Aromatic L-amino acid decarboxylase enzyme activity in deficient patients and heterozygotes

BACKGROUND: Aromatic L-amino acid decarboxylase (AADC) deficiency is a rare autosomal recessive disorder characterised by developmental delay, motor retardation and autonomic dysfunction. Very low concentrations in cerebrospinal fluid (CSF) of homovanillic acid (HVA) and 5-hydroxy indole acetic acid (5-HIAA) are suggestive, but not specific, for this disorder. Confirmation of the diagnosis AADC deficiency is then required by enzyme activity measurement or genetic analysis. METHODS: We describe assays for plasma AADC enzyme activity using both of its substrates, 5-hydroxytryptophan (5-HTP) and 3,4-dihydroxyphenylalanine (L-dopa). We measured AADC activity in controls, AADC deficient patients and heterozygotes. RESULTS: AADC enzyme activity in control plasma on average is a factor 8-12 higher with L-dopa as substrate than with 5-HTP. Both substrates of AADC compete for the same active site of the enzyme resulting in equally decreased residual enzyme activities in AADC deficient patients. In AADC deficient patients, the enzyme activity towards both substrates, L-dopa and 5-HTP, are equally decreased, as are the CSF concentrations of HVA, 5-HIAA and MHPG, whereas heterozygotes have intermediate AADC activity levels. CONCLUSIONS: The presently described assays for AADC activity measurement allow an efficient, reproducible and non-invasive way to confirm the diagnosis of AADC deficiency. Since AADC enzyme activity is much higher with L-dopa as a substrate, this method is to be preferred over activity measurement with 5-HTP as a substrate for diagnostic purposes.     

Nonparallel changes in brain monoamines of pyridoxine-deficient growing rats

Summary The effects of a large number of neurotropic drugs have been attributed to changes in the metabolism of 5-hydroxytryptamine. The aromatic amino acid decarboxylase considered to decarboxylate both dihydroxyphenylalanine and 5-hydroxytryptophan requires pyridoxal phosphate as coenzyme. Thus, in pyridoxine deficiency one would expect a decrease of serotonin as well as the catecholamines of the brain. In the present study we have found a very significant decrease in brain serotonin of the pyridoxine-deficient growing rat. However, the brain levels of norepinephrine and dopamine were not altered. This decrease in serotonin does not result from a decrease either in the brain level of tryptophan or the activity of tryptophan hydroxylase. Increased degradation of serotonin measured by the levels of its metabolite, 5-hydroxyindoleacetic acid is also excluded, thus suggesting the possibility that the decarboxylation of 5-hydroxytryptophan is decreased in pyridoxine deficiency.     

Studies on the enzymatic blood-brain barrier: quantitative measurements of DOPA decarboxylase in the wall of microvessels as related to the parenchyma in various CNS regions.

The presence of DOPA decarboxylase in cerebral microvessels (capillaries and venules) impedes the passage of circulating amine precursors into the brain. The relative amount of DOPA decarboxylase in this trapping mechanism as compared to the parenchyma per se was estimated in various CNS regions, measuring the formation of dopamine from L-DOPA in vitro or in vivo in two experimental models on rats and rabbits: (1) On the basis of the treatment with a peripheral decarboxylase inhibitor (carbidopa, which inhibits also microvascular DOPA decarboxylase in the CNS) it could be calculated that the enzyme in the microvessels of the caudate nucleus (rich in catecholamine nerve terminals), cerebellum (poor in catecholamine nerves), and spinal cord comprised 25, 91 and 79 per cent, respectively, of the total enzyme activity. (2) Measurement of dopamine formation in the spinal cord following transection at the midthoracic level (which causes degeneration of the catecholamine neurons caudal to the lesion since they are all descending) indicated that a similar fraction as found in the carbidopa model, 71%, of the total tissue decarboxylase activity resided in the microvessel walls. The results show that a considerable portion of tissue decarboxylase in the CNS is present in the microvessel walls, where it represents part of an enzymatic blood-brain barrier mechanism.     

Long-term therapy of myoclonus and other neurologic disorders with L-5-hydroxytryptophan and carbidopa.

We evaluated the therapeutic effect of L-5-hydroxytryptophan (L-5HTP), the precursor of serotonin (5-hydroxytryptamine), combined with carbidopa, a peripheral decarboxylase inhibitor, in patients with intention myoclonus and examined the serotonin metabolites in spinal fluid, blood and urine before and during therapy. In 18 patients with intention myoclonus due to anoxia or other brain damage, 11 derived more than 50% overall improvement during treatment with L-5HTP and carbidopa. Spinal-fluid 5-hydroxyindoleacetic acid was 35% lower in patients with intention myoclonus than in controls (P less than 0.05). Therapy with L-5HTP and carbidopa increased the concentration of serotonin metabolites in urine and spinal fluid. We postulate that a deficiency of brain serotonin is causally related to intention myoclonus and that the therapeutic effect of L-5HTP and carbidopa may be due to the repletion of serotonin in regions of the brain where serotoninergic neurons have degenerated.     

Studies on the enzymatic blood-brain barrier: Quantitative measurements of DOPA decarboxylase in the wall of microvessels as related to the parenchyma in various CNS regions

The presence of DOPA decarboxylase in cerebral microvessels (capillaries and venules) impedes the passage of circulating amine precursors into the brain. The relative amount of DOPA decarboxylase in this trapping mechanism as compared to the parenchyma per se was estimated in various CNS regions, measuring the formation of dopamine from L-DOPA in vitro or in vivo in two experimental models on rats and rabbits: (1) On the basis of the treatment with a peripheral decarboxylase inhibitor (carbidopa, which inhibits also microvascular DOPA decarboxylase in the CNS) it could be calculated that the enzyme in the microvessels of the caudate nucleus (rich in catecholamine nerve terminals), cerebellum (poor in catecholamine nerves), and spinal cord comprised 25, 91 and 79 per cent, respectively, of the total enzyme activity. (2) Measurement of dopamine formation in the spinal cord following transection at the midthoracic level (which causes degeneration of the catecholamine neurons caudal to the lesion since they are all descending) indicated that a similar fraction as found in the carbidopa model, 71 per cent, of the total tissue decarboxylase activity resided in the microvessel walls. The results show that a considerable portion of tissue decarboxylase in the CNS is present in the microvessel walls, where it represents part of an enzymatic blood-brain barrier mechanism.     

Decreased availability of intestinal dopamine in transmural colitis may relate to inhibitory effects of interferon‐γ upon L‐DOPA uptake

Aims: The present study aimed to evaluate the relationship between intestinal inflammation, interferon‐γ (IFN‐γ) levels and intestinal levels of dopamine, its precursor l ‐3,4‐dihydroxyphenylalanine (l ‐DOPA), and the activity of aromatic l ‐amino acid decarboxylase (AADC) activity along the digestive tract in a rat experimental model of colitis. Methods: Colitis was induced by rectal administration of 2,4,6‐trinitrobenzene sulphonic acid (TNBS). Catechol derivatives were assayed by means of HPLC‐EC. Results: It is shown that dopamine and noradrenaline levels in the distal colon (inflamed mucosa), but not in the ileum (non‐inflamed mucosa), of TNBS‐treated rats were markedly lower than in control animals. A slight decrease in l ‐DOPA tissue levels, no changes in AADC activity and an increase in plasma IFN‐γ levels accompanied this decrease in dopamine levels. Exposure of Caco‐2 cells, a human intestinal epithelial cell line, to human IFN‐γ resulted in a concentration‐dependent and long‐lasting inhibition of l ‐DOPA uptake, which most likely explains the decrease in dopamine levels in the inflamed mucosa. Conclusion: Changes in tissue levels of noradrenaline and dopamine in experimental colitis in the rat follow a similar pattern to that observed in patients with Crohn's disease and ulcerative colitis. In this model of experimental colitis, the decrease in dopamine levels is most likely explained by the inhibitory effect of IFN‐γ on l ‐DOPA uptake by intestinal epithelial cells.     

5-Hydroxytryptophan reversal of reserpine enhancement of audiogenic seizure susceptibility in mice

Increased sensitivity to audiogenic seizures by reserpine was antagonized by 5-hydroxytryptophan (5HTP). The antagonism was dependent upon the conversion of 5HTP to 5 hydroxytryptamine (5HT) in brain since blockade of both cerebral and extracerebral decarboxylase prevented the 5HTP effect, whereas selective blockade of extracerebral decarboxylase did not affect the 5HTP antagonism. Increased seizure susceptibility occurred when brain concentrations of 5HT were decreased, while decreased susceptibility occurred when brain concentrations of 5HT were elevated. 5HTP did not alter norepinephrine or dopamine concentrations in brain. The results of this study indicate that 5HT plays a role in modulating audiogenic seizure susceptibility.     

Genes for human catecholamine-synthesizing enzymes.

Catecholamine neurotransmitters--dopamine, noradrenaline (norepinephrine), adrenaline (epinephrine)--are synthesized in catecholaminergic neurons from tyrosine, via dopa, dopamine and noradrenaline, to adrenaline. Four enzymes are involved in the biosynthesis of adrenaline: (1) tyrosine 3-mono-oxygenase (tyrosine hydroxylase, TH); (2) aromatic L-amino acid decarboxylase (AADC, or DOPA decarboxylase, DDC); (3) dopamine beta-mono-oxygenase (dopamine beta-hydroxylase, DBH); and (4) noradrenaline N-methyltransferase (phenylethanolamine N-methyltransferase, PNMT). We cloned full-length complementary DNAs (cDNAs) and genomic DNAs of human catecholamine-synthesizing enzymes (TH, AADC, DBH, PNMT) and determined the nucleotide sequences and the deduced amino acid sequences. We discovered multiple messenger RNAs (mRNAs) of human TH, human DBH, and human PNMT. Four types (types 1, 2, 3, and 4) of human TH mRNAs are produced by alternative mRNA splicing mechanism from a single gene. We found the multiple forms of TH in two species of monkeys, but only a single mRNA corresponding to human TH type 1 in Sunkus murinus and rat, suggesting that the multiplicity of TH mRNA is primate-specific. Total TH mRNA, especially the most abundant type 2 and type 1 mRNAs in the human brain, were found to be reduced during the process of aging. The multiple forms of human TH may give additional regulation to the human enzyme, probably through altered phosphorylation and activation. We have succeeded in producing transgenic mice carrying multiple copies of the human TH gene in brain and adrenal medulla. The level of human TH mRNA in brain was about 50-fold higher than that of endogenous mouse TH mRNA. In situ hybridization demonstrated an enormous region-specific expression of the transgene in substantia nigra and ventral tegmental area. TH immunoreactivity in these regions, Western blot analysis, and TH activity measurements proved definitely increased TH in transgenic mice, though not comparable to the increment of the mRNA. However, catecholamine levels in transgenics were not significantly different from those in non-transgenics. The results suggest complex regulatory mechanisms for human TH gene expression and for the catecholamine levels in transgenic mice. Kohsaka and Uchida in collaboration with us applied genetically engineered (human TH cDNA-transfected) non-neuronal cells to brain tissue transplantation in parkinsonian rat models. We isolated and sequenced a full-length cDNA encoding human AADC.(ABSTRACT TRUNCATED AT 400 WORDS)     

Unusually mild phenotype of AADC deficiency in 2 siblings

Aromatic L-amino acid decarboxylase deficiency is a rare neurotransmitter defect leading to serotonin, dopamine and norepinephrine deficiency. Affected individuals usually present in infancy with severe developmental delay, oculogyric crises and extrapyramidal movements. We present the clinical, molecular and biochemical features of a pair of siblings who presented with fatigability, hypersomnolence and dystonia and who showed excellent response to treatment. Analysis of CSF biogenic amines, plasma AADC levels and direct sequencing of the DDC gene was performed. CSF catecholamine metabolites were reduced, with elevation of 3-O-methyldopa. Plasma AADC activity was undetectable in both siblings, and decreased in their carrier parents. One missense mutation (853C>T) was found in exon 8, and a donor splice site mutation was found in the intron after exon 6 (IVS6+4A>T). Both siblings showed excellent response to MAO inhibitor and dopamine agonist treatment. This report expands the clinical spectrum of AADC deficiency and contributes to the knowledge of the genotype and phenotype correlation for the DDC gene. It is important to recognize the milder phenotypes of the disease as these patients might respond well to therapy.     

Progesterone receptor and dopamine synthesizing enzymes in hypothalamic neurons of the guinea pig: an immunohistochemical triple-label analysis

Interactions among gonadal steroid hormones and the dopamine synthesizing enzymes, tyrosine hydroxylase (TH) or aromatic L-amino acid decarboxylase (AADC), participate in hypothalamic functions. Several findings suggest that the expression patterns of the progesterone receptor (PR), TH and AADC overlap in the guinea pig brain. However, it remained to be determined whether or not these two enzymes coexist in the same neurons which contain the PR. To test this hypothesis and quantify these colocalization relationships in the hypothalamus, we used a triple-labeling immunofluorescence procedure. Only PR/AADC-immunoreactive cells were seen in the preoptic area but no PR/TH cells and, therefore, no triple immunoreactive cells were found. An occasional colocalization between PR and the two enzymes was observed throughout the rostrocaudal extent of the arcuate nucleus with the greatest concentration of triple-labeled cells in the medial subdivision. In this region, quantitative estimation of cellular immunoreactivity showed that the triple immunoreactive cells represented about 29% of PR/TH cells, 9% of PR/AADC cells and 22% of TH/AADC cells in spite of a very low percentage in relation to total populations of neurons expressing only PR, TH or AADC. Thus, the PR are only present in monoenzymatic AADC expressing neurons in the preoptic area while they can be observed in neurons expressing both enzymes in the arcuate nucleus.     

Dopa-decarboxylation in the striata of rats with unilateral substantia nigra lesions.

The source and site of the DOPA decarboxylation to dopamine in Parkinson's disease (PD) and animal models of PD are controversial. Since most of aromatic L-amino acid decarboxylase (AADC) are lost along with the degenerating dopaminergic neurons, we addressed the possibility that other decarboxylases or a novel protein that is structurally different from AADC decarboxylate L-DOPA in the denervated striatum. Immunotitration of the extracts from the denervated striatum with AADC antibody showed that all activity can be attributed to AADC-immunoreactive protein. We then investigated if there are non-dopaminergic intrinsic striatal neurons that express AADC. No evidence of such neurons was noted by immunocytochemistry and in situ hybridization.     

Aromatic l-aminoacid decarboxylase deficiency: unusual neonatal presentation and additional findings in organic acid analysis

Aromatic l-aminoacid decarboxylase (AADC) deficiency is a neurotransmitter defect leading to a combined deficiency of catecholamines and serotonin. Patients are usually detected in infancy due to developmental delay, hypotonia, and extrapyramidal movements. Diagnosis is based on an abnormal neurotransmitter metabolite profile in CSF and reduced AADC activity in plasma. An elevation of vanillactic acid (VLA) has been described as the only abnormality detected in organic acid analysis (OA) of urine. We report a patient who presented in the neonatal period with lethargy, hypotonia, metabolic acidosis, and hypoglycemia. Blood ammonia, lactic acid, and acylcarnitines were normal, but OA of a urine sample showed a small increase of VLA, raising the suspicion of AADC deficiency. The patient was lost to follow-up until the age of 8 months, when he presented with dystonia, abnormal movements, oculogyric crises, and hypothermia. Repeat OA showed not only increased levels of VLA, but also increased vanilpyruvic acid (VPA), N-acetyl-vanilalanine (AVA) and N-acetyl-tyrosine (NAT). Neurotransmitter analysis in CSF showed increased vanilalanine (1200 nmol/L, ref<100) with decreased levels of 5-hydroxy-indoleacetic acid (5-HIAA, < 5 nmol/L; ref 152-462), homovanillic acid (HVA, 83 nmol/L; ref 302-845), and methoxy-hydroxy-phenyl-glycol (<5 nmol/L; ref 51-112). AADC activity in plasma was nearly undetectable. In the urine, low excretion of vanilmandelic acid (<0.3 micromol/mmol creat; ref 0.3-20) and 5-HIAA (0.9 micromol/mmol creat; ref 4-18), was found, but HVA was normal and dopamine even elevated. This contradictory phenomenon of hyperdopaminuria has been described earlier in AADC deficient patients. We postulate that VPA and AVA could originate from vanilalanine (through a transaminase and an acetylase respectively), while NAT could originate from tyrosine through an AA acetylase. This report expands the clinical presentation of AADC deficiency and adds new markers of the disease for OA analysis, improving detection of AADC deficient patients in general metabolic screening procedures.     

Aromatic l-amino acid decarboxylase-immunoreactive structures in human midbrain, pons, and medulla

The objective of the present study was to determine with precision the localization of neurons and fibers immunoreactive (ir) for aromatic l-amino acid decarboxylase (AADC), the second-step enzyme responsible for conversion of l-dihydroxyphenylalanine (l-DOPA) to dopamine (DA) and 5-hydroxytryptophan (5-HTP) to serotonin (5-hydroxytryptamine: 5-HT) in the midbrain, pons, and medulla oblongata of the adult human brain. Intense AADC immunoreactivity was observed in a large number of presumptive 5-HT neuronal cell bodies distributed in all of the raphe nuclei, as well as in regions outside the raphe nuclei such as the ventral portions of the pons and medulla. Moderate to strong immunoreaction was observable in presumptive DA cells in the mesencephalic reticular formation, substantia nigra, and ventral tegmental area of Tsai, as well as in presumptive noradrenergic (NA) cells, which were aggregated in the locus coeruleus and dispersed in the subcoeruleus nuclei. In the medulla oblongata, immunoreaction of moderate intensity was distributed in the mid and ventrolateral portions of the intermediate reticular nucleus, which constitutes the oblique plate of A1/C1 presumptive adrenergic and/or NA neurons. The dorsal vagal AADC-ir neurons were fewer in number and stained more weakly than cells immunoreactive for tyrosine hydroxylase (TH). AADC immunoreactivity was not identified in an aggregate of TH-ir neurons lying in the gelatinous subnucleus of the solitary nucleus, a restricted region just rostroventral to the area postrema. Nonaminergic AADC-positive neurons (D neurons), which are abundant in the rat and cat midbrain, pons, and medulla, were hardly detectable in homologous regions in the human brain, although they were clearly distinguishable in the forebrain.     

Identification of the aromatic L-amino acid decarboxylase gene expression in various mice tissues and its modulation by immobilization stress in stellate ganglia

Despite of the fact that the impact of various stressful stimuli on catecholamine biosynthetic enzyme gene expression, activity and immunoreactive protein has been intensively studied, less is known about the aromatic L-amino acid decarboxylase (AADC), the enzyme, which catalyzes decarboxylation of L-dihydroxyphenylalanine to dopamine. We focused on the identification of AADC mRNA and immunoprotein in various mice tissues and detected both in selected mice neuronal tissues (adrenal medulla, sympathetic stellate and cervical ganglia) and also in non-neuronal tissues (liver, spleen, kidney and all four parts of the heart). Surprisingly, although we failed to detect AADC mRNA in mice thymus, lungs and abdominal fat, we found presence of the AADC immunoprotein in lungs as well as in the abdominal fat. We also tested the hypothesis, whether single or repeated immobilization stress can affect the AADC mRNA or immunoprotein levels in mice stellate ganglia. We revealed that single immobilization stress exposure did not affect the AADC mRNA or immunoprotein levels, while repeated immobilization stress produced significant elevation of both, AADC mRNA and immunoprotein levels in stellate ganglia. The aromatic L-amino acid decarboxylase is generally not considered to be limiting in regulation of the catecholamine biosynthesis. However, our data suggest a possible participation of this enzyme in the regulation of catecholamine biosynthesis in stellate ganglia of repeatedly stressed mice.     

Influence of B vitamins on binding properties of serotonin receptors in the CNS of rats

Summary Treatment of normal adult rats with pyridoxine or a B-vitamin mixture resembling Neurobion^® 1 led to an increase in serotonin content of various brain areas and to a decrease in the number of serotonin S₂ receptors. The results indicate that the pyridoxal phosphate level in regions of the brain regulates the extent of decarboxylation of 5-hydroxytryptophan, the precursor of serotonin. The results also suggest a continuum from deficiency in pyridoxine to treatment of animals with a moderate excess of pyridoxine which is reflected in the synthesis and secretion into the synaptic cleft of the neurotransmitter serotonin.     

Restoration of the striatal dopamine synthesis for Parkinson's disease: viral vector-mediated enzyme replacement strategy

Parkinson's disease is the second most common neurodegenerative disease. It is charaterized by a progressive loss of dopamine (DA) producing neurons in the midbrain, which result in a decline of DA innervations present in the forebrain, in particular, the striatum. The disease leads to appearance of motor symptoms involving akinesia/bradykinesia, gait disturbances, postural imbalance and tremor. Oral administration of L-3,4-dihydroxyphenylalanine (L-DOPA), the precursor of DA, provides very good symptomatic relief, but this intermittent and pharmacological treatment is compromised by severe side effects, such as the appearance of abnormal involuntary movements. Viral vector-mediated direct gene transfer techniques are currently being explored in order to provide continuous and stable synthesis of DA in the brain. This review focuses on the basic idea of DA replacement, first describing the enzymatic machinery important for DA synthesis and secondly the various alternative strategies pursued in several laboratories. The DOPA delivery strategy, based on the co-transduction of tyrosine hydroxylase (TH), and GTP cyclohydrolase 1 (GCH1) genes, has been shown to be a powerful approach providing a robust behavioral recovery and reversal of side effects of the pulsatile administration of L-DOPA medication. The DA delivery strategy, on the other hand, aims at triple transduction of the TH, GCH1 and aromatic amino-acid decarboxylase (AADC) enzymes, and thereby provide a higher rate of conversion of DOPA to DA. Finally, transduction of AADC alone has been proposed as a means to improve the conversion of peripherally administered L-DOPA. As the basic scientific rationale behind these strategies are well understood and the results of the animal experiments are very encouraging, we are now entering into an exciting phase with increasing momentum toward the first clinical applications using this experimental therapy in patients suffering from PD.     

大鼠脑组织中谷氨酸脱羧酶65基因的克隆和序列测定

目的探讨克隆大鼠脑组织中谷氨酸脱羧酶65基因。方法采用RT-PCR方法,将大鼠脑组织中的mRNA逆转录成cDNA,再以cDNA为模板,扩增谷氨酸脱羧酶65基因片段,克隆入T载体,并经序列测定。结果RT-PCR法扩增出一特异产物与预期长度1758bp相符,T载体克隆测序与大鼠谷氨酸脱羧酶65100%同源。结论采用RT-PCR和T载体技术获得了大鼠脑组织中的谷氨酸脱羧酶GAD65基因克隆,为该基因的体外表达打下基础。     

Quinpirole--a 5-HT receptor antagonist?

The rate of brain monoamine synthesis was estimated in the rat by measuring the accumulation of dihydroxyphenylalanine (DOPA) and 5-hydroxytryptophan (5-HTP) following inhibition of cerebral aromatic amino acid decarboxylase by NSD-1015 (475 mumol/kg, i.p., 30 min before decapitation). As expected, pretreatment with reserpine, (8.2 mumol/kg, s.c., -18 h) produced a marked and statistically significant increase in the DOPA accumulation in the ventral striatum and in the neocortex, whereas only minor changes were noted in 5-HTP accumulation in the same brain areas. The administration of terguride or quinpirole (30 mumol/kg, s.c., -65 min) resulted in both cases in an antagonism of the reserpine-induced increase in the DOPA accumulation. The effect was less marked in the neocortex than in the ventral striatum, but there was no difference between the effects produced by either compound. In contrast, the two drugs produced opposite effects on the 5-HTP accumulation in the ventral striatum as well as in the neocortex. Thus, there was a decrease and an increase in the 5-HTP accumulation by terguride and quinpirole administration, respectively. Together the results suggest that, in the reserpine treated rat, both terguride and quinpirole to the same degree stimulate dopamine receptors in the ventral striatum and noradrenaline receptors in the neocortex. To the extent that serotonin receptors in these two brain areas mediate the effects on 5-HTP accumulation of terguride and quinpirole, respectively, these receptors appear differently affected by the two compounds: stimulation by terguride and blockade by quinpirole.     

Circadian rhythm of aromatic L-amino acid decarboxylase in the rat suprachiasmatic nucleus: gene expression and decarboxylating activity in clock oscillating cells

BACKGROUND: Aromatic L-amino acid decarboxylase (AADC) is the enzyme responsible for the decarboxylation step in both the catecholamine and indoleamine synthetic pathways. In the brain, however, a group of AADC containing neurones is found outside the classical monoaminergic cell groups. Since such non-monoaminergic AADC is expressed abundantly in the suprachiasmatic nucleus (SCN), the mammalian circadian centre, we characterized the role of AADC in circadian oscillation. RESULTS: AADC gene expression was observed in neurones of the dorsomedial subdivision of the SCN and its dorsal continuant in the anterior hypothalamic area. These AADC neurones could uptake exogenously applied L-DOPA and formed dopamine. AADC was co-expressed with vasopressin and the clock gene Per1 in the neurones of the SCN. Circadian gene expression of AADC was observed with a peak at subjective day and a trough at subjective night. The circadian rhythm of AADC enzyme activity in the SCN reflects the expression of the gene. CONCLUSIONS: Non-monoaminergic AADC in the SCN is expressed in clock oscillating cells, and the decarboxylating activity of master clock cells are under the control of the circadian rhythm.