Effects of ethanol on brain monoamine content of spontaneously hypertensive rats (SHR)

Development of a simple and rapid solid phase microextraction-gas chromatography-triple quadrupole mass spectrometry method for the analysis of dopamine, serotonin and norepinephrine in human urine

The work aims at developing a simple and rapid method for the quantification of dopamine (DA), serotonin (5-HT) and norepinephrine (NE) in human urine. The urinary levels of these biogenic amines can be correlated with several pathological conditions concerning heart disease, stress, neurological disorders and cancerous tumors. The proposed analytical approach is based on the use of solid phase microextraction (SPME) combined with gas chromatography-triple quadrupole mass spectrometry (GC-QqQ-MS) after a fast derivatization of both aliphatic amino and phenolic moieties by propyl chloroformate. The variables influencing the derivatization reaction were reliably optimized by the multivariate approach of "Experimental design". The optimal conditions were obtained by performing derivatization with 100μL of propyl chloroformate and 100μL of pyridine. The extraction ability of five commercially available SPME fibers was evaluated in univariate mode and the best results were obtained using the polyacrylate fiber. The variables affecting the efficiency of SPME analysis were again optimized by the multivariate approach of "Experimental design" and, in particular, a central composite design (CCD) was applied. The optimal values were extraction in 45min at room temperature, desorption temperature at 300°C, no addition of NaCl. Assay of derivatized analytes was performed by using a gas chromatography-triple quadrupole mass spectrometry (GC-QqQ-MS) system in selected reaction monitoring (SRM) acquisition. An evaluation of all analytical parameters demonstrates that the developed method provides satisfactory results. Indeed, very good linearities were achieved in the tested calibration range with correlation coefficient values of 0.9995, 0.9999 and 0.9997 for DA, 5-HT and NE, respectively. Accuracies and RSDs calculated for between-run and tested at concentrations of 30, 200, and 800μg L(-1) were in the range from 92.8% to 103.0%, and from 0.67 to 4.5%, respectively. Finally, the LOD values obtained can be considered very good (0.587, 0.381 and 1.23μg L(-1) for DA, 5-HT and NE, respectively).

Enhanced 5-HT(2A) receptors in brain stem and ALDH activity in brain stem and liver: 5-HT(2A) regulation on ALDH in primary hepatocytes cultures in vitro

Brain serotonin (5-HT) modulates the neural effects of ethanol. In the present study, we investigated the changes in 5-HT level, 5-HT(2A) receptor binding and aldehyde dehydrogenase (ALDH) activity in brain stem and liver of ethanol treated rats and 5-HT(2A) regulation on ALDH in hepatocyte cultures in vitro. The 5-HT content in the brain stem and liver significantly decreased with an increased 5-HIAA/5-HT ratio in the ethanol treated rats compared to control. Scatchard analysis of [(3)H] (+/-)2,3-dimethoxyphenyl-1-[2-(-4-piperidine)-methanol] [(3)H] MDL 100907 against ketanserin in brain stem of ethanol treated rats showed a significant increase in B (max) without any change in K (d) compared to control. The competition curve for [(3)H] MDL 100907 against ketanserin fitted one-site model in both control and ethanol treated rats with unity as Hill slope value. A significant increase in V (max) of ALDH activity in liver and a significant decrease in K (m) in liver and brain stem of ethanol treated rats compared to control was observed. In 24 h culture studies, an increase in enzyme activity was observed in cells in medium with 10% ethanol. The elevated ALDH activity in ethanol treated cells was reversed to control level in presence of 10(-5) and 10(-7) M 5-HT. Ketanserin, an antagonist of 5-HT(2A), reversed the effect of 5HT on 10% ethanol induced ALDH activity in hepatocytes. Our results showed that there was a decreased 5-HT content with an enhanced 5-HT(2A) receptor and aldehyde dehydrogenase activity in the brain stem of alcohol treated rats and in vitro hepatocyte cultures. The enhanced ALDH activity in ethanol supplemented hepatocytes was reversed to control level in presence of 10(-5) and 10(-7) M 5-HT.

Liquid chromatography method for detecting native fluorescent bioamines in urine using post-column derivatization and intramolecular FRET detection

Liquid chromatography (LC) with fluorescence detection is described for simultaneous determination of native fluorescent bioamines (indoleamines and catecholamines). This is based on intramolecular fluorescence resonance energy transfer (FRET) in an LC system following post-column derivatization of native fluorescent bioamines' amino groups with o-phthalaldehyde (OPA). OPA fluorescence was achieved through an intramolecular FRET process when the molecules were excited at maximum excitation wavelength of the native fluorescent bioamines. Bioamines separated by reversed-phase LC on ODS column were derivatized with OPA and 2-mercaptoethanol. This method provides sufficient selectivity and sensitivity for the determination of normetanephrine, dopamine, tyrosine, 5-hydroxytryptamine, tryptamine, and tryptophan in healthy human urine without prior sample purification.

Determination of Catecholamines and Indoleamines in Human Urine Based on Intramolecular Excimer-forming Derivatization and Fluorescence Detection

A liquid chromatographic (LC) determination of catecholamines and indoleamines is described. This is based on intramolecular excimer-forming fluorescence derivatization with 4-(1-pyrene)butanoyl chloride, followed by reversed-phase LC. The analytes, containing an amino moiety and phenolic hydroxyl moieties in a molecule, were converted to the corresponding polypyrene-labeled derivatives by one-step derivatization. They afforded intramolecular excimer fluorescence, which can clearly be discriminated from the normal fluorescence emitted from reagent blanks. The detection limits (S/N = 3) for catecholamines and indoleamines were femto-mole levels per 20-microL injection. Furthermore, this method was applied to a urine assay.

Derivatization chemistries for determination of serotonin, norepinephrine and dopamine in brain microdialysis samples by liquid chromatography with fluorescence detection

The present paper provides an overview on currently developed derivatization chemistries and techniques for determination of monoamine neurotransmitters serotonin (5-HT), norepinephrine (NE) and dopamine (DA) in microdialysis samples by microbore liquid chromatography with fluorescence detection. In mild alkaline conditions, 5-hydroxyindoles and catecholamines react with benzylamine (BA), forming highly fluorescent 2-phenyl-4,5-pyrrolobenzoxazoles and 2-phenyl(4,5-dihydropyrrolo) [2,3-f]benzoxazoles, respectively. However, for derivatization of DA a higher fluorescence intensity was achieved for reaction with 1,2-diphenylethylenediamine (DPE) rather than with BA, therefore for simultaneous determination of 5-HT, NE and DA in brain microdialysates, a two-step derivatization with BA followed by DPE was developed. The detection limits for 5-HT, NE and DA were 0.2, 0.08 and 0.13 fmol, respectively, in an injection volume of 20 microL, which corresponds to concentrations of 30, 12 and 19.5 pm, respectively in standard solution prior to derivatization. The experimental data presented demonstrate the ability of the technique to simultaneously monitor neuronally releasable pools of monoamine neurotransmitters in the rat and mouse brains at basal conditions and following pharmacological treatments or physiological stimuli. These techniques play an important role in drug discovery and clinical investigation of psychiatric and neurological diseases such as depression, schizophrenia and Parkinson's disease.

Effect of ethanol on reductions in norepinephrine electrochemical signal in the rostral ventrolateral medulla and hypotension elicited by I1-receptor activation in spontaneously hypertensive rats

BACKGROUND

The mechanism of the antagonistic hemodynamic interaction between ethanol and centrally acting sympatholytics is not known. In this study, we tested the hypothesis that the imidazoline (I1)-receptor modulation of norepinephrine (NE) release within the rostral ventrolateral medulla (RVLM) plays a pivotal role in this clinically relevant hemodynamic interaction. METHOD In anesthetized spontaneously hypertensive rats, the effects of centrally acting sympatholytics on RVLM NE electrochemical signal were investigated by in vivo electrochemistry along with cardiovascular responses in the absence and presence of ethanol. In vivo microdialysis in conscious spontaneously hypertensive rats was used to confirm the electrochemical findings. RESULTS Clonidine (30 microg/kg, intravenously) or rilmenidine (400, 600, or 800 microg/kg) significantly reduced RVLM NE electrochemical signal (index of neuronal activity) and mean arterial pressure; rilmenidine effects were dose-related, and ethanol (1 g/kg) counteracted these responses. Ethanol (1 g/kg) pretreatment increased both RVLM NE electrochemical signal and blood pressure but did not influence the reductions in both variables elicited by subsequently administered clonidine. The alpha2-adrenergic antagonist 2-methoxyidazoxan (30 microg/kg) counteracted rilmenidine (800 microg/kg)-evoked responses. In vivo microdialysis in conscious spontaneously hypertensive rats confirmed the electrochemical findings since clonidine- (30 microg/kg, intravenously) evoked reductions in RVLM NE and the associated hypotension were counteracted by ethanol (1 g/kg). CONCLUSIONS (1) Ethanol counteracts centrally mediated hypotension, at least in part, by increasing RVLM NE; (2) the interaction involves the I1 receptor modulation of RVLM neuronal activity; (3) the alpha2-adrenergic receptor contributes to the electrochemical and cardiovascular effects of high doses of rilmenidine, and (4) the RVLM is a neuroanatomical target for systemically administered ethanol.

Simultaneous determination of 5-hydroxyindoles and catechols by high-performance liquid chromatography with fluorescence detection following derivatization with benzylamine and 1,2-diphenylethylenediamine

A highly selective and sensitive method for the simultaneous determination of 5-hydroxyindoles and catechols (serotonin, norepinephrine, dopamine and related compounds) by high-performance liquid chromatography with fluorescence detection is described. The method is based on the two-step precolumn derivatization of 5-hydroxyindoles and catechols with benzylamine (BA) and 1,2-diphenylethylenediamine (DPE), respectively, resulting in highly fluorescent and stable benzoxazole derivatives. The first derivatization with BA proceeds at room temperature (ca. 23 degrees C) for 2 min in a mixture of 0.3 M 3-cyclohexylamino-1-propanesulfonic acid buffer (pH 10.0) and methanol in the presence of potassium hexacyanoferrate(III). The subsequent second derivatization with DPE is carried out at 50 degrees C for 20 min in the presence of glycine. The resulting fluorescent derivatives of five 5-hydroxyindoles and seven catechols are separated on a reversed-phase column (150 x 1.5 mm I.D., packed with C18 silica, 5 microm) with isocratic elution using a mixture of acetonitrile-15 mM acetate buffer (pH 4.5) (34:66, v/v) containing 1 mM octanesulfonic acid sodium salt, and are detected spectrofluorimetrically at 480 nm with excitation at 345 nm. The detection limits (signal-to-noise ratio of 3) of the related compounds are 80 amol to 86 fmol for a 20-microl injection.

Pharmacological Studies of Alcohol Susceptibility and Brain Monoamine Function in Stroke-Prone Spontaneously Hypertensive Rats (SHRSP) and Stroke-Resistant Spontaneously Hypertensive Rats (SHRSR)

Differences of alcohol drinking behavior, brain dopamine (DA) and serotonin (5-HT) levels and releases in the striatum were investigated in stroke-prone spontaneously hypertensive rats (SHRSP) and age-matched stroke-resistant spontaneously hypertensive rats (SHRSR). Voluntary alcohol (EtOH) consumption in SHRSP rats increased at 1 and 2 hours in the 4 hour time access. In the DA level, SHRSP showed decreases in the caudate-putamen (C/P) and dorsal raphe nucleus (DRN) compared with in SHRSR. 5-HT levels in the C/P, ventral tegmental area-subtantia nigra (V/S) and DRN of the SHRSP were decreased compared with that in SHRSR. The basal extracellular levels of 5-HT release in the C/P were increased in SHRSP as compared with those in SHRSR. K(+)- or EtOH-induced DA and 5-HT releases in the C/P of the SHRSP were a lower magnitude than those in SHRSR. Increased basal extracellular 5-HT releases showing low levels of 5-HT in the C/P of SHRSP mean an abnormality of serotonergic neuronal functions in a normal physiological condition. Higher voluntary alcohol drinking behavior, so called lower susceptibility to EtOH, in the SHRSP may be associated with the degenerated rewarding system including the DRN. These results suggest that the hypertensive state causes the dysfunction in the striatum of the brain rewarding system and induces the risk for increasing alcohol consumption to compensate for the alteration of serotonergic neurons.

Prolonged changes in neurochemistry of dopamine neurones after chronic ethanol consumption

The effects of 3 weeks of chronic ethanol consumption in mice on brain concentrations and turnover of monamine transmitters was examined. The measurements were made at 24 h, 6 days and 2 months after cessation of the ethanol intake to examine changes that might be relevant to relapse drinking. Increases in noradrenaline and dopamine concentrations, and decreases in the ratios of dopamine metabolites to dopamine, were seen in ventral tegmental tissue at 24 h after alcohol consumption. Increased noradrenaline was also evident at the 6-day interval, but no other changes were seen at this time. At the 2-month interval, the ventral tegmentum from ethanol-treated animals showed decreases in metabolite/dopamine ratios. No changes were seen in 5-hydroxytryptamine or its metabolite. In striatal tissue, none of these changes were seen, but at 24 h decreases occurred in the content of dopamine and its metabolites and a decrease in 5-hydroxyindoleacetic acid. The results indicate changes occur in monoamine turnover in the VTA as long as 2 months after cessation of chronic ethanol consumption; such changes may be related to the prolonged nature of alcohol dependence.

Central serotonergic lesions increase voluntary alcohol consumption in Sprague Dawley rats: moderation by long-term ethanol administration

The relationship between central serotonergic activities and voluntary alcohol consumption was studied in Sprague-Dawley rats, which normally have low alcohol preference. After initial screening for an evenly matched baseline alcohol preference, selective central serotonergic lesioning was induced by intracisternal injection of the serotonergic neurotoxin 5,7-dihydroxytryptamine (5,7-DHT). Control rats received injections of vehicle only. Both 5,7-DHT and vehicle-treated rats were further divided into two subgroups, which either had continued free access to ethanol (alcohol-drinking) or were deprived of it (alcohol-free). All rats were then tested again for alcohol preference. All rats were then killed, and the levels of monoamines in the brains were determined by high performance liquid chromatography with electrochemical detection. Behavioral results indicated that all 5,7-DHT-treated rats had significantly higher alcohol preference and consumption than the corresponding sham controls. Except in the cerebellum, the 5,7-DHT-treated rats had significantly lower levels of serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in most brain regions compared with those in the corresponding sham controls. Treatment with 5,7-DHT also resulted in a decrease in serotonin turnover in all brain regions in the alcohol-free rats, except in the cerebellum. In alcohol-drinking rats, however, 5,7-DHT treatment only reduced serotonin turnover in the pons. The levels of norepinephrine and dopamine in several brain regions were not significantly different. Thus, it appeared that in the Sprague Dawley rats, 5,7-DHT treatment depleted 5-HT and 5-HIAA levels in most brain regions while increasing alcohol consumption. Chronic alcohol-drinking attenuated the increase in alcohol consumption associated with serotonergic lesions. Voluntary alcohol consumption seemed more associated with 5-HT turnover than with tissue 5-HT levels. Our data also suggested that tolerance to alcohol-induced hypothermia was primarily attributable to long-term alcohol drinking rather than serotonergic lesioning.