DA Synthesis Research Articles

Differential roles of hypothalamic serotonin receptor subtypes in the regulation of prolactin secretion in the turkey hen

In the turkey, exogenous serotonin (5-hydroxytryptamine, 5-HT) increases prolactin (PRL) secretion by acting through the dopaminergic (DAergic) system. In the present study, infusion of the 5-HT2C receptor agonist, (R)(−)-DOI hydrochloride (DOI), into the third ventricle stimulates PRL secretion, whereas the 5-HT1A receptor agonist, (+/−)-8-OH-DPAT hydrobromide (DPAT), inhibits PRL secretion. Using the immediate-early gene, c-fos, as an indicator of neuronal activity, in situ hybridization histochemistry showed preferential c-fos co-localization within tyrosine hydroxylase immunoreactive neurons (the rate limiting enzyme in DA synthesis) in the areas of the nucleus preopticus medialis (POM) and the nucleus premammillaris (PMM), in response to DPAT and DOI, respectively. To clarify the involvement of 5-HT1A and 5-HT2C receptors in PRL regulation, their mRNA expression was determined on hypothalamic tissue sections from birds in different reproductive stages. A significant difference in 5-HT1A receptor was observed, with the POM of hypoprolactinemic short day and photorefractory birds showing the highest expression. 5-HT2C receptors mRNA did not change during the reproductive cycle. The data presented support the notion that DA neurons in the PMM and POM mediate the stimulatory and inhibitory effects of 5-HT, respectively, on PRL secretion and the 5-HTergic system can both stimulate and inhibit PRL secretion.

The state of the tuberoinfundibular dopaminergic system during modeling of parkinsonism in mice

Parkinson’s disease (PD) is one of the most widespread neurodegenerative diseases; it develops as a result of the death of dopaminergic (DA-ergic) neurons of the nigrostriatal system of the brain. It has been shown in autopsy material that the neurodegenerative process spreads to other populations of neurons of the peripheral and central nervous system. In PD patients the tuberoinfundibular DA-ergic system (TIDAS) undergoes degradation; however, no experimental models exist that can reproduce the combined degradation of the nitrostriatal system and the TIDAS. In this work, we analyzed the state of the TIDAS during presymptomatic and symptomatic stages of parkinsonism induced by the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). These stages of parkinsonism develop as a result of subthreshold and threshold degradation of the nigrostriatal DA-ergic system. To evaluate the morphofunctional state of the TIDAS, we determined: (a) the number of neurons with tyrosine hydroxylase (TH), a key enzyme of DA synthesis; (b) the sizes of the terminals of TH-positive axons; (c) the levels of TH in the neuronal somas and the terminals of axons; and (d) the contents of DA, noradrenaline, and 3,4-dihydroxyphenyl acetic acid. According to the data that was obtained during the presymptomatic stage, for the TIDAS no changes were found in all the measured parameters. During the symptomatic stage, we observed (a) a decrease in DA content by 50%; (b) a decrease in the level of TH protein in axonal terminals and an increase in neuronal somas; and (c) an increase in the turnover of DA by 149% as compared to the control. The data we obtained suggest that the functional activity of the TIDAS was insufficient; this was seen in the form of alterations of DA metabolism, a decrease in the level of synthesis, probably in axonal terminals, and compensatory acceleration of the functional cycle from synthesis to enzymatic degradation. Although no changes in the number of neurons and axons that express TH was found in the TIDAS, the question of organic degradation of the TIDAS in parkinsonism is still open because TH is a marker of not only DA-ergic neurons that degenerate in the presence of neurotoxins but also of non-DA-ergic neurons that are insensitive to neurotoxins. Thus, during experimental modeling of Parkinsonism, we observed at least the metabolic characteristics of TIDAS degradation only at the symptomatic stage of the disease.

Rotenone induces KATP channel opening in PC12 cells in association with the expression of tyrosine hydroxylase

The activation of ATP-sensitive potassium (KATP) channels in PC12 cells play a pivotal role in protection against the neurotoxic effect of rotenone. However, it remains unclear why rotenone seems to preferentially affect activation of KATP channels and if this could affect its physiological activity. In this study, we sought to determine how the different energy states caused by various doses of rotenone affect the KATP opening state and whether the KATP opening state influences the expression of tyrosine hydroxylase (TH) which is related with DA synthesis. With patch clamp technology, results showed that treatment of PC12 cells with rotenone (0.2-1 µg/ml) for 15min can cause KATP channel opening with significantly increased intracellular ROS production. Treatment with rotenone (2-16ng/ml) for 24h also caused the channels to open with gently increased ROS. In order to study if the rather long-term action on KATP channel opening states could affect the specified function of PC12 cells, the KATP channel opener pinacidil and the inhibitor glibenclamide were used to treat cells for 24 h, and the expression of TH was detected. Our results showed that treatment of PC12 cells with glibenclamide for 24h can notably promote TH expression and can also enhance the expression of TH which were reduced by rotenone. These data indicate that the energy states in PC12 induced by various doses of rotenone could significantly influence the opening states of KATP channels. However long-term energy stress may raise the opening rate and opening sensitivity of this channel. In addition, our results demonstrate for the first time that activation of plasma membrane KATP channels induced by rotenone inhibits TH expression which influences DA synthesis in PC12 cells.

Redox Sensitivity of Tyrosine Hydroxylase Activity and Expression in Dopaminergic Dysfunction

Oxidant molecules generated during neuronal metabolism appear to play a significant role in the processes of aging and neurodegeneration. Increasing experimental evidence suggests the noteworthy relevance of the intracellular reduction-oxidation (redox) balance for the dopaminergic (DA-ergic) neurons of the substantia nigra pars compacta. These cells possess a distinct physiology intrinsically associated with elevated reactive oxygen species production, conferring on them a high vulnerability to free radical damage, one of the major causes of selective DA-ergic neuron dysfunction and degeneration related to neurological disorders such as Parkinson's disease. Tyrosine hydroxylase (tyrosine 3-monooxygenase; E.C. 1.14.16.2; TH) activity represents the rate-limiting biochemical event in DA synthesis. TH activity, metabolism and expression are finely tuned by several regulatory systems in order to maintain a crucial physiological condition in which DA synthesis is closely coupled to its secretion. Alterations of these regulatory systems of TH functions have indeed been thought to be key events in the DA-ergic degeneration. TH has seven cysteine residues presenting thiols. Depending on the oxido-reductive (redox) status of the cellular environment, thiols exist either in the reduced form of free thiols or oxidized to disulfides. The formation of disulfides in proteins exerts critical regulatory functions both in physiological and in pathological conditions when oxidative stress is sustained. Several reports have recently shown that redox state changes of thiol residues, as consequence of an oxidative injury, can directly or indirectly affect the TH activity, metabolism and expression. The major focus of this review, therefore, is to report recent evidence on the redox modulation of TH activity and expression, and to provide an overview of a cellular phenomenon that might represent a target for new therapeutic strategies against the DA-ergic neurodegenerative disorders.

Knocking Out the Dopamine Reuptake Transporter (DAT) Does not Change the Baseline Brain Arachidonic Acid Signal in the Mouse

ABSTRACTBackground. Dopamine transporter (DAT) homozygous knockout (DAT−/−) mice have a 10-fold higher extracellular (DA) concentration in the caudate-putamen and nucleus accumbens than do wildtype (DAT+/+) mice, but show reduced presynaptic DA synthesis and fewer postsynaptic D2 receptors. One aspect of neurotransmission involves DA binding to postsynaptic D2-like receptors coupled to cytosolic phospholipase A2 (cPLA2), which releases the second messenger, arachidonic acid (AA), from synaptic membrane phospholipid. We hypothesized that tonic overactivation of D2-like receptors in DAT−/− mice due to the excess DA would not increase brain AA signaling, because of compensatory downregulation of postsynaptic DA signaling mechanisms. Methods: [1–14C]AA was infused intravenously for 3 min in unanesthetized DAT+/+, heterozygous (DAT+/−), and DAT−/− mice. AA incorporation coefficients k* and rates Jin, markers of AA metabolism and signaling, were imaged in 83 brain regions using quantitative autoradiography; brain cPLA2-IV activity also was measured. Results: Neither k* nor Jin for AA in any brain region, or brain cPLA2-IV activity, differed significantly among DAT−/−, DAT+/–, and DAT+/+ mice. Conclusions: These results differ from reported increases in k* and Jin for AA, and in brain cPLA2 expression, in serotonin reuptake transporter (5-HTT) knockout mice, and suggest that postsynaptic dopaminergic neurotransmission mechanisms involving AA are downregulated despite elevated DA in DAT–/– mice.

Midbrain presynaptic dopamine tone predicts sustained and transient neural response to emotional salience in humans: fMRI, MEG and FDOPA PET

Midbrain presynaptic dopamine tone predicts sustained and transient neural response to emotional salience in humans: fMRI, MEG and FDOPA PET

Recovery of hypothalamic tuberoinfundibular dopamine neurons from acute toxicant exposure is dependent upon protein synthesis and associated with an increase in parkin and ubiquitin carboxy-terminal hydrolase-L1 expression

Hypothalamic tuberoinfundibular dopamine (TIDA) neurons remain unaffected in Parkinson disease (PD) while there is significant degeneration of midbrain nigrostriatal dopamine (NSDA) neurons. A similar pattern of susceptibility is observed in acute and chronic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse and rotenone rat models of degeneration. It is not known if the resistance of TIDA neurons is a constitutive or induced cell-autonomous phenotype for this unique subset of DA neurons. In the present study, treatment with a single injection of MPTP (20mg/kg; s.c.) was employed to examine the response of TIDA versus NSDA neurons to acute injury. An acute single dose of MPTP caused an initial loss of DA from axon terminals of both TIDA and NSDA neurons, with recovery occurring solely in TIDA neurons by 16h post-treatment. Initial loss of DA from axon terminals was dependent on a functional dopamine transporter (DAT) in NSDA neurons but DAT-independent in TIDA neurons. The active metabolite of MPTP, 1-methyl, 4-phenylpyradinium (MPP+), reached higher concentration and was eliminated slower in TIDA compared to NSDA neurons, which indicates that impaired toxicant bioactivation or distribution is an unlikely explanation for the observed resistance of TIDA neurons to MPTP exposure. Inhibition of protein synthesis prevented TIDA neuron recovery, suggesting that the ability to recover from injury was dependent on an induced, rather than a constitutive cellular mechanism. Further, there were no changes in total tyrosine hydroxylase (TH) expression following MPTP, indicating that up-regulation of the rate-limiting enzyme in DA synthesis does not account for TIDA neuronal recovery. Differential candidate gene expression analysis revealed a time-dependent increase in parkin and ubiquitin carboxyl-terminal hydrolase-L1 (UCH-L1) expression (mRNA and protein) in TIDA neurons during recovery from injury. Parkin expression was also found to increase with incremental doses of MPTP. The increase in parkin expression occurred specifically within TIDA neurons, suggesting that these neurons have an intrinsic ability to up-regulate parkin in response to MPTP-induced injury. These data suggest that TIDA neurons have a compensatory mechanism to deal with toxicant exposure and increased oxidative stress, and this unique TIDA neuron phenotype provides a platform for dissecting the mechanisms involved in the natural resistance of central DA neurons following toxic insult.

Effects of dietary amino acids and repeated handling on stress response and brain monoaminergic neurotransmitters in Senegalese sole ( Solea senegalensis) juveniles

The present study aimed to assess the effects of increased availability of dietary amino acids (AA) on brain monoamine neurotransmitters and the metabolic processes resulting from stressful situations in fish. Senegalese sole ( Solea senegalensis) juveniles (24.2 ± 0.4 g wet mass) were weekly subjected to an acute handling stressor (HDLG) or remained undisturbed (CTL). Additionally, both treatments were fed a control or a high protein (HP) diet (CTL, CTL HP, HDLG and HDLG HP). The HP diet slightly increased the levels of digestible indispensable AA, together with tyrosine and cysteine. Repeated handling induced a stress response after 14 and 28 days in fish held at both HDLG and HDLG HP treatments. While dietary treatment and handling stress activated the serotonergic system at 14 days, these effects were not observed after 28 days. In addition, the HP diet minimized the decrease in plasma indispensable AA due to repeated handling stress after 28 days. It was concluded that HP diet decreased post-stress plasma glucose and lactate levels in HDLG HP specimens only at 14 days of treatment. Moreover, dietary treatment was also effective in stimulating DA synthesis and release, thus dietary phenylalanine supplementation can increase DA biosynthesis in fish.

Melanopsin expression in dopamine-melatonin neurons of the premammillary nucleus of the hypothalamus and seasonal reproduction in birds

Melanopsin (OPN4) is a photoreceptive molecule regulating circadian systems in mammals. Previous studies from our laboratory have shown that co-localized dopamine-melatonin (DA-MEL) neurons in the hypothalamic premammillary nucleus (PMM) are putatively photosensitive and exhibit circadian rhythms in DAergic and MELergic activities. This study investigates turkey OPN4x (tOPN4x) mRNA distribution in the hypothalamus and brainstem, and characterizes its expression in PMM DA-MEL neurons, using in situ hybridization (ISH), immunocytochemistry (ICC), double-label ISH/ICC, and real time-PCR. The mRNA encoding tOPN4x was found in anatomically discrete areas in or near the hypothalamus and the brainstem, including nucleus preopticus medialis (POM), nucleus septalis lateralis (SL), PMM and the pineal gland. Double ICC, using tyrosine hydroxylase (TH, the rate limiting enzyme in DA synthesis)—and OPN4x antibodies, confirmed the existence of OPN4x protein in DA-MEL neurons. Also, tOPN4x mRNA expression was verified with double ISH/ICC using tOPN4x mRNA and TH immunoreactivity. PMM and pineal gland tOPN4x mRNA expression levels were diurnally high during the night and low during the day. A light pulse provided to short day photosensitive hens during the photosensitive phase at night significantly down-regulated tOPN4x expression. The expression level of tOPN4x mRNA in PMM DA-MEL neurons of photorefractory hens was significantly lower as compared with that of short or long day photosensitive hens. The results implicate tOPN4x in hypothalamic PMM DA-MEL neurons as an important component of the photoreceptive system regulating reproductive activity in temperate zone birds.

Role of noradrenaline in the development of dopamine-induced hyperprolactinemia

Hyperprolactinemia is neurodegenerative disease that develops in humans as a result of degeneration of dopaminergic (DA-ergic) neurons of the arcuate nucleus, which synthesize DA, a neurohormone inhibiting prolactin secretion by pituitary lactotropes. The design and detailed analysis of good experimental models of hyperprolactinemia may help us to understand the causes and mechanisms of the disease development and develop early diagnostics and treatment of the disease. Hyperprolactinemia is usually modeled in experiments using 6-hydroxydopamine (6-HDA), a neurotoxin causing degeneration of DA-ergic neurons of the arcuate nucleus. However, 6-HAD also induces degeneration of noradrenergic (NA-ergic) axons involved in the regulation of prolactin secretion. Therefore, in this study, we evaluated the role of NA in the development of hyperprolactinemia during degeneration of DA-ergic neurons of the arcuate nucleus. To this aim, we compared changes in DA and NA metabolism in the arcuate nucleus and the blood level of prolactin in rats after treatment with 6-HDA alone and 6-HDA in the presence of desmethylimipramine, drug that prevents degeneration of NA-ergic neurons. Studies were performed in 14 days after toxin administration, i.e., at a time point when toxin-induced degenerative processes are finished, and in 45 days, i.e., after initiation of compensatory processes. We found that, in 14 days after administration of pharmacological agents, hyperprolactinemia, which resulted from DA deficit due to degeneration of DA-ergic neurons of the arcuate nucleus, is enhanced when NA-ergic afferents are protected, which may be related to the inhibitory effect of NA on DA synthesis. The latter hypothesis is supported by the fact that in 45 days after treatment with 6-HDA alone, i.e., after combined degeneration of DA-ergic and NA-ergic neurons, DA synthesis in the arcuate nucleus returns back to the normal level, which is accompanied by recovery of the normal blood level of prolactin. In contrast, in 45 days after administration of 6-HDA and desmethylimipramine, NA synthesis increases to the normal level but DA synthesis in the arcuate nucleus remains at low level, which is accompanied by an increased blood level of prolactin. Thus, our data suggest that NA inhibits DA synthesis in the arcuate nucleus and prevents a compensatory increase in DA synthesis and the normalization of the blood level of prolactin during degeneration of DA-ergic neurons.

Optimization of continuous in vivo DOPA production and studies on ectopic DA synthesis using rAAV5 vectors in Parkinsonian rats

Viral vector-mediated gene transfer is emerging as a novel therapeutic approach with clinical utility in treatment of Parkinson's disease. Recombinant adeno-associated viral (rAAV) vector in particular has been utilized for continuous l-3,4 dihydroxyphenylalanine (DOPA) delivery by expressing the tyrosine hydroxylase (TH) and GTP cyclohydrolase 1 (GCH1) genes which are necessary and sufficient for efficient synthesis of DOPA from dietary tyrosine. The present study was designed to determine the optimal stoichiometric relationship between TH and GCH1 genes for ectopic DOPA production and the cellular machinery involved in its synthesis, storage, and metabolism. For this purpose, we injected a fixed amount of rAAV5-TH vector and increasing amounts of rAAV5-GCH1 into the striatum of rats with complete unilateral dopamine lesion. After 7 weeks the animals were killed for either biochemical or histological analysis. We show that increasing the availability of 5,6,7,8-tetrahydro-l-biopterin (BH4) in the same cellular compartment as the TH enzyme resulted in better efficiency in DOPA synthesis, most likely by hindering inactivation of the enzyme and increasing its stability. Importantly, the BH4 synthesis from ectopic GCH1 expression was saturable, yielding optimal TH enzyme functionality between GCH1 : TH ratios of 1 : 3 and 1 : 7.

Alterations in the anterior hypothalamic dopamine system in aggressive adolescent AAS-treated hamsters

Anabolic androgenic steroid (AAS) treatment throughout adolescence facilitates offensive aggression in male Syrian hamsters ( Mesocricetus auratus). The present study was conducted to investigate the role of the dopaminergic system in the modulation of AAS-induced aggressive behavior. Hamsters were administered AAS during adolescence, scored for offensive aggression using the resident–intruder paradigm, and then examined for alterations in DA immunoreactivity in brain regions implicated in the aggressive phenotype, including the anterior hypothalamus (AH), the bed nucleus of the stria terminalis (BNST), the medial and central amygdala (MeA and CeA), the lateral septum (LS) and the ventrolateral hypothalamus (VLH). When compared with non-aggressive sesame-oil-treated controls, aggressive AAS-treated animals showed increased tyrosine hydroxylase immunoreactivity in anterior hypothalamic subnuclei, namely the nucleus circularis (NC) and medial supraoptic nucleus (mSON). In addition, AAS-treated animals showed altered D 2 receptor expression in the AH and the VLH, as measured by D 2-immunoreactivity. Together these results suggest that alterations in DA synthesis and function together with modifications in D 2 receptor expression in the AH may underlie neuroplastic events which facilitate AAS-induced aggression.

P.1.30 Inflammation down-regulates β2-adrenoceptor expression on primary glia: reversal by the glucocorticoid dexamethasone

GARCÍA-GIL, L., J. A. RAMOS, T. RUBINO, D. PAROLARO AND J. J. FERNÁNDEZ-RUIZ. Perinatal Δ9-tetrahydrocannabinol exposure did not alter dopamine transporter and tyrosine hydroxylase mRNA levels in midbrain dopaminergic neurons of adult male and female rats. NEUROTOXICOL TERATOL 20(5) 549–553, 1998.—We have recently demonstrated that the magnitude of L-3,4-dihydroxyphenylacetic acid (DOPAC) lowering effect caused by amphetamine in midbrain dopaminergic neurons of adult rats was lesser in animals that had been perinatally exposed to Δ9-tetrahydrocannabinol (Δ9-THC) than controls. In the present study, we have examined whether this loss in the responsiveness to amphetamine might be due to changes at the level of dopamine transporter (DAT), the main molecular site for the action of amphetamine, following the perinatal exposure to Δ9-THC. To this end, we have analyzed DAT mRNA levels, by using in situ hybridization, in the substantia nigra and ventral tegmental area, the areas where cell bodies of DAT-containing midbrain neurons are located, of adult male and female rats that had been perinatally exposed to Δ9-THC. In addition, we also analyzed mRNA levels of tyrosine hydroxylase (TH), the rate-limiting enzyme in DA synthesis. Results were as follows. Both adult male and female rats that had been perinatally exposed to Δ9-THC exhibited similar mRNA levels to controls for both DAT and TH in the substantia nigra as well as in the ventral tegmental area. This observation makes it difficult to support the idea that the differences found in adulthood after pharmacological challenges were caused by irreversible changes at the level of gene expression for these two key proteins.

Working Memory Capacity Predicts Dopamine Synthesis Capacity in the Human Striatum

Evidence from psychopharmacological research has revealed that dopamine receptor agents have opposite effects on cognitive function depending on baseline levels of working memory capacity. These contrasting effects have been interpreted to reflect differential baseline levels of dopamine. Here we demonstrate for the first time that working memory capacity as measured by listening span predicts dopamine synthesis capacity in the striatum, indicating that subjects with low working memory capacity have low DA synthesis capacity in the striatum, whereas subjects with high working memory capacity have high DA synthesis capacity in the striatum.

Abnormally increased CSF 3- Ortho-methyldopa (3-OMD) in untreated restless legs syndrome (RLS) patients indicates more severe disease and possibly abnormally increased dopamine synthesis

Background Abnormally high CSF 3-OMD occurs frequently for RLS patients indicating either increased l-dopa synthesis, limitations in l-dopa decarboxylation or increased MAT/COMT activity, or some combination of these. Increased tyrosine hydroxylase activity was found on both the RLS autopsy and the rodent iron-deprivation model of RLS, suggesting increased DA synthesis in RLS. We, therefore, hypothesized elevated 3-OMD in RLS results from increased DA synthesis and that this should occur accordingly with increased HVA. It would then also reflect both the more severe iron insufficiency pathology of RLS and greater clinical severity, shown by the objective measure of PLMS/hr. Methods Patients off RLS medications and matched controls had lumbar punctures at either 10 a.m. or 10 p.m.; RLS patients were grouped by normal or abnormally high 3-OMD (>10 nmol/l). Results Forty-nine RLS patients (30 high, 19 normal 3-OMD) and 36 age- and gender-matched controls, analyzed separately by time of CSF collection, did not significantly differ in age or gender. RLS patients with high 3-OMD had significantly higher CSF HVA, while those with normal 3-OMD had consistently lower CSF HVA than controls. CSF ferritin was consistently lower compared to controls for the high 3-OMD but not the normal 3-OMD RLS patients. The PLMS/hr was significantly higher for RLS patients with high compared to normal 3-OMD, indicating high 3-OMD patients had more severe RLS. Conclusions Abnormal elevation in 3-OMD for RLS patients may reflect increased dopamine synthesis for more severe but perhaps not mild RLS. These differences in the putative dopamine pathology of RLS may indicate different phases or expression of RLS biology or different underlying disease processes.

Effects of aripiprazole and terguride on dopamine synthesis in the dorsal striatum and medial prefrontal cortex of preweanling rats

The purpose of this study was to determine whether aripiprazole, a D2-like partial agonist increasingly prescribed to children, alters DA synthesis via actions at autoreceptors in the dorsal striatum and medial prefrontal cortex (mPFC) of preweanling rats. The ability of dopaminergic agents to alter DOPA accumulation in the striatum and mPFC was measured after NSD-1015 on postnatal day (PD) 20. Dopaminergic tone was manipulated by administering reserpine, gamma-butyrolactone (GBL), or through amphetamine withdrawal. Results showed that the partial agonists aripiprazole and terguride increased striatal DOPA accumulation under normosensitive conditions, but decreased DOPA accumulation in states of low dopaminergic tone. A different pattern of results was observed in the mPFC, because terguride and haloperidol, but not aripiprazole, increased DOPA accumulation under normosensitive conditions. In conclusion, the present data show that aripiprazole affects striatal synthesis modulating autoreceptors in an adult-typical manner during the late preweanling period. Unlike in adult rats, however, the mPFC of preweanling rats appears to contain transitory synthesis modulating autoreceptors that are sensitive to drug manipulation.

Highly diastereoselective synthesis of nucleoside adducts from the carcinogenic benzo[a]pyrene diol epoxide and a computational analysis.

A diastereoselective synthesis of the nucleoside adducts corresponding to a cis ring-opening of the carcinogen (+/-)-7 beta, 8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BaP DE-2) by 2'-deoxyadenosine and 2'-deoxyguanosine is described. The key intermediate (+/-)-10alpha-amino-7beta,8alpha,9alpha-trihydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene was synthesized by a highly diastereoselective dihydroxylation wherein phenylboronic acid was a water surrogate. The resulting boronate ester was converted to a tetraol derivative in which two of the four hydroxyl groups (trans 7, 8) were protected as benzoate esters while the remaining two (cis 9, 10) were free. The cis glycol entity was then subjected to a reaction with 1-chlorocarbonyl-1-methylethylacetate to yield an intermediate chloro monoacetoxy dibenzoate. Displacement of the halide with azide, complete cleavage of the esters, and catalytic reduction of the azide yielded the requisite amino triol. Fluoride displacement from appropriately protected nucleoside derivatives, 6-fluoropurine 2'-deoxyribonucleoside and 2-fluoro-2'-deoxyinosine, by the amino triol then yielded diastereomeric pairs of diol epoxide-adducted 2'-deoxyadenosine (dA) and 2'-deoxyguanosine (dG) nucleosides. Small aliquots of these adducts were separated for characterization purposes. The present approach provides the first diastereoselective synthesis of the cis adducts of BaP DE-2 with 2'-deoxyguanosine as well as the first synthesis of both dA and dG adducts from a common intermediate. An informative analysis of the 1H NMR spectra of the cis adducts synthesized and comparisons to the trans adducts are reported. To gain insight into the diastereoselectivity in the key dihydroxylation step, a computational analysis, including molecular mechanics (MMFF94) and semiempirical AM1 geometry optimizations, yielded results that are in fairly good agreement with the experimental observations.

Effect of acute and chronic inhibition of the DA transporter on DA synthesis and DA D2 receptors

Effect of acute and chronic inhibition of the DA transporter on DA synthesis and DA D2 receptors

Vitamin A deficiency induces motor impairments and striatal cholinergic dysfunction in rats

Vitamin A and its derivatives, retinoids, are involved in the regulation of gene expression by binding two nuclear receptor families, retinoic acid receptors and retinoid X receptors. Retinoid receptors are highly expressed in the striatum, revealing an involvement of this system in the control of movement as demonstrated by previous observations in knockout mice. To further assess the role of retinoids in adult striatal function, the present study investigated the effect of vitamin A deprivation on rat motor activity and coordination, the rate of synthesis and release of dopamine, the functioning of D1 and D2 receptors and their expression in the striatum. Moreover, the content of acetylcholine in the striatum was measured. Results show that 24 weeks of postnatal vitamin A deprivation induced severe locomotor deficits and impaired motor coordination. Vitamin A deprivation rats showed a significant hyperactivity following D1 receptor stimulation by R(+)-6-chloro-7,8-dihydroxy-1-phenyil-2,3,4,5-tetrahydro-1H-3-benzazepine or amphetamine and reduced catalepsy in response to haloperidol treatment. This different response to the above drugs is not due to a change in striatal DA release or synthesis between vitamin A deprivation and control animals. In situ hybridization experiments showed identical level of expression for the D1 and D2 receptor transcripts. On the other hand, the striatal tissue content of acetylcholine was reduced significantly by about 30% starting from the initial manifestation of motor deficits. We suggest that the locomotor impairment could be imputable to the dysfunction in striatal cholinergic interneurons. Our results stress the basic role of vitamin A in the maintenance of basal ganglia motor function in the adult rat brain.

Impaired synthesis or cellular storage of norepinephrine, dopamine, and 5-hydroxytryptamine in human inflammatory bowel disease.

The present study was aimed at evaluating the extent of dysfunction of the enteroendocrine and enteric nervous system, as indicated by changes in tissue levels of monoamines (dopamine, DA; norepinephrine, NE; 5-hydroxytryptamine, 5-HT) and their precursors and metabolites in the colonic mucosa of patients afflicted with ulcerative colitis (UC, N = 21) and Crohn's disease (CD, N = 22). In CD, but not in UC, NE tissue levels in both the noninflamed and inflamed colonic mucosa were markedly lower than in control subjects (N = 16). In the inflamed mucosa of CD and in UC patients levels of L-DOPA were twice those in controls. DA levels in the inflamed mucosa of CD and UC patients were markedly lower than in controls. This resulted in significant reductions in DA/L-DOPA tissue ratios, a rough measure of L-amino acid decarboxylase activity. 5-HT levels in the inflamed mucosa of CD and UC patients were markedly lower than in controls. In conclusion, intestinal cellular structures responsible for the synthesis and storage of DA, NE, and 5-HT may have been affected by the associated inflammatory process in both CD and UC.