This file was created by the Typo3 extension sevenpack version 0.7.14 --- Timezone: CEST Creation date: 2013-06-19 Creation time: 10-46-23 --- Number of references 9 article vonPfostlLZGZSLR2012 NeuroImage 2012 5 61 1 98–105 In contrast to the limited use of functional magnetic resonance imaging (fMRI) in clinical diagnostics, it is currently a mainstay of neuroimaging in clinical and basic brain research. However, its non-invasive use in combination with its high temporal and spatial resolution would make fMRI a perfect diagnostic tool. We are interested in whether a pharmacological challenge imposed on the brain can be reliably traced by the blood oxygen level-dependent (BOLD) signal and possibly further exploited for diagnostics. We have chosen a systemic challenge with lactate and pyruvate to test whether the physiological formation of these monocarboxylic acids contributes to the BOLD signal and can be detected using fMRI. This information is also of interest because lactate levels in the cerebrospinal fluid rise concomitantly with reduced vascular responsiveness of the brain during the progression of Alzheimer disease (AD). We studied the BOLD response after a low-dose lactate challenge and monitored the induced plasma lactate levels in anesthetized non-human primates. We observed reliable lactate-induced BOLD responses, which could be confirmed at population and individual level by their strong correlation with systemic lactate concentrations. Comparable BOLD effects where observed after a slow infusion of pyruvate. We show here that physiological changes in lactate and pyruvate levels are indeed reflected in the BOLD signal, and describe the technical prerequisites to reliably trace a lactate challenge using BOLD-fMRI. http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de Department Logothetis http://www.sciencedirect.com/science/article/pii/S1053811912002698 10.1016/j.neuroimage.2012.02.082 vpfoestlVvon Pföstl juanJLi dzaldivarDZaldivar jozienJGoense xiaozheXZhang nserrNSerr nikosNKLogothetis arauchARauch article LivZZLR2011 Analytical and Bioanalytical Chemistry 2012 3 402 8 2545-2554 In vivo measurement of multiple functionally related neurochemicals and metabolites (NMs) is highly interesting but remains challenging in the field of basic neuroscience and clinical research. We present here an analytical method for determining five functionally and metabolically related polar substances, including acetylcholine (quaternary ammonium), lactate and pyruvate (organic acids), as well as glutamine and glutamate (amino acids). These NMs are acquired from samples of the brain and the blood of non-human primates in parallel by dual microdialysis, and subsequently analyzed by a direct capillary hydrophilic interaction chromatography (HILIC)–mass spectrometry (MS) based method. To obtain high sensitivity in electrospray ionization (ESI)–MS, lactate and pyruvate were detected in negative ionization mode whereas the other NMs were detected in positive ionization mode during each HILIC-MS run. The method was validated for linearity, the limits of detection and quantification, precision, accuracy, stability and matrix effect. The detection limit of acetylcholine, lactate, pyruvate, glutamine, and glutamate was 150 pM, 3 μM, 2 μM, 5 nM, and 50 nM, respectively. This allowed us to quantitatively and simultaneously measure the concentrations of all the substances from the acquired dialysates. The concentration ratios of both lactate/pyruvate and glutamine/glutamate were found to be higher in the brain compared to blood (p < 0.05). The reliable and simultaneous quantification of these five NMs from brain and blood samples allows us to investigate their relative distribution in the brain and blood, and most importantly paves the way for future non-invasive studies of the functional and metabolic relation of these substances to each other. http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de Department Logothetis http://www.springerlink.com/content/m75q3716w21h6u5g/fulltext.pdf 10.1007/s00216-011-5427-z juanJLi vpfoestlVvon Pföstl dzaldivarDZaldivar xiaozheXZhang nikosNKLogothetis arauchARauch poster ViswanathZvRL2012 2012 11 13 48 In this study, CPX, an antagonist of adenosine was used to determine the role of adenosine in uncoupling the vascular and neuronal response observed by the BOLD signal after a strong visual stimulation in primary visual cortex (V1). We systemically and locally applied CPX and pharmacologically manipulated the sensory response in the early visual cortex of anaesthetized macaques. Pharmacological magnetic resonance imaging (phMRI) in combination with electrophysiology was used to determine the impact of CPX on V1. Results were obtained from recordings of the BOLD and electrophysiological activity during the injections. Systemic application of CPX resulted in a disruption of the visual modulation in the BOLD signal. Local applications of CPX resulted in a decrease in the power of low LFP and an increase in the power of MUA. In addition it resulted in a decrease in the CV and FF. No significant changes were observed in the BOLD signal after systemic application of phosphate buffered saline, which was used as a control. The results show that we indeed observe dissociation between the vascular and the neuronal activity during adenosinergic modulation. Apparently adenosine reduces functional hyperaemia, which is reflected by the reduction in BOLD signal, while underlying neuronal activity is increased, indicated by an increase in MUA. Further studies have to be conducted using simultaneous sampling of neurochemicals and phMRI to fully elucidate the functional role of adenosine for the vascular and neuronal interplay in V1. http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de Department Logothetis http://www.neuroschool-tuebingen-nena.de/ Schramberg, Germany 13th Conference of the Junior Neuroscientists of Tübingen (NeNA 2012) sviswanathSViswanath dzaldivarDZaldivar vpfoestlVvon Pföstl arauchARauch nikosNKLogothetis poster vonPfostlZLVZLR2012 2012 7 8 p140.27 Recent evidence suggests that increased metabolic demand of neurons can be met by lactate, a metabolite of glucose. In addition, during neuronal activation lactate production in the brain is increased. We already demonstrated that this physiological formation of lactate can contribute to the BOLD signal. Here we set out to determine the underlying mechanism that drives the observed increase in BOLD baseline. This effect could be explained by an increase in CBF or also increased neuronal activity. The influence of lactate on cerebral blood flow has been already established. To test if lactate has also an effect on neuronal activity we performed electrophysiological recordings in V1 of anesthetized non-human primates. Lactate was applied slow and continuously (0.04 mmol/kg/min). This infusion induced a significant increase in local field potential (LfpH, 24-90 Hz) power and visual stimulus induced modulation. An average increase of 23.0±1.2% and 76.0±20% was recorded for power and modulation of LfpH respectively; this effect reached significance 4.8±3.1 min after the start of the injection and lasted for 19.5±5.0 min. The timing of the effects is comparable to the timing of the BOLD signal increase evoked by the same infusion protocol of lactate. In the multiunit activity (MUA, 400-3000 Hz) no significant effect was observed. In summary, by applying lactate, a potential fuel for activated neurons, we increase LfpH power and modulation but not the spiking activity. Since LfpH is a reliable driver of the BOLD signal at least part of the lactate effect on the BOLD signal can be explained by an increase in neuronal activity. http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de Department Logothetis http://fens.ekonnect.co/FENS_331/poster_35355/program.aspx Barcelona, Spain 8th Forum of European Neuroscience (FENS 2012) vpfoestlVvon Pföstl dzaldivarDZaldivar juanJLi sviswanathSViswanath xiaozheXZhang nikosNKLogothetis arauchARauch poster ZaldivarLvWGRL2012 2012 7 8 p063.19 The presence of dopamine-(DA)-receptors-(DARs) and innervations in early sensory pathways has previously been demonstrated in monkeys and humans. Nonetheless, their possible role in the sensory processing is still far from being understood. Anatomical evidence has shown that DARs are expressed in early-visual-system. These studies indicated that D1Rs are found in primary-visual-cortex, while D2Rs are predominantly expressed in the lateral-geniculate-nucleus-(LGN). D1Rs have a facilitating effect on neuronal processing whereas D2Rs show a dampening effect. Given their differences in anatomical distribution and functionality the two kinds of DARs may have a differential effect on thalamocortical information transfer. Here, we set out to investigate DAergic impact on V1 by using combined fMRI, neurophysiology and neurochemistry measurements in anesthetized non-human-primates, during systemic-application of L-DOPA-Carbidopa (2.1/0.5mg/kg, respectively). Our results show that the stimulus-induced modulation of the BOLD-signal decreases by 40±5% for 10±3min (n=8,p < 0.05). This decrease is concomitant with an improvement in the signal-to-noise-ratio-(SNR) in multi-unit-activity-(MUA: 900-3200Hz) as well as in the CV (p< 0.05) of the theta (4-8Hz), low-gamma (20-60Hz) and gamma (65-120Hz) bands of LFP. In contrast, local application of DA in V1 did not induce any changes in neuronal activity indicating that the observed effects are most probably mediated by D2Rs of LGN. DAergic neuromodulation decreased the SNR of the neuronal recordings in V1 which reflects a sparse and dampened firing pattern. Neurochemical sampling in V1 has shown an increased glutamate/GABA-ratio which might reflect a change in the excitation/inhibition balance induced by DA. The additional measured lactate/pyruvate-ratio has also shown a change indicating a decreased metabolic demand. These findings suggest that the visual inputs are attenuated by the local DAergic-circuitry of LGN (D2Rs) generating sparse and precise neuronal firing in V1. At the same time, however, the reduced mass-activity appears to reduce the energy demands, and the stimulus-induced-modulation of the BOLD-signal. http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de Department Logothetis http://fens.ekonnect.co/FENS_331/poster_33040/program.aspx Barcelona, Spain 8th Forum of European Neuroscience (FENS 2012) dzaldivarDZaldivar juanJLi vpfoestlVvon Pföstl kevinKWhittingstall jozienJGoense arauchARauch nikosNKLogothetis poster ZaldivarLvZLR2011 2011 11 41 175.01 Dopamine (DA) is thought to have a gating role in the communication between thalamus and primary sensory areas. In the primary visual pathway D2-receptors (D2Rs) are predominantly found in lateral geniculate nucleus (LGN) while D1-receptors (D1Rs) show higher density in primary visual cortex. D1Rs have a facilitating effect on neuronal processing whereas D2Rs show a dampening effect. Given their differences in anatomical distribution and functionality the two dopaminergic (DAergic) receptors may have a differential effect on thalamocortical information transfer. Here we set out to investigate DAergic impact on V1 by using combined fMRI and neurophysiological measurements in anesthetized non-human primates, during systemic application of L-DOPA (LD: 2.1 mg/kg) and Carbidopa (C: 0.5 mg/kg). Our results show that the stimulus-induced modulation of the BOLD signal decreases by 45 ± 8% for 10 ± 3 min (n=6, p < 0.05). This decrease is concomitant with an improvement in signal-to-noise ratio (SNR) in multi unit activity (MUA: 900-3200 Hz) as well as decrease in CV (p<0.05) of the theta (4-8 Hz), low-gamma (20-60 Hz) and gamma (65-120 Hz) bands of LFP. In contrast, local application of DA in V1 did not induce any changes in neuronal activity indicating that the observed effects are most probably mediated by D2Rs of LGN. DAergic neuromodulation improved SNR of the neuronal recordings in V1 which reflects a sparse and dampened firing pattern with little background interferences. These findings suggest that the visual inputs are attenuated by the local DAergic circuitry of LGN (D2Rs) generating sparse and precise neuronal firing in V1. At the same time, however, the reduced mass-activity appears to reduce the energy demands, and the stimulus-induced modulation of the BOLD signal. Our findings confirm the important role of D2Rs in gating inputs to primary visual cortex by achieving sparse and adequate neuronal firing. http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de Department Logothetis http://www.sfn.org/am2011/ Washington, DC, USA 41st Annual Meeting of the Society for Neuroscience (Neuroscience 2011) dzaldivarDZaldivar juanJLi vpfoestlVvon Pföstl xiaozheXZhang nikosNKLogothetis arauchARauch poster LiZvSZLR2011 2011 11 41 864.17 In macaques, cholinergic subreceptors of nicotine (nAChRs) are predominantly found in the excitatory afferents of the primary visual cortex (V1, layer 4c) originating from the lateral geniculate nucleus (LGN). This strategic termination pattern allows nicotine to up regulate thalamocortical activity, while in parallel activity outside layer 4c can be down regulated by nicotinic effects on GABAergic inhibition. In addition to this gain-modulating role, nicotine has also distinct neuroprotective effects. Here, we have examined whether such neuroprotective effects could be at least partially explained by the gain modulation itself which tunes neuronal networks to a most efficient input-output mode with little other interferences. We investigated nicotinic effects (systemic: 0.2mg/kg) in V1 by neurophysiological recordings using multi-laminar probes and sampling of intracortical glutamate, GABA and glutamine by microdialysis in anesthetized non-human primates. Multi unit activity (MUA: 900-3200 Hz) and gamma (65-120 Hz) activity showed an improved signal-to-noise ratio (SNR) while theta activity (4-8Hz) was significantly reduced (p<0.5). The neurochemical analysis on the other hand showed increased concentrations of GABA (+40%) while glutamate (-60%) and glutamine levels (-50%) were reduced. Taken together nicotine shifts the ratio between glutamate and GABA clearly to GABA inducing inhibitory effects which reduce excitation and result in low glutamate levels. The decrease in excitatory neuronal activity is reflected in the reduced theta activity and the improved SNR in MUA and the gamma band resulting in an efficient input-output relation due to little excitatory interferences. The low levels of glutamine are most likely caused by the increased synthesis of GABA for which glutamine is a metabolic precursor. The neuroprotective effects of nicotine can be explained by the reduction of glutamate sparing neuronal networks from abundant excitatory activity resulting in excitotoxic effects by glutamate itself and other potentially toxic metabolites. http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de Department Logothetis http://www.sfn.org/am2011/ Washington, DC, USA 41st Annual Meeting of the Society for Neuroscience (Neuroscience 2011) juanJLi dzaldivarDZaldivar vpfoestlVvon Pföstl nserrNSerr xiaozheXZhang nikosNKLogothetis arauchARauch poster 7071 2010 11 40 648.9 Proper brain function is tightly controlled by neurochemically active compounds (NACs). These NACs can be directly detected in the brain. However the actual NACs and their metabolites can also be monitored in the blood. Measuring the concentrations and ratios of NACs simultaneously collected in the blood and brain can therefore provide important insights in their intracortical release and metabolism. This will allow interpolation of brain NACs concentrations/ratios from systemically sampled NACs concentrations (blood), which can serve as biomarker for dysfunctional processes in the brain. We report here a method for the simultaneous neurochemical analysis of five polar compounds, acetylcholine, lactate, pyruvate, glutamine and glutamate. We sampled these NACs from venous blood as well as intracortically from the primary visual cortex of anesthetized non-human primates during visual stimulation. Simultaneous systemic and intracortical microdialysis was used for sample collection. Great care was taken to synchronize to two sampling devices and to adjust the sample preparation for direct comparability. After sample collection we used a capillary hydrophilic interaction liquid chromatography (HILIC) for optimal separation of the sample’s components. For detection of the NACs tandem mass spectrometry (MS/MS) was coupled to HILIC without using any additional chemical treatment. The detection limit of acetylcholine, lactate, pyruvate, glutamine and glutamate was 45 amol, 0.9 pmol, 0.6 pmol, 1.5 fmol and 15 fmol, respectively. Our results demonstrate that we can reliably and simultaneously quantify the concentrations of these five compounds in brain and blood microdialysate from non-human primates. The concentration of all tested NACs was higher in the blood compared to the brain tissue (p<0.05). Blood and brain values were in agreement with the Human Metabolome Database Version 2.5 which we used since corresponding non-human primate data are not available. We can now compare the different ratios of the sampled NACs and test for specific changes under pharmacological interventions mimicking dysfunctional states of brain function. http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de Department Logothetis http://www.sfn.org/am2010/index.aspx?pagename=abstracts_main Biologische Kybernetik Max-Planck-Gesellschaft San Diego, CA, USA 40th Annual Meeting of the Society for Neuroscience (Neuroscience 2010) en juanJLi vpfoestlVvon Pföstl dzaldivarDZaldivar xiaozheXZhang nikosNKLogothetis arauchARauch poster 7072 2010 11 40 648.15 Lactate is a common metabolic product of anaerobic glucose metabolism. It can freely pass the blood brain barrier and it’s known to play also an important role in brain metabolism. We used pharmaco MRI and tested the effect of systemic lactate application on the BOLD signal in primary visual cortex (V1) of anesthetized non-human primates during visual stimulation. We also monitored the pharmacokinetics of the applied lactate in the blood using microdialysis and HPLC (high performance liquid chromatography) coupled to MS/MS (mass spectrometry). The lactate pharmacokinetics allows us to investigate the actual plasma concentrations of lactate, and thus, how this correlates to changes in the BOLD signal. After lactate infusion of 0.6 mmol/kg, we observed two consistent effects in the BOLD signal: An initial decrease in visually-induced modulation followed by a subsequent positive baseline shift (n = 10, p < 0.05). The plasma lactate levels significantly increased approximately 9 minutes after systemic application and were correlated with the positive baseline shift in the BOLD signal (p < 0.05). This is in line with a lactate-induced increase of CBF in sensory stimulated regions observed in earlier studies. However, the onsets of lactate increases were late - thereby indicating a lactate buffering mechanism. This could be due to an uptake of lactate by erythrocytes buffering lactate until this capacity is saturated, and plasma levels start to rise with some delay. We conclude that the positive baseline shift in the BOLD signal is triggered by a rise in CBF due to increased plasma lactate. Interestingly, during the observed decrease in visual modulation, (though lactate was already being applied), the lactate levels in the blood were still comparable to the pre-injection concentrations (p < 0.05). How this lactate uptake by erythrocytes influences the BOLD signal has to be further investigated. Nonetheless, our results reveal a complex interaction of lactate in the brain which was only detectable by using pharmaco MRI in combination with neurochemical monitoring of lactate. http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de Department Logothetis http://www.sfn.org/am2010/index.aspx?pagename=abstracts_main Biologische Kybernetik Max-Planck-Gesellschaft San Diego, CA, USA 40th Annual Meeting of the Society for Neuroscience (Neuroscience 2010) en vpfoestlVvon Pföstl juanJLi dzaldivarDZaldivar jozienJGoense xiaozheXZhang nikosNKLogothetis arauchARauch