The characteristic endogenous circadian rhythm of plasma glucocorticoid concentrations is made up from an underlying ultradian pulsatile secretory pattern. Recent evidence has indicated that this... Show moreThe characteristic endogenous circadian rhythm of plasma glucocorticoid concentrations is made up from an underlying ultradian pulsatile secretory pattern. Recent evidence has indicated that this ultradian cortisol pul-satility is crucial for normal emotional response in man. In this study, we investigate the anatomical tran-scriptional and cell type signature of brain regions sensitive to a loss of ultradian rhythmicity in the context of emotional processing. We combine human cell type and transcriptomic atlas data of high spatial resolution with functional magnetic resonance imaging (fMRI) data. We show that the loss of cortisol ultradian rhythm alters emotional processing response in cortical brain areas that are characterized by transcriptional and cellular profiles of GABAergic function. We find that two previously identified key components of rapid non-genomic GC signaling - the ANXA1 gene and retrograde endocannabinoid signaling - show most significant differential expression (q = 3.99e- 10) and enrichment (fold enrichment = 5.56, q = 9.09e-4). Our results further indicate that specific cell types, including a specific NPY-expressing GABAergic neuronal cell type, and specific G protein signaling cascades underly the cerebral effects of a loss of ultradian cortisol rhythm. Our results provide a biological mechanistic underpinning of our fMRI findings, indicating specific cell types and cascades as a target for manipulation in future experimental studies. Show less
Context: Patients with critical illness are thought to be at risk of adrenal insufficiency. There are no models of dynamic hypothalamic-pituitary-adrenal (HPA) axis function in this group of... Show moreContext: Patients with critical illness are thought to be at risk of adrenal insufficiency. There are no models of dynamic hypothalamic-pituitary-adrenal (HPA) axis function in this group of patients and thus current methods of diagnosis are based on aggregated, static models.Objective: To characterize the secretory dynamics of the HPA axis in the critically ill (CI) after cardiac surgery.Design: Mathematical modeling of cohorts.Setting: Cardiac critical care unit.Patients: 20 male patients CI at least 48 hours after cardiac surgery and 19 healthy (H) male volunteers. Interventions: None.Main Outcome Measures: Measures of hormone secretory dynamics were generated from serum adrenocorticotrophic hormone (ACTH) sampled every hour and total cortisol every 10 min for 24 h.Results: All CI patients had pulsatile ACTH and cortisol profiles. CI patients had similar ACTH secretion (1036.4 [737.6] pg/mL/24 h) compared to the H volunteers (1502.3 [1152.2] pg/mL/24 h; P=.20), but increased cortisol secretion (CI: 14 447.0 [5709.3] vs H: 5915.5 [1686.7)] nmol/L/24 h; P<.0001). This increase in cortisol was due to nonpulsatile (CI: 9253.4 [3348.8] vs H: 960 [589.0] nmol/L/24 h, P<.0001), rather than pulsatile cortisol secretion (CI: 5193.1 [3018.5] vs H: 4955.1 [1753.6] nmol/L/24 h; P=.43). Seven (35%) of the 20 CI patients had cortisol pulse nadirs below the current international guideline threshold for critical illness-related corticosteroid insufficiency, but an overall secretion that would not be considered deficient.Conclusions: This study supports the premise that current tests of HPA axis function are unhelpful in the diagnosis of adrenal insufficiency in the CI. The reduced ACTH and increase in nonpulsatile cortisol secretion imply that the secretion of cortisol is driven by factors outside the HPA axis in critical illness. Show less
Glucocorticoid hormones are released in rapid hourly hormone bursts by the adrenal gland. These ultradian oscillations are fundamental to hypothalamic-pituitary-adrenal activity and transcriptional... Show moreGlucocorticoid hormones are released in rapid hourly hormone bursts by the adrenal gland. These ultradian oscillations are fundamental to hypothalamic-pituitary-adrenal activity and transcriptional regulation of glucocorticoid responsive genes. The physiological relevance of glucocorticoid pulsatility is however unknown. Using a novel automated infusion system, we artificially created different patterns (modulating pulse amplitude) of corticosterone (cort). Identical amounts of cort either in constant or in hourly pulses were infused into adrenalectomized rats. At the end of the infusion period, either during rising or falling concentrations of a cort pulse, animals were exposed to 99 dB noise stress (10 min). Pulsatile cort infusion led to a differential stress response, dependent on the phase of the pulse during which the stress was applied. Although constant administration of cort resulted in a blunted ACTH response to the stressor, a brisker response occurred during the rising phase of plasma cort than during the falling phase. This phase-dependent effect was also seen in the behavioral response to the stressor, which was again greater during the rising phase of each cort pulse. Within the brain itself, we found differential C-fos activation responses to noise stress in the pituitary, paraventricular nucleus, amygdala, and hippocampus. This effect was both glucocorticoid pulse amplitude and phase dependent, suggesting that different stress circuits are differentially responsive to the pattern of glucocorticoid exposure. Our data suggest that the oscillatory changes in plasma glucocorticoid levels are critical for the maintenance of normal physiological reactivity to a stressor and in addition modulate emotionality and exploratory behavior. (Endocrinology 151: 5369-5379, 2010) Show less
In vivo glucocorticoid (GC) secretion exhibits a distinctive ultradian rhythmicity. The lipophilic hormone can rapidly diffuse into cells, although only the pulse peak is of sufficient amplitude to... Show moreIn vivo glucocorticoid (GC) secretion exhibits a distinctive ultradian rhythmicity. The lipophilic hormone can rapidly diffuse into cells, although only the pulse peak is of sufficient amplitude to activate the low affinity glucocorticoid receptor (GR). Discrete pulses readily access brain regions such as the hippocampus where GR expression is enriched and known to regulate neuronal function, including memory and learning processes. In the present study, we have tested the hypothesis that GR brain targets are responsive to ultradian GC rhythmicity. We have used adrenalectomised rats replaced with pulses of corticosterone to determine the transcriptional effects of ultradian pulses in the hippocampus. Confocal microscopy confirmed that each GC pulse results in transient GR nuclear localisation in hippocampal CA1 neurones. Concomitant GR activation and DNA binding was demonstrated by synthetic glucocorticoid response element oligonucleotide binding, and verified for the Clock gene Period 1 promoter region by chromatin immunoprecipitation assays. Strikingly each GC pulse induced a 'burst' of transcription of Period 1 measured by heterogeneous nuclear RNA quantitative polymerase chain reaction. The net effect of pulsatile GC exposure on accumulation of the mature transcript was also assessed, revealing a plateau of mRNA levels throughout the time course of pulsatile exposure, indicating the pulse timing works optimally for steady state Per1 expression. The plateau dropped to baseline within 120 min of the final pulse, indicating a relatively short half-life for hippocampal Per1. The significance of this strict temporal control is that any perturbation to the pulse frequency or duration would have rapid quantitative effects on the levels of Per1. This in turn could affect hippocampal function, especially circadian related memory and learning processes. Show less
Ultradian release of glucocorticoids is thought to be essential for homeostasis and health. Furthermore, deviation from this pulsatile release pattern is considered to compromise resilience to... Show moreUltradian release of glucocorticoids is thought to be essential for homeostasis and health. Furthermore, deviation from this pulsatile release pattern is considered to compromise resilience to stress-related disease, even after hormone levels have normalised. In the present study, we investigate how constant exposure to different concentrations of corticosterone affects diurnal and ultradian pulsatility. The rate of recovery in pulsatile hypothalamic-pituitary-adrenal (HPA) activity after withdrawal of exogenous corticosterone is also examined. Finally, the behavioural and neuroendocrine responsiveness to an audiogenic stressor is studied. Adrenally intact male rats were subcutaneously implanted with vehicle, 40% or 100% corticosterone pellets for 7 days. The continuous release of corticosterone from these implants abolished diurnal and ultradian corticosterone variation, as measured with high-frequency automated blood sampling. Pellet removal on post-surgery day 8 allowed rapid recovery of endogenous rhythms in animals previously exposed to daily average concentrations (40%) but not after exposure to high concentrations (100%) of corticosterone. Behavioural and neuroendocrine responsiveness to stress was distinctly different between the treatment groups. Audiogenic stimulation 1 day after pellet removal resulted in a similar corticosterone response in animals previously exposed to 40% corticosterone or vehicle. The 40% pellet group, however, showed less and shorter behavioural activity (i.e. locomotion, risk assessment) to noise stress compared to 100% corticosterone and vehicle-treated animals. In conclusion, unlike the animals impanted with 100% corticosterone, we find that basal HPA axis activity in the 40% group, which had mean daily levels of circulating corticosterone in the physiological range, rapidly reverts to the characteristic pulsatile pattern of corticosterone secretion. Upon reinstatement of the ultradian rhythm, and despite the fact that these animals did not differ from controls in their response to noise stress, they did show substantial changes in their behavioural response to stress. Show less
