Does phenylethylamine have a role in schizophrenia?: LSD and PCP up-regulate aromatic L-amino acid decarboxylase mRNA levels

Cannabinoid receptor gene CNR1 is downregulated in subcortical brain samples and upregulated in blood samples of individuals with schizophrenia: A participant data systematic meta-analysis

Cannabis use leads to symptom exacerbation in schizophrenia patients, and endocannabinoid ligands have been studied as tentative schizophrenia therapeutics. Here, we aimed to characterise the connection between schizophrenia and the cannabinoid receptor 1 gene (CNR1) and explore possible mechanisms affecting its expression in schizophrenia. We performed a participant data systematic meta-analysis of CNR1 gene expression and additional endocannabinoid system genes in both brain (subcortical areas) and blood samples. We integrated eight brain sample datasets (overall 316 samples; 149 schizophrenia and 167 controls) and two blood sample datasets (overall 90 samples; 53 schizophrenia and 37 controls) while following the PRISMA meta-analysis guidelines. CNR1 was downregulated in subcortical regions and upregulated in blood samples of patients with schizophrenia. CNR2 and genes encoding endocannabinoids synthesis and degradation did not show differential expression in the brain or blood, except fatty acid amide hydrolase (FAAH), which showed a downregulation trend in blood. In addition, the brain expression levels of CNR1 and three GABA receptor genes, GABRA1, GABRA6 and GABRG2, were positively correlated (R = .57, .36, .54; p = 2.7 × 10-14 , 6.9 × 10-6 and 1.1 × 10-12 , respectively). Brain CNR1 downregulation and the positive correlation with three GABA receptor genes suggest an association with GABA neurotransmission and possible effects on negative schizophrenia symptoms. Further studies are required for clarifying the opposite CNR1 dysregulation in the brain and blood of schizophrenia patients and the potential of endocannabinoid ligands as schizophrenia therapeutics.

Trace Amines and Their Receptors

Trace amines are endogenous compounds classically regarded as comprising β-phenylethyalmine, p-tyramine, tryptamine, p-octopamine, and some of their metabolites. They are also abundant in common foodstuffs and can be produced and degraded by the constitutive microbiota. The ability to use trace amines has arisen at least twice during evolution, with distinct receptor families present in invertebrates and vertebrates. The term "trace amine" was coined to reflect the low tissue levels in mammals; however, invertebrates have relatively high levels where they function like mammalian adrenergic systems, involved in "fight-or-flight" responses. Vertebrates express a family of receptors termed trace amine-associated receptors (TAARs). Humans possess six functional isoforms (TAAR1, TAAR2, TAAR5, TAAR6, TAAR8, and TAAR9), whereas some fish species express over 100. With the exception of TAAR1, TAARs are expressed in olfactory epithelium neurons, where they detect diverse ethological signals including predators, spoiled food, migratory cues, and pheromones. Outside the olfactory system, TAAR1 is the most thoroughly studied and has both central and peripheral roles. In the brain, TAAR1 acts as a rheostat of dopaminergic, glutamatergic, and serotonergic neurotransmission and has been identified as a novel therapeutic target for schizophrenia, depression, and addiction. In the periphery, TAAR1 regulates nutrient-induced hormone secretion, suggesting its potential as a novel therapeutic target for diabetes and obesity. TAAR1 may also regulate immune responses by regulating leukocyte differentiation and activation. This article provides a comprehensive review of the current state of knowledge of the evolution, physiologic functions, pharmacology, molecular mechanisms, and therapeutic potential of trace amines and their receptors in vertebrates and invertebrates.

Trace Amines and the Trace Amine-Associated Receptor 1: Pharmacology, Neurochemistry, and Clinical Implications

Biogenic amines are a collection of endogenous molecules that play pivotal roles as neurotransmitters and hormones. In addition to the "classical" biogenic amines resulting from decarboxylation of aromatic acids, including dopamine (DA), norepinephrine, epinephrine, serotonin (5-HT), and histamine, other biogenic amines, present at much lower concentrations in the central nervous system (CNS), and hence referred to as "trace" amines (TAs), are now recognized to play significant neurophysiological and behavioral functions. At the turn of the century, the discovery of the trace amine-associated receptor 1 (TAAR1), a phylogenetically conserved G protein-coupled receptor that is responsive to both TAs, such as β-phenylethylamine, octopamine, and tyramine, and structurally-related amphetamines, unveiled mechanisms of action for TAs other than interference with aminergic pathways, laying the foundations for deciphering the functional significance of TAs and its mammalian CNS receptor, TAAR1. Although, its molecular interactions and downstream targets have not been fully elucidated, TAAR1 activation triggers accumulation of intracellular cAMP, modulates PKA and PKC signaling and interferes with the β-arrestin2-dependent pathway via G protein-independent mechanisms. TAAR1 is uniquely positioned to exert direct control over DA and 5-HT neuronal firing and release, which has profound implications for understanding the pathophysiology of, and therefore designing more efficacious therapeutic interventions for, a range of neuropsychiatric disorders that involve aminergic dysregulation, including Parkinson's disease, schizophrenia, mood disorders, and addiction. Indeed, the recent development of novel pharmacological tools targeting TAAR1 has uncovered the remarkable potential of TAAR1-based medications as new generation pharmacotherapies in neuropsychiatry. This review summarizes recent developments in the study of TAs and TAAR1, their intricate neurochemistry and pharmacology, and their relevance for neurodegenerative and neuropsychiatric disease.

Behavioral and molecular biomarkers in translational animal models for neuropsychiatric disorders

Modeling neuropsychiatric disorders in animals poses a significant challenge due to the subjective nature of diverse often overlapping symptoms, lack of objective biomarkers and diagnostics, and the rudimentary understanding of the pathophysiology. Successful translational research requires animal models that can inform about disease mechanisms and therapeutic targets. Here, we review behavioral and neurobiological findings from selected animal models, based on presumed etiology and risk factors, for schizophrenia, bipolar disorder, and major depressive disorder. We focus on the use of appropriate statistical tools and newly developed Research Domain Criteria (RDoC) to link biomarkers from animal models with the human disease. We argue that this approach will lead to development of only the most robust animal models for specific psychiatric disorders and may ultimately lead to better understanding of the pathophysiology and identification of novel biomarkers and therapeutic targets.

Enhancing aromatic L-amino acid decarboxylase activity: implications for L-DOPA treatment in Parkinson's disease

Aromatic L-amino acid decarboxylase (AAAD) is an essential enzyme for the formation of catecholamines, indolamines, and trace amines. Moreover, it is a required enzyme for converting L-DOPA to dopamine when treating patients with Parkinson's disease (PD). There is now substantial evidence that the activity of AAAD in striatum is regulated by activation and induction, and second messengers play a role. Enzyme activity can be modulated by drugs acting on a number of neurotransmitter receptors including dopamine (D1-4), glutamate (NMDA), serotonin (5-HT(1A), 5-HT(2A)) and nicotinic acetylcholine receptors. Generally, antagonists enhance AAAD activity; while, agonists may diminish it. Enhancement of AAAD activity is functional, as the formation of dopamine from exogenous L-DOPA mirrors activity. Following a lesion of nigrostriatal dopaminergic neurons, AAAD in striatum responds more robustly to pharmacological manipulations, and this is true for the decarboxylation of exogenous L-DOPA as well. We review the evidence for parallel modulation of AAAD activity and L-DOPA decarboxylation and propose that this knowledge can be exploited to optimize the formation of dopamine from exogenous L-DOPA. This information can be used as a blue print for the design of novel L-DOPA treatment adjuvants to benefit patients with PD.

Effects of haloperidol and risperidone on the expression of heat shock protein 70 in MK-801-treated rat C6 glioma cells

Non-competitive N-methyl-D-aspartate (NMDA) receptor antagonists such as dizocilpine (MK-801) produce schizophrenia-like psychosis in humans and induce the expression of heat shock protein 70 (HSP70) in rats. The present study examines the effects of antipsychotic drugs, haloperidol and risperidone, on the expression of HSP70 produced by MK-801 in rat C6 glioma cells. After pretreating with haloperidol and risperidone for 1 h, 6 h, 24 h and 72 h, respectively, C6 glioma cells were cultivated again in MK-801 for 6 h, and then, the extent of HSP70 expression was measured by immunoblotting using anti-HSP70 monoclonal antibody. The expression of HSP70 induced by MK-801 significantly decreased as the duration of haloperidol pretreatment was extended (p=0.002). Risperidone also increasingly attenuated the expression of HSP70 produced by MK-801 as the duration of pretreatment grew longer (p=0.003). The present findings show that haloperidol and risperidone decrease the HSP70 expression in MK-801-treated rat C6 glioma cells. These results suggest that HSP70 and NMDA receptors may play a significant role in the pathophysiology of schizophrenia.

Detection, purification and identification of an endogenous inhibitor of L-Dopa decarboxylase activity from human placenta

An endogenous inhibitor of L-Dopa decarboxylase activity was identified and purified from human placenta. The endogenous inhibitor of L-Dopa decarboxylase (Ddc) was localized in the membrane fraction of placental tissue. Treatment of membranes with phosphatidylinositol-specific phospholipase C or proteinase K did not affect membrane-associated Ddc inhibitory activity, suggesting that a population of the inhibitor is embedded within membranes. Purification was achieved by extraction from a nondenaturing polyacrylamide gel. The purification scheme resulted in the isolation of a single 35 kDa band, bearing L-Dopa decarboxylase inhibitory activity. The purified inhibitor was identified as Annexin V. The elucidation of the biological importance of the presence of an L-Dopa decarboxylase activity inhibitor in normal human tissues could provide us with new information leading to the better understanding of the biological pathways that Ddc is involved in.

Mecp2-null mice provide new neuronal targets for Rett syndrome

Background

Rett syndrome (RTT) is a complex neurological disorder that is one of the most frequent causes of mental retardation in women. A great landmark in research in this field was the discovery of a relationship between the disease and the presence of mutations in the gene that codes for the methyl-CpG binding protein 2 (MeCP2). Currently, MeCP2 is thought to act as a transcriptional repressor that couples DNA methylation and transcriptional silencing. The present study aimed to identify new target genes regulated by Mecp2 in a mouse model of RTT.

Methodology/Principal Findings

We have compared the gene expression profiles of wild type (WT) and Mecp2-null (KO) mice in three regions of the brain (cortex, midbrain, and cerebellum) by using cDNA microarrays. The results obtained were confirmed by quantitative real-time PCR. Subsequent chromatin immunoprecipitation assays revealed seven direct target genes of Mecp2 bound in vivo (Fkbp5, Mobp, Plagl1, Ddc, Mllt2h, Eya2, and S100a9), and three overexpressed genes due to an indirect effect of a lack of Mecp2 (Irak1, Prodh and Dlk1). The regions bound by Mecp2 were always methylated, suggesting the involvement of the methyl-CpG binding domain of the protein in the mechanism of interaction.

Conclusions

We identified new genes that are overexpressed in Mecp2-KO mice and are excellent candidate genes for involvement in various features of the neurological disease. Our results demonstrate new targets of MeCP2 and provide us with a better understanding of the underlying mechanisms of RTT.

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.

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.

Purification of an endogenous inhibitor of L-Dopa decarboxylase activity from human serum

An endogenous inhibitor of L-Dopa decarboxylase was identified and purified from human serum. In Triton X-114 partitioning experiments, the inhibitor was recovered in the detergent enriched phase, suggesting a hydrophobic nature. Purification was achieved by means of proteinase K digestion, ammonium sulphate precipitation, phenyl sepharose hydrophobic chromatography and subsequent extraction from a nondenaturing polyacrylamide gel. This purification scheme resulted in the isolation of a single 25 kDa band, bearing L-Dopa decarboxylase inhibitory activity. The purified molecule was found to be resistant to heat and digestion by various proteases. Proteolytic digestion of the purified inhibitor by pronase and aminopeptidase M was achieved only following carboxymethylation. The biological importance of the presence of an L-Dopa decarboxylase activity inhibitor in normal biological fluids remains to be elucidated. The better understanding of the regulation of Ddc enzymatic activity could prove valuable in the clarification of the enzyme's role in a series of pathological conditions, as well as, in physiological regulatory mechanisms.

Endogenous psychoactive tryptamines reconsidered: an anxiolytic role for dimethyltryptamine

The presence of the potent hallucinogenic psychoactive chemical N,N-dimethyltryptamine (DMT) in the human body has puzzled scientists for decades. Endogenous DMT was investigated in the 1960s and 1970s and it was proposed that DMT was involved in psychosis and schizophrenia. This hypothesis developed from comparisons of the blood and urine of schizophrenic and control subjects. However, much of this research proved inconclusive and conventional thinking has since held that trace levels of DMT, and other endogenous psychoactive tryptamines, are insignificant metabolic byproducts. The recent discovery of a G-protein-coupled, human trace amine receptor has triggered a reappraisal of the role of compounds present in limited concentrations in biological systems. Interestingly enough, DMT and other psychoactive tryptamine hallucinogens elicit a robust response at the trace amine receptor. While it is currently accepted that serotonin 5-HT(2A) receptors play a pivotal role in the activity of hallucinogenic/psychedelic compounds, we propose that the effects induced by exogenous DMT administration, especially at low doses, are due in part to activity at the trace amine receptor. Furthermore, we suggest that endogenous DMT interacts with the TA receptor to produce a calm and relaxed mental state, which may suppress, rather than promote, symptoms of psychosis. This hypothesis may help explain the inconsistency in the early analysis of endogenous DMT in humans. Finally, we propose that amphetamine action at the TA receptor may contribute to the calming effects of amphetamine and related drugs, especially at low doses.

Significance of human striatal D-neurons: implications in neuropsychiatric functions

The human striatum, especially its ventral part, the nucleus accumbens (Acc), contains numerous nonmonoaminergic aromatic L-amino acid decarboxylase (AADC) [=dopa decarboxylase (DDC)] neurons (D-neurons). AADC is the second-step synthesizing enzyme for monoamines and is also the rate-limiting enzyme of phenylethylamine (PEA) synthesis. D-neurons may participate in the manifestation of efficacy of pharmacotherapy for Parkinson's disease by taking up monoamine precursors including L-dopa or droxidopa (L-threo-DOPS) and by converting them to dopamine or noradrenaline, respectively. Although previous studies have shown that AADC activity was elevated in the striatum of drug-naive schizophrenia, the number of striatal D-neurons was reduced in autopsy brains of schizophrenia. It is unclear whether or not such reduction of striatal D-neurons implies downregulation. Possible pluripotentiality of D-neurons, including compensatory functions against aging and degeneration, was discussed based on recent published works.

Number of striatal D-neurons is reduced in autopsy brains of schizophrenics

The human striatum, especially its ventral part, the nucleus accumbens, contains numerous neurons immunoreactive for aromatic L-amino acid decarboxylase (AADC, the second-step monoamine synthesizing enzyme, =DDC: dopa decarboxylase), but not for tyrosine hydroxylase (TH, the first-step catecholamine synthesizing enzyme) or tryptophan hydroxylase (TPH, the first-step serotonin synthesizing enzyme) (Neurosci Lett 232 (1997) 111-114). These AADC (+)/TH (-)/TPH (-) neurons are named as D-neurons (Jaeger CB, Ruggiero DA, Albert VR, Joh TH, Reis DJ. Immunocytochemical localization of aromatic-L-amino acid decarboxylase. In: Bjorklund A, Hokfelt T, editors. Classical transmission in the CNS, Part I, Handbook of chemical neuroanatomy, vol. 2. Amsterdam: Elsevier, 1984. pp. 387-418). The nucleus accumbens is one of the brain regions that is involved in the pathogenesis of schizophrenia. We examined the distribution of striatal D-neurons using AADC immunohistochemistry and postmortem brains obtained by legal and pathological autopsies (nine controls (27-75 years old) and nine schizophrenics (32-78 years old), postmortem interval to fixation (PMI): 2-30 h). Because the number of AADC-positive neurons per section had a tendency to reduce in the case with longer PMI, we analyzed specimens of five controls (27-64 years old) and six schizophrenics (51-78 years old) in which the PMI was less than 8 h. The number of AADC-positive neurons was reduced in the striatum of schizophrenics compared to that of controls. The reduction was significant in the nucleus accumbens (P<0.05, t-test). D-Neurons might be involved in the pathogenesis of schizophrenia. Further studies using sex-, age- and PMI-matched controls are essential.

Dopa decarboxylase genotypes may influence age at onset of schizophrenia

Several lines of evidence implicate dopa decarboxylase (DDC) with schizophrenia. By analysis of two putative functional DDC variants in 173 schizophrenic patients and 204 controls we tested the hypotheses that DDC is involved in: (1) predisposition to schizophrenia; and (2) modulation of age at disease onset. No association was observed with schizophrenia as a whole, whereas an association between DDC genotypes and age at disease onset was suggested in males (P = 0.03). This association was most pronounced in relation to genotypes of haplotypes comprising both variants, suggesting an additive model where one variant mediates early and the other late onset. Accordingly, the haplotype-based genotypes could be assigned into three groups by their possible relative effect on age at onset: an "early", "neutral" and "late" group. Dividing the male schizophrenics into four groups with increasing age at onset, the "early" genotypes were seen to decrease in frequency from 51.5% to 16.7% while the "late" genotypes increased from 12.1% to 33.3% (P = 0.02). The difference in mean age at onset between male patients with "early" genotypes vs patients with "late" genotypes was close to 5 years (95% CI: 0.7-8.8). Thus, DDC may possibly act as a modulator of age at onset in male schizophrenics.

Interferons: potential roles in affect

A review of the literature on interferons was conducted and possible roles in neuropsychiatric disorders with affective disturbances are assessed. Interferons and interferon receptors are present in the limbic system where they appear to exert physiological effects pertinent to affect, most potently when levels rise during CNS infections. Interferons interact closely with cytokines and nitric oxide, signaling molecules implicated in depression. Results from knock-out mice suggest a role for interferon-gamma in moderating fear and anxiety, while other lines of evidence point to a role in arousal and circadian rhythms. The interferon-alpha receptor deploys an arginine methyltransferase affecting RNA editing and splicing, which seem to be disrupted in schizophrenia and bipolar disorder. S-Adenosylmethionine (SAMe), an effective antidepressant, may owe its effects in the latter disorders in part to variations in the strength of interferon-alpha signaling impacting RNA processing. Antiviral effects of interferons are of interest in lieu of viral theories of affective disorders. Finally, the relative levels of interferons gamma and alpha might play important roles in neural, and glial, development, as well as the dialog between the CNS and the immune system.

L-DOPA decarboxylase association with membranes in mouse brain

This work presents evidence on the association of active DDC molecules with membranes in mammalian brain. L-DOPA decarboxylase (DDC) is generally considered to be a cytosolic enzyme. Membrane-associated DDC was detected by immunoblotting and enzymatic assay experiments. DDC activity and immunoreactivity could be partially extracted from mammalian brain membranes by detergent. Fractionation of membranes by temperature-induced phase separation in Triton X-114, resulted in the recovery of membrane-associated DDC in separation phases where integral and hydrophobic membrane proteins separate. Treatment of membranes with phosphatidylinositol-specific phospholipase C or proteinase K, did not elute membrane-associated DDC activity, suggesting that a population of DDC molecules exist embedded within membranes. The elucidation of the functional significance of the enzyme's association with membranes could provide us with new information leading to the better understanding of the biological pathways that DDC is involved in.

Striatal cells containing aromatic L-amino acid decarboxylase: an immunohistochemical comparison with other classes of striatal neurons

In a previous study, we described a population of striatal cells in the rat brain containing aromatic L-amino acid decarboxylase, the enzyme involved in the conversion of L-DOPA into dopamine. We have also presented evidence that these cells produce dopamine in the presence of exogenous L-DOPA. In this paper, we further characterize these striatal aromatic L-amino acid decarboxylase-containing cells in order to determine whether they form a subclass of one of the known categories of striatal neurons or if they represent a novel cell type. Using immunohistochemical methods, we compared the morphology and distribution of the aromatic L-amino acid decarboxylase-immunolabeled cells with those of other classes of striatal neurons. Our results show that both the morphology and distribution of aromatic L-amino acid decarboxylase-immunolabeled cells are very distinctive and do not resemble those of cells labeled for other striatal neuronal markers. Double-labeling procedures revealed that aromatic L-amino acid decarboxylase cells do not co-localize somatostatin or parvalbumin, and only a very small percentage of them co-localize calretinin. However, the population of aromatic L-amino acid decarboxylase cells label intensely for GABA.Overall, our results suggest that these aromatic L-amino acid decarboxylase-containing cells represent a class of striatal GABAergic neurons not described previously.

Comparative sequencing and association studies of aromatic L-amino acid decarboxylase in schizophrenia and bipolar disorder

Aromatic L-amino acid decarboxylase (AADC) is a relatively non specific enzyme involved in the biosynthesis of several classical neurotransmitters including dopamine and 5-hydroxytryptamine (5HT; serotonin). AADC does not catalyse the rate limiting step in either pathway, but is rate limiting in the synthesis of 2-phenylethylamine (2PE) which is a positive modulator of dopaminergic transmission and a candidate natural psychotogenic compound.1 We and others have proposed that polymorphism in AADC resulting in altered 2PE activity might contribute to the pathogenesis of psychosis. In order to test this hypothesis, we have used denaturing high performance liquid chromatography (DHPLC)3 to screen 3943 bases of the AADC gene and its promoter regions for variants that might affect protein structure or expression in 15 unrelated people with schizophrenia, and 15 unrelated people with bipolar disorder. Three polymorphisms were identified by DHPLC: a insertion/deletion polymorphism in the 5' UTR of the neuronal specific mRNA (g.-33-30delAGAG, bases 586-589 of GenBank M77828), a T>A variant in the non-neuronal exon 1 (g. -67T>A, GenBank M88070), and a G>A polymorphism within intron 8 (g. IVS8 +75G>A, GenBank M84598). Case-control analysis did not suggest that genetic polymorphism in the AADC gene is associated with liability for developing schizophrenia or bipolar disorder.