Preserved cholinergic forebrain integrity reduces structural connectome vulnerability in mild cognitive impairment

Effects of Cigarette Smoking on Resting-State Functional Connectivity of the Nucleus Basalis of Meynert in Mild Cognitive Impairment

Background: Mild cognitive impairment (MCI) is the prodromal phase of Alzheimer’s disease (AD) and has a high risk of progression to AD. Cigarette smoking is one of the important modifiable risk factors in AD progression. Cholinergic dysfunction, especially the nucleus basalis of Meynert (NBM), is the converging target connecting smoking and AD. However, how cigarette smoking affects NBM connectivity in MCI remains unclear.

Objective: This study aimed to evaluate the interaction effects of condition (non-smoking vs. smoking) and diagnosis [cognitively normal (CN) vs. MCI] based on the resting-state functional connectivity (rsFC) of the NBM.

Methods: After propensity score matching, we included 86 non-smoking CN, 44 smoking CN, 62 non-smoking MCI, and 32 smoking MCI. All subjects underwent structural and functional magnetic resonance imaging scans and neuropsychological tests. The seed-based rsFC of the NBM with the whole-brain voxel was calculated. Furthermore, the mixed effect analysis was performed to explore the interaction effects between condition and diagnosis on rsFC of the NBM.

Results: The interaction effects of condition × diagnosis on rsFC of the NBM were observed in the bilateral prefrontal cortex (PFC), bilateral supplementary motor area (SMA), and right precuneus/middle occipital gyrus (MOG). Specifically, the smoking CN showed decreased rsFC between left NBM and PFC and increased rsFC between left NBM and SMA compared with non-smoking CN and smoking MCI. The smoking MCI showed reduced rsFC between right NBM and precuneus/MOG compared with non-smoking MCI. Additionally, rsFC between the NBM and SMA showed a significant negative correlation with Wechsler Memory Scale-Logical Memory (WMS-LM) immediate recall in smoking CN (r = −0.321, p = 0.041).

Conclusion: Our findings indicate that chronic nicotine exposure through smoking may lead to functional connectivity disruption between the NBM and precuneus in MCI patients. The distinct alteration patterns on NBM connectivity in CN smokers and MCI smokers suggest that cigarette smoking has different influences on normal and impaired cognition.

Clinical study of central cholinergic pathway damage in two mild cognitive impairment patients

OBJECTIVES

To explore the role of the central cholinergic system in amnestic mild cognitive impairment (aMCI) and mild vascular cognitive impairment (vMCI).

METHODS

Twenty-five aMCI patients and 25 vMCI patients were enrolled in this study, and 25 healthy people were chosen as a control group. All participants performed a set of cognitive function scales and were subjected to a brain MRI. We analyzed differences in neuropsychological damage between groups, as well as the degree of brain atrophy and changes in the microstructure of central cholinergic pathways (CCP) in relation to effects on neuropsychological scores.

RESULTS

(1) Regarding neuropsychological characteristics of the three groups, scores on the MoCA scale, immediate memory, delayed recall, cued recall, long time prolonged recognition, and CDR-SB of the control group were significantly better than those of the aMCI and vMCI groups. Scores on immediate memory, delayed memory, cued recall, long time delayed recognition, and Forward of Digital Span Test (FDST) in the aMCI group were lower than those in the vMCI group. Compared with the aMCI group, the vMCI group was significantly delayed in Trail Making Test (TMA)-A, TMT-B, and TMT B-A. There were no significant differences in HAMA, HAMD, MMSE, MoCA, the Boston Naming Test (BNT), language fluency or visual scale of posterior atrophy (Koedam score) between the vMCI and aMCI groups. (2) As for microstructure changes in the central cholinergic pathway, vMCI group had a decreased FA value in the cingulum (Cing) of the medial pathway, but an increased MD value in the external capsule (Excap) of the lateral pathway when compared to other two groups. Furthermore, the CingMD value of the vMCI group was higher than that of the control group, but the difference was not obvious when compared to the aMCI group. (3) Last, we researched microstructural changes to CCP, degree of brain atrophy, and neuropsychological scores by using partial correlation analysis for all participants. CingFA was negatively correlated with TMT-B, B-A, and FDST. CingMD was negatively correlated with FDST. ExcapFA was positively correlated with MMSE and Backward of BDST, while ExcapMD was negatively correlated with MMSE and MoCA. Claustrum (Claus)FA was positively related to MoCA and FDST, but was negatively related to TMT-A. ClausMD was negatively correlated with MoCA and language fluency. Koedam score was positively correlated with CDR-SB, ExcapMD, and ClausMD, but negatively correlated with MMSE score and inverse BDST.

CONCLUSION

The central cholinergic system is involved in the cognitive impairment of both aMCI and vMCI, and their mechanisms may be distinct. aMCI patients may present with primary CCP impairment while vMCI patients probably exhibit impairment secondary to vasogenic damage to the cholinergic system projection network. The lateral cholinergic pathway was more severely impaired than the medial pathway in vMCI patients, in addition to being associated with decreased executive and general cognitive functions. The damage to CCP was related to the degree of brain atrophy, and both may be involved in the development and progression of cognitive dysfunction.