Estimation of mental effort in learning visual search by measuring pupil response

Perceptual learning refers to the improvement of perceptual sensitivity and performance with training. In this study, we examined whether learning is accompanied by a release from mental effort on the task, leading to automatization of the learned task. For this purpose, we had subjects conduct a visual search for a target, defined by a combination of orientation and spatial frequency, while we monitored their pupil size. It is well known that pupil size reflects the strength of mental effort invested in a task. We found that pupil size increased rapidly as the learning proceeded in the early phase of training and decreased at the later phase to a level half of its maximum value. This result does not support the simple automatization hypothesis. Instead, it suggests that the mental effort and behavioral performance reflect different aspects of perceptual learning. Further, mental effort would be continued to be invested to maintain good performance at a later stage of training.     

Seasonal variation in the expression of five subtypes of gonadotropin-releasing hormone receptor genes in the brain of masu salmon from immaturity to spawning

Seasonal variation in the expression of five subtypes of gonadotropin-releasing hormone receptor (GnRH-R) genes, designated as msGnRH-R1, -R2, -R3, -R4, and -R5, was examined in the brain of masu salmon (Oncorhynchus masou). In addition, responses of these genes to GnRH were examined in a GnRH analog (GnRHa) implantation experiment. Brain samples were collected one week after the implantation every month from immaturity through spawning. The absolute amount of GnRH-R mRNA in single forebrains was determined by real-time PCR assays. Among the five genes, R4 and R5 were dominantly expressed in both sexes. R1, R4, and R5 mRNAs showed similar changes throughout the experimental period in both sexes. Levels tended to be high in winter and low in the pre-spawning season, followed by elevations in the spawning period. The mRNA levels had weak to moderate negative correlations with the plasma level of estradiol-17beta (E2) in females. The effects of GnRHa on msGnRH-R mRNAs were not apparent for all the subtypes. These results indicate that the msGnRH-R1, -R4, and -R5 genes are synchronously expressed during sexual maturation. There was a trend toward decreased levels of their expression prior to the spawning period and then increased levels at spawning, possibly causing GnRH target neurons to sensitize to a GnRH stimulus. Furthermore, E2 may be involved in msGnRH-R gene expression in the brain of female masu salmon during sexual maturation.     

Sex difference and postnatal change of maternal behavioral patterns in juvenile male and female rats

Juvenile rats are known to show certain elements of maternal behavior. In this experiment, to investigate sex difference and postnatal change of retrieving and pup-cleaning (licking) behaviors in juvenile rats, these behaviors were recorded using new observation method at 20, 30 and 45 days of age in female and male Wistar rats. At 20 days of age, maternal behavior was observed in a common plastic observation cage (test A) and then test B was performed. In the test B, observation was carried out using a cage with a wooden box that was open on one side, helping the juveniles to establish a nest. As the results of day 20, most rats in all groups showed licking behavior in both the test A and B. The incidence of retrieving behavior increased from the test A to the test B with the box in both sexes, especially in males (p<0.01). The box is thought to play a facilitative role in induction of retrieving. Moreover, the incidence in males was higher than that in females in the test B (p<0.001). At 30 and 45 days of age, only a test B with box was performed. The incidences of licking and retrieving behaviors at 30 days of age were decreased significantly compared to those at 20 days of age in both sexes(p<0.001). Further decrease from 30 days to 45 days was observed. These results suggest that in juvenile rat, incidence of retrieving behavior in males is higher than that in females but there is no sex difference in incidence of licking behavior. Potency to show these behaviors decreases acutely before puberty in rats.     

Progenitor cell injury after irradiation to the developing brain can be modulated by mild hypothermia or hyperthermia

Ionizing radiation induced acute cell death in the dentate gyrus subgranular zone (SGZ) and the subventricular zone (SVZ). Hypomyelination was also observed. The effects of mild hypothermia and hyperthermia for 4 h after irradiation (IR) were studied in postnatal day 9 rats. One hemisphere was irradiated with a single dose of 8 Gy and animals were randomized to normothermia (rectal temperature 36 degrees C for 4 h), hypothermia (32 degrees C for 4 h) or hyperthermia (39 degrees C for 4 h). Cellular injury, e.g. chromatin condensation and nitrotyrosine formation, appeared to proceed faster when the body temperature was higher. Caspase-3 activation was more pronounced in the hyperthermia group and nuclear translocation of p53 was less pronounced in the hypothermia group 6 h after IR. In the SVZ the loss of nestin-positive progenitors was more pronounced (48%) and the size was smaller (45%) in the hyperthermia group 7 days post-IR. Myelination was not different after hypo- or hyperthermia. This is the first report to demonstrate that hypothermia may be beneficial and that hyperthermia may aggravate the adverse side-effects after radiation therapy to the developing brain.     

Involvement of alpha-amylase I-1 in starch degradation in rice chloroplasts

To determine the role of alpha-amylase isoform I-1 in the degradation of starch in rice leaf chloroplasts, we generated a series of transgenic rice plants with suppressed expression or overexpression of alpha-amylase I-1. In the lines with suppressed expression of alpha-amylase I-1 at both the mRNA and protein levels, seed germination and seedling growth were markedly delayed in comparison with those in the wild-type plants. However, the growth retardation was overcome by supplementation of sugars. Interestingly, a significant increase of starch accumulation in the young leaf tissues was observed under a sugar-supplemented condition. In contrast, the starch content of leaves was reduced in the plants overexpressing alpha-amylase I-1. In immunocytochemical analysis with specific anti-alpha-amylase I-1 antiserum, immuno-gold particles deposited in the chloroplasts and extracellular space in young leaf cells. We further examined the expression and targeting of alpha-amylase I-1 fused with the green fluorescent protein in re-differentiated green cells, and showed that the fluorescence of the expressed fusion protein co-localized with the chlorophyll autofluorescence in the transgenic cells. In addition, mature protein species of alpha-amylase I-1 bearing an oligosaccharide side chain were detected in the isolated chloroplasts. Based on these results, we concluded that alpha-amylase I-1 targets the chloroplasts through the endoplasmic reticulum-Golgi system and plays a significant role in the starch degradation in rice leaves.     

Changes in responses of UVB irradiated skin of brownish guinea pigs with aging

It is known that skin often shows irregular pigmentation during aging, which is frequently associated with hyperpigmentation. Many studies have utilized brownish A1 guinea pigs to investigate the pathogenesis of ultraviolet B (UVB)-induced skin pigmentation, however, responses associated with aging following UVB irradiation have not been elucidated. To characterize those responses, dorsal skin of A1 guinea pigs from 14-weeks to 5-yr old were investigated. The minimal erythema dose was found to increase with aging. Further, in pigmentation induced by UVB radiation, skin brightness (DeltaL*-value) decreased equally in both the 14-week old (young) group and in the 3-yr old (old) group of guinea pigs. The DeltaL*-value recovered in the young group from 21 d after UVB irradiation, whereas no such recovery was seen in the old group. In addition, the amount of melanin and the number of melanocytes returned near pre-irradiation levels in the young group, while they remained high in the old group. Our results therefore demonstrate for the first time that skin responses following UVB irradiation change with aging in A1 guinea pigs.     

Dynamics of methane in mesotrophic Lake Biwa,Japan

As a part of a core project of IGBP (International Geosphere-Biosphere Programme), distribution, production, oxidation and transport processes of methane in bottom sediments and lake water in a mesotrophic lake (Lake Biwa) have been studied with special reference to the spatial heterogeneity of each process. In this study, we attempted to synthesize previously reported results with newly obtained ones to depict the methane dynamics in the entire lake. The pelagic water column exhibited subsurface maxima of dissolved methane during a stratified period. Transect observation at the littoral zone suggested that horizontal transportation may be a reason for the high methane concentration in epilimnion and thermocline at the offshore area. Tributary rivers and littoral sediments were suggested to be the source. Observations also showed that the internal wave caused resuspension of the bottom sediment and release of methane from the sediment into the lake water. The impact of the internal waves was pronounced in the late stage of a stratified period. The littoral sediment showed much higher methanogenic activity than the profundal sediments, and the bottom water of the littoral sediments had little methanotrophic activity. In the profundal sediment, most of the methane that diffused up from the deeper part was oxidized when it passed through the oxic layer. Active methane oxidation was also observed in the hypolimnetic water, while the lake water in the epilimnion and thermocline showed very low methane oxidation, probably due to the inhibitory effect of light. These results mean a longer residence time for methane in the epilimnion than in the hypolimnion. Horizontal inflow of dissolved methane from the river and/or littoral sediment, together with the longer residence time in the surface water, may cause the subsurface maxima, which have also been observed in other lakes and in the ocean.     

O(2)- and H(2)O(2)-dependent verdoheme degradation by heme oxygenase: reaction mechanisms and potential physiological roles of the dual pathway degradation

Heme oxygenase (HO) catalyzes the catabolism of heme to biliverdin, CO, and a free iron through three successive oxygenation steps. The third oxygenation, oxidative degradation of verdoheme to biliverdin, has been the least understood step despite its importance in regulating HO activity. We have examined in detail the degradation of a synthetic verdoheme IXalpha complexed with rat HO-1. Our findings include: 1) HO degrades verdoheme through a dual pathway using either O(2) or H(2)O(2); 2) the verdoheme reactivity with O(2) is the lowest among the three O(2) reactions in the HO catalysis, and the newly found H(2)O(2) pathway is approximately 40-fold faster than the O(2)-dependent verdoheme degradation; 3) both reactions are initiated by the binding of O(2) or H(2)O(2) to allow the first direct observation of degradation intermediates of verdoheme; and 4) Asp(140) in HO-1 is critical for the verdoheme degradation regardless of the oxygen source. On the basis of these findings, we propose that the HO enzyme activates O(2) and H(2)O(2) on the verdoheme iron with the aid of a nearby water molecule linked with Asp(140). These mechanisms are similar to the well established mechanism of the first oxygenation, meso-hydroxylation of heme, and thus, HO can utilize a common architecture to promote the first and third oxygenation steps of the heme catabolism. In addition, our results infer the possible involvement of the H(2)O(2)-dependent verdoheme degradation in vivo, and potential roles of the dual pathway reaction of HO against oxidative stress are proposed.