Detection of the acute effects of hydrocortisone in the hippocampus using pharmacological fMRI

Memory under pressure: The impact of acute stress across different memory tasks

In the present study, we aimed to investigate how acute stress exerts its heterogeneous effects. Based on biophysical network models, we hypothesized that acute stress would improve occipital-mediated ultra-short-term and to a lesser degree affect occipital- and frontal-mediated short-term and working, and impairs hippocampal-mediated long-term memory processes and their respective behavioral measures. To test this, 111 healthy individuals (57 female) underwent both the Trier Social Stress Test (TSST) and a control test. Immediately afterward, participants' performance was measured in four memory tasks (Rapid Serial Visual Presentation, RSVP, Match-to-Sample, MTS, N-Back, NB and Free-Recall, FR tasks). TSST exposure seems to impair long-term memory (ACFR; β = -1.50 ± 0.62; when free recall was tested approx. 80 minutes after initial encoding, immediately after the TSST), and working memory (ACNB; β= -0.42 ± 0.20 %) but did not affect ultra-short-term (ACRSVP; β = -0.03 ± 0.31 %) and short-term (ACMTS; β=-0.18 ± 0.31 %) memory accuracies (ACs). Interestingly, TSST exposure increased the exploratory included measure of response times in MTS (RTMTS; β =16.42 ± 7.18 msec) and impaired T1 detection in the RSVP (ACT1; β=-0.48 ± 0.22 %) tasks. Contrary to the hypothesis, TSST exposure did not have the hypothesized effects on the memory processes. Instead, TSST exposure appeared to affect secondary behavioral indicators of motivation or task instruction adherence.

Hippocampal Mechanisms Support Cortisol-Induced Memory Enhancements

Stress can powerfully influence episodic memory, often enhancing memory encoding for emotionally salient information. These stress-induced memory enhancements stand at odds with demonstrations that stress and the stress-related hormone cortisol can negatively affect the hippocampus, a brain region important for episodic memory encoding. To resolve this apparent conflict and determine whether and how the hippocampus supports memory encoding under cortisol, we combined behavioral assays of associative memory, high-resolution fMRI, and pharmacological manipulation of cortisol in a within-participant, double-blinded procedure (in both sexes). Behaviorally, hydrocortisone promoted the encoding of subjectively arousing, positive associative memories. Neurally, hydrocortisone led to enhanced functional connectivity between hippocampal subregions, which predicted subsequent memory enhancements for emotional associations. Cortisol also modified the relationship between hippocampal representations and associative memory: whereas hippocampal signatures of distinctiveness predicted memory under placebo, relative integration predicted memory under cortisol. Together, these data provide novel evidence that the human hippocampus contains the necessary machinery to support emotional associative memory enhancements under cortisol.SIGNIFICANCE STATEMENT Our daily lives are filled with stressful events, which powerfully shape the way we form episodic memories. For example, stress and stress-related hormones can enhance our memory for emotional events. However, the mechanisms underlying these memory benefits are unclear. In the current study, we combined functional neuroimaging, behavioral tests of memory, and double-blind, placebo-controlled hydrocortisone administration to uncover the effects of the stress-related hormone cortisol on the function of the human hippocampus, a brain region important for episodic memory. We identified novel ways in which cortisol can enhance hippocampal function to promote emotional memories, highlighting the adaptive role of cortisol in shaping memory formation.

Stress-induced brain responses are associated with BMI in women

Overweight and obesity are associated with altered stress reactivity and increased inflammation. However, it is not known whether stress-induced changes in brain function scale with BMI and if such associations are driven by peripheral cytokines. Here, we investigate multimodal stress responses in a large transdiagnostic sample using predictive modeling based on spatio-temporal profiles of stress-induced changes in activation and functional connectivity. BMI is associated with increased brain responses as well as greater negative affect after stress and individual response profiles are associated with BMI in females (pperm < 0.001), but not males. Although stress-induced changes reflecting BMI are associated with baseline cortisol, there is no robust association with peripheral cytokines. To conclude, alterations in body weight and energy metabolism might scale acute brain responses to stress more strongly in females compared to males, echoing observational studies. Our findings highlight sex-dependent associations of stress with differences in endocrine markers, largely independent of peripheral inflammation.

Circadian distribution of epileptiform discharges in epilepsy: Candidate mechanisms of variability

Epilepsy is a serious neurological disorder characterised by a tendency to have recurrent, spontaneous, seizures. Classically, seizures are assumed to occur at random. However, recent research has uncovered underlying rhythms both in seizures and in key signatures of epilepsy-so-called interictal epileptiform activity-with timescales that vary from hours and days through to months. Understanding the physiological mechanisms that determine these rhythmic patterns of epileptiform discharges remains an open question. Many people with epilepsy identify precipitants of their seizures, the most common of which include stress, sleep deprivation and fatigue. To quantify the impact of these physiological factors, we analysed 24-hour EEG recordings from a cohort of 107 people with idiopathic generalized epilepsy. We found two subgroups with distinct distributions of epileptiform discharges: one with highest incidence during sleep and the other during day-time. We interrogated these data using a mathematical model that describes the transitions between background and epileptiform activity in large-scale brain networks. This model was extended to include a time-dependent forcing term, where the excitability of nodes within the network could be modulated by other factors. We calibrated this forcing term using independently-collected human cortisol (the primary stress-responsive hormone characterised by circadian and ultradian patterns of secretion) data and sleep-staged EEG from healthy human participants. We found that either the dynamics of cortisol or sleep stage transition, or a combination of both, could explain most of the observed distributions of epileptiform discharges. Our findings provide conceptual evidence for the existence of underlying physiological drivers of rhythms of epileptiform discharges. These findings should motivate future research to explore these mechanisms in carefully designed experiments using animal models or people with epilepsy.

Hippocampal mechanisms support cortisol-induced memory enhancements

Stress can powerfully influence episodic memory, often enhancing memory encoding for emotionally salient information. These stress-induced memory enhancements stand at odds with demonstrations that stress and the stress-related hormone cortisol can negatively affect the hippocampus, a brain region important for episodic memory encoding. To resolve this apparent conflict and determine whether and how the hippocampus supports memory encoding under cortisol, we combined behavioral assays of associative memory, high-resolution functional magnetic resonance imaging (fMRI), and pharmacological manipulation of cortisol in a within-participant, double-blinded procedure. Hydrocortisone led to enhanced functional connectivity between hippocampal subregions, which predicted subsequent memory enhancements for emotional information. Cortisol also modified the relationship between hippocampal representations and memory: whereas hippocampal signatures of distinctiveness predicted memory under placebo, relative integration predicted memory under cortisol. Together, these data provide novel evidence that the human hippocampus contains the necessary machinery to support emotional memory enhancements under stress.

Acute Cortisol Profile Associations With Cognitive Impairment After Severe Traumatic Brain Injury

BACKGROUND

Cognitive impairments commonly occur after traumatic brain injury (TBI) and affect daily functioning. Cortisol levels, which are elevated during acute hospitalization for most individuals after severe TBI, can influence cognition, but this association has not been studied previously in TBI.

OBJECTIVE

We hypothesized that serum and cerebral spinal fluid (CSF) cortisol trajectories over days 0-5 post-injury are associated with cognition 6-month post-injury.

METHODS

We examined 94 participants with severe TBI, collected acute serum and/or CSF samples over days 0-5 post-injury, and compared cortisol levels to those in 17 healthy controls. N = 88 participants had serum, and n = 84 had CSF samples available for cortisol measurement and had neuropsychological testing 6 months post-injury. Group based trajectory analysis (TRAJ) was used to generate temporal serum and CSF cortisol profiles which were examined for associations with neuropsychological performance. We used linear regression to examine relationships between cortisol TRAJ groups and both overall and domain-specific cognition.

RESULTS

TRAJ analysis identified a high group and a decliner group for serum and a high group and low group for CSF cortisol. Multivariable analysis showed serum cortisol TRAJ group was associated with overall cognitive composites scores (P = .024) and with executive function (P = .039) and verbal fluency (P = .029) domain scores. CSF cortisol TRAJ group was associated with overall cognitive composite scores (P = .021) and domain scores for executive function (P = .041), verbal fluency (P = .031), and attention (P = .034).

CONCLUSIONS

High acute cortisol trajectories are associated with poorer cognition 6 months post-TBI.

Poly (I:C)-induced maternal immune activation modifies ventral hippocampal regulation of stress reactivity: prevention by environmental enrichment

Environmental enrichment (EE) has been successfully implemented in human rehabilitation settings. However, the mechanisms underlying its success are not understood. Incorporating components of EE protocols into our animal models allows for the exploration of these mechanisms and their role in mitigation. Using a mouse model of maternal immune activation (MIA), the present study explored disruptions in social behavior and associated hypothalamic pituitary adrenal (HPA) axis functioning, and whether a supportive environment could prevent these effects. We show that prenatal immune activation of toll-like receptor 3, by the viral mimetic polyinosinic-polycytidylic acid (poly(I:C)), led to disrupted maternal care in that dams built poorer quality nests, an effect corrected by EE housing. Standard housed male and female MIA mice engaged in higher rates of repetitive rearing and had lower levels of social interaction, alongside sex-specific expression of several ventral hippocampal neural stress markers. Moreover, MIA males had delayed recovery of plasma corticosterone in response to a novel social encounter. Enrichment housing, likely mediated by improved maternal care, protected against these MIA-induced effects. We also evaluated c-Fos immunoreactivity associated with the novel social experience and found MIA to decrease neural activation in the dentate gyrus. Activation in the hypothalamus was blunted in EE housed animals, suggesting that the putative circuits modulating social behaviors may be different between standard and complex housing environments. These data demonstrate that augmentation of the environment supports parental care and offspring safety/security, which can offset effects of early health adversity by buffering HPA axis dysregulation. Our findings provide further evidence for the viability of EE interventions in maternal and pediatric settings.

Glucocorticoids, metabolism and brain activity

The review integrates different experimental approaches including biochemistry, c-Fos expression, microdialysis (glutamate, GABA, noradrenaline and serotonin), electrophysiology and fMRI to better understand the effect of elevated level of glucocorticoids on the brain activity and metabolism. The available data indicate that glucocorticoids alter the dynamics of neuronal activity leading to context-specific changes including both excitation and inhibition and these effects are expected to support the task-related responses. Glucocorticoids also lead to diversification of available sources of energy due to elevated levels of glucose, lactate, pyruvate, mannose and hydroxybutyrate (ketone bodies), which can be used to fuel brain, and facilitate storage and utilization of brain carbohydrate reserves formed by glycogen. However, the mismatch between carbohydrate supply and utilization that is most likely to occur in situations not requiring energy-consuming activities lead to metabolic stress due to elevated brain levels of glucose. Excessive doses of glucocorticoids also impair the production of energy (ATP) and mitochondrial oxidation. Therefore, glucocorticoids have both adaptive and maladaptive effects consistently with the concept of allostatic load and overload.

Glucocorticoid ultradian rhythmicity differentially regulates mood and resting state networks in the human brain: A randomised controlled clinical trial

Adrenal glucocorticoid secretion into the systematic circulation is characterised by a complex rhythm, composed of the diurnal variation, formed by changes in pulse amplitude of an underlying ultradian rhythm of short duration hormonal pulses. To elucidate the potential neurobiological significance of glucocorticoid pulsatility in man, we have conducted a randomised, double-blind, placebo-controlled, three-way crossover clinical trial on 15 healthy volunteers, investigating the impact of different glucocorticoid rhythms on measures of mood and neural activity under resting conditions by recruiting functional neuroimaging, computerised behavioural tests and ecological momentary assessments. Endogenous glucocorticoid biosynthesis was pharmacologically suppressed, and plasma levels of corticosteroid restored by hydrocortisone replacement in three different regimes, either mimicking the normal ultradian and circadian profile of the hormone, or retaining the normal circadian but abolishing the ultradian rhythm of the hormone, or by our current best oral replacement regime which results in a suboptimal circadian and ultradian rhythm. Our results indicate that changes in the temporal mode of glucocorticoid replacement impact (i) the morning levels of self-perceived vigour, fatigue and concentration, (ii) the diurnal pattern of mood variation, (iii) the within-network functional connectivity of various large-scale resting state networks of the human brain, (iv) the functional connectivity of the default-mode, salience and executive control networks with glucocorticoid-sensitive nodes of the corticolimbic system, and (v) the functional relationship between mood variation and underlying neural networks. The findings indicate that the pattern of the ultradian glucocorticoid rhythm could affect cognitive psychophysiology under non-stressful conditions and opens new pathways for our understanding on the neuropsychological effects of cortisol pulsatility with relevance to the goal of optimising glucocorticoid replacement strategies.

Alternation of Resting-State Functional Connectivity Between Visual Cortex and Hypothalamus in Guinea Pigs With Experimental Glucocorticoid Enhanced Myopia After the Treatment of Electroacupuncture

Excessive glucocorticoids (GC) may lead to the aggravation of several basic diseases including myopia, due to plasma hormone imbalances associated with the hypothalamic–pituitary–adrenal axis (HPAA). Electroacupuncture (EA) is an effective therapeutic method to treat many diseases, although it remains unclear whether EA at acupoints on the foot or back would be effective in treating eye diseases. It was recently found that visual cortex activity for responses to visual stimuli with spatial frequency and resting-state functional connectivity (FC) between the supramarginal gyrus and rostrolateral prefrontal cortex was significantly reduced in patients with high myopia. The present study aims to investigate the role of the alternation of resting-state FC among the bilateral visual cortex and hypothalamus in exerting anti-myopia effects of EA in GC-enhanced lens-induced myopic (LIM) guinea pigs such that the mechanisms of EA to treat GC-enhanced myopia at Shenshu (BL23) acupoints can be probed. To confirm the effects of EA, ocular parameters including axial length and GC-associated physiological parameters such as animal appearance, behavior, bodyweight, and levels of four HPAA-associated plasma hormones [free triiodothyronine (FT3), free thyroxine (FT4), estradiol (E2), and testosterone (T)] were also collected. Increased resting-state FC between the left and right visual cortex was detected in GC-enhanced lens-induced myopic guinea pigs with EA at BL23 acupoints (LIM+GC+EA) guinea pigs compared to GC-enhanced lens-induced myopic guinea pigs with EA at sham acupoints (LIM+GC+Sham) guinea pigs, as well as suppressed myopia and recovery of symptoms initially caused by overdose of GC. Recovered symptoms included improved animal appearance, behavior, bodyweight, and HPAA-associated plasma hormone levels were observed after 4 weeks of EA treatment. In contrast, the LIM+GC+Sham group showed decreased FC with elongation of axial length for myopization as compared to the control group and LIM group and exhibited a deterioration in physiological parameters including reduced body weight and balance disruption in the four measured HPAA-associated plasma hormones. Our findings suggest that EA could effectively treat GC-enhanced myopia by increasing resting-state FC between the left and right visual cortices, which may be pivotal to further understanding the application and mechanisms of EA in treating GC-enhanced myopia.

Psychosocial stress reactivity habituates following acute physiological stress

Acute and chronic stress are important factors in the development of mental disorders. Reliable measurement of stress reactivity is therefore pivotal. Critically, experimental induction of stress often involves multiple “hits” and it is an open question whether individual differences in responses to an earlier stressor lead to habituation, sensitization, or simple additive effects on following events. Here, we investigated the effect of the individual cortisol response to intravenous catheter placement (IVP) on subsequent neural, psychological, endocrine, and autonomous stress reactivity. We used an established psychosocial stress paradigm to measure the acute stress response (Stress) and recovery (PostStress) in 65 participants. Higher IVP‐induced cortisol responses were associated with lower pulse rate increases during stress recovery (b = −4.8 bpm, p = .0008) and lower increases in negative affect after the task (b = −4.2, p = .040). While the cortisol response to IVP was not associated with subsequent specific stress‐induced neural activation patterns, the similarity of brain responses Pre‐ and PostStress was higher IVP‐cortisol responders (t[64] = 2.35, p = .022) indicating faster recovery. In conclusion, preparatory stress induced by IVP reduced reactivity in a subsequent stress task by modulating the latency of stress recovery. Thus, an individually stronger preceding release of cortisol may attenuate a second physiological response and perceived stress suggesting that relative changes, not absolute levels are crucial for stress attribution. Our study highlights that considering the entire trajectory of stress induction during an experiment is important to develop reliable individual biomarkers.

First-Trimester Prenatal Dexamethasone Treatment Is Associated With Alterations in Brain Structure at Adult Age

CONTEXT

Prenatal treatment of human disease is rare. Dexamethasone (DEX) is used in pregnancies at risk for congenital adrenal hyperplasia (CAH) to prevent virilization in an affected female fetus. The safety and long-term consequences of prenatal DEX exposure on the brain are largely unknown.

OBJECTIVE

We investigate whether first-trimester prenatal DEX treatment is associated with alterations in brain structure at adult age, and if these alterations are associated with DNA methylation, mood, and cognitive abilities.

DESIGN, SETTING, AND PARTICIPANTS

T1-weighted and diffusion-weighted imaging scans, from a single research institute, are compared between 19 (9 women) first-trimester DEX-treated individuals, at risk of CAH but not having CAH, and 43 (26 women) controls (age range, 16.0-26.4 years).

RESULTS

DEX-treated participants showed bilateral enlargement of the amygdala, increased surface area and volume of the left superior frontal gyrus, and widespread increased radial, mean, and axial diffusivity of white matter, in particular in the superior longitudinal fasciculi and corticospinal tracts. In the DEX-treated group, increased mean and radial diffusivity correlated with increased methylation of the promotor region of the FKBP5 gene. There were no group differences in cognition or in scales assessing depression or anxiety, and the relationship between brain structure and cognition did not differ between DEX-treated and controls.

CONCLUSIONS

First-trimester prenatal DEX treatment is associated with structural alterations of the brain at adult age, with an accompanying change in gene methylation. The findings add to the safety concerns of prenatal DEX treatment in the context of CAH.

Spatiotemporal brain activation pattern following acute citalopram challenge is dose dependent and associated with neuroticism: A human phMRI study

BACKGROUND

The initial effects of selective serotonin reuptake inhibitors (SSRIs) in the human living brain are poorly understood. We carried out a 3T resting state fMRI study with pharmacological challenge to determine the brain activation changes over time following different dosages of citalopram.

METHODS

During the study, 7.5 mg i.v. citalopram was administered to 32 healthy subjects. In addition, 11.25 mg citalopram was administered to a subset of 9 subjects to investigate the dose-response. Associations with neuroticism (assessed by the NEO PI-R) of the emerging brain activation to citalopram was also investigated.

RESULTS

Citalopram challenge evoked significant activation in brain regions that are part of the default mode network, the visual network and the sensorimotor network, extending to the thalamus, and midbrain. Most effects appeared to be dose-dependent and this was statistically significant in the middle cingulate gyrus. Individual citalopram-induced brain responses were positively correlated with neuroticism scores and its subscales in specific brain areas; anxiety subscale scores in thalamus and midbrain and self-consciousness scores in middle cingulate gyrus. There were no sex differences.

LIMITATIONS

We investigated only healthy subjects and we used a relatively low sample size in the 11.25 mg citalopram analysis.

DISCUSSION

Our results suggest that SSRIs acutely induce an increased arousal-like state of distributed cortical and subcortical systems that is mediated by enhanced serotonin neurotransmission according to levels of neuroticism and underpins trait sensitivity to environmental stimuli and stressors. Studies in depression are needed to determine how therapeutic effects eventually emerge. This article is part of the special issue entitled 'Serotonin Research: Crossing Scales and Boundaries'.

Resting-state functional connectivity after hydrocortisone administration in patients with post-traumatic stress disorder and borderline personality disorder

In a previous study, we found that - in contrast to healthy individuals - patients with borderline personality disorder (BPD) and post-traumatic stress disorder (PTSD) showed better memory retrieval performance after hydrocortisone administration compared to placebo. As these results suggest an altered function of corticosteroid receptors in the brain in PTSD and BPD, we examined the effect of hydrocortisone on brain activation in both disorders. We recruited 40 female healthy controls, 20 female unmedicated patients with PTSD and 18 female unmedicated patients with BPD. We conducted a placebo-controlled cross-over study, in which all participants underwent two resting state MRI measurements after they received either a placebo or 10 mg hydrocortisone orally and in randomized order. There was a time interval of one week between the measurements. We analysed resting state functional connectivity (RSFC) with the hippocampus and the amygdala as seed regions. Compared to healthy controls, both patient groups showed reduced hippocampus RSFC to dorsomedial prefrontal cortex (dmPFC). Positive hippocampus dmPFC RSFC correlated negatively with childhood trauma (r = -0.47) and with severity of clinical symptoms, measured with the Borderline Symptom List (r = -0.44) and the Posttraumatic Stress Diagnostic Scale (r = -0.45). We found neither differences in amygdala RSFC nor an effect of hydrocortisone administration. Childhood trauma might lead to decreased positive hippocampus dmPFC RSFC. This might explain symptoms of PTSD and BPD that are characterized by dysfunctional fear regulation.

Glucocorticoids and Hippocampal Structure and Function in PTSD

This review examines the putative link between glucocorticoid and hippocampal abnormalities in posttraumatic stress disorder (PTSD). Increased glucocorticoid receptor (GR) sensitivity in PTSD may permit enhanced negative feedback inhibition of cortisol at the pituitary, hypothalamus, or other brain regions comprising the hypothalamic-pituitary-adrenal (HPA) axis and would be expected to affect other physiological systems that are regulated by glucocorticoids. Molecular and transcriptional studies of cortisol are consistent with the hypothesis that cortisol actions may be amplified in PTSD as a result of enhanced GR sensitivity in monocytes and some brain regions, although cortisol levels themselves are unchanged and oftentimes lower than normal. Concurrently, magnetic resonance imaging studies have demonstrated that individuals with PTSD have smaller hippocampal volume than individuals without PTSD. Initial hypotheses regarding the mechanism underlying hippocampal alterations in PTSD focused on elevated glucocorticoid levels in combination with extreme stress as the primary cause, but this explanation has not been well supported in human studies. Lack of data from neuroimaging studies preclude a firm link between PTSD onset and hippocampal volume changes. Rather, the available evidence is consistent with the possibility that smaller hippocampal volume (like reduced cortisol levels and enhanced GR sensitivity) may be a vulnerability factor for developing the disorder; limitations of hippocampal-based models of PTSD are described. We further review neuroimaging studies examining hippocampal structure and function following manipulation of glucocorticoid levels and also examining changes in the hippocampus in relationship to other brain regions. Evidence that the GR may be an important therapeutic target for the treatment of PTSD, especially for functions subserved by the hippocampus, is discussed. Implications of the current review for future research are described, with an emphasis on the need to integrate findings of glucocorticoid abnormalities with functional-imaging paradigms to formulate a comprehensive model of HPA-axis functioning in PTSD.

Ultradian rhythmicity of plasma cortisol is necessary for normal emotional and cognitive responses in man

Glucocorticoids (GCs) are secreted in an ultradian, pulsatile pattern that emerges from delays in the feedforward-feedback interaction between the anterior pituitary and adrenal glands. Dynamic oscillations of GCs are critical for normal cognitive and metabolic function in the rat and have been shown to modulate the pattern of GC-sensitive gene expression, modify synaptic activity, and maintain stress responsiveness. In man, current cortisol replacement therapy does not reproduce physiological hormone pulses and is associated with psychopathological symptoms, especially apathy and attenuated motivation in engaging with daily activities. In this work, we tested the hypothesis that the pattern of GC dynamics in the brain is of crucial importance for regulating cognitive and behavioral processes. We provide evidence that exactly the same dose of cortisol administered in different patterns alters the neural processing underlying the response to emotional stimulation, the accuracy in recognition and attentional bias toward/away from emotional faces, the quality of sleep, and the working memory performance of healthy male volunteers. These data indicate that the pattern of the GC rhythm differentially impacts human cognition and behavior under physiological, nonstressful conditions and has major implications for the improvement of cortisol replacement therapy.

Actions and interactions of estradiol and glucocorticoids in cognition and the brain: Implications for aging women

Menopause involves dramatic declines in estradiol production and levels. Importantly, estradiol and the class of stress hormones known as glucocorticoids exert countervailing effects throughout the body, with estradiol exerting positive effects on the brain and cognition, glucocorticoids exerting negative effects on the brain and cognition, and estradiol able to mitigate negative effects of glucocorticoids. Although the effects of these hormones in isolation have been extensively studied, the effects of estradiol on the stress response and the neuroprotection offered against glucocorticoid exposure in humans are less well known. Here we review evidence suggesting that estradiol-related protection against glucocorticoids mitigates stress-induced interference with cognitive processes. Animal and human research indicates that estradiol-related mitigation of glucocorticoid damage and interference is one benefit of estradiol supplementation during peri-menopause or soon after menopause. The evidence for estradiol-related protection against glucocorticoids suggests that maintaining estradiol levels in post-menopausal women could protect them from stress-induced declines in neural and cognitive integrity.

Ketamine interactions with biomarkers of stress: a randomized placebo-controlled repeated measures resting-state fMRI and PCASL pilot study in healthy men

Ketamine, an NMDA receptor antagonist, is increasingly used to study the link between glutamatergic signaling dysregulation and mood and chronic pain disorders. Glutamatergic neurotransmission and stress corticosteroids (cortisol in human) are critical for Ca(2+) mediated neuroplasticity and behavioral adaptation. The mechanisms of action of glutamatergic neurotransmission and stress corticosteroids on the NMDA-receptors of the hippocampus have been long investigated in animals, but given little attention in human studies. In this randomized single-blinded placebo-controlled crossover study (12 healthy young men), five sets of resting-state fMRI (RSFMRI), pseudocontinuous arterial spin labeling (PCASL), and corresponding salivary cortisol samples were acquired over 4h, at given intervals under pharmacokinetically-controlled infusion of subanesthetic ketamine (20 & 40mg/70kg/h). An identical procedure was repeated under a sham placebo condition. Differences in the profile of ketamine versus placebo effect over time were examined. Compared to placebo, ketamine mimicked a stress-like response (increased cortisol, reduced calmness and alertness, and impaired working memory). Ketamine effects on the brain included a transient prefrontal hyperperfusion and a dose-related reduction of relative hippocampal perfusion, plus emerging hyperconnectivity between the hippocampus and the occipital, cingulate, precuneal, cerebellar and basal ganglia regions. The spatiotemporal profiles of ketamine effects on different hippocampal subnetworks suggest a topographically dissociable change in corticohippocampal functional connectivity. We discuss our findings in the context of the negative feedback inhibition theory of the hippocampal stress-control. This pilot study provides a methodological framework for multimodal functional neuroimaging under resting-state conditions, which may be generalized for translational studies of glutamatergic- or stress-related etiology of neuropsychiatric disorders.

For whom the bell (curve) tolls: cortisol rapidly affects memory retrieval by an inverted U-shaped dose-response relationship

Stress and cortisol are generally considered to impair declarative memory retrieval, although opposite results have also been reported. Dose-dependent effects and differences between genomic and non-genomic cortisol effects are possible reasons for these discrepancies. The aim of the current experiment was to assess the non-genomic effects of escalating doses of intravenous cortisol on cued recall of socially relevant information in humans. 40 participants (age range 20-30 years; 20 females) learned associations between male faces with a neutral facial expression and descriptions of either positive or negative social behaviors and were tested one week later in a cued recall paradigm. Escalating doses of cortisol (0, 3, 6, 12, 24 mg) were administered 8 min before testing according to a between-subjects design. An inverted U-shaped dose-response relationship between salivary cortisol levels and recall performance was observed, with moderate elevation of salivary cortisol resulting in the best recall performance. This is the first study in humans demonstrating that cortisol rapidly modulates declarative memory retrieval via a dose-dependent, non-genomic mechanism that follows an inverted U-shaped curve. Our result further emphasizes the importance of fast cortisol effects for human cognition.