples of at least 50 subjects and a follow-up longer than 1 year. Periodontal pathology was associated with asymptomatic M3s. At baseline, 25% of 329 asymptomatic subjects enrolled in studies had at least 1 probing depth (PD) of at least 5 mm in the M3 region, distal of the second molars, or around the M3s, with at least 1-mm attachment lost in each patient. PDs deeper than 5 mm were associated with an attachment loss of at least 2 mm in 80 of 82 subjects. The clinical findings of increased periodontal PDs and periodontal attachment loss coupled with the colonization of periodontal pathogens supported the concept that clinical and microbial changes associated with the initiation of periodontitis may present first in the M3 region in young adults. For subjects with a baseline PD of at least 4 mm in the M3 region or baseline "orange and red" complex periodontal bacteria of at least 10(5), the odds were significantly increased for the progression of periodontal disease in the M3 region. The visible presence of M3s in young adults was significantly associated with periodontal inflammatory disease in non-M3s. The data suggest that the absence of symptoms associated with retained M3s does not equal the absence of disease or pathology. The clinical implications of these findings suggest that patients who elect to retain their M3s should have regular periodic clinical and radiographic examinations to detect disease before it becomes symptomatic.

Numerical simulations of the ionosphere of Mars during a solar flare

Electron densities in planetary ionospheres increase substantially during solar flares in response to the increased solar irradiance at soft X‐ray and extreme ultraviolet wavelengths. Here we modify an existing model of the ionosphere of Mars to incorporate time‐dependent solar irradiances and use it to simulate ionospheric conditions during the X14.4 and M7.8 solar flares of 15 and 26 April 2001, respectively. Simulations were validated by comparison to Mars Global Surveyor radio occultation measurements of vertical profiles of ionospheric electron density. Adjustments to the model's representation of the neutral atmosphere were required to adequately reproduce the observations before and during these solar flares. An accurate representation of electron‐impact ionization, an important process in the lower ionosphere of Mars, is required in order to adequately simulate the doubling of electron densities that can occur in the lower ionosphere of Mars during a solar flare. We used the W‐value representation of electron‐impact ionization, in which the number of ion‐electron pairs created per photon absorbed equals the ratio of the difference between photon energy and the ionization potential of carbon dioxide to the W‐value. A range of possible W‐values for Mars have been suggested in the literature, and a value of 28 eV led to the best reproduction of flare‐affected observations. Simulated enhancements in the electron density are largest and persist the longest in the M1 region. We predict that the peak electron density in the M1 region can exceed that of the M2 region for short periods during intense solar flares.

Effect of induced Dalton's lymphoma on circadian locomotor activity rhythm of adult male mice

Dalton's lymphoma (DL) is a spontaneous and highly invasive T-cell lymphoma that develops as an ascitic tumor in murines. DL was induced by serial implantation of live ascite cells in laboratory-acclimated age-matched male AKR mice. The effects of DL on the locomotor activity rhythm were studied under 12:12 h light:dark (LD) cycle. A significant decrease in the total and peak wheel-running activity was seen after the induction of DL, in comparison with the vehicle-injected control group. Durations of activity and rest were altered in DL mice, with a sharp daily increase in the duration of rest in the DL group. Circadian time period and acrophase of the rhythm remained similar in both control and DL mice. The mean estimate of statistic of rhythmicity (MESOR) and the amplitude of the locomotor activity rhythm were significantly lesser in post-DL-induced mice. A reduction in the span of the M1 and M2 motor cortex regions in DL mice and anatomical changes in the dentate gyrus were also seen. Thus, the effects of DL on the circadian clock seem restricted and mouse can still synchronize to an LD cycle. Impact of DL extends to motor cortices and may be the cause of the dampening of the amplitude of the rest-activity rhythm.

Amino acid residues of both the extracellular and transmembrane domains influence binding of the antiparasitic agent milbemycin to Haemonchus contortus AVR-14B glutamate-gated chloride channels

Glutamate-gated chloride (GluCl) channels are pentameric receptors for the inhibitory neurotransmitter glutamate in invertebrates and are a major target for macrolide anthelmintics. Three amino acids in GluCl channels are reported to render macrolide resistance in nematodes and insects. To examine whether these three amino acids are involved in binding of the antiparasitic agent milbemycin (MLM) to the GluCl channels of the nematode parasite Haemonchus contortus, the equivalent amino acids (L256, P316, and G329) of the Hco-AVR-14B subunit were substituted with various amino acids. cDNAs encoding the wild type and mutants of this subunit were transfected into COS-1 cells for transient expression and analysis of GluCl channels. The abilities of these mutant channels to bind [3H]MLM A4 were remarkably decreased when compared with the wild-type channel. In patch clamp analysis, L256F and P316S mutant channels were 37- and 100-fold less sensitive to MLM A4 when compared with the wild-type channel, respectively. These findings indicate that amino acid changes in the β10 strand, the M2–M3 linker, and the M3 region influence MLM A4 binding to the channel. Homology modeling and ligand docking studies suggest the presence of two potential binding sites for MLM A4.

Alpha6∗ Nicotinic Receptors and P2X Receptors: Physical and Functional Interactions

Several neuronal cell types co-express nicotinic acetylcholine receptors (nAChRs) and P2X receptors (P2XRs); and previous experiments from several laboratories show that these two ligand-gated channel subtypes interact with each other, both functionally and physically. We extended these studies to interactions between alpha6 subunit-containing (alpha6∗) nAChRs and P2X2 or P2X3 receptors (P2X2Rs, P2X3Rs). In Xenopus oocytes, alpha6 subunits mutated in the M2 region co-expressed with beta4 subunits displayed ACh-induced currents. P2X2 or P2X3 receptors expressed in the same oocytes displayed ATP-induced currents. When ACh and ATP were applied simultaneously, the total current was less than the sum of the individual currents_the conventional definition of cross-inhibition_for alpha6beta4-P2X2 oocytes. Several combinations of fluorescent protein (FP)-fused alpha6, beta4, P2X2, and P2X3 subunits were expressed in cultured mouse cortical cells and Neuro2a cells. In Forster resonance energy transfer (FRET) measurements using fluorescent lifetime imaging microscopy (FLIM) and normalized FRET (NFRET), we detected physical contact between alpha6beta2 nAChRs and P2X2Rs, between alpha6beta4 nAChRs and P2X2Rs, and between alpha6beta4 nAChRs and P2X3Rs. Thus, two lines of evidence show interactions between alpha6∗ nAChRs and P2XRs.Support: Beckman fellowship to CIR, NIH (NRSA to CIR, DA-19375, NS034407), Wellcome Trust, Yousef Jameel Award.

Desensitization of α7 Nicotinic Receptor Is Governed by Coupling Strength Relative to Gate Tightness

Binding of a neurotransmitter to its membrane receptor opens an integral ion conducting pore. However, prolonged exposure to the neurotransmitter drives the receptor to a refractory state termed desensitization, which plays an important role in shaping synaptic transmission. Despite intensive research in the past, the structural mechanism of desensitization is still elusive. Using mutagenesis and voltage clamp in an oocyte expression system, we provide several lines of evidence supporting a novel hypothesis that uncoupling between binding and gating machinery is the underlying mechanism for α7 nicotinic receptor (nAChR) desensitization. First, the decrease in gate tightness was highly correlated to the reduced desensitization. Second, nonfunctional mutants in three important coupling loops (loop 2, loop 7, and the M2-M3 linker) could be rescued by a gating mutant. Furthermore, the decrease in coupling strength in these rescued coupling loop mutants reversed the gating effect on desensitization. Finally, coupling between M1 and hinge region of the M2-M3 linker also influenced the receptor desensitization. Thus, the uncoupling between N-terminal domain and transmembrane domain, governed by the balance of coupling strength and gate tightness, underlies the mechanism of desensitization for the α7 nAChR.