Early effects of a high-caloric diet and physical exercise on brain volumetry and behavior: a combined MRI and histology study in mice

Excessive intake of high-caloric diets as well as subsequent development of obesity and diabetes mellitus may exert a wide range of unfavorable effects on the central nervous system (CNS) in the long-term. The potentially harmful effects of such diets were suggested to be mitigated by physical exercise. Here, we conducted a study investigating early effects of a cafeteria-diet on gray and white brain matter volume by means of voxel-based morphometry (VBM) and region-of-interest (ROI) analysis. Half of the mice performed voluntary wheel running to study if regular physical exercise prevents unfavorable effects of a cafeteria-diet. In addition, histological analyses for myelination and neurogenesis were performed. As expected, wheel running resulted in a significant increase of gray matter volume in the CA1–3 areas, the dentate gyrus and stratum granulosum of the hippocampus in the VBM analysis, while a positive effect of the cafeteria-diet was shown for the whole hippocampal CA1–3 area only in the ROI analysis, indicating a regional volume effect. It was earlier found that hippocampal neurogenesis may be related to volume increases after exercise. Interestingly, while running resulted in a significant increase in neurogenesis assessed by doublecortin (DCX)-labeling, this was not true for cafeteria diet. This indicates different underlying mechanisms for gray matter increase. Moreover, animals receiving cafeteria diet only showed mild deficits in long-term memory assessed by the puzzle-box paradigm, while executive functioning and short term memory were not affected. Our data therefore highlight that high caloric diet impacts on the brain and behavior. Physical exercise seems not to interact with these mechanisms.     

pH as a biomarker of neurodegeneration in Huntington's disease: a translational rodent-human MRS study

Early diagnosis and follow-up of neurodegenerative diseases are often hampered by the lack of reliable biomarkers. Neuroimaging techniques like magnetic resonance spectroscopy (MRS) offer promising tools to detect biochemical alterations at early stages of degeneration. Intracellular pH, which can be measured noninvasively by (31)P-MRS, has shown variations in several brain diseases. Our purpose has been to evaluate the potential of MRS-measured pH as a relevant biomarker of early degeneration in Huntington's disease (HD). We used a translational approach starting with a preclinical validation of our hypothesis before adapting the method to HD patients. (31)P-MRS-derived cerebral pH was first measured in rodents during chronic intoxication with 3-nitropropionic acid (3NP). A significant pH increase was observed early into the intoxication protocol (pH=7.17±0.02 after 3 days) as compared with preintoxication (pH=7.08±0.03). Furthermore, pH changes correlated with the 3NP-induced inhibition of succinate dehydrogenase and preceded striatum lesions. Using a similar MRS approach implemented on a clinical MRI, we then showed that cerebral pH was significantly higher in HD patients (n=7) than in healthy controls (n=6) (7.05±0.03 versus 7.02±0.01, respectively, P=0.026). Altogether, both preclinical and human data strongly argue in favor of MRS-measured pH being a promising biomarker for diagnosis and follow-up of HD.     

Rapid adaptation of rat brain and liver metabolism to a ketogenic diet: an integrated study using 1H- and 13C-NMR spectroscopy

The ketogenic diet (KD) is an effective alternative treatment for refractory epilepsy in children, but the mechanisms by which it reduces seizures are poorly understood. To investigate how the KD modifies brain metabolism, we infused control (CT) and 7-day KD rats with either [1-¹³C]glucose (Glc) or [2,4-¹³C₂]β-hydroxybutyrate (β-HB). Specific enrichments of amino acids (AAs) measured by ¹H- and ¹³C-NMR in total brain perchloric acid extracts were similar between CT and KD rats after [1-¹³C]Glc infusion whereas they were higher in KD rats after [2,4-¹³C₂]β-HB infusion. This suggests better metabolic efficiency of ketone body utilization on the KD. The relative rapid metabolic adaptation to the KD included (1) 11%-higher brain γ-amino butyric acid (GABA)/glutamate (Glu) ratio versus CT, (2) liver accumulation of the ketogenic branched-chain AAs (BCAAs) leucine (Leu) and isoleucine (ILeu), which were never detected in CT, and (3) higher brain Leu and ILeu contents. Since Glu and GABA are excitatory and inhibitory neurotransmitters, respectively, higher brain GABA/Glu ratio could contribute to the mechanism by which the KD reduces seizures in epilepsy. Increased BCAA on the KD may also contribute to better seizure control.     

Hippocampal glutamate-glutamine (Glx) in adults with Down syndrome: a preliminary study using in vivo proton magnetic resonance spectroscopy (1H MRS)

Background

Down syndrome (DS), or trisomy 21, is one of the most common autosomal mutations. People with DS have intellectual disability (ID) and are at significantly increased risk of developing Alzheimer’s disease (AD). The biological associates of both ID and AD in DS are poorly understood, but glutamate has been proposed to play a key role. In non-DS populations, glutamate is essential to learning and memory and glutamate-mediated excitotoxicity has been implicated in AD. However, the concentration of hippocampal glutamate in DS individuals with and without dementia has not previously been directly investigated. Proton magnetic resonance spectroscopy (¹H MRS) can be used to measure in vivo the concentrations of glutamate-glutamine (Glx). The objective of the current study was to examine the hippocampal Glx concentration in non-demented DS (DS-) and demented DS (DS+) individuals.

Methods

We examined 46 adults with DS (35 without dementia and 11 with dementia) and 39 healthy controls (HC) using ¹H MRS and measured their hippocampal Glx concentrations.

Results

There was no significant difference in the hippocampal Glx concentration between DS+ and DS-, or between either of the DS groups and the healthy controls. Also, within DS, there was no significant correlation between hippocampal Glx concentration and measures of overall cognitive ability. Last, a sample size calculation based on the effect sizes from this study showed that it would have required 6,257 participants to provide 80% power to detect a significant difference between the groups which would indicate that there is a very low likelihood of a type 2 error accounting for the findings in this study.

Conclusions

Individuals with DS do not have clinically detectable differences in hippocampal Glx concentration. Other pathophysiological processes likely account for ID and AD in people with DS.     

Evidence for a relationship between body mass and energy metabolism in the human brain

Cerebral energy metabolism has been suggested to have an important function in body weight regulation. We therefore examined whether there is a relationship between body mass and adenosine triphosphate (ATP) metabolism in the human brain. On the basis of our earlier findings indicating a neuroprotective preferential energy supply of the brain, as compared with peripheral muscle on experimentally induced hypoglycemia, we examined whether this physiological response is preserved also in low-weight and obese participants. We included 45 healthy male subjects with a body mass index (BMI) ranging from 17 to 44 kg/m². Each participant underwent a hypoglycemic glucose-clamp intervention, and the ATP metabolism, that is, the content of high-energy phosphates phosphocreatine (PCr) and ATP, was measured repeatedly by ³¹phosphor magnetic resonance spectroscopy (³¹P-MRS) in the cerebral cortex and skeletal muscle. Results show an inverse correlation between BMI and high-energy phosphate content in the brain (P<0.01), whereas there was no such relationship found between skeletal muscle and BMI. The hypoglycemic clamp intervention did not affect the ATP metabolism in both tissues. Our data show an inverse correlation between BMI and cerebral high-energy phosphate content in healthy humans, suggesting a close relationship between energetic supply of the brain and body weight regulation.     

Effects of kainate-induced seizures on cerebral metabolism: a combinedH and P NMR study in rat

The cerebral metabolic changes elicited by kainate-induced seizures in the rat were investigated by in vivo combined NMR spectroscopy of ³¹P and ¹H. Systemic injection of kainate induced no significant changes in cerebral ATP or PCr levels during up to 90 min of continuous, generalised seizures, and the cerebral³¹P spectra showed only a transient mild cerebral acidosis 30 min after kainate administration. In parallel with the changes in intracellular cerebral pH, the ¹H spectra showed a significant increase in lactate, which remained elevated throughout the seizures. These findings indicate that oxidative metabolism does not completely match the increased glycolysis during seizures though the energy homeostasis is maintained. This suggests that oxidative metabolism has a limited capacity to satisfy the brain's energy needs during the kainate-induced seizures, but that the different pathways of energy production in the brain cells can overcome this limitation. Thus the brain damage associated with this experimental model of epilepsy is not due to extended major failure of the energy supply.     

Monitoring the effects of chronic alcohol consumption and abstinence on brain metabolism: a longitudinal proton magnetic resonance spectroscopy study.

BACKGROUND: This study focused on metabolic brain alterations in recently detoxified alcohol-dependent patients (S1) and their possible reversibility after 3 (S2) and 6 months (S3) of abstinence. METHODS: Thirty-three alcohol-dependent patients and 30 healthy control subjects were studied with multislice proton magnetic resonance spectroscopic imaging (echo time = 135 msec at 1.5 T at three time points). RESULTS: In the patient group, we found that choline-containing compounds (Ch) in three frontal and cerebellar subregions at S1 were significantly below normal, whereas N-acetyl aspartate (NAA) differences did not reach significance but showed a trend toward below-normal values in frontal white matter. Abstinent patients showed a significant increase of Ch in all subregions at S2. At S3, no further significant metabolite changes in abstinent patients compared with S2 could be detected. No significant increase of NAA could be detected at follow-up. CONCLUSIONS: The increase of the Ch signal in the follow-up measurement after 3 months in abstinent alcohol-dependent patients supports the hypotheses of an alcohol- or alcohol detoxification-induced altered cerebral metabolism of lipids in membranes or myelin, which seems to be reversible with duration of alcohol abstinence.     

A proton magnetic resonance spectroscopic study in autism spectrum disorders: Amygdala and orbito-frontal cortex

We previously reported neural dysfunction in the anterior cingulate cortex and dorsolateral prefrontal cortex in autistic patients using proton magnetic resonance spectroscopy (¹H-MRS). In this investigation, we measured chemical metabolites in the left amygdala and the bilateral orbito-frontal cortex (OFC), which are the main components of the social brain. We also examined the association between these metabolic findings and social abilities in subjects with autism. The study group included 77 autistic patients (3–6 years old; mean age 4.1; 57 boys and 20 girls). The control subjects were 31 children (3–6 years old; mean age 4.0; 23 boys and 8 girls). Conventional proton MR spectra were obtained using the STEAM sequence with parameters of TR = 5 sec and TE = 15 msec by a 1.5-tesla clinical MRI system. We analyzed the concentrations of N-acetylaspartate (NAA), creatine/phosphocreatine (Cr), and choline-containing compounds (Cho) using LCModel (Ver. 6.1). The concentrations of NAA in the left amygdala and the bilateral OFC in autistic patients were significantly decreased compared to those in the control group. In the autistic patients, the NAA concentrations in these regions correlated with their social quotient. These findings suggest the presence of neuronal dysfunction in the amygdala and OFC in autism. Dysfunction in the amygdala and OFC may contribute to the pathogenesis of autism.     

Effects of chlorpromazine on plasma membrane permeability and fluidity in the rat brain: a dynamic positron autoradiography and fluorescence polarization study

Antipsychotic drugs have been widely used in psychiatry for the treatment of various mental disorders, but the underlying biochemical mechanisms of their actions still remain unclear. Although phenothiazine antipsychotic drugs have been reported to directly interact with the peripheral plasma membrane, it is not known whether these drugs actually affect plasma membrane integrity in the central nervous system. To clarify these issues, we investigated the effect of chlorpromazine (CPZ), a typical phenothiazine antipsychotic drug, on plasma membrane permeability in fresh rat brain slices using a dynamic positron autoradiography technique and [(18)F]2-fluoro-2-deoxy-D-glucose ([(18)F]FDG) as a tracer. Treatment with CPZ (> or =100 microM) resulted in the leakage of [(18)F]FDG-6-phosphate, but not [(18)F]FDG, suggesting that the [(18)F]FDG-6-phosphate efflux was not mediated by glucose transporters, but rather by plasma membrane permeabilization. The leakage of [(18)F]FDG-6-phosphate was followed by slower leakage of cytoplasmic lactate dehydrogenase, suggesting that CPZ could initially induce small membrane holes that enlarged with time. Furthermore, the addition of CPZ (> or =100 microM) caused a decrease in 1,6-diphenyl-1,3,5-hexatriene fluorescence anisotropy, which implies an increase in membrane fluidity. CPZ loading dose-dependently increased both membrane permeability and membrane fluidity, which suggested the involvement of a perturbation of membrane order in the mechanisms of membrane destabilization induced by antipsychotic drugs.     

Effects of ammonia on the anaplerotic pathway and amino acid metabolism in the brain: an ex vivo C NMR spectroscopic study of rats after administering [2-C] glucose with or without ammonium acetate

The ¹³C-label incorporation into glutamate, glutamine, aspartate and γ-aminobutyric acid (GABA) from [2-¹³C] glucose was measured by ¹³C nuclear magnetic resonance (NMR) spectroscopy to directly examine the effects of ammonia on the activity of pyruvate carboxylase (i.e., the anaplerotic pathway) and the amino acid metabolism in the rat brain in vivo. Rats were sacrificed by exposure to microwaves at 7.5, 15, 30, and 60 min after an i.v. injection of [2-¹³C] glucose with or without ammonium acetate. After the injection of ammonium acetate, the brain contents of glutamate, aspartate and GABA had decreased, however, the percentage of ¹³C enrichment of C3 of glutamine, glutamate and GABA, and C2 and C3 of aspartate had increased. The ¹³C entered the TCA cycle via pyruvate carboxylase from [2-¹³C] glucose, labeling the C2 or C3 positions of aspartate, the C2 or C3 positions of glutamate and glutamine, and the C3 or C4 positions of GABA first and second turns of the tricarboxylic acid (TCA) cycle. The C4/C3 labeling ratio in GABA was lower than the analogous ratio in glutamate (C2/C3) and higher than that of glutamine (C2/C3). The order of these ratios (glutamate>GABA>glutamine) was not altered by the injection of ammonium acetate. These findings directly indicate that ammonia increases the anaplerotic pathway and that the ¹³C-skeletons entered glial glutamine through the anaplerotic pathway flow from glia to neuron. A fraction of the glutamine is used in the direct synthesis of GABA via glutamate, whereas the remaining fraction of glutamine passed through the neuronal TCA cycle before synthesizing GABA.     

Effects of antidepressive therapy on auditory processing in severely depressed patients: a combined MRS and MEG study

BACKGROUND: Alterations in brain metabolism as well as in brain function in different brain areas can be observed in severely depressed patients. METHODS: The present study combined proton magnetic resonance spectroscopy (1H MRS, n=16; healthy controls n=27) and magnetoencephalography (MEG, n=17, controls n=18) of the left auditory cortex in severely depressed inpatients pre- and post successful antidepressive therapy. For MEG recordings, patients were stimulated with trains of 4 successive vowels or 4 sine tones, respectively. For each of the 4 stimuli, the amplitude and latency of the N1m was calculated. As a measure of habituation the decrease of the individual amplitudes of the second, third and fourth N1m compared to the first N1m was calculated. RESULTS: Prior to therapy, a subset of patients presented clearly disturbed auditory processing to stimuli (missing of distinct N1m1 and subsequent habituation; 5 of 17 patients (vowels) and 9/17 (tones, respectively)). After treatment, compared to controls, a normalized habituation pattern was observed in all patients for vowels, but not for tones. In contrast, MRS revealed no significant differences between the metabolite concentrations of patients and healthy controls in both measurements. CONCLUSION: Depression may be accompanied by impaired auditory processing, which seems to improve with reduction in depressive symptoms. Auditory cortical dysfunction probably reflects only a part from more widespread aberrations of brain function occurring with severe mood disorder.     

Cognitive impairment and in vivo metabolites in first-episode neuroleptic-naive and chronic medicated schizophrenic patients: a proton magnetic resonance spectroscopy study

Involvement of the prefrontal cortex in schizophrenia has been implicated by neuropsychological, as well as neuropathological and imaging studies. Reductions of N-acetylaspartate (NAA), an in vivo marker of neuronal integrity, have repeatedly been detected in the frontal lobes of patients with schizophrenia by proton magnetic resonance spectroscopy (1H-MRS). In chronic medicated patients, a positive correlation between NAA levels of the prefrontal cortex and cognitive functioning has been observed, but to date, there have been no studies in first-episode neuroleptic-naive patients. In this study, single-voxel 1H-MRS was used to investigate neuronal function of the dorsolateral prefrontal cortex in 15 first-episode and 20 chronic schizophrenic patients. Outcomes were compared to 20 age-matched healthy controls to assess the relationship between prefrontal metabolism and neuropsychological performance. Patients with chronic schizophrenia had significant reductions of NAA, glutamate/glutamine, and choline levels compared to first-episode patients and healthy controls. Furthermore, creatine and phosphocreatine were significantly reduced in both patient groups compared to healthy controls. In the neuropsychological tests, chronic schizophrenic patients performed significantly poorer in the Auditory Verbal Learning Task (AVLT) compared to first-episode patients. In both patient groups, NAA levels of the left frontal lobe significantly correlated with performances in verbal learning and memory. These results corroborate data from recent structural and spectroscopic imaging studies of the frontal lobes in schizophrenia, in which cortical gray matter reductions after onset of symptoms as well as reduced levels of NAA in chronic, but not in first-episode schizophrenic patients have been reported.     

Modeling of brain metabolism and pyruvate compartmentation using 13C NMR in vivo: caution required

Two variants of a widely used two-compartment model were prepared for fitting the time course of [1,6-¹³C₂]glucose metabolism in rat brain. Features common to most models were included, but in one model the enrichment of the substrates entering the glia and neuronal citric acid cycles was allowed to differ. Furthermore, the models included the capacity to analyze multiplets arising from ¹³C spin-spin coupling, known to improve parameter estimates in heart. Data analyzed were from a literature report providing time courses of [1,6-¹³C₂]glucose metabolism. Four analyses were used, two comparing the effect of different pyruvate enrichment in glia and neurons, and two for determining the effect of multiplets present in the data. When fit independently, the enrichment in glial pyruvate was less than in neurons. In the absence of multiplets, fit quality and parameter values were typical of those in the literature, whereas the multiplet curves were not modeled well. This prompted the use of robust statistical analysis (the Kolmogorov–Smirnov test of goodness of fit) to determine whether individual curves were modeled appropriately. At least 50% of the curves in each experiment were considered poorly fit. It was concluded that the model does not include all metabolic features required to analyze the data.     

Lithium effects on brain glutamatergic and GABAergic systems of healthy volunteers as measured by proton magnetic resonance spectroscopy

Lithium is a first-line medicinal treatment for acute bipolar disorder and is also used prophylactically in manic depressive illnesses; however, its mechanism of action is still largely unknown. Animal and human studies have suggested that lithium modulates glutamatergic and GABAergic neurotransmissions. The aim of this study is to investigate the effects of lithium on brain glutamate (Glu), glutamine (Gln), and gamma-aminobutyric acid (GABA) levels in healthy individuals using proton magnetic resonance spectroscopy (1H-MRS). In vivo 3 Tesla 1H-MRS was performed on the anterior cingulate cortex and bilateral basal ganglia initially and after two weeks of lithium administration on 8 healthy male subjects who had a mean age of 34.9 years. After two weeks of lithium administration, Gln significantly decreased in the left basal ganglia and showed a decreasing trend in the right basal ganglia. Additionally, Glu+Gln (Glx) significantly decreased in the right basal ganglia and showed a decreasing trend in the left basal ganglia. Glu did not significantly change in any of the three tested areas, and GABA exhibited no significant change after the lithium administration when measured in the anterior cingulate cortex and left basal ganglia. This study is the first to demonstrate that subchronic lithium treatment decreases Gln and Glx levels in the bilateral basal ganglia of healthy individuals. Our finding might suggest that the decrease of Glx levels is associated with the pharmacological actions of subchronic lithium treatment.     

In vivo quantification of monoamine oxidase A in baboon brain: a PET study using [11C]befloxatone and the multi-injection approach

[¹¹C]befloxatone is a high-affinity, reversible, and selective radioligand for the in vivo visualization of the monoamine oxidase A (MAO-A) binding sites using positron emission tomography (PET). The multi-injection approach was used to study in baboons the interactions between the MAO-A binding sites and [¹¹C]befloxatone. The model included four compartments and seven parameters. The arterial plasma concentration, corrected for metabolites, was used as input function. The experimental protocol—three injections of labeled and/or unlabeled befloxatone—allowed the evaluation of all the model parameters from a single PET experiment. In particular, the brain regional concentrations of the MAO-A binding sites (B′_max) and the apparent in vivo befloxatone affinity (K_d) were estimated in vivo for the first time. A high binding site density was found in almost all the brain structures (170±39 and 194±26 pmol/mL in the frontal cortex and striata, respectively, n=5). The cerebellum presented the lowest binding site density (66±13 pmol/mL). Apparent affinity was found to be similar in all structures (K_dV_R=6.4±1.5 nmol/L). This study is the first PET-based estimation of the B_max of an enzyme.     

Reversal of metabolic deficits by lipoic acid in a triple transgenic mouse model of Alzheimer's disease: a 13C NMR study

Alzheimer''s disease is an age-related neurodegenerative disease characterized by deterioration of cognition and loss of memory. Several clinical studies have shown Alzheimer''s disease to be associated with disturbances in glucose metabolism and the subsequent tricarboxylic acid (TCA) cycle-related metabolites like glutamate (Glu), glutamine (Gln), and N-acetylaspartate (NAA). These metabolites have been viewed as biomarkers by (a) assisting early diagnosis of Alzheimer''s disease and (b) evaluating the efficacy of a treatment regimen. In this study, 13-month-old triple transgenic mice (a mouse model of Alzheimer''s disease (3xTg-AD)) were given intravenous infusion of [1-¹³C]glucose followed by an ex vivo ¹³C NMR to determine the concentrations of ¹³C-labeled isotopomers of Glu, Gln, aspartate (Asp), GABA, myo-inositol, and NAA. Total (¹²C+¹³C) Glu, Gln, and Asp were quantified by high-performance liquid chromatography to calculate enrichment. Furthermore, we examined the effects of lipoic acid in modulating these metabolites, based on its previously established insulin mimetic effects. Total ¹³C labeling and percent enrichment decreased by ∼50% in the 3xTg-AD mice. This hypometabolism was partially or completely restored by lipoic acid feeding. The ability of lipoic acid to restore glucose metabolism and subsequent TCA cycle-related metabolites further substantiates its role in overcoming the hypometabolic state inherent in early stages of Alzheimer''s disease.     

Clinical response of quetiapine in rapid cycling manic bipolar patients and lactate level changes in proton magnetic resonance spectroscopy

The aim of the current study was to evaluate the relationship between quetiapine's effect on the improvement of mood symptoms in bipolar patients and brain metabolite level changes as measured by proton magnetic resonance spectroscopy ((1)H-MRS). Rapid cycling bipolar patients in the manic state were recruited and treated with quetiapine for 12 weeks. Clinical assessment was performed using the Young Mania Rating Scale (YMRS), the 17-item Hamilton Depression Rating Scale (HDRS) and the Clinical Global Impression-Severity scale (CGI-S) at baseline and weekly intervals during the 12-week period. In order to evaluate metabolite level changes over time, (1)H-MRS scans were acquired at baseline and week 12. There were significant reductions in YMRS scores (by 43.0%), HDRS scores (by 27.5%) and CGI-S score (by 44.6%) over the 12 week-period. Lactate levels significantly decreased over the 12-week study period (22.4%). This change in lactate levels was more prominent in quetiapine responders than in non-responders. Additionally, there was a positive correlation between changes in lactate levels and those in YMRS scores (r=0.52, p=0.003). Our findings suggest that quetiapine's antimanic and antidepressant efficacy in patients with rapid cycling bipolar disorder may potentially be related to decreased lactate levels in frontal regions of the brain.     

Effects of Hg and CH3Hg on Ca fluxes in rat brain microsomes

A permanent increase in cytosolic Ca²⁺ levels seems to be associated with various pathological situations which may result in cell death. Hg²⁺ and CH₃Hg⁺ are potent neurotoxic agents, but the precise molecular mechanism(s) underlying their effects are not sufficiently understood. In the present study we investigated the potential role of Ca²⁺-ATPase located in the endoplasmic reticulum as a molecular target for mercury. Hg²⁺ and CH₃Hg⁺ inhibited Ca²⁺-ATPase and Ca²⁺ uptake by brain microsomes with similar potencies. However, the inhibitory potency of Hg²⁺ was higher than that of CH3Hg+, probably reflecting differences in the affinity for the sulfhydryl groups of these compounds. Passive or unidirectional Ca²⁺ efflux (measured in the absences of Ca²⁺-ATPase ligands) was increased significantly by CH₃Hg⁺ and Hg²⁺. Again, the potency of Hg²⁺ was higher than that of CH₃Hg⁺. Blockers of Ca²⁺ channels (ruthenium red, procaine, heparin) did not affect the increase in passive Ca t+ efflux induced by mercury compounds, possibly indicating that Ca²⁺ release occurs through Ca²⁺-ATPase. Addition of physiological concentrations of glutathione (GSH) simultaneously with mercury abolished the inhibitory effects of both forms of Hg on Ca Z+-transport. However, if the enzyme was first inhibited with Hg²⁺ or CH₃Hg⁺ and subsequently treated with GSH, the reversal of inhibition was about 50%, suggesting that part of the cysteinyl residues involved in the inhibitory actions of mercury in Ca t+-transport bind to mercury with an extremely high affinity.     

Effects of inhibitors of Na,K-ATPase on the membrane potentials and neurotransmitter efflux in rat brain slices

The potassium potential EK, of rat brain slices was estimated by determining the uptake of 86Rb+. The ERb was the same for slices prepared from five rostral brain regions, the average value being 66.4 mV. The ERb values in the presence of 20 microM ouabain were only slightly lower than the resting values; increasing concentrations of ouabain above 20 microM resulted in a graded depolarization in all five brain regions. High concentrations (1 mM) of two other inhibitors of Na+,K+-ATPase, dihydro-ouabain and strophanthidin, produced no more depolarization than did 20 microM ouabain. Competitive binding studies indicated that the differential effects were due to the relative binding to brain slices. Erythrosin B, an inhibitor of Na+,K+-ATPase, had no measurable effect on ERb. Intermediate concentrations of the Na+/H+ ionophore monensin slightly hyperpolarized striatal slices, whereas the same monensin concentrations plus 20 microM ouabain, 1 mM strophanthidin or 70 microM erythrosin B resulted in marked depolarization. Measurement of the membrane potential via uptake of methyltriphenylphosphonium cation indicated that ERb was indeed a valid estimation of the membrane potential. EK was measured directly by monitoring 42K+ uptake in striatal slices and was found to be essentially identical to ERb. Uptake of 22Na+ was consistent with the values for ERb or EK. Several conditions that resulted in little or no measurable depolarization of striatal slices did induce efflux of exogenously loaded GABA and dopamine; these conditions included 20 microM ouabain, 1 mM dihydro-ouabain or strophanthidin, and 70 microM erythrosin B. Neurotransmitter efflux in the absence of general cell depolarization was not accompanied by altered rates of respiration or decreased ATP levels.     

Combined 123I-FP-CIT and 123I-IBZM SPECT for the diagnosis of parkinsonian syndromes: study on 72 patients

Summary. 72 consecutive patients with suspected parkinsonian syndromes (PS) were studied by dopamine transporter (DAT) and D2 receptor SPECT in order to evaluate the accuracy of combined SPECT imaging. In the follow-up, the patients were diagnosed as having Parkinsons disease (PD, n=25), dementia with Lewy bodies (DLB, n=6), multiple system atrophy (MSA, n=13), progressive supranuclear palsy (PSP, n=8), corticobasal degeneration (CBD, n=9), and essential tremor (ET, n=11). Using the iteratively estimated optimal cutoffs, DAT was reduced in 57/61 PS patients, whereas all ET patients were identified as normal. Reduced D2 receptor binding had 7/13 patients with MSA, 6/8 patients with PSP, 2/9 patients with CBD and no ET, PD or DLB patients. FP-CIT SPECT allows an accurate detection of nigrostriatal affection in neurodegenerative PS. IBZM SPECT is useful to approve the diagnosis of PSP and MSA although a normal finding cannot exclude an atypical PS. IBZM SPECT seems to be of restricted value in CBD.