Bettina Weber

With aging in humans the activity of the hypothalamus-pituitary-adrenal system increases and its diurnal amplitude flattens.

There is compelling evidence for feedback disturbances in the hypothalamus-pituitary-adrenal system associated with human aging as assessed by challenge tests. However, reports about age-related changes in human basal activity are ambiguous and to date little is known about changes in the pulsatile features of the HPA system. To investigate these changes we studied twenty-two healthy male and eleven healthy female subjects ranging from 23 to 85 and 24 to 81 years respectively. 24-hour blood sampling with 30 minute sampling intervals was performed. From 18.00 to 24.00 hours blood was sampled every 10 minutes for analysis of pulsatile features of HPA activity. Statistical analysis revealed that age in particular had major effects upon basal HPA-system activity: there was a significant age-associated increase in minimal (p < 0.0001) and mean (p < 0.02) cortisol plasma concentrations, but no alteration in pulsatile features. We found no age-cortisol correlation during daytime, but were able to demonstrate a strong impact of age upon cortisol plasma levels from 20.00 to 1.30 hours. The diurnal amplitude of cortisol (p < 0.005) and ACTH (p < 0.006), relative to the 24-hour mean of the hormones, showed an age-associated decline. Additionally, the evening cortisol quiescent period (p < 0.01) was shortened in the elderly, suggesting increasingly impaired circadian function in aging. Our results suggest an increased basal activity and a flattened diurnal amplitude of the HPA system in the elderly.

Testosterone, gonadotropin, and cortisol secretion in male patients with major depression.

OBJECTIVE Previous studies of sex hormone concentrations in depression yielded inconsistent results. However, the activation of the hypothalamic-pituitary-adrenal system seen in depression may negatively affect gonadal function at every level of regulation. The objective of this study was to explore whether major depressive episodes are indeed associated with an alteration of gonadal function. METHODS Testosterone, pulsatile LH secretion, FSH, and cortisol were assessed using frequent sampling during a 24-hour period in 15 male inpatients with major depression of moderate to high severity and in 22 healthy comparison subjects (age range 22-85 years). RESULTS An analysis of covariance model showed that after adjustment for age only, daytime testosterone (p < .01), nighttime testosterone (p < .05), and 24-hour mean testosterone secretion (p < .01) were significantly lower in the depressed male inpatients. There was also a trend for a decreased LH pulse frequency in the depressed patients (p < .08). CONCLUSIONS Gonadal function may be disturbed in men with a depressive episode of moderate to high severity.

Donepezil-induced REM sleep augmentation enhances memory performance in elderly, healthy persons

Previous research in younger individuals has shown that acetylcholinesterase inhibitors may enhance REM sleep. The present study indicates that in the elderly, donepezil, an acetylcholinesterase inhibitor, also exerts a marked effect on REM sleep parameters--percentage of REM sleep and REM density were increased whereas REM latency was reduced. In addition, we also found a correlation between memory performance and REM sleep. Based on these findings, we conclude that there is an interrelationship between cognitive performance and amount of REM sleep in elderly humans as has been previously shown in animals and young adults.

Testosterone, androstenedione and dihydrotestosterone concentrations are elevated in female patients with major depression

Hyperactivity of the HPA-system in major depression is reflected by an increased secretion of adrenal hormones especially cortisol and dehydroepiandrosterone (DHEA). In women for whom androgenicity is associated with cardiovascular disorders the dominant source of androstenedione and testosterone secretion are the adrenal glands. To date, there is only sparse information about the regulation of androstenedione, testosterone and dihydrotestosterone (DHT) concentrations in women with severe major depression.Therefore, 11 pre- and postmenopausal, severely depressed, hypercortisolemic women (Hamilton Depression Scale, 31.3+/-5.9; age, 28-77 yrs; mean, 48. 1+/-18.1 yrs) and 11 age-matched healthy female controls (age, 24-81 yrs; mean, 47.9+/-21.5 yrs) underwent a 24 hour (h) blood sampling starting at 0800 h with 30-minute sampling intervals. By applying multivariate analysis of covariance with age as covariate, androstenedione, testosterone and DHT plasma levels at 0900 h show a trend for elevated concentrations in depressed women compared to controls (F(1,19)=2.7; P=0.057). Univariate F tests reveal a significant difference between the groups for androstenedione (4. 19+/-1.571 vs 2.584+/-1.257 nmol/l; P<0.05) testosterone (1.110+/-0. 278 vs 0.833+/-0.347 nmol/l; P<0.05) and DHT (0.656+/-0.207 vs 0. 483+/-0.242 nmol/l; P<0.05). Mean ACTH (16.4+/-10.4 vs 10.4+/-2.4 pmol/l; P=0.89), LH (13.5+/-11.8 vs 8.9+/-9.2 IU/l; P=0.12), FSH (35. 2+/-33.1 vs 31.3+/-35.7 IU/l; P=0.67) and estradiol (135.4+/-157.4 vs 82.2+/-85.1 pmol/l; P=0.20) plasma levels did not differ between patients and controls. Further, there was a trend towards an age related decline in testosterone secretion in healthy controls (r=-0. 24; P=0.08) which did not occur in depressed patients (r=0.17; P=0. 96), while the calculated ratio of DHEA to testosterone was similar in both groups (0.2+/-0.14 vs 0.13+/-0.7; P=0.21, unpaired t-test). In conclusion, androstenedione, testosterone and DHT concentrations all were increased in hypercortisolemic women with severe major depression. These findings are best explained as a consequence of an overstimulation of the adrenal glands through pituitary and hypothalamic sites of the HPA-system.

Dreaming and insomnia: dream recall and dream content of patients with insomnia.

The present study investigated dream recall frequency and dream content of patients with insomnia in comparison to healthy controls. Patients’ dream recall frequency was elevated, due mainly to their heightened frequency of nocturnal awakenings. Dream content seems to reflect waking life stressors found in these patients, i.e. dream emotions were more negative and dreams were characterized by themes of depression, ‘negatives’ in self‐description and health themes. Patients taking antidepressants showed lower dream recall frequency than patients without any medication; benzodiazepine intake, however, did not affect dream recall frequency. Both drug groups reported more positively toned dreams than drug‐free patients. It is suggested that future studies should use more dreams per subject in order to reduce error variance of the dream content measures and more detailed measures of waking life stress.

Mineralocorticoid Receptor also Modulates Basal Activity of Hypothalamus-Pituitary-Adrenocortical System in Humans

Hippocampal mineralocorticoid (MRs) and glucocorticoid receptors (GRs) have been demonstrated to regulate the activity of the hypothalamus-pituitary-adrenocortical (HPA) system. To elucidate the role of the hippocampal MR in the circadian activity of the human HPA system, we studied diurnal secretory profiles of corticotropin (ACTH) and cortisol in 10 healthy male humans before and after an 8-day treatment with the MR antagonist spironolactone. 24-hour blood sampling at 30-min intervals was performed for estimation of cortisol (q30) and ACTH (q120). Saliva cortisol was measured for estimation of unbound cortisol. At the end of the 24-hour sampling period a corticotropin-releasing hormone (CRH) challenge was performed. High plasma concentrations of the active metabolite canrenone were achieved (begin of sampling: 2,653 ± 693 nmol/l; end of sampling: 747 ± 177 nmol/l). There was a significant increase in the diurnal minima (37.1 ± 13.3 vs. 23.7 ± 8.9 nmol/l, p < 0.02) and mean cortisol (193.5 ± 25.8 vs. 173.0 ± 23.0 nmol/l, p < 0.03) plasma concentrations. However, the diurnal peak concentrations and pulsatile secretory features were unchanged after spironolactone treatment. For saliva cortisol, the only significant treatment difference was a decrease in the diurnal amplitude of cortisol relative to the diurnal mean concentration (2.56 ± 0.47 vs. 3.11 ± 0.87, p < 0.03). After spironolactone treatment there was a decrease in diurnal mean ACTH concentrations (46.2 ± 14.4 vs. 41.8 ± 10.3 pmol/l). There was no difference in the ACTH and cortisol response after infusion of CRH before and after spironolactone treatment. CBG plasma concentrations were significantly increased (22.4 ± 2.3 vs. 19.2 ± 2.7 mg/l, p < 0.01) after spironolactone treatment, which possibly contributed to the observed increase in plasma cortisol. In summary, as predicted from animal studies we found significant effects of MR antagonization to be restricted to time windows of low HPA system activity. These findings are similar to the effects of aging upon the HPA system. However, the effect of spironolactone treatment was small, suggesting that the HPA system activity in humans is modulated but not regulated by the hippocampal MR.

Insulin-like growth factor-I (IGF-I) plasma concentrations are increased in depressed patients

There is some evidence that the somatotrophic system in depression, as assessed by basal growth hormone (GH) concentrations and by GH releasing hormone (GHRH) challenge, might be dysfunctional. However, the rather limited data have been inconclusive so far and plasma concentrations of both insulin-like growth factor-1 (IGF-I) and binding proteins (IGFBP 1 to IGFBP-6) have not been measured simultaneously in depressed patients. We studied 24 severely depressed patients and 33 healthy controls and estimated 24-hour mean plasma cortisol, six-hour evening mean plasma growth hormone (GH), morning plasma IGF-I, IGFBP 2 and 3 and GH-binding protein (GH-BP). Twenty-four-hour mean cortisol (306 +/- 69 vs. 196 +/- 30 nmol/l, p < .001) and IGF-I (157 +/- 40 vs. 120 +/- 33 micrograms/l, p < .01) plasma concentrations were found to be significantly increased in depressed patients, while there was no difference in GH or binding proteins between both groups. MANOVA analysis revealed age and diagnosis to have main effects upon plasma IGF-I. Especially young age and a diagnosis of major depression are associated with higher plasma IGF-I. After treatment only patients in remission had attenuated IGF-I plasma concentrations. We conclude that plasma IGF-I is increased in acutely depressed patients similar to other states of hypercortisolemia.

Biological soil crusts accelerate the nitrogen cycle through large NO and HONO emissions in drylands

Significance Biological soil crusts (biocrusts), occurring on ground surfaces in drylands throughout the world, are among the oldest life forms consisting of cyanobacteria, lichens, mosses, and algae plus heterotrophic organisms in varying proportions. They prevent soil erosion and nurture ecosystems by fixing carbon and nitrogen from the atmosphere. Here, we show that the fixed nitrogen is processed within the biocrusts, and during this metabolic activity, nitrogen oxide and nitrous acid are released to the atmosphere. Both of these gases are highly relevant, as they influence the radical formation and oxidizing capacity of the lower atmosphere, also interacting with climate change. In drylands, biocrusts appear to play a key role both in nitrogen fixation and the release of atmospheric reactive nitrogen. Reactive nitrogen species have a strong influence on atmospheric chemistry and climate, tightly coupling the Earth’s nitrogen cycle with microbial activity in the biosphere. Their sources, however, are not well constrained, especially in dryland regions accounting for a major fraction of the global land surface. Here, we show that biological soil crusts (biocrusts) are emitters of nitric oxide (NO) and nitrous acid (HONO). Largest fluxes are obtained by dark cyanobacteria-dominated biocrusts, being ∼20 times higher than those of neighboring uncrusted soils. Based on laboratory, field, and satellite measurement data, we obtain a best estimate of ∼1.7 Tg per year for the global emission of reactive nitrogen from biocrusts (1.1 Tg a−1 of NO-N and 0.6 Tg a−1 of HONO-N), corresponding to ∼20% of global nitrogen oxide emissions from soils under natural vegetation. On continental scales, emissions are highest in Africa and South America and lowest in Europe. Our results suggest that dryland emissions of reactive nitrogen are largely driven by biocrusts rather than the underlying soil. They help to explain enigmatic discrepancies between measurement and modeling approaches of global reactive nitrogen emissions. As the emissions of biocrusts strongly depend on precipitation events, climate change affecting the distribution and frequency of precipitation may have a strong impact on terrestrial emissions of reactive nitrogen and related climate feedback effects. Because biocrusts also account for a large fraction of global terrestrial biological nitrogen fixation, their impacts should be further quantified and included in regional and global models of air chemistry, biogeochemistry, and climate.

Modeling of subsurface calcite dissolution, including the respiration and reoxidation processes of marine sediments in the region of equatorial upwelling off Gabon

Abstract Mineralization of organic matter and the subsequent dissolution of calcite were simulated for surface sediments of the upper continental slope off Gabon by using microsensors to measure O2, pH, pCO2 and Ca2+ (in situ), pore-water concentration profiles of NO3−, NH4+, Fe2+, and Mn2+ and SO42− (ex situ), as well as sulfate reduction rates derived from incubation experiments. The transport and reaction model CoTReM was used to simulate the degradation of organic matter by O2, NO3−, Fe(OH)3 and SO42−, reoxidation reactions involving Fe2+ and Mn2+, and precipitation of FeS. Model application revealed an overall rate of organic matter mineralization amounting to 50 μmol C cm−2 yr−1, of which 77% were due to O2, 17% to NO3− and 3% to Fe(OH)3 and 3% to SO42−. The best fit for the pH profile was achieved by adapting three different dissolution rate constants of calcite ranging between 0.01 and 0.5% d−1 and accounting for different calcite phases in the sediment. A reaction order of 4.5 was assumed in the kinetic rate law. A CaCO3 flux to the sediment was estimated to occur at a rate of 42 g m−2 yr−1 in the area of equatorial upwelling. The model predicts a redissolution flux of calcite amounting to 36 g m−2 yr−1, thus indicating that ∼90% of the calcite flux to the sediment is redissolved.

Biological Soil Crusts: An Organizing Principle in Drylands

This volume summarizes our current understanding of biological soil crusts (biocrusts), which are omnipresent in dryland regions. Since they cover the soil surface, they influence, or even control, all surface exchange processes. Being one of the oldest terrestrial communities, biocrusts comprise a high diversity of cyanobacteria, algae, lichens and bryophytes together with uncounted bacteria, and fungi. The authors show that biocrusts are an integral part of dryland ecosystems, stabilizing soils, influencing plant germination and growth, and playing a key role in carbon, nitrogen and water cycling. Initial attempts have been made to use biocrusts as models in ecological theory. On the other hand, biocrusts are endangered by local disruptions and global change, highlighting the need for enhanced recovery methods. This book offers a comprehensive overview of the fascinating field of biocrust research, making it indispensable not only for scientists in this area, but also for land managers, policy makers, and anyone interested in the environment