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Background: The association of impaired dopaminergic neurotransmission with the development and maintenance of alcohol use disorder is well known. More specifically, reduced dopamine D2/3 receptors in the striatum of subjects with alcohol dependence (AD) compared to healthy controls have been found in previous studies. Furthermore, alterations of gamma‐aminobutyric acid (GABA) and glutamate (Glu) levels in the anterior cingulate cortex (ACC) of AD subjects have been documented in several studies. However, the interaction between cortical Glu levels and striatal dopamine D2/3 receptors has not been investigated in AD thus far. Methods: This study investigated dopamine D2/3 receptor availability via 18F‐fallypride positron emission tomography (PET) and GABA as well as Glu levels via magnetic resonance spectroscopy (MRS) in 19 detoxified AD subjects, 18 healthy controls (low risk, LR) controls and 19 individuals at high risk (HR) for developing AD, carefully matched for sex, age and smoking status. Results: We found a significant negative correlation between GABA levels in the ACC and dopamine D2/3 receptor availability in the associative striatum of LR but not in AD or HR individuals. Contrary to our expectations, we did not observe a correlation between Glu concentrations in the ACC and striatal D2/3 receptor availability. Conclusions: The results may reflect potential regulatory cortical mechanisms on mesolimbic dopamine receptors and their disruption in AD and individuals at high risk, mirroring complex neurotransmitter interactions associated with the pathogenesis of addiction. This is the first study combining 18F‐fallypride PET and MRS in AD subjects and individuals at high risk. [ABSTRACT FROM AUTHOR]

Background: Blood‐based biomarkers (BBM) have shown promising potential in diagnosis and prognosis of patients affected by Alzheimer's disease (AD) pathology. This observational study analyzed the cross‐sectional relation between BBMs and disease relevant outcomes (e.g., cognition, imaging modalities). Method: The study sample comprised individuals with subjective cognitive decline (N = 35), mild cognitive impairment (N = 30), dementia due to suspected AD (N = 27) and healthy controls (N = 35). Data for the following measures were assessed: 1) AD‐related BBMs measured in plasma on Simoa: amyloid beta ratio 42/40 (Ab42/40), tau phosphorylated at threonine‐181 (p‐Tau 181), glial fibrilic acid protein (GFAP), and neurofilament light chain (NfL), 2) several cognitive parameters, 3) structural volumes, functional connectivity and brain metabolite concentrations measured by 7T magnetic resonance imaging (MRI) and spectroscopy (MRS), and 4) concentrations of general blood count. Linear mixed models were used to assess associations between the AD‐related BBMs (1) and the other measures (2 to 4). Result: While none of the associations between Ab42/40 and the AD‐related outcome measures reached significance (p > 0.05), higher concentrations of p‐Tau 181, GFAP and NfL were associated with lower values for MMSE, memory and executive function and parietal cortical thickness, as well as higher concentrations of MRS Myo‐inositol and blood creatinine (figure 1). Additionally, GFAP and NfL were associated with lower MRS N‐Acetylaspartic acid (NAA), and GFAP was associated with smaller hippocampus volume. Beta‐coefficients and p‐values for all associations are provided in table 1. Conclusion: Unlike Ab42/40, abnormal concentrations of p‐Tau 181, GFAP and NfL showed strong and robust associations to other AD‐related outcome measures making them a better target for screening, diagnosis and possibly prognosis for individuals with AD. [ABSTRACT FROM AUTHOR]

Alcohol use disorder (AUD) is the most common substance use disorder worldwide. Although dopamine-related findings were often observed in AUD, associated neurobiological mechanisms are still poorly understood. Therefore, in the present study, we investigate D2/3 receptor availability in healthy participants, participants at high risk (HR) to develop addiction (not diagnosed with AUD), and AUD patients in a detoxified stage, applying 18 F-fallypride positron emission tomography (18 F-PET). Specifically, D2/3 receptor availability was investigated in (1) 19 low-risk (LR) controls, (2) 19 HR participants, and (3) 20 AUD patients after alcohol detoxification. Quality and severity of addiction were assessed with clinical questionnaires and (neuro)psychological tests. PET data were corrected for age of participants and smoking status. In the dorsal striatum, we observed significant reductions of D2/3 receptor availability in AUD patients compared with LR participants. Further, receptor availability in HR participants was observed to be intermediate between LR and AUD groups (linearly decreasing). Still, in direct comparison, no group difference was observed between LR and HR groups or between HR and AUD groups. Further, the score of the Alcohol Dependence Scale (ADS) was inversely correlated with D2/3 receptor availability in the combined sample. Thus, in line with a dimensional approach, striatal D2/3 receptor availability showed a linear decrease from LR participants to HR participants to AUD patients, which was paralleled by clinical measures. Our study shows that a core neurobiological feature in AUD seems to be detectable in an early, subclinical state, allowing more individualized alcohol prevention programs in the future. [ABSTRACT FROM AUTHOR]

Background: Myo‐inositol (MI) is a presumed marker for glial activation which can be quantified by non‐invasive Magnetic Resonance Spectroscopy (MRS) and is suspected to be elevated in early Alzheimer's disease (AD). In the framework of the NeuroMET2 project, we investigated the relationship between MI and other AD‐relevant measures. Methods: Absolute concentrations of MI were measured by 7 tesla MRS in the posterior cingulate cortex (PCC)/precuneus of 26 cognitively healthy individuals (HC), 23 patients with subjective cognitive decline (SCD), 23 with mild cognitive impairment (MCI) and 24 with dementia due to suspected AD. Using linear models, MI's association with memory ability (NeuroMET Memory Metric), volumes of the hippocampus and PCC/precuneus, and seed‐based functional connectivity were investigated. Interaction terms involving the apolipoprotein E (APOE) ε4 allele were analyzed additionally. All models were adjusted to age and education and weighted based on Cramér‐Lao lower bounds. Results: Absolute MI concentrations were substantially elevated in AD patients (adjusted mean [95% CI]=8.5 mmol/l [7.8; 9.3]). However, there were no relevant differences between SCD (6.7 mmol/l [6.0; 7.3]) or MCI (7.5 mmol/l [6.8; 8.2]) and participants of the HC group (7.2 mmol/l [6.6, 7.9]). Across the whole cohort, higher levels of MI were associated with lower memory ability (ß [95% CI]=‐0.31 [‐0.44; ‐0.17], std. ß=‐0.40, p<0.001), smaller hippocampus volume (ß=‐59.89 [‐131.40; 11.62], std. ß=‐0.16, p=0.100) and lower seed‐based functional connectivity (ß=‐3948.41 [‐6480.69; ‐1416.13], std. ß=‐0.34, p=0.003). There was no relevant effect between MI and PCC/precuneus volume (ß=83.27 [‐117.89; 284.43], std. ß=0.08, p=0.413). Finally, there was no substantial mediation effect of APOE ε4 carriership on the association between MI and neither memory ability (ß=0.09 [‐0.18; 0.36], std. ß=0.37, p=0.519), hippocampus volume (ß=‐55.60 [‐223.48; 112.29], std. ß=‐0.45, p=0.511), PCC/precuneus volume (ß=‐110.68 [‐546.22; 324.86], std. ß=‐0.32, p=0.614) nor seed‐based functional connectivity (ß=2009.46 [‐4207.40; 8226.32], std. ß=0.55, p=0.520). Conclusions: Across a cohort with participants ranging from healthy to AD, we showed that glial activation, measured by MI concentration, was associated with key AD‐related processes. The potential of MI as a non‐invasive biomarker for increasing memory impairment in pre‐dementia stages remains to be explored in longitudinal studies. [ABSTRACT FROM AUTHOR]

The two-fold benefit of 1H magnetic resonance spectroscopy (MRS) at high B0 fields - enhanced sensitivity and increased spectral dispersion - has been used previously to study dynamic changes in metabolite concentrations in the human brain in response to visual stimulation. In these studies, a strong visual on/off stimulus was combined with MRS data acquisition in a voxel location in the occipital cortex determined by an initial functional magnetic resonance imaging experiment. However, 1) to exclude the possibility of systemic effects (heartbeat, blood flow, etc.), which tend to be different for on/off conditions, a modified stimulation condition not affecting the target voxel needs to be employed, and 2) to assess important neurotransmitters of low concentration, in particular γ-aminobutyric acid (GABA), it may be advantageous to analyze steady-state, rather than dynamic, conditions. Thus, the aim of this study was to use short-TE 1H MRS methodology at 7 T to detect differences in steady-state metabolite levels in response to a varying stimulation paradigm in the human visual cortex. The two different stimulation conditions were termed voxel and control activation. Localized MR spectra were acquired using the SPECIAL (spin-echo full-intensity acquired localized) sequence. Data were analyzed using LCModel. Fifteen individual metabolites were reliably quantified. On comparison of steady-state concentrations for voxel versus control activation, a decrease in GABA of 0.05 mmol/L (5%) and an increase in lactate of 0.04 mmol/L (7%) were found to be the only significant effects. The observed reduction in GABA can be interpreted as reduced neuronal inhibition during voxel activation, whereas the increase in lactate hints at an intensification of anaerobic glycolysis. Differences from previous studies, notably the absence of any changes in glutamate, are attributed to the modified experimental conditions. This study demonstrates that the use of advanced 1H MRS methodology at 7 T allows the detection of subtle changes in metabolite concentrations involved in neuronal activation and inhibition. [ABSTRACT FROM AUTHOR]