Role of epoxyeicosatrienoic acids (EETs) in mediation of dopamine's effects in the kidney.

We have recently demonstrated that intrarenal dopamine plays an important role in preventing the development of systemic hypertension. Similarly, renal cytochrome P-450 (CYP)-epoxygenase-derived arachidonic acid metabolites, epoxyeicosatrienoic acids (EETs), also are antihypertensive through inhibiting sodium reabsorption and vasodilation. The potential interaction between renal dopamine and epoxygenase systems was investigated. Catechol-O-methyl-transferase (COMT)(-/-) mice with increased intrarenal dopamine levels and proximal tubule deletion of aromatic amino acid decarboxylase (ptAADC(-/-)) mice with renal dopamine deficiency were treated with a low-salt diet or high-salt diet for 2 wk. Wild-type or Cyp2c44(-/-) mice were treated with gludopa, which selectively increased renal dopamine levels. In low salt-treated mice, urinary EET levels were related to renal dopamine levels, being highest in COMT(-/-) mice and lowest in ptAADC(-/-) mice. In high salt-treated mice, total EET and individual EET levels in both the kidney and urine were also highest in COMT(-/-) mice and lowest in ptAADC(-/-) mice. Selective increases in renal dopamine in response to gludopa administration led to marked increases in both total and all individual EET levels in the kidney without any changes in blood levels. qRT-PCR and immunoblotting indicated that gludopa increased renal Cyp2c44 mRNA and protein levels. Gludopa induced marked increases in urine volume and urinary sodium excretion in wild-type mice. In contrast, gludopa did not induce significant increases in urine volume or urinary sodium excretion in Cyp2c44(-/-) mice. These studies demonstrate that renal EET levels are maintained by intrarenal dopamine, and Cyp2c44-derived EETs play an important role in intrarenal dopamine-induced natriuresis and diuresis.

Aromatic L-amino acid decarboxylase (AADC) is crucial for brain development and motor functions.

Aromatic L-amino acid decarboxylase (AADC) deficiency is a rare pediatric neuro-metabolic disease in children. Due to the lack of an animal model, its pathogenetic mechanism is poorly understood. To study the role of AADC in brain development, a zebrafish model of AADC deficiency was generated. We identified an aadc gene homolog, dopa decarboxylase (ddc), in the zebrafish genome. Whole-mount in situ hybridization analysis showed that the ddc gene is expressed in the epiphysis, locus caeruleus, diencephalic catecholaminergic clusters, and raphe nuclei of 36-h post-fertilization (hpf) zebrafish embryos. Inhibition of Ddc by AADC inhibitor NSD-1015 or anti-sense morpholino oligonucleotides (MO) reduced brain volume and body length. We observed increased brain cell apoptosis and loss of dipencephalic catecholaminergic cluster neurons in ddc morphants (ddc MO-injected embryos). Seizure-like activity was also detected in ddc morphants in a dose-dependent manner. ddc morphants had less sensitive touch response and impaired swimming activity that could be rescued by injection of ddc plasmids. In addition, eye movement was also significantly impaired in ddc morphants. Collectively, loss of Ddc appears to result in similar phenotypes as that of ADCC deficiency, thus zebrafish could be a good model for investigating pathogenetic mechanisms of AADC deficiency in children.

Biochemical evaluation of the decarboxylation and decarboxylation-deamination activities of plant aromatic amino acid decarboxylases.

Plant aromatic amino acid decarboxylase (AAAD) enzymes are capable of catalyzing either decarboxylation or decarboxylation-deamination on various combinations of aromatic amino acid substrates. These two different activities result in the production of arylalkylamines and the formation of aromatic acetaldehydes, respectively. Variations in product formation enable individual enzymes to play different physiological functions. Despite these catalytic variations, arylalkylamine and aldehyde synthesizing AAADs are indistinguishable without protein expression and characterization. In this study, extensive biochemical characterization of plant AAADs was performed to identify residues responsible for differentiating decarboxylation AAADs from aldehyde synthase AAADs. Results demonstrated that a tyrosine residue located on a catalytic loop proximal to the active site of plant AAADs is primarily responsible for dictating typical decarboxylase activity, whereas a phenylalanine at the same position is primarily liable for aldehyde synthase activity. Mutagenesis of the active site phenylalanine to tyrosine in Arabidopsis thaliana and Petroselinum crispum aromatic acetaldehyde synthases primarily converts the enzymes activity from decarboxylation-deamination to decarboxylation. The mutation of the active site tyrosine to phenylalanine in the Catharanthus roseus and Papaver somniferum aromatic amino acid decarboxylases changes the enzymes decarboxylation activity to a primarily decarboxylation-deamination activity. Generation of these mutant enzymes enables the production of unusual AAAD enzyme products including indole-3-acetaldehyde, 4-hydroxyphenylacetaldehyde, and phenylethylamine. Our data indicates that the tyrosine and phenylalanine in the catalytic loop region could serve as a signature residue to reliably distinguish plant arylalkylamine and aldehyde synthesizing AAADs. Additionally, the resulting data enables further insights into the mechanistic roles of active site residues.

Patterns of renal dopamine release to regulate diuresis and natriuresis during volume expansion. Role of renal monoamine-oxidase.

Diuretic and natriuretic effects of renal dopamine (DA) are well established. However, in volume expansion the pattern of renal DA release into urine (UDAV) and the role of enzymes involved in DA synthesis/degradation have not yet been defined. The objective was to determine the pattern of UDAV during volume expansion and to characterize the involvement of monoamine-oxidase (MAO) and aromatic amino-acid decarboxylase (AADC) in this response. In this study male Wistar rats were expanded with NaCl 0.9% at a rate of 5% BWt per hour. At the beginning of expansion three groups received a single drug injection as follows: C (vehicle, Control), IMAO (MAO inhibitor Pargyline, 20 mg/kg BWt, i.v.) and BNZ (AADC inhibitor Benserazide, 25 mg/kg BWt, i.v.). Results revealed that in C rats UDAV (ng/30 min/100g BWt) increased in the first 30 min expansion from 11.5 +/- 1.20 to 21.8 +/- 3.10 (p < 0.05) and decreased thereafter. IMAO showed a similar pattern but significantly higher than C at 30 min expansion (32.5 +/- 2.20, p < 0.05). IMAO greatly reduced MAO activity from 8.29 +/- 0.35 to 1.1 +/- 0.03 nmol/mg tissue/hour and significantly increased diuresis and natriuresis over controls. BNZ abolished the early UDAV peak to 3.2+/-0.72 (p < 0.01) and though, UDAV increased over C after 60 min expansion, natriuresis and diuresis were diminished by BNZ treatment. Results indicate that an increment in renal DA release into urine occurs early in expansion and in a peak-shaped way. In this response MAO plays a predominant role.

Patterns of renal dopamine release to regulate diuresis and natriuresis during volume expansion: Role of renal monoamine-oxidase / Perfiles de secreción de dopamina renal en la expansión de volumen para regular diuresis y natriuresis: Rol de la monoaminoxidasa renal

Diuretic and natriuretic effects of renal dopamine (DA) are well established. However, in volume expansion the pattern of renal DA release into urine (U DA V) and the role of enzymes involved in DA synthesis/degradation have not yet been defined. The objective was to determine the pattern of U DA V during volume expansion and to characterize the involvement of monoamine-oxidase (MAO) and aromatic amino-acid decarboxylase (AADC) in this response. In this study male Wistar rats were expanded with NaCl 0.9% at a rate of 5% BWt per hour. At the beginning of expansion three groups received a single drug injection as follows: C (vehicle, Control), IMAO (MAO inhibitor Pargyline, 20 mg/kg BWt, i.v.) and BNZ (AADC inhibitor Benserazide, 25 mg/kg BWt, i.v.). Results revealed that in C rats U DA V (ng/30 min/100g BWt) increased in the first 30 min expansion from 11.5 ± 1.20 to 21.8 ± 3.10 (p < 0.05) and decreased thereafter. IMAO showed a similar pattern but significantly higher than C at 30 min expansion (32.5 ± 2.20, p < 0.05). IMAO greatly reduced MAO activity from 8.29 ± 0.35 to 1.1 ± 0.03 nmol/mg tissue/hour and significantly increased diuresis and natriuresis over controls. BNZ abolished the early U DA V peak to 3.2±0.72 (p < 0.01) and though, U DA V increased over C after 60 min expansion, natriuresis and diuresis were diminished by BNZ treatment. Results indicate that an increment in renal DA release into urine occurs early in expansion and in a peak-shaped way. In this response MAO plays a predominant role.

La dopamina (DA) intrarrenal ejerce efectos diuréticos y natriuréticos. Sin embargo, en los estado de expansión de volumen aún no está bien definido el patrón de liberación de dopamina renal hacia la orina y si cumplen un rol las enzimas involucradas en la síntesis o degradación de la amina. El objetivo del presente trabajo fue determinar el patrón de excreción urinaria de DA (U DA V) durante la expansión de volumen, caracterizando la participación de las enzimas monoaminooxidasa (MAO) y decarboxilasa de aminoácidos aromáticos (AADC) en esta respuesta. Para ello ratas Wistar macho fueron expandidas de volumen con NaCl 0.9% al 5% del peso corporal por hora durante dos horas y divididas en tres grupos, los que al comienzo de la expansión recibieron: C (vehículo, Control), IMAO (Pargilina, inhibidor de MAO, 20 mg/kg PC, i.v.) y BNZ (Benserazida, inhibidor de AADC, 25 mg/kg PC, i.v.). Se observó que en C la U DA V (ng/30min/100gPC) aumentó durante los primeros 30 minutos de expansión de 11.5 ± 1.20 a 21.8 ± 3.10 (p < 0.05), disminuyendo posteriormente. IMAO mostró un patrón de liberación similar pero significativamente mayor que C a los 30 min de expansión (32.5 ± 2.20, p < 0.05). En este grupo la actividad de MAO disminuyó de 8.29 ± 0.35 a 1.1 ± 0.03 nmol/mg tejido/hora y aumentaron la diuresis y natriuresis por sobre los controles. En BNZ, el pico de U DA V observado a los 30 min de la expansión disminuyó a 3.2 ± 0.72 (p < 0.01), aunque luego de 60 minutos fue mayor que en C. BNZ disminuyó tanto la diuresis como la natriuresis. Podemos concluir que al comienzo de la expansión de volumen se produce un pico de excreción de dopamina renal hacia la orina. La enzima MAO juega un rol fundamental en esta respuesta.

Senescence-induced serotonin biosynthesis and its role in delaying senescence in rice leaves.

Serotonin, which is well known as a pineal hormone in mammals, plays a key role in conditions such as mood, eating disorders, and alcoholism. In plants, although serotonin has been suggested to be involved in several physiological roles, including flowering, morphogenesis, and adaptation to environmental changes, its regulation and functional roles are as yet not characterized at the molecular level. In this study, we found that serotonin is greatly accumulated in rice (Oryza sativa) leaves undergoing senescence induced by either nutrient deprivation or detachment, and its synthesis is closely coupled with transcriptional and enzymatic induction of the tryptophan biosynthetic genes as well as tryptophan decarboxylase (TDC). Transgenic rice plants that overexpressed TDC accumulated higher levels of serotonin than the wild type and showed delayed senescence of rice leaves. However, transgenic rice plants, in which expression of TDC was suppressed through an RNA interference (RNAi) system, produced less serotonin and senesced faster than the wild type, suggesting that serotonin is involved in attenuating leaf senescence. The senescence-retarding activity of serotonin is associated with its high antioxidant activity compared to either tryptophan or chlorogenic acid. Results of TDC overexpression and TDC RNAi plants suggest that TDC plays a rate-limiting role for serotonin accumulation, but the synthesis of serotonin depends on an absolute amount of tryptophan accumulation by the coordinate induction of the tryptophan biosynthetic genes. In addition, immunolocalization analysis revealed that serotonin was abundant in the vascular parenchyma cells, including companion cells and xylem-parenchyma cells, suggestive of its involvement in maintaining the cellular integrity of these cells for facilitating efficient nutrient recycling from senescing leaves to sink tissues during senescence.

[Expression of the enzymes of dopamine synthesis in non-dopaminergic neurons: functional significance and regulation].

Dopamine(DA), the most widely distributed in the nervous system and functionally important chemical signal, is synthesized in DA-ergic neurons from L-tyrosine by means of two enzymes, tyrosine hydroxylase (TH) and aromatic L-amino acid decarboxylase (AADC). Apart from the enzymes, specific DA transporter is an attribute of DA-ergic neurons. In the mid eighties of the last century, in addition to DA-ergic neurons, those expressing only one enzyme, TH or AADC, have been discovered. These "monoenzymatic" neurons occurred to be more numerous and more widely distributed in the brain compared to DA-ergic neurons that manifests their wide involvement to the brain functioning. It has been demonstrated that the monoenzymatic neurons expressing complementary enzymes of DA synthesis produce this neurotransmitter in cooperation. In this case, L-tyrosine is transformed to L-DOPA in TH containing neurons that is followed by L-DOPA release and uptake from the intercellular space to AADC containing neurons for DA synthesis. Moreover, the L-DOPA uptake to DA-ergic or serotoninergic neurons results either in the increase or the onset of DA synthesis in addition to serotonin, respectively. The expression of the enzymes of DA synthesis in non-dopaminergic neurons is one of the adaptive reactions serving to compensate the functional insufficiency of DA-ergic neurons. For instance, hyperprolactinemia and the deficiency of DA, prolactin-inhibiting hormone, which is developed under degeneration of DA-ergic neurons of the arcuate nucleus, are compensated with time due to the increase of the number of monoenzymatic neurons and cooperative synthesis of DA in the nucleus. It is supposed that the same compensatory cooperative synthesis of DA is turned on under the degeneration of DA-ergic neurons of the nigrostriatal system that is manifested by the appearance of non-dopaminergic neurons expressing enzymes of DA synthesis in the deafferentated striatum. The expression of the enzymes of DA synthesis in non-dopaminergic neurons is under the control by intercellular signals, catecholamines, neurotrophic (growth) factors and, perhaps, hormones. Thus, non-dopaminergic monoenzymatic neurons expressing enzymes of DA synthesis produce this neurotransmitter in cooperation that is a compensatory reaction under functional insufficiency of DA-ergic neurons, in neurodegenerative diseases, hyperprolactinemia and Parkinson's disease, in particular.

Serotonin (5-HT) in veins: not all in vain.

The circulatory system consists of veins and arteries. Compared with arteries, veins have been neglected in cardiovascular research. Although veins are significantly less muscular than similarly sized arteries, the contribution of veins to cardiovascular homeostasis cannot be left un-noted because veins accommodate 70% of the circulating blood. Circulating blood platelets contain the majority of systemic 5-HT (5-hydroxytryptamine; serotonin). Similar to venous function, the physiological role of 5-HT in the cardiovascular system is not well understood. Here, we present not only a review on 5-HT and veins but ways in which these two topics might intersect in a physiologically relevant manner. Here we show the novel findings that veins exhibit higher amounts of intracellular 5-HT than arteries. Moreover, we also show evidence that, similar to arteries, veins have the ability to uptake 5-HT. In this review, we introduce the venous system as a reservoir for 5-HT in the periphery, suggesting that veins, in addition to arteries, may represent an important target for drugs that interfere with the serotonergic system. In addition, the serotonergic system from synthesis to metabolism, 5-HT receptor activation and venous diseases will also be discussed.

Tomato aromatic amino acid decarboxylases participate in synthesis of the flavor volatiles 2-phenylethanol and 2-phenylacetaldehyde.

An important phenylalanine-derived volatile compound produced by plants is 2-phenylethanol. It is a major contributor to flavor in many foods, including fresh fruits, such as tomato, and an insect-attracting scent in roses and many other flowers. Despite the centrality of 2-phenylethanol to flavor and fragrance, the plant genes responsible for its synthesis have not been identified. Here, we describe a biosynthetic pathway for 2-phenylethanol and other phenylalanine-derived volatiles in tomato fruits and a small family of decarboxylases (LeAADC1A, LeAADC1B, and LeAADC2) that can mediate that pathway's first step. These enzymes each catalyze conversion of phenylalanine to phenethylamine and tyrosine to tyramine. Although tyrosine is the preferred substrate in vitro, phenylalanine levels in tomato fruits far exceed those of tyrosine, indicating that phenylalanine is a physiological substrate. Consistent with this view, overexpression of either LeAADC1A or LeAADC2 in transgenic tomato plants resulted in fruits with up to 10-fold increased emissions of the products of the pathway, including 2-phenylacetaldehyde, 2-phenylethanol, and 1-nitro-2-phenylethane. Further, antisense reduction of LeAADC2 significantly reduced emissions of these volatiles. Besides establishing a biosynthetic route, these results show that it is possible to change phenylalanine-based flavor and aroma volatiles in plants by manipulating expression of a single gene.

Focal striatal dopamine may potentiate dyskinesias in parkinsonian monkeys.

Striatal neurons convert L-dopa to dopamine (DA) following gene transfer of aromatic L-amino acid decarboxylase (AADC) via adeno-associated virus (AAV) in parkinsonian monkeys. We investigated whether AAV-AADC could reduce or eliminate L-dopa-induced dyskinesias (LIDs) and side effects in MPTP-treated monkeys. Five monkeys were made parkinsonian by bilateral MPTP lesions. The optimal therapeutic dose of L-dopa was determined using an acute dose response regimen. After 3 weeks of chronic L-dopa treatment, AAV-AADC or control vector was bilaterally injected into the striatum. Animals were assessed for 6 months with the same L-dopa dosing as presurgery as well as chronic oral L-dopa treatment. Presurgery LID was observed at doses greater than 5 mg/kg. The AAV-AADC-treated animals displayed an average 7.3-fold decrease in the therapeutic dose of L-dopa throughout the 6-month follow-up period. Only AAV-AADC-treated monkeys were susceptible to dyskinesias even at sub-clinical doses. Immunohistochemical analysis revealed well-delineated foci of AADC within the striatum. These results suggest that high levels of focal DA were generated in response to L-dopa administration and may be responsible for the exacerbation of dyskinesias. This may be similar to focal dopaminergic activity in PD patients that developed off-drug or "runaway" dyskinesias following fetal mesencephalic grafts.

L-DOPA reverses the hypokinetic behaviour and rigidity in rotenone-treated rats.

Peripherally and locally administered rotenone (an inhibitor of mitochondrial complex I) has been proposed as a model of Parkinson's disease (PD) as it induces nigrostriatal degeneration associated with alpha-synuclein inclusions. If rotenone-induced symptoms represent a model of PD, than they should be counteracted by L-DOPA. To answer this question, rats were treated with rotenone 2.5 mg/kg over 48 days. Behavioural data showed a strong increase in catalepsy, a decrease in locomotor activity and biochemical data showed a significant depletion of dopamine levels in the striatum (Cpu) and substantia nigra in rotenone treated animals compared to vehicle. To examine the effectiveness of L-DOPA in reversing the motor deficit in rats, a dose of L-DOPA (10 mg/kg) in combination with the peripheral amino acid decarboxylase inhibitor benserazide were daily administrated intraperitonially for a period of 10 days in the rotenone-treated rats. This treatment counteracted catalepsy and increased locomotor activity and number of rearings but decreased inactive sitting. In this animal model (rotenone model), catalepsy tests and motor activities showed that the clinically used anti-parkinsonian drug L-DOPA substitutes rotenone-induced dopamine (DA) deficiency.

Tyrosine hydroxylase- and/or aromatic L-amino acid decarboxylase-expressing neurons in the rat arcuate nucleus: ontogenesis and functional significance.

This study has evaluated in vivo, ex vivo and in vitro the ontogenesis and functional significance of the neurons of the arcuate nucleus (AN) expressing either individual enzymes of dopamine (DA) synthesis, tyrosine hydroxylase (TH) or aromatic L-amino acid decarboxylase (AADC) as well as both of them in rats from the 17th embryonic day (E) till adulthood. Immunocytochemistry, image analysis, confocal microscopy, high performance liquid chromatography with electrochemical detection and radioimmunoassay were used to solve this problem. Monoenzymatic TH-containing neurons were initially observed on E18 located in the ventrolateral AN whereas the neurons expressing only AADC or both AADC and TH first appeared on E20 in the dorsomedial AN. On E21, the monoenzymatic TH- or AADC-expressing neurons comprised more than 99% of the whole neuron population expressing the DA-synthesizing enzymes. In spite of an extremely small number (<1%) of the neurons expressing both enzymes (DArgic neurons), the dissected AN (ex vivo) and its primary cell culture (in vitro) contained a surprisingly high amount of DA and L-dihydroxyphenylalanine (L-DOPA) which were released in response to membrane depolarization. Furthermore, DA production in the AN of fetuses occurred to be sufficient to provide an inhibitory control of prolactin secretion, as in adults. The above data suggest that DA could be synthesized, at least in the AN of fetuses, by monoenzymatic neurons containing either TH or AADC, in co-operation. This hypothesis may be extended to adult animals as their AN contained the same populations of the neurons expressing DA-synthesizing enzymes as in fetuses though the proportion of true DArgic neurons increased up to 38%. During ontogenesis, the monoenzymatic TH- and AADC-containing neurons established axosomatic and axo-axonal junctions that might facilitate the L-DOPA transport from the former to the latter. Moreover, the monoenzymatic AADC-expressing neurons project their axons to the median eminence, thereby, providing the pathway for the DA transport toward the hypophysial portal circulation. Thus, DA appears to be synthesized in the AN not only by DArgic neurons but also by monoenzymatic TH- and AADC-expressing neurons in co-operation.

Uptake of L-3,4-dihydroxyphenylalanine and dopamine formation in cultured renal epithelial cells.

In the presence of benserazide (50 microM), L-3,4-dihydroxyphenylalanine (L-DOPA) was rapidly accumulated in both LLC-PK1 and OK cells; equilibrium was attained at 30 min of incubation. For these LLC-PK1 and OK cells, the analysis revealed a rate constant of inward transport (k(in) in pmol/mg protein/min) of 3.6 +/- 0.4 and 18.1 +/- 0.3 and a rate constant of outward transport (k(out) in pmol/mg protein/min) of 1.0 +/- 0.1 and 5.2 +/- 0.1, respectively. Nonlinear analysis of the saturation curves for LLC-PK1 and OK cells revealed a Km (in microM) of 86 +/- 12 and 14 +/- 4, respectively. The cellular accumulation of the substrate was temperature-dependent and stereoselective. Aromatic L-amino acid decarboxylase (AAAD) activity was determined in cell homogenates; nonlinear analysis of the saturation curves revealed, for LLC-PK1 and OK cells, a Km (in microM) of 1866 +/- 107 and 845 +/- 153 and a Vmax (in nmol/mg protein/15 min) of 4.4 +/- 0.1 and 0.9 +/- 0.1, respectively. In the absence of benserazide, only a limited amount of the L-DOPA taken up was decarboxylated to dopamine in cell monolayers; the Km value (in microM) for decarboxylation of intracellular L-DOPA in LLC-PK1 and OK cells was 61 +/- 14 and 108 +/- 36, respectively. A low amount of newly formed dopamine was found to escape to the apical bathing fluid. This outward transfer of newly formed dopamine was a nonsaturable process up to 300 microM intracellular dopamine. In conclusion, the data presented here show that OK cells are endowed with a more efficient L-DOPA uptake system than LLC-PK1 cells, but the latter are endowed with a significantly higher AAAD activity than OK cells. In both cell lines, intracellular L-DOPA is rapidly converted to dopamine, some of which diffuses out of the cell.

Acid stress responses in enterobacteria.

The enteric microogranisms Salmonella, Escherichia coli and Shigella flexneri prefer to grow in neutral pH environments. They nevertheless experience dramatic pH fluctuations in nature and during pathogenesis. In response to environmental encounters with acid, these organisms have evolved complex, inducible acid survival strategies. Regulatory features include an alternative factor (sigma S), 2- component signal transduction systems (PhoP/Q; MviA/?) and the major iron regulatory protein Fur. Specific survival mechanisms include emergency pH homeostasis by inducible amino acid decarboxylases and probable roles for DNA repair, chaparonins, membrane biogenesis as well as others that remain poorly defined. Continued study of acid survival in these organisms will provide insights regarding stress management and will have a direct impact on our understanding of pathogenesis.

Aromatic L-amino acid decarboxylase: biological characterization and functional role.

1. Aromatic L-amino acid decarboxylase is the enzyme responsible for the decarboxylation step in both the catecholamine and the indolamine synthetic pathways. Immunological and molecular biological studies suggest that it is a single enzyme with one catalytic site but with different locations for attachment of the substrates. The enzyme is widely distributed in the brain and in peripheral tissues. 2. Recent investigations have shown that the enzyme is regulated by short term mechanisms that may involve activation of adenyl cyclase or protein kinase C. In addition, a long-term mechanism of activation by altered gene expression has also been suggested.

[Expression of aromatic L-amino acid decarboxylase in the rat suprachiasmatic nucleus--immunocytochemistry and in situ hybridization study].

We investigated the distribution, diurnal variation, and time of expression of aromatic L-amino acid decarboxylase (AADC), a second-step enzyme of the monoamine synthetic pathway, in the rat suprachiasmatic nucleus (SCN), by immunocytochemistry and in situ hybridization. AADC immunoreactive and mRNA expressing cells were observed in the dorsomedial and dorsolateral portions of the SCN. Double labeling immunofluorescence demonstrated that about 70% of AADC neuron in the dorsomedial portion contained vasopressin immunoreactivity. AADC mRNA expression in the SCN showed day-night variation, with higher signals in the daytime than at night. Developmental study demonstrated that AADC immunoreactivity and mRNA in the SCN were expressed at embryonic day 18, the onset time for fetal circadian rhythm. These findings suggest that AADC neurons in the SCN may play some role in the generation and entrainment of circadian rhythm.

The role of amino acid decarboxylase in the stimulation of gastrin release in man.

As amino acid-induced gastrin release is dependent on amino acid decarboxylase activity in rat, we examined the gastrin response to intragastric phenylalanine before and after treatment with carbidopa in 12 healthy male volunteers; carbidopa is an inhibitor of aromatic amino acid decarboxylation. Our results showed no significant difference between the pre- and postcarbidopa periods in the same subjects, suggesting that decarboxylation is not a necessary step for amino acids to stimulate G-cells in man. However, carbidopa seems to have an inhibitory effect on gastrin release, independently of its action on decarboxylase activity.

Roles of dopa decarboxylase and phenoloxidase in the melanization of the tobacco hornworm and their control by 20-hydroxyecdysone.

When Manduca sexta larvae are allatectomized 5 h before head capsule slippage (HCS) in the final larval molt, the new larval cuticle contains granules that melanize 3 h before ecdysis when the ecdysteroid titer falls (Curtis et al. 1984). In both the epidermis and hemolymph of these allatectomized larvae dopamine was higher than dopa prior to and at the time of melanization. Dopamine also increased in the new cuticle as melanization began. Dopa decarboxylase (DDC) activity increased in the epidermis, cuticle, and fat body beginning 16 h after HCS, with a two-fold greater increase in the epidermis of allatectomized larvae. Both alpha-MDH and alpha-fluoromethyl-dopa inhibited epidermal DDC activity and inhibited melanization in vitro when dopa was used as a precursor. Addition of dopamine to the medium allowed melanization in the presence of the inhibitors. All these results indicate that dopamine is likely the primary precursor of cuticular melanin. The diphenoloxidase in the premelanin granules was activated in vivo between 19 and 21 h after HCS and was found to prefer dopamine to dopa and not to convert tyrosine to melanin. The activation of the prophenoloxidase was inhibited by 20-hydroxyecdysone (20-HE), both in vivo and in vitro, if hormone was given by 16 h after HCS. Infusion of 1.2 microgram/ml 20-HE into allatectomized larvae for 24 h from HCS prevented both the increase in DDC activity and the activation of the premelanin granules. Although the larvae ecdysed after a 15 h delay, melanization never occurred.

Mutations in the dopa decarboxylase gene affect learning in Drosophila.

Fruit flies synthesize several monoamine neurotransmitters. Dopa decarboxylase (Ddc) mutations affect synthesis of two of these, dopamine and serotonin. Both transmitters are implicated in vertebrate and invertebrate learning. Therefore, we bred flies of various Ddc genotypes and tested their learning ability in positively and negatively reinforced learning tasks. Mutations in the Ddc gene diminished learning acquisition approximately in proportion to their effect on enzymatic activity. Courtship and mating sequences of the mutants appeared normal, except for one aspect of male courtship that had previously been shown to be experience dependent. In contrast, the effect on behavior patterns that do not involve learning--phototaxis, geotaxis, olfactory acuity, responsiveness to sucrose--was relatively slight under these conditions. Moderate Ddc mutations affected the acquisition of learned responses while leaving memory retention unaltered. This is in contrast to the mutations dunce , rutabaga , and amnesiac , which primarily affect short-term memory.