Neural mechanisms for learning hierarchical structures of information

Spatial and temporal information from the environment is often hierarchically organized, so is our knowledge formed about the environment. Identifying the meaningful segments embedded in hierarchically structured information is crucial for cognitive functions, including visual, auditory, motor, memory, and language processing. Segmentation enables the grasping of the links between isolated entities, offering the basis for reasoning and thinking. Importantly, the brain learns such segmentation without external instructions. Here, we review the underlying computational mechanisms implemented at the single-cell and network levels. The network-level mechanism has an interesting similarity to machine-learning methods for graph segmentation. The brain possibly implements methods for the analysis of the hierarchical structures of the environment at multiple levels of its processing hierarchy.

Multiscale representations of community structures in attractor neural networks

Our cognition relies on the ability of the brain to segment hierarchically structured events on multiple scales. Recent evidence suggests that the brain performs this event segmentation based on the structure of state-transition graphs behind sequential experiences. However, the underlying circuit mechanisms are poorly understood. In this paper we propose an extended attractor network model for graph-based hierarchical computation which we call the Laplacian associative memory. This model generates multiscale representations for communities (clusters) of associative links between memory items, and the scale is regulated by the heterogenous modulation of inhibitory circuits. We analytically and numerically show that these representations correspond to graph Laplacian eigenvectors, a popular method for graph segmentation and dimensionality reduction. Finally, we demonstrate that our model exhibits chunked sequential activity patterns resembling hippocampal theta sequences. Our model connects graph theory and attractor dynamics to provide a biologically plausible mechanism for abstraction in the brain.

Our experiences are often hierarchically organized, so is our knowledge. Identifying meaningful segments in hierarchically structured information is crucial for many cognitive functions including visual, auditory, motor, memory, language processing, and reasoning. Herein, we show that the attractor dynamics of recurrent neural circuits offer a biologically plausible way for hierarchical segmentation. We found that an extended model of associative memory autonomously performs segmentation by finding groups of tightly linked memories. We proved that the neural dynamics of our model mathematically coincide with optimal graph segmentation in graph theory and are consistent with the experimentally observed nature of human behaviors and neural activities. Our model established a previously unexpected relationship between attractor neural networks and the graph-theoretic processing of knowledge structures. Our model also provides experimentally testable predictions, particularly regarding the role of inhibitory circuits in controlling representational granularity.

P6452Circulating human epididymis protein 4 is a novel prognostic predictor in ambulatory patients with non-ischemic dilated cardiomyopathy

Background

Myofibroblasts, which are activated fibroblasts, play an important role in interstitial fibrosis in non-ischemic dilated cardiomyopathy (NIDCM). Recently, human epididymal body protein 4 (HE4) has attracted attention as a marker specific to myofibroblasts. However, the prognostic impact of HE-4 on cardiovascular events in NIDCM patients has not been reported.

Purposes

The purpose of this study was to investigate the impact of circulating serum HE4 on the prognosis in patients with NIDCM.

Methods

Forty-four NIDCM patients underwent echocardiography, laboratory measurements, cardiac catheterization, and endomyocardial biopsy within one week under stable heart failure condition. Patients with cancer were excluded from this study. We collected blood samples from peripheral vain, ascending aorta, and coronary sinus during cardiac catheterization and measured serum HE4 level. They were divided into two groups at the median of HE4 level: High-HE4 group (HE4 >69 pmol/L); n=22, Low-HE4 group (HE4 <69 pmol/L); n=22. Cardiac composite event was defined as cardiac related deaths and hospitalization due to worsening heart failure.

Results

The mean age, left ventricular ejection fraction (LVEF), and plasma brain natriuretic peptide level were 56 years, 32%, and 205 pg/mL. Between two groups, there were no significant differences in age, gender, LVEF, left ventricular end-diastolic diameter, cardiac index, and pulmonary capillary wedge pressure. However, estimated glomerular filtration rate was significantly lower in the High-HE4 group (p=0.025). Kaplan-Meier survival analysis revealed that the High-HE group had a higher rate of cardiac composite event (p=0.011, see Figure). However, as for the pathological analysis, not only the peripheral HE4 level but also HE4 value subtracting coronary sinus from ascending aorta did not significantly correlate with collagen volume fraction in biopsy samples.

Circulating HE4 level and prognosis

Conclusion

Elevated circulating HE4 is associcated with poor prognosis in ambulatory patients with NIDCM.

P5417Splenic volume changes as a hemodynamic parameter in advanced heart failure with left ventricular assist device

Background

The spleen has been recognized as an important organ to reserve 20–30% of the total blood volume. Generally, splenomegaly has been thought to be related to congestion. However, in the setting of hypovolemic shock or hypoxemia, it has been reported that spleen contracted and splenic volume decreased. On the other hand, in advanced heart failure (HF), the hemodynamics is characterized by both low cardiac output (LO) and systemic congestion, and patients sometimes need support of left ventricular assist device (LVAD). However, it remains unclear about the association between spleen size and hemodynamic parameters in patients with LO who need LVAD support.

Purpose

The purpose of this study was to investigate the relationship between spleen size and hemodynamic parameters in advanced HF before and after LVAD implantation.

Methods

We enrolled 12 advanced HF patients with LVAD (11 males, 45±10 years). All patients underwent blood test, echocardiography, right heart catheterization, and computed tomography (CT) before and after LVAD implantation. Spleen size was measured by CT volumetry. We excluded patients with splenic infarction, or any infections, or mean right atrial pressure (RAP) <5mmHg because of a possibility of hypovolemic status. LO was defined as CI less than 2.2L/min/m2.

Results

At pre- and post-LVAD implantation, cardiac output, cardiac index (CI), mean RAP, and mean pulmonary capillary wedge pressure were 3.1±0.6 vs. 4.9±0.9L/min, p=0.002; 1.7±0.3 vs. 2.8±0.3L/min/m2, p=0.002; 14±5 vs. 9±3mmHg, p=0.059; and 30±7 vs. 10±3mmHg, p=0.002, respectively. The serum brain natriuretic peptide level had significantly decreased (1101 [517–1446] vs 74 [35–216] pg/mL, p=0.002). In all patients, CI had increased to over 2.2L/min/m2. The splenic volume significantly increased from pre- to post-LVAD implantation (172±48 vs. 233±78mL, p=0.002) (Figure). Furthermore, all patients were divided into two groups; elevated RAP group (n=4) and non-elevated RAP group (n=8) after LVAD support. In elevated RAP group, there were no significant changes in the spleen size between pre- and post-LVAD implantation (167±45 vs. 223±111mL, p=0.068). On the other hand, in non-elevated RAP group, the spleen volume had significantly increased from pre- to post-LVAD support (172±53 vs. 231±62mL, p=0.011). In addition, there was one patient whose hemodynamic state had changed to LO again because of LVAD failure due to pump thrombosis. In this case, the splenic volume was 212mL before LVAD implantation with LO, and increased to 418mL after LVAD implantation with non-LO, although decreased to 227mL after LVAD pump failure with LO again.

Splenic volume changes

Conclusions

The spleen may change its size in order to keep cardiac output by regulating cardiac preload depending on the systemic perfusion in advanced HF with LVAD.

Acknowledgement/Funding

None

P1581Early blood pressure reduction by intravenous vasodilators associates with acute kidney injury in patients with hypertensive acute decompensated heart failure

Background

In patients with hypertensive acute decompensated heart failure (ADHF), intravenous vasodilators are commonly used. However, little is known about optimal use in blood pressure (BP) management to avoid acute kidney injury (AKI).

Purpose

To investigate the association between systolic BP (SBP) changes in first 6 h and incidence of AKI within 48 h in patients with hypertensive ADHF.

Methods

Post-hoc analysis was performed on a prospectively enrolled cohort. We investigated 245 patients with ADHF and SBP >140 mmHg on arrival (mean age, 76 years; 40% female). We defined “SBP-fall” as maximum percent reduction in SBP 6h after intravenous treatment. AKI was defined as serum creatinine (SCr) ≥0.3 mg/dL, or urine output <0.5 mL/kg/h at 48 h.

Results

Mean SBP, SBP-fall and SCr level at arrival were 180 mmHg, 29.4%, and 1.21 mg/dL, respectively. Sixty-six patients experienced AKI. There were no significant differences in age, NYHA functional class, SBP and SCr at admission between AKI and Non-AKI group. AKI group had the greater SBP-fall compared with Non-AKI (36.7%versus 27.2%, p≤0.0001). Logistic regression analyses revealed that SBP-fall had an independent predictor of AKI (Table). In addition, SBP-fall had positive association with the number of concomitant used intravenous vasodilators in first 6 h (Figure).

Logistic regression analyses for AKI Univariate Multivariate AUC OR 95% CI P OR 95% CI P Ages, years, per 10 years 1.04 0.82–1.33 0.17 0.75 SBP at arrival, per 10 mmHg 1.01 0.93–1.11 0.77 SBP-fall, per 10% 1.49 1.22–1.81 <0.001 1.54 1.24–1.91 <0.001 HR, per 10 beat/min 1.12 1.00–1.25 0.049 1.07 0.95–1.21 0.28 COPD 2.95 1.06–8.21 0.04 3.06 0.99–9.43 0.054 SCr, per 1 mg/dL 1.40 0.83–2.37 0.21 Furosemide i.v. 1.12 0.42–2.95 0.82 Carperitide 3.22 1.69–6.13 0.0002 4.39 2.16–8.93 <0.001 NTG/ISDN i.v. 0.97 0.54–1.74 0.92 CCB i.v. 1.86 0.76–4.53 0.18 OR, odds ratio; CI, confidence interval; AUC, area under the curve; SBP, systolic blood pressure; COPD, chronic obstructive pulmonary disease; SCr, serum creatinine; i.v., intravenous; NTG, nitroglycerin; ISDN, isosorbide dinitrate; CCB, calcium channel blocker.

SBP-fall odds ration for AKI

Conclusion

In the first 6h of management for hypertensive ADHF patients, aggressive SBP reduction by the combination use of vasodilator agents predicted the incidence of AKI.

Extended Temporal Association Memory by Modulations of Inhibitory Circuits

Hebbian learning of excitatory synapses plays a central role in storing activity patterns in associative memory models. Interstimulus Hebbian learning associates multiple items by converting temporal correlation to spatial correlation between attractors. Growing evidence suggests the importance of inhibitory plasticity in memory processing, but the consequence of such regulation in associative memory has not been understood. Noting that Hebbian learning of inhibitory synapses yields an anti-Hebbian effect, we show that the combination of Hebbian and anti-Hebbian learning can significantly increase the span of temporal association between correlated attractors as well as the sensitivity of these states to external input. Furthermore, these effects are regulated by changing the ratio of local and global recurrent inhibition after learning weights for excitation-inhibition balance. Our results suggest a nontrivial role of plasticity and modulation of inhibitory circuits in associative memory.

Unsupervised Detection of Cell-Assembly Sequences by Similarity-Based Clustering

Neurons which fire in a fixed temporal pattern (i.e., "cell assemblies") are hypothesized to be a fundamental unit of neural information processing. Several methods are available for the detection of cell assemblies without a time structure. However, the systematic detection of cell assemblies with time structure has been challenging, especially in large datasets, due to the lack of efficient methods for handling the time structure. Here, we show a method to detect a variety of cell-assembly activity patterns, recurring in noisy neural population activities at multiple timescales. The key innovation is the use of a computer science method to comparing strings ("edit similarity"), to group spikes into assemblies. We validated the method using artificial data and experimental data, which were previously recorded from the hippocampus of male Long-Evans rats and the prefrontal cortex of male Brown Norway/Fisher hybrid rats. From the hippocampus, we could simultaneously extract place-cell sequences occurring on different timescales during navigation and awake replay. From the prefrontal cortex, we could discover multiple spike sequences of neurons encoding different segments of a goal-directed task. Unlike conventional event-driven statistical approaches, our method detects cell assemblies without creating event-locked averages. Thus, the method offers a novel analytical tool for deciphering the neural code during arbitrary behavioral and mental processes.

Neuronal stability in medial frontal cortex sets individual variability in decision-making

In the brain, decision making is instantiated in dedicated neural circuits. However, there is considerable individual variability in decision-making behavior, particularly under uncertainty. The origins of decision variability within these conserved neural circuits are not known. Here we demonstrate in the rat medial frontal cortex (MFC) that individual variability is a consequence of altered stability in neuronal populations. In a sensory-guided choice task, rats trained on familiar stimuli were exposed to unfamiliar stimuli, resulting in variable choice responses across individuals. We created a recurrent network model to examine the source of variability in MFC neurons, and found that the landscape of neural population trajectories explained choice variability across different unfamiliar stimuli. We experimentally confirmed model predictions showing that trial-by-trial variability in neuronal activity indexes the landscape and predicts individual variation. These results show that neural stability is a critical component of the MFC neural dynamics that underpins individual variation in decision-making.

Dendritic processing of spontaneous neuronal sequences for single-trial learning

Spontaneous firing sequences are ubiquitous in cortical networks, but their roles in cellular and network-level computations remain unexplored. In the hippocampus, such sequences, conventionally called preplay, have been hypothesized to participate in learning and memory. Here, we present a computational model for encoding input sequence patterns into internal network states based on the propagation of preplay sequences in recurrent neuronal networks. The model instantiates two synaptic pathways in cortical neurons, one for proximal dendrite-somatic interactions to generate intrinsic preplay sequences and the other for distal dendritic processing of extrinsic signals. The core dendritic computation is the maximization of matching between patterned activities in the two compartments through nonlinear spike generation. The model performs robust single-trial learning with long-term stability and independence that are modulated by the plasticity of dendrite-targeted inhibition. Our results demonstrate that dendritic computation enables somatic spontaneous firing sequences to act as templates for rapid and stable memory formation.

Correction to: Reproducibility and Validity of a Questionnaire Measuring Treatment Burden on Patients with Type 2 Diabetes: Diabetic Treatment Burden Questionnaire (DTBQ)

In the original publication, second author's name was incorrectly published as Hiroki Shin. The correct name should read as 'Koki Shin'.

Recurrent network model for learning goal-directed sequences through reverse replay

Reverse replay of hippocampal place cells occurs frequently at rewarded locations, suggesting its contribution to goal-directed path learning. Symmetric spike-timing dependent plasticity (STDP) in CA3 likely potentiates recurrent synapses for both forward (start to goal) and reverse (goal to start) replays during sequential activation of place cells. However, how reverse replay selectively strengthens forward synaptic pathway is unclear. Here, we show computationally that firing sequences bias synaptic transmissions to the opposite direction of propagation under symmetric STDP in the co-presence of short-term synaptic depression or afterdepolarization. We demonstrate that significant biases are created in biologically realistic simulation settings, and this bias enables reverse replay to enhance goal-directed spatial memory on a W-maze. Further, we show that essentially the same mechanism works in a two-dimensional open field. Our model for the first time provides the mechanistic account for the way reverse replay contributes to hippocampal sequence learning for reward-seeking spatial navigation.

Reproducibility and Validity of a Questionnaire Measuring Treatment Burden on Patients with Type 2 Diabetes: Diabetic Treatment Burden Questionnaire (DTBQ)

INTRODUCTION

To measure the burden of pharmacotherapy on patients with type 2 diabetes mellitus (T2DM), we developed the Diabetes Treatment Burden Questionnaire (DTBQ), a patient-administered questionnaire composed of 18 questions, and evaluated its reproducibility and validity.

METHODS

We enrolled 240 patients with T2DM under pharmacotherapy over 20 years of age at seven institutes in Japan. Their physicians filled out report forms on patient backgrounds, and the patients answered both the DTBQ and the Diabetes Treatment Satisfaction Questionnaire (DTSQ). For evaluation of reproducibility, 48 of the enrolled subjects completed a 2nd DTBQ at home after leaving the medical institutes.

RESULTS

Statistical analyses were performed for two sets of subjects, the validity analysis set (N = 236) and the reproducibility analysis set (N = 47). Factor analysis found a simple structure in the DTBQ item scores using a three-factor model with varimax rotation; the three subscales were designated as "implementation burden", "flexibility burden", and "blood glucose control burden". All intraclass correlation coefficients for the subscale scores were 0.8 or higher, indicating high reproducibility. Negative correlations were observed between the DTSQ satisfaction score and the DTBQ subscale scores. Moreover, as the dosing frequency of diabetic medicines increased, the DTBQ total score (total burden score) also became higher. Likewise, expected associations were observed between patient backgrounds and DTSQ scores.

CONCLUSION

The DTBQ has adequate reproducibility and validity as a measurement scale for treatment burden on T2DM patients.

TRIAL REGISTRATION

University Hospital Medical Information Network (UMIN) 000026382.

FUNDING

Eli Lilly Japan.

Temporal relation between neural activity and neurite pruning on a numerical model and a microchannel device with micro electrode array

Synapse elimination and neurite pruning are essential processes for the formation of neuronal circuits. These regressive events depend on neural activity and occur in the early postnatal days known as the critical period, but what makes this temporal specificity is not well understood. One possibility is that the neural activities during the developmentally regulated shift of action of GABA inhibitory transmission lead to the critical period. Moreover, it has been reported that the shifting action of the inhibitory transmission on immature neurons overlaps with synapse elimination and neurite pruning and that increased inhibitory transmission by drug treatment could induce temporal shift of the critical period. However, the relationship among these phenomena remains unclear because it is difficult to experimentally show how the developmental shift of inhibitory transmission influences neural activities and whether the activities promote synapse elimination and neurite pruning. In this study, we modeled synapse elimination in neuronal circuits using the modified Izhikevich's model with functional shifting of GABAergic transmission. The simulation results show that synaptic pruning within a specified period like the critical period is spontaneously generated as a function of the developmentally shifting inhibitory transmission and that the specific firing rate and increasing synchronization of neural circuits are seen at the initial stage of the critical period. This temporal relationship was experimentally supported by an in vitro primary culture of rat cortical neurons in a microchannel on a multi-electrode array (MEA). The firing rate decreased remarkably between the 18-25 days in vitro (DIV), and following these changes in the firing rate, the neurite density was slightly reduced. Our simulation and experimental results suggest that decreasing neural activity due to developing inhibitory synaptic transmission could induce synapse elimination and neurite pruning at particular time such as the critical period. Additionally, these findings indicate that we can estimate the maturity level of inhibitory transmission and the critical period by measuring the firing rate and the degree of synchronization in engineered neural networks.

Mr Imaging of Chronic Alcoholism

We evaluated the brain lesions of patients with chronic alcoholism (n = 34) in comparison with age- and sex-matched controls (n = 40) by MR imaging. T1-weighted sagittal and axial images and T2-weighted axial images were obtained with a 0.5 T superconducting MR unit. Various brain measurements were then performed, and the presence of regions of abnormal signal intensity was also compared between the two groups. The brain measurements revealed significant cerebral atrophy (characterized by lateral and 3rd ventricular dilatation, and widening of the interhemispheric fissure) as well as significant cerebellar atrophy (represented by 4th ventricular dilatation) in the alcoholic group. These changes were more prominent in patients in their fifties and sixties than in those aged in the thirties and forties. Focal hypointense lesions were observed in 20.6% of the alcoholics and in 5% of the controls (p < 0.01), while focal hyperintense lesions were observed in 61.8% of the alcoholics and in 20% of the controls (p < 0.001). The severity of these MR findings correlated well with the age of the patients. These observations suggest that alcohol is an important promotor of brain aging.

Zachsia zenkewitschi (Teredinidae), a Rare and Unusual Seagrass Boring Bivalve Revisited and Redescribed

The sea-grass borer Zachsia zenkewitschi belongs to a group of economically and ecologically important bivalves, commonly referred to as shipworms. The sole recognized representative of the genus Zachsia, this species displays an unusual life history and reproductive strategy that is now understood to include: environmental sex determination of free swimming larvae, extreme sexual and size dimorphism between males and females, internal fertilization, maintenance of often large harems of male dwarfs within a specialized cavity of the female mantle, and complex maternal care of larvae in specialized brood pouches within the gill. It is also the only shipworm species known to burrow in sea grass rhizomes rather than terrestrial wood. Although Z. zenkewitschi is rare and little studied, understanding of its biology and anatomy has evolved substantially, rendering some aspects of its original description inaccurate. Moreover, no existing type specimens are known for this species. In light of these facts, we designate a neotype from among specimens recently collected at the type location, and undertake a re-description of this species, accounting for recent reinterpretation of its life history and functional anatomy.

Role of the third intracellular loop in the subtype-specific internalization and recycling of muscarinic M2 and M4 receptors

Muscarinic M2, M4, and M2-M4 chimera receptors were transiently expressed in HEK-293 tsA201 cells, and agonist-dependent internalization of these receptors and recycling of internalized receptors were examined by measuring the amount of cell-surface receptors as [3H]N-methylscopolamine (NMS) binding activity. Coexpression of a dominant negative form of dynamin (DN-dynamin,dynamin K44A) greatly reduced the agonist-dependent internalization of M4 receptors but not of M2 receptors, as was reported by Vögler et al. (J Biol Chem 273, 12155-12160, 1998).The agonist-dependent internalization of M2/M4-i3/M2 chimera receptors (M2 receptors with the i3 loop replaced by that of M4 receptors) was greatly reduced by co-expression of DN-dynamin as was the case for M4 receptors, whereas the agonist-dependent internalization of M4/M2-i3/M4 chimera receptors was hardly affected by co-expression of DN-dynamin as was the case for M2 receptors.Internalized M2/M4-i3/M2 receptors as well as internalized M4 receptors were shown to be recycled back to the cell surface after removal of agonists, whereas no recycling was observed for M4/M2-i3/M4 receptors as well as M2 receptors. These results indicate that the i3 loops of M2 and M4 receptors take a major role in their agonist-dependent internalization and recycling.

Wearable blood flowmeter appcessory with low-power laser Doppler signal processing for daily-life healthcare monitoring

A new appcessory for monitoring peripheral blood flow in daily life consists of a wearable laser Doppler sensor device and a cooperating smart phone application. Bluetooth Low Energy connects them wirelessly. The sensor device features ultralight weight of 15 g and an intermittent signal processing technique that reduces power consumption to only 7 mW at measurement intervals of 0.1 s. These features enable more than 24-h continuous monitoring of peripheral blood flow in daily life, which can provide valuable vital-sign information for healthcare services.

Molecular properties of the high-affinity choline transporter CHT1

This article summarizes molecular properties of the high-affinity choline transporter (CHT1) with reference to the historical background focusing studies performed in laboratories of the author. CHT1 is present on the presynaptic terminal of cholinergic neurons, and takes up choline which is the precursor of acetylcholine. The Na(+)-dependent uptake of choline by CHT1 is the rate-limiting step for synthesis of acetylcholine. CHT1 is the integral membrane protein with 13 transmembrane segments, belongs to the Na(+)/glucose co-transporter family (SLC5), and has 20-25% homology with members of this family. A single nucleotide polymorphism (SNP) for human CHT1 has been identified, which has a replacement from isoleucine to valine in the third transmembrane segment and shows the choline uptake activity of 50-60% as much as that of wild-type CHT1. The proportion of this SNP is high among Asians. Possible importance of choline diet for those with this SNP was discussed.

Interaction of the muscarinic acetylcholine receptor M₂ subtype with G protein Gα(i/o) isotypes and Gβγ subunits as studied with the maltose-binding protein-M₂-Gα(i/o) fusion proteins expressed in Escherichia coli

We expressed the fusion proteins of the muscarinic acetylcholine receptor M2 subtype (M2 receptor) with a maltose-binding protein (MBP) and various G protein α subunits (Gα(i1-i3/o)) at its N- and C-terminals, respectively (MBP-M2-Gα(i/o)), in Escherichia coli, and examined the effect of G protein βγ subunits (Gβγ) on the receptor-Gα interaction as assessed by agonist- and GDP-dependent [(35)S]GTPγS binding of the fusion proteins. We found that (i) Gβγ promoted both the agonist-dependent and -independent [(35)S]GTPγS binding with little effect on the guanine nucleotide-sensitive high-affinity agonist binding, (ii) the specific [(35)S]GTPγS binding activity was much greater for MBP-M2-Gα(oA) than for MBP-M2-Gα(i1-i3) in the absence of Gβγ, whereas Gβγ preferentially promoted the agonist-dependent decrease in the affinity for GDP of MBP-M2-Gα(i1-i3) rather than of MBP-M2-Gα(oA), and (iii) the proportion of agonist-dependent [(35)S]GTPγS binding was roughly 50% irrespective of species of Gα and the presence or absence of Gβγ. These results demonstrate that receptor-Gα fusion proteins expressed in E. coli could be useful for studies of receptor-G interaction.

Estimation of templates and timings of spikes in extracellular voltage signals containing overlaps of the arbitrary number of spikes

Development of methods to detect and classify neural spikes in extracellular voltage signals (e.g. commonly referred to as spike sorting) have been one of important subjects in neuroscience and neural engineering. Most of previous spike sorting methods suffer from unresolved overlaps of spike waveforms which make timings and shapes of spikes unclear. Some methods have got a handle on this problem, but they had restrictions about the type of electrodes or complexity of overlaps. In this paper, we attempted to develop a spike sorting method for the signal containing overlaps of the arbitrary number of spikes recorded with arbitrary electrodes. We estimated templates and timings of spikes by the inference based on hidden Markov model. In order to avoid the problem of too high computational cost and too much decomposition caused by assuming arbitrary overlaps, we imposed the weak probabilistic penalty on overlaps in the model and reduced computation of estimation by approximating low probabilities to zero. As the result of assessments using simulated signal and real extracellular recordings, we showed that proposed method could robustly detect and sort complexly overlapped spikes.

Efficient sequential Bayesian inference method for real-time detection and sorting of overlapped neural spikes

Overlapping of extracellularly recorded neural spike waveforms causes the original spike waveforms to become hidden and merged, confounding the real-time detection and sorting of these spikes. Methods proposed for solving this problem include using a multi-trode or placing a restriction on the complexity of overlaps. In this paper, we propose a rapid sequential method for the robust detection and sorting of arbitrarily overlapped spikes recorded with arbitrary types of electrodes. In our method, the probabilities of possible spike trains, including those that are overlapping, are evaluated by sequential Bayesian inference based on probabilistic models of spike-train generation and extracellular voltage recording. To reduce the high computational cost inherent in an exhaustive evaluation, candidates with low probabilities are considered as impossible candidates and are abolished at each sampling time to limit the number of candidates in the next evaluation. In addition, the data from a few subsequent sampling times are considered and used to calculate the "look-ahead probability", resulting in improved calculation efficiency due to a more rapid elimination of candidates. These sufficiently reduce computational time to enable real-time calculation without impairing performance. We assessed the performance of our method using simulated neural signals and actual neural signals recorded in primary cortical neurons cultured on a multi-electrode array. Our results demonstrated that our computational method could be applied in real-time with a delay of less than 10 ms. The estimation accuracy was higher than that of a conventional spike sorting method, particularly for signals with multiple overlapping spikes.

Molecular properties of muscarinic acetylcholine receptors

Muscarinic acetylcholine receptors, which comprise five subtypes (M1-M5 receptors), are expressed in both the CNS and PNS (particularly the target organs of parasympathetic neurons). M1-M5 receptors are integral membrane proteins with seven transmembrane segments, bind with acetylcholine (ACh) in the extracellular phase, and thereafter interact with and activate GTP-binding regulatory proteins (G proteins) in the intracellular phase: M1, M3, and M5 receptors interact with Gq-type G proteins, and M2 and M4 receptors with Gi/Go-type G proteins. Activated G proteins initiate a number of intracellular signal transduction systems. Agonist-bound muscarinic receptors are phosphorylated by G protein-coupled receptor kinases, which initiate their desensitization through uncoupling from G proteins, receptor internalization, and receptor breakdown (down regulation). Recently the crystal structures of M2 and M3 receptors were determined and are expected to contribute to the development of drugs targeted to muscarinic receptors. This paper summarizes the molecular properties of muscarinic receptors with reference to the historical background and bias to studies performed in our laboratories.

Transmembrane topology and oligomeric structure of the high-affinity choline transporter

The high-affinity choline transporter CHT1 mediates choline uptake essential for acetylcholine synthesis in cholinergic nerve terminals. CHT1 belongs to the Na(+)/glucose cotransporter family (SLC5), which is postulated to have a common 13-transmembrane domain core; however, no direct experimental evidence for CHT1 transmembrane topology has yet been reported. We examined the transmembrane topology of human CHT1 using cysteine-scanning analysis. Single cysteine residues were introduced into the putative extra- and intracellular loops and probed for external accessibility for labeling with a membrane-impermeable, sulfhydryl-specific biotinylating reagent in intact cells expressing these mutants. The results provide experimental evidence for a topological model of a 13-transmembrane domain protein with an extracellular amino terminus and an intracellular carboxyl terminus. We also constructed a three-dimensional homology model of CHT1 based on the crystal structure of the bacterial Na(+)/galactose cotransporter, which supports our conclusion of CHT1 transmembrane topology. Furthermore, we examined whether CHT1 exists as a monomer or oligomer. Chemical cross-linking induces the formation of a higher molecular weight form of CHT1 on the cell surface in HEK293 cells. Two different epitope-tagged CHT1 proteins expressed in the same cells can be co-immunoprecipitated. Moreover, co-expression of an inactive mutant I89A with the wild type induces a dominant-negative effect on the overall choline uptake activity. These results indicate that CHT1 forms a homo-oligomer on the cell surface in cultured cells.

Microfabrication- and microfluidics-based patterning of cultured neuronal network

The cultured neuronal monolayer has been a promising model system for studying the neuronal dynamics, from single cell to network-wide level. Randomness in the reconstituted network structure has, however, hindered regulated signal transmissions from one neuron to another or from one neuronal population to another. Applying microfabrication-based cell patterning techniques is a promising approach to handling these problems. In the present study, we attempt to regulate the direction of axon development and the pathway of signal transmissions in cultured neuronal networks using micro-fabrication and - fluidic techniques. We created a PDMS-based culture device, which consisted of arrays of U-shaped cell trapping microwells, and placed it onto a chemically micropatterned glass substrate. After 6 days in vitro, we confirmed that cortical neurons extended neurites along the medium flow direction and the micropatterned regions.

The high-affinity choline transporter CHT1 is regulated by the ubiquitin ligase Nedd4-2

The high-affinity choline transporter (CHT1), which is specifically expressed in cholinergic neurons, constitutes a rate-limiting step for acetylcholine synthesis. We have found that the exogenous ubiquitin ligase Nedd4-2 interacts with CHT1 expressed in HEK293 cells decreasing the amount of cell surface CHT1 by approximately 40%, and that small interfering RNA for endogenous Nedd4-2 enhances the choline uptake activity by CHT1 in HEK293 cells. These results indicate that Nedd4-2-mediated ubiquitination regulates the cell surface expression of CHT1 in cultured cells and suggest a possibility that treatments or drugs which inhibit the interaction between CHT1 and Nedd4-2 might be useful for diseases involving decrease in acetylcholine level such as Alzheimer's disease.

Platform for the rapid construction and evaluation of GPCRs for crystallography in Saccharomyces cerevisiae

BACKGROUND

Recent successes in the determination of G-protein coupled receptor (GPCR) structures have relied on the ability of receptor variants to overcome difficulties in expression and purification. Therefore, the quick screening of functionally expressed stable receptor variants is vital.

RESULTS

We developed a platform using Saccharomyces cerevisiae for the rapid construction and evaluation of functional GPCR variants for structural studies. This platform enables us to perform a screening cycle from construction to evaluation of variants within 6-7 days. We firstly confirmed the functional expression of 25 full-length class A GPCRs in this platform. Then, in order to improve the expression level and stability, we generated and evaluated the variants of the four GPCRs (hADRB2, hCHRM2, hHRH1 and hNTSR1). These stabilized receptor variants improved both functional activity and monodispersity. Finally, the expression level of the stabilized hHRH1 in Pichia pastoris was improved up to 65 pmol/mg from negligible expression of the functional full-length receptor in S. cerevisiae at first screening. The stabilized hHRH1 was able to be purified for use in crystallization trials.

CONCLUSIONS

We demonstrated that the S. cerevisiae system should serve as an easy-to-handle and rapid platform for the construction and evaluation of GPCR variants. This platform can be a powerful prescreening method to identify a suitable GPCR variant for crystallography.

Detection of aqueous glucose based on a cavity size- and optical-wavelength-independent continuous-wave photoacoustic technique

Toward the achievement of noninvasive and continuous monitoring of blood glucose level, we developed a new measurement method based on the continuous-wave photoacoustic (CW-PA) technique and performed the first validation in vitro with calibrated aqueous glucose solutions. The PA technique has been studied in the past but exclusively based on the pulse setup since the CW one exhibits dependence on the cavity dimensions, which is not compatible with the final application requirements. This paper describes a new strategy relying on the monitoring of the resonant-frequency relative shift induced by the change of glucose concentrations rather than amplitude signal levels at a fixed frequency. From in vitro results, we demonstrate a stable and reproducible response to glucose at various cavity dimensions and optical wavelengths, with a slope of 0.19 ±0.01%/g/dL. From theoretical considerations, this method is consistent with a relative acoustic velocity measurement, which also explains the aforementioned stability. The proposed method then resolves most of the issues usually associated with the CW-PA technique and makes it a potential alternative for the noninvasive and continuous monitoring of glycemia levels. However, experimental determination of sensor responses to albumin and temperature as two potential interferents shows similar levels, which points to the selectivity to glucose as a major issue we should deal with in future development.

stx genotype and molecular epidemiological analyses of Shiga toxin-producing Escherichia coli O157:H7/H- in human and cattle isolates

The relationship between human diseases caused by infection with Shiga toxin (Stx)-producing Escherichia coli (STEC) O157 strains and O157 strains isolated from cattle was investigated in an area where stockbreeding is prolific. For this purpose, the stx genotypes, the molecular epidemiological characteristics of 268 STEC O157 strains including 211 human-origin strains and 57 cattle-origin strains, and clinical manifestations of 210 STEC-infected people were analyzed. Of 211 human-origin strains, 92 strains (44%) were of the stx1/stx2 genotype, and 74 strains (35%) were of the stx2c genotype. Most of the people infected with stx2c genotype strains presented no symptoms or mild symptoms such as slight diarrhea, except for 3 patients with bloody diarrhea. Of the 57 cattle-origin strains, 27 strains (47%) were of the stx2c genotype and 17 strains (30%) were of the stx1/stx2 genotype. Pulsed-field gel electrophoresis (PFGE) and insertion sequence (IS) analysis demonstrated that 11 isolates (41%) of the 27 cattle isolates of the stx2c genotype had high homology (>95% identity) with human isolates. These results suggest that some genetic patterns of the stx2c genotype strains might be preserved in cattle or their surrounding environment for several years, and during these periods, they might have opportunities to infect people through various routes. Because of the mild virulence of the stx2c genotype strains, they seemed to be transmitted asymptomatically from cattle to humans and then spread from person to person. It may be a public health concern. Further, they occasionally cause severe symptoms in humans; therefore, caution is warranted for infections by stx2c genotype O157 strains, in addition to stx2-possessing genotype O157 strains.

Evaluation of the Pichia pastoris expression system for the production of GPCRs for structural analysis

Background

Various protein expression systems, such as Escherichia coli (E. coli), Saccharomyces cerevisiae (S. cerevisiae), Pichia pastoris (P. pastoris), insect cells and mammalian cell lines, have been developed for the synthesis of G protein-coupled receptors (GPCRs) for structural studies. Recently, the crystal structures of four recombinant human GPCRs, namely β₂ adrenergic receptor, adenosine A_2a receptor, CXCR4 and dopamine D3 receptor, were successfully determined using an insect cell expression system. GPCRs expressed in insect cells are believed to undergo mammalian-like posttranscriptional modifications and have similar functional properties than in mammals. Crystal structures of GPCRs have not yet been solved using yeast expression systems. In the present study, P. pastoris and insect cell expression systems for the human muscarinic acetylcholine receptor M2 subtype (CHRM2) were developed and the quantity and quality of CHRM2 synthesized by both expression systems were compared for the application in structural studies.

Results

The ideal conditions for the expression of CHRM2 in P. pastoris were 60 hr at 20°C in a buffer of pH 7.0. The specific activity of the expressed CHRM2 was 28.9 pmol/mg of membrane protein as determined by binding assays using [³H]-quinuclidinyl benzilate (QNB). Although the specific activity of the protein produced by P. pastoris was lower than that of Sf9 insect cells, CHRM2 yield in P. pastoris was 2-fold higher than in Sf9 insect cells because P. pastoris was cultured at high cell density. The dissociation constant (Kd) for QNB in P. pastoris was 101.14 ± 15.07 pM, which was similar to that in Sf9 insect cells (86.23 ± 8.57 pM). There were no differences in the binding affinity of CHRM2 for QNB between P. pastoris and Sf9 insect cells.

Conclusion

Compared to insect cells, P. pastoris is easier to handle, can be grown at lower cost, and can be expressed quicker at a large scale. Yeast, P. pastoris, and insect cells are all effective expression systems for GPCRs. The results of the present study strongly suggested that protein expression in P. pastoris can be applied to the structural and biochemical studies of GPCRs.

Acetylcholine synthesis and release in NIH3T3 cells coexpressing the high-affinity choline transporter and choline acetyltransferase

Acetylcholine (ACh) is known to be a key neurotransmitter in the central and peripheral nervous systems, but it is also produced in a variety of non-neuronal tissues and cells, including lymphocytes, placenta, amniotic membrane, vascular endothelial cells, keratinocytes, and epithelial cells in the digestive and respiratory tracts. To investigate contribution made by the high-affinity choline transporter (CHT1) to ACh synthesis in both cholinergic neurons and nonneuronal cells, we transfected rat CHT1 cDNA into NIH3T3ChAT cells, a mouse fibroblast line expressing mouse choline acetyltransferase (ChAT), to establish the NIH3T3ChAT 112-1 cell line, which stably expresses both CHT1 and ChAT. NIH3T3ChAT 112-1 cells showed increased binding of the CHT1 inhibitor [(3)H]hemicholinium-3 (HC-3) and greater [(3)H]choline uptake and ACh synthesis than NIH3T3ChAT 103-1 cells, a CHT1-negative control cell line. HC-3 significantly inhibited ACh synthesis in NIH3T3ChAT 112-1 cells but did not affect synthesis in NIH3T3ChAT 103-1 cells. ACh synthesis in NIH3T3ChAT 112-1 cells was also reduced by amiloride, an inhibitor of organic cation transporters (OCTs) involved in low-affinity choline uptake, and by procaine and lidocaine, two local anesthetics that inhibit plasma membrane phospholipid metabolism. These results suggest that CHT1 plays a key role in ACh synthesis in NIH3T3ChAT 112-1 cells and that choline taken up by OCTs or derived from the plasma membrane is also utilized for ACh synthesis in both cholinergic neurons and nonneuronal cholinergic cells, such as lymphocytes.

Comparison of functional non-glycosylated GPCRs expression in Pichia pastoris

N-linked glycosylation is the most common post-translational modification of G-protein-coupled receptors (GPCRs) and is correlated to the localization and function of the receptors depending on each receptor. However, heterogeneity of glycosylation can interfere with protein crystallization. The removal of N-linked glycosylation from membrane proteins improves the ability to crystallize these proteins. We screened 25 non-glycosylated GPCRs for functional receptor production in the methylotrophic yeast Pichia pastoris using specific ligand-receptor binding assays. We found that five clones were expressed at greater than 10 pmol/mg, 9 clones at 1-10 pmol/mg and 11 clones at less than 1 pmol/mg of membrane protein. Further optimization of culture parameters including culture scale, induction time, pH and temperature enabled us to achieve expression of a functional human muscarinic acetylcholine receptor subtype 2 (CHRM2) with a B(max) value of 51.2 pmol/mg of membrane protein. Approximately 1.9 mg of the human CHRM2 was produced from a 1-L culture.

Differential rate constants of racemization of aspartyl and asparaginyl residues in human alpha A-crystallin mutants

Asp58 and Asp151 in alpha A-crystallin of human eye lenses become highly inverted and isomerized to d-beta-Asp residues with age. Racemization was previously shown to proceed rapidly when the residue on the carboxyl side of the Asp residue is small. Asn was also demonstrated to be more susceptible to racemization than Asp in protein. In this study, the changes of rate constants for racemization at Asp58 and Asp151 and at Asn58 and Asn151 were investigated using D58N, S59T, D151N and A152V mutants obtained through site-directed mutagenesis. The rate constant of racemization at Asn151 in D151N was found to be 1.5 times more rapid than Asp151 in the wild-type. For A152V, the rate constant at Asp151 was 1/4 that of the wild-type. There were no significant differences in the rate constants of racemization for both Asp58 and Asn58 residues. The aggregate size of D58N, S59T and D151N mutants increased or increased in polydispersity and their chaperone activities decreased. The size and chaperone activity of A152V was unchanged. These results suggest that structures close to Asp58 and Asp151 residues in the protein affect the rate constant of Asp racemization and the size and chaperone function of alpha A-crystallin.

Muscarinic M4 receptor recycling requires a motif in the third intracellular loop

The present study was performed to identify sequence(s) in the third intracellular loop (i3) of the muscarinic acetylcholine receptor M4 subtype (M4 receptor) involved in its internalization and recycling. In transiently transfected human embryonic kidney 293-tsA201 cells, 40 to 50% of cell-surface M4 receptors are internalized in an agonist-dependent manner, and approximately 65% of internalized receptors are recycled back to the cell surface after removal of the agonist. We examined the internalization and recycling of M4 receptor mutants with partial deletion in i3 and found that various mutants (M4del-K(235)-K(240), M4del-T(241)-K(271), and M4del-W(339)-N(372)) showed internalization and cell-surface recycling in a similar manner to the M4 receptor. We also found that the mutant M4del-L(272)-R(338) was internalized to only half the extent of the M4 receptor and was recycled after agonist removal, and the mutant M4del-V(373)-A(393) was also internalized to half the extent of the wild type but was not recycled back to the cell surface after agonist removal. When the sequence corresponding to Val(373)-Ala(393) was grafted onto the i3 portion of a recycling-negative mutant of muscarinic M2 receptor with deletion of almost the whole of the i3 sequence, approximately 40% of the chimeric receptor on the cell surface was internalized, and more than 65% of the internalized receptors were recycled back to the cell surface. These results indicate that the regions including Leu(272)-Arg(338) and Val(373)-Ala(393) are involved in internalization of the M4 receptor, and the region including Val(373)-Ala(393) is indispensable for its recycling, whereas the other regions of i3 are dispensable for internalization and recycling.

Relationship between pathogenicity for humans and stx genotype in Shiga toxin-producing Escherichia coli serotype O157

To examine the reason why people infected with Shiga toxin (Stx) producing Escherichia coli (STEC) O157 strains develop varying clinical manifestations, 65 STEC O157 isolates originating from 64 different occurrences of infection in Miyazaki Prefecture in 2001-2003 and their 79 infected individuals were analyzed by stx genotyping, quantitative analysis of reversed passive latex agglutination (RPLA), genomic DNA analysis using pulsed-field gel electrophoresis (PFGE), and clinical manifestations. The isolates were found to carry the following stx genes: stx2vha alone (60.0%), stx1/stx2 (27.7%), stx1/stx2vha (6.1%), stx2 alone (3.1%), and stx2/stx2vha (3.1%). No strain carried the stx1 gene alone. STEC strains carrying stx2 were more frequently associated with clinical manifestations of hemolytic-uremic syndrome (HUS) or bloody diarrhea than those carrying stx2vha. Clusters of PFGE banding patterns were correlated well with the stx genotypes. We conclude that stx genotype is one of the important factors of clinical outcome of STEC O157 infection and that pathogenicity for humans was higher in the stx2 genotype strains than in the stx2vha genotype strains, as reported previously by other researchers. Further, we newly found that four clusters identified by PFGE using restriction enzyme XbaI, stx genotypes and clinical manifestations were well correlated with each other.

Ligand screening system using fusion proteins of G protein-coupled receptors with G protein alpha subunits

G protein-coupled receptors (GPCRs) constitute one of the largest families of genes in the human genome, and are the largest targets for drug development. Although a large number of GPCR genes have recently been identified, ligands have not yet been identified for many of them. Various assay systems have been employed to identify ligands for orphan GPCRs, but there is still no simple and general method to screen for ligands of such GPCRs, particularly of G(i)-coupled receptors. We have examined whether fusion proteins of GPCRs with G protein alpha subunit (Galpha) could be utilized for ligand screening and showed that the fusion proteins provide an effective method for the purpose. This article focuses on the followings: (1) characterization of GPCR genes and GPCRs, (2) identification of ligands for orphan GPCRs, (3) characterization of GPCR-Galpha fusion proteins, and (4) identification of ligands for orphan GPCRs using GPCR-Galpha fusion proteins.