MK-7 and Its Effects on Bone Quality and Strength.

Vitamin K acts as a cofactor and is required for post-translational γ-carboxylation of vitamin K-dependent proteins (VKDP). The current recommended daily intake (RDI) of vitamin K in most countries has been established based on normal coagulation requirements. Vitamin K1 and menaquinone (MK)-4 has been shown to decrease osteocalcin (OC) γ-carboxylation at RDI levels. Among the several vitamin K homologs, only MK-7 (vitamin K2) can promote γ-carboxylation of extrahepatic VKDPs, OC, and the matrix Gla protein at a nutritional dose around RDI. MK-7 has higher efficacy due to its higher bioavailability and longer half-life than other vitamin K homologs. As vitamin K1, MK-4, and MK-7 have distinct bioactivities, their RDIs should be established based on their relative activities. MK-7 increases bone mineral density and promotes bone quality and strength. Collagen production, and thus, bone quality may be affected by MK-7 or MK-4 converted from MK-7. In this review, we comprehensively discuss the various properties of MK-7.

[Representing Spatial Information in the Parietal Association Cortex].

Several clinical studies have shown that the parietal association cortex plays an important role in spatial perception. Electrophysiological studies on behaving monkeys initiated in the 1970s have revealed the presence of neurons in the parietal association cortex whose activity is related to spatial vision. Herein, we review previous studies on non-human primates and we present an overview of the neuronal representation of spatial information in the parietal association cortex.

Contribution of color signals to ocular following responses.

Ocular following responses (OFRs) are elicited at ultra-short latencies (< 60 ms) by sudden movements of the visual scene. In this study, we investigated the roles of color signals in OFRs in monkeys. To make physiologically isoluminant sinusoidal color gratings, we estimated the physiologically isoluminant points using OFRs and found that the physiologically isoluminant points were nearly independent of the spatiotemporal frequency of the gratings. We recorded OFRs induced by the motion of physiologically isoluminant color gratings and found that OFRs elicited by the motion of color gratings had different spatiotemporal frequency tuning from those elicited by the motion of luminance gratings. Additionally, OFRs to isoluminant color gratings had smaller peak responses, suggesting that color signals weakly contribute to OFRs compared with luminance signals. OFRs to the motion of stimuli composed of luminance and color signals were also examined. We found that color signals largely contributed to OFRs under low luminance signals regardless of whether color signals moved in the same or opposite direction to luminance signals. These results provide evidence of the multichannel visual computations underlying motor responses. We conclude that, in everyday situations, color information contributes cooperatively with luminance information to the generation of ocular tracking behaviors.

Similarity in Neuronal Firing Regimes across Mammalian Species.

UNLABELLED: The architectonic subdivisions of the brain are believed to be functional modules, each processing parts of global functions. Previously, we showed that neurons in different regions operate in different firing regimes in monkeys. It is possible that firing regimes reflect differences in underlying information processing, and consequently the firing regimes in homologous regions across animal species might be similar. We analyzed neuronal spike trains recorded from behaving mice, rats, cats, and monkeys. The firing regularity differed systematically, with differences across regions in one species being greater than the differences in similar areas across species. Neuronal firing was consistently most regular in motor areas, nearly random in visual and prefrontal/medial prefrontal cortical areas, and bursting in the hippocampus in all animals examined. This suggests that firing regularity (or irregularity) plays a key role in neural computation in each functional subdivision, depending on the types of information being carried. SIGNIFICANCE STATEMENT: By analyzing neuronal spike trains recorded from mice, rats, cats, and monkeys, we found that different brain regions have intrinsically different firing regimes that are more similar in homologous areas across species than across areas in one species. Because different regions in the brain are specialized for different functions, the present finding suggests that the different activity regimes of neurons are important for supporting different functions, so that appropriate neuronal codes can be used for different modalities.

Eye position effects on the remapped memory trace of visual motion in cortical area MST.

After a saccade, most MST neurons respond to moving visual stimuli that had existed in their post-saccadic receptive fields and turned off before the saccade ("trans-saccadic memory remapping"). Neuronal responses in higher visual processing areas are known to be modulated in relation to gaze angle to represent image location in spatiotopic coordinates. In the present study, we investigated the eye position effects after saccades and found that the gaze angle modulated the visual sensitivity of MST neurons after saccades both to the actually existing visual stimuli and to the visual memory traces remapped by the saccades. We suggest that two mechanisms, trans-saccadic memory remapping and gaze modulation, work cooperatively in individual MST neurons to represent a continuous visual world.

Low-Dose Daily Intake of Vitamin K(2) (Menaquinone-7) Improves Osteocalcin γ-Carboxylation: A Double-Blind, Randomized Controlled Trials.

Vitamin K is essential for bone health, but the effects of low-dose vitamin K intake in Japanese subjects remain unclear. We investigated the effective minimum daily menaquinone-7 dose for improving osteocalcin γ-carboxylation. Study 1 was a double-blind, randomized controlled dose-finding trial; 60 postmenopausal women aged 50-69 y were allocated to one of four dosage group and consumed 0, 50, 100, or 200 µg menaquinone-7 daily for 4 wk, respectively, with a controlled diet in accordance with recommended daily intakes for 2010 in Japan. Study 2 was a double-blind, randomized placebo-controlled trial based on the results of Study 1; 120 subjects aged 20-69 y were allocated to the placebo or MK-7 group and consumed 0 or 100 µg menaquinone-7 daily for 12 wk, respectively. In both studies, circulating carboxylated osteocalcin and undercarboxylated osteocalcin were measured. The carboxylated osteocalcin/undercarboxylated osteocalcin ratio decreased significantly from baseline in the 0 µg menaquinone-7 group, in which subjects consumed the recommended daily intake of vitamin K with vitamin K1 and menaquinone-4 (Study 1). Menaquinone-7 increased the carboxylated osteocalcin/undercarboxylated osteocalcin ratio dose dependently, and significant effects were observed in both the 100 and 200 µg groups compared with the 0 µg group. Undercarboxylated osteocalcin concentrations decreased significantly, and the carboxylated osteocalcin/undercarboxylated osteocalcin ratio increased significantly in the 100 µg menaquinone-7 group compared with the placebo group (Study 2). Daily menaquinone-7 intake ≥100 µg was suggested to improve osteocalcin γ-carboxylation.

Neurons in cortical area MST remap the memory trace of visual motion across saccadic eye movements.

Perception of a stable visual world despite eye motion requires integration of visual information across saccadic eye movements. To investigate how the visual system deals with localization of moving visual stimuli across saccades, we observed spatiotemporal changes of receptive fields (RFs) of motion-sensitive neurons across periods of saccades in the middle temporal (MT) and medial superior temporal (MST) areas. We found that the location of the RFs moved with shifts of eye position due to saccades, indicating that motion-sensitive neurons in both areas have retinotopic RFs across saccades. Different characteristic responses emerged when the moving visual stimulus was turned off before the saccades. For MT neurons, virtually no response was observed after the saccade, suggesting that the responses of these neurons simply reflect the reafferent visual information. In contrast, most MST neurons increased their firing rates when a saccade brought the location of the visual stimulus into their RFs, where the visual stimulus itself no longer existed. These findings suggest that the responses of such MST neurons after saccades were evoked by a memory of the stimulus that had preexisted in the postsaccadic RFs ("memory remapping"). A delayed-saccade paradigm further revealed that memory remapping in MST was linked to the saccade itself, rather than to a shift in attention. Thus, the visual motion information across saccades was integrated in spatiotopic coordinates and represented in the activity of MST neurons. This is likely to contribute to the perception of a stable visual world in the presence of eye movements.

Difference in visual motion representation between cortical areas MT and MST during ocular following responses.

The middle temporal (MT) and medial superior temporal (MST) areas are successive stations of the visual motion-processing stream and project in parallel to the pontine nucleus, which is closely associated with rapid stabilization of gaze. We recorded the neural activities of MT and MST neurons of monkeys during short-latency ocular following responses (OFRs) elicited by large-field sinusoidal gratings with different spatial frequencies drifting at different temporal frequencies, and examined the dependence on spatiotemporal frequency. The results indicate that most MT/MST neurons were tuned almost separately for spatial and temporal frequencies of motion stimuli. The difference between MT and MST neurons was particularly striking for the optimal spatial frequency (higher for MT and lower for MST). The spatiotemporal frequency dependence of the OFRs could be reproduced by a weighted sum of the population activities of the MT and MST neurons. We conclude that MT and MST neurons work as spatiotemporal frequency sensors that extract motions of finer and coarser visual features and that both areas contribute to generation of OFRs.

Direction and speed tuning to visual motion in cortical areas MT and MSTd during smooth pursuit eye movements.

When tracking a moving target in the natural world with pursuit eye movement, our visual system must compensate for the self-induced retinal slip of the visual features in the background to enable us to perceive their actual motion. We previously reported that the speed of the background stimulus in space is represented by dorsal medial superior temporal (MSTd) neurons in the monkey cortex, which compensate for retinal image motion resulting from eye movements when the direction of the pursuit and background motion are parallel to the preferred direction of each neuron. To further characterize the compensation observed in the MSTd responses to the background motion, we recorded single unit activities in cortical areas middle temporal (MT) and MSTd, and we selected neurons responsive to a large-field visual stimulus. We studied their responses to the large-field stimulus in the background while monkeys pursued a moving target and while fixated a stationary target. We investigated whether compensation for retinal image motion of the background depended on the speed of pursuit. We also asked whether the directional selectivity of each neuron in relation to the external world remained the same even during pursuit and whether compensation for retinal image motion occurred irrespective of the direction of the pursuit. We found that the majority of the MSTd neurons responded to the visual motion in space by compensating for the image motion on the retina resulting from the pursuit regardless of pursuit speed and direction, whereas most of the MT neurons responded in relation to the genuine retinal image motion.

Cloning new small RNA sequences.

Small RNAs are key molecules in RNA silencing pathways that exert sequence-specific regulation of gene expression and chromatin modifications in many eukaryotes. In plants, endogenous small RNAs, including microRNAs (miRNAs) and trans-acting small interfering RNAs (tasiRNAs) play an important role in biological processes such as development and stress responses. In addition, viral genome-derived siRNAs are produced during viral infection, and they exhibit anti-viral defense by an RNA silencing pathway. These endogenous and exogenous small RNAs are mainly 21-24 nucleotides in length. Here, we describe a method to identify small RNA sequences from plant tissues. Small RNAs are purified by column fractionation and gel excision from total RNAs. These small RNAs are ligated at both termini to DNA/RNA chimeric adapters and reverse-transcribed to produce cDNAs. By the following PCR amplification, BanI restriction sites are added to cDNAs, which enables directional concatamerization. Concatamerized-fragments are cloned and sequenced. This method could be applied to identify small RNA sequences from many sources, e.g., mutant plants, plants in various stress environments, and virus-infected plants.

Responses of MSTd and MT neurons during smooth pursuit exhibit similar temporal frequency dependence on retinal image motion.

When our eyes are in constant motion, the world around us remains perceptually stable; although eye movements produce slips of the visual scene on our retinae. In our previous study, we suggested that visual motion in space is served by neurons, which compensate retinal-image motion due to pursuit eye movements, in the dorsal part of the medial superior temporal (MSTd) area. Additionally, neurons in the middle temporal (MT) area respond to retinal-image motion. In the present study, to further elucidate the visual properties of MSTd/MT neurons, we investigated the neuronal response to the motion of checkerboard patterns (CBPs) in addition to the random-dot pattern used in the previous study. We found that neuronal responses in both areas decreased regardless of fixation or pursuit when the temporal frequency of the CBPs exceeded 20 Hz on the retina. Our results support the idea that pursuit-speed compensation observed in area MSTd might be formed by the reception of retina-based visual information from MT neurons because both areas MT and MSTd were dependent on retina-based information during pursuit eye movements.

Relating neuronal firing patterns to functional differentiation of cerebral cortex.

It has been empirically established that the cerebral cortical areas defined by Brodmann one hundred years ago solely on the basis of cellular organization are closely correlated to their function, such as sensation, association, and motion. Cytoarchitectonically distinct cortical areas have different densities and types of neurons. Thus, signaling patterns may also vary among cytoarchitectonically unique cortical areas. To examine how neuronal signaling patterns are related to innate cortical functions, we detected intrinsic features of cortical firing by devising a metric that efficiently isolates non-Poisson irregular characteristics, independent of spike rate fluctuations that are caused extrinsically by ever-changing behavioral conditions. Using the new metric, we analyzed spike trains from over 1,000 neurons in 15 cortical areas sampled by eight independent neurophysiological laboratories. Analysis of firing-pattern dissimilarities across cortical areas revealed a gradient of firing regularity that corresponded closely to the functional category of the cortical area; neuronal spiking patterns are regular in motor areas, random in the visual areas, and bursty in the prefrontal area. Thus, signaling patterns may play an important role in function-specific cerebral cortical computation.

Specific enrichment of miRNAs in Arabidopsis thaliana infected with Tobacco mosaic virus.

RNA silencing is a broadly conserved machinery and is involved in many biological events. Small RNAs are key molecules in RNA silencing pathway that guide sequence-specific gene regulations and chromatin modifications. The silencing machinery works as an anti-viral defense in virus-infected plants. It is generally accepted that virus-specific small interfering (si) RNAs bind to the viral genome and trigger its cleavage. Previously, we have cloned and obtained sequences of small RNAs from Arabidopsis thaliana infected or uninfected with crucifer Tobacco mosaic virus. MicroRNAs (miRNAs) accumulated to a higher percentage of total small RNAs in the virus-infected plants. This was partly because the viral replication protein binds to the miRNA/miRNA* duplexes. In the present study, we mapped the sequences of small RNAs other than virus-derived siRNAs to the Arabidopsis genome and assigned each small RNA. It was demonstrated that only miRNAs increased as a result of viral infection. Furthermore, some newly identified miRNAs and miRNA candidates were found from the virus-infected plants despite a limited number of examined sequences. We propose that it is advantageous to use virus-infected plants as a source for cloning and identifying new miRNAs.

Binding of tobamovirus replication protein with small RNA duplexes.

The sequence profiles of small interfering RNAs (siRNAs) in Arabidopsis infected with the crucifer tobamovirus tobacco mosaic virus (TMV)-Cg were determined by using a small RNA cloning technique. The majority of TMV-derived siRNAs were 21 nt in length. The size of the most abundant endogenous small RNAs in TMV-infected plants was 21 nt, whilst in mock-inoculated plants, it was 24 nt. Northern blot analysis revealed that some microRNAs (miRNAs) accumulated more in TMV-infected plants than in mock-inoculated plants. The question of whether the TMV-Cg-encoded 126K replication protein, an RNA-silencing suppressor, caused small RNA enrichment was examined. Transient expression of the replication protein did not change the pattern of miRNA processing. However, miRNA, miRNA* (the opposite strand of the miRNA duplex) and hairpin-derived siRNA all co-immunoprecipitated with the replication protein. Gel mobility-shift assays indicated that the replication protein binds small RNA duplexes. These results suggest that the tobamovirus replication protein functions as a silencing suppressor by binding small RNA duplexes, changing the small RNA profile in infected plants.

MST neurons code for visual motion in space independent of pursuit eye movements.

When a person tracks a small moving object, the visual images in the background of the visual scene move across his/her retina. It, however, is possible to estimate the actual motion of the images despite the eye-movement-induced motion. To understand the neural mechanism that reconstructs a stable visual world independent of eye movements, we explored areas MT (middle temporal) and MST (medial superior temporal) in the monkey cortex, both of which are known to be essential for visual motion analysis. We recorded the responses of neurons to a moving textured image that appeared briefly on the screen while the monkeys were performing smooth pursuit or stationary fixation tasks. Although neurons in both areas exhibited significant responses to the motion of the textured image with directional selectivity, the responses of MST neurons were mostly correlated with the motion of the image on the screen independent of pursuit eye movement, whereas the responses of MT neurons were mostly correlated with the motion of the image on the retina. Thus these MST neurons were more likely than MT neurons to distinguish between external and self-induced motion. The results are consistent with the idea that MST neurons code for visual motion in the external world while compensating for the counter-rotation of retinal images due to pursuit eye movements.

The visual motion detectors underlying ocular following responses in monkeys.

Psychophysical evidence indicates that visual motion can be sensed by low-level (energy-based) and high-level (feature-based) mechanisms. The present experiments were undertaken to determine which of these mechanisms mediates the initial ocular following response (OFR) that can be elicited at ultra-short latencies by sudden motion of large-field images. We used the methodology of Sheliga, Chen, Fitzgibbon, and Miles (Initial ocular following in humans: A response to first-order motion energy. Vision Research, 2005a), who studied the initial OFRs of humans, to study the initial OFRs of monkeys. Accordingly, we applied horizontal motion to: (1) vertical square-wave gratings lacking the fundamental ("missing fundamental stimulus") and (2) vertical grating patterns consisting of the sum of two sinusoids of frequency 3f and 4f, which created a repeating pattern with beat frequency, f. Both visual stimuli share a critical property: when subject to 1/4-wavelength steps, their overall pattern (feature) shifts in the direction of the steps, whereas their major Fourier component shifts in the reverse direction (because of spatial aliasing). We found that the initial OFRs of monkeys to these stimuli, like those of humans, were always in the opposite direction to the 1/4-wavelength shifts, i.e., in the direction of the major Fourier component, consistent with detection by (low-level) oriented spatio-temporal filters as in the well-known energy model of motion analysis. Our data indicate that the motion detectors mediating the initial OFR have quantitatively similar properties in monkeys and humans, suggesting that monkeys provide a good animal model for the human OFR.

Changes in cerebellar fastigial burst activity related to saccadic gain adaptation in the monkey.

The accuracy of saccades is ensured by an adaptive mechanism that probably involves the cerebellum. We examined the discharge of saccade-related neurons in the fastigial oculomotor region (FOR) during adaptation. Using a conventional intrasaccadic step paradigm, we changed the gain of saccades elicited by a 10 degrees horizontal target step to the side of unit recording. As a measure of neural activity, we took the number of spikes occurring in a 30 or 40 ms time window starting at 30 ms before saccade onset, which corresponded roughly to the foot and rising phase of the burst. A gain decrease was accompanied by a significant increase in spike discharge (6/6), and a gain increase by a significant reduction in discharge (3/3). During the course of adaptation, the neural activity and gain exhibited changes with a similar course but in the opposite direction. Regression analysis indicated that the two variables were significantly correlated (7/8). The present study has shown that activity of FOR neurons is altered during adaptive modification of saccade size. Our data are consistent with the hypothesized suppressive action of the FOR on ipsiversive saccades and provide support on a single-neuron basis for the cerebellar involvement in short-term saccade adaptation.