Tryptamine: a neuromodulator or neurotransmitter in mammalian brain?

Agaricus bisporus and its in vitro culture as a source of indole compounds released into artificial digestive juices

The popularity of Agaricus bisporus results not only from the quality of the flavors, but also from the content of many substances of therapeutic properties. This paper presents a study on RP-HPLC determination of the content of indole compounds released from the lyophilized biomass from in vitro cultures of A. bisporus into artificial digestive juices at 37°C. A. bisporus in vitro cultures were grown on media enriched with zinc salts. The release of 5-hydroxy-l-tryptophan and l-tryptophan was found in the greatest number of samples. The content of 5-hydroxy-l-tryptophan in the investigated samples ranged from 86.62 to 531 mg/100g d.w. The amount of l-tryptophan was determined within the range of 1.63-4.68 mg/100g d.w. and for melatonin 0.43-0.64 mg/100g d.w. It was demonstrated for the first time that in vitro cultures of A. bisporus release indole compounds in conditions simulating the human digestive tract.

Crystal structures and hydrogen bonding in the anhydrous tryptaminium salts of the isomeric (2,4-di-chloro-phen-oxy)acetic and (3,5-di-chloro-phen-oxy)acetic acids

The anhydrous salts of 2-(1H-indol-3-yl)ethanamine (tryptamine) with isomeric (2,4-di-chloro-phen-oxy)acetic acid (2,4-D) and (3,5-di-chloro-phen-oxy)acetic (3,5-D), both C10H13N2 (+)·C8H5Cl2O3 (-) [(I) and (II), respectively], have been determined and their one-dimensional hydrogen-bonded polymeric structures are described. In the crystal of (I), the aminium H atoms are involved in three separate inter-species N-H⋯O hydrogen-bonding inter-actions, two with carboxyl-ate O-atom acceptors and the third in an asymmetric three-centre bidentate carboxyl-ate O,O' chelate [graph set R 1 (2)(4)]. The indole H atom forms an N-H⋯Ocarboxyl-ate hydrogen bond, extending the chain structure along the b-axis direction. In (II), two of the three aminium H atoms are also involved in N-H⋯Ocarboxyl-ate hydrogen bonds similar to (I) but with the third, a three-centre asymmetric inter-action with carboxyl-ate and phen-oxy O atoms is found [graph set R 1 (2)(5)]. The chain polymeric extension is also along b. There are no π-π ring inter-actions in either of the structures. The aminium side-chain conformations differ significantly between the two structures, reflecting the conformational ambivalence of the tryptaminium cation, as found also in the benzoate salts.

Recreational use, analysis and toxicity of tryptamines

The definition New psychoactive substances (NPS) refers to emerging drugs whose chemical structures are similar to other psychoactive compounds but not identical, representing a "legal" alternative to internationally controlled drugs. There are many categories of NPS, such as synthetic cannabinoids, synthetic cathinones, phenylethylamines, piperazines, ketamine derivatives and tryptamines. Tryptamines are naturally occurring compounds, which can derive from the amino acid tryptophan by several biosynthetic pathways: their structure is a combination of a benzene ring and a pyrrole ring, with the addition of a 2-carbon side chain. Tryptamines include serotonin and melatonin as well as other compounds known for their hallucinogenic properties, such as psilocybin in 'Magic mushrooms' and dimethyltryptamine (DMT) in Ayahuasca brews.

AIM

To review the scientific literature regarding tryptamines and their derivatives, providing a summary of all the available information about the structure of these compounds, their effects in relationship with the routes of administration, their pharmacology and toxicity, including articles reporting cases of death related to intake of these substances.

METHODS

A comprehensive review of the published scientific literature was performed, using also non peer-reviewed information sources, such as books, government publications and drug user web fora.

CONCLUSIONS

Information from Internet and from published scientific literature, organized in the way we proposed in this review, provides an effective tool for specialists facing the emerging NPS threat to public health and public security, including the personnel working in Emergency Department.

Comparative Analysis of Therapeutically Important Indole Compounds in in vitro Cultures of Hypericum perforatum Cultivars by HPLC and TLC Analysis Coupled with Densitometric Detection

Five indole compounds (5-hydroxy-L-tryptophan, L-tryptophan, indole-3-acetic acid, melatonin, serotonin) and hypericin were identified and quantified in methanolic extracts of shoot cultures of three Hypericum perforatum cultivars (Helos, Elixir, Topas) growing on two variants of Murashige -Skoog medium differing in concentrations of growth regulators (naphthalene-1-acetic acid and 6-benzylaminopurine). Extracts of the aboveground parts of field-grown plants ( Hyperici herba) were also analyzed by HPLC and TLC analysis coupled with densitometric detection. Determination of four compounds was based on our assay described earlier. The methods of determination of 5-hydroxy-L-tryptophan and hypericin were developed and validated in this study. The composition and contents of the metabolites under study differed between the cultivars cultured in vitro and between medium variants containing diverse contents of growth regulators. The contents of individual indole compounds in the biomass from in vitro cultures ranged from 39.6 to 343.2 mg/100 g dry mass. 5-Hydroxy-L-tryptophan was the dominating metabolite (from 78.2 to 343.2 mg/100 g dry mass). Extracts from shoots of the cultivar Helos also contained high contents of serotonin (319.9 and 197.4 mg/100 g dry mass). The contents of indole compounds in Hyperici herba were also diverse (from 7.1 to 55.3 mg/100 g dry mass). 5-Hydroxy-L-tryptophan was the dominating metabolite as well. Hypericin content of Hyperici herba, equaling 12.2 mg/100 g dry mass was from 3.3 to 10 times higher than in extracts from shoots cultured in vitro. The present report is the first analysis of endogenous accumulation of indole compounds in Hyperici herba which involves, apart from melatonin, four other compounds.

Discovery of a natural product-like iNOS inhibitor by molecular docking with potential neuroprotective effects in vivo

In this study, we applied structure-based virtual screening techniques to identify natural product or natural product-like inhibitors of iNOS. The iNOS inhibitory activity of the hit compounds was characterized using cellular assays and an in vivo zebrafish larvae model. The natural product-like compound 1 inhibited NO production in LPS-stimulated Raw264.7 macrophages, without exerting cytotoxic effects on the cells. Significantly, compound 1 was able to reverse MPTP-induced locomotion deficiency and neurotoxicity in an in vivo zebrafish larval model. Hence, compound 1 could be considered as a scaffold for the further development of iNOS inhibitors for potential anti-inflammatory or anti-neurodegenerative applications.

Antioxidant components of selected indigenous edible mushrooms of the obsolete order Aphyllophorales

BACKGROUND

Species of phylum Basidiomycota are of great interest in many studies as a source of valuable biological compounds.

AIMS

To estimate the levels of antioxidant compounds (phenolic acids, indole compounds and sterols) in edible species of Aphyllophorales (sensu lato): Hydnum repandum L. and Sparassis crispa (Wulf.) Fr.

METHODS

A reversed-phase high performance liquid chromatography (RP-HPLC) method was used for the quantitative and qualitative analyses of antioxidant components (phenolic acids, indole compounds, and sterols).

RESULTS

Analysis of phenolic acids revealed that 8 out of the 10 analyzed compounds were present. The quantitatively predominant in Hydnum repandum was protocatechuic acid (75.23 mg/100 g DW), and in Sparassis crispa it was p-hydroxybenzoic acid (43.92 mg/100 g DW). In turn, analysis of indole compounds identified 5 out of the 12 analyzed compounds: indole, melatonin, serotonin, tryptamine, and l-tryptophan. Moreover, ergosterol was also identified and quantitatively determined (150.37 mg/100 g DW) in Sparassis crispa extracts.

CONCLUSIONS

The data presented in this paper confirm the significant potential of chemical components with recognized antioxidant activity. The species can be considered as an alternative source of phenolic acids and ergosterol.

Intoxications with the monoamine oxidase inhibitor tranylcypromine: an analysis of fatal and non-fatal events

Tranylcypromine (TCP) is a non-selective and irreversible monoamine oxidase inhibitor and an effective agent in the treatment of major depression. It features a complex pharmacologic profile and overdoses might induce severe intoxications. To identify typical clinical presentations of TCP-intoxications, range of associated TCP-dosages and possible differences between fatal and non-fatal intoxications a systematic review of all previously published cases of TCP-intoxications was conducted. We detected n=20 reports of TCP-intoxications in the literature (fatalities n=10). Mean age was 36.7 years (median 37); the majority of patients were female (60%). Frequent findings in patients with TCP-intoxications were disturbance of consciousness/cognitive dysfunction (90%), cardio-vascular symptoms (55%), hyperthermia (50%), respiratory distress (45%), delirium (45%), muscular rigidity (30%) and renal failure (20%). Suicidal intent was present in n=18 (90%) patients. First clinical symptoms related to TCP-intoxication developed on average in less than 1 day. The average dosage related to TCP-intoxication was 677 mg. The highest survived TCP-dosage was 4000 mg and the lowest fatal dosage was 170 mg. Patients with fatal intoxications were on average older (40.5 vs. 32.8 years) and developed a more rapid onset of symptoms (0.2 vs. 0.8 days). Death occurred after a mean time of 0.6 days; symptom relief in patients with non-fatal intoxications developed on average after 3.2 days. Considering the large dose spectrum between survived and lethal TCP-dosages individual susceptibility factors might play a role regarding the severity of clinical symptoms independently of the ingested dosage.

Biomedical importance of indoles

The indole nucleus is an important element of many natural and synthetic molecules with significant biological activity. This review covers some of the relevant and recent achievements in the biological, chemical and pharmacological activity of important indole derivatives in the areas of drug discovery and analysis.

Effect of N-salicyloyltryptamine (STP), a novel tryptamine analogue, on parameters of cell viability, oxidative stress, and immunomodulation in RAW 264.7 macrophages

Immunomodulatory actions exerted by some classes of tryptamines, such as benzoyltryptamine analogues, suggest these molecules as promising candidates to develop new therapies to treat conditions associated to acute and chronic pain and inflammation. N-salicyloyltryptamine (STP) was observed to act as an anticonvulsive agent and exert antinociceptive effects in mouse. In the present work, we performed a screening of cytotoxic, cytoprotective, immunomodulatory, and redox properties of STP in RAW 264.7 macrophages challenged with hydrogen peroxide and LPS. Our results show that STP presents no cytotoxicity in the range of 0.001 to 1 μg/mL, but doses of 50 and 100 μg/mL caused loss of cell viability (IC(50) = 22.75 μg/mL). Similarly, STP at 0.001 to 1 μg/mL did not cause oxidative stress to RAW 264.7 cells, although it did not prevent cell death induced by H(2)O(2) 0.5 mM. At 1 μg/mL, STP reversed some redox and inflammatory parameters induced by LPS. These include thiol (sulfhydryl) oxidation, superoxide dismutase activation, and morphological changes associated to macrophage activation. Besides, STP significantly inhibited LPS-induced TNF-α and IL-1β release, as well as CD40 and TNF-α protein upregulation. Signaling events induced by LPS, such as phosphorylation of ERK 1/2 and IκBα and p65 nuclear translocation (NF-kB activation) were also inhibited by STP. These data indicate that STP is able to modulate inflammatory parameters at doses that do not interfere in cell viability.

The recreational tryptamine 5-MeO-DALT (N,N-diallyl-5-methoxytryptamine): a brief review

5-MeO-DALT (N,N-diallyl-5-methoxytryptamine) is a psychoactive substance, sold primarily over the Internet as a 'research chemical' or 'plant food'. Although details for the synthesis of this tryptamine have been available since 2004, its use as a hallucinogenic drug has been reported only occasionally in on-line user fora. It is controlled in only a few countries world-wide. There is little scientifically-based literature on the pharmacological, physiological, psychopharmacological, toxicological and epidemiological characteristics of 5-MeO-DALT. Here we review what is known about these aspects. We also report what we believe to be the first death involving the use of this substance. The case involved a man in his mid-20s who died in mid-2010. The coroner concluded that the deceased "died from injuries sustained after being hit by a lorry whilst under the influence of 5-MeODALT". It is critical that any other cases, including non-fatal instances, are documented so that a scientific evidence-base can be established for this drug.

Tryptamine serves as a proligand of the AhR transcriptional pathway whose activation is dependent of monoamine oxidases

The function of the aryl hydrocarbon receptor (AhR) in mediating the biological effect to environmental pollutants is well established. However, accumulated evidence indicates a wide range of physiological and pathological functions mediated by the AhR, suggesting the existence of endogenous AhR ligand(s). The nature of an AhR ligand remain elusive; however, it is known that the AhR is activated by several compounds, such as 2,3,7,8-tetrachlorodibenzo-p-dioxin or the tryptophan photoproduct 6-formylindolo[3,2-b]carbazole. In this study, we show that physiological concentrations of tryptamine (TA) lead to induction of cytochrome P4501A1 transcription through an AhR-dependent mechanism. In addition, we show that activation of the AhR by TA requires a functional monoamino oxidase system, suggesting that TA acts as an AhR proligand possibly by converting to a high-affinity AhR ligand. Taken together, we show a possible mechanism, through which AhR signaling is activated by endogenous conversion of TA involving monoamine oxidases.

Electrochemical sensor based on molecularly imprinted film at polypyrrole-sulfonated graphene/hyaluronic acid-multiwalled carbon nanotubes modified electrode for determination of tryptamine

An imprinted electrochemical sensor based on polypyrrole-sulfonated graphene (PPy-SG)/hyaluronic acid-multiwalled carbon nanotubes (HA-MWCNTs) for sensitive detection of tryptamine was presented. Molecularly imprinted polymers (MIPs) were synthesized by electropolymerization using tryptamine as the template, and para-aminobenzoic acid (pABA) as the monomer. The surface feature of the modified electrode was characterized by cyclic voltammetry (CV). The proposed sensor was tested by chronoamperometry. Several important parameters controlling the performance of the molecularly imprinted sensor were investigated and optimized. The results showed that the PPy-SG composites films showed improved conductivity and electrochemical performances. HA-MWCNTs bionanocomposites could enhance the current response evidently. The good selectivity of the sensor allowed three discriminations of tryptamine from interferents, which include tyramine, dopamine and tryptophan. Under the optimal conditions, a linear ranging from 9.0×10(-8) mol L(-1) to 7.0×10(-5) mol L(-1) for the detection of tryptamine was observed with the detection limit of 7.4×10(-8) mol L(-1) (S/N=3). This imprinted electrochemical sensor was successfully employed to detect tryptamine in real samples.

L-Tryptophan: Basic Metabolic Functions, Behavioral Research and Therapeutic Indications

An essential component of the human diet, L-tryptophan is critical in a number of metabolic functions and has been widely used in numerous research and clinical trials. This review provides a brief overview of the role of L-tryptophan in protein synthesis and a number of other metabolic functions. With emphasis on L-tryptophan's role in synthesis of brain serotonin, details are provided on the research uses of L-tryptophan, particularly L-tryptophan depletion, and on clinical trials that have been conducted using L-tryptophan supplementation. The ability to change the rates of serotonin synthesis in the brain by manipulating concentrations of serum tryptophan is the foundation of much research. As the sole precursor of serotonin, experimental research has shown that L-tryptophan's role in brain serotonin synthesis is an important factor involved in mood, behavior, and cognition. Furthermore, clinical trials have provided some initial evidence of L-tryptophan's efficacy for treatment of psychiatric disorders, particularly when used in combination with other therapeutic agents.

Trace amine-associated receptor 1-Family archetype or iconoclast?

Interest has recently been rekindled in receptors that are activated by low molecular weight, noncatecholic, biogenic amines that are typically found as trace constituents of various vertebrate and invertebrate tissues and fluids. The timing of this resurgent focus on receptors activated by the "trace amines" (TA) beta-phenylethylamine (PEA), tyramine (TYR), octopamine (OCT), synephrine (SYN), and tryptamine (TRYP) is the direct result of 2 publications that appeared in 2001 describing the cloning of a novel G protein-coupled receptor (GPCR) referred to by their discoverers Borowsky et al. as TA1 and Bunzow et al. as TA receptor 1 (TAR1). When heterologously expressed in Xenopus laevis oocytes and various eukaryotic cell lines, recombinant rodent and human TAR dose-dependently couple to the stimulation of adenosine 3',5'-monophosphate (cAMP) production. Structure-activity profiling based on this functional response has revealed that in addition to the TA, other biologically active compounds containing a 2-carbon aliphatic side chain linking an amino group to at least 1 benzene ring are potent and efficacious TA receptor agonists with amphetamine (AMPH), methamphetamine, 3-iodothyronamine, thyronamine, and dopamine (DA) among the most notable. Almost 100 years after the search for TAR began, numerous TA1/TAR1-related sequences, now called TA-associated receptors (TAAR), have been identified in the genome of every species of vertebrate examined to date. Consequently, even though heterologously expressed TAAR1 fits the pharmacological criteria established for a bona fide TAR, a major challenge for those working in the field is to discern the in vivo pharmacology and physiology of each purported member of this extended family of GPCR. Only then will it be possible to establish whether TAAR1 is the family archetype or an iconoclast.

NMR spectral assignments of a new chlorotryptamine alkaloid and its analogues from Acacia confusa

A new chlorotryptamine alkaloid, N-chloromethyl-N,N-dimethyltryptamine, was isolated from a methanol extract of the Chinese shrub Acacia confusa Merr., together with its known hallucinogenic analogues, N-methyltryptamine, N,N-dimethyltryptamine and N,N-dimethyltryptamine-N-oxide. The new compound was an artefact of the isolation conditions. The complete (1)H and (13)C NMR assignments for these compounds were carried out using (1)H, (13)C, DEPT, gCOSY, gHSQC and gHMBC NMR experiments.

The mysterious trace amines: protean neuromodulators of synaptic transmission in mammalian brain

The trace amines are a structurally related group of amines and their isomers synthesized in mammalian brain and peripheral nervous tissues. They are closely associated metabolically with the dopamine, noradrenaline and serotonin neurotransmitter systems in mammalian brain. Like dopamine, noradrenaline and serotonin the trace amines have been implicated in a vast array of human disorders of affect and cognition. The trace amines are unique as they are present in trace concentrations, exhibit high rates of metabolism and are distributed heterogeneously in mammalian brain. While some are synthesized in their parent amine neurotransmitter systems, there is also evidence to suggest other trace amines may comprise their own independent neurotransmitter systems. A substantial body of evidence suggests that the trace amines may play very significant roles in the coordination of biogenic amine-based synaptic physiology. At high concentrations, they have well-characterized presynaptic "amphetamine-like" effects on catecholamine and indolamine release, reuptake and biosynthesis; at lower concentrations, they possess postsynaptic modulatory effects that potentiate the activity of other neurotransmitters, particularly dopamine and serotonin. The trace amines also possess electrophysiological effects that are in opposition to these neurotransmitters, indicating to some researchers the existence of receptors specific for the trace amines. While binding sites or receptors for a few of the trace amines have been advanced, the absence of cloned receptor protein has impeded significant development of their detailed mechanistic roles in the coordination of catecholamine and indolamine synaptic physiology. The recent discovery and characterization of a family of mammalian G protein-coupled receptors responsive to trace amines such as beta-phenylethylamine, tyramine, and octopamine, including socially ingested psychotropic drugs such as amphetamine, 3,4-methylenedioxymethamphetamine, N,N-dimethyltryptamine, and lysergic acid diethylamide, have revitalized the field of scientific studies investigating trace amine synaptic physiology, and its association with major human disorders of affect and cognition.

Tranylcypromine: new perspectives on an "old" drug

The irreversible inhibitor of monoamine oxidase, tranylcypromine, is a potent antidepressant, but its use is limited to special indications due to side effects and dietary restrictions. The antidepressant action of tranylcypromine is not completely explainable by its effects on monoamine oxidase. Tranylcypromine also leads to an increase in brain trace amines, which are believed to play a key role in the pathophysiology of depression. It also affects other pathophysiological pathways associated with depression. Tranylcypromine treatment leads to an up-regulation of GABA(B)-receptors and modulates the phospholipid metabolism, which is essential for normal brain function. These findings implicate that the efficacy of tranylcypromine as an antidepressant may be due to its multiple actions within the human brain.

Polymorphic cytochrome P450 2D6: humanized mouse model and endogenous substrates

Cytochrome P450 2D6 (CYP2D6) is the first well-characterized polymorphic phase I drug-metabolizing enzyme, and more than 80 allelic variants have been identified for the CYP2D6 gene, located on human chromosome 22q13.1. Human debrisoquine and sparteine metabolism is subdivided into two principal phenotypes--extensive metabolizer and poor metabolizer--that arise from variant CYP2D6 genotypes. It has been estimated that CYP2D6 is involved in the metabolism and disposition of more than 20% of prescribed drugs, and most of them act in the central nervous system or on the heart. These drug substrates are characterized as organic bases containing one nitrogen atom with a distance about 5, 7, or 10 A from the oxidation site. Aspartic acid 301 and glutamic acid 216 were determined as the key acidic residues for substrate-enzyme binding through electrostatic interactions. CYP2D6 transgenic mice, generated using a lambda phage clone containing the complete wild-type CYP2D6 gene, exhibits enhanced metabolism and disposition of debrisoquine. This transgenic mouse line and its wild-type control are models for human extensive metabolizers and poor metabolizers, respectively, and would have broad application in the study of CYP2D6 polymorphism in drug discovery and development, and in clinical practice toward individualized drug therapy. Endogenous 5-methoxyindole- thylamines derived from 5-hydroxytryptamine were identified as high-affinity substrates of CYP2D6 that catalyzes their O-demethylations with high enzymatic capacity and specificity. Thus, polymorphic CYP2D6 may play an important role in the interconversions of these psychoactive tryptamines, including a crucial step in a serotonin-melatonin cycle.

Synergic effects of tryptamine and octopamine on ophiuroid luminescence(Echinodermata)

In ophiuroids, bioluminescence is under nervous control. Previous studies have shown that acetylcholine is the main neurotransmitter triggering light emission in Amphipholis squamata and Amphiura filiformis. By contrast, none of the neurotransmitters tested so far induced luminescence in two other ophiuroid species, Ophiopsila aranea and Ophiopsila californica. The aim of this work was thus to investigate the putative involvement of two biogenic amines, tryptamine and octopamine, in light emission of three ophiuroid species. A. filiformis responds to both tryptamine and octopamine, mainly on its arm segments, while O. californica only responds to tryptamine stimulation. By contrast,tryptamine and octopamine do not seem to be involved in O. aranealuminescence control since none of these substances induced light emission in this species. The synergic effects of several other drugs with tryptamine and octopamine were also tested.

The relative contribution of monoamine oxidase and cytochrome p450 isozymes to the metabolic deamination of the trace amine tryptamine

Tryptamine is a trace amine in mammalian central nervous system that interacts with the trace amine TA(2) receptor and is now thought to function as a neurotransmitter or neuromodulator. It had been reported that deamination of tryptamine to tryptophol was mediated by CYP2D6, a cytochrome P450 that is expressed in human brain, suggesting that tryptamine may be an endogenous substrate for this polymorphic enzyme. We were unable to confirm this report and have reinvestigated tryptamine metabolism in human liver microsomes (HLM) and in microsomes expressing recombinant human cytochrome P450 and monoamine oxidase (MAO) isozymes. Tryptamine was oxidized to indole-3-acetaldehyde by HLM and recombinant human MAO-A in the absence of NADPH, and indole-3-acetaldehyde was further reduced to tryptophol by aldehyde reductase in HLM in the presence of NADPH. Steady-state kinetic parameters were estimated for each reaction step by HLM and MAO-A. The CYP2D6 substrates bufuralol and debrisoquine showed strong inhibition of both tryptophol production from tryptamine in HLM and the formation of indole-3-acetaldehyde from tryptamine catalyzed by recombinant MAO-A. Anti-CYP2D6 monoclonal antibody did not inhibit these reactions. Pargyline, a nonselective MAO inhibitor, did not show cross inhibition to debrisoquine 4-hydroxylation and dextromethorphan O-demethylation by HLM and recombinant CYP2D6 enzyme. This is the first unequivocal report of the selective conversion of tryptamine to tryptophol by MAO-A. CYP2D6 does not contribute to this reaction.

Trace amines: identification of a family of mammalian G protein-coupled receptors

Tyramine, beta-phenylethylamine, tryptamine, and octopamine are biogenic amines present in trace levels in mammalian nervous systems. Although some "trace amines" have clearly defined roles as neurotransmitters in invertebrates, the extent to which they function as true neurotransmitters in vertebrates has remained speculative. Using a degenerate PCR approach, we have identified 15 G protein-coupled receptors (GPCR) from human and rodent tissues. Together with the orphan receptor PNR, these receptors form a subfamily of rhodopsin GPCRs distinct from, but related to the classical biogenic amine receptors. We have demonstrated that two of these receptors bind and/or are activated by trace amines. The cloning of mammalian GPCRs for trace amines supports a role for trace amines as neurotransmitters in vertebrates. Three of the four human receptors from this family are present in the amygdala, possibly linking trace amine receptors to affective disorders. The identification of this family of receptors should rekindle the investigation of the roles of trace amines in mammalian nervous systems and may potentially lead to the development of novel therapeutics for a variety of indications.

Amphetamine and vigabatrin down regulate aromatic L-amino acid decarboxylase mRNA levels

Aromatic L-amino acid decarboxylase (AADC) has previously been shown to be up-regulated at the level of its protein activity and its mRNA abundance by antipsychotic drugs. Its activity has also been shown to be down-regulated by dopamine agonists including amphetamine. In this study we have injected rats for up to 32 days with amphetamine and the anti-epileptic drug vigabatrin, both of which can cause psychosis with similarities to schizophrenia. We have shown that AADC mRNA levels are reduced in most brain regions by both drugs. Cocaine and other non-psychotogenic anti-epileptic drugs had no effect in this paradigm. Two products of this enzyme are implicated in psychotogenesis.

The trace amines and their acidic metabolites in depression--an overview

1. Investigations of the role of the trace amines (phenylethylamine, tryptamine, m- and p-tyramine) and their acidic metabolites (phenylacetic, indoleacetic, m- and p-hydroxyphenylacetic acids) in depression are reviewed. 2. The evidence for the phenylethylamine hypothesis of depression is mixed. 3. Reduced phenylacetic acid levels in urine, plasma and CSF and changes in those levels during treatment with antidepressants show potential as state markers for depression. 4. Impaired p-tyramine conjugation following a tyramine challenge may be a good trait marker for depression.

Effects of tryptamine on plasma glucagon levels in mice

Our previous study indicated that tryptamine induces a dose-related increase in plasma glucagon levels of mice and that this effect is mediated by the peripheral serotonin2 (5-HT2) receptor. The present paper further investigated the involvement of serotonergic and catecholaminergic systems in hyperglucagonemia elicited by tryptamine. An inhibitor of 5-HT synthesis, p-chlorophenylalanine, did not affect tryptamine-induced increases in plasma glucagon levels. Tryptamine-induced hyperglucagonemia was not inhibited by adrenalectomy or by an inhibition of catecholamine synthesis by alpha-methyl-p-tyrosine. These findings indicate that tryptamine-induced hyperglucagonemia is elicited by its direct activation of 5-HT2 receptors and is not mediated by levels of endogenous 5-HT and catecholamines. The results further suggest that the peripheral 5-HT2 receptor has a possible role in the release of glucagon.

Inhibitory effects of tryptamine on tolbutamide-induced hypoglycemia in mice: mediation by 5-HT receptors

Effects of tryptamine on tolbutamide-induced hypoglycemia were investigated in mice. Tryptamine significantly inhibited hypoglycemia elicited by tolbutamide. The inhibitory effects of tryptamine were strongly blocked by the 5-HT1 and 5-HT2 receptor antagonist methysergide and the 5-HT2 receptor antagonist ketanserin, while the 5-HT3 receptor antagonist ICS 205-930 was without effect. Tryptamine induced hyperglucagonemia in tolbutamide-treated mice, and this effect elicited by tryptamine was strongly inhibited by the 5-HT2 receptor antagonist ketanserin. These results suggest that the inhibitory effects of tryptamine on tolbutamide-induced hypoglycemia are mediated by 5-HT2 receptors and that tryptamine is involved in glucagon release.

Identification of tryptamine and tryptamine-serotonin neurons in the rat dorsal raphe nuclei using specific antibodies

Previous studies have shown that tryptamine (T) is closely associated with the serotonergic system but have failed to determine whether neurons containing only T exist in the raphe nuclei (RN) and/or if T colocalizes with serotonin (5-HT). The use of rabbit-conjugated T antisera (TAS) and rat-conjugated 5-HT antisera (5-HTAS) in a double-labelling technique has made the study of the colocalization of T and 5-HT in neurons of the rat dorsal RN (DR) possible. Slices taken from the same zone of the DR were treated following four different procedures of double-immunolabelling: DAB coloration for the rabbit TAS and DAB-nickel coloration for the rat 5-HTAS either first or second; or DAB coloration for the 5-HTAS and DAB-nickel coloration for the TAS first or second. Control sections were treated according to a single immunoperoxidase staining in the same zone. The immunolabelled neurons were computed using the Biocom 200 program at the same magnification. The results of this double-immunolabelling show that three different cell types exist in the rat DR: (1) T-only-containing neurons, (2) 5-HT-only-containing neurons displaying either homogeneous DAB or homogeneous DAB-nickel, and (3) neurons where T colocalizes with 5-HT (T-positive/5-HT-positive neurons) displaying heterogeneous DAB-nickel coloration. The results were identical whatever the procedure performed or the order of the DAB-nickel revelation.(ABSTRACT TRUNCATED AT 250 WORDS)

Tryptamine: a metabolite of tryptophan implicated in various neuropsychiatric disorders

Although early interest in the biomedical relevance of tryptamine has waned in recent years, it is clear from the above discussion that the study of tryptamine is worthy of serious consideration as a factor in neuropsychiatric disorders. The study of [3H]-tryptamine binding sites indicates an adaptive responsiveness characteristic of functional receptors. The question raised by Jones (1982d) on whether tryptamine is acting centrally as a neurotransmitter or a neuromodulator still remains mostly unanswered, although the evidence cited within this review strongly suggests a modulatory role for this neuroactive amine (see also Juorio and Paterson, 1990). The synthesis and degradative pathways of tryptamine, as well as the intricate neurochemical and behavioral consequences of altering these pathways, are now more fully understood. It is not yet clear what the role of tryptamine is under normal physiological [homeostatic] conditions, however, its role during pathological conditions such as mental and physical stress, hepatic dysfunction and other disorders of metabolism (i.e. electrolyte imbalance, increased precursor availability, enzyme induction or alterations in enzyme co-factor availability) may be quite subtle, perhaps accounting for various sequelae hitherto considered idiopathic. The evidence for a primary role for tryptamine in the etiology of mental or neurological diseases is still relatively poor, although the observations that endogenous concentrations of tryptamine are particularly susceptible to pharmacological as well as physiological manipulations serve to reinforce the proposition that this indoleamine is not simply a metabolic accident but rather a neuroactive compound in its own right. Finally, one might wonder what proportion of the data attributed to modifications of 5-HT metabolism might, in fact, involve unrecognized changes in the concentrations of other neuroactive metabolites of tryptophan such as tryptamine.

Thermogenic actions of tryptophan in the rat are mediated independently of 5-HT

Serotonin (5-HT) has been implicated in the central control of energy balance, via inhibition of food intake and stimulation of thermogenesis. Its rate of synthesis in brain is dependent on the availability of its precursor amino acid, tryptophan. The objective of the present study was therefore to investigate the thermogenic actions of tryptophan and to determine whether these actions are mediated by 5-HT. Central or peripheral injections of 5-HT (i.c.v.; 0.5-40 micrograms), 5-hydroxytryptophan (5-HTP) (i.c.v.; 20 micrograms) or tryptophan (i.p.; 20 mg/kg, i.c.v.; 12-60 micrograms) significantly increased resting oxygen consumption (VO2 by approximately 15-20%) in conscious rats, without apparent effects on physical activity. Small increases (5-7%) in VO2 were also observed following peripheral injections of aspartate or glycine (20 mg/kg) but not taurine, whilst central injections of tyrosine or leucine (15-18 micrograms) significantly increased VO2 by 15%. We have previously reported that the thermogenic and anorexic actions of 5-HT are mediated by corticotropin-releasing factor (CRF). In the present study, the thermogenic actions of 5-HTP, like those of 5-HT, were significantly reduced by pretreatment (5 min before) with the CRF antagonist alpha-helical CRF9-41 (25 micrograms, i.c.v.) or a polyclonal antibody to CRF. However, the thermogenic actions of tryptophan were not significantly modified by pretreatment with either the 5-HT antagonist, methysergide (20 micrograms, i.c.v.) or with the CRF antagonist or antibody and thus appear to act through different mechanisms to 5-HT.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of different photoperiods on the diurnal rhythm of 5-methoxytryptamine in the pineal gland of golden hamsters (Mesocricetus auratus)

This study tested the photo-dependency of the rhythmic synthesis of 5-methoxytryptamine (5-MT) in the pineal gland of golden hamsters. After pargyline administration, pineal 5-methoxytryptamine and melatonin were measured by HPLC in male golden hamsters kept under short and long photoperiod. In both photoperiodic regimes, a clear 5-MT rhythm was observed which fitted a sinusoidal function with high values occurring during the daytime and low values occurring during the night-time. The duration of the low night-time levels was clearly proportional to the length of the dark phase. A marked rhythm of melatonin synthesis was also seen with low daytime levels and high night-time values. An inverse relationship between 5-MT and melatonin levels was observed. Thus, after pargyline administration, the rhythms of 5-MT and melatonin in the pineal gland of golden hamsters are photoperiod-dependent and show a reciprocal relationship.

The involvement of insulin in tryptamine-induced hypoglycemia in mice

The effects of tryptamine on plasma glucose and serum insulin levels were studied in mice. Tryptamine elicited dose-dependent hypoglycemia and hyperinsulinemia in intact mice. In streptozotocin-diabetic mice, tryptamine did not change plasma glucose nor serum insulin levels. Tryptamine significantly inhibited glucose-induced hyperglycemia and enhanced insulin release elicited by glucose. These results indicate that tryptamine-induced hypoglycemia is brought on by its releasing effects of insulin.

Phenylethylaminergic modulation of catecholaminergic neurotransmission

1. PE is present in the brain in tiny quantities; it is heterogeneously distributed and present in synaptosomes. 2. It is synthesised from phenylalanine by L-AADC and oxidatively deaminated by MAO-B. Its turnover is remarkably fast. 3. Its concentration, particularly in the caudate nucleus, is affected by MAO inhibition (increased), lesion of the Substantia nigra (decreased), amine depletion (increased) and antipsychotic drugs (increased). 4. When iontophoresed (or injected) it amplifies the effects of DA and NA (and their agonists) but is without effect on other neurotransmitters. 5. It is suggested that it acts postsynaptically as a neuromodulator of catecholaminergic neurotransmission and that it is involved in the mechanism of action of Deprenyl; it is also suggested that it, or its principal metabolite PAA, may be involved in the aetiology of schizophrenia, depression and aggression as well as perhaps in other neuropsychiatric conditions.

Upper motor neurone effects in sheep of some beta-carboline alkaloids identified in zygophyllaceous plants

The beta-carbolines harmane, norharmane, tetrahydronorharmane, harmine, harmaline and harmol were administered to sheep to assess their effects on upper motor neurone function. Harmane at a dose rate of 54 mg/kg induced hypomotility, head tremors, pelvic limb paresis, hypermetria and a wide based stance. A range of similar effects were observed with norharmane at the same dose rate. Tetrahydronorharmane at a dose rate of 54 mg/kg induced hypermotility followed by hypomotility, asymmetrical pelvic limb paresis, hypermetria, a wide based stance, and stereotyped eating behaviour. Harmine and harmaline at 6 mg/kg induced mild head and body tremors, and at 18 mg/kg induced hypomotility, intense head and body tremors, pelvic limb paresis, crossing over of limbs, neck extension and head swaying. Harmol was not effective at 54 mg/kg by either the subcutaneous or intraperitoneal routes, but at an intravenous dose of 27 mg/kg it induced hypermotility followed by hypomotility, body tremors, limb paresis, muscle asynergy, a wide based stance and jumping behaviour. Harmane, tetrahydronorharmane, harmaline and harmol were convulsive in some sheep at high dose rates.

Down-regulation of tryptamine binding sites following chronic molindone administration. A comparison with responses of dopamine and 5-hydroxytryptamine receptors

The present study assessed changes of tryptamine, dopamine D2, 5-HT1 and 5-HT2 binding sites in rat brain following chronic treatment with low (5 mg/kg/day) and high (40 mg/kg/day) doses of molindone, a clinically effective psychotropic drug. The high-dose molindone treatment produced a decrease in the number of tryptamine binding sites while both high and low doses caused an increase in the number of dopamine D2 binding sites in the striatum. No significant changes were observed in either 5-HT1 or 5-HT2 binding sites in the cerebral cortex. Competition binding experiments showed that molindone was a potent inhibitor at dopamine D2 but less effective at tryptamine, 5-HT1 and 5-HT2 binding sites. The inhibition activity of molindone towards type A monoamine oxidase produced a significant increase in endogenous tryptamine accumulation rate which was much higher than that of dopamine and 5-HT. These findings suggest that the reduction in the number of tryptamine binding sites produced by chronic molindone administration is related to monoamine oxidase inhibition and that the increase in the number of dopamine D2 binding sites is correlated to receptor blocking activity of the drug.

Binding sites for brain trace amines

1. Neurochemical, neuropharmacological, and neurophysiological studies suggest that some of the so-called trace amines may have a role in the modulation of neurotransmission. This review examines the possible existence and characterization of brain binding sites for the trace amines. 2. The results of radioligand binding studies carried out so far suggest the existence of tryptamine binding sites that possibly constitute a true functional receptor. This is supported by evidence obtained from the saturation studies, drug-mediated inhibition of binding, and the changes in the number of sites induced by pharmacological and lesion studies. In addition, the existence of a functional tryptamine binding site is supported by the increased neurophysiological responses of tryptamine obtained from the striatum of rat with unilateral substantia nigra lesions. 3. It has been shown that the brain contains saturable binding sites for rho-tyramine that appear to be related to the transport of dopamine into synaptic vesicles. There are, however, some questions with respect to the homogenization technique employed and some inconsistencies with respect to the number of binding sites estimated in neuronal membrane preparations. 4. The existence of rho-octopamine binding sites has been demonstrated in crude membranes obtained from fruitflies but not shown so far in vertebrates. 5. The presence of brain binding sites for beta-phenylethylamine are suggested but they are not so well defined and its physiological implication remains to be elucidated.

A comparison of the effects of tryptamine and 5-hydroxytryptamine on feeding following injection into the paraventricular nucleus of the hypothalamus

The effects of 5-hydroxytryptamine (5-HT) and tryptamine injected into the paraventricular nucleus of the hypothalamus (PVN) on food intake, and on noradrenaline- (NA) induced feeding were examined. In nondeprived rats, 12.5-100 nmol 5-HT reduced the intake of palatable wet mash diet over a 30-minute period. Tryptamine (50 and 100 nmol) was without effect in this paradigm. However, when tryptamine was injected into the PVN of rats pretreated with the monoamine oxidase inhibitor, pargyline, a strong anorectic effect was observed. The action of tryptamine in pargyline-treated rats was not affected by depletion of 5-HT levels in the PVN with PCPA. This indicates that the effect of tryptamine is not mediated by a release of endogenous 5-HT. Tryptamine injected into the PVN potentiated the effect of a low dose of 5-HT on food intake. This effect may be due to a prolongation of the activity of 5-HT resulting from tryptamine competing with 5-HT for the same reuptake system. Tryptamine and 5-HT attenuated the feeding response elicited by injection of 25 nmol NA into the PVN. Both tryptamine and 5-HT were more potent at attenuating the effects of NA than in reducing the intake of the palatable wet mash diet. Overall, the results suggest that tryptamine may act via the serotonergic system in the PVN to affect food intake, but it is a weaker compound than 5-HT in this respect.

Tryptamine receptors: neurochemical and electrophysiological evidence for postsynaptic and functional binding sites

[3H]Tryptamine binding characteristics and responsiveness of spontaneously active caudate nucleus neurons to intravenous application of drugs were assessed 6 weeks following unilateral application of 6-hydroxydopamine (6-OHDA, 8 micrograms) to the substantia nigra of male Wistar rats. The effects of this lesion procedure on caudatal levels of dopamine, 5-hydroxytryptamine (5-HT) and their acid metabolites, and on pargyline-induced (200 mg/kg, 2 h, s.c.) accumulation of tryptamine in the caudate nucleus were also assessed. Levels of caudatal dopamine and metabolites were reduced ipsilateral to the lesion. Concurrently there was a reduction in the extent of pargyline-induced tryptamine accumulation. Caudatal [3H]tryptamine binding was increased ipsilateral to the lesion, indicating a postsynaptic localization of this binding site. Bmax values in the caudatal samples ipsilateral to the lesion were increased by an average of 34% relative to the contralateral side. Contralateral Bmax values were equivalent to those routinely obtained in control animals. The affinity (Kd) of these binding sites for [3H]tryptamine was unchanged by the lesion procedure. The firing rate of caudate neurons was inhibited by intravenous application of tryptamine, apomorphine and 5-MeODMT. The lesion procedure did not affect these responses to 5-MeODMT. Responses to tryptamine and to apomorphine were enhanced ipsilateral to the lesion by 10- and 3-fold respectively. Haloperidol (0.5 mg/kg, i.v.) reversed apomorphine-induced inhibition of caudatal neuronal firing rate. The effects of tryptamine were not reversed by haloperidol. These data indicate a classical adaptive increase in [3H]tryptamine binding in caudate following 6-OHDA lesions.(ABSTRACT TRUNCATED AT 250 WORDS)

Tryptamine impairs the acquisition of a one-way active avoidance task

The effects of intraperitoneal administration of tryptamine to rats pretreated with iproniazid, on the acquisition of an unsignalled one-way active avoidance task, were examined. Tryptamine at 2.5 and 5 mg/kg significantly increased the number of trials required to perform this task to a 9/10 consecutive avoidances criterion, without affecting escape performance. The iproniazid pretreatment had no affect on acquisition, or any other performance variable, of the task. Tryptamine did not significantly affect the avoidance response, or escape response latencies; further tryptamine did not alter gross locomotor activity measured as photocell counts. These results suggest that the acquisition deficit was not the result of nonassociative effects such as changes in response capability, general activity level or nociception. The acquisition deficit induced by tryptamine may involve a direct stimulation of central 5-HT receptors since it was not induced by systemically administered 5-HT, was reversed by the 5-HT antagonists methysergide and metergoline, but was not affected by depletion of brain 5-HT, with PCPA, or by the dopamine antagonist haloperidol. Possible behavioural mechanisms for the action of tryptamine are discussed.

Release of some endogenous trace amines from rat striatal slices in the presence and absence of a monoamine oxidase inhibitor

The basal and 50 mM K+-stimulated release of m-tyramine (mTA), p-tyramine (pTA), tryptamine (TR) and phenylethylamine (PE) from striatal slices obtained from rats pretreated with a monoamine oxidase inhibitor (MAOI) was investigated. A K+-stimulated release of mTA and pTA was observed, but K+ did not stimulate either TR or PE release. The latter two amines, therefore, are unlikely to be conventional neurotransmitters in the rat striatum. The release of endogenous striatal pTA from control rats was also investigated. Veratridine stimulated endogenous pTA release, but 50 mM K+ did not. It is possible, therefore, that endogenous pTA can be released in a transmitter-like fashion.

The hypoglycemic effects of tryptamine in mice: mediation by 5-HT receptors

The effects of tryptamine on blood glucose levels were studied. Tryptamine induced significant hypoglycemia in mice. The hypoglycemia elicited by tryptamine was strongly antagonized by methysergide, an antagonist of both 5-HT1 and 5-HT2 receptors. A 5-HT2 receptor antagonist, ketanserin, partially inhibited the tryptamine-induced hypoglycemia. These results suggest that tryptamine-induced hypoglycemia is mediated by 5-HT1 and 5-HT2 receptors.

[3H]tryptamine binding sites are not identical to monoamine oxidase in rat brain

Competition binding studies, subcellular distribution, and in vitro autoradiography were employed to compare the binding in rat brain of [3H]tryptamine with two radioligands for monoamine oxidase (MAO), [3H]pargyline, and [3H]1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine ([3H]MPTP). The MAO inhibitors pargyline, clorgyline, and deprenyl all yielded biphasic competition curves versus [3H]tryptamine. At low concentrations, these drugs stimulated binding by protecting the radioligand from MAO oxidation; at considerably higher concentrations, they inhibited binding by direct competition at the [3H]tryptamine binding site. In subcellular distribution studies, [3H]tryptamine was localized preferentially to the synaptosomal fraction, whereas [3H]pargyline showed greater binding to the mitochondrial fraction. Equilibrium binding studies revealed that the potencies of a series of seven compounds at inhibiting [3H]tryptamine binding were completely different from their potencies at inhibiting [3H]MPTP binding. Finally, the autoradiographic distribution of [3H]tryptamine binding in rat brain was different from that of [3H]MPTP and [3H]pargyline. We conclude that the [3H]tryptamine binding site in rat brain is not equivalent to MAO.

Cerebrospinal fluid indoleacetic acid in autistic subjects

Cerebrospinal fluid (CSF) levels of the tryptamine metabolite, indoleacetic acid (IAA), have been measured in groups of autistic and control subjects. No significant difference was seen in group mean (+/- SEM) levels of CSF IAA (autistics 5.53 +/- 0.47 ng/ml, N = 10). The finding indicates that central metabolism of the behaviorally active trace amine tryptamine is probably normal in autism.

Formation of a new biogenic aldehyde adduct by incubation of tryptamine with rat brain tissue

Tryptamine was degraded by incubation with rat brain homogenate to an unknown product. The reaction was stimulated by the nonionic detergents Triton X-100 and Lubrol PX and less by the zwitterionic detergent 3-[(3-cholamidopropyl)dimethylammonio]1-propanesulfonate (CHAPS). The same results were obtained with pig brain and bovine brain. The monoamine oxidase inhibitor pargyline inhibited the reaction strongly, indicating the participation of the enzyme on the reaction. Addition of 17,000 g supernatant from rat brain homogenate increased the formation effectively whereas phospholipids or chloroform/methanol (7:3) extract from the 17,000 g supernatant showed only little or no effect. Chromatographic and electrophoretic properties as well as the chemical reaction of the product with specific reagents suggest that the compound consists of an indole part and an amino acid part. The product could be identified by fast atom bombardment mass spectrometry and by comparison with the synthetic substance (4R)-2-(3-indolylmethyl)-1,3-thiazolidine-4-carboxylic acid. It is formed by the enzymatic oxidation of tryptamine producing indole-3-acetaldehyde which spontaneously cyclizes with free L-cysteine from the tissue. The results suggest that the reaction of biogenic aldehydes with brain macromolecules may proceed via an analogous reaction.