Altered neurovascular coupling and associated neurotransmitter profiles in inflammatory bowel disease with distinct depressive symptoms

Abstract

Neurovascular coupling (NVC) provides a new mechanistic perspective into understanding numerous brain diseases. Previous studies revealed the effects of depressive symptoms on NVC and neurotransmitters in certain neuropsychiatric disorders. However, whether the effects of depressive symptoms on NVC and neurotransmitters would be exhibited in inflammatory bowel diseases (IBD) is hitherto unknown. Forty IBD patients and forty-five healthy controls (HCs) underwent multiparametric magnetic resonance imaging scan. NVC metrics were investigated by exploring Pearson correlation coefficients and ratios between cerebral blood flow (CBF) and functional connectivity strength (FCS). Correlation analysis was applied to evaluate relationships between imaging-related alterations and clinical features as well as neurotransmitter profiles. The effects of depressive symptoms on brain functional alterations and distribution of specific neurotransmitters were explored in IBD subgroups. Multivariate pattern analysis (MVPA) was further applied to select features. Global coupling strength (i.e., short-range CBF-FCS) was significantly higher in IBD than that in HCs. Meanwhile, CBF, FCS and regional NVC (i.e., CBF/FCS) changes in the default mode network, insula, orbitofrontal cortex (OFC), middle cingulate cortex and pre-/postcentral gyrus (Pre-/PostCG) were found in IBD. Image-based machine-learning techniques were capable of differentiating IBD patients from HCs. Significant correlation was found between the decreased long-range FCS in fusiform gyrus and IBD questionnaire score in patients. IBD-related brain functional abnormalities were associated with the specific dopamine, glutamate, acetylcholine and serotonin neurotransmitter profiles. The effects of depressive symptoms on FCS and CBF/FCS were detected in IBD subgroups, mainly located in the OFC, fusiform gyrus, supplementary motor area, PostCG and/or caudate. The effects of depressive symptoms on distribution of aforementioned neurotransmitters were also revealed in IBD subgroups. Furthermore, these findings were implicated in the integration of emotion, cognition and visceral nociceptive perception in IBD patients. This study provides a new perspective for understanding the neuropathological underpinning of IBD by revealing these brain functional abnormalities and corresponding neurotransmitter profiles.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-025-03676-0.

Introduction

The inflammatory bowel diseases (IBD), including Crohn’s disease (CD) and ulcerative colitis (UC), are chronic disorders causing inflammation of the gastrointestinal tract [1]. The incidence and prevalence of IBD are increasing worldwide, and IBD widely occurs in people of all ages [2]. Besides gastrointestinal symptoms, IBD patients experience a spectrum of behavioral, cognitive, and emotional symptoms, such as anxiety, depressive symptoms, sleep, fatigue, cognitive dysfunction, and social withdrawal [3]. The pathogenesis of IBD is considered to be multifactorial, involving the presence of pathogenic factors such as abnormal gut microbiota, immune response dysregulation, environmental changes, and gene variants [4]. Accumulating evidence has suggested a bidirectional link between the neuropathology and gastrointestinal inflammation based on the concept of the brain-gut axis, which has a key role in the pathogenesis of IBD [5, 6]. However, the pathophysiologic mechanism of IBD has yet to be fully elucidated.

Numerous neuroimaging studies have reported an extensive distribution of functional alterations and identified distinct perfusion patterns in IBD patients, especially in the insula, prefrontal cortex, cingulate cortex, parietal cortex and temporal cortex [7–13]. However, these studies of IBD have focused on either brain activity from blood-oxygen-level-dependent or cerebral blood flow (CBF) derived from arterial spin labeling (ASL), ignoring the integrity of the coupling between the two. Combining resting-state functional magnetic resonance imaging (rs-fMRI) and ASL techniques can provide a more comprehensive understanding of pathophysiological mechanisms [14, 15]. Based on the neurovascular coupling (NVC) hypothesis, blood-oxygen-level-dependent signals reflect microvascular hemodynamic and metabolic changes and are inherently closely linked to CBF [15]. To comprehensively measure the integration of brain function, functional connectivity strength (FCS) was calculated at a voxel level derived from rs-fMRI [16]. The efficient and well-organized function of the human brain network depends on short- and long-range connections [17]. NVC is a mechanism of the neurovascular unit (NVU) that regulates CBF to meet the energy demands of the neuronal activity and maintain balance between blood supply and neuronal activity [18]. The structural basis for NVC is the NVU, which consists of neurons, glial cells, and microvessels [19]. By integrating regional perfusion with neural activity, the short- and long-range CBF/FCS ratios provide a non-invasive and reliable index of regional NVC [15, 20, 21]. Meanwhile, a possible neuropathological mechanism underlying brain dysfunction has been successfully identified through analysis of NVC alterations in several neuropsychiatric disorders [20, 22, 23]. In line with the evidence of vulnerabilities of neurons, glial cells, and vascular elements in IBD [24–28]. Therefore, investigating the NVC characteristics may provide novel insights into neural mechanisms of IBD.

Furthermore, disease-related changes in the brain functional organization patterns might be regulated or reflected by some microscale factors, such as neurotransmitters. Positron emission tomography (PET) and single photon computed tomography (SPECT) imaging provides the whole-brain density distribution of some neurotransmitter systems such serotonin, dopamine, norepinephrine and glutamate systems [29]. Using the cross-modal evaluation of neuroimaging and neurotransmitter profiles, previous studies have revealed a biologically meaningful framework in depression [30], schizophrenia [31] and mild cognitive impairment [32]. Thus, exploring the relevant neurotransmitter profiles could shed more light on the understanding of disease pathogenesis and consequently tailor interventions. However, there is limited knowledge regarding whether and how neurotransmitter systems reflect the abnormal CBF, FCS and NVC in IBD.

Recent studies have shown that the abnormalities of NVC [22, 23] and neurotransmitter systems [30, 32] were affected by the severity of depressive symptoms. Especially, Chao et al. reported that the reduced regional NVC in the middle orbitofrontal cortex (OFC) facilitated the emergence of corresponding depressive symptoms through reducing the ability of glymphatic clearance of metabolic waste [22]. Moreover, the spatial correspondences between the neurotransmitters and functional brain organization alterations were detected in patients with depressive symptoms [32]. Depressive symptoms are main psychiatric symptoms of IBD [3, 33–35]. Meanwhile, prior studies contributed to explain the effects of depressive symptoms on brain function and neurotransmitters in IBD patients [33, 36]. However, available studies on how depressive symptoms affect NVC and corresponding neurotransmitter systems in IBD patients remain limited.

Therefore, to address the above issues, we applied (1) a combination of CBF, FCS and NVC in IBD patients to comprehensively explore the brain functional organization patterns; (2) multivariate pattern analysis (MVPA) to evaluate the classification performance of these abnormalities between IBD patients and healthy controls (HCs); (3) association analyses between imaging findings and clinical features as well as neurotransmitter profiles. Meanwhile, we explored the effects of depressive symptoms on neuroimaging findings and the corresponding distribution of neurotransmitter profiles in IBD subgroups.

Methods

Participants

Participants were individually diagnosed by the same two professional gastroenterologist with more than 10 years of working experience. Clinical assessment of IBD patients including characteristic manifestations of colonoscopy, mucosal biopsy, and barium enema, IBD questionnaire (IBDQ), Pittsburgh sleep quality index (PSQI), multidimensional fatigue inventory (MFI), platelet levels and disease duration. And the current and past psychiatric status of all participants were evaluated by an experienced psychiatrist. For all participants, the self-rating anxiety scale (SAS), self-rating depression scale (SDS) were applied to assess the severity of anxiety/depression symptoms. Based on SDS scores (SDS ≥ 53) [37], patients were divided into IBD with depressive and IBD without depressive symptoms. More details of inclusion and exclusion criteria of IBD and HCs in Additional file 1: Method S1.

Image acquisition and preprocessing

An overview of the study design and analyses is provided in Fig. 1. The MRI data of all participants were conducted on a 3.0T MR Scanner (GE Discovery 750w) equipped with 32-channel phased-array head coil. Details of imaging acquisition and preprocessing were available in Additional file 1: Method S1.

Fig. 1.

Study overview and workflow. A Schematic of calculation of CBF, FCS, global NVC and regional NVC. B Classification performance analysis of CBF, FCS and regional NVC features. C Flowchart of spatial association estimation with neurotransmitters. The inter-group comparison t-maps were employed to identify associations with neurotransmitters. Abbreviations: ASL, arterial spin labeling; CBF, cerebral blood flow; LFCS, long-range functional connectivity strength; SFCS, short-range functional connectivity strength; NVC, neurovascular coupling; IBD, inflammatory bowel disease; HCs: healthy controls; rs-fMRI, resting-state functional magnetic resonance imaging; SVM, support vector machine; RF, random forest; AUC, area under the curve

Global and regional NVC analysis

To quantitatively evaluate NVC at the global level in this study, Pearson correlation coefficients were calculated between CBF and FCS with long- and short-range values of all voxels within the gray matter mask of each participant. That means the correlation coefficients of CBF-LFCS and CBF-SFCS coupling were used to characterize the global NVC, respectively. Ultimately, for each functional metric, a single coupling coefficient was obtained for each subject to represent the global coupling strength.

To evaluate the metabolic consumption per unit of neural activity, the regional perfusion/neural activity ratios (CBF/LFCS and CBF/SFCS) were assessed as proxies of regional NVC. Here, CBF/LFCS and CBF/SFCS ratios were applied to quantify corresponding metabolic energy per unit of functional integration. The CBF/FCS ratio map with long- and short-range for each subject was computed by using their original CBF map (without z-transformation) divided by their original FCS map across all voxels within the gray matter mask, and then standardized into z-scores for subsequent comparisons to reflect the potential regional coupling abnormalities. All regional NVC maps were smoothed with a 6-mm full-width at half-maximum Gaussian kernel.

Statistical analysis

Group comparisons of demographic, clinical, and global NVC correlation coefficients were conducted using SPSS software. The Chi-square test was employed for categorical data. The two-sample t-test was used for comparisons of continuous variables between IBD patients and HCs as well as between IBD patients’ subgroups. Statistical significance was set as p < 0.05.

Two-sample t-test was also applied to compare global NVC correlation coefficients between all IBD patients and HCs. The between-group differences in CBF, LFCS, SFCS, CBF/LFCS and CBF/SFCS ratio were investigated using a two-sample t-test (Gaussian random field (GRF) correction: voxel-level p < 0.005, cluster-level p < 0.05). Age, sex, education years and BMI were considered as covariates for the above analyses. Further, to explore the effect of depressive symptoms on imaging findings in IBD subgroups, we repeated these comparisons between IBD subgroups.

The mean values of each significant brain regions (3 mm radius sphere centered at the peak t value) in all IBD patients and HCs. Pearson’s correlation analysis was performed to explore the relationship between the values of regions of interest (ROIs) and clinical features of all IBD patients (p < 0.05).

Multivariate Pattern Analysis

For the classification performance analysis to differentiate IBD patients from HCs, all MVPA procedures were implemented in the MVPA for Neuroimaging (MVPANI, http://funi.tmu.edu.cn.) toolbox. MRI features were from ROIs that showed significant inter-group differences in the CBF, LFCS, SFCS, CBF/LFCS and CBF/SFCS analyses. To enhance the predictive power of classification model and avoid overfitting possibility of the model, Least Absolute Shrinkage and Selection Operator (LASSO) model was employed. After that, features with nonzero coefficients remained as the input feature vectors for training classification models. Pattern classification was performed using support vector machine (SVM) and random forest (RF) implemented by MVPANI. The number of decision trees in RF was set at 500. A leave-one-out cross-validation was used for modal validation. In each repetition, the data of individual was removed one at a time as a test sample, and predictions were then made for the remaining individual data. In addition to computing classification accuracy, the performance of the classifiers was also evaluated using receiver operating characteristic (ROC) curve and corresponding area under the curve (AUC). Meanwhile, permutation tests with 5000 iterations were conducted to determine whether the classification accuracy obtained was significantly higher than chance.

Spatial correlation with neurotransmitter density maps

Furthermore, fMRI (CBF, LFCS, SFCS, CBF/LFCS or CBF/SFCS) maps that significantly differed between-group comparisons were used as input for spatial correlation with PET- and SPECT-derived maps in JuSpace (https://github.com/juryxy/JuSpace_v1.5) to explore the specific molecular architecture of neurotransmitter profiles underlying the altered imaging findings. Thirteen PET/SPECT maps were considered, including the serotonergic (serotonin 5-hydroxytryptamine receptor subtypes 1a, 1b, and 2a: 5-HT1a, 5-HT1b, 5-HT2a; serotonin transporter: SERT), noradrenergic (noradrenaline transporter: NAT); dopaminergic (dopamine D1 and D2; dopamine transporter: DAT; 6-fluoro-(18 F)-L-3,4-dihydroxyphenylalanine: FDOPA); gamma-aminobutyric acid type a (GABAa); the vesicular acetylcholine transporter (VAChT); N-methyl-D-aspartic acid receptor (NMDA) and metabotropic glutamate receptor type 5 (mGluR5) [29]. Spearman’s rank correlations were computed between the significant CBF, LFCS, SFCS, regional NVC (CBF/LFCS, CBF/SFCS) maps and 13 neurotransmitter profiles. Based on previous studies, exact permutation-based p values as implemented in JuSpace (adjusted for spatial autocorrelation [38, 39]: 10,000 permutations randomly assigning group labels using orthogonal permutations) were computed to test if the observed spearman’s rank correlation coefficients deviate from a null distribution [29]. Moreover, a larger neurotransmitter database (https://github.com/netneurolab/hansen_receptor) was used to validate the robustness of the abovementioned neurotransmitter findings [40]. Most of the selected neurotransmitter profiles were in line with the abovementioned analysis.

Results

Demographic and clinical results

Participants with distinct head motion of were excluded in this study. Finally, 40 IBD patients and 45 HCs were included (Table 1). IBD patients had higher SAS, SDS, PSQI and MFI scores (p < 0.05) than HCs. More details of IBD subgroups in the Table S1.

Table 1.

Clinical and demographic features for IBD patients and HCs

Features	IBD	HCs	p value
Sex (M/F)	23/17	17/28	0.069a
Age (years)	34.33 (11.97)	33.71 (9.57)	0.794b
Education	12.38 (3.27)	13.49 (3.07)	0.109 b
BMI	20.73 (3.37)	22.49 (3.04)	0.013b
SAS	41.75 (9.25)	37.87 (6.03)	0.023b
SDS	50.00 (12.29)	35.49 (6.23)	< 0.001 b
PSQI	6.98 (3.26)	3.38 (2.27)	< 0.001 b
MFI	54.75 (17.67)	31.38 (5.34)	< 0.001 b
Platelet levels (×10^9)	304.76 (151.44)	/	/
IBDQ	162.28 (29.47)	/	/

Data are expressed as the mean (standard deviation)

Abbreviations: IBD inflammatory bowel disease, HCs healthy controls, M male, F female, BMI body mass index, SAS self-rating anxiety scale, SDS self-rating depression scale, PSQI Pittsburgh sleep quality index, MFI Multidimensional fatigue inventory, IBDQ inflammatory bowel disease questionnaire

^a The p value was obtained by the two-tailed chi-squared test between the IBD patients and HCs

^b The p value was obtained by two sample t-tests between the IBD patients and HCs

CBF and FCS changes between IBD and HCs

As shown in Fig. 2, compared with HCs, patients with IBD exhibited significantly (1) increased CBF in the right supplementary motor area (SMA), right superior parietal cortex (SPC), right pre-/postcentral gyrus (Pre-/PostCG), left precuneus (PCNU), left cuneus (CUN), right angular gyrus (ANG), and decreased CBF in the bilateral anterior cingulate cortex (ACC), bilateral medial prefrontal cortex (mPFC), right OFC, bilateral temporal pole (TP), left inferior temporal cortex (ITC); (2) increased LFCS in the right middle temporal cortex (MTC), and decreased LFCS in the right mPFC and right fusiform gyrus (FG); and (3) increased SFCS in the bilateral middle frontal cortex (MFC) and right ANG, and decreased SFCS in the bilateral FG, left insula and left superior temporal cortex/MTC (STC/MTC). Scatter plots of these imaging findings are presented in Fig. 3.

Fig. 2.

Between group differences of CBF and FCS. Altered CBF, LFCS and SFCS between IBD patients and HCs. Abbreviations: CBF, cerebral blood flow; LFCS, long-range functional connectivity strength; SFCS, short-range functional connectivity strength; IBD, inflammatory bowel disease; HCs: healthy controls; R, right; SMA, supplementary motor area; SPC, superior parietal cortex; Pre-/PostCG, pre-/postcentral gyrus; PCUN, precuneus; ANG, angular gyrus; CUN, cuneus; ACC, anterior cingulate cortex; mPFC, medial prefrontal cortex; OFC, orbitofrontal cortex; TP, temporal pole; ITC, inferior temporal cortex; MTC, middle temporal cortex; FG, fusiform gyrus; MFC, middle frontal cortex; STC, superior temporal cortex

Fig. 3.

Scatter plots in the ROIs with significant CBF and FCS alterations. The corresponding scatter plots of CBF, LFCS and SFCS alterations between IBD patients and HCs. Abbreviations: ROIs, regions of interest; CBF, cerebral blood flow; LFCS, long-range functional connectivity strength; SFCS, short-range functional connectivity strength; IBD, inflammatory bowel disease; HCs: healthy controls; SMA, supplementary motor area; SPC, superior parietal cortex; Pre-/PostCG, pre-/postcentral gyrus; PCUN, precuneus; ANG, angular gyrus; CUN, cuneus; ACC, anterior cingulate cortex; mPFC, medial prefrontal cortex; OFC, orbitofrontal cortex; TP, temporal pole; ITC, inferior temporal cortex; MTC, middle temporal cortex; FG, fusiform gyrus; MFC, middle frontal cortex; STC, superior temporal cortex

Global and regional NVC changes between IBD and HCs

As shown in Fig. 4A, significant across-voxel spatial correlations between CBF and FCS (short- and long-range) in both IBD patients and HCs; two representative correlation maps are presented. IBD patients had the significant increased CBF-SFCS (p < 0.001, Fig. 4B) coupling compared with HCs.

Fig. 4.

Global NVC in IBD patients and HCs. The scatter plot of the across-voxel spatial correlation between average CBF and average LFCS (A), average SFCS (B) in the IBD and HC groups, respectively. IBD patients exhibited increased global CBF-SFCS coupling compared to HCs. Abbreviations: NVC, neurovascular coupling; CBF, cerebral blood flow; LFCS, long-range functional connectivity strength; SFCS, short-range functional connectivity strength; IBD, inflammatory bowel disease; HCs: healthy controls; ns, not significant

Compared with HCs, IBD patients exhibited significantly (1) increased CBF/LFCS ratio in the left Pre-/PostCG and decreased CBF/LFCS ratio in the left dorsolateral prefrontal cortex (dlPFC); and (2) increased CBF/SFCS ratio in the right middle cingulate cortex (MCC), left Pre-/PostCG, and decreased CBF/SFCS ratio in the right mPFC (Fig. 5). Further ROI-based analysis results in Additional file 1: Fig. S1.

Fig. 5.

Between group differences of regional NVC in IBD patients and HCs. A Altered CBF/LFCS and CBF/SFCS ratios in IBD patients compared to HCs. B The corresponding scatter plots of regional NVC alterations between groups. Abbreviations: NVC, neurovascular coupling; CBF, cerebral blood flow; LFCS, long-range functional connectivity strength; SFCS, short-range functional connectivity strength; IBD, inflammatory bowel disease; HCs: healthy controls; R, right; Pre-/PostCG, pre-/postcentral gyrus; dlPFC, dorsolateral prefrontal cortex; mPFC, medial prefrontal cortex; MCC, middle cingulate cortex

CBF, FCS and NVC changes between IBD subgroups

Compared with IBD patients without depressive symptoms, those with depressive symptoms showed (1) increased LFCS in the right OFC and left FG; and decreased LFCS in the left SMA and right caudate; (2) increased SFCS in the right CUN and left FG and decreased SFCS in the right ITC and right PostCG; (3) increased CBF/LFCS ratio in the right caudate and decreased CBF/LFCS ratio in the left calcarine and left FG (Fig. 6 and Fig. 7). There were no significant differences of global NVC between the IBD subgroups.

Fig. 6.

Effect of depressive symptoms on the imaging findings in IBD subgroups. Between-group differences of FCS and CBF/FCS ratio in IBD patients according the presence of depressive symptoms. Abbreviations: CBF, cerebral blood flow; LFCS, long-range functional connectivity strength; SFCS, short-range functional connectivity strength; IBD, inflammatory bowel disease; D IBD, IBD with depressive symptoms; ND IBD, IBD without depressive symptoms; R, right; OFC, orbitofrontal cortex; FG, fusiform gyrus; SMA, supplementary motor area; CUN, cuneus; ITC, inferior temporal cortex; PostCG, postcentral gyrus; CAL, calcarine

Fig. 7.

The corresponding scatter plots of the imaging findings in IBD subgroups. Scatter plots in the ROIs with significant FCS and CBF/FCS ratio in IBD subgroups. Abbreviations: ROIs, regions of interest; CBF, cerebral blood flow; LFCS, long-range functional connectivity strength; SFCS, short-range functional connectivity strength; IBD, inflammatory bowel disease; D IBD, IBD with depressive symptoms; ND IBD, IBD without depressive symptoms; R, right; OFC, orbitofrontal cortex; FG, fusiform gyrus; SMA, supplementary motor area; CUN, cuneus; ITC, inferior temporal cortex; PostCG, postcentral gyrus; CAL, calcarine

Correlations between imaging findings and clinical features

No significant correlation was found between the abnormalities of ROIs and clinical features in IBD patients. However, IBD patients exhibited marginal significant positive correlations between the increased SFCS in the right MFC and the platelet levels (r = 0.311, p = 0.051), and between the increased CBF/SFCS in the right MCC and SAS scores (r = 0.307, p = 0.054). The marginal significant negative correlation was found between the increased CBF/SFCS in the right MCC and IBDQ scores in IBD patients (r = -0.301, p = 0.059).

Classification performances of MRI features

The LASSO selection result is shown in Additional file 1: Fig. S2, with a vertical dashed line (red) indicating the Lambda value corresponding to the minimum cross-validation error. As shown in Fig. 8, classification performance analyses showed the superiority of aforementioned MRI features. The classification accuracies achieved for each model were as follows: SVM (Fig. 8A, AUC = 0.917, accuracy = 0.847, sensitivity = 0.850, and specificity = 0.844); RF (Fig. 8C, AUC = 0.915, accuracy = 0.800, sensitivity = 0.800, and specificity = 0.800). All permutation tests confirmed that the classification accuracy was significantly higher than the random classifier (Fig. 8B, SVM: p < 0.0002; Fig. 8D, RF: p = 0.0018).

Fig. 8.

Classification performances. The ROC curves of MRI features and classification performances. Abbreviations: ROC, receiver operating characteristic; AUC, area under the curve; MRI, magnetic resonance imaging; SVM, support vector machine; RF, random forest

Our findings indicated that these MRI features made the major contribution to classification models, including: CBF in the bilateral mPFC, right ANG, right TP and right Pre-/PostCG; LFCS in the right mPFC; SFCS in the bilateral MFC, left STC, left MTC and left FG; CBF/SFCS in the right MCC, right mPFC and left Pre-/PostCG.

Spatial associations with neurotransmitters results

Compared with HCs, the altered CBF in IBD patients were significantly associated with the spatial distribution of 5HT1a (r = -0.131; p < 0.001), D2 (r = 0.185; p < 0.001), NAT (r = 0.101; p = 0.015), NMDA (r = 0.101; p = 0.004) and VAChT (r = 0.137; p = 0.046); LFCS alterations were significantly associated with the 5HT1b (r = 0.084; p = 0.026) and D2 (r = 0.104; p = 0.026); SFCS alterations were significantly associated with the 5HT1b (r = 0.101; p = 0.018) (Fig. 9A). No significant association was found between the abnormal regional NVC in IBD patients and neurotransmitters.

Fig. 9.

Spatial association estimation. Spatial correlation analysis of neurotransmitters with t-maps for all IBD patients and HCs (A), and the effects of depressive symptoms in IBD subgroups (B). The radar plots showed the correlation coefficients value. The “*” means the correlation value was significant (Exact p < 0.05, 10000 times permutation tests). Abbreviations: CBF, cerebral blood flow; LFCS, long-range functional connectivity strength; SFCS, short-range functional connectivity strength; IBD, inflammatory bowel disease; HCs, healthy controls; 5HT1a/1b/2a, serotonin 5-hydroxytryptamine receptor subtype 1a/1b/2a; D1/D2, dopamine D1/D2 receptor; DAT, dopamine transporter; FDOPA, dopamine synthesis capacity; GABAa, gamma-aminobutyric acid type a; NMDA, N-methyl-D-aspartic acid receptor; NAT, noradrenaline transporter; SERT, serotonin transporter; VAChT, vesicular acetylcholine transporter; mGluR5, metabotropic glutamate receptor 5

Compared with IBD patients without depressive symptoms, the changes of LFCS in in patients with depressive symptoms were significantly associated with the spatial distribution of 5HT1a (r = 0.133; p = 0.032), 5HT2a (r = 0.157; p = 0.008), D2 (r = -0.180; p = 0.002), DAT (r = -0.144; p = 0.007), GABAa (r = 0.169; p = 0.005), NAT (r = -0.127; p = 0.032) and VAChT (r = -0.195; p = 0.001); SFCS alterations were significantly associated with the 5HT2a (r = 0.121; p = 0.041), GABAa (r = 0.172; p = 0.003) and VAChT (r = -0.186; p = 0.020); CBF/LFCS ratio alterations were significantly associated with the 5HT1a (r = -0.126; p = 0.038), 5HT2a (r = -0.200; p = 0.005) and GABAa (r = -0.206; p = 0.002) (Fig. 9B). Detailed validation of the current findings based on a larger neurotransmitter database in Additional file 1: Fig. S3.

Discussion

This study explored the underlying NVC mechanisms in IBD patients by analyzing the relationship between intrinsic brain neural connectivity and corresponding blood perfusion. Compared with HCs, IBD patients mainly exhibited significantly (1) abnormal CBF in the ACC, mPFC, ANG, CUN, PCNU, TP, ITC, and OFC; (2) altered LFCS in the MTC, mPFC and FG; (3) altered SFCS in the MFC, ANG, FG, STC/MTC and insula; (4) increased global NVC of CBF-SFCS correlations; (5) increased regional coupling in the Pre-/PostCG, MCC and FG, and decreased regional coupling in the dlPFC and mPFC. SVM and RF classifiers integrating CBF, FCS and NVC ratio, demonstrated strong discriminatory ability. Spatial associations were detected between the abnormal CBF, FCS and neurotransmitters (5HT1a, 5HT1b, D2, NAT, NMDA and VAchT). The effects of depressive symptoms on imaging findings and distribution of specific neurotransmitters were uncovered in IBD subgroups.

The altered CBF in IBD patients were mainly located in the OFC, and default mode network (DMN), including the ACC, mPFC, ANG, CUN, PCNU, TP and ITC. Building upon the evidence that long-term inflammation causes alterations in the brain [41], and may impact brain function. The OFC is involved in emotion regulation, with neurons in the OFC encoding the association between sensory stimuli in the external world and internal states related to emotionally relevant events [42]. The DMN was associated with self-referential processing and emotional regulation [43]. Especially, the ACC activations were linearly related to the subjective pleasantness or unpleasantness of the stimuli [44, 45]. ACC plays a pivotal role in IBD along the bidirectional pathway of brain-gut axis [46]. Specifically, ACC processes information transmitted by visceral nociceptive afferents and undergoes long-term potentiation, which affects excitatory synapses and results in cortical plasticity [47]. Lv et al. revealed that IBD patients with pain exhibited higher glutamate concentrations in the ACC [48], and Jung et al. indicated the potential influence of excessive glutamate on cell death and synaptic loss in the ACC [49]. These regions showing regional CBF changes were similar to the previous rs-fMRI findings of IBD [11–13], the CBF changes were associated with abnormal neuronal activity [20]. Thereby, the altered CBF in the OFC and DMN in IBD patients might be associated with the emotion regulation and visceral sensition processing.

Supporting this view, we detected FCS alterations in IBD patients that paralleled the CBF changes observed in the mPFC and ANG. Besides, the FCS alterations were also found in the MFC, insula, STC/MTC and FG. As parts of the “pain matrix”, the MFC and insula are thought to be responsible for cognitive and attentional modulation of interoceptive information [50]. Bernstein et al. found that controls had greater frontal deactivation than IBD patients, and interpreted this as the emotional response to visceral pain anticipation in IBD patients might have suppressed frontal deactivations [51]. Recently, Chen et al. uncovered the higher FCS in MFC was related to the stronger emotional arousal in patients with functional dyspepsia [52]. The insula plays an integral role in the response and experience of emotional states, visceroception and behavior regulation in response to salient environmental stimuli [53]. By using tract-tracing and direct electrocortical stimulation methods, researchers found that the insula received visceral afferent signals and transmitted sensory information from the entire body [54]. Furthermore, the decreased insular glutamate levels are a cerebral metabolic feature of IBD, and these changes were associated with depressive symptoms and inflammatory biomarkers [36]. In the present study, the depressive symptom scores of IBD patients were significantly higher than that of HCs. The STC/MTC and FG were also involved in the regulation of emotional and cognitive in IBD patients [55, 56]. Taken together, these findings might indicate the dysregulation of cognitive processing, pain regulation and visceral sensory afferent responses of IBD patients.

The global NVC patterns reflect the coordination between blood supply and metabolic demand in the neural activity of functional integration [57]. Significant spatial correlations were found between CBF and FCS in both IBD patients and HCs, however, the coupling strength in IBD was higher than that in HCs. The normal NVC mechanism represents a complete structure of neurons, astrocytes and vascular components [58]. Astrocytes are indispensable in maintaining the stability of the blood-brain barrier. Cytokines may modulate neural plasticity by inducing astrocyte and oligodendrocyte apoptosis, which decreases neurogenesis [59]. In a healthy brain, NVC ensures a proportionate CBF response to neural activity [15, 60], whereas abnormalities may lead to cerebral pathologies and neurologic disorders [20, 21]. Brain regions with increased neuronal activity have higher metabolic demands and therefore require more perfusion [61]. Our results demonstrated that tighter NVC in IBD was constructed. These findings may be partly correlated with the higher global NVC observed in IBD.

Meanwhile, IBD patients also showed regional NVC changes. The regional NVC (CBF/LFCS and CBF/SFCS ratio) is like a balance with two ends and keeps balance in the normal brain [15, 60]. However, in patients with IBD, deviations from the balance, signifying abnormal NVC, could result in either increased or decreased ratio. The former indicates redundant blood supply per unit of neural activity, whereas the latter denotes inadequate blood supply per unit of neural activity [20].

Interestingly, further ROI-based analysis conducted that these increased CBF/LFCS and CBF/SFCS ratios in the Pre-/PostCG in IBD were primarily influenced by significant increased CBF and/or decreased FCS (Additional file 1: Fig. S1). IBD patients also showed increased CBF/SFCS ratio in the MCC, whereas the differences in CBF and SFCS were not significant in the MCC. This finding suggests that measuring the CBF/FCS ratio may improve the ability to detect significant intergroup differences and identify regional alterations earlier than with a single CBF or FCS analysis. As the key hub of the sensorimotor network, the Pre-/PostCG is mainly responsible for integrating various somatosensory stimuli information to achieve correct recognition of objects and external stimuli [62]. Additionally, it was proved that Pre-/PostCG plays a key role in understanding and recognizing other’s emotional states utilizing social cues [62, 63]. Recent studies have demonstrated the altered brain activity in the Pre-/PostCG may represent the dysregulated gastrointestinal symptoms and more severe depressive symptoms in IBD patients [64, 65]. The MCC participates in the processing of nociceptive stimuli [66], and the dysfunction of MCC in IBD may indicate damages to the endogenous pain suppressing system [11]. We suppose that increased NVC in the Pre-/PostCG and MCC may disrupt the balance between vascular response and neural activity, and the increased NVC could be involved in the integration of visceral stimuli and emotional information in IBD.

Decreased CBF/FCS ratios in the dlPFC and mPFC were also detected in IBD. The changes in the two regions were primarily driven by the significantly increased FCS and slightly decreased CBF (Additional file 1: Fig. S1). Combining these indicators may provide more exact information to understand the neuropathological mechanisms of IBD. The dlPFC and mPFC are implicated in higher-order cognitive, affective and sensory processing [43, 67]. The dlPFC is crucial for the top-down pain modulation and nociceptive processing, potentially resulting in enhanced negative effect [68]. The activation of the left dlPFC in HCs was revealed in responses to aversive rectal distension [69]. The mPFC is also known to be involved in regulating chronic pain [70]. Therefore, the decoupling of visceral perception and nociceptive integration might suggest that a synergistic effect in dlPFC and mPFC may be disrupted in IBD.

By combining LASSO regression with MVPA, the results from SVM (AUC = 0.917) and RF (AUC = 0.915) uncovered that the multi-dimensional neuroimaging features (CBF, FCS and CBF/FCS) had robust discriminative ability in distinguishing IBD patients from HCs, indicating these alterations may reveal potential marker candidates for IBD patients. It is noteworthy that the CBF in the mPFC, Pre-/PostCG and TP, SFCS in the STC, MTC and FG, as well as CBF/SFCS in the mPFC and MCC not only demonstrated statistically significant importance but also exhibited substantial contributions to the classification prediction. Previous neuroimaging studies have revealed that functional alterations in these brain regions are closely related to IBD patients [11, 55, 56, 64, 65]. The mPFC and temporal lobe are the key brain regions for emotional regulation and cognitive integration in IBD patients [43, 55, 56]. The MCC plays a crucial role in converting emotional signals into motivated behavior [66, 71]. Furthermore, increased CBF/SFCS alterations in the MCC marginally correlated with both anxiety symptom and IBDQ scores. This finding supports the notion that MCC might serve as a potential imaging biomarker for intervention trials. Therefore, by integrating ASL and rs-fMRI data into the classification model, this study further verified and expanded their crucial roles in the mechanism of IBD, and provided new insights for the clinical individualized treatment of IBD patients.

The effects of depressive symptoms on FCS or regional NVC in the OFC, FG, SMA, CUN, ITC, PostCG and caudate were detected in IBD subgroups. Our aforementioned findings support that infammation-mediated IBD is associated with the pathogenesis of psychiatric disorders, especially depressive symptoms [35, 72, 73]. The depressive symptoms are usually associated with poor sleep [74]. We also found the poor sleep in IBD patients than HCs in this study. The declined sleep quality was associated with abnormal functional communication of widespread brain regions, and further impact cognitive, emotional regulation and sensory functions [75–77]. Besides, the distinct NVC in the caudate and FG was found in IBD subgroups. Previous studies have suggested the interactions between depressive symptoms, sleep, inflammation, and the immune system [73, 74, 78]. Therefore, we speculated that imbalance in psychological state and insufficient sleep might contribute to the decline in self-evaluation of IBD patients, and might further affect the gastrointestinal inflammatory response through brain-gut axis.

Our findings demonstrated the associations between the abnormalities of CBF or FCS in IBD patients and dopamine (D2), glutamate (NMDA), serotonin (5HT1a, 5HT1b), acetylcholine (VAchT) and noradrenaline (NAT) systems. Neurotransmitters play the crucial roles in maintaining homeostasis in the human body. It was demonstrated that neurotransmitters could be implicated in the gastrointestinal and central nervous system physiology [79]. Accumulating studies have indicated the changes in the levels of neurotransmitters in IBD, such as dopamine, serotonin, acetylcholine and glutamate [80–84]. Previous animal models demonstrated that treatment with D2 receptor agonists decreased the severity of IBD [82]. Located in the peripheral nervous system and central terminals of primary afferent neurons, NMDA receptors were related to in chronic visceral pain and hypersensitivity that is present in the setting of colonic inflammation [85]. As an NMDA antagonist, memantine exerted an anti-inflammatory and protective effect on colon and attenuated all features of experimental colitis [86]. Previous studies confirmed the inflammatory state in IBD was associated with changed expression of VAChT [87, 88]. Moreover, serotonin and noradrenaline strongly influence mental behavior patterns [89]. The serotonin system is closely linked to emotional regulation [90], and selective serotonin reuptake inhibitors (SSRIs) are regarded as the preferred pharmacological treatment for depressive symptoms [91]. Meanwhile, the changed neurotransmitter levels on a local level were also associated with depressive symptoms in individuals with IBD [33, 36]. Consistent with these perspectives, in IBD subgroups, we found significant changes in the spatial correspondence between imaging abnormalities and the distribution of dopamine, glutamate, serotonin, acetylcholine and GABAa. Moreover, the animal study demonstrated that electroacupuncture therapy enhanced the release of GABA levels and reduced the release of glutamate levels in mice with IBD [92]. Therefore, elucidating the functioning of these abnormal neurotransmitters in IBD provided a more comprehensive understanding and novel targeted therapeutic strategies in the future.

There were several limitations that should be acknowledged in this study. First, the sample of participants was relatively small, which may limit the generalizability of the findings. Second, we are not able to measure NVC directly and had to rely on proxy measures to characterize NVC and thus we cannot exactly identify the specific pathophysiological mechanisms that contribute to changes of NVC in IBD. We expect that more direct NVC indicators could provide further pathophysiological information for IBD in the future. Third, future studies should consider incorporating multimodal neuroimaging data to improve the classification of IBD from HCs. Fourth, previous studies have demonstrated that the effects of motion on functional connectivity may not be completely removed by regression of motion parameters [93, 94], future studies would consider using the censoring and independent component analysis-based automatic removal of motion artifacts methods to minimize the impact of head motion. Fifth, the neurotransmitter maps derived from PET and SPECT data were collected from independent cohorts, not from the individuals with MRI data. Thus, to fully understand how regional variations in receptor densities affect brain function, a comprehensive laminar-resolved receptor atlas implemented in JuSpace is required in future studies [95]. Group-averaged maps of different neurotransmitters were used for correlation analysis. Therefore, the interpretation of these correlations between different PET/SPECT images and specific receptors must be cautious.

Conclusions

In conclusion, we provided evidence for NVC abnormalities with the combination of CBF and FCS in IBD patients. We explored the effects of depressive symptoms on neuroimaging findings in IBD subgroups. Meanwhile, the associations between altered spatial patterns of MRI features (CBF, FCS and CBF/FCS) and the corresponding distribution of neurotransmitter profiles were further evaluated. IBD patients exhibited increased global NVC than HCs. IBD patients also showed abnormal CBF, FCS and regional NVC changes mainly in the DMN, insula, OFC, MCC and Pre-/PostCG, and the alterations were correlated with the integration of emotion and visceral nociceptive perception. Our findings may signify the disrupted balance between blood supply and neural activity in IBD patients. These abnormal neuroimaging features exhibited superior discriminate ability, proposing potential biomarkers for distinguishing IBD patients from HCs. Furthermore, the underlying neuromechanism of these brain functional abnormalities were mainly associated with the dopamine, glutamate, acetylcholine and serotonin neurotransmitter profiles, and provided a new perspective for understanding the neuropathological underpinning of IBD.

Abbreviations

ACC

Anterior cingulate cortex

ANG

Angular gyrus

AUC

Areas under the curve

BMI

Body mass index

CBF

Cerebral blood flow

CD

Crohn’s disease

dlPFC

Dorsolateral prefrontal cortex

DMN

Default mode network

FCS

Functional connectivity strength

GRF

Gaussian random field

HCs

Healthy controls

IBDQ

Inflammatory bowel disease questionnaire

ITC

Inferior temporal cortex

LASSO

Least Absolute Shrinkage and Selection Operator

MCC

Middle cingulate cortex

MFC

Middle frontal cortex

MFI

Multidimensional fatigue inventory

mPFC

Medial prefrontal cortex

MRI

Magnetic resonance imaging

MTC

Middle temporal cortex

MVPA

Multivariate pattern analysis

NVC

Neurovascular coupling

OFC

Orbitofrontal cortex

PCUN

Precuneus

PET

Positron emission tomography

PSQI

Pittsburgh sleep quality index

Pre-/PostCG

Pre-/Postcentral gyrus

RF

Random forest

ROC

Receiver operating characteristic

SAS

Self-rating anxiety scale

SDS

Self-rating depression scale

SMA

Supplementary motor area

SPECT

Single photon computed emission tomography

SPC

Superior parietal cortex

STC

Superior temporal cortex

SVM

Support vector machine

TP

Temporal pole

UC

Ulcerative colitis

Authors’ contributions

C.L. contributed to the inception, conception, design and publication of the study, data collection and analysis, drafting of the manuscript, and critical revisions of the manuscript. M.L. contributed to the data collection and critical revisions of the manuscript. Y.L. and Y.L. contributed to the data analysis. M.M. and L.X. contributed to the data collection. P.L. contributed to the inception, conception, design and publication of the study, data collection and analysis, drafting of the manuscript, funding acquisition, project administration, and critical revisions of the manuscript. H.L. designed the research and supervised the work. All authors read and approved the final manuscript.

Funding

This study was financially supported by the National Natural Science Foundation of China under (grant No. 82270696; grant No. 82441050); Xidian University Specially Funded Project for Interdisciplinary Exploration (grant No. TZJHF202521); Key Basic Research Program of Guizhou Province (grant N0. Qiankehejichu-ZK[2022]zhongdian 051); Innovation Talent team of Science and Technology in Zunyi City (grant No. Zunshikerencai[2024]5); Talent Program for Future Famous Clinical Doctors of Zunyi Medical University (grant No. rc220211205).

Data availability

No datasets were generated or analysed during the current study.

Declarations

Ethics approval and consent to participant

All research procedures were conducted in accordance with the Declaration of Helsinki. Before the experiment, written informed consent was obtained from each participant for this study. This study was approved by the Medicine Ethics Committee of Zunyi Medical University (KLL-2024-100).

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.