Preparation of an optimum mobile phase for the simultaneous determination of neurochemicals in mouse brain tissues by high-performance liquid chromatography with electrochemical detection

Octopamine cyclic release and its modulation of visual sensitivity in crayfish

The biogenic amine octopamine (OA) modulates invertebrate behavior by changing neuronal responses from sensory inputs to motor outputs. However, the OA modulation of visual sensitivity and its possible coupling to diurnal cycles remains unexplored. Here we studied the diurnal variations in the OA levels in the hemolymph of the crayfish Procambarus clarkii, its release from the structures in the eyestalk and its modulation of the retinal light sensitivity. The hemolymph concentration of OA and its amino acid precursor tyrosine was measured by high-resolution liquid chromatography; OA varied along the 24-hcycle. The peak value appeared about 2h before the light offset which preceded the peak locomotor activity. OA was found in every structure of the eyestalk but displayed higher levels in the retina-lamina ganglionaris. Moreover, OA was released from isolated eyestalks at a rate of 92nmol/eyestalk/min and a calcium-dependent release was evoked by incubation in a high potassium solution. OA injected into dark-adapted crayfish or applied to the isolated retina at concentrations of 1, 10 and 100μM produced a proportionally increasing reduction in the amplitude of the photoreceptor light responses. These OA concentrations did not affect the position of the visual accessory pigments. Our results suggest that OA release in the crayfish eyestalk is coupled to the 24-hcycle to regulate the diurnal reduction of the photoreceptor sensitivity and to favor the expression of exploratory locomotion during the dark phase of the circadian cycle.

Chemiluminescence of synephrine based on the cerium(IV)–rhodamine B system

A new chemiluminescence (CL) method is described for the determination of synephrine. It is based on the reaction between synephrine and Ce(IV) in a nitric acid medium and measurement of the CL intensity produced by rhodamine B used as a luminophore, similar to luminol or lucigenin in basic media, instead of as a sensitizer. In the optimum conditions, the increase of CL intensity was correlated with synephrine concentration over the range 5.0 x 10(-9)-1.0 x 10(-6) g/mL with a detection limit of 1.0 x 10(-9) g/mL. The relative standard deviation (RSD) was 2.9% for 1.0 x 10(-7) g/mL synephrine (n = 11). The method was applied to the determination of a drug in herbal products, citrus fruit and biological samples, with satisfactory results. The results given by the proposed method are in good agreement with those given by HPLC-UV and UV spectrophotometry.

Determination of octopamine, synephrine and tyramine in Citrus herbs by ionic liquid improved ‘green’ chromatography

Without adding any volatile organic solvents, aqueous solutions of room temperature ionic liquids (RTILs) were used as 'green' mobile phases to determine octopamine, synephrine and tyramine by liquid chromatography. The problems of the adrenergic amines separation, such as band tailing, low retention and low resolution were solved successfully by using RTIL. The effect of 1-ethyl-3-methylimidazolium tertafluoroborate ([EMIM][BF4]) was the best in the six investigated RTILs. The concentration of [EMIM][BF4], mobile phase pH and column temperature, which influenced the chromatographic behaviors of the analytes, were investigated in detail. The change of retention factors caused by pH shift was obviously suppressed by [EMIM][BF4]. The sensitivity, accuracy and repeatability of this method were found to be satisfactory. The contents of adrenergic amines in several Citrus herbs and extracts, such as Fructus aurantii immaturus, were simultaneously determined by this 'green' chromatographic method.

Sensitive determination of synephrine by flow-injection chemiluminescence

It was found that light emission produced by the oxidation of luminol by potassium ferricyanide in basic medium was enhanced by synephrine, an anti-obesity drug. The optimum conditions for this chemiluminescent reaction were studied in detail in a flow injection system and employed in a new, simple and rapid method for the determination of synephrine. A mechanism for this reaction is proposed, based on the chemiluminescence reaction spectra. In the optimum conditions, CL intensity is proportional to concentration of synephrine in the 0.008-1 microg/mL range. The limit of detection is 1.6 ng/mL for synephrine (3sigma), and the relative standard deviation (n = 11) is 2.6% for 0.5 microg/mL synephrine. The method was applied to the determination of synephrine in herbal products, citrus fruit and biological fluids. The recoveries were satisfactory (90-102%). The results given by the proposed method are in good agreement with those given by HPLC-UV.

Methods for measuring DNA adducts and abasic sites II: methods for measurement of DNA adducts

This unit contains protocols for analyzing DNA adducts separated from the DNA backbone. HPLC is used to quantify total guanine or ribo- or deoxynucleotides as well as methods for analyzing specific adducts. These methods include HPLC with electrochemical detection, immunoaffininty chromatography to enrich for specific adducts, and gas and liquid chromatography in combination with HPLC and mass spectrometry.

Determination of adrenergic agonists from extracts and herbal products of Citrus aurantium L. var. amara by LC

The purpose of this study was to set up a HPLC method to separate adrenergic amines (dl-octopamine, dl-synephrine and tyramine) and to determine their content in fruits, extracts and herbal products of Citrus aurantium L. var. amara. A rapid method for the quantitative analysis of these amines is described, based on their separation by RP-HPLC technique with UV detection. The analysis were conducted on a Lichrospher RP-18 column at room temperature, using a mobile phase consisting of 0.02 M citric acid-0.02 M NaH2PO4 (7:3 v/v) and adjusted to a final pH of 3. The detection was at 220 nm. Since some of these amines are chiral compounds and their enantiomers showed different pharmacological activity, the direct separation of synephrine enantiomers was carried out with HPLC on a beta-cyclodextrin stationary phase. The mobile phase consisted of methanol-NaH2PO4 25 mM pH 3.5 (20:80 v/v) and tetrabutylammonium hydrogen sulfate 10 mM in ratio of 30:70 v/v in isocratic condition and the detection was at 220 nm. The two proposed methods were applied to the analysis of fruits, extracts and herbal products of C. aurantium L. var. amara. Taking into account that some authors have reported that l-synephrine may be converted into its d-form by high temperature, this optical isomerization was monitored by the same HPLC method used for the separation of enantiomers.

Monoamines in the albumen gland, plasma, and central nervous system of the snail Biomphalaria glabrata during egg-laying

The potential role of selected biogenic monoamines and related compounds in the reproductive physiology of the freshwater snail Biomphalaria glabrata was investigated. Extracts of the albumen gland (AG), plasma, and central nervous system (CNS) were subjected to high pressure liquid chromatography with electrochemical detection (HPLC-ED), and under the extraction and separation conditions employed the following amines were detected: tyrosine, dihydroxyphenylalanine (DOPA), dopamine, and tryptophan in the AG; DOPA, tyrosine, and tryptophan in the plasma; DOPA, tyrosine, dopamine and 5-hydroxytryptamine in the CNS. These compounds were then quantified in individual samples taken from snails known to be in a particular stage of the egg-laying process. AG dopamine levels were highest in snails in the first stage of the reproductive process, when the AG is secreting perivitelline fluid around each fertilized ovum. Significant decreases in AG protein content during the later stages of the egg-laying process were also evident. Plasma tyrosine and DOPA levels were lowest in snails that contained a fully packaged egg mass, while no changes in monoamine content were observed in the CNS. These data provide insights into the role(s) that monoamines, especially catecholamine-related compounds, may play in B. glabrata reproductive physiology.

Reversed-phase high-performance liquid chromatography of catecholamines and indoleamines using a simple gradient solvent system and native fluorescence detection

A reversed-phase HPLC method using a C18 column and a two-mobile-phase gradient elution system containing only volatile components has been developed for separation of norepinephrine, octopamine, epinephrine, dopamine, dihydroxyphenylalanine, tyramine, tyrosine, serotonin, 5-hydroxytryptophan, N-acetyl-serotonin and tryptophan. Mobile phase A contains 0.05% aqueous trifluoroacetic acid and methanol (97.5:2.5, v/v) and mobile phase B contains 0.05% aqueous trifluoracetic acid and methanol (40:60, v/v). This method has the advantage that the mobile phase can be removed completely, without salt residues, from the eluted fractions thus simplifying further analytical procedures on isolated fractions. The elution profile of standards is related to structural characteristics allowing prediction of retention times of known compounds and insight into possible structural characteristics of unknown components in a mixture. Detection is via native fluorescence using excitation at 220 nm and emission at 320 nm and under the conditions described has a sensitivity range from 2.5 to 25 pmol, although the sensitivity range can be extended depending on the emission wavelength used.

Simultaneous measurement of dopamine, serotonin, their metabolites and tryptophan in mouse brain homogenates by high-performance liquid chromatography with dual coulometric detection

A new rapid and sensitive high-performance liquid chromatography (HPLC) method for the simultaneous determination of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC), 3-methoxytyramine, 5-hydroxytryptamine (serotonin), 5-hydroxyindoleacetic acid (5-HIAA), homovanillic acid and tryptophan has been developed and applied to mouse frontal cortex, caudate nucleus and dorsal raphe assays. A dual coulometric detector was used with detection at +0.25 and +0.55 V, which allowed the determination of tryptophan. Detection limits for all compounds (0.8-9.0 pg per injection, depending on the compounds) were useful for this application. Owing to great sensitivity of the method, the brain tissue samples can be very small, less than 2 mg. Linearity of standards was excellent (r > 0.999 in all cases). Intraday and interday precisions for samples analytes were generally acceptable (intraday assay CV < 8.7% and interday assay CV < 7.0% except for DOPAC and 5-HIAA, which was 11.4% for the low concentrations). Average recoveries of standard additions to sample analytes were > 90%. Attention was paid to stability of standard and sample analytes when stored at +4 degrees C or at -70 degrees C with two different homogenizing agents (0.1 M HClO4 with 10(-7) M ascorbic acid and 0.05 M HClO4 without ascorbic acid). This simple, rapid and efficient method can be used as a basic research tool for modification of brain neurotransmitters in experimental pharmacological protocols for following psychotropic drug treatments in animals.

An isocratic assay for norepinephrine, dopamine, and 5-hydroxytryptamine using their native fluorescence by high-performance liquid chromatography with fluorescence detection in discrete brain areas of rat

A rapid and simple isocratic chromatographic procedure for simultaneous determination of norepinephrine (NE), dopamine (DA), and 5-hydroxytryptamine (5-HT) using their native fluorescence by high-performance liquid chromatography coupled to fluorescence detection (HPLC-FD) is described. Since the present procedure does not involve sample prepurification, the recovery of monoamines was more than 97% (n = 12) and within a given run, coefficient of variation was less than 3.1% (n = 12). Accordingly, use of an internal standard is not mandatory. In a single chromatographic run, levels of NE, DA, and 5-HT can be determined in less than 30 min. The minimum concentration of monoamines which could be detected by this method was found to be 250 pg for NE and DA and 100 pg for 5-HT. The validity of the method was confirmed by the estimation of levels of monoamines in the hypothalamus and striatum of rat brain following treatment with clorgyline, a monoamine oxidase inhibitor.

Competitive enzyme immunoassay with monoclonal antibody for homovanillic acid measurement in human urine samples

A fast competitive enzyme immunoassay (EIA) for measuring homovanillic acid in human urine samples was developed with a monoclonal antibody and acetylcholinesterase as enzyme label. Enzyme detection was performed by an easy colorimetric assay. Monoclonal antibodies were screened on the basis of sensitivity, specificity, and correlation studies. EIA has a detection limit of 0.5 μmol/L, a CV &lt;10% in the 1.25–10 μmol/L range, and intra- and interassay CVs of &lt;10%. Cross-reactivity with vanillylmandelic acid was 0.5% and &lt;8% for other structurally related catecholamine metabolites. Parallelism of the EIA was shown in dilution studies and the correlation with routine HPLC assay in 62 normal and pathologic samples was EIA = 1.492 (HPLC) − 3.46, Sy|x = 47.52, range = 4–1800 μmol/L, r2 = 0.977. Additional data concerning the validity of this assay were provided by HPLC analysis of urinary immunoreactive material.

Fetal alcohol syndrome: early olfactory learning as a model system to study neurobehavioral deficits

The goal of basic research examining the deficits underlying fetal alcohol syndrome is to develop an animal model which allows investigation and assessment of the neural and cognitive impairments resulting from prenatal alcohol exposure. The following review focuses on animal models and their relationship to human deficits following prenatal alcohol exposure. In addition, this review examines a unique, well-established model system which may permit an increased understanding of the role of alcohol on the developing brain and cognitive behavior. Specifically, large metabolic, neurochemical, neuropharmacological, morphological and neurophysiological changes in young rats have been reported as a consequence of early olfactory preference conditioning, a form of learning that normally occurs during both human and rat development. This olfactory odor preference training paradigm can be used to assess changes in learning as well as the neural substrates underlying this learning. Olfactory preference training has been used to examine: 1) learning, as demonstrated by a behavioral preference for an odor previously paired with stimulation which mimics maternal care; 2) metabolism, by measuring 2-deoxyglucose uptake and distribution in response to the trained odor; 3) neurotransmitter levels, by using in vivo microdialysis, to examine changes in neurotransmitter levels in the olfactory bulb in response to a trained odor. Using in vivo microdialysis enables measurement of both baseline responsiveness of alcohol-exposed pups as well as learned responses at several different developmental ages. The established neural features of this olfactory model include an increase in behavioral preference for a trained odor, increases in 2-DG uptake in specific foci within the olfactory bulb in response to the odor, and increases in dopamine in response to olfactory preference training stimuli, as well as conditioned increases in norepinephrine following olfactory preference training. Using these known behavioral, metabolic and neurochemical indices in control pups allows identification of some of the neurotransmitter systems involved in deficits and the neurobiological basis for impairments induced by prenatal alcohol exposure.