Metabolites In Rat Brain Research Articles

4-Aminoazobenzene: A novel negative ion matrix for enhanced MALDI tissue imaging of metabolites

Endogenous metabolites play key functions in many important physiological and biochemical processes. The comprehensive in situ detection and direct imaging of metabolites in bio-tissues by matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) is very important for understanding complex and diverse biological processes and has become an essential aspect of spatial omics. In this work, 4-aminoazobenzene (AAB) was successfully screened and optimized as a new negative ion (−)MALDI matrix to enhance the in situ detection and imaging of metabolites in tissues using MALDI-MSI. Obviously, AAB exhibited superior properties in terms of ultraviolet absorption, background ion interference, matrix morphology, and metabolite ionization efficiency. AAB was used for in situ detection and imaging of metabolites in rat brain and germinating Chinese yew seed tissue sections, where 264 and 339 metabolite ion signals were successfully detected and imaged using (-)MALDI-MS, respectively. In addition, high-resolution imaging of mouse eyeball section using MALDI-timsTOF MSI with spatial resolution of up to 10 µm was successfully carried out, showing that AAB is an efficient (-)MALDI matrix for capturing high-resolution images of metabolites in biological tissue sections.

Determination and disposition kinetics of phellamurin metabolites in rat brain

Phellamurin is a flavanone glycoside that is abundant in the leaves of Phellodendron wilsonii Hayata et Kanehira (Rutaceae). The disposition kinetics of phellamurin metabolites in rat brain was investigated in this study. Doses of 100 mg/kg and 200 mg/kg were orally administered to rats. At 0.33, 2, 4 and 6 hr after dosing, rats were dissected and the brain concentrations of the aglycone neophellamuretin were determined by an HPLC method prior to and after hydrolysis with β-glucuronidase. The mobile phase was acetonitrile: H 2O (containing 1 % acetic acid, 38:62, v/v). Our results indicated that neophellamuretin glucuronide might be able to cross the blood-brain barrier and its concentration in the brain was dose-dependent at the two doses investigated, whereas the aglycone neophellamuretin was present in a trace amount in the brain.

Addressing the instability issue of dopamine during microdialysis: the determination of dopamine, serotonin, methamphetamine and its metabolites in rat brain.

Dopamine is a catecholamine neurotransmitter that degrades rapidly in aqueous solutions; hence, its analysis following brain microdialysis is challenging. The aim of the current study was to develop and validate a new microdialysis coupled LC-MS/MS system with improved accuracy, precision, simplicity and turnaround time for dopamine, serotonin, methamphetamine, amphetamine, 4-hydroxymethamphetamine and 4-hydroxyamphetamine analysis in the brain. Dopamine degradation was studied with different stabilizing agents under different storage conditions. The modified microdialysis system was tested in vitro, and was optimized for best probe recovery, assessed by %gain. LC-MS/MS assay was developed and validated for the targeted compounds. Stabilizing agents (ascorbic acid, EDTA and acetic acid) as well as internal and cold standards were added on-line to the dialysate flow. Assay linearity range was 0.01-100ng/mL, precision and accuracy passed criteria, and LOQ and LLOQ were 0.2 and 1.0 pg, respectively. The new microdialysis coupled LC-MS/MS system was used in Wistar rats striatum after 4mg/kg subcutaneous methamphetamine. Methamphetamine rapidly distributed to rat striatum reaching an average ~200ng/mL maximum, ~82.5min post-dose. Amphetamine, followed by 4-hydroxymethamphetamine, was the most abundant metabolite. Dopamine was released following methamphetamine injection, while serotonin was not altered. In conclusion, we proposed and tested an innovative and simplified solution to improve stability, accuracy and turnover time to monitor unstable molecules, such as dopamine, by microdialysis.

Nicotine Pharmacokinetics in Rat Brain and Blood by Simultaneous Microdialysis, Stable-Isotope Labeling, and UHPLC-HRMS: Determination of Nicotine Metabolites.

The disposition and metabolism of nicotine in the brain is an important determinant of its exposure. We have developed a novel method for the dynamic determination of nicotine and its metabolites in rat brain and blood by simultaneous microdialysis sampling, stable-isotope labeling, and ultra high-performance liquid chromatography-high-resolution mass spectrometry (UHPLC-HRMS) assaying. Microdialysis probes were inserted into both the right striatum and jugular vein of Sprague-Dawley rats. The collections of dialystes after nicotine intraperitoneal injection were analyzed by the optimized UHPLC-HRMS. Nicotine-pyridyl- d4 was used as a metabolic tracer, and several stably labeled isotopes were applied to calibrate the in vivo recoveries of retrodialysis. The quadrupole-Orbitrap HRMS provided reliable characterization of the nicotine derivatives with less than 3.5 ppm mass measurement accuracy. Good precision and accuracy were obtained for different analytes within the predefined limits of acceptability and the range of the standard curve. Nicotine and its 11 metabolites were identified in most microdialysis samples from the blood and brain tissue samples. Besides cotinine as the main metabolic product of nicotine, trans-3'-hydroxy-cotinine, nicotine- N-oxide, and norcotinine were proven to be the second most abundant metabolites. The other seven nicotine products, including 4-oxo-4-(3-pyridyl)-butanoic acid, 4-hydroxy-4-(3-pyridyl)-butanoic acid, cotinine- N-oxide, nicotine- N-glucuronide, cotinine- N-glucuronide, and trans-3'- hydroxy-cotinine- O-glucuronide, which have not been determined previously in animal brain, were present in minor amounts. The pharmacokinetic profile of nicotine metabolites indicated that the metabolic characteristic of nicotine in the brain was relatively different from that in the blood. The present work would provide comprehensive evidence for clarifying the differences between nicotine metabolism in the brain and peripheral system.

Antidepressant-like Effect of a Chalcone Compound, DHIPC and Its Possible Mechanism.

DHIPC (2,4-dichloro-2´-hydroxyl-4´,6´-diisoprenyloxychalcone) is a new chalcone compound. In this study, its antidepressant-like activity of compound DHIPC was evaluated by the forced swimming test and the tail suspension test in mice. The results showed that DHIPC significantly reduced the immobility time for 2 h after treatment through the oral administration at dose of 10, 20, and 30 mg/kg in the forced swimming test and the tail suspension test, indicating a significant antidepressant-like effect. The maximal effect was obtained at 30 mg/kg, which is similar to the positive control fluoxetine. The main monoamine neurotransmitters and their metabolites in rat brain were also simultaneously determined. It was found that DHIPC significantly increased the concentrations of the main neurotransmitters serotonin and noradrenalin, and also significantly increased 5-hydroxyindoleacetic acid contents in hippocampus, hypothalamus, and cortex in brain part. So, the probable mechanism of action of DHIPC is thought to be related to increase in serotonin and noradrenalin in the brain.

The impact of 1MeTIQ on the dopaminergic system function in the 6-OHDA model of Parkinson's disease.

Parkinson's disease (PD) is a progressive neurodegenerative disorder which is caused by degeneration of dopaminergic neurons of the nigrostriatal pathway. As a model of PD we used 6-hydroxydopamine (6-OHDA) which exerts toxic effects on catecholaminergic neurons and 1-methyl-1,2,3,4-tetrahydroisoquinoline (1MeTIQ) as neuroprotective compound. The aim of the present study, was to investigate the potential neuroprotective properties of 1MeTIQ against 6-OHDA-induced neurotoxic effects in the rat. In the behavioral study, we measured locomotor activity and catalepsy. In the biochemical studies using HPLC methodology, we analyzed the concentration of dopamine and its metabolites in rat brain. Behavioral tests showed that 6-OHDA decreased rat locomotor activity and produced an increase of catalepsy. These effects did not blocked by 1MeTIQ injections. Biochemical studies indicated that 6-OHDA lesion significantly reduced the concentration of dopamine and its metabolites in the nigro-striatal pathway in the lesioned (ipsilateral) side. Moreover, 6-OHDA induced an increase in the rate of dopamine oxidation. Both acute and chronic administration of 1MeTIQ did not reverse the effects of 6-OHDA lesion on the ipsilateral side, however, it produced a significant elevation of the dopamine concentration in the contralateral side. It is evident that multiple treatments with 1MeTIQ stimulate undamaged neurons to increased activity. 1MeTIQ was shown to possess neuroprotective potential to the dopaminergic neurons damaged by 6-OHDA lesion. This compound has a protective effect but does not have neurorestorative capacity. It does not reverse damage already caused but will maintain the function and activity of undamaged dopamine neurons at physiological level.

Target-based metabolomics for the quantitative measurement of 37 pathway metabolites in rat brain and serum using hydrophilic interaction ultra-high-performance liquid chromatography-tandem mass spectrometry.

Amino acids, neurotransmitters, purines, and pyrimidines are bioactive molecules that play fundamental roles in maintaining various physiological functions. Their metabolism is closely related to the health, growth, development, reproduction, and homeostasis of organisms. Most recently, comprehensive measurements of these metabolites have shown their potential as innovative approaches in disease surveillance or drug intervention. However, simultaneous measurement of these metabolites presents great difficulties. Here, we report a novel quantitative method that uses hydrophilic interaction ultra-high-performance liquid chromatography-tandem mass spectrometry (HILIC-UPLC-MS/MS), which is highly selective, high throughput, and exhibits better chromatographic behavior than existing methods. The developed method enabled the rapid quantification of 37 metabolites, spanning amino acids, neurotransmitters, purines, and pyrimidines pathways, within 6.5 min. The compounds were separated on an ACQUITY UPLC® BEH Amide column. Serum and brain homogenate were extracted by protein precipitation. The intra- and interday precision of all of the analytes was less than 11.34 %, and the accuracy was between -11.74 and 11.51 % for all quality control (QC) levels. The extraction recoveries of serum ranged from 84.58 % to 116.43 % and those of brain samples from 80.80 % to 119.39 %, while the RSD was 14.61 % or less for all recoveries. This method was used to successfully characterize alterations in the rat brain and, in particular, their dynamics in serum. The following study was performed to simultaneously test global changes of these metabolites in a serotonin antagonist p-chlorophenylalanine (PCPA)-induced anxiety and insomnia rat model to understand the effect and mechanism of PCPA. Taken together, these results show that the method is able to simultaneously monitor a large panel of metabolites and that this protocol may represent a metabolomic method to diagnose toxicological and pathophysiological states.

Effect of Some Psychoactive Drugs Used as 'Legal Highs' on Brain Neurotransmitters.

New psychoactive “designer drugs” are synthetic compounds developed to provide similar effects to illicit drugs of abuse, but not subjected to legal control. The rapidly changing legal status of novel psychoactive drugs triggers the development of new compounds, analogs of well-known amphetamine or mescaline. New designer drugs used as substitutes in ecstasy pills are the least investigated and can cause life-threatening effects on users. The aim of our research was to examine the effects of acute administration of 4-methoxyamphetamine (PMA, 5 and 10 mg/kg), 4-methoxy-N-methylamphetamine (PMMA, 5 and 10 mg/kg), and mephedrone (MEPH, 5, 10 and 20 mg/kg) on extracellular and tissue level of dopamine (DA), 5-hydroxytryptamine (5-HT) and their metabolites in rat brain, by microdialysis method in freely moving animals and HPLC. Similarly to 3,4-methylenedioxymethamphetamine (MDMA, 5 and 10 mg/kg) PMA, PMMA and MEPH enhanced the release of DA and 5-HT in rat striatum, nucleus accumbens, and frontal cortex. DA tissue content was increased by MEPH and PMMA in striatum, by MEPH, PMA, and PMMA in nucleus accumbens, and by PMA in frontal cortex. Instead, cortical DA level was decreased by MEPH and PMMA. MEPH did not influence 5-HT tissue level in striatum and nucleus accumbens, but decreased its level in frontal cortex. PMMA increased 5-HT content in striatum, while PMA enhanced it in nucleus accumbens and frontal cortex. Observed changes in brain monoamines and their metabolites by new psychoactive drugs suggest that these drugs may be capable of development of dependence. Further experiments are needed to fully investigate the neurotoxic and abuse potential of those drugs.

Effect of carr‐purcell refocusing pulse trains on transverse relaxation times of metabolites in rat brain at 9.4 Tesla

To investigate the effect of Carr-Purcell (CP) pulse trains on transverse relaxation times, T2, of tissue water and metabolites (both noncoupled and J-coupled spins) in the rat brain at 9.4 Tesla (T) using LASER, CP-LASER, and T2ρ-LASER sequences. Proton NMR spectra were measured in rat brain in vivo at 9.4T. Spectra were acquired at multiple echo times ranging from 18 to 402 ms. All spectra were analyzed using LCModel with simulated basis sets. Signals of metabolites as a function of echo time were fitted using a mono-exponential function to determine their T2 relaxation times. Measured T2 s for tissue water and all metabolites were significantly longer with CP-LASER and T2ρ-LASER compared with LASER. The T2 increased by a factor of ∼ 1.3 for noncoupled and weakly coupled spins (e.g., N-acetylaspartate and total creatine) and by a factor of ∼ 2 (e.g., glutamine and taurine) to ∼ 4 (e.g., glutamate and myo-inositol) for strongly coupled spins. Application of a CP pulse train results in a larger increase in T2 relaxation times for strongly coupled spins than for noncoupled (singlet) and weakly coupled spins. This needs to be taken into account when correcting for T2 relaxation in CP-like sequences such as LASER.

Development of ultrasound-assisted dispersive liquid–liquid microextraction–large volume injection–gas chromatography–tandem mass spectrometry method for determination of pyrethroid metabolites in brain of cypermethrin-treated rats

3-Phenoxybenzoic acid (3-PBA) and 4-hydroxy-3-phenoxybenzoic acid (OH-PBA) are the two common metabolites for most pyrethroid insecticides. A rapid, sensitive, and eco-friendly method has been developed based on ultrasound-assisted dispersive liquid–liquid microextraction (DLLME) coupled to large volume injection–gas chromatography–tandem mass spectrometry for the simultaneous determination of pyrethroid metabolites in rat brain treated with cypermethrin (CYP). Brain samples were homogenized in methanol (disperser solvent) followed by derivatization with methyl chloroformate (MCF) and extraction using DLLME. Factors that influence the extraction and derivatization efficiency such as type and volume of extraction and disperser solvent, sonication time, pH, ionic strength, and volumes of MCF and pyridine were optimized. Under optimized conditions, the limits of detection were 1 and 4 ng/g for 3-PBA and OH-PBA, respectively. Mean recoveries of pyrethroid metabolites in rat brain were in the range of 83–95 %. The developed method was successfully applied for determination of 3-PBA and OH-PBA in brain samples of CYP-treated rats. The developed method can be adopted for rapid and sensitive analysis of pyrethroid metabolites in toxicological and forensic laboratories.

Age-Related Differences in the Disposition of Nicotine and Metabolites in Rat Brain and Plasma

Studies have evaluated the behavioral and neurochemical impact of nicotine administration in rodents. However, the distribution of nicotine and metabolites in rat brain and plasma as a function of age has not been investigated. This is a significant issue because human adolescents have a greater risk for developing nicotine addiction than adults, and reasons underlying this observation have not been fully determined. Thus, in this present study, we evaluated the impact of the transition from adolescence (postnatal day [PND 40]) to adulthood (PND 90) on nicotine distribution in rats. PND 40, 60, and 90 rats received a single injection of (-) nicotine (0.8 mg/kg, subcutaneously). Liquid chromatography tandem-mass spectrometry was used to measure concentration of nicotine and metabolites in selected biological matrices. Nicotine, cotinine, and nornicotine were detected in rat striata and frontal cortex 30 min, 1 hr, 2 hr, and 4 hr after a single administration. These and several additional metabolites (nicotine-1'-oxide, cotinine-N-oxide, norcotinine, and trans-3'-hydroxycotinine) were also detected in plasma at these same timepoints. The mean concentration of nicotine in brain and plasma was lower in PND 40 versus PND 90 rats. In contrast, the mean concentration of nornicotine was higher in the plasma and brain of PND 40 versus PND 90 rats. Nicotine and metabolite distribution differs between adolescent and adult rats. These data suggest that adolescent rats metabolize nicotine to some metabolites faster than adult rats. Further studies are needed to investigate the potential correlation between age, drug distribution, and nicotine addiction.

Single spin-echo T 2 relaxation times of cerebral metabolites at 14.1 T in the in vivo rat brain

To determine the single spin-echo T2 relaxation times of uncoupled and J-coupled metabolites in rat brain in vivo at 14.1 T and to compare these results with those previously obtained at 9.4 T. Measurements were performed on five rats at 14.1 T using the SPECIAL sequence and TE-specific basis-sets for LCModel analysis. The T2 of singlets ranged from 98 to 148 ms and T2 of J-coupled metabolites ranged from 72 ms (glutamate) to 97 ms (myo-inositol). When comparing the T2s of the metabolites measured at 14.1 T with those previously measured at 9.4 T, a decreasing trend was found (p<0.0001). We conclude that the modest shortening of T2 at 14.1 T has a negligible impact on the sensitivity of the 1H MRS when performed at TE shorter than 10 ms.

Application of microdialysis for elucidating the existing form of hyperoside in rat brain: Comparison between intragastric and intraperitoneal administration

Ethnopharmacological relevanceHypericum perforatum (St. John's wort) is an important anti-depressant herb used in clinic and commonly prescribed for mild depression. Hyperoside is one of the major components of H. perforatum and is also detected in many plant species such as Abelmoschus manihot, Black Currant, Rosa agrestis, Apocynum venetum and Nelumbo nucifera. Aim of the study: As the hyperoside showed CNS (central nervous system) protective activity (e.g. anti-depressant-like effect), the possibility of hyperoside or its metabolites to reach CNS should be investigated. Moreover, the pharmacokinetics profile of hyperoside or its metabolites in rat brain should be studied for further elucidating the mechanism of hyperoside action on CNS. Material and MethodsA simple method for simultaneous determination of unbound hyperoside and its metabolite 3′-O-methyl-hyperoside in rat brain was developed by using ultra-high performance liquid chromatography coupled with tandem mass spectrometry (UPLC–MS/MS) and microdialysis technique. This method was applied for pharmacokinetics study of hyperoside and 3′-O-methyl-hyperoside in rat brain after intragastric (i.g.) and intraperitoneally (i.p.) administration of hyperoside in vivo. ResultsResults showed that neither hyperoside nor its metabolites were detected in rat brain after i.g. administration but both compounds could be detected after i.p. administration. Considering the activity of hyperoside through both i.g. and i.p. administration, our results imply that the active components of hyperoside in vivo might be different. Therefore, further studies are needed to identify the active components of hyperoside in vivo through these two different routes. Moreover, non-oral administration route (e.g., i.p.) should be further investigated and be explored to obtain higher bioavailability and better activity for hyperoside. Our results also showed that the real existing form of hyperoside in rat brain were hyperoside and its methylated metabolite with maximum concentration to be 63.78ng/mL and 24.66ng/mL after 20mg/kg i.p. administration, respectively. Therefore, a more reasonable concentration of hyperoside should be considered in in vitro assay to reflect the real situation of hyperoside concentration in vivo. ConclusionDue to the wide use of herbal remedies containing hyperoside, our investigation will contribute to further clarifying the action of this substance. Moreover, this method will be applied for clinical pharmacokinetics study of hyperoside and its metabolite as well as herbs that contain hyperoside.

Simultaneous quantification of nicotine and metabolites in rat brain by liquid chromatography–tandem mass spectrometry

A liquid chromatography–tandem mass spectrometry (LC–MS/MS) method for simultaneous quantification of nicotine (NIC), cotinine (COT), nornicotine (NNIC), norcotinine (NCOT), nicotine-N-β- d-glucuronide (NIC GLUC), cotinine-N-β- d-glucuronide (COT GLUC), nicotine-1′-oxide (NNO), cotinine-N-oxide (CNO), trans-3′-hydroxycotinine (3-HC), anabasine (AB) and anatabine (AT) was modified and validated for quantification of these selected analytes in rat brain tissue. This analytical method provides support for preclinical NIC pharmacokinetic and toxicological studies after controlled dosing protocols. After brain homogenization and solid-phase extraction, target analytes and corresponding deuterated internal standards were chromatographically separated on a Discovery ® HS F5 HPLC column with gradient elution and analyzed by LC–MS/MS in positive electrospray ionization (ESI) mode with multiple reaction monitoring (MRM) data acquisition. Method linearity was assessed and calibration curves were determined over the following ranges: 0.1–7.5 ng/mg for NIC, COT GLUC and AB; and 0.025–7.5 ng/mg for COT, NNIC, NCOT, NIC GLUC, NNO, CNO, 3-HC and AT ( R 2 ≥ 0.99 for all analytes). Extraction recoveries ranged from 64% to 115%, LC–MS/MS matrix effects were ≤21%, and overall process efficiency ranged from 57% to 93% at low and high quality control concentrations. Intra- and inter-assay imprecisions and accuracy for all analytes were ≤12.9% and ≥86%, respectively. The method was successfully applied to quantification of NIC and metabolites in the brain of post-natal day 90 rats that were sacrificed 2-h after a single 0.8 mg/kg s.c. administration of (−)NIC. In these tissues, striatal concentrations were 204.8 ± 49.4, 138.2 ± 14.2 and 36.1 ± 6.1 pg/mg of NIC, COT and NNIC, respectively. Concentrations of NIC, COT and NNIC in the remaining whole brain (RWhB) were 183.3 ± 68.0, 130.0 ± 14.1 and 46.7 ± 10.3 pg/mg, respectively. Quantification of these same analytes in plasma was also performed by a previously validated method. NIC, COT, NNIC, NCOT, NNO and CNO were detected in plasma with concentrations comparable to those reported in previous studies. However, and in contrast to brain tissues, COT concentrations in plasma were significantly higher than were those of NIC (194.6 ± 18.6 ng/mL versus 52.7 ± 12.9 ng/mL). Taken together, these results demonstrate that a sensitive and selective method has been developed for the determination of NIC biomarkers in rat brain.

Lowering of dopamine metabolites in rat brain by harmaline.

Journal Article Lowering of dopamine metabolites in rat brain by harmaline Get access Ray W Fuller, Ray W Fuller The Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana 46285 USA The Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana 46285 U.S.A. Search for other works by this author on: Oxford Academic Google Scholar Susan K Hemrick-Luecke, Susan K Hemrick-Luecke The Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana 46285 USA Search for other works by this author on: Oxford Academic Google Scholar Kenneth W Perry Kenneth W Perry The Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana 46285 USA Search for other works by this author on: Oxford Academic Google Scholar Journal of Pharmacy and Pharmacology, Volume 33, Issue 1, September 1981, Pages 255–256, https://doi.org/10.1111/j.2042-7158.1981.tb13773.x Published: 12 April 2011 Article history Received: 03 December 1980 Published: 12 April 2011

Rat strain‐dependent variations in brain metabolites detected by in vivo1H NMR spectroscopy at 16.4T

Localized in vivo (1) H NMR spectroscopy is playing an increasing role in preclinical studies, because of its ability to quantify the concentrations of up to 20 metabolites in rat brain. To assess the differences between often-used rat strains, the neurochemical profiles of Sprague-Dawley, Wistar and Fischer rats were determined at ultrashort TE at 16.4 T. To ascertain high-qualitative quantification, a first experiment examined the dependence of the measuring time on the quantification results and precision by precisely the number of averages between 16 and 320. It was shown that most metabolites can be quantified accurately within a short scan time, yielding Cramér-Rao lower bounds below 20% and stable concentrations for 16 metabolites with as few as 32 or 64 averages in the thalamus and hippocampus, respectively. Interstrain differences in metabolite concentrations were shown to be moderate, with taurine varying significantly between Sprague-Dawley and Wistar rats, and slightly more distinct differences from Fischer rats, including variations in glutamate and myo-inositol. The high spectral quality and quantification precision of all data again demonstrated the potential of in vivo (1)H NMR spectroscopy at ultrahigh field.

Analyzing the Effects of Psychotropic Drugs on Metabolite Profiles in Rat Brain Using1H NMR Spectroscopy

The mechanism of action of standard drug treatments for psychiatric disorders remains fundamentally unknown, despite intensive investigation in academia and the pharmaceutical industry. So far, little is known about the effects of psychotropic medications on brain metabolism in either humans or animals. In this study, we investigated the effects of a range of psychotropic drugs on rat brain metabolites. The drugs investigated were haloperidol, clozapine, olanzapine, risperidone, aripiprazole (antipsychotics); valproate, carbamazapine (mood stabilizers) and phenytoin (antiepileptic drug). The relative concentrations of endogenous metabolites were determined using high-resolution proton nuclear magnetic resonance (1H NMR) spectroscopy. The results revealed that different classes of psychotropic drugs modulated a range of metabolites, where each drug induced a distinct neurometabolic profile. Some common responses across several drugs or within a class of drug were also observed. Antipsychotic drugs and mood stabilizers, with the exception of olanzapine, consistently increased N-acetylaspartate (NAA) levels in at least one brain area, suggesting a common therapeutic response on increased neuronal viability. Most drugs also altered the levels of several metabolites associated with glucose metabolism, neurotransmission (including glutamate and aspartate) and inositols. The heterogenic pharmacological response reflects the functional and physiological diversity of the therapeutic interventions, including side effects. Further study of these metabolites in preclinical models should facilitate the development of novel drug treatments for psychiatric disorders with improved efficacy and side effect profiles.

Quantitative Magnetic Resonance Spectroscopy Reveals a Potential Relationship between Radiation-Induced Changes in Rat Brain Metabolites and Cognitive Impairment

To test the efficacy of magnetic resonance spectroscopy (MRS) in identifying radiation-induced brain injury, adult male Fischer 344 rats received fractionated whole-brain irradiation (40 or 45 Gy given in 5-Gy fractions twice a week for 4 or 4.5 weeks, respectively); control rats received sham irradiation. Twelve and 52 weeks after whole-brain irradiation, rats were subjected to high-resolution MRI and proton MRS. No apparent lesions or changes in T(1)- or T(2)-weighted images were noted at either time. This is in agreement with no gross changes being found in histological sections from rats 50 weeks postirradiation. Analysis of the MR spectra obtained 12 weeks after fractionated whole-brain irradiation also failed to show any significant differences (P > 0.1) in the concentration of brain metabolites between the whole-brain-irradiated and sham-irradiated rats. In contrast, analysis of the MR spectra obtained 52 weeks postirradiation revealed significant differences between the irradiated and sham-irradiated rats in the concentrations of several brain metabolites, including increases in the NAA/tCr (P < 0.005) and Glx/tCr (P < 0.001) ratios and a decrease in the mI/tCr ratio (P < 0.01). Although the cognitive function of these rats measured by the object recognition test was not significantly different (P > 0.1) between the irradiated and sham-irradiated rats at 14 weeks postirradiation, it was significantly different (P < 0.02) at 54 weeks postirradiation. These findings suggest that MRS may be a sensitive, noninvasive tool to detect changes in radiation-induced brain metabolites that may be associated with the radiation-induced cognitive impairments observed after prolonged fractionated whole-brain irradiation.

Proton T2 relaxation time of J‐coupled cerebral metabolites in rat brain at 9.4 T

Knowledge of proton T2 relaxation time of metabolites is essential for proper quantitation of metabolite concentrations in localized proton spectroscopy, especially at moderate to long TEs. Although the T2 relaxation time of singlets, such as that of creatine and N-acetylaspartate, has been characterized in several studies, similar information is lacking from coupled spin resonances of cerebral metabolites. In this study, the T2 relaxation time of coupled spin resonances and singlet resonances of cerebral metabolites was measured in rat brain in vivo at 9.4 T. Spectra were acquired at 11 TEs using the SPin ECho, full Intensity Acquired Localized (SPECIAL) spectroscopy method. Data analysis was performed in the frequency domain with the LCModel software using simulated TE-specific basis sets. The T2 relaxation times in compounds showing singlet resonances were 113 +/- 3 ms (total creatine), 178 +/- 29 ms (total choline) and 202 +/- 12 ms (N-acetylaspartate). The T2 values of J-coupled metabolites ranged from 89 +/- 8 ms (glutamate) to 148 +/- 14 ms (myo-inositol).

Accumulation of Neurotoxic Thioether Metabolites of 3,4-(±)-Methylenedioxymethamphetamine in Rat Brain

The serotonergic neurotoxicity of 3,4-(+/-)-methylenedioxymethamphetamine (MDMA) appears dependent upon systemic metabolism because direct injection of MDMA into the brain fails to reproduce the neurotoxicity. MDMA is demethylenated to the catechol metabolite N-methyl-alpha-methyldopamine (N-Me-alpha-MeDA). Thioether (glutathione and N-acetylcysteine) metabolites of N-Me-alpha-MeDA are neurotoxic and are present in rat brain following s.c. injection of MDMA. Because multidose administration of MDMA is typical of drug intake during rave parties, the present study was designed to determine the effects of multiple doses of MDMA on the concentration of neurotoxic thioether metabolites in rat brain. Administration of MDMA (20 mg/kg s.c.) at 12-h intervals for a total of four injections led to a significant accumulation of the N-Me-alpha-MeDA thioether metabolites in striatal dialysate. The area under the curve (AUC)(0-300 min) for 5-(glutathion-S-yl)-N-Me-alpha-MeDA increased 33% between the first and fourth injections and essentially doubled for 2,5-bis-(glutathion-S-yl)-N-Me-alpha-MeDA. Likewise, accumulation of the mercapturic acid metabolites was reflected by increases in the AUC(0-300 min) for both 5-(N-acetylcystein-S-yl)-N-Me-alpha-MeDA (35%) and 2,5-bis-(N-acetylcystein-S-yl)-N-Me-alpha-MeDA (85%), probably because processes for their elimination become saturated. Indeed, the elimination half-life of 5-(N-acetylcystein-S-yl)-N-Me-alpha-MeDA and 2,5-bis-(N-acetylcystein-S-yl)-N-Me-alpha-MeDA increased by 53 and 28%, respectively, between the first and third doses. Finally, although the C(max) values for the monothioether conjugates were essentially unchanged after each injection, the values increased by 38 and approximately 50% for 2,5-bis-(glutathion-S-yl)-N-Me-alpha-MeDA and 2,5-bis-(N-acetylcystein-S-yl)-N-Me-alpha-MeDA, respectively, between the first and fourth injections. The data indicate that neurotoxic metabolites of MDMA may accumulate in brain after multiple dosing.