The sex differences in anhedonia in major depressive disorder: A resting-state fMRI study

Abnormal Structure-Function Coupling in Major Depressive Disorder Patients With and Without Anhedonia

Background: As a core symptom of major depressive disorder (MDD), previous magnetic resonance studies have demonstrated that MDD with anhedonia may exhibit distinctive brain structural and functional alterations. Nevertheless, the impact of anhedonia on synchronized alterations in the structure and function of brain regions in MDD remains uncertain. Methods: A total of 92 individuals were enrolled in the study, including 29 MDD patients with anhedonia, 33 MDD patients without anhedonia, and 30 healthy controls (HCs). All subjects underwent structural and resting-state functional magnetic resonance imaging (MRI) scans. The structure-function coupling of cortical and subcortical regions was constructed by using the obtained structural and functional data to quantify the distributional similarity of gray matter volume (GMV) and amplitude of low-frequency fluctuations (ALFFs). Analysis of covariance (ANCOVA) was used to compare differences in structure-function coupling among the three groups. Partial correlation analyses were conducted to identify relationships between structure-function coupling and clinical features. Finally, receiver operating characteristic (ROC) curve and support vector machine (SVM) analysis were employed to verify the capacity to distinguish between MDD with anhedonia and MDD without anhedonia, MDD with anhedonia and HCs, and MDD without anhedonia and HCs. Results: The ANCOVA revealed significant differences in structure-function coupling among three groups in the bilateral precentral gyrus (PrG), right insular gyrus (INS), right cingulate gyrus (CG), right thalamus (Tha), left superior temporal gyrus (STG), and left middle temporal gyrus (MTG). Compared to HCs, both MDD groups showed reduced coupling in the right INS, bilateral PrG, while increased coupling in the right CG. Additionally, MDD with anhedonia showed reduced coupling in the right Tha, right PrG, and left MTG, while increased coupling in the left STG, compared to the other two groups. Furthermore, ROC analyses indicated that structure-function coupling in the right PrG, right CG, and left MTG exhibited the greatest capacity to distinguish between the following groups: MDD with anhedonia from HCs, MDD without anhedonia from HCs, and MDD with anhedonia from MDD without anhedonia. The combined metrics demonstrated greater diagnostic value in two-by-two comparisons. Conclusion: The present findings highlight that altered structure-function synchrony in the frontal, temporal lobes, and Tha may be implicated in the development of symptoms of anhedonia in MDD patients. Altered structure-function coupling in the aforementioned brain regions may serve as a novel neuroimaging biomarker for MDD with anhedonia.

Mice lacking the serotonin transporter do not respond to the behavioural effects of psilocybin

BACKGROUND AND PURPOSE

Psilocybin is a serotonergic psychedelic with therapeutic potential for several neuropsychiatric disorders, including depression and anxiety disorders. Serotonin transporter (5-HTT) knockout mice (KO) are a well-validated mouse model of anxiety/depression and are relevant to both chronic treatment with serotonin transporter reuptake inhibitors (SSRIs) and polymorphisms in the serotonin transporter-linked polymorphic region (5-HTTLPR) associated with depression/anxiety and resistance to classic antidepressant treatments. However, there is yet to be a study assessing the effect of psilocybin in 5-HTT KO mice.

EXPERIMENTAL APPROACH

We investigated the effects of a single dose of psilocybin (1 mg/kg) on locomotor activity and the head-twitch response as well as anxiety- and depressive-like behaviour in KO versus wild-type (WT) mice using the light-dark box and Porsolt swim test respectively.

KEY RESULTS

We found that both the psilocybin-induced head-twitch and hyperlocomotor responses observed in WT mice were completely absent in KO animals. In female WT mice only, psilocybin was also able to block the weight loss observed one day after intraperitoneal injection. While psilocybin did not alter anxiety- and depression-like behaviours for both genotypes, we revealed a genotype-specific trend for a main effect of treatment for WT females (p = 0.054) in the Porsolt swim test. Finally, we found that only female KO mice exhibit anhedonia-like behaviour in the saccharin-preference test.

CONCLUSION AND IMPLICATIONS

Our findings highlight the complexity of psilocybin's effects and suggest that functional integrity of 5-HTT is essential for psilocybin's acute behavioural effects. This could also have implications for pharmacogenetics, including individuals with polymorphisms or mutations in 5-HTT.

Applying the Research Domain Criteria to Rodent Studies of Sex Differences in Chronic Stress Susceptibility

Women have a 2-fold increased rate of stress-associated psychiatric disorders such as depression and anxiety, but the mechanisms that underlie this increased susceptibility remain incompletely understood. Historically, female subjects were excluded from preclinical studies and clinical trials. Additionally, chronic stress paradigms used to study psychiatric pathology in animal models were developed for use in males. However, recent changes in National Institutes of Health policy encourage inclusion of female subjects, and considerable work has been performed in recent years to understand biological sex differences that may underlie differences in susceptibility to chronic stress-associated psychiatric conditions. Here, we review the utility as well as current challenges of using the framework of the National Institute of Mental Health's Research Domain Criteria as a transdiagnostic approach to study sex differences in rodent models of chronic stress including recent progress in the study of sex differences in the neurobehavioral domains of negative valence, positive valence, cognition, social processes, and arousal.

Neural correlates of anhedonia in young adults with subthreshold depression: A graph theory approach for cortical-subcortical structural covariance

BACKGROUND

Anhedonia is an enduring symptom of subthreshold depression (StD) and predict later onset of major depressive disorder (MDD). Brain structural covariance describes the inter-regional distribution of morphological changes compared to healthy controls (HC) and reflects brain maturation and disease progression. We investigated neural correlates of anhedonia from the structural covariance.

METHODS

T1-weighted brain magnetic resonance images were acquired from 79 young adults (26 StD, 30 MDD, and 23 HC). Intra-individual structural covariance networks of 68 cortical surface area (CSAs), 68 cortical thicknesses (CTs), and 14 subcortical volumes were constructed. Group-level hubs and principal edges were defined using the global and regional graph metrics, compared between groups, and examined for the association with anhedonia severity.

RESULTS

Global network metrics were comparable among the StD, MDD, and HC. StD exhibited lower centralities of left pallidal volume than HC. StD showed higher centralities than HC in the CSAs of right rostral anterior cingulate cortex (ACC) and pars triangularis, and in the CT of left pars orbitalis. Less anhedonia was associated with higher centralities of left pallidum and right amygdala, higher edge betweenness centralities in the structural covariance (EBSC) of left postcentral gyrus-parahippocampal gyrus and LIPL-right amygdala. More anhedonia was associated with higher centralities of left inferior parietal lobule (LIPL), left postcentral gyrus, left caudal ACC, and higher EBSC of LIPL-left postcentral gyrus, LIPL-right lateral occipital gyrus, and left caudal ACC-parahippocampal gyrus.

LIMITATIONS

This study has a cross-sectional design.

CONCLUSIONS

Structural covariance of brain morphologies within the salience and limbic networks, and among the salience-limbic-default mode-somatomotor-visual networks, are possible neural correlates of anhedonia in depression.

Anhedonia is associated with a specific depression profile and poor antidepressant response

BACKGROUND

Anhedonic features within major depressive disorder (MDD) have been associated with worse course and outcome and may predict nonresponse to treatment. However, a detailed clinical profile of anhedonia in MDD is still lacking.

MATERIALS AND METHODS

One thousand two hundred ninety-four patients with MDD were selected from the cross-sectional European multicenter Group for the Study of Resistant Depression study. Anhedonia was assessed through the Montgomery-Åsberg Depression Rating Scale anhedonia item "inability to feel." Clinical and demographic features were then analyzed.

RESULTS

The presence of anhedonia related to a distinct demographical (living alone) and clinical profile (thyroid diseases, diabetes, suicide risk, high number of previous depressive episodes, more severe MDD, and more frequent inpatient status). Furthermore, anhedonia was associated with nonresponse to treatment and treatment resistance, even after adjusting for confounding variables.

CONCLUSIONS

Our findings support the role of anhedonia as a modulating feature of MDD, being associated with a more severe depression profile. Moreover, anhedonic features are independent predictors of poor treatment response.

Altered resting-state brain activity of the superior parietal cortex and striatum in major depressive disorder and schizophrenia

BACKGROUND

Resting-state functional magnetic resonance imaging (fMRI) studies have shown altered brain activity in major depressive disorder (MDD) and schizophrenia (SZ). Despite differing diagnoses, SZ and MDD share similar features. However, functional brain activity similarities and differences between SZ and MDD remain unclear.

METHODS

Participants with MDD, SZ, and normal controls (n=36 each) underwent resting-state fMRI scans. Amplitude of low-frequency fluctuations (ALFF) was used to analyze the preprocessed rs-fMRI data. One-way ANOVAs and post hoc analyses compared ALFF values in different brain regions. Pearson correlation analysis examined associations with clinical symptoms.

RESULTS

Comparison among the three groups revealed significant differences in ALFF values within the left superior parietal cortex (L-SPC) and bilateral striatum. Through pairwise comparisons, patients with SZ but not patients with MDD were found to exhibit increased striatum ALFF values relative to NC individuals, but decreased in MDD. Meanwhile, L-SPC ALFF values were significantly increased in patients with SZ relative to both normal control individuals and patients with MDD, while no differences in these values were observed between the normal control and MDD groups. The Pearson correlation analyses showed significant positive correlations between ALFF in the striatum and PANSS positive score, but no significant correlation with other symptom severity in SZ and MDD.

CONCLUSION

These findings support the hypothesis of alterations in brain functional activity as a fundamental component of the pathogenesis of MDD and SZ. The observed differences in functional brain activity in the superior parietal cortex and striatum between MDD and SZ provide a neuroimaging basis that can contribute to the differential diagnosis of these debilitating conditions.

Sex moderates the effect of anhedonia on parietal alpha asymmetry

Anhedonia, a transdiagnostic symptom present in many neuropsychiatric disorders, differs in males and females. Parietal EEG alpha asymmetry is associated with reduced arousal and low positive emotionality, and is, therefore, a promising neurophysiologic biomarker of anhedonia. To date, however, no prior studies have determined whether this measure captures sex differences in anhedonic expression. This preliminary study (N = 36) investigated whether anhedonia severity is associated with EEG resting-state parietal alpha asymmetry in adults and whether sex moderates this relationship. Results showed that there was a significant moderating effect of sex such that, only for females, higher levels of anhedonia were associated with increased parietal alpha asymmetry. These findings suggest that parietal alpha asymmetry is a promising biomarker of anhedonia severity in female adults and reinforces the need to account for sex differences in future research.

Sex-Specific Mechanisms Underlie Long-Term Potentiation at Hippocampus→Medium Spiny Neuron Synapses in the Medial Shell of the Nucleus Accumbens

Sex differences have complicated our understanding of the neurobiological basis of many behaviors that are key for survival. As such, continued elucidation of the similarities and differences between sexes is necessary to gain insight into brain function and vulnerability. The connection between the hippocampus (Hipp) and nucleus accumbens (NAc) is a crucial site where modulation of neuronal activity mediates reward-related behavior. Our previous work demonstrated that long-term potentiation (LTP) of Hipp→NAc synapses is rewarding, and mice can establish learned associations between LTP of these synapses and the contextual environment in which LTP occurred. Here, we investigated sex differences in the mechanisms underlying Hipp→NAc LTP using whole-cell electrophysiology and pharmacology. We observed similarities in basal synaptic strength between males and females and found that LTP occurs postsynaptically with similar magnitudes in both sexes. However, key sex differences emerged as LTP in males required NMDA receptors (NMDAR), whereas LTP in females utilized an NMDAR-independent mechanism involving L-type voltage-gated Ca2+ channels (VGCCs) and estrogen receptor α (ERα). We also uncovered sex-similar features as LTP in both sexes depended on CaMKII activity and occurred independently of dopamine-1 receptor (D1R) activation. Our results have elucidated sex-specific molecular mechanisms for LTP in an integral pathway that mediates reward-related behaviors, emphasizing the importance of considering sex as a variable in mechanistic studies. Continued characterization of sex-specific mechanisms underlying plasticity will offer novel insight into the neurophysiological basis of behavior, with significant implications for understanding how diverse processes mediate behavior and contribute to vulnerability to developing psychiatric disorders.

Sex differences in anhedonia in bipolar depression: a resting-state fMRI study

Previous studies about anhedonia symptoms in bipolar depression (BD) ignored the unique role of gender on brain function. This study aims to explore the regional brain neuroimaging features of BD with anhedonia and the sex differences in these patients. The resting-fMRI by applying fractional amplitude of low-frequency fluctuation (fALFF) method was estimated in 263 patients with BD (174 high anhedonia [HA], 89 low anhedonia [LA]) and 213 healthy controls. The effects of two different factors in patients with BD were analyzed using a 3 (group: HA, LA, HC) × 2 (sex: male, female) ANOVA. The fALFF values were higher in the HA group than in the LA group in the right medial cingulate gyrus and supplementary motor area. For the sex-by-group interaction, the fALFF values of the right hippocampus, left medial occipital gyrus, right insula, and bilateral medial cingulate gyrus were significantly higher in HA males than in LA males but not females. These results suggested that the pattern of high activation could be a marker of anhedonia symptoms in BD males, and the sex differences should be considered in future studies of BD with anhedonia symptoms.

Sex-specific mechanisms underlie long-term potentiation at hippocampus-nucleus accumbens synapses

Sex differences have complicated our understanding of the neurobiological basis of many behaviors that are key for survival. As such, continued elucidation of the similarities and differences between sexes is necessary in order to gain insight into brain function and vulnerability. The connection between the hippocampus (Hipp) and nucleus accumbens (NAc) is a crucial site where modulation of neuronal activity mediates reward-related behavior. Our previous work demonstrated that long-term potentiation (LTP) of Hipp-NAc synapses is rewarding, and that mice can make learned associations between LTP of these synapses and the contextual environment in which LTP occurred. Here, we investigate sex differences in the mechanisms underlying Hipp-NAc LTP using whole-cell electrophysiology and pharmacology. We found that males and females display similar magnitudes of Hipp-NAc LTP which occurs postsynaptically. However, LTP in females requires L-type voltage-gated Ca 2+ channels (VGCC) for postsynaptic Ca 2+ influx, while males rely on NMDA receptors (NMDAR). Additionally, females require estrogen receptor α (ERα) activity for LTP while males do not. These differential mechanisms converge as LTP in both sexes depends on CAMKII activity and occurs independently of dopamine-1 receptor (D1R) activation. Our results have elucidated sex-specific molecular mechanisms for LTP in an integral excitatory pathway that mediates reward-related behaviors, emphasizing the importance of considering sex as a variable in mechanistic studies. Continued characterization of sex-specific mechanisms underlying plasticity will offer novel insight into the neurophysiological basis of behavior, with significant implications for understanding how diverse processes mediate behavior and contribute to vulnerability to developing psychiatric disorders.

SIGNIFICANCE STATEMENT

Strengthening of Hipp-NAc synapses drives reward-related behaviors. Male and female mice have similar magnitudes of long-term potentiation (LTP) and both sexes have a predicted postsynaptic locus of plasticity. Despite these similarities, we illustrate here that sex-specific molecular mechanisms are used to elicit LTP. Given the bidirectional relationship between Hipp-NAc synaptic strength in mediating reward-related behaviors, the use of distinct molecular mechanisms may explain sex differences observed in stress susceptibility or response to rewarding stimuli. Discovery and characterization of convergent sex differences provides mechanistic insight into the sex-specific function of Hipp-NAc circuitry and has widespread implications for circuits mediating learning and reward-related behavior.