Cardiovascular responses of Type A and Type B behavior patterns to visual stimulation during rest, stress and recovery

Differences in the cardiovascular responses of individuals with behavior patterns of Type A and Type B were investigated during rest, stress, and recovery by visual stimulation. Thirty healthy undergraduate and graduate students (mean age: 22.18+/-1.44 years) were categorized as Type A (N=14), or Type B (N=16) based on the Kwansei Gakuin's daily life questionnaire. The cardiovascular reactivity of all participants was repetitively monitored for 6 sessions, with each session comprising 3 conditional phases, viz., resting, stress, and post-stress recovery. A gray screen was displayed during resting, displeasure-evoking images were displayed under the stress condition, and video clips of a forest or a control image (a gray screen) were displayed during the recovery condition. When participants were subjected to different stimuli on a 42-inch plasma television screen in each session, electrocardiograms (ECG), impedance cardiograms and the blood pressure (BP) of the respective participants were continuously monitored. According to the results, Type A indicated higher sympathetic reactivity than Type B during resting and under stress. As such, Type A indicated a shorter pre-ejection period (PEP) level during resting and a greater cardiac output (CO) increase under stress than Type B. Furthermore, parasympathetic predominance and parasympathetic antagonism accompanying the enhanced sympathetic activity induced by the unpleasant stress images decreased heart rate (HR) in both Type A and Type B, although the decrease in Type A was relatively meager. Unlike previous studies, the present study demonstrated that Type A indicated more enhanced sympathetic reactivity than Type B in resting physiological arousal levels and visual stimulus-induced stress.     

Dexamethasone stimulates the expression of ghrelin and its receptor in rat hypothalamic 4B cells

Growth hormone (GH)-releasing peptides (GHRPs) are synthetic peptides that strongly induce GH release. GHRPs act via a specific receptor, the GHRP receptor (GHSR), of which ghrelin is a natural ligand. GHRPs also induce adrenocorticotropic hormone (ACTH) release in healthy subjects. GHRPs or ghrelin stimulate ACTH release via corticotropin-releasing factor (CRF) and arginin vasopressin in the hypothalamus. Stress-activated CRF neurons are suppressed by glucocorticoids in the hypothalamic paraventricular nucleus (PVN), while CRF gene is up-regulated by glucocorticoids in the PVN cells without the influence of input neurons. However, little is known about the regulation of ghrelin and GHSR type 1a (GHSR1a) genes by glucocorticoids in PVN cells. To elucidate the regulation of ghrelin and GHSR gene expression by glucocorticoids in PVN cells, here we used a homologous PVN neuronal cell line, hypothalamic 4B, because these cells show characteristics of the parvocellular neurons of the PVN. These cells also express ghrelin and GHSR1a mRNA. Dexamethasone increased ghrelin mRNA levels. A potent glucocorticoid receptor antagonist, RU-486, significantly blocked dexamethasone-induced increases in ghrelin mRNA levels. Dexamethasone also significantly stimulated GHSR1a mRNA and protein levels. Finally, ghrelin increased CRF mRNA levels, as did dexamethasone. Incubation with both dexamethasone and ghrelin had an additive effect on CRF and ghrelin mRNA levels. The ghrelin-GHSR1a system is activated by glucocorticoids in the hypothalamic cells.     

Consistent individual variations in aggressiveness and a behavioral syndrome across breeding contexts in different environments in the Black-tailed Gull

Individual behaviors of animals do not evolve separately; they do so in association with other behaviors caused by single shared genetic or physiological constraints and/or favored by selection. Thus, measuring behavioral syndromes—suites of correlated behaviors across different contexts—leads to a better understanding of the adaptive significance of variations in behaviors. However, relatively few studies have examined behavioral syndromes in wild animal populations in changing environments. We investigated a potential behavioral syndrome across antipredator nest defense, territorial defense, chick provisioning, and mating behaviors of male Black-tailed Gulls Larus crassirostris in two successive years under different conspecific territorial intrusion risks and food conditions. Males that presented high levels of antipredator nest defense (aggressive antipredator defenders) against a crow decoy (crows are egg predators) defended their territories against conspecific intruders more frequently than did other males (nonaggressive antipredator defenders), independent of the risk of intrusion. Aggressive antipredator defenders also fed their chicks more frequently than nonaggressive males, but only in a year of low food availability. Taken together, this indicates that males show consistent aggressiveness regardless of breeding context (antipredator and territorial defense), but can regulate food provisioning according to food availability.     

Effect of interannual variations in sea-surface temperature on egg-laying parameters of black-tailed gulls (Larus crassirostris) at Teuri Island, Japan

Sea-surface temperature (SST) directly and indirectly affects the distribution and abundance of prey species for seabirds, so we expect variation in SST to be associated with variation in seabird life history traits. In black-tailed gulls (Larus crassirostris) at Teuri Island in northern Hokkaido, Japan, we investigated the diet of the gulls prior to egg laying in 2004 and 2005, and examined the influences of SST in March or April, when the gulls congregate in the colony, on egg-laying parameters using 13 years of data (1992–2004). The gulls fed on krill (Thysanoessa inermis) and fish prior to the egg laying. Mean first egg dates and clutch sizes were significantly and quadratically related to SST anomalies in March, but were not influenced by SST anomalies in April. There was no significant effect of SSTs in either March or April on egg volume. Sea-surface temperature anomalies in March of the years of early laying (−1 to 1°C) were higher than those in 2001 (−2.2°C), but lower than those in 1992 (+1.2°C) and 2004 (+1.1°C). Thysanoessa inermis congregates to spawn at the sea surface, when SSTs rise 3−4°C. Thus, a mismatch between food availability and the timing of egg production in the gulls could have occurred in these 3 years. This study suggests that SST fluctuations prior to laying are important in breeding success of black-tailed gulls.     

Electroencephalographic responses and subjective evaluation on unpleasantness induced by sanitary napkins

Correlation of unpleasantness and electroencephalography (EEG)-based responses induced by persistent mechanical/dry stimulation and acute wet stimulation via wearing sanitary napkins (SN) was investigated in the present study. Mesh and nonwoven SN were employed, and the effects were studied during the follicular and menstrual phases. The mesh SN characteristically displayed a higher textural surface-roughness. The results in the follicular phase revealed no change in EEG responses to nonwoven SN-induced persistent mechanical stimulation, while the same dry stimulus induced significant increases in alpha2 and beta activities in the bilateral frontal areas accompanied by markedly exacerbated unpleasantness with mesh compared with nonwoven SN. The present result with SN application confirms the previous finding that unpleasantness is well correlated with EEG responses of bilateral frontal areas. Interestingly, although the alpha2 activities were enhanced more with mesh than nonwoven SN during the menstrual phase, unpleasantness between the two textural materials was not different. Moreover, it is suggested that acute unpleasantness induced by wet stimulation is related with elevated EEG responses in the left hemisphere. These data suggest that subjective evaluation of effects of physical stimulation on the human body may not be adequately reliable, and objective assessment of physiological activities with EEG is warranted.