Measurements Of GABA In Upper Brainstem Of Parkinson’s Disease Using MEGA-PRESS With Small Voxel

Parkinson’s disease(also called PD)is the common gradual-happening neurodegenerative conditions of the nervous system(especially in brain)in older adults,that mainly affects the motor system.Distinctive features described as both motor clinical symptoms(difficulty with walking,rest tremor,rigidity,bradykinesia)and non-motor clinical signs(autonomic dysfunction,cognitive changes,sensory symptoms,and sleep disturbances).PD’s pathological sign was famous for the derease and degeneration in neurons in upper brainstem(substantia nigra),in the result of the injury of the dopaminergic projections from the substantia nigra pars compacta to the basal ganglia(caudate nucleus and putamen of the striatum).The main neurons are dopaminergic ones.The pathological hallmarks of PD are intraneuronal Lewy bodies and Lewy neurites.Gamma-amino butyric acid(GABA)is the major inhibitory neurotransmitter in the developmentally mature mammalian central nervous system.Many circuits involving dopaminergic projections from the midbrain also include GABAergic inhibitory projections.Abnormal GABA level in the basal ganglia and other areas of PD patients has been confirmed in previous studies.It is reported that the brainstem lesions of PD patients are earlier than the pathological changes of the basal ganglia.However,no 3T-MRS studies are exploring the GABA level in the upper brainstem of PD patients.Magnetic resonance spectroscopy is currently the best and most widely used non-invasive examination method for neurological metabolites.Mescher Garwood Point Resolved Spectroscopy(MEGA-PRESS)MRS uses frequency-selective GABA-targeted pulses to reduce overlap in the spectrum.However,few studies have investigated GABA+levels in the brainstem of PD patients,likely due to its small size and challenging location.Therefore,we used the edited MRS technique,MEGA-PRESS,to explore GABA levels in the upper brainstem in PD,by comparing to those of age-and gender-matched healthy controls.This research contains three parts:Part 1 Feasibility of Measuring GABA Levels in the Upper Brainstem in Healthy Volunteers Using Edited MRSPurpose:Gamma-amino butyric acid(GABA)is the major inhibitory neurotransmitter in the developmentally mature mammalian central nervous system.GABA acts at inhibitory synapses in the brain by binding to specific transmembrane receptors in both pre-and postsynaptic neuronal processes.Magnetic resonance spectroscopy is currently the best and most widely used non-invasive examination method for neurological metabolites.To date,MEGA-PRESS has been measured both in the healthy brain and in various neurodegenerative disorders,such as Alzheimer’s disease(AD),multiple sclerosis(MS),as well as psychiatric diseases.The brainstem is the recipient of projections from the cortex,limbic structures,and striatum,and exerts essential modulating influences on those descending and ascending projections.The objectives of this preliminary study were to assess the feasibility of small-voxel MEGA-PRESS in detecting gamma-aminobutyric acid(GABA)levels of the upper brainstem in healthy volunteers.Materials required and Methods required:Forty-two physically fit cases were accepted here(their age is betwixt 20 years old,76 years old),and underwent a 3.0T MRI scan using an eight-channel phased-array head coil.A whole-brain structural 3-dimensional MPRAGE(magnetization-prepared rapid-acquisition gradient echo)scan was acquired with 1×1×1 mm3 isotropic resolution.The MEGA-PRESS sequence was used to edit GABA signal from a 10×25×30 mm3 voxel in the upper brainstem.We’ve got some GABA signals,with contributions of macromolecules(MM)signals,homocamosine signals,and it is therefore referred to as GABA+.All the data were processed using Gannet.The primary data quality metric generated by Matlab is fitting error(FitErr,%),calculated as the ratio of the standard deviation of the fitting residual to the GABA+signal amplitude.A data quality cut-off of 15%has been applied previously for brain applications with good SNR.In this study,we used a cut-off of 20%to reject spectra of poor quality,using a less stringent criterion to reflect the lower SNR of the smaller-ROI(region of interest)brainstem acquisition.Results:Thirty-four cases were successful in measuring GABA in the upper brainstem and 8 cases failed(based on poor modeling of spectra).The GABA+levels were 2.66±0.75 i.u.in the upper brainstem of healthy volunteers,ranging from 1.50 to 4.40 i.u.The normalized fitting residual(FitErr in Gannet)was 12.1±2.8%,ranging from 7.4%to 19.1%;it was below 15.5%in 30 cases(71%).No significant correlations(p=0.215>0.05)with age were observed.There are no significant gender-related differences in the GABA+levels in upper midbrain in the healthy volunteers(p=0.735>0.05).Conclusions:It is possible to measure GABA levels in the upper brainstem using MEGA-PRESS with a relatively small ROI,with a moderate between-subject variance of under 30%.Part 2 Upper brainstem GABA levels in Parkinson’s diseaseObjective:PD’s predominent changes in pathology is characteriazed by the reduction and degeration of special neurons in brainstem(substantia nigra).The dopaminergic pathology of Parkinson’s disease impacts circuits involving GABAergic neurons,especially in the brainstem,where the disease manifests early.The γ-aminobutyrie acid is the leading neurotransmitter with the role of inhibiting neurons’ activity,which is difficult to detect due to its low concentration and the presence of overlapping signals from other compounds such as creatine and N-acetyl aspartate(NAA).Mescher-Garwood point-resolved spectroscopy(with abbreciation of MEGA-PRESS)is able to estimate GABA+content reliably utilizing an editing technique based on refocusing J-couplings.It is reported that the brainstem lesions of PD patients are earlier than the pathological changes of the basal ganglia.The plan of here is testing a hypothesis that levels of gamma-aminobutyric acid(GABA)in the upper brainstem are reduced in patients who are diagnosed as PD compared to healthy controls,taking advantage of edited magnetic resonance spectroscopy(GABA+-edited MRS).Materials and Methods:To examine matabolites levels(GABA+)in two groups(PD and HC).In these two group,the same number of cases,similar age distribution and similar sex ratio were required.GABA+-edited MRS was performed in 7.5-ml voxels in the upper brainstem.The Gannet software was useful for processing the spectra.The Unified Parkinson’s Disease Rating Scale(with abbreciation of UPDRS)(Ⅲ)and Hoehn and Yahr(with abbreciation of H-Y)Stage were applied to evaluate the conditon stage in PD patients.The Non-Motor Symptom Questionnaire(NMSQ)was administered to the patient group to evaluate non-motor symptoms.The concentrations of metabolites such as GABA+in PD patients and healthy controls were compared using the two-tailed independent samples t-test,and differences were considered significant for p<0.05.A multiple regression model(Enter method)was used to test for the relationship between GABA+and the clinical assessment of non-motor symptoms.The disease duration,PD subtype,and levodopa equivalent dose were also included as factors in the multivariate regression.Results:Significantly smaller GABA+concerntrations were shown(p<0.05)in the upper brainstem of the patients with PD(4.57±0.94 i.u.)than the HCs(5.89±1.16 i.u.).No correlation between metabolite levels and NMSQ scores(GABA+:adjusted R2=0.150,p=0.234;Glx:adjusted R2=0.030,p=0.407),or UPDRS III scores(GABA+:adjusted R2=0.030,p=0.407;Glx:adjusted R2<0,p=0.487).Conclusion:The smaller GABA+levels in upper brainstem in PD imply that a GABAergic deficit in brainstem may contribute to the pathology in these disorders.Part 3 Single-dose L-dopa increases upper brainstem GABA in Parkinson’s disease:A preliminary studyPurpose:Parkinson’s disease(one of the neurodegenerative diseases),is characterized by the dysfunction between dopaminergic and GABAergic neuronal activities.Dopamine(DA)replacement by its precursor L-dopa remains the primary treatment for PD.In this preliminary study,we test the hypotheses that GABA+levels would be lower in PD patients than controls,and normalized by L-dopa.Methods:Eleven PD patients and eleven age-and gender-matched healthy controls underwent a 1H-MRS scan of the upper brainstem using a J-difference-edited sequence to resolve signals of GABA.PD patients did not take all dopaminergic medicines for at least twelve hours prior to the first scan,and were scanned again after resuming L-dopa(pre-and post-L-dopa).Disease severity was scored in accordance with the Unified Parkinson’s Disease Rating Scale(UPDRS)subitem III and the Hoehn and Yahr(H-Y)stage.UPDRS subitem III was completed a second time after treatment to evaluate the improvement of motor symptoms.The structure of this study includes both within-subject(PD-pre vs.PD-post L-dopa)and between-subject comparisons(HC vs.PD-pre or PD-post),making ANOVA analysis inappropriate.Therefore,we used linear mixed-effects models with Holm-Bonferroni correction applied to pairwise comparisons.Age,duration of disease,and UPDRS scores were added as covariates to the primary analysis testing for GABA+differences.Pearson correlation coefficients were applied to study correlations between the clinical data(%LR,%Levodopa Responsiveness)and the GABA+levels(pre-and post-L-dopa,Respectively.Statistical analyses were conducted using R(v4.0.3)and SPSS(v22.0)(Chicago,IL).Results:Significant increased GABA+levels were observed in the upper brainstem of PD patients post-L-dopa compared with pre-L-dopa(p<0.001).Patients’ GABA+levels before administration of L-dopa were significantly lower than HCs(p=0.001).Increased GABA+level by administration of L-dopa in PD patients(post-L-dopa)was lower compared with HCs,but not significantly(p=0.52).L-dopa usage yielded a significant improving in motor symptoms,based on%Levodopa Responsiveness(%LR)(cut-off was set at 30%).No significant correlations were detected between%LR and GABA+level change(p=0.316)or GABA+levels either pre-L-dopa(p=0.678)or post-L-dopa(p=0.640).Conclusion:Increased GABA+levels were present in the upper brainstem with PD patients post-L-dopa,suggesting dopaminergic therapy capable of improving dopamine may improve the GABA+levels in the upper brainstem,thereby achieving the effect of modulating the GABAergic system in the treatment of PD.