Higher Corticosterone Response Research Articles

Stress coping and evolution of aerobic exercise performance: corticosterone levels in voles from a selection experiment.

The locomotor performance achieved in a challenging situation depends not only on physiological limitations, such as the aerobic exercise capacity, but also on behavioral characteristics, such as adequate coping with stress. The stress response is mediated largely by the hypothalamic-pituitary-adrenal (HPA) axis, through modulated release of glucocorticoids. We used a unique experimental evolution model system to test the hypothesis that the evolution of an increased aerobic exercise performance can be facilitated by modification of the glucocorticoid-related stress-coping mechanisms. Bank voles (Myodes glareolus) from 'aerobic' (A) lines, selected for 22 generations for high maximum swim-induced rate of oxygen consumption (V̇O2,swim), achieved a 64% higher V̇O2,swim than those from unselected, control lines. The temporal pattern of exercise during the swimming trial also evolved, and the A-line voles achieved V̇O2,swim later in the course of the trial, which indicates a modification of the stress response characteristics. Both V̇O2,swim and the average metabolic rate measured during the trial tended to increase with baseline corticosterone level, and decreased with the post-exercise corticosterone level. Thus, increased baseline corticosterone level promotes high metabolic performance, but a high corticosterone response to swimming acts as an inhibitor rather than stimulator of intense activity. However, neither of the corticosterone traits differed between the A-selected and control lines. Thus, the experiment did not provide evidence that evolution of increased aerobic performance is facilitated by the modification of glucocorticoid levels. The results, however, do not exclude the possibility that other aspects of the HPA axis function evolved in response to the selection.

Corticosterone responses and personality in birds: Individual variation and the ability to cope with environmental changes due to climate change

Birds can respond to an internal or external stimulus with activation of the HPA axis and secretion of corticosterone. There is considerable individual variation in corticosterone responses, and individual responses can be very different from the mean response for a group of birds. Corticosterone responses and behavioural responses to environmental stimuli are determined by individual characteristics called personality. It is proposed that birds with low corticosterone responses and proactive personalities are likely to be more successful (have greater fitness) in constant or predictable conditions, whilst birds with reactive personalities and high corticosterone responses will be more successful in changing or unpredictable conditions. The relationship between corticosterone responses and fitness thus depends on the prevailing environmental conditions, so birds with either low or high corticosterone responses can have the greatest fitness and be most successful, but in different situations. It is also proposed that birds with reactive personalities and high corticosterone responses will be better able to cope with environmental changes due to climate change than birds with proactive personalities and relatively low corticosterone responses. Phenotypic plasticity in corticosterone responses can be quantified using a reaction norm approach, and reaction norms can be used to determine the degree of plasticity in corticosterone responses of individual birds, and mean levels of plasticity in responses of species of birds. Individual corticosterone responses and personality, and reaction norms for corticosterone responses, can in future be used to predict the ability of birds to cope with environmental changes due to climate change.

Fecal corticosterone metabolites and plasma corticosterone in Japanese quail selected for low or high plasma corticosterone responses to brief restraint

Fecal corticosterone metabolites and plasma corticosterone in Japanese quail selected for low- or high-plasma corticosterone responses to brief mechanical restraint (low- and high-stress lines), and in a line of unselected quail, were measured in this study. No line differences were observed in baseline plasma corticosterone concentrations, but fecal corticosterone metabolite concentrations and daily fecal corticosterone metabolite production were 20% higher in quail of the high-stress line than in unselected or low-stress quail for males and females living together in group cages (P < 0.05). No differences were observed between lines in corticosterone metabolite concentrations and production for male birds in individual cages. Baseline plasma corticosterone concentrations, fecal corticosterone metabolite concentrations, and production appeared to be higher for males and females in group cages compared with males in individual cages. This difference might have been because of greater corticosterone secretion by male quail living in mixed sex groups than living individually. Correlations between baseline plasma corticosterone concentrations and fecal corticosterone metabolite concentrations in low-stress and high-stress quail, and for all birds combined, were r = 0.521 (P = 0.038), r = 0.604 (P = 0.013), and r = 0.431 (P = 0.002), respectively. The low- and high-stress lines that have been selected for low- and high-corticosterone responses differ in other characteristics, including growth and reproductive performance, and the current results are consistent with the assumption that these other differences are a consequence of greater daily corticosterone secretion in quail of the high-stress line.

Plasma corticosterone responses to handling in Japanese quail selected for low or high plasma corticosterone responses to brief restraint

1. Plasma corticosterone responses to handling in Japanese quail selected for low or high corticosterone responses to brief mechanical restraint (low and high stress lines) were measured in this study. 2. Initial corticosterone concentrations did not differ between the two lines. Corticosterone concentrations increased 15 min after handling began in quail handled for 5 or 15 min, with greater increases in quail from the high stress than the low stress line. Integrated corticosterone responses were higher in high stress than low stress quail, although the difference between the lines was not significant in quail handled for 5 min. 3. Patterns of plasma corticosterone after 15 min differed between quail handled for 5 or 15 min. Corticosterone increased further or did not change from 15 to 30 min then decreased from 30 to 60 min in quail handled for 5 min, whereas corticosterone decreased from 15 to 30 min then did not change in quail handled for 15 min. Corticosterone concentrations at 60 min remained elevated above initial concentrations, and were similar in quail handled for 5 or 15 min. Corticosterone concentrations at 15 min were more than twice as high in quail handled for 15 min compared with quail handled for 5 min. 4. Although the lines of quail have been selected on the magnitude of corticosterone responses, there was still marked variation in responses between birds within each line. Some quail in the high stress line showed little or no corticosterone response to handling, whilst large responses were seen in some birds of the low stress line. The lines of quail differ in characteristics other than corticosterone responses, including fear behaviour and reproductive development, so the lines provide valuable opportunities to investigate the potential significance of differences between individual birds in their corticosterone responses.

Behavior and pro-inflammatory cytokine variations among submissive and dominant mice engaged in aggressive encounters: moderation by corticosterone reactivity.

Psychosocial stressors contribute to the pathophysiology of affective disorders and variations of cytokine functioning have been implicated in this process. The present investigation demonstrated, in mice, the impact of stressful aggressive encounters on activity levels, plasma corticosterone and cytokine concentrations, and on cytokine mRNA expression within the prefrontal cortex (PFC) and hippocampus. As glucocorticoids have been tied to cytokine variations, mice were subdivided into low or high corticosterone responders, defined in terms of circulating hormone levels 75 min post-confrontation. Interestingly, stressor-induced effects among low and high responders varied as a function of whether mice were submissive or dominant during the aggressive bout. Agonistic encounters elicited subsequent hyperactivity, particularly among low corticosterone responders and among dominant mice. Plasma levels of corticosterone and interleukin (IL)-6 concomitantly increased after aggressive encounters and varied with dominance status and with the low versus high corticosterone response. Among the low responders corticosterone and IL-6 increases were modest and only apparent among submissive mice, whereas among high responders these elevations were more pronounced and comparable in submissive and dominant mice. Aggressive episodes also increased IL-1β and IL-6 mRNA brain expression. The IL-1β rise was greater in the PFC and hippocampus of submissive mice that were low responders. Among high responders IL-1β and IL-6 increased in both groups, although in the PFC this effect was specific to dominant mice. The data are discussed in terms of their relevance to the impact of aggressive encounters on affective behaviors, and to the role that cytokines might play in this regard.

Corticosterone responses in birds: Individual variation and repeatability in Adelie penguins ( Pygoscelisadeliae) and other species, and the use of power analysis to determine sample sizes

Plasma corticosterone concentrations increase when birds experience a stressor, and in this study we quantified variation in corticosterone responses for the first time in a species of free-living bird. Adelie penguins ( Pygoscelis adeliae) nesting at Cape Bird on Ross Island in Antarctica were sampled on three occasions. Penguins with relatively low or high corticosterone responses on the first occasion had consistently low or high responses, as previously found for great tits and chickens. A model for birds is proposed in which birds with low corticosterone responses and proactive personalities are likely to be more successful (have greater fitness) in constant or predictable conditions, whilst birds with reactive personalities and high corticosterone responses will be more successful in changing or unpredictable conditions. There is thus no linear relationship between the size of a corticosterone response and fitness. Whilst the absolute magnitude of corticosterone responses varies markedly across species of birds, coefficients of variation are similar. Individual corticosterone responses are generally repeatable, with significant statistical repeatabilities for 30 min corticosterone concentrations and integrated corticosterone concentrations in the Adelie penguin, great tit and chicken. Coefficients of variation in corticosterone responses between birds and power analyses were used to provide a rule of thumb for determining differences between groups of birds in mean corticosterone concentrations to enable statistical analyses to have acceptable levels of statistical power for given sample sizes. It is suggested that power analyses and this rule of thumb be adopted in future investigations of corticosterone responses in birds.

Maternal postpartum learned helplessness (LH) affects maternal care by dams and responses to the LH test in adolescent offspring

It is known that the early environment affects the mental development of rodent and human offspring. However, it is not known specifically whether a postpartum depressive state influences the depressive state in offspring. Using learned helplessness (LH) in rats as an animal model of depression, we examined the influence of maternal postpartum LH on responses to the LH test of offspring. Dam rats were judged as LH or non-helpless (nLH) on postnatal days (PN) 2–3, and maternal behavior was recorded during PN2–14. On PN 45–46, offspring were subjected to the LH test. Plasma corticosterone (CORT) levels, hippocampal levels of glucocorticoid receptor (GR) and brain-derived neurotrophic factor (BDNF) mRNA were measured before and after the LH test in offspring. Active nursing in LH dams was significantly lower than that in nLH dams. Susceptibility to LH in the offspring of LH dams was significantly higher than in those of nLH dams, and was negatively correlated with active nursing by LH dams. The GR mRNA levels before and after the LH test were lower in the offspring of LH dams than in those of nLH dams, and the reduced basal GR mRNA and protein might have resulted in the higher CORT response after the LH test. There was no significant difference in BDNF mRNA in the offspring of LH and nLH dams. These findings suggest that early postpartum LH decreased active nursing and increased depression-like behavior in the adolescent offspring via dysfunction of the hypothalamic–pituitary–adrenal axis.

Gene array analysis of adrenal glands in broiler chickens following ACTH treatment.

BackgroundDifference in adaptability responses to stress has been observed amongst bird species, strains, and individuals. Components of the HPA axis, one of the internal systems involved in homeostasis re-establishment following stress, could play a role in this variability of responses. The aim of the present study was 1) to identify genes involved in the regulation of adrenal activity following ACTH stimulation and 2) to examine adrenal genes differentially expressed in individuals with high and low plasma corticosterone response following ACTH treatment.ResultsAnalysis with 21 K poultry oligo microarrays indicated that ACTH treatment affected the expression of 134 genes. Several transcripts assigned to genes involved in the adrenal ACTH signaling pathway and steroidogenic enzymes were identified as differentially expressed by ACTH treatment. Real-time PCR on 18 selected genes confirmed changes in transcript levels of 11 genes, including MC2R, CREM, Cry, Bmal1, Sqle, Prax1, and StAR. Only 4 genes revealed to be differentially expressed between higher and lower adrenal responders to ACTH treatment.ConclusionThe results from the present study reveal putative candidate genes; their role in regulation of adrenal functions and adaptability to stress should be further investigated.

Intensity and duration of corticosterone response to stressful situations in Japanese quail divergently selected for tonic immobility

Two genotypes of Japanese quail have been divergently selected since the 1980s for long (LTI) or short (STI) duration of tonic immobility [Mills, A.D., Faure, J.M., 1991. Divergent selection for duration of tonic immobility and social reinstatement behavior in Japanese quail ( Coturnix coturnix japonica) chicks. J. Comp. Psychol. 105(1), 25–38.], an unlearnt catatonic state characteristic of a behavioral fear response ([Jones, R.B., 1986. The tonic immobility reaction of the domestic fowl: a review. World’s Poult. Sci. J. 42(1), 82–97.]; [Mills, A.D., Faure, J.M., 1991. Divergent selection for duration of tonic immobility and social reinstatement behavior in Japanese quail ( Coturnix coturnix japonica) chicks. J. Comp. Psychol. 105(1), 25–38.]). The results of several behavioral tests conducted in LTI and STI quail have led to the conclusion that LTI quail are more fearful than STI quail [Faure, J.M., Mills, A.D., 1998. Improving the adaptability of animals by selection. In: Grandin, T. (Eds.), Genetics and the behavior of domestic animals. Academic Press, San Diego, pp. 235–264.]). However, few studies to date have focused on the Hypothalamic-Pituitary-Adrenal (HPA) axis response to stressful situations in LTI and STI quail, although the HPA axis is involved in fear responses [Siegel, H.S., 1971. Adrenals, Stress and the Environment. World’s Poult. Sci. J. 27, 327–349.]. The corticosterone (CORT) response to various putatively stressful situations was therefore assessed in LTI and STI genotypes of quail in order to investigate their HPA axis reactivity to stress. Repeated induction of TI or 1 min manual restraint induced significant and comparable increases in CORT levels in both genotypes as a TI response. On the other hand, higher CORT responses were found in STI than in LTI quail when the manual restraint period lasted for 2 min or after restraint in a crush cage. Maximum CORT responses and genotype differences were maintained throughout the latter test even when it lasted for 120 min. Investigation of the CORT response to a single TI episode showed that CORT levels at the end of TI were negatively correlated with TI duration. Other experimental contexts consisting of isolation in a familiar or novel environment or the presentation of a novel object induced slight but significant and comparable increases in CORT response in both genotypes, whereas change of cagemates did not. In conclusion, the present findings indicate that differences in HPA axis response are observed between LTI and STI genotypes when quail are submitted to intense stressors, resulting in a high and prolonged CORT response. By contrast, plasma corticosterone concentrations do not differ between STI and LTI quail in response to stressful situations of lower intensity, which evoke responses limited in amplitude and duration. Genetic selection for divergent duration of TI has thus affected the HPA axis response to stress, and LTI and STI quail constitute an interesting model to investigate genetic variability of HPA axis activity in birds. More specifically, these genotypes of quail could be used to investigate the occurrence of functional differences at different levels of the HPA axis in order to explain the present findings.

Spatial ability is impaired and hippocampal mineralocorticoid receptor mRNA expression reduced in zebra finches ( Taeniopygia guttata ) selected for acute high corticosterone response to stress

In mammals, stress hormones have profound influences on spatial learning and memory. Here, we investigated whether glucocorticoids influence cognitive abilities in birds by testing a line of zebra finches selectively bred to respond to an acute stressor with high plasma corticosterone (CORT) levels. Cognitive performance was assessed by spatial and visual one-trial associative memory tasks. Task performance in the high CORT birds was compared with that of the random-bred birds from a control breeding line. The birds selected for high CORT in response to an acute stressor performed less well than the controls in the spatial task, but there were no significant differences between the lines in performance during the visual task. The birds from the two lines did not differ in their plasma CORT levels immediately after the performance of the memory tasks; nevertheless, there were significant differences in peak plasma CORT between the lines. The high CORT birds also had significantly lower mineralocorticoid receptor mRNA expression in the hippocampus than the control birds. There was no measurable difference between the lines in glucocorticoid receptor mRNA density in either the hippocampus or the paraventricular nucleus. Together, these findings provide evidence to suggest that stress hormones have important regulatory roles in avian spatial cognition.

Heritability of corticosterone response and changes in life history traits during selection in the zebra finch

Vertebrates respond to environmental stressors through the neuro-endocrine stress response, which involves the production of glucocorticoids. We have selected independent, duplicate divergent lines of zebra finches for high, low and control corticosterone responses to a mild stressor. This experiment has shown that over the first four generations, the high lines have demonstrated a significant realized heritability of about 20%. However, the low lines have apparently not changed significantly from controls. This asymmetry in response is potentially because of the fact that all birds appear to be showing increased adaptation to the environment in which they are housed, with significant declines in corticosterone response in control lines as well as low lines. Despite the existence of two- to threefold difference in mean corticosterone titre between high and low lines, there were no observed differences in testosterone titre in adult male birds from the different groups. In addition, there were no consistent, significant differences between the lines in any of the life history variables measured--number of eggs laid per clutch, number of clutches or broods produced per pair, number of fledglings produced per breeding attempt, nor in any of egg, nestling and fledgling mortality. These results highlight the fact that the mechanisms that underlie variation in the avian physiological system can be modified to respond to differences between environments through selection. This adds an additional level of flexibility to the avian physiological system, which will allow it to respond to environmental circumstances.

Japanese Quail Selected for High Plasma Corticosterone Response Deposit High Levels of Corticosterone in Their Eggs

Poor habitat quality or body condition often correlates with high responsiveness of the hypothalamo-pituitary-adrenal (HPA) axis rather than with elevated baseline levels of glucocorticoids. We hypothesized that, for egg-laying vertebrates, high responsiveness of the HPA axis would correspond to high concentrations of corticosterone in yolk. We tested the prediction that Japanese quail (Coturnix coturnix japonica) selected for high plasma corticosterone response to brief immobilization (HS quail) would lay eggs with higher yolk corticosterone concentrations than birds selected for low response (LS quail). Quail from both lines were left undisturbed, outside of the stressors associated with daily management, before a first round of egg collection. In a second experiment, quail of both lines were experimentally stressed during the week before egg collection. In both cases we found quail from the HS line to lay eggs with significantly higher yolk corticosterone concentrations than quail of the LS line. After exposure to added experimental stressors, the line difference was more pronounced (increasing from 62% to 96%). There was no line difference in concentrations of yolk testosterone. Our results suggest that (1) genetic differences underly differences in the transfer of maternal corticosterone to yolk and (2) females may be able to control deposition of corticosterone into yolk through a mechanism independent of baseline corticosterone titers.

A Testicular Influence on Restraint-Induced Activation of Medial Parvocellular Neurons in the Paraventricular Nucleus in the Male Rat

To gauge the strength by which the testes influence stress-induced activation of neurosecretory neurons in the paraventricular nucleus, we studied within medial parvocellular neurons the effects of gonadectomy on restraint-induced Fos-immunoreactivity and on CRH and arginine vasopressin (AVP) heteronuclear (hn) RNA expression levels. Relative to intact male rats (sham-gonadectomized), gonadectomized rats showed a significantly greater number of medial parvocellular neurons recruited to express Fos protein evident at 0.5 h and from 1-4 h after the onset of 30-min restraint exposure. Restraint provoked a transient increase in hnCRH levels that was maximal at the end of restraint and this was significant only in gonadectomized rats. Both intact and gonadectomized rats displayed an increase in AVP hnRNA expression levels in response to restraint exposure; however, it was significantly greater in gonadectomized rats. All of these responses were accompanied by a higher corticosterone response in gonadectomized compared with intact rats and negatively correlated with plasma testosterone concentrations, with the exception of stress-induced CRH transcription. These findings indicate an inhibitory role for testosterone on stress-induced indexes of synaptic (Fos) and transcriptional (AVP hnRNA) activation among hypophysiotropic paraventricular neurons and provide meaningful end points with which to pursue how and where androgens operate on stress-related input to the paraventricular nucleus motor neurons.

Ecophysiological constraints associated with aggression, and evolution toward pacifism in Spalax ehrenbergi

Evolution from a solitary way of life to sociality involves changes in the modalities of within-population aggression. This paper is concerned with environmental causes of variation in aggression within the complex of mole-rat species Spalax ehrenbergi. We focus on physiological constraints associated with aggressive behaviour, i.e. those resulting from emotional arousal and thus stress. Aggression, social stress sensitivity and urine osmolarity were studied in males of two chromosomal species of Spalax ehrenbergi, 2n = 52 (occurring in cool humid areas) and 2n = 60 (occurring in warm arid zones). Males with 2n = 52 reached a higher level of within-population aggression during a 3-round tournament (an average, 488 ± 140 acts) than males with 2n = 60 (163 ± 54 acts). The species with 2n = 52 displayed a higher corticosterone response after a social encounter (in average, 5.15 ± 0.54 μg/100 ml) than that with 2n = 60 (3.0 ± 0.3 μg/100 ml) whereas resting levels of this hormone were low and not different between the two species. Urine osmolarity was significantly higher in males with 2n = 60 (331.9 ± 18.6 mmol/kg) than males with 2n = 52 (267.3 ± 10.9 mmol/kg). Considering the overall general trend urine osmolarity tended to be negatively related to the level of aggression, while corticosterone levels tended to vary positively with aggressiveness (Fig. 3). Our results allow further discussion of the hypothesis that high levels of aggression could be selected against in arid habitats due to their physiological correlates (decrease in water economy, increased corticosterone leading to potential energy mobilisation and loss). We propose that behavioural ecophysiology could have contributed to the radiation of the S. ehrenbergi superspecies into increasingly arid environments, and may favour evolution toward social tolerance.

Both Bone Marrow- and Non-Bone Marrow-Associated Factors Determine Susceptibility to Experimental Autoimmune Encephalomyelitis of BUF and WAG Rats

To determine the feasibility of treatment with allogeneic bone marrow for experimental autoimmune encephalomyelitis, we investigated the susceptibility to experimental autoimmune encephalomyelitis of bone marrow chimeras using BUF, (WAG×BUF)F1 (high responder), and WAG (low responder) rats. In contrast to previous studies in which other rat strains were used, the response was largely determined by the genotype of the grafted bone marrow, but the influence of a non-bone marrow-associated factor was evident. The latter factor was identified as a low corticosterone response in BUF rats and a high corticosterone response in WAG rats. After adrenalectomy, a significant proportion of WAG rats developed clinical experimental autoimmune encephalomyelitis. The bone marrow-associated factor of resistance appeared to be the activity of cyclophosphamide-sensitive suppressor cells. The latter cells were found to interfere with the formation of inflammatory foci in the central nervous system, while corticosterone primarily prevents the clinical expression of lesions.

Short-Latency Stressor Effects on Tonic Immobility Fear Reactions of Japanese Quail Divergently Selected for Adrenocortical Responsiveness to Immobilization

Despite evidence for a positive association between adrenocortical activation and fearfulness, the effects of chronic (12 to 20 h) exposure to stressful stimulation on the fear reactions of Japanese quail genetically selected for high (HS) or low (LS) plasma corticosterone response to immobilization stress are not straightforward. The present study examined tonic immobility fear responses in quail of both lines that, immediately prior to testing, either had been allowed to remain undisturbed or had been exposed to an acute stressor similar to that used in the selection program (i.e., a short-latency stressor; 5 min of immobilization). Tonic immobility responses were generally more pronounced in quail of the HS line than the LS line, and they were exaggerated in both lines after exposure to stress treatment. The findings provide further support for the suggestion that selection for exaggerated or reduced adrenocortical responsiveness may have been accompanied by a concomitant and unconscious effect on underlying fearfulness.

Effects of Vitamin C supplementation on the adrenocortical and tonic immobility fear reactions of Japanese quail genetically selected for high corticosterone response to stress

Japanese quail chicks (18 days of age), from a line genetically selected for high plasma corticosterone response to brief immobilization stress, were treated for 24 h with either untreated drinking water or with a Vitamin C (1200 ppm of ascorbic acid: AA) solution. The chicks were subsequently either exposed to a stressful cooping procedure (which lasted for 12–21 h and incorporated animal capture inescapable exposure to novelty, a reduction in floor space and in ambient temperature, and food and water deprivation), or they remained undisturbed. Cooping caused considerable elevation of circulating corticosterone concentrations, thus illustrating its stressful nature. Treatment with AA failed to affect the adrenocortical response to cooping, but it significantly attenuated the tonic immobility fear reactions of stressed and unstressed quail. The mechanisms underpinning the behavioural consequences of AA supplementation have yet to be determined. The results are discussed in terms of, first, the relationship between adrenocortical activation and fearfulness, and second, their implications for poultry welfare and performance.

Research Note: Open-Field Behavior of Japanese Quail Chicks Genetically Selected for Low or High Plasma Corticosterone Response to Immobilization Stress

Open-field behavior was examined in Japanese quail chicks genetically selected for either reduced (LS, low stress) or exaggerated (HS, high stress) plasma corticosterone response to immobilization stress. Chicks of the LS line showed less freezing and ambulated sooner than did their HS counterparts. These findings suggest that exposure to an open-field or novel environment elicited less fear in LS than in HS chicks. They also support the suggestion that fearfulness and adrenocortical activation are positively associated and indicate that selection for differential adrenocortical responsiveness exerted concomitant effects on fear-related behavior.

Glucocorticoids in the nonobese diabetic (NOD) mouse: Basal serum levels, effect of endocrine manipulation and immobilization stress

The NOD mouse is a recognized model for studying immunologically mediated insulin-dependent diabetes mellitus (IDDM). In most colonies, the disease appears with a greater preponderance in females than in males and castration alters the expression of the disease. The prevalence of diabetes may also vary depending upon environmental factors such as stress. Therefore, we measured in the NOD mouse serum glucocorticoid concentrations in basal and stress conditions. We observed in NOD as well as in C57BL/6 mice, taken as controls, a circadian rhythm of corticosterone, with females having higher values than males. After a single restraint stress, female and male NOD mice exhibit a comparable response, whereas after repeated stress, males respond significantly less than females, suggesting an adaptation phenomenon. In contrast, there is no difference in the pattern of corticosterone response of C57BL/6 females and males to both types of stress, but females always respond better than males. Moreover, whatever the stress considered, NOD mice generally exhibit a higher corticosterone response than C57BL/6 mice. The sexual dimorphism in diabetes expression in NOD mice may be related to the levels of corticosterone, a hyperglycemic hormone, in both basal and stress conditions. However, the understanding of corticosteroid effects in this model of type I IDDM is rather complex given their well known anti-inflammatory and immunosuppressive effects in other models of autoimmune diseases.

The influence of stress treatment on femur cortical bone porosity and medullary bone status in Japanese quail selected for high and low blood corticosterone response to stress

1. 1. Femurs taken from Japanese quail ( Coturnix coturnix japonica) genetically selected for either exaggerated (HS; high-stress) or reduced (LS; low-stress) blood corticosterone (B) response to unfamiliar environments were examined to determine their cortical bone porosity (CBP; degree of osteoporosis) and medullary bone (MB) status following treatment with or without stress. 2. 2. Femur CBP was elevated in both sexes of stressed, HS-line quail and was attributed directly to the presumably exaggerated blood B responses known to occur in this line as a consequence of the stress treatments used. 3. 3. The increase in CBP in stressed, HS-line birds occurred independently of changes in the numbers of osteoclast cells (CLASTS) associated with cortical bone. 4. 4. Stress treatment was associated with lower CLAST numbers/mm 2 of MB and with increased MB accretion. 5. 5. These stress-induced effects were considered to be the consequence of a reduced rate of lay found in stressed quail hens. 6. 6. There was only marginal evidence for a direct effect of B in stimulating MB resorption.