A method for concurrent measurement of picomole quantities of acetylcholine, choline, dopamine, norepinephrine, serotonin, 5-hydroxytryptophan, 5-hydroxyindoleacetic acid, tryptophan, tyrosine, glycine, aspartate, glutamate, alanine, and gamma-aminobutyric acid in single tissue samples from different areas of rat central nervous system

Simultaneous measurement of tyrosine, tryptophan and related monoamines for determination of neurotransmitter turnover in discrete rat brain regions by liquid chromatography with electrochemical detection

Concomitant measurement of monoamine neurotransmitter turnover in discrete rat brain areas with the use of radiolabeled amino acid precursors permits simultaneous evaluation of interacting transmitter systems. [3H]Tyrosine and [3H]tryptophan were administered via indwelling catheters to unrestrained rats. Content and specific activity of norepinephrine, dopamine, 5-hydroxytryptamine, and the metabolites dihydroxyphenylacetic acid, homovanillic acid, and 5-hydroxyindoleacetic acid in addition to tyrosine and tryptophan were quantified by liquid chromatography with electrochemical detection and liquid scintillation counting. The method employs a simple extraction procedure without prior cleanup for chromatography. Neurotransmitter turnover rates that incorporated tyrosine- or tryptophan-specific activities were found to be two to four times greater than those that did not include them.

Chromatographic analysis of glutamic acid decarboxylase in biological samples

A number of non-chromatographic and chromatographic methods for analysis of GAD activity in biological tissues have been described. The majority of these chromatographic methods utilize the analysis of GABA formed from incubation homogenates. Depending upon the analytical technique selected, limits of detection range from nanogram to picogram levels of GABA. Also discussed have been some of the commonly associated problems and their resolution with sample collection, postmortem changes and alternative pathways of CO2 and GABA production which can lead to errors in accurate determination of GAD activity in biological samples.

Effects of acrylamide on locomotion and central monoamine function in the rat

Male rats receiving acrylamide (ACR) in their drinking water (100 ppm) for a six-week period displayed increased psychomotor stimulation to d-amphetamine (d-A; 1.0 mg/kg SC) under several conditions of handling and drug administration. Following behavioral tests a subset of the animals was sacrificed at 15, 50, 80 and 120 minutes following d-A and the brains removed and dissected for determinations of regional brain levels of several monoamine neurotransmitters and metabolites. ACR rats had elevated levels of 5-hydroxyindoleacetic acid (5-HIAA) in the striatum, septal area, and thalamus. The effect was most pronounced at 15 minutes post-drug with ACR rats not demonstrating a depression in 5-HIAA levels present in controls. Increases in accumben's dopamine and norepinephrine levels, evident after d-A, were of lesser magnitude in ACR-exposed rats. Decreases in dihydroxyphenylacetic acid and homovanillic acid, also evident after d-A, persisted for a longer duration in ACR-exposed rats. Light and electron microscopy of spinal cord, striatum, nucleus accumbens and thalamus did not reveal morphologic abnormalities. Sciatic nerves showed histopathological changes characteristic of multi-focal dying-back peripheral nerve degeneration. It was concluded that acrylamide's effect on the psychomotor stimulant properties of d-A may be related to changes in a serotonergic inhibitory system.

Etomidate inhibits prolactin release but not through a dopaminergic mechanism

A short-acting non-barbiturate intravenous general anaesthetic, etomidate, when administered i.v. lowered serum prolactin levels in the rat. The effect was evident at rest, after surgical stress or after injection of 5-hydroxytryptophan. Haloperidol-induced hyperprolactinaemia was not modified. Administered via the intracerebroventricular route, etomidate strongly reduced serum prolactin levels in unanesthetized rats. Studies performed on superfused synaptosomes from brain areas rich in dopaminergic nerve endings did not show any influence of the etomidate, 10(-7) M-10(-6) M, on [3H]dopamine release. A peculiar GABA-like mechanism and/or possible interplay with serotonergic control of the prolactin release may be postulated in order to explain the suppressive effects of the drug on secretion of lactotrophs.

The regulation of 5-hydroxytryptamine release from superfused synaptosomes by 5-hydroxytryptamine and its immediate precursors

The effect of L-tryptophan, 5-hydroxy-L-tryptophan (5-HTP), and 5-hydroxytryptamine (5-HT) on the K+-evoked release of [3H]5-HT from superfused rat brain synaptosomes was studied. 5-HT at concentrations above 10 nM significantly inhibited the K+-evoked release of [3H]5-HT. A slight enhancement of [3H]5-HT release was observed at a concentration of 5nM. In contrast tryptophan at a concentration of 10 nM significantly enhanced [3H]5-HT release with little effect at higher concentrations. 5-HTP did not significantly effect [3H]5-HT release. The results confirm previous findings that 5-HT inhibits its own release from nerve endings, and demonstrate that low concentrations of tryptophan in the synaptic region may act as a positive feedback regulator of 5-HT release.

Effect of a stereospecific D2-dopamine agonist on acetylcholine concentration in corpus striatum of rat brain

The enantiomers of LY141865, trans(+/-)-4,4a,5,6,7,8a,9-octahydro-5-propyl-2H-pyrazolo[3,4-g]qu inoline, were compared as dopamine D2 agonists by determining their abilities to elevate acetylcholine concentrations in rat corpus striatum. The levorotatory isomer, LY156258, increased striatal acetylcholine concentration at doses of 0.1-1 mg/kg i.p., whereas the dextrorotatory isomer had no effect even at doses as high as 30 mg/kg. The levorotatory isomer also decreased striatal concentrations of the dopamine metabolites, 3,4-dihydroxyphenylacetic acid and homovanillic acid, but did not significantly alter dopamine or 5-hydroxyindoleacetic acid concentration. The dextrorotatory isomer had no effect on any of these substances alone and did not alter the effects of the levorotatory isomer. The elevation of striatal acetylcholine levels by LY156258 was mimicked by pergolide, a dopamine agonist, and was totally prevented by pretreatment with haloperidol, a dopamine antagonist. The elevation of striatal acetylcholine concentration by LY157258 was maximal at 0.5 hour and declined thereafter, following a time course similar to that of pergolide. Neither LY141865 nor LY156258 shared with peroglide and dopamine the ability to activate striatal adenylate cyclase in vitro, an effect mediated by D1 receptors. LY141865 and LY156258 (but not the dextrorotatory isomer) inhibited the binding of tritiated apomorphine and spiperone to striatal membrane receptors, but were not as potent as pergolide, they also had less effect, or no effect, on the binding of other tritiated ligands (dopamine, WB4101, clonidine, dihydroalprenolol, pyrilamine or quinuclidinyl benzilate) to their membrane receptors. These results indicate that LY156258 stereospecifically activates dopamine D2 receptors and the studies are the first evidence of sterospecificity of dopamine receptors mediating an increase in striatal acetylcholine concentration.

Biogenic amine levels in the mid-term human fetus

Spectrophotofluorometric assays were used to measure concentrations of DA, NA, 5-HT and 5-HIAA present in extracts of brain tissue and CSF taken from midterm gestational fetuses of both sexes. The presence of biogenic amines was demonstrated in fetuses as early as 10.5 weeks gestation. In the hypothalamus, the concentrations (expressed in ng/100 mg tissue) ranged from 10.2 to 62.2 for NA, 11.6 to 258.8 for DA, 7.6 to 38.6 for 5-HT and 56.6 to 114.1 for 5-HIAA. Concentrations of DA and 5-HT were found to be significantly (P less than 0.05) higher in the hypothalamus than in the cortex, but those of NA and 5-HIAA were similar in both areas. No sex difference was observed. The concentrations of biogenic amines in the CSF (expressed in ng/ml) were 63.1-286.7 for NA, 43.2-108.1 for DA, 30.9-87.5 for 5-HT and 8.0-42.8 for 5-HIAA.

Effects of leptophos on rat brain levels and turnover rates of biogenic amines and their metabolites

Leptophos is a potent acetylcholinesterase inhibitor which causes delayed central-peripheral neuropathy. Rats were administered multiple doses of leptophos until motor deficits were observed in rotorod performance in the highest dosage group. Doses lower than the median effective dose were then administered to other rats and alterations of brain catecholamine and serotonin levels and turnover rates were determined. Turnover rates of brain norepinephrine and dopamine were elevated in rats administered cumulative doses of 75 mg/kg leptophos over a 15-day period. Levels of the major dopamine metabolite, 3,4-dihydroxyphenylacetic acid, appeared to be slightly elevated at this dose level and levels of dopamine were also higher than controls. These observations suggest that leptophos increases brain adrenergic activity. Rats administered the same dose levels had significantly reduced serotonin turnover rates. This observation was possibly artifactual, because rats administered a cumulative dose of 225 mg/kg leptophos showed no difference from controls.

Methylmercury induced alterations in brain amine syntheses in rats

Male Sprague-Dawley rats were treated with a cumulative dose of 0, 5, 15 and 50 mg methylmercury/kg body weight. The doses were adequate to provide a clinical neuromuscular dysfunction at the highest dose whereas no toxicity was observed at the lowest treatment level. Whole brain concentrations of tyrosine but not tryptophan were slightly reduced by the treatment. No effect of methylmercury was observed in the levels of norepinephrine (NE), dopamine (DA), serotonin (5-HT), dihydroxyphenylacetic acid (DOPAC), or 5-hydroxyindoleacetic acid (5-HIAA). The synthesis rate for DA, but not the other biogenic amines, was decreased at all treatment levels of methylmercury. The results suggested a sensitivity of dopaminergic pathways to methylmercury toxicity in the central nervous system and are consistent with interference with cholinergic mechanisms and neurotransmitter enzymes by methylmercury as previously reported.

Presynaptic muscarinic receptors increase striatal dopamine release evoked by "quashi-physiological" depolarization

The effects of acetylcholine on the release of [3H]dopamine was studied in superfused rat striatal synaptosomes prelabeled with the radioactive amine. The results confirm the presence of muscarinic presynaptic receptors mediating potentiation of the spontaneous release of the catecholamine. However, under depolarizing conditions, the release of dopamine evoked by 15 mM KC1 was increased by the activation of muscarinic receptors and not decreased, as previously found in striatal synaptosomes or slices depolarized with higher (50-60 mM) KC1 concentrations.

The stimulus-induced release of 5-hydroxytryptamine and tryptophan from superfused rat brain synaptosomes

The synthesis of 5-hydroxytryptamine (5-HT) from 3H-tryptophan in rat forebrain synaptosomes was studied. Synaptosomes which had been preincubated with 3H-tryptophan were perfused with Krebs solution and the release of tryptophan, 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) was determined. K+ depolarization induced a Ca2+ -dependent release of 5-HT and tryptophan but had no effect on 5-HIAA efflux. This finding suggests that the release of tryptophan is unlikely to be a non-specific effect of depolarization.

Use of a single compartment LCEC cell in the determinations of biogenic amine content and turnover

Content and specific radioactivity of the biogenic monoamines and content of their precursors and metabolites were simultaneously determined in CNS tissue extracts with a high pressure liquid chromatography system (HPLC). The content of dopamine, norepinephrine, serotonin. 5-hydroxyindoleacetic acid, homovanillic acid, 3,4-dihydroxyphenylacetic acid and 4-hydroxy-3-methoxyphenylethyleneglycol and the turnover rate of dopamine, norepinephrine and serotonin were measured in discrete rat brain regions using a one compartment electrochemical detector cell coupled to a C18-reverse phase HPLC column. The small fluid volume dead space of the cell allows the direct and precise collection of individual peaks for determining specific radioactivities. This method is especially suitable for central nervous system tissue samples from 8-20 mg wet weight and the sensitivity of the system in its routine configuration is approximately 2 pmol. This method for determinations of turnover is appropriate for investigations of animals in sensitive behavioral paradigms.U

Brain neurotransmitter turnover correlated with morphine-seeking behavior of rats

Neurochemical substrates of intravenous opiate self-administration were investigated in rats using littermate controls for vehicle and passive morphine infusion. The rates of turnover of the putative neurotransmitters, dopamine, norepinephrine, serotonin, gamma-aminobutyric acid, aspartate and glutamate were concurrently measured in eleven brain regions of rats intravenously self-administering morphine and yoked-morphine or yoked-vehicle infused littermates. The passive infusion of morphine resulted in significant changes in the rates of turnover of the biogenic monoamine and amino acid neurotransmitters in six brain regions with the caudate nucleus-putamen-globus pallidus showing the most changes. The contingent infusion of morphine resulted in changes in utilization rates that were generally greater in both magnitude and number than the effects of the drug itself. Twenty-nine significant changes were observed in the self-administering group with most changes occurring in limbic structures. The neurotransmitter turnover rate changes resulting from contingent administration suggest that the drug administration environment is an important factor that should be considered in studies of interactions between drugs and neuronal systems.

Determination of gamma-aminobutyric acid by liquid chromatography with electrochemical detection

gamma-Aminobutyric acid (GABA) has been determined in rat brain by derivatization with 2,4,6-trinitrobenzenesulfonic acid. The derivative and an internal standard, 2,4,6-trinitrophenyl-delta-aminovaleric acid, are extracted into toluene and separated by reversed-phase chromatography. Electrochemical reduction of these derivatives permits picomole measurements of GABA in microgram amounts of brain tissue.

A rapid and simple method to determine the specific activities of serotonin, 5-hydroxyindoleacetic acid, and 5-hydroxytryptophan in brain by HPLC with electrochemical detection

The specific activities of 5-hydroxytryptophan (5-HTP), serotonin (5-HT), and 5-hydroxyindoleacetic acid (5-HIAA) have been determined in the brain of rats by HPLC using electrochemical detection. The method allows, from a single sample, the simultaneous measurement of all three compounds and collection of each peak for radioactivity determinations. Five male Wistar rats were injected i.v. with 2.0 mCi/kg of DL-5-hydroxy-[G-3H]tryptophan (2.6 Ci/mmol) and 30 min later the animals were killed by near freezing. Whole brains were removed and homogenized in an acid medium. The content of 5-HTP, 5-HT, and 5-HIAA were determined by HPLC. Each peak of interest was immediately collected after detection in scintillation vials by use of a small dead space detector (TL-9A, Bioanalytical Systems, Inc.). The amounts of radioactivity were determined and specific activities calculated from the results. A second chromatography system (TLC) was used to check the authenticity and purity of compounds separated by the HPLC.

The stimulus-induced release of unmetabolized 5-hydroxytryptamine from superfused rat brain synaptosomes

A number of existing techniques have been modified to produce an improved technique for examining the depolarization-induced release of unmetabolized 5-hydroxytryptamine (5-HT) from drug-free superfused synaptosomes. Synaptosomes which have been pre-loaded with [3H]5-HT are set up in perfusion chambers and continuously perfused with medium. Serial samples of effluent perfusate are collected on ice and the released 5-HT and 5-hydroxy-indole acetic acid (5-HIAA) are separated by ion exchange chromatography. The technique provides reproducible Ca2+-dependent responses to K+ depolarization in the absence of monoamineoxidase inhibition and free from the interference of re-uptake. The advantages of the use of the system in examining transmitter release and its modulation is discussed.

Dopamine biosynthesis is regulated by the amine newly recaptured by dopaminergic nerve endings

The synthesis of dopamine from labeled tyrosine (but not from labeled DOPA) in rat striatal synaptosomes was effectively inhibited by exogenous dopamine only when the amine was allowed to enter the nerve endings. In the presence of the uptake blocker nomifensine, extracellular dopamine was almost inactive. The evolution of 14CO2 from [14C]tyrosine was consistently higher when synaptosomes were 'incubated' in the presence of nomifensine than in its absence. This effect disappeared when synaptosomes were 'superfused' with labeled tyrosine (with or without nomifensine) in conditions in which dopamine reuptake cannot occur. The monoaminoxidase inhibitor pargyline inhibited 14CO2 evolution from [14C]tyrosine. However, the effect was almost abolished if dopamine reuptake was prevented (by nomifensine or in superfusion). Our results suggest that dopaminergic nerve endings do not possess autoreceptors controlling dopamine synthesis. In the present paper it is proposed that the regulation of dopamine synthesis occurs through inhibition of tyrosine hydroxylase, according to the classical and end-product concept; however, the function of 'end-product' would be primarily exerted by the amine newly taken up by the nerve terminals.

Hypothermia induced in mice by enzyme-mediated depletion of serotonin

Injection of a purified serotonin (and tryptophan)-degrading enzyme into mice produced a pronounced hypothermia when the mice were maintained at 22 degrees C, but not at 30 degrees C. Brain levels of serotonin and tryptophan were strikingly depleted, but concentrations of norepinephrine and dopamine remained unchanged.

[3H]Acetylcholine and [3H]5-hydroxytryptamine release from rat midbrain slices and the effects of calcium and phenobarbital

The K-stimulated release of [3H]ACh from rat midbrain slices prelabeled by incubation with [3H]choline was dependent on extracellular Ca. Phenobarbital inhibited the K-stimulated [3H]ACh release and the IC50 was equal to that found for K-stimulated endogenous ACh release. These results support the suggestion that barbiturates primarily inhibit the Ca-dependent stimulated release of ACh and affect ACh synthesis only indirectly. K-Stimulated release of [3H]5-HT was also inhibited by removing Ca from the medium or by adding phenobarbital which further supports the effects of barbiturates on the depolarization-induced release process. Fluoxetine, an inhibitor of 5-HT uptake, increased the amount of [3H]5-HT found in the medium but did not fully block the uptake of [3H]5-HT in this slice preparation.

Evidence for a similar compartmentation of recaptured and endogenously synthesized dopamine in striatal synaptosomes

The aim of the present study was to compare the release pattern of [3H]dopamine ([(3H]DA) originated from [3H]tyrosine or by uptake in striatal synaptosomes. Synaptosomes prelabeled either with [3H]DA or with [3H]tyrosine were superfused in three conditions stimulating DA release by different mechanisms: (1) depolarization with high K+ (2) inversion of the NA+ gradient across the plasma membrane; (3) exposure to d-amphetamine. Since DA contained in different pools may exit from nerve endings by different processes, DA release was analyzed in the presence or in the absence of nomifensine which allows discrimination between carrier-mediated and carrier-independent processes. The pattern of DA release in the three conditions tested was idential, whether [(3)H]DA originated from synthesis or from uptake. Nomifensine did not affect the high-K+-induced release and inhibited that induced by the other two stimuli. The results suggest that newly synthesized and recaptured DA have similar compartmentation in nerve endings.

Characterization of experimental phenylketonuria. Augmentation of hyperphenylalaninemia with alpha-methylphenylalanine and p-chlorophenylalanine

Phenylalanine in conjunction with p-chlorophenylalanine or alpha-methylphenylalanine was administered to suckling rats to induce hyperphenylalaninemia reminiscent of untreated phenylketonuria, and developmental parameters were monitored. The experimental model utilizing p-chlorophenylalanine was found to be unsatisfactory, in that the drug had general deleterious effects on growth, numerous side effects including increased mortality, and affected brain levels of biogenic monoamine neurotransmitters. The model utilizing alpha-methylphenylalanine was relatively free from nonspecific effects and thus, changes observed in the animals were attributable to experimental phenylketonuria. The latter animals had slightly decreased body and brain weights, and exhibited grossly elevated serum phenylalanine and urinary excretion of phenylketone metabolites. Hyperphenylalaninemia produced greatly disrupted brain amino acids at 10 days of age (prior to the formalization of the blood-brain barrier and specific transport systems) which was limited by 30 days of age to changes in glycine, gamma-aminobutyric acid and the aliphatic and aromatic amino acids which compete for uptake in the brain by a common carrier. These animals also exhibited a myelin deficit and changes in proteins from isolated nerve cell preparations. Mature animals which had daily treatment up to 60 days of age exhibited a long-term learning impairment. These observations are consistent with many aspects of the clinical picture of untreated phenylketonuric patients, and suggest that this animal model will be beneficial in studying the disease.

Elevation of histamine levels in rat and mouse tissues by the deacetylation of administered N-acetylhistamine

N-Acetylhistamine administered to mice and rats (200-800 mg/kg, i.p.) elevated tissue histamine levels to a considerable extent. N-Acetylhistamine was more potent to elevate histamine than was histidine, a precursor amino acid of histamine. From the present results and the distribution of N-acetylhistamine deacetylase in tissues, it could be concluded that the elevation of histamine was due to the deacetylation of N-acetylhistamine. In addition, a slight but significant amount of N-acetylhistamine was found in tissues of normal rats. The physiological role of the deacetylation of N-acetylhistamine is discussed on the basis of these results.

A column chromatographic method for the determination of 5-hydroxytryptamine (serotonin) and 5-hydroxyindole acetic acid in cerebrospinal fluid

A method is described for measurement of 5-hydroxytryptamine (5-HT) and 5-hydroxyindole acetic acid (5-HIAA) in cerebrospinal fluid. 5-HT and 5-HIAA are isolated from columns of Biorex BR-70 and Sephadex G-10 with recoveries of 85 and 89% respectively. The indoles are quantitated by fluorometric measurement of the ortho-phthaldialdehyde derivatives in acidic solution. Correction for interfering 5-methoxytryptamine and 5-methoxyindole acetic acid is accomplished by a second measurement at alkaline pH. Thin-layer chromatographic analysis of column eluates has revealed no other interfering indoles in the 5-HT and 5-HIAA fractions. Preliminary results in normal cerebrospinal fluid samples have been in the ranges 10--60 ng/ml 5-HIAA and 0--13 ng/ml 5-HT.

Progress toward a voluntary oral consumption model of alcoholism

With the goal of obtaining a suitable animal model for voluntary oral consumption of ethanol, the investigators selectively bred lines of alcohol-preferring and alcohol-nonpreferring rats, with preference considered as a function of the concentration of ethanol ingested. Studies with these animals showed that drinking is voluntary and not contingent on caloric restriction; that they will work to obtain ethanol even when food and water are freely available, and in so doing, show psychological or behavioral tolerance; that the amount of ethanol voluntarily consumed approaches their apparent maximum capacity for ethanol elimination. This amount of ethanol was capable of altering brain neurotransmitter content, thus exerting a CNS pharmocologic effect. In addition, the rats will bar-press for intravenous administration of ethanol, and with prolonged, free-choice consumption, ethanol intake increases to as much as 12 g per kg body weight per day without producing behavioral deficits, suggesting the development of tolerance.

Neurochemical and operant behavioral studies of a strain of alcohol-preferring rats

The levels of serotonin (5-HT), 5-hydroxyindoleacetic acid, tyrosine (TYR), norepinephrine (NE), acetylcholine, GABA, glutamate (GLU), aspartate (ASP), alanine, glycine (GLY) and taurine were measured in the CNS of adult male rats selectively inbred to the F8 generation for alcohol preference (P) and non-preference (NP). With respect to the values found in the NP group, higher levels of 5-HT, GABA, GLU and GLY and lower levels of ASP were found in the diencephalon-mesencephalon (D-M) and higher levels of NE were found in the telencephalon (TEL) of the P group. The animals in the P and NP strains were further subdivided into two additional groups, one given only H2O (W) and the second given 10% ethanol (A) during a one week period, thereby producing four groups (NP-W, NP-A, P-W and P-A). With these conditions, the level of (a) TYR in the D-M was higher in the P-A and NP-A animals than in the P-W and NP-W groups respectively; (b) 5-HT in the TEL was higher in the NP-A group than NP-W group; and (c) GABA in the TEL was higher in the P-A than P-W animals. No differences were observed in the cerebellum between the two strains or between the subgroups within each strain. The present study also demonstrated that the P animals will work in an operant situation to obtain 10% ethanol, even when H2O is freely available, and will voluntarily bar-press up to 6-7 times for each ethanol reinforcement.

Combination operant conditioning--liquid nitrogen immersion chamber for studying neurotransmitter systems and behavior

Studies of neurochemical events associated with behavior require a method of tissue fixation that is rapid and does not itself produce neurochemical changes. An apparatus is described that permits immediate immersion of an unrestrained behaving animal into liquid nitrogen. This method of tissue fixation has the greatest versatility for studying multiple neurotransmitter systems. In addition to the measurement of neurotransmitter content and turnover, investigation of neurotransmitter receptors, enriched nerve ending fractions and enzyme activities are possible. The operant conditioning-liquid nitrogen immersion chamber described here can be used for studying these neurotransmitter systems as they relate to animal's responding on operant schedules of reinforcement.