Dynamics of Visual Adaptation With Simultaneous Stimulation of Two Visual Pathways

Primates’ retinal ganglion cells in different visual pathways have been shown to adapt independently (Current Biology 22 (2012) 220–224). However, the manner in which adaptation occurs under simultaneous stimulation of two visual pathways has not yet been explored. In this study, the dynamics of color afterimages were measured while stimulating one or two visual pathway using a time-varying afterimage paradigm. The dynamics of adaptation was approximately equivalent among the three primary visual pathways, but adaptation was slower for simultaneous stimulation of two visual pathways compared to the stimulation of one visual pathway. In addition, we found that the speed of adaptation also depends upon which two pathways are combined. We developed a two-stage adaptation model, both with the same dynamics, to account for the results with simultaneous stimulation of two pathways.

Tempo-spatial integration of nociceptive stimuli assessed via the nociceptive withdrawal reflex in healthy humans.

Spatial information of nociceptive stimuli applied in the skin of healthy humans is integrated in the spinal cord to determine the appropriate withdrawal reflex response. Double-simultaneous stimulus applied in different skin sites are integrated, eliciting a larger reflex response. The temporal characteristics of the stimuli also modulate the reflex e.g. by temporal summation. The primary aim of this study was to investigate how the combined tempo-spatial aspects of two stimuli are integrated in the nociceptive system. This was investigated by delivering single and double simultaneous stimulation, and sequential stimulation with different inter-stimulus intervals (ISIs ranging 30-500 ms.) to the sole of the foot of fifteen healthy subjects. The primary outcome measure was the size of the nociceptive withdrawal reflex (NWR) recorded from the Tibialis Anterior (TA) and Biceps Femoris (BF) muscles. Pain intensity was measured using an NRS scale. Results showed spatial summation in both TA and BF when delivering simultaneous stimulation. Simultaneous stimulation provoked larger reflexes than sequential stimulation in TA, but not in BF. Larger ISIs elicited significantly larger reflexes in TA, while the opposite pattern occurred in BF. This differential modulation between proximal and distal muscles suggests the presence of spinal circuits eliciting a functional reflex response based on the specific tempo-spatial characteristics of a noxious stimulus. No modulation was observed in pain intensity ratings across ISIs. Absence of modulation in the pain intensity ratings argues for an integrative mechanism located within the spinal cord governed by a need for efficient withdrawal from a potentially harmful stimulus.

Effect of Hyperhomocysteinemia on a Murine Model of Smoke-Induced Pulmonary Emphysema.

Hyperhomocysteinemia (HHcy) was reported to enhance endoplasmic reticulum (ER) stress and subsequent apoptosis in several cells. However, the precise mechanisms of smoking susceptibility associated with HHcy has not been fully elucidated. This study included seven- to nine-week-old C57BL6 male mice induced with HHcy and were exposed to cigarette smoke (CS). A549 cells (human alveolar epithelial cell line) were cultured with homocysteine and were exposed to cigarette smoke extract (CSE) to observe cell viability and expression of proteins related to the ER stress. After 6 months of CS exposure, pulmonary emphysema was more severely induced in the group under the condition of HHcy compared to that in the control group. The apoptotic A549 cells increased as Hcy concentration increased and that was enhanced by CSE. Protein expression levels of ER stress markers were significantly increased after simultaneous stimulation. Notably, vitamin B12 and folate supplementation improved ER stress after simultaneous stimulation of A549 cells. HHcy exacerbated smoking-induced pulmonary emphysema and ER stress-induced alveolar cell apoptosis. ER stress in alveolar cells was reversed by vitamin B12 and folate supplementation, suggesting that HHcy could be the new therapeutic target to improve smoking susceptibility.

Enhancement of Porphyromonas gingivalis-Lipopolysaccharide Induced MCP-1 Expression by High Glucose in Human Endothelial Cells

To investigate the synergistic effects of periodontal disease and diabetes mellitus on atherosclerosis, we evaluated the monocyte chemoattractant protein-1 (MCP-1) expression of endothelial cells induced by Porphyromonas gingivalis-lipopolysaccharide (LPS) and high glucose. We also tested whether antioxidants could inhibit the MCP-1 expression induced by the simultaneous stimulation of LPS and high glucose. Human umbilical vein endothelial cells (HUVECs) were stimulated with various concentrations of P. gingivalis-LPS (0.1, 1.0, and 10 µg/mL) in normal glucose (5.5 mM), with high glucose (10 mM and 20 mM), and with 0.1 µg/mL P. gingivalis-LPS in high glucose. MCP-1 expressions were measured by realtime RT-PCR and ELISA. Vitamin C (100 µM) and vitamin E (50 µM) were administered before simultaneous stimulation with 0.1 µg/mL P. gingivalis-LPS and 20 mM glucose. LPS ≥ 1.0 μg/mL increased the expression of MCP-1 mRNA and protein compared to unstimulated HUVECs. High glucose in the culture medium increased the MCP-1 mRNA expression slightly but significantly at 2 hr of incubation, but the MCP-1 protein level was not increased. Simultaneous stimulation with 0.1 μg/mL LPS and high glucose increased the expression of MCP-1 mRNA and protein compared to unstimulated HUVECs. By contrast, pre-incubation of vitamin C or E inhibited the increase of MCP-1 mRNA expression induced by 0.1 μg/mL LPS and 20 mM glucose. Our finding that high glucose enhanced the MCP-1 expression with even a low level of LPS suggests that caution is advisable regarding the atherogenicity of diabetic patients with periodontal disease.

Wild hummingbirds discriminate nonspectral colors

Many animals have the potential to discriminate nonspectral colors. For humans, purple is the clearest example of a nonspectral color. It is perceived when two color cone types in the retina (blue and red) with nonadjacent spectral sensitivity curves are predominantly stimulated. Purple is considered nonspectral because no monochromatic light (such as from a rainbow) can evoke this simultaneous stimulation. Except in primates and bees, few behavioral experiments have directly examined nonspectral color discrimination, and little is known about nonspectral color perception in animals with more than three types of color photoreceptors. Birds have four color cone types (compared to three in humans) and might perceive additional nonspectral colors such as UV+red and UV+green. Can birds discriminate nonspectral colors, and are these colors behaviorally and ecologically relevant? Here, using comprehensive behavioral experiments, we show that wild hummingbirds can discriminate a variety of nonspectral colors. We also show that hummingbirds, relative to humans, likely perceive a greater proportion of natural colors as nonspectral. Our analysis of plumage and plant spectra reveals many colors that would be perceived as nonspectral by birds but not by humans: Birds’ extra cone type allows them not just to see UV light but also to discriminate additional nonspectral colors. Our results support the idea that birds can distinguish colors throughout tetrachromatic color space and indicate that nonspectral color perception is vital for signaling and foraging. Since tetrachromacy appears to have evolved early in vertebrates, this capacity for rich nonspectral color perception is likely widespread.

Simultaneous stimulation of RuBP regeneration and electron transport increases productivity and water use efficiency under field conditions

Previous studies have demonstrated that independent stimulation of either electron transport or RuBP regeneration can increase the rate of photosynthetic carbon assimilation and plant biomass. In this paper, we present evidence that a multi-gene approach to simultaneously manipulate these two processes provides a further stimulation of photosynthesis. We report on the introduction of the cyanobacterial bifunctional enzyme fructose-1,6-bisphosphatase/sedoheptulose-1,7-bisphosphatase or overexpression of the plant enzyme sedoheptulose-1,7-bisphosphatase, together with expression of the red algal protein cytochrome c6, and show that a further increase in biomass accumulation under both glasshouse and field conditions can be achieved. Furthermore, we provide evidence that the simultaneous stimulation of electron transport and RuBP regeneration can lead to enhanced intrinsic water use efficiency under field conditions.One sentence summarySimultaneous stimulation of RuBP regeneration and electron transport results in improvements in biomass yield in glasshouse and field grown tobacco.