Acute Stress-induced Levels Research Articles

Stress modulates cortical excitability via α-2 adrenergic and glucocorticoid receptors: As assessed by spreading depression

An increase in cortical excitability may be one of the factors mediating stress-induced vulnerability to neuropsychiatric disorders. Since stress increases extracellular glutamate and predisposes to migraine with aura attacks, we aimed to study the effect of stress on cortical spreading depression (CSD), the biological substrate of migraine aura and a measure of cortical excitability. CSD was induced by increasing concentrations of KCl applied over the dura with 5-minute intervals and recorded from parieto-occipital cortex to assess the CSD-induction threshold in acutely-stressed, chronically-stressed and naive mice. To study the mechanisms of acute stress-induced decrease in CSD threshold, we systemically administered clonidine, yohimbine, propranolol, CRH1 receptor antagonist NBI27914, mifepristone and spironolactone at doses shown to be effective on stress as well as a central noradrenergic neurotoxin (DSP-4) before acute stress. CSD threshold was significantly lowered by acute and chronic stress as well as central noradrenergic denervation. Clonidine and mifepristone further decreased the CSD threshold below the acute stress-induced levels, whereas yohimbine reversed the acute stress-induced decrease in CSD threshold compared to the saline-injected and stressed control groups. Propranolol, NBI27914 and spironolactone did not modify the effect of acute stress on CSD threshold. Stress increases cortical excitability as illustrated by a decrease in CSD-induction threshold. This action of acute stress is mediated by α2-adrenergic and glucocorticoid receptors. The decrease in CSD threshold may account for the stress-induced susceptibility to migraine. CSD may be used as a tool to study the link between stress-related disorders and cortical excitability.

Reversed hatching order, body condition and corticosterone levels in chicks of southern rockhopper penguins ( Eudyptes chrysocome chrysocome)

In altricial and semi-altricial species, asynchronous hatching gives the first chicks to hatch an initial advantage over other siblings and often leads to the elimination of the smallest chicks. Both baseline corticosterone and acute stress-induced corticosterone levels have been shown to be higher in food deprived chicks than in chicks fed ad libitum. However, first-hatched chicks have also been shown to exhibit higher corticosterone levels than last-hatched chicks, suggesting an influence of the initial differences between eggs on corticosterone levels. We subjected single-chicks of southern rockhopper penguins Eudyptes chrysocome chrysocome to a standardised capture-stress protocol. In this species having very dimorphic two-egg clutches, we examined whether corticosterone levels were different between the two chick categories and tested for the effect of body condition controlled by the chick category. Neither body sizes, nor corticosterone levels differed between A- and B-chicks at 18 days. In contrast to baseline corticosterone levels, acute stress-induced levels of corticosterone were negatively correlated to body condition: chicks with a good body condition had lower acute stress-induced levels of corticosterone than chicks with a poor condition, whatever the chick category. Our results do not support the idea that initial differences in egg characteristics could drive the difference in corticosterone levels between siblings. On the contrary, they show that the A-egg of rockhopper penguins has, when reared alone, the same intrinsic potential to develop into a fledged chick as the B-egg. Later differences in body condition appear to lead to variation in the acute stress-induced levels of corticosterone.

Effect of nestling status and brood size on concentration of corticosterone of free-living kittiwake chicks

Vertebrates respond to perceived stressors through increased plasma concentrations of glucocorticoids. However, there is considerable variation within and across species in the circumstances and degree to which glucocorticoid levels are elevated. We measured baseline and acute stress-induced levels of corticosterone of free-living, black-legged kittiwake chicks ( Rissa tridactyla) across four consecutive breeding seasons in the northern Gulf of Alaska to determine the effect of hatching order and brood size on corticosterone levels of chicks. We sampled 12- to 15-day-old chicks from intact broods (i.e., no brood reduction) at three colonies from 2002–2005 ( n = 164). Baseline and stress-induced levels of corticosterone did not vary by hatching order or brood size. These results suggest that the adrenocortical function of kittiwake chicks from broods that survive intact through 12–15 days is not affected by either hatching order or brood size.

Stress response of red sea bream Pagrus major to acute handling and chronic photoperiod manipulation

A number of primary and secondary features used as stress indicators in fish were investigated in red sea bream, Pagrus major exposed to different photoperiod regimes. In Experiment 1, fish weighing from 17 to 25 g were subjected to acute stress consisted of netting the fish from the rearing tanks and confinement in a small tank (30 L) half-full of water. The fish were then sampled at 0.5, 1, 4, 24, 48, and 72 h post-stress to investigate the stress-induced levels of different parameters. In Experiment 2, fish were exposed to different photoperiods (6L : 6D, 12L : 12D, 16L : 8D and 24L : 0D) for eight weeks. Blood samples were collected from the fish at the 1st, 4th and 8th week after exposure to the photoperiods. Acute stress significantly increased the plasma levels of cortisol (190.1 ng ml − 1 ) and glucose (109.5 mg dl − 1 ) and returned back to the basal levels within 24 h. In contrast, plasma levels of cholesterol (180.5 mg dl − 1 ), total protein (3.0 g dl − 1 ), potassium (4.1 mMol l − 1 ) and Ca ++ (11.3 mg dl − 1 ) were decreased significantly and returned to levels indistinguishable from those of control within 72 h except cholesterol, which did not recover within 72 h. In Experiment 2, fish exposed to 6L : 6D, 16L : 8D and 24L : 0D photoperiods had significantly higher cortisol levels than those exposed to the 12L : 12D photoperiod during the first week ( P < 0.05); however, there was no major difference in cortisol levels among the treatments during other sampling times. There were no significant differences in other parameters among the treatments during the course of the study ( P > 0.05). Fish exposed to the 24L : 0D photoperiod showed significantly higher weight gain and SGR followed by 16L : 8D, 6L : 6D and 12L : 12D photoperiods. The plasma levels of different stress indicators in different photoperiods in Experiment 2 were far lower than those of acute stress-induced levels observed in Experiment 1. On the other hand, no apparent signs of chronic stress were observed in fish exposed to different photoperiods. The results demonstrated that photoperiod manipulation caused no significant acute or chronic stress response in red sea bream.

The adrenocortical response of tufted puffin chicks to nutritional deficits

In several seabirds, nutritional state of a nest-bound chick is negatively correlated with the activity of its hypothalamus–pituitary–adrenal (HPA) axis. Increased corticosterone (cort) secretion has been shown to facilitate changes in behavior that allow hungry chicks to obtain more food from parents. However, if parents are not willing/able to buffer their young from temporary food shortages, increased cort secretion could be detrimental to undernourished chicks. In a system where parents are insensitive to chick demands, low benefits and high costs of activation of the HPA-axis in hungry chicks should lead to a disassociation of the nutritional state of the young and the activity of its HPA-axis. We tested this novel hypothesis for the tufted puffin ( Fratercula cirrhata), a seabird with intermittent provisioning of a nest-bound semi-precocial chick. We examined the HPA-axis activity of captive chicks exposed to the following: (1) a short-term (24 h) food deprivation; and (2) an array of prolonged (3 weeks) restrictions in feeding regimens. We found that in response to a short-term food deprivation chicks decreased baseline levels of cort and thyroid hormones. In response to prolonged restrictions, food-limited chicks exhibited signs of nutritional deficit: they had lower body mass, endogenous lipid reserves, and thyroid hormone titers compared to chicks fed ad libitum. However, baseline and maximum acute stress-induced levels of cort were also lower in food-restricted chicks compared to those of chicks fed ad libitum. These results support a major prediction of the study hypothesis that puffin chicks suppress HPA-axis activity in response to short- and long-term nutritional deficits. This physiological adaptation may allow a chick to extend its development in the nest, while eluding detrimental effects of chronic cort elevation.

Dietary restriction causes chronic elevation of corticosterone and enhances stress response in red-legged kittiwake chicks.

Release of corticosterone in hungry kittiwake chicks facilitates begging and allows them to restore depleted energy reserves by increasing parental food provisioning. However, in order to avoid detrimental effects of chronic elevation of corticosterone, chicks might suppress adrenocortical activity in response to prolonged food shortages. In this study we examined temporal dynamics of corticosterone release in red-legged kittiwake (Rissa brevirostris) chicks exposed to prolonged restrictions in energy content and/or nutritional quality (low versus high lipid content) of their food. Starting at the age of 15 days, chicks were fed either high- or low-lipid fish at 40%, 65%, and 100% of ad libitum energy intake. Body mass measurements and baseline plasma samples were taken on a weekly basis after beginning of the treatment. After 3 weeks of treatment, chicks were exposed to a standardized acute handling and restraint stress protocol, where in addition to a baseline sample, three plasma samples were taken at intervals up to 50 min. We found that food-restricted chicks had lower body mass, chronically (during 2-3 weeks) elevated baseline and higher acute stress-induced levels of corticosterone compared to chicks fed ad libitum. Low lipid content of food further exacerbated these effects. An increase in baseline levels of corticosterone was observed within a week after energy requirements of food-restricted chicks exceeded their daily energy intake. A tendency for suppression of adrenocortical activity was observed in treatments fed low-lipid diets only at the end of the experiment. We suggest that nest-bound chicks, if food-stressed, might suffer deleterious effects of chronic elevation of corticosterone.

The adrenocortical stress-response of Black-legged Kittiwake chicks in relation to dietary restrictions

In this study we examined hormonal responses of Black-legged Kittiwake (Rissa tridactyla) chicks to experimental variations in energy content and nutri- tional quality (low or high lipid to protein ratio, LPR) of their food. Starting at the age of 10 days, chicks were fed either high or low LPR fish at 30, 50, 70 and 100% of ad libitum energy intake. After 20 days of treatment, chicks were exposed to a standardized acute handling and re- straint stress protocol, where a baseline sample was ta- ken immediately after taking a chick from the nest, and three additional blood samples were taken at intervals up to 50 min. Testosterone and corticosterone titres in plasma were measured via radioimmunoassay. We found that baseline testosterone levels were not significantly aAected by the experimental treatments. Food-restricted chicks had elevated baseline and acute stress-induced levels of corticosterone compared to chicks fed ad libi- tum. An elevation of circulating levels of corticosterone in energetically stressed individuals was further magni- fied by low nutritional quality of food. Baseline and acute stress-induced corticosterone levels of chicks were negatively correlated with their fat reserves. We con- clude that the physiological condition of Black-legged Kittiwake chicks can be assessed reliably by measuring circulating levels of corticosterone. We discuss short- and long-term eAects of elevated corticosterone secretion in food-stressed nest-bound chicks.