A rapid assay for neurotransmitter amino acids, aspartate, glutamate, glycine, taurine and ?-aminobutyric acid in the brain by high-performance liquid chromatography with electrochemical detection

Simultaneous determination of five amino acid neurotransmitters in rat and porcine blood and brain by two-dimensional liquid chromatography

A method for the simultaneous determination of aspartic acid (Asp), glutamic acid (Glu), glycine (Gly), taurine (Tau) and gamma-aminobutyric acid (GABA) in animal blood and brain by two-dimensional liquid chromatography (2D-LC) combined with ultraviolet detection was established for the first time. First, the amino acid neurotransmitters (AANTs) were labeled on the corresponding fluorescent derivatives with 4-fluoro-7-nitrobenzofurazan (NBD-F), enriched on the extraction column and automatically transferred to the analytical column to achieve on-line extraction and complete separation of the target components. This method exhibited good selectivity, and the correlation coefficients for the analyte calibration curves of were > 0.99. The intra- and inter-day precisions were ≤ 16.03, and the accuracies were in the range of 70.59-116.20%. The system realizes the rapid detection and stability quantification of the five AANTs, which proves that the alternative dilution method is feasible. The results show that the system has high loading capacity, excellent resolution, and good peak shape and is not affected by other endogenous substances. Moreover, the developed method has been successfully applied to the analysis of biological samples in the blood and whole brain of rats and pigs. The content of AANTs in the hippocampus and cortex of rats was higher than that in those of pigs. This method is expected to provide applicability for the determination of AANTs in pharmacological, pharmaceutical and clinical research in nervous science.

Simultaneous determination of thirteen substances related to NAFLD in mouse brain tissue using 3-aminobutyric acid as internal standard by HPLC-FLD

Disorders of certain branched-chain amino acids may be associated with the occurrence and development of non-alcoholic fatty liver disease. Measurement of related branched-chain amino acid levels could provide a reference for the clinical and scientific research of the non-alcoholic fatty liver disease. An established HPLC-FLD method was used to quantify aspartic acid, glutamate, glutamine, glycine, taurine, tyrosine, 4-amino butanoic acid, tryptophan, methionine, valine, phenylalanine, isoleucine and leucine in mouse brain tissue. Brain tissue samples mixed with internal standard (3-aminobutyric acid) were processed, then derivatized with 2-O-phthaldialdehyde, and finally separated on an ODS2 column through gradient elution at a flow rate of 1.0 ml·min^-1 . The excitation and emission wavelengths were set at 340 and 455 nm, respectively. The mobile phase A was 100% methanol and the mobile phase B consisted of 30 mmol·L^-1 sodium acetate (pH 6.8). The injection volume was 20 μl and the single run time was 45 min. Several parameters, accuracy, precision, and stability, were verified and the results showed the established method had good sensitivity and resolution for all of the 13 compounds and internal standard in mouse brain.

Determination of l-glutamic acid and γ-aminobutyric acid in mouse brain tissue utilizing GC-MS/MS

A rapid and selective method for the quantitation of neurotransmitters, l-Glutamic acid (GA) and γ-Aminobutyric acid (GABA), was developed and validated using gas chromatography-tandem mass spectrometry (GC-MS/MS). The novel method utilized a rapid online hot GC inlet gas phase sample derivatization and fast GC low thermal mass technology. The method calibration was linear from 0.5 to 100μg/mL, with limits of detections of 100ng/mL and 250ng/mL for GA and GABA, respectively. The method was used to investigate the effects of deletion of organic anion transporter 1 (Oat1) or Oat3 on murine CNS levels of GA and GABA at 3 and 18 mo of age, as compared to age matched wild-type (WT) animals. Whole brain concentrations of GA were comparable between WT, Oat1^-/-, and Oat3^-/- 18 mo at both 3 and 18 mo of age. Similarly, whole brain concentrations of GABA were not significantly altered in either knockout mouse strain at 3 or 18 mo of age, as compared to WT. These results indicate that the developed GC-MS/MS method provides sufficient sensitivity and selectivity for the quantitation of these neurotransmitters in mouse brain tissue. Furthermore, these results suggest that loss of Oat1 or Oat3 function in isolation does not result in significant alterations in brain tissue levels of GA or GABA.

The effects of chronic administration of ethosuximide on learning and memory: a behavioral and biochemical study on nonepileptic rats

Long-term use of antiepileptic drugs is common in the treatment of epilepsy. Clinical reports exist of cognitive impairment attributed to antiepileptic drugs. Hence, this study evaluates the effect of chronic administration of one antiepileptic drug, ethosuximide, on spatial and fear learning and memory in nonepileptic rats. High performance liquid chromatography with electrochemical detection was used for quantification of glutamate, glycine, taurine, gamma-aminobutyric acid, dopamine, and serotonin in the frontal cortex and hippocampus to elucidate the neurobiological basis of the effect of ethosuximide on learning and memory. We found that 21 days of ethosuximide treatment produced negative effects on fear memory (passive avoidance) at all doses (100, 200 and 250 mg/kg body weight), but had no effect on spatial learning (T-maze). Fear memory impairment was associated with decreased hippocampal dopamine levels. Ethosuximide (at all doses) had a minimal effect on the GABAergic and glutamatergic systems in all brain regions studied, with the exception of elevated levels of gamma-aminobutyric acid in the frontal cortex with the 250 mg/kg body weight dose. We have shown that long-term administration of ethosuximide adversely affects fear memory, but does not affect spatial learning and memory.

Histotypic mouse parietal cortex cultures: Excitation/inhibition ratio and ultrastructural analysis

Primary cultures of mouse parietal cortex, prepared between postnatal day 3 (P3) and P9, were studied using transmission electron microscopy and HPLC of excitatory (aspartate and glutamate) and inhibitory neurotransmitters (glycine, GABA and taurine) to determine their morphological and functional development. Relations between excitation and inhibition (E/I) were contrasted with ultrastructural features over the time course of in vitro development. After 6 days in vitro, cultured parietal cortex neurons prepared from mice at P3 had immature morphological characteristics, whereas P5 cultures showed a more developed histological structure but still with scarce synapses. The acquirement of histotypic characteristics was seen in P7 cultures, which contained numerous symmetric and asymmetric synaptic contacts. On P9, the cultures showed signs of tissue damage. In terms of neurotransmitter levels and E/I ratios, P7 cultures had relatively low E/I ratio as compared with the rest of the cultures prepared before or after P7. These results demonstrated that the development of inhibitory synaptic transmission, as indicated in the fall of E/I ratio, marked the maturation of cerebral cortical tissue and that the critical period to obtain histotypic cultures of mouse parietal cerebral cortex coincides between P5 and P7. This work provides useful information regarding the balance between excitation and inhibition as an indicative parameter for in vitro nerve cell survival, differentiation and maturation and reinforces the great value of histotypic cultures in the study of central nervous system development.

d-Aspartate as a putative cell-cell signaling molecule in theAplysia californicacentral nervous system

The content, synthesis and transport of D-aspartate (D-Asp) in the CNS of Aplysia californica is investigated using capillary electrophoresis (CE) with both laser-induced fluorescence and radionuclide detection. Millimolar concentrations of D-Asp are found in various regions of the CNS. In the cerebral ganglion, three adjacent neuronal clusters have reproducibly different D-Asp levels; for example, in the F- and C-clusters, up to 85% of the free Asp is present in the D-form. Heterogeneous distribution of D-Asp is also found in the individual identified neurons tested, including the optical ganglion top-layer neurons, metacerebral cells, R2 neurons, and F-, C- and G-cluster neurons. The F-cluster neurons have the highest percentage of D-Asp (approximately 58% of the total Asp), whereas the lowest value of approximately 8% is found in R2 neurons. In pulse-chase experiments with radiolabeled D-Asp, followed by CE with radionuclide detection, the synthesis of D-Asp from L-aspartate (L-Asp) is confirmed. Is D-Asp in the soma, or is it transported to distantly located release sites? D-Asp is clearly detected in the major nerves of A. californica, including the pleuroabdominal and cerebrobuccal connectives and the anterior tentacular nerves, suggesting it is transported long distances. In addition, both D-Asp and L-Asp are transported in the pleuroabdominal connectives in a colchicine-dependent manner, whereas several other amino acids are not. Finally, d-Asp produces electrophysiological effects similar to those induced by L-Asp. These data are consistent with an active role for D-Asp in cell-to-cell communication.

Immunohistochemistry as a tool for topographical semi-quantification of neurotransmitters in the brain

Immunohistochemistry is a powerful tool to detect neurotransmitter (NT) presence in different brain structures with a high spatial resolution. However, it is only scarcely used in quantitative approach due to lack of reproducibility and sensitivity. We developed a protocol of NT detection based on immunohistochemistry and image analysis to show that this approach could also be useful to evaluate NT content variations. We focused our study on the GABAergic system in the cerebellum and measured different accurate parameters, namely the optical density (O.D.), the stained area and the number of immunoreactive cells in each cerebellar cell layer. In order to modify the GABA content, we used gamma-vinyl-GABA (GVG), an inhibitor of GABA-transaminase, known to dramatically increase GABA concentration in the central nervous system (CNS) and especially in the cerebellum. We observed a significant increase in the three parameters measured in the molecular and the granular layers of the cerebellum after treatment with GVG, reflecting the well-established increase in GABA content after such a treatment. Therefore, our technical approach allows not only a precise determination of the effects in particular cell layers but also a semi-quantification of GABA content variations. This technique could be suitable for monitoring NT variations following any treatment.

Amino acid neurotransmitters: separation approaches and diagnostic value

Amino acids in the central nervous system can be divided into non-neurotransmitter or neurotransmitter depending on their function. The measurement of these small molecules in brain tissue and extracellular fluid has been used to develop effective treatment strategies for neuropsychiatric and neurodegenerative diseases and for the diagnosis of such pathologies. Here we describe the separation and detection techniques that have been used for the measurement of amino acids at trace levels in brain tissue and dialysates. An overview of the function of amino acid transmitters in the brain is given. In addition, the type of sampling techniques that are used for the determination of amino acid levels in the brain is described.

Increased glutamate, GABA and glutamine in lateral geniculate nucleus but not in medial geniculate nucleus caused by visual attention to novelty

This study is concerned with cortico-thalamic neural mechanisms underlying attentional phenomena. Previous results from this laboratory demonstrated that the visual sector of the GABAergic thalamic reticular nucleus is selectively c-fos activated in rats that are naturally paying attention to features of a novel-complex environment, and that this activation is dependent on top-down glutamatergic inputs from the primary visual cortex. By contrast, the acoustic sector of the thalamic reticular nucleus is not activated despite noise generated by exploration and c-fos activation of brainstem acoustic centers (e.g. dorsal cochlear nucleus, inferior colliculus). A prediction of these results is that the levels of the neurotransmitters glutamate and GABA, and the glutamate-related amino acid glutamine, will be increased in the lateral geniculate nucleus (LGN), but not in the medial geniculate nucleus (MGN) of rats that explore a novel-complex environment in comparison to levels of these amino acids in control rats. By means of neurochemical analysis of these amino acids (HPLC) the results of this study confirmed this prediction. The results are consistent with the previously proposed 'focal attention' hypothesis postulating that a focus of attention in the primary visual cortex generates top-down center-surround facilitatory-inhibitory effects on geniculocortical transmission via corticoreticulogeniculate pathways. The results also supports the notion that a main function of corticothalamic pathways to relay thalamic nuclei is attention-dependent modulation of thalamocortical transmission.

An improved method for assaying phosphocholine and glycerophosphocholine in mouse tissue

INTRODUCTION

To measure the levels of phosphocholine (PCh) and glycerophosphocholine (GPCh) in the tissues and organs of mice, we developed a simple and rapid method using high-performance liquid chromatography (HPLC) with electrochemical detection (ECD) and an immobilized enzyme column.

METHODS

Under our modifications of the separation procedure of Klein et al. [Neurochem. Int. 2 (1993) 293], PCh and GPCh in the hydrophilic phase of the homogenate samples were selectively hydrolyzed into free choline by alkaline phosphatase and a 0.4-N perchloric acid solution, respectively, and the resulting hydrolyzed mixtures were directly injected into the HPLC system for analysis.

RESULTS

The present method permits PCh or GPCh assay within 5 min in one chromatographic run. Recoveries from tissue samples were 97% for PCh and 101% for GPCh. The percentages of the crossover reaction to the authentic PCh and GPCh were 0.4% and 3.8%, respectively. The within-run coefficients of variation for choline derived from PCh and GPCh in the tissue samples were 1.2% and 1.4%, respectively.

DISCUSSION

The method is effective and has been applied to the measurement of PCh and GPCh levels in several tissues of mice.

Effects of radiofrequency exposure on the GABAergic system in the rat cerebellum: clues from semi-quantitative immunohistochemistry

The widespread use of cellular phones raises the problem of interaction of electromagnetic fields with the central nervous system (CNS). In order to measure these effects on neurotransmitter content in the CNS, we developed a protocol of neurotransmitter detection based on immunohistochemistry and image analysis. Gamma-vinyl-GABA (GVG), an inhibitor of the GABA-transaminase was injected in rats to increase GABA concentration in the CNS. The cellular GABA contents were then revealed by immunohistochemistry and semi-quantified by image analysis thanks to three parameters: optical density (O.D.), staining area, and number of positive cells. The increase in cerebellar GABA content induced by GVG 1200 mg/kg was reflected in these three parameters in the molecular and the granular layers. Therefore, control of immunohistochemistry parameters, together with appropriate image analysis, allowed both the location and the detection of variations in cellular neurotransmitter content. This protocol was used to investigate the effects of exposure to 900 MHz radiofrequencies on cerebellar GABA content. Both pulsed emission with a specific absorption rate (SAR) of 4 W/kg and continuous emission with high SAR (32 W/kg) were tested. We observed a selective diminution of the stained processes area in the Purkinje cell layer after exposure to pulsed radiofrequency and, in addition, a decrease in O.D. in the three cell layers after exposure to continuous waves. Whether this effect is, at least partly, due to a local heating of the tissues is not known. Overall, it appears that high energetic radiofrequency exposure induces a diminution in cellular GABA content in the cerebellum.

Rapid and sensitive step gradient assays of glutamate, glycine, taurine and gamma-aminobutyric acid by high-performance liquid chromatography-fluorescence detection with o-phthalaldehyde-mercaptoethanol derivatization with an emphasis on microdialysis samples

We developed a rapid step-gradient HPLC method for determination of glutamate, glycine and taurine, and a separate method for determination of gamma-aminobutyric acid (GABA) in striatal microdialysates. The amino acids were pre-column derivatized with o-phthalaldehyde-2-mercaptoethanol by using an automated refrigerated autoinjector. Separation of the amino acids was established with a non-porous ODS-II HPLC column, late-eluting substances were washed out with a one-step low-pressure gradient. Concentrations of the amino acids were determined with a fixed-wavelength fluorescence detector. The detection limit for GABA was 80 fmol in a 15 microl sample, detection limits for glutamate, glycine and taurine were not determined because their concentrations in striatal perfusates were far above their detection limits. Total analysis time was less than 12 min, including the wash-out step. The methods described are relatively simple, sensitive, inexpensive, and fast enough to keep up with the microdialysis sampling.

Simultaneous determination of basal and evoked output levels of aspartate, glutamate, taurine and 4-aminobutyric acid during microdialysis and from superfused brain slices

A HPLC method, involving pre-column derivatisation with o-phthalaldehyde and fluorescence detection, is described. It allows the resolution of aspartate, glutamate, taurine and GABA, in a single run with detection limits of 3.2, 1.7, 1.4 and 2 fmol/microl of perfusate, respectively. It is sufficiently sensitive and rapid (15 min) for the determination "on line" of the four amino acids in perfusates obtained during in vivo microdialysis experiments. The procedure has been used to determine basal, K+ - or veratridine-stimulated release of these amino acids in different brain areas during microdialysis and from perfused tissue slices.

Levels of monoamine and amino acid neurotransmitters in the developing male mouse hypothalamus and in histotypic hypothalamic cultures

The variation in the levels of the monoamine and amino acid neurotransmitters was studied during the period of neurogenesis in male mouse hypothalamus, from embryonic day 15 until the age of young adult. The results shown in this study demonstrate that the monoamines appear early in the fetal brain and that the maximum expression of the catecholaminergic system, particularly that of dopamine, occurs during the late neonatal period or mouse infancy, when the role played by the catecholamines on the maturation of the neurosecretory systems is more significant. In relation to the amino acid neurotransmitters, glutamate and taurine seem to be the principal transmitters of the hypothalamus since their concentrations were about five-tenfold higher than the levels of glycine and GABA. Both amino acids had the same pattern of variation during development, showing elevated values during the prenatal, late neonatal and early pubertal period. Increased concentrations of the inhibitory neurotransmitter GABA were observed on the day before birth, at the end of the neonatal period and throughout the prepubertal period, suggesting that the influence of GABA on hypothalamic neurogenesis increases by the time when the hypothalamic nuclei have reached maturity and the local circuits have been established. To determine the intrinsic neurotransmitter production, primary hypothalamic histotypic cultures prepared from mice at postnatal days 8-10 were analyzed for their content of neurotransmitters. The in vitro analysis revealed that the hypothalamic neurons intrinsically produce dopamine, glutamate, taurine and glycine in homologable amounts with those of young adult animals. The comparative analysis also showed that about 50% of the GABA content and less than 5% of the hypothalamic epinephrine level are locally produced, while serotonin comes mainly from extrinsically located neurons.

Granule cell disinhibition in dentate gyrus of genetically seizure susceptible El mice

Paired-pulse inhibition was investigated electrophysiologically in the dentate gyrus using hippocampal slices from epileptic El mice. At short interpulse intervals (IPIs), the inhibition was 30% in the El, and 90% in the control ddY mice at the ages of 10 and 15 weeks. No difference in inhibition was observed at the age of 5 weeks. Bicuculline, a GABAA receptor antagonists, attenuated the inhibition during short IPIs n the ddY mice, while in the El mice, phenobarbital and flunitrazepam, which enhance GABAA receptor function, restored the inhibitory activity comparable to that of the ddY. The disinhibition progressed with growth, closely correlating with seizure development in El mice. These results suggest that decrease in the GABAergic inhibition occurs in the dentate gyrus of the El mice with growth. GABA concentration in the hippocampus was also quantified using HPLC. In El mice, GABA level was significantly lower than that in ddY mice at the ages of 5 and 15 weeks. Thus, the disinhibition observed in the El dentate gyrus at 15 weeks of age does not appear to be directly related to the content of GABA. GABAergic disinhibition suggests possible loss of unknown inhibition control factor(s) in the El dentate gyrus as growth progresses. The growth-dependent disinhibition in the granule cells may be prerequisite for epileptogenesis in El mice.

Duration-dependent increase in striatal glutamate following prolonged fluphenazine administration in rats

Chronic neuroleptic administration has been shown to selectively increase striatal extracellular glutamate concentration. In the current study, age-matched female rats were administered chronic oral fluphenazime or no drug via their drinking water for 3 or 32 weeks. Microdialysis probes were inserted into the ventrolateral caudate putamen and the medial nucleus accumbens and dialysis samples were analyzed for glutamate and gamma-aminobutyric acid (GABA) concentrations Glutamate levels were significantly increased only in the ventrolateral caudate putamen after 32 weeks. No significant effects were seen for GABA levels. Neuroleptic-induced enhancement of striatal glutamate levels thus appears to increase with chronic exposure and this increase may relate to late onset motor side effects.

Blood-brain barrier taurine transport during osmotic stress and in focal cerebral ischemia

Little is known about blood to brain taurine transport despite substantial evidence suggesting a role of taurine in brain volume regulation during osmotic stress or conditions inducing cell swelling, such as ischemia. We have made measurements of the taurine influx rate constant (K1) with [3H]taurine in three conditions: raised plasma taurine concentrations induced by infusion with 50 mM taurine (10 microliters/100 g/min); osmotic stress induced by i.p. injections of 1.5 M NaCl (2 ml/100 g) or distilled water (10 ml/100 g); and 4 h of middle cerebral artery occlusion (MCAo). In rats with MCAo, additional determinations were made of tissue water and taurine contents, and blood-brain barrier passive permeability with [3H]alpha-aminoisobutyric acid. Taurine infusion increased plasma taurine from 110 +/- 63 microM (SD) to 407 +/- 63 (p < 0.001) and decreased taurine K1 at the blood-brain barrier by 70% (p < 0.001), signifying saturable uptake that maintained unidirectional influx constant. Similarly, although hypo- and hyperosmolality increased and decreased plasma taurine concentration, respectively, a reciprocal relationship between K1 and plasma taurine in these experiments ensured that unidirectional fluxes of taurine into brain were unchanged by osmotic stress. During MCAo, the taurine K1 was reduced 80% in the ipsilateral ischemic tissue compared with the contralateral nonischemic tissue (p < 0.001). This decline may be due to a release of taurine into the brain circulation, because there was a concomitant loss of tissue taurine of 7.4 +/- 2.4 mmol/g dry weight (p < 0.05). Alternately, if taurine uptake is sodium dependent, the decline might reflect a disruption of the endothelial sodium gradient.

The analysis of excitatory, inhibitory and other amino acids in rat brain microdialysates using microbore liquid chromatography

Three microbore liquid chromatography (LC) assays for determination of amino acids in rat brain dialysates are described: one for separation of amino acids by gradient elution and electrochemical detection, one for analysis of GABA by isocratic elution and electrochemical detection, and one for fast measurement of glutamate and aspartate by gradient elution and fluorescence detection. The assays are reliable, reproducible and sensitive. In comparison with conventional LC, a 5-fold increase in sensitivity was obtained for GABA. Optimization of the derivatization chemistry and the microbore LC system are discussed, as well as important practical aspects.

Rapid HPLC assay with coulometric detection for norepinephrine and 3-methoxy-4-hydroxyphenylglycol in the mouse brain

For the rapid assay of norepinephrine (NE) and its major metabolite, 3-methoxy-4-hydroxyphenylglycol (MHPG) in the mouse brain, we developed a simple method using isocratic HPLC with coulometric detection. This method permits NE and MHPG assay within 5 min in one chromatographic run. Within-run coefficients of variation for NE and MHPG in the working standard solution were 0.8% and 0.6% (n = 50), respectively. The detector responses were linear from 0.025 to 100 pmol for NE and from 0.05 to 100 pmol for MHPG in the working standard solution. Using this method, the NE and MHPG concentrations were measured in discrete brain areas of the mouse prior treatment with or without alpha-methyl-p-tyrosine or N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4).

Excitatory and inhibitory amino acids in the cerebral cortex of nucleus basalis magnocellularis lesioned rats

It is well known that pathways arising from the nucleus basalis magnocellularis in the basal forebrain which terminate in the cerebral cortex are involved in cognitive function. The cholinergic system is generally thought to play a large part in these processes from lesion, pharmacological and transplantation studies. With increasing evidence suggesting the involvement of amino acid transmitters in learning and memory processes, it is of interest to also evaluate possible changes in the levels of amino acid transmitters in the cortex of nucleus basalis magnocellularis-lesioned rats. In the present study, 9 cortical amino acids were measured in rats with bilateral lesions of the nucleus basalis magnocellularis. We measured significant reductions in aspartate, alanine and gamma-aminobutyric acid; these were 80%, 75%, and 81%, respectively, of control brain values. These results suggest that changes in the amino acid content of the cerebral cortex following lesion of the nucleus basalis magnocellularis-lesioned rat should perhaps also be considered when evaluating behavioral effects in this model.

Reversal by 3,3?,5-triido-l-thyronine of the working memory deficit, and the decrease in acetylcholine, glutamate and ?-aminobutyric acid induced by ethylcholine aziridinium ion in mice

The effect of 3,3',5-triiodo-L-thyronine (T3) on working memory in ethylcholine aziridinium ion (AF64A)-treated mice was studied in a delayed non-matching to sample task using a T-maze. After behavioural testing was completed, mice were killed by microwave irradiation and regional brain levels of acetylcholine, aspartate, glutamate, glutamine, glycine, taurine, and gamma-aminobutyric acid (GABA) were measured by high-performance liquid chromatography with electrochemical detection. Treatment with AF64A (7 nmol, i.c.v.) produced a deficit in working memory performance in the non-matching to sample task at 30 s delay, and decreased acetylcholine, glutamate, and GABA levels in the hippocampus, but not in the septum and cerebral cortex. Administration of T3 (0.3 mg/kg, p.o., once daily for 6 days) to AF64A-treated animals improved the deficit in working memory performance and reversed the decrease in acetylcholine, glutamate, and GABA levels in the hippocampus. These results indicate that the deficit in performance induced by AF64A can be improved by T3 administration.