Gas chromatographic/mass spectrometric evidence for the identification of 1,2,3,4-tetrahydro-beta-carboline as an in vivo constituent of rat brain

LC/MS/MS analysis of the endogenous dimethyltryptamine hallucinogens, their precursors, and major metabolites in rat pineal gland microdialysate

We report a qualitative liquid chromatography-tandem mass spectrometry (LC/MS/MS) method for the simultaneous analysis of the three known N,N-dimethyltryptamine endogenous hallucinogens, their precursors and metabolites, as well as melatonin and its metabolic precursors. The method was characterized using artificial cerebrospinal fluid (aCSF) as the matrix and was subsequently applied to the analysis of rat brain pineal gland-aCSF microdialysate. The method describes the simultaneous analysis of 23 chemically diverse compounds plus a deuterated internal standard by direct injection, requiring no dilution or extraction of the samples. The results demonstrate that this is a simple, sensitive, specific and direct approach to the qualitative analysis of these compounds in this matrix. The protocol also employs stringent MS confirmatory criteria for the detection and confirmation of the compounds examined, including exact mass measurements. The excellent limits of detection and broad scope make it a valuable research tool for examining the endogenous hallucinogen pathways in the central nervous system. We report here, for the first time, the presence of N,N-dimethyltryptamine in pineal gland microdialysate obtained from the rat.

Determination of biological markers for alcohol abuse

Alcoholism is one of the most frequent addictions and an important subject in forensic medicine and clinical toxicology. Several laboratory abnormalities are associated with excessive alcohol consumption. They are useful in the diagnosis of alcoholism especially during the follow-up of various treatment programs. The biological markers mostly used for diagnosis of alcoholism are presented. Especially, methods for the determination of the following diagnostic tools are reviewed: congener alcohols, gamma-glutamyltransferase, aspartate and alanine aminotransferase, beta-hexosaminidase, erythrocyte aldehyde dehydrogenase, alpha-amino-n-butyric acid to leucine ratio, macrocytosis, carbohydrate-deficient transferrin, (apo)lipoproteins, fatty acid ethyl esters, blood acetate, acetaldehyde adducts, 5-hydroxytryptophol, dolichol and condensation products. No laboratory test exists that is reliable enough for the exact diagnosis of alcoholism. The combination of physician interview, questionnaire and laboratory markers is necessary for the diagnosis of alcoholism.

Studies on the interaction between 1,2,3,4-tetrahydro-beta-carboline and cigarette smoke: a potential mechanism of neuroprotection for Parkinson's disease

1,2,3,4-Tetrahydro-beta-carboline (TH beta C) is an endogenous or environmental neurotoxic factor putatively involved in the development of Parkinson's disease (PD). As part of our efforts to characterize the mechanism of the reported protection of smoking against PD, we have examined the interaction between TH beta C and cigarette smoke. We found that TH beta C reacts in vitro and under physiological conditions with some components of cigarette smoke to form N2-(cyanomethyl)-TH beta C (CM-TH beta C), N2-(gamma-cyanoethyl)-TH beta C (CE-TH beta C), N2-(1'-cyanopropyl)-TH beta C (CP-TH beta C), N2-(1'-cyanobutyl)-TH beta C (CB-TH beta C) and N2-formyl-TH beta C (F-TH beta C). Significant differences in the recovery of some of these TH beta C-derivatives were obtained for Burley and Bright tobacco. Several of the reported compounds showed reversible and competitive MAO-A inhibitory properties. The detection of some of these compounds in rat brain after chronic administration of TH beta C and a solution of cigarette smoke proved that the reported interactions also occur in vivo. These results are discussed as a potential mechanism of neuroprotection in the development of PD.

Formaldehyde-derived tetrahydroisoquinolines and tetrahydro-beta-carbolines in human urine

Human urine samples were examined for the occurrence of formaldehyde-derived tetrahydroisoquinolines and tetrahydro-beta-carbolines generated by condensation of the methanol oxidation product with biogenic amines. Positive results were obtained for the tryptamine condensation product 1,2,3,4-tetrahydro-beta-carboline and the serotonine condensation product 6-hydroxy-1,2,3,4-tetrahydro-beta-carboline as well as for the condensation products with tyramine, dopamine, adrenaline and noradrenaline 1,2,3,4-tetrahydroisoquinoline, 6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline, N-methyl-4,6,7-trihydroxy-1,2,3,4-tetrahydroisoquinoline, 4,6,7-trihydroxy-1,2,3,4-tetrahydroisoquinoline, and the metabolite 6-methoxy-7-hydroxy-1,2,3,4-tetrahydroisoquinoline. Negative results were obtained for N-methyl-1,2,3,4-tetrahydroisoquinoline and 6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline, N-methyl-1,2,3,4-tetrahydro-beta-carboline, 6-methyl-1,2,3,4-tetrahydro-beta-carboline, and 6-methoxy-1,2,3,4-tetrahydro-beta-carboline in samples of chronic alcoholics as well as in the urine of healthy volunteers. No correlation between alcohol ingestion or state of alcoholization could be demonstrated.

Gas chromatographic-mass spectrometric screening procedure for the identification of formaldehyde-derived tetrahydro-beta-carbolines in human urine

A gas chromatographic-mass spectrometric method for the identification of 1,2,3,4-tetrahydro-beta-carboline and four metabolites extracted from urine is described. In a first step the substances, formed by reaction of formaldehyde with biogenic amines, were derivatized in aqueous solution with methyl chloroformate to eliminate an artificial formation of these compounds via condensation of endogenous indole ethylamines with aldehydes or alpha-keto acids during the work-up procedure. This initial derivatization formed stable hydrophobic compounds and improved the extractability for a liquid-liquid extraction. Further clean-up was performed by solid-phase extraction on C18 sample preparation columns. The method can identify these compounds in the picogram range.

Highly sensitive method for the determination of 1-methyl-1,2,3,4-tetrahydro-beta-carboline using combined capillary gas chromatography and negative-ion chemical ionization mass spectrometry

A sensitive method was developed for the determination of deuterated and non-deuterated 1-methyl-1,2,3,4-tetrahydro-beta-carboline by combined capillary gas chromatography and negative-ion chemical ionization mass spectrometry. 1-Methyl-1,2,3,4-tetrahydro-beta-carboline was converted into a trifluoroacetyl derivative after pretreatment with fluorescamine and extraction with ethyl acetate. The derivative was separated by capillary gas chromatography and determined by selected-ion monitoring. In the determination, [3,3,4,4-2H4]-1-methyl-1,2,3,4-tetrahydro-beta-carboline was used as an internal standard. The method developed in this work was used for the determination of deuterated and non-deuterated 1-methyl-1,2,3,4-tetrahydro-beta-carboline in human urine samples collected before and after administration of [3,3-2H2]-L-tryptophan.

Determination of pharmacological levels of harmane, harmine and harmaline in mammalian brain tissue, cerebrospinal fluid and plasma by high-performance liquid chromatography with fluorimetric detection

Increased blood aldehyde levels, as occur in alcohol intoxication, could lead to the formation of beta-carbolines such as harmane by condensation with indoleamines. Endogenous beta-carbolines, therefore, should occur in specific brain areas where indoleamine concentrations are high, whilst exogenous beta-carbolines should exhibit an even distribution. The author presents direct and sensitive methods for assaying the beta-carbolines harmane, harmine and harmaline in brain tissue, cerebrospinal fluid and plasma at picogram sample concentrations using reversed-phase high-performance liquid chromatography with fluorimetric detection and minimal sample preparation. Using these assay methods, it was found that the distribution of beta-carbolines from a source exogenous to the brain results in a relatively even distribution within the brain tissue.

Concentrations of tryptoline and methtryptoline in rat brain

Combined gas chromatography-mass spectrometry and gas chromatography-tandem mass spectrometry have been used to identify and quantify tryptoline, methtryptoline, 5-hydroxytryptoline, and 5-hydroxymethtryptoline as their heptafluorobutyryl derivatives in extracts of rat brain. Tryptoline and methtryptoline were identified on the basis of their retention times and mass spectral characteristics: they were reliably detected in brain tissue extracts without interference from artifactual formation; their whole brain concentrations ranged between 0.2 and 3 ng/g; and they had a similar neuroanatomical distribution, with the highest concentrations in the cerebellum and the cortex. Smaller quantities of 5-hydroxytryptoline and 5-hydroxymethtryptoline were also identified on the basis of their retention times and mass spectral characteristics. However, the significance of this finding is unclear, because these two compounds were accompanied by larger quantities of their tetradeuterated analogues formed from tetradeuterated-5-hydroxytryptamine added at the time of tissue homogenization; this result suggests that formation of 5-hydroxytryptoline and 5-hydroxymethtryptoline occurred during tissue homogenization, sample preparation, or both.

Interaction of ethanol and tetrahydro-beta-carboline (THBC) in a discriminative task

Rats (n = 10) were trained to discriminate between ethanol (600 mg/kg, IP) and its vehicle, or between THBC (20 mg/kg) and its vehicle in a two-lever food-motivated operant task. Once the discriminative training criterion was attained, rats in each group were administered different doses of both ethanol and THBC. The ED50 of ethanol in the ethanol-trained rats was 298.0 mg/kg and 15 mg/kg THBC produced ethanol-like responding. The ED50 of THBC in the THBC-trained rats was 3.63 mg/kg and 1200 mg/kg ethanol produced THBC-like responding. The cross-generalization between ethanol and THBC is, thus, indicated and relates to previous evidence in which both ethanol- and THBC-trained rats generalize to a common agent, TFMPP, a putatively specific 5HT1B receptor agonist. Taken together, these observations suggest that beta-carbolines may play a role in the discriminative stimulus properties of ethanol.

Acetaldehyde and its condensation products as markers in alcoholism

Several studies show that recently abstaining alcoholics generate higher circulating levels of acetaldehyde than nonalcoholics following ethanol administration. It is conceivable that levels of stable adducts (tetrahydroisoquinolines and tetrahydro-beta-carbolines) derived from acetaldehyde condensations with biogenic amines also might be increased in alcoholics consuming ethanol, thus serving in body fluids as chemical markers that are more persistent than acetaldehyde itself. Limited human and rat studies indicate that urinary excretion of an oxidized tryptamine condensation product (harmane) and of an acetaldehyde/serotonin condensation product is elevated by chronic ethanol. Salsolinol, the derivative of acetaldehyde and dopamine, does not appear to be a meaningful urinary marker, but levels of the related pyruvic acid/dopamine product may be increased by ethanol. Blood assays of condensation products have been limited in number and equivocal. Condensation product measurements are complicated not only by artifacts (formation during analyses), but by other inherent problems. Products of interest often are constituents of diets and alcoholic beverages. For this and perhaps endogenous metabolic reasons, traces of condensation products are normally excreted by nondrinking individuals. Furthermore, the assays require high sensitivity and specificity and are not easily adapted to routine use. Thus, although several condensation products have initial appeal as clinical or pathological indicators in chronic alcoholism, thorough and statistically sound studies are needed before conclusions can be reached concerning any particular biogenic amine-derived product.

Behavioural and electrocortical power spectrum effects of 5-methoxytryptoline and other analogs after intraventricular administration in rats

The behavioural and electrocortical power spectrum effects of tryptoline and the 5-hydroxy and 5-methoxy derivatives were studied after microinjection of the drugs into the third cerebral ventricle in freely moving rats. The three compounds produced a dose-dependent desynchronication in electrocortical activity with a concomitant syndrome of behavioural stimulation. The most potent compound was 5-methoxytryptoline, already active at 4 nmol. When given into the third cerebral ventricle, 5-methoxytryptoline antagonized the sedation and hypothermia induced by reserpine. The relative order of potencies was 5-methoxytryptoline greater than 5-hydroxytryptoline greater than tryptoline. Melatonin, the 5-methoxy-N-acetyl derivative of serotonin, when injected into the third cerebral ventricle, did not produce desynchronization and elicited only mild sedation. The high potency of 5-methoxytryptoline following injection into the third cerebral ventricle and the relative order of potencies with 5-hydroxytryptoline and tryptoline is compared to the affinity of these compounds for the modulatory site of the serotonin transporter which was labelled with [3H]imipramine or [3H]paroxetine.

Endocrine effects of 5-methoxytryptoline, 5-hydroxytryptoline and tryptoline, putative modulators of rat serotonergic system

The effects of tryptolines (TH beta Cs), putative endogenous compounds acting on the serotonergic function, have been studied on endocrine parameters in rats. In particular, graded doses of 5-methoxytryptoline (5-MeOT), 5-hydroxytryptoline (5-OHT) and tryptoline (Tp) were ip or iv administered to the animals and the circulating titers of prolactin (PRL), growth hormone (GH) and luteinizing hormone (LH) were assayed either at 20 min or at various times after the injection of the compounds. The data herein reported show that TH beta Cs exert endocrine effects, at least in a pharmacological condition. However, the three compounds unequally affect anterior pituitary function. In fact, while 5-MeOT, 5-OHT and Tp all enhance plasma PRL concentrations in a quick, short lasting and dose-related manner, 5-MeOT and Tp induce also decreases of serum LH levels in ovariectomized rats, and 5-MeOT only is able to diminish plasma GH titers. These findings underline an endocrine effect for TH beta Cs in pharmacological conditions and may suggest a functional role for these compounds in the control of anterior pituitary function.

Serotonergic mediation of tetrahydro-beta-carboline

Rats were trained to discriminate between the stimulus properties of tetrahydro-beta-carboline (THBC) and its vehicle in a two-lever, food-motivated operant task. By steadily increasing the training dose, the discrimination was attained at 20.0 mg/kg THBC. Dose-response experiments subsequently indicated that decreasing doses of THBC produced decreased discrimination and generated an ED50 = 3.63 mg/kg. Administration of the serotonergically-active drug, fenfluramine, produced THBC-appropriate responding in a dose-responsive manner. In addition, LSD and yohimbine produced partial generalizations in the THBC-trained rats. These data suggest that the discriminative stimulus properties of THBC are mediated by serotonergic neurons in the central nervous system.

Quantification of tryptamine in brain using high-performance liquid chromatography

The concentration of endogenously formed tryptamine in central nervous system tissue was determined after extraction into ethyl acetate, purification on a weak cation-exchange resin and analysis using high-performance liquid chromatography with fluorometric detection. Final chromatographic separation of this indoleamine was achieved using a muBondapak C18 reversed-phase column under isocratic conditions. Using this method, the concentration of tryptamine in the whole brain of normal rats was found to be 0.60 +/- 0.06 ng/g of tissue, while pretreatment with dl-p-chlorophenylalanine, tranylcypromine and l-tryptophan increased the concentration to 96.7 +/- 21.9 ng/g.

Drug-induced activation of the inferior olivary nucleus in young rabbits. Differential effects of harmaline and quipazine

Ontogenic evolution of behavioural and electrophysiological responses to the serotonergic agents, quipazine and harmaline, was studied in the maturing rabbit in normal and pretreated conditions. As regards behavioural effects, tremor induced by quipazine was present from the first postnatal day and was antagonized by methysergide, but not by p-chlorophenylalanine (PCPA) or pretreatment with 5,7-dihydroxytryptamine (5,7-DHT). In contrast, tremor induced by harmaline could not be elicited before the second postnatal week and was partially antagonized by methysergide and 5,7-DHT, but not by PCPA. Electrophysiological studies of cell activity in the inferior olivary nucleus revealed a similar dependency on age since rhythmic activation of the inferior olivary nucleus could be registered from the first postnatal day with quipazine and only from the 8th postnatal day with harmaline; drug interactions with methysergide, PCPA and 5,7-DHT were the same as for the behavioural observations. It is suggested that quipazine directly activates serotonin receptors which are already present at birth, whereas harmaline requires the presence of serotonergic fibres for such activation.

Derivatization in aqueous solution, isolation and separation of tetrahydro-beta-carbolines and their precursors by liquid chromatography

Derivatization of indole ethylamines and 1,2,3,4-tetrahydro-beta-carbolines in aqueous solution with methyl chloroformate has been used to facilitate the isolation of these compounds. The initial derivatization eliminated the potential for the artifactual formation of these compounds via the condensation of the indole ethylamine with an aldehyde or alpha-keto acid during the work-up procedure. The derivatized compounds possessed improved chromatographic properties which allowed for their facile separation by reversed-phase liquid chromatography and their fluorescent detection at the nanogram level.

Gas chromatographic analysis of endogenous catecholamines, phenolic amines and derived isoquinolines using short glass capillary columns and electron-capture detection

A gas chromatographic method is described for the concomitant separation and analysis of catecholamines, catecholamine or 3,4-dihydroxyphenylethylamine condensation products (tetrahydroisoquinolines), and their isomeric mono-O-methyl (phenolic) metabolites which may be present in neuronal tissues, utilizing short glass capillary columns and electron-capture detection. Isomeric phenolic amines that were not generally separable with conventional-packed gas chromatographic columns were rapidly resolved on the capillary system, and with their catecholamine or catechol isoquinoline precursors, quantitated with high sensitivity (0.25-7.0 pg) and reproducibility. Key steps in the approach with tissues include initial amine isolation with a weak cation-exchange resin (BioRex-70), fluoracyl derivative formation, and brief washing of the derivatives with ammonium phosphate buffer (pH 5.8) just prior to capillary analysis; overall recoveries of amines or alkaloids added to rat brain homogenates ranged from 79% to 89%. Application of the method is demonstrated in an assay of endogenous dopamine in rat corpus striatum and hypothalamus. This new procedure should complement and in some instances may be preferred over liquid chromatographic assays for catecholic and phenolic amines and isoquinolines, and ought to be applicable to mass spectrometric detectors as well.

Ontogeny of N,N-dimethyltryptamine and related indolealkylamine levels in neonatal rats

The present study deals with the measurement of the brain levels of the two potent hallucinogens N,N-dimethyltryptamine (DMT) and 5-methoxy-N,N-dimethyltryptamine (OMB), the biogenic amine tryptamine (TA), and its condensation product 1,2,3,4-tetrahydro-beta-carboline (THBC) in rats of various ages. Using gas chromatography-mass spectrometry with isotope dilution, we detected DMT, OMB, and THBC in neonatal rats from birth. DMT levels remained low until days 12 and 17 at which time they increased significantly and then returned to the initial low levels for all subsequent ages. The levels of OMB were higher than those measured for DMT with the highest levels being observed at days 12 and 17, and also on day 31. However, the levels for OMB showed much more variation. Although elevated levels of DMT and OMB have been correlated with stress, there are no known functions for these compounds. TA levels remained below detection limits until day 19. THBC levels were observed to be highest on days 22 and 31. The role that THBC plays in mammalian tissues is not known.

In vivo metabolism of alpha,alpha,beta,beta-tetradeutero-N, N-dimethyltryptamine in rodent brain

The metabolism of alpha,alpha,beta,beta- tetradeutero -N,N -dimethyltryptamine ( D4DMT ) in rat brain in vivo as a function of time and dose was examined. Quantification of D4DMT and its respective deutero-metabolites was accomplished using gas chromatographic/mass spectrometric/selected ion monitoring/isotope dilution techniques. The results of this study indicate that D4DMT is metabolized to the corresponding deutero-N-methyltryptamine, tryptamine, 1,2,3,4-tetrahydro-beta-carboline, and 2-methyl-1, 2,3,4-tetrahydro-beta-carboline in rat brain. The subcellular distribution of D4DMT and the aforementioned metabolites is also reported.

Distribution of 1,2,3,4-tetrahydro-beta-carboline and 6-methoxy-1,2,3,4-tetrahydro-beta-carboline in mice

The distribution of radioactivity after intravenous injection of 14C-labelled 1,2,3,4-tetrahydro-beta-carboline (THBC) and 6-methoxy-1,2,3,4-tetrahydro-beta-carboline (6-MeO-THBC) was studied on mice by whole-body autoradiography and by liquid scintillation counting (LSC). Following intravenous injection they rapidly distributed into different organs and were excreted into urine and the gut contents. A considerable uptake of the compounds was seen in the lungs, kidney, liver, bone marrow, urinary bladder, gastrointestinal tract and in various glands e.g. adrenal, Harderian and salivary glands. THBC moderately penetrated the blood-brain barrier and the placenta but 6-MeO-THBC seemed to penetrate poorly both. At early stages of the experiment the values of tissue radioactivity in LSC were generally much higher in the THBC group but 24 hours following injections the reverse was true with higher activities in the 6-MeO-THBC group. The initial excretion of 6-MeO-THBC seemed to be more rapid judged by the superfluous accumulation of activity in the bladder and a high accumulation of activity into the gut contents.

Effects of 6-methoxytetrahydro-beta-carboline on 5-hydroxytryptamine binding in rat brain

6-MeOTHBC competes for 5-HT binding sites in rat brain in-vitro and in-vivo. The beta-carboline is significantly more active at the type 1 [3H]-5-HT, than the type 2 [3H]spiperone receptors, in-vitro. Following injection, 6-MeOTHBC significantly decreases [3H]-5-HT binding in the cortex. The ineffectiveness on [3H]spiperone binding in-vivo corresponds with the low affinity in-vitro. The effect of 6-MeOTHBC on central 5-HT binding may be a significant aspect of its 5-HT-ergic activity.

Characterization of [3H]tryptamine binding sites in brain

[3H]Tryptamine binds with high affinity to sites on rat brain membranes. The sites have the characteristics of tryptamine receptor recognition sites. These sites are widely distributed among rat brain regions with the highest density occurring in the cerebral cortex, striatum and hippocampus. The site is also found in human cerebral cortex. The binding site is localized mainly to the synaptosomal fraction. Drug competition studies indicate that the [3H]tryptamine binding site is distinct from serotonin receptors. Drugs that are potent inhibitors of [3H]tryptamine binding include tetrahydro-beta-carboline, quipazine, phenylethylamine, amphetamine, p-chloroamphetamine and methamphetamine.

Pharmacokinetics of tetrahydronorharmane (tetrahydro-beta-carboline) in rats

The distribution, metabolism and elimination into the urine of (14C)-tetrahydronorharmane (THN) as well as of (14C)-6-hydroxy-tetrahydronorharmane (6-OH-THN) are investigated in female and male rats. Following intravenous injection of (14C)-THN radioactivity was detected in all organs examined, namely blood, brain, lung, adrenal gland, small intestine, fat tissue, kidney and liver. In the brain the elimination half life of THN was calculated to be 1.8 h, the elimination half life of the radioactivity in the blood 6.24 h, and the accumulation half life in the urine 9.24 h. The elimination of 6-OH-THN into the urine is faster than that of THN. At least four metabolites of (14C)-THN were found in the urine of female rats. Two different metabolic pathways are discussed, firstly, hydroxylation followed by conjugation with glucuronic and sulfuric acids and secondly, dehydrogenation, followed by oxygenation. In female rats only traces of the conjugated metabolites are hydrolysed by arylsulfatase, whereas in male rats approximately 2/5 are cleaved by this enzyme. Pretreatment of male rats with 3-methylcholanthrene induced conjugation, whereas phenobarbital had no obvious effect on the pattern of metabolites. SKF 525 A and CFT 1201 both prevented almost completely the formation of conjugates from THN.

Presence of formaldehyde in biological media and organic solvents: artifactual formation of tetrahydro-beta-carbolines

A gas chromatography-mass spectrometry method is described for the identification and quantitation of 6-hydroxy-1,2,3,4-tetrahydro-beta-carboline (6OHTHBC). During the analysis of 6OHTHBC in human platelets, the artifactual formation of 6OHTHBC was observed and shown to be due to the presence of formaldehyde in both organic solvents and in platelet homogenates. Formaldehyde was facilely removed from the organic solvent via a Pictet-Spengler reaction; however, removal from tissue homogenates was not possible by using conventional aldehyde-trapping agents. The solution of these problems and their consequences for persons attempting to establish the in vivo presence of tetrahydro-beta-carbolines or biochemically study tissue preparations are discussed.

Blood platelets in psychopharmacological research

Blood platelets are a very good model for nerve endings, for study of serotonin uptake and imipramine binding. The efficiency of various drugs, mainly antidepressants, can be evaluated using blood platelets instead of synaptosomes. A few neuronal active compounds are effective in inducing platelet secretion and shape change reaction. Platelet MAO and c-AMP levels are not yet established as useful in psychopharmacological studies.

Behavioral and biochemical evidence for serotonergic actions of tetrahydro-beta-carbolines

In two groups of rats trained to discriminate LSD (0.1 mg/kg or 0.24 mg/kg) from saline, tetrahydro-beta-carboline (THBC; 1-12 mg/kg as free base) and its derivative 6-methoxy-THBC (1-12 mg/kg as free base) substituted partially for LSD. The substitution of THBC for 0.1 mg/kg of LSD was analyzed further with antagonism tests in 16 animals and was attenuated by the serotonin (5-HT) antagonist BC-105 (pizotifen; 3 mg/kg) but not by the dopamine (DA) antagonist haloperidol (0.1 mg/kg). It was abolished by pretreatment with the 5-HT synthesis inhibitor p-chlorophenylalanine (100 mg/kg/day for 3 days). In addition, THBC was found to inhibit 3H-LSD binding to homogenates of rat frontal cortex with an IC50 value of 4 microM which is similar to that previously reported for other 5-HT agonists. These data indicate that THBCs exert potent 5-HT agonist actions. Since THBCs have recently been found in mammalian brain and other tissues, the present results are of interest in relation to a possible role of these substances in endogenous psychosis.

Comparison of the brain levels of N,N-dimethyltryptamine and alpha, alpha, beta, beta-tetradeutero-N-N-dimethyltryptamine following intraperitoneal injection. The in vivo kinetic isotope effect

A comparison of the brain levels (microgram/g wet weight of tissue) of the hallucinogen N,N-dimethyltryptamine (DMT) and its deuterated analog alpha, alpha, beta, beta-tetradeutero-DMT (D4DMT) as a function of time and dose is reported. It was observed that the presence of deuterium in the alpha- and beta-positions of the ethylamine side-chain led to a potentiation of the level of DMT in brain. Strikingly different dynamics of uptake and clearance were also noted. We propose that these results are due to primary kinetic isotope effect, illustrating the importance of the alpha-position in the metabolism of DMT.

In vitro studies of 5, 10-methylenetetrahydrofolate reductase: inhibition by folate derivatives, folate antagonists, and monoamine derivatives

Folate monoglutamates and folate antagonists have an inhibitory action on the activity of 5,10-methylenetetrahydrofolate reductase in rat brain. The type of inhibition was studied for dihydrofolic acid using the Lineweaver--Burk transformation. Some of the monoamine alkaloids, the in vitro products of 5,10-methylenetetrahydrofolate reductase, have either a stimulatory or inhibitory effect on the enzyme activity.

The route and significance of endogenous synthesis of alkaloids in animals

There is now substantial evidence that several TIQs and beta-carbolines are present in vivo and increase during certain pathological conditions. It still remains to be determined, however, precisely what roles they play in endogenous functions and whether or not they are critical for the expression of these pathological conditions. Accumulating biochemical information continues to support the notion that these compounds can act as false transmitters. The exciting new findings, which will certainly receive a great deal more attention, concern the interaction of some of the beta-carbolines with the benzodiazepine receptor. Determining if a beta-carboline is an endogenous receptor ligand will attract further research interest on the theoretical and specifically clinically-directed levels. Biochemical, morphological, and behavioral data indicate that some of the condensation products can act as neurotoxins. Very few experiments have included an examination of long-term effects of exposure to one of these alkaloids, so the amount of information on this issue is limited. Chronic rather than acute administration of an alkaloid is more likely to mimic the pathological states in which these compounds are hypothesized to play a role. Biochemically, both the dopaminergic and serotonergic systems have been shown to be affected by chronic treatments with certain alkaloids. Progressive and long-term behavioral alterations also have been reported. Such changes may reflect an adaptation to an increase or decrease in activity of particular systems or a neurotoxic action.

[3H]propyl beta-carboline-3-carboxylate binds specifically to brain benzodiazepine receptors

Ethyl beta-carboline-3-carboxylate has recently been isolated from human urine and it was proposed that derivatives of this compound might be related to an endogenous ligand for benzodiazepine receptors. In the present study we investigated high-affinity binding of [3H]propyl beta-carboline-3-carboxylate ([3H]PrCC) to rat brain membranes. [3H]PrCC binds specifically and with high affinity (half-maximal binding at ca. 1nM) to rat brain membranes. The regional and subcellular distributions of specific [3H]PrCC binding are similar, but not identical, to the distributions of [3H]flunitrazepam or [3H]-diazepam binding. The total numbers of binding sites labelled by [3H]PrCC and [3H]flunitrazepam in rat cerebellum are closely similar, and both ligands bind to cerebellar membranes in a mutually exclusive way. The pharmacological selectivity of [3H]PrCC and [3H]diazepam binding is almost identical. Binding of [3H]PrCC like binding of [3H]diazepam, can be increased in vitro by muscimol, GABA and SQ 20.009. Although subtle differences in binding characteristics were observed, these results indicate that [3H]PrCC and benzodiazepines bind to a common recognition site on benzodiazepine receptors.

Identification by selective ion monitoring of 1-methyl-1,2,3,4-tetrahydro-beta-carboline in human platelets and plasma after ethanol intake

1-Methyl-1,2,3,4-tetrahydro-beta-carboline (tetrahydroharman) has been quantified in human platelets and plasma following acute intake of ethanol using a selective ion monitoring method. It was not possible to detect this compound before ethanol intake.

Quantitative gas chromatographic mass spectrometric determination of 1,2,3,4-tetrahydro-beta-carboline in human plasma and platelets

A sensitive and specific method is described for the determination of 1,2,3,4-tetrahydro-beta-carboline in human plasma, based on selected ion monitoring gas chromatography mass spectrometry and employing a deuterium analogue as internal standard. The identification of 1,2,3,4-tetrahydro-beta-carboline is based on monitoring ions m/z 143, 171, 199 and 368 for the heptafluorobutyryl derivative of 1,2,3,4-tetrahydro-beta-carboline or the normal mass spectrum. For quantitation the ratio of ions m/z 368/370 was used. The mean of 1,2,3,4-tetrahydro-beta-carboline level in human plasma (n = 10) was 8.78 +/- 1.94 ng ml-1 and 5.68 +/- 1.34 ng in platelets corresponding 1 ml of platelet rich plasma.

6-Methoxy-1,2,3,4-tetrahydro-beta-carboline: a specific monoamine oxidase-A inhibitor in CF-1 mouse brain

The activities of monoamine oxidase (MAO)-A and MAO-B (using [3H]serotonin and [14C]beta-phenylethylamine, respectively, as substrates) were determined in homogenates of whole mouse brains using a solvent extraction procedure. 6-Methoxy-1,2,3,4-tetrahydro-beta-carboline (6-MeO-TH beta C) had an IC50 of 1.6 microM, in vitro, for MAO-A using whole brain homogenate. A time course of apparent in vivo MAO-A inhibition using 6-MeO-TH beta C (100 mg/kg i.p.) showed a maximal inhibition by 1 h (56%), a decline to 30% at 12 h, and no inhibition at 24 h. There was a maximal inhibition of MAO-B by 4 h (16%). A dose-effect study done at 1 h after injection showed 6-MeO-TH beta C to inhibit MAO-A by 23% at 25 mg/kg, 43% at 50 mg/kg, 58% at 100 mg/kg and 73% at 150 mg/kg; for MAO-B there was no inhibition at 25 and 50 mg/kg and 16% inhibition at 100 mg/kg. The data thus indicate that, at doses less than or equal to 50 mg/kg, 6-MeO-TH beta C is a specific MAO-A inhibitor in vivo.

Hyperformaldehydism: a unifying hypothesis for the major biochemical theories of schizophrenia

A biochemical hypothesis concerning the etiology of schizophrenia is presented. This hypothesis postulates the presence of a genetically determined lesion in the disposition of one-carbon units leading to elevated levels of formaldehyde, i.e hyperformaldehydism. The relationships between this hypothesis and the existing major biochemical hypotheses of schizophrenia regarding dopamine and transmethylation are discussed.

Identification of tetrahydronorharmane (tetrahydro-beta-carboline) in human blood platelets

The present paper shows that tetrahydronorharmane (tetrahydro-beta-carboline) exists in human platelets. The concentration of tetrahydronorharmane in platelets from 10 ml platelet rich plasma was in the range of 9.3 to 25.6 pmol (n=8). Ingestion of tryptamine hydrochloride (n=4) three times daily for three consecutive days and of 19.6 mmol D,L-tryptophan (n=7) the evening (10 p.m.) before the blood collection did not lead to an increase of tetrahydronorharmane in platelets.