Circadian Variation in Cortisol Reactivity to an Acute Stressor

To investigate the role of the circadian pacemaker in cortisol reactivity to a cold pressor challenge, 26 diurnally subjects participated in a constant‐routine protocol and were divided into two groups. Group 1 started immediately after a monitored sleep period at 09:00 h, while group 2 started 12 h later. After 2 h of adaptation, a cold pressor test was presented every 3 h. The cortisol response was assessed by means of saliva samples that were taken before and after the test. The pretest samples were considered to be base‐rate measures and base‐rate values as subtracted from post‐test values were considered as reactivity measures. Both measures showed distinct Time‐of‐Day variations (respectively: F_7,168 = 16.92, p < 0.001, ε = 0.383; and F_7,175 = 8.01, p < 0.001, ε = 0.523). These findings are interpreted as evidence for the existence of an endogenous circadian periodicity underlying the sensitivity of the hypothalamus–pituitary–adrenal (HPA)‐axis to acute stress.     

Coping with an Acute Psychosocial Challenge: Behavioral and Physiological Responses in Young Women

Despite the relevance of behavior in understanding individual differences in the strategies used to cope with stressors, behavioral responses and their relationships with psychobiological changes have received little attention. In this study on young women, we aimed at analyzing the associations among different components of the stress response and behavioral coping using a laboratory psychosocial stressor. The Ethological Coding System for Interviews, as well as neuroendocrine, autonomic and mood parameters, were used to measure the stress response in 34 young women (17 free-cycling women in their early follicular phase and 17 oral contraceptive users) subjected to the Trier Social Stress Test (TSST) and a control condition in a crossover design. No significant differences in cardiac autonomic, negative mood and anxiety responses to the stressor were observed between the two groups of women. However, women in the follicular phase showed a higher cortisol response and a larger decrease in positive mood during the social stress episode, as well as greater anxiety overall. Interestingly, the amount of displacement behavior exhibited during the speaking task of the TSST was positively related to anxiety levels preceding the test, but negatively related to baseline and stress response values of heart rate. Moreover, the amount of submissive behavior was negatively related to basal cortisol levels. Finally, eye contact and low-aggressiveness behaviors were associated with a worsening in mood. Overall, these findings emphasize the close relationship between coping behavior and psychobiological reactions, as well as the role of individual variations in the strategy of coping with a psychosocial stressor.     

Effect of Acute Stressor and Serotonin Transporter Genotype on Amygdala First Wave Transcriptome in Mice

The most prominent brain region evaluating the significance of external stimuli immediately after their onset is the amygdala. Stimuli evaluated as being stressful actuate a number of physiological processes as an immediate stress response. Variation in the serotonin transporter gene has been associated with increased anxiety- and depression-like behavior, altered stress reactivity and adaptation, and pathophysiology of stress-related disorders. In this study the instant reactions to an acute stressor were measured in a serotonin transporter knockout mouse model. Mice lacking the serotonin transporter were verified to be more anxious than their wild-type conspecifics. Genome-wide gene expression changes in the amygdala were measured after the mice were subjected to control condition or to an acute stressor of one minute exposure to water. The dissection of amygdalae and stabilization of RNA was conducted within nine minutes after the onset of the stressor. This extremely short protocol allowed for analysis of first wave primary response genes, typically induced within five to ten minutes of stimulation, and was performed using Affymetrix GeneChip Mouse Gene 1.0 ST Arrays. RNA profiling revealed a largely new set of differentially expressed primary response genes between the conditions acute stress and control that differed distinctly between wild-type and knockout mice. Consequently, functional categorization and pathway analysis indicated genes related to neuroplasticity and adaptation in wild-types whereas knockouts were characterized by impaired plasticity and genes more related to chronic stress and pathophysiology. Our study therefore disclosed different coping styles dependent on serotonin transporter genotype even directly after the onset of stress and accentuates the role of the serotonergic system in processing stressors and threat in the amygdala. Moreover, several of the first wave primary response genes that we found might provide promising targets for future therapeutic interventions of stress-related disorders also in humans.     

Variations of Some Physiological and Immunological Parameters in Siberian Sturgeon (Acipenser baerii,Brandt, 1869) Subjected to an Acute Stressor

This study was carried out to investigate the effect of an acute stressor on the variation of some physiological and immunological parameters of Siberian sturgeon (Acipenser baerii) juveniles. Fish, reared in 3 tanks for 10 weeks, were used for this study. The acute stress of fish consisted of 2 min of air exposure stress. Plasma levels of cortisol, glucose, and lactate as well as lysozyme activity in plasma were measured before stress and 1 hr, 3 hr, 6 hr, 9 hr, 12 hr, and 24 hr after stress. The plasma cortisol significantly increased in the highest level 1 hr after stress, yet it gradually declined after 3 hr. The glucose significantly increased only 1 hr after stress. There was no significant difference between plasma lactate prestress and poststress. Moreover, lysozyme activity was enhanced by stress, thus reaching the highest level 9 hr after stress. The results of this study indicate that Siberian sturgeon not only have a rapid response to acute stress, but also a great capacity for recovery from stress, thus returning physiological parameters to prestress levels after 6 hr.     

Selective Inhibition of Acetylcholinesterase in the Cerebellum and Hippocampus of Mice Following an Acute Treatment with Malathion

Adult male ICR mice were treated by intraperitoneal injection with 250?mg/kg of bodyweight of commercial malathion (a dose corresponding to 1/12 the LD50). After 6?h, acetylcholinesterase (AChE) activity in blood, liver, and six brain regions was determined. A statistically significant inhibition was observed in whole blood (23%), liver (21%), and, in particular, the central nervous system; the greatest degree of AChE inhibition was observed in the cerebellum (45%), followed by the hippocampus (29%). There was no significant change in AChE activity in the caudate putamen, frontal cortex, midbrain, or pons medulla. These results demonstrate that the magnitude of AChE inhibition in peripheral tissues does not accurately reflect the central-inhibitory effects of malathion on AChE activity in specific brain regions.     

Cell Reactions Following Acute Brain Injury: A Review

The proliferative behavior of glia following a cerebral stab wound in adult rats is reviewed. Proliferation was determined by both PCNA and [³H]thymidine labeling. Microglia were the first cells to divide and constituted the bulk of dividing cells. Both ramified and ameboid microglia divided. A smaller number of astrocytes entered the cell cycle a day later and were shown to derive from differentiated reactive cells. No differentiated oligodendroglia were labeled by thymidine, although a small number of dividing immature oligodendroglia could be detected in cultures of cells labeled in vivo. Recent studies of the properties of oligodendroglial precursors in brain repair mechanisms are discussed. The results so far support our conclusion that differentiated oligodendrocytes do not divide.     

The Importance of Social Condition in the Hormonal and Behavioral Responses to an Acute Social Stressor in the Male Siberian Dwarf Hamster (Phodopus sungorus)

Social condition is an important factor in determining the behavioral and hormonal responses to a social stressor in the Siberian dwarf hamster (Phodopus sungorus). We predict that males housed with a female or a family (female and pups) will show an increase in the magnitude of the behavioral and hormonal responses to a male intruder compared to those of individually housed males. Three treatment groups were studied: individually housed males that had been previously group-housed in same-sex colonies (males,n= 10), males housed with a female (male + female,n= 9), and males housed with their female and pups (male + family,n= 12). Males were monitored for aggressive behavior toward an intruder male for 10 min. Blood samples were taken at baseline and after the encounter. Male + female and male + family groups spent more time in aggressive behavior (P< 0.05), such as attacking (P< 0.05) and fighting (P<0.05), than did individually housed males. These same groups showed significant increases in plasma cortisol after the encounter (P< 0.01) whereas there were no significant increases in plasma cortisol in solitary males. All groups showed significantly lower levels of plasma testosterone (male,P< 0.001, male + female,P< 0.05; male + family,P< 0.01) whereas a significant increase in prolactin occurred only in the male + family group (P< 0.05). There was a significant positive correlation between postencounter cortisol levels and total number of minutes spent in aggressive behavior (P< 0.05). These results demonstrate that the introduction of a novel intruder male results in an activation of the hypothalamic–pituitary–adrenocortical axis and a suppression of the reproductive axis. Furthermore, pairing of a male with a female alters the behavioral and hormonal responses to an intruder male.     

Posttraumatic Stress Disorder (PTSD) Patients Exhibit a Blunted Parasympathetic Response to an Emotional Stressor

Diminished parasympathetic reactivity is a physiological feature of posttraumatic stress disorder (PTSD). The objective of this study was to compare female PTSD patients with non-traumatized healthy women with respect to autonomic cardiovascular regulation during exposure to two stressors. Hospitalized PTSD patients (n = 52) and controls (n = 37) completed standardized laboratory-based stress testing including a mental arithmetic test and a standardized audiotape recording of a crying infant. Controls and PTSD patients both showed a significantly increased heart rate and reduced pre-ejection period from baseline rest to the arithmetic stressor. However, as judged from nonsignificant changes in baroreflex sensitivity, parasympathetic activation caused by the crying infant stressor was blunted in PTSD patients as compared to healthy individuals. Under the crying infant condition, a vagal dominance was observed only in controls, and not in PTSD patients. Our data demonstrate that, in PTSD patients, diminished parasympathetic reactivity is not restricted to trauma-related events but can also be observed in response to a social stimulus such as listening to a crying infant. This finding suggests that the altered vagal reactivity in PTSD patients reflects the physiological consequences of a generally disturbed autonomous response to emotionally relevant stressors.