Beata R. Godlewska

Ebselen has been shown to induce a positive emotional processing bias and brain neurochemistry in healthy volunteers. However, little is known about its effects on resting-state functional connectivity (rs-FC) in depressed patients who show inadequate responses to standard antidepressants. The study aimed to investigate the effect of ebselen as an add-on treatment on rs-FC in this population. We conducted a randomised, double-blind, placebo-controlled trial involving depressed patients who were not responsive to their current treatment. Participants received either ebselen 600 mg twice daily or placebo for seven days. Resting-state functional magnetic resonance imaging was conducted at baseline and on day seven. Resting-state data were analysed using seed-based analysis and independent component analysis. Greater changes in rs-FC between the pregenual anterior cingulate cortex and the cerebellum were observed in ebselen than in placebo, but became negligible after corrections for multiple comparisons. We identified treatment effects within visual networks and between visual and sensorimotor networks, however, these did not survive correction for multiple comparisons. Short-term ebselen treatment in depressed patients with inadequate antidepressant responses did not produce significant changes in rs-FC. These findings may reflect limitations related to the short treatment duration and small and heterogeneous sample.

Depression is a leading cause of global disability and is increasingly linked to systemic metabolic dysfunctions, including insulin resistance. However, the biological pathways connecting metabolic state to affective symptoms are unresolved. A growing body of evidence indicates that insulin, beyond its role in systemic glucose homeostasis, supports brain metabolism, synaptic function and cognition, yet its contribution to mood regulation remains unclear. Here, we identify a human hippocampal metabolic signature associated with glycaemic variation in individuals with depression. Using multimodal neuroimaging, we show that hippocampal concentrations of GABA and lactate correlate with HbA1c and with mood severity, while functional connectivity between the hippocampus and the default mode network tracks affective symptoms independently of adiposity. To causally probe these relationships, we generated a mouse model of hippocampus-specific insulin receptor depletion. Unexpectedly, reducing insulin signalling at the blood brain barrier enhanced neuronal metabolism and attenuated anxiety-like behaviour. Notably, hippocampal lactate and GABA levels similarly tracked anxiety-related behaviour in mice, mirroring their association with symptom severity in humans. Together, these findings identify a conserved neurometabolic signature linking hippocampal insulin signalling to affective state, and reveal that brain insulin resistance exerts context- and cell-type-specific effects on behaviour. This work establishes a mechanistic basis for brain insulin resistance in depression and highlights the hippocampus as a critical hub for metabolic modulation of mood.

Cognitive impairment is a common but under-treated feature of Major Depressive Disorder (MDD). Preclinical and early human studies suggest that 5-HT ₄ receptor (5-HT ₄ R) agonists rapidly improve learning and memory, consistent with this receptor’s role in hippocampal neuroplasticity. However, their effects in clinically depressed patients, remain unexplored. In this double-blind, randomised experimental medicine study, 52 right-handed, unmedicated individuals with MDD received 6–9 days of the 5-HT ₄ R agonist PF-04995274 (15 mg, once daily) or placebo. Participants subsequently underwent fMRI scanning during a memory encoding task and completed behavioural measures of auditory verbal learning and spatial working memory. Compared to placebo, PF-04995274 significantly increased activity in the hippocampus (ROI analysis) in response to novel versus familiar images, particularly in the left hemisphere. Whole brain analysis also revealed greater activation in the left inferior parietal lobule, a key region for memory processing. In contrast with previous studies using the 5-HT ₄ R agonist prucalopride, PF-04995274 had notably limited effects on behavioural measures of memory. The results demonstrate that short term 5-HT ₄ R agonism enhances hippocampal and parietal activity during memory encoding in patients with depression. This replicates and extends previous findings in healthy volunteers using prucalopride, and is consistent with preclinical evidence establishing a key role for 5-HT ₄ Rs in hippocampal-dependent learning and memory. This translational evidence supports a role for 5-HT ₄ R activation in modulating memory-related brain circuits in MDD and previously identified beneficial effects of another 5-HT4 receptor agonist, prucalopride, on cognitive performance.

Background: Major depressive disorder (MDD) is clinically heterogeneous, hindering identification of reproducible biomarkers. Using a semi-supervised machine learning approach, HYDRA, we previously identified two neuroanatomical dimensions from structural MRI in medication-free MDD from COORDINATE-MDD consortium. These dimensions (D1, D2) showed differential responses to selective serotonin reuptake inhibitor (SSRI) antidepressants and placebo. External replication in UK Biobank linked D2, characterized by widespread subtle neuroanatomical reductions, to an immuno-metabolic profile. Here, we examined whether these dimensions are detectable early in the course of illness. Methods: We applied the pre-trained model to structural MRI data from the multisite PRONIA cohort, comprising individuals with recent-onset depression (ROD; n = 377; mean age 25.8 years, SD 6.0; 51.3% female) and healthy controls (n = 267; mean age 25.5 years, SD 6.4; 61.0% female). Participants were assigned to clusters (C1, C2) corresponding to the previously identified dimensions (D1, D2). Clusters were compared on clinical symptom profiles, peripheral inflammatory markers, and in a subset (n = 107), proteomic ageing indices. Results: Two neuroanatomical clusters were identified in PRONIA. C1 (n = 265) showed higher negative symptom severity and elevated interleukin-2 levels. C2 (n = 140) was associated with higher residual proteomic age. Overall depressive symptom severity did not differ significantly between clusters. Conclusions: Neuroanatomical dimensions of MDD are reproducible and detectable at illness onset. Associations with negative symptom severity, inflammatory signalling, and proteomic ageing suggest these dimensions capture biologically meaningful heterogeneity early in depression. These findings support a biologically informed framework for stratified treatment approaches in MDD.

Background: Selective serotonin reuptake inhibitors (SSRIs) are limited by inadequate response in a significant proportion of patients, slow onset, minimal cognitive benefit and side-effects. Preclinical studies suggest selective serotonin 4 receptor (5-HT ₄ R) agonists may produce faster antidepressant effects via distinct mechanisms; however, there has been no experimental research in clinical populations to date. Aims: To test whether the novel 5-HT ₄ R partial agonist PF-04995274 produces early behavioural and neural changes in emotional cognition similar to SSRIs in patients with unmedicated major depressive disorder (MDD). Method: In a double-blind, placebo-controlled trial, 90 participants with MDD were randomised to 7 days of PF-04995274 (15 mg), citalopram (20 mg) or placebo. Emotional processing was assessed using a behavioural facial expression recognition task and functional magnetic resonance imaging (fMRI) of implicit emotional face processing (days 6–9). Observer- and self-reported symptoms of depression were also measured at baseline and study end. Results: As anticipated, citalopram reduced relative accuracy and increased relative reaction time to identify negative faces, with corresponding changes in neural activity (reduced left amygdala activation to emotional faces and valence-specific shifts in cortical regions). In contrast, PF-04995274 produced no change in behavioural negative bias or amygdala activity but increased medial-frontal cortex activation across valences. While this was not a clinical trial, both active treatments demonstrated an early treatment response with reduced observer-rated depression severity relative to placebo; PF-04995274 also reduced self-reported depression, state anxiety and negative affect. Conclusions: PF-04995274 did not show the typical antidepressant profile of negative bias reductions observed with citalopram. Instead, it was associated with distinct increased medial-frontal activation during an emotional faces task, coupled with preliminary evidence of early clinical improvement, suggesting a potential alternative pathway for antidepressant effects. Findings support further clinical trials of 5-HT ₄ R agonists and investigation of pro-cognitive and mood effects. Clinical trials registration number: NCT03516604.

Lithium is an effective treatment for mood disorders. However, its mechanism of action concerning its effect on impulsivity and emotional processing is still unclear. The current study aimed to investigate the effect of a 5-day lithium treatment on decision-making, reward-seeking and emotional processing in healthy volunteers. We conducted a double-blind, placebo-controlled, cross-over design study involving sixteen participants aged 18–50 years. Participants received lithium 800 mg once daily followed by matching placebo or vice versa for five days in a random order. Impulsivity and emotional processing were assessed on day six using the Cambridge Gambling Task and the Emotional Testing Battery, respectively. There were significant interactions with large effect sizes between treatment and order for delay aversion (F _1,14 = 13.79, p = 0.002, partial η ² = 0.496) and reward-seeking (F _1,14 = 34.065, p = < 0.001, partial η ² = 0.709), but the post-hoc tests suggested only moderate, inconclusive effects at either visit. There was a significant interaction between treatment, emotion and order with a large effect size for the facial expression recognition task. The post-hoc analyses found that during the first visit, relative to placebo, lithium-treated participants showed a higher accuracy in recognising disgust and lower misclassification rates and response bias in recognising sad facial expressions, but higher accuracy and response bias in recognising fear during the second visit. We found a significant interaction between treatment and valence with a large effect size for emotional encoding of self-referent words. Post-hoc analysis showed that lithium was associated with a longer reaction time to encode negative self-referent words than placebo. Short-term lithium treatment in healthy participants produced a positive emotional bias in facial expression recognition and emotional encoding of self-referent words, but no significant effects on impulsivity and reward seeking. The early induction of positive bias in emotional processing may contribute to lithium’s effectiveness in mood disorders.

Background Major depressive disorder (MDD) is a leading cause of disability worldwide, yet its diagnosis relies on clinical symptoms alone. Methods Using the semi-supervised machine learning algorithm, Heterogeneity through Discriminative Analysis (HYDRA), we had identified two neuroanatomical dimensions in deeply phenotyped (i.e., comprehensively assessed across neuroimaging, clinical, and behavioural domains), medication-free participants with MDD from the COORDINATE-MDD consortium. In the present study, we apply this pre-trained HYDRA model to the UK Biobank (UKB) to validate these dimensions in a large general population and a subsample with current depressive symptoms. Results Dimension 2 (D2), compared to Dimension 1 (D1), is characterized by reduced grey and white matter volumes and limited treatment response to antidepressant and placebo medications. Out-of-sample validation in the UKB general population (n = 37,235) confirms these neuroanatomical features and reveals D2 associations with cognitive impairments, adverse life events, self-harm and suicide attempts, a pro-atherogenic lipid profile, and genetic links to neurodegenerative traits. Similar profiles are observed in the UKB subsample with current depressive symptoms (n = 1455). Conclusions D1 and D2 represent distinct neurobiological mechanisms underlying MDD. The validation in a general population-based cohort and in a cohort sample with depressive symptoms delineates mechanisms underlying heterogeneity in MDD.

The understanding of how antidepressant (AD) use is associated with brain structure in individuals with major depressive disorder (MDD) remains incomplete. We aimed to examine the association between AD medication use and brain morphology in relation to age and sex by pooling structural neuroimaging and clinical data from 32 cohorts within the ENIGMA-MDD working group. Interaction effects of group (2076 cases with current AD use (AD), 1495 cases not currently taking AD (nAD) and 5125 healthy controls (HC)) with age and sex, and main effects of group on regional brain structure (cortical surface area and thickness, and subcortical volume) were examined. Additionally, we examined the effect of AD type (SSRI, SNRI or mirtazapine) and duration of use on brain morphology. Younger individuals in the AD group showed lower bilateral middle temporal gyrus thickness compared to nAD and HC, but this was not seen in older individuals (crossover around 50 years). Lower hippocampal volume and thinner inferior temporal gyrus were shown in AD compared to nAD. These effects were independent of group differences in disease-course-related measures, but were driven by depressive symptom severity. Greater bilateral rostral anterior cingulate thickness was found in individuals older than approximately 40 years taking mirtazapine compared to individuals taking SSRIs or SNRIs. Evidence for subtle structural brain differences in temporal and limbic regions in individuals with MDD who currently use AD medication were found compared to those not currently taking AD medication. Future longitudinal studies are needed to determine the causality of these associations.

Myalgic encephalitis/chronic fatigue syndrome (ME/CFS) is a common debilitating medical condition, whose main symptoms - fatigue, post-exertional malaise and cognitive dysfunction – are also present in many cases of long COVID. Magnetic resonance spectroscopy (MRS) allows the insight into their pathophysiology through exploration of a range of biochemicals putatively relevant to aetiological processes, in particular mitochondrial dysfunction and energy metabolism. 24 patients with ME/CFS, 25 patients with long COVID and 24 healthy controls (HC) underwent brain (pregenual and dorsal anterior cingulate cortex, respectively, pgACC and dACC) and calf muscle MRS scanning at 7 Tesla, followed by a computerised cognitive assessment. Compared to HC, ME/CFS patients had elevated levels of lactate in both pgACC and dACC, while long COVID patients had lowered levels of total choline in dACC. By contrast, skeletal muscle metabolites at rest did not significantly differ between the groups. The changes in lactate in ME/CFS are consistent with the presence of energetic stress and mitochondrial dysfunction. A reduction in total choline in long COVID is of interest in the context of the recently reported association between blood clots and ‘brain fog’, and earlier animal studies showing that choline might prevent intravascular coagulation. Importantly, differences in findings between ME/CFS and long COVID suggest that the underlying neurobiological mechanisms, while leading to similar clinical presentations, may differ. An important implication is that patients with ME/CFS and those with fatigue in the course of long COVID should not be studied as a single group, at least until the mechanisms are better understood.