Dopamine Synthesis In Striatum Research Articles

P677. Sex-Specific Polygenic Regulation of Dopamine Synthesis in Striatum in Vivo

Striatal presynaptic dopamine synthesis is implicated in neuropsychiatric illnesses like schizophrenia but shows considerable unexplained individual variability. We hypothesized that cumulative functional genetic variation in a network of proteins regulating tyrosine hydroxylase (TH), the dopamine synthesis rate-limiting enzyme, would contribute to dopamine synthesis capacity in the living human brain, measured by [18F]-FDOPA PET. Given prior work suggesting sex differences in the regulation of dopamine, we also tested for sex-specific effects.

GMP production of 6-[18F]Fluoro-l-DOPA for PET/CT imaging by different synthetic routes: a three center experience

BackgroundThe radiofluorinated levodopa analogue 6-[18F]F-l-DOPA (3,4-dihydroxy-6-18F-l-phenylalanine) is a commonly employed radiotracer for PET/CT imaging of multiple oncological and neurological indications. An unusually large number of different radiosyntheses have been published to the point where two different Ph. Eur. monographs exist depending on whether the chemistry relies on electrophilic or nucleophilic radiosubstitution of appropriate chemical precursors. For new PET imaging sites wishing to adopt [18F]FDOPA into clinical practice, selecting the appropriate production process may be difficult and dependent on the clinical needs of the site.MethodsData from four years of [18F]FDOPA production at three different clinical sites are collected and compared. These three sites, Aarhus University Hospital (AUH), Odense University Hospital (OUH), and Herlev University Hospital (HUH), produce the radiotracer by different radiosynthetic routes with AUH adopting an electrophilic strategy, while OUH and HUH employ two different nucleophilic approaches. Production failure rates, radiochemical yields, and molar activities are compared across sites and time. Additionally, the clinical use of the radiotracer over the time period considered at the different sites are presented and discussed.ResultsThe electrophilic substitution route suffers from being demanding in terms of cyclotron operation and maintenance. This challenge, however, was found to be compensated by a production failure rate significantly below that of both nucleophilic approaches; a result of simpler chemistry. The five-step nucleophilic approach employed at HUH produces superior radiochemical yields compared to the three-step approach adopted at OUH but suffers from the need for more comprehensive synthesis equipment given the multi-step nature of the procedure, including HPLC purification. While the procedure at OUH furnishes the lowest radiochemical yield of the synthetic routes considered, it produces the highest molar activity. This is of importance across the clinical applications of the tracer discussed here, including dopamine synthesis in striatum of subjects with schizophrenia and congenital hyperinsulinism in infants.ConclusionFor most sites either of the two nucleophilic substitution strategies should be favored. However, which of the two will depend on whether a given site wishes to optimize the radiochemical yield or the ease of the use.

Effects of the dopamine D3 antagonist PD 58491 and its interaction with the dopamine D3 agonist PD 128907 on brain dopamine synthesis in rat.

The dopamine (DA) D3 receptor antagonist PD 58491 [3-[4-[1-[4-[2-[4-(3-diethylaminopropoxy)phenyl]benzoimidazol++ +-1-yl-butyl]-1H-benzoimidazol-2-yl]phenoxy]propyl]diethylamine] bound with high affinity and selectivity to recombinant human DA D3 versus D2L and D4.2 receptors transfected into Chinese hamster ovary cells: Ki values of 19.5 nM versus 2,362 and >3,000 nM, respectively. In contrast, the putative DA D3 receptor antagonist (+)-AJ76 displayed low affinity and selectivity for D3 versus D2L and D4.2 receptors (91 nM vs. 253 and 193 nM, respectively). In vitro, PD 58491 (1 nM-1 microM) exhibited D3 receptor antagonist activity, reversing the quinpirole (10 nM)-induced stimulation of [3H]thymidine uptake in D3 CHOpro-5 cells, but did not have any significant intrinsic activity by itself in this assay. PD 58491 did not decrease the gamma-butyrolactone-induced increase in DA synthesis (L-3,4-dihydroxyphenylalanine accumulation) in rat striatum, indicating that the compound possessed no in vivo DA D2/D3 receptor agonist action at DA autoreceptors. PD 58491 (3-30 mg/kg, i.p.) generally did not alter DA or serotonin synthesis in either the striatum or mesolimbic region of rat brain. The D3-preferring agonist PD 128907 decreased DA synthesis in striatum and mesolimbic regions, and this effect was attenuated by pretreatment with PD 58491. These findings support the hypothesis that DA D3 autoreceptors may in part modulate the synthesis and release of DA in striatum and mesolimbic regions.

Determination of amino acids and monoamine neurotransmitters in caudate nucleus of seizure-resistant and seizure-prone BALB/c mice.

Amino acid and monoamine concentrations were examined in tissue extracts of caudate nucleus of genetic substrains of BALB/c mice susceptible or resistant to audiogenic seizures. Amino acids [aspartate, glutamate, glycine, taurine, serine, gamma-aminobutyric acid (GABA)], monoamines, and related metabolites were separated by isocratic reverse-phase chromatography and detected by a coulometric electrode array system. In situ activity of tyrosine hydroxylase and tryptophan hydroxylase were determined by measuring the accumulation of L-DOPA and 5-hydroxytryptophan after administration of the decarboxylase inhibitor NSD-1015. Highly significant decreases in concentrations of both excitatory (glutamate and aspartate) and inhibitory amino acids (GABA and taurine) were observed in extracts of caudate nucleus of seizure-prone mice. Substantial decreases in concentrations of dopamine (DA) and its metabolites, 3,4-dihydroxyphenylacetic acid and homovanillic acid, were also noted. Decreased accumulation of L-DOPA after NSD-1015 administration provided evidence for decreased tyrosine hydroxylase activity and decreased DA synthesis in striatum of seizure-prone mice compared with seizure-resistant mice. Decreased concentrations of the DA metabolite 3-methoxytyramine (after NSD-1015 administration) suggested that DA release was also compromised in seizure-prone mice. No significant difference in 5-hydroxytryptophan accumulation in striatum of seizure-prone and seizure-resistant mice suggested that tryptophan hydroxylase activity and serotonin synthesis were not affected. The data suggest that seizure-prone BALB/c mice have a deficiency in intracellular content of both excitatory and inhibitory amino acids. The data also raise the issue of whether GABAergic interactions with the nigrostriatal DA system are important in the regulation of audiogenic seizure susceptibility.

Dopamine D 1 autoreceptor function: possible expression in developing rat prefrontal cortex and striatum

Synthesis-modulating dopamine (DA) autoreceptor function was studied in vivo using γ-butyrolactone (GBL) to block propagation along DA axons. DA synthesis was measured by the accumulation of l-3,4-dihydroxyphenylalanine ( l-DOPA) after inhibition of aromatic l-amino acid decarboxylase. GBL treatment markedly increased DOPA accumulation in both the striatum and prefrontal cortex of developing rats. The selective DA partial D 1 agonist SKF-38393 inhibited this GBL-induced rise in DA synthesis in both the striatum and prefrontal cortex of 15- and 22-day-old rats, but not in adults. The effects of SKF-38393 in developing rats were mimicked by the non-catechol D 1 partial agonist CY-208-243, and were blocked by the D 1 antagonist SCH-23390, suggesting receptor mediation. The mixed D 2/D 3 agonist quinpirole attenuated DA synthesis in striatum of both two-week-old and adult rats, but failed to inhibit the GBL-induced increase in DA synthesis in the developing prefrontal cortex. These findings suggest that synthesis-modulating D 1-like receptor function may emerge transiently in the developing mammalian forebrain. In the adult striatum these functions appear to be subsumed by D 2-like receptors, whereas all synthesis-modulating DA receptor function in prefrontal cortex appears to be essentially lost with maturation.

R-(+)-HA-966, a glycine/NMDA receptor antagonist, selectively blocks the activation of the mesolimbic dopamine system by amphetamine.

1. The effects of the glycine/NMDA receptor antagonist, (+)-HA-966 on the neurochemical and behavioural responses to amphetamine have been determined in the mouse and rat. 2. In vehicle-treated control mice, (+)-HA-966 (30-100 mg kg-1) did not affect dopamine synthesis in either the nucleus accumbens or striatum and was without marked effect on spontaneous locomotor activity. 3. In the mouse, (+)-HA-966 (30 and 100 mg kg-1) dose-dependently blocked the enhancement of dopamine synthesis induced in the nucleus accumbens by amphetamine, but was without effect on the increase in dopamine synthesis in the striatum. 4. Intracerebroventricular administration of the glycine/NMDA receptor antagonist, 5,7-dichlorokynurenic acid, in the mouse (10 micrograms) also significantly attenuated amphetamine-enhanced DOPA accumulation in the nucleus accumbens, but not in the striatum. 5. The decrease of dopamine synthesis in striatum and nucleus accumbens induced by the dopamine receptor agonist, apomorphine, was unaffected by (+)-HA-966 (100 mg kg-1). 6. (+)-HA-966 (30 mg kg-1) failed to attenuate the hyperactivity induced by the systemic administration of amphetamine in the mouse, but totally prevented the hyperlocomotion following infusion of amphetamine into the rat nucleus accumbens. In contrast, stereotyped behaviour induced by infusion of amphetamine into the rat striatum was not altered following pretreatment with (+)-HA-966 (30 mg kg-1). 7. The results are consistent with a selective facilitatory role of glycine/NMDA receptors on mesolimbic dopaminergic neurones.

Effects of Ethanol and Low-Carbohydrate Diet on Contents of Noradrenalin, Dopamine, Serotonin and their Metabolites in Rat Brain.

Effects of ethanol consumption and intake of low-carbohydrate (low-CHO) diet on noradrenaline (NA), dopamine (DA) and its metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), serotonin (5HT) and its metabolite, 5-hydroxyindoleacetic acid (5HIAA) contents in six brain regions of rats were investigated. 1) Change of DA neuron Ethanol-containing control diet (hypercaloric ethanol diet) did not affect DA content in any area of brain, but decreased HVA in cortex and hypothalamus and increased DOPAC and HVA in midbrain. Low-CHO diet increased DA content in striatum, DOPAC and HVA in midbrain, but decreased DOPAC in hippocampus and hypothalamus, and HVA in cortex, pons and medulla, hippocampus and hypothalamus. Ethanol-containing low-CHO diet (isocaloric ethanol diet) increased DA level in striatum, DOPAC and HVA in midbrain, but decreased HVA in cortex, hippocampus, striatum and hypothalamus. These results suggest that i) hypercaloric ethanol diet has an opposite effect to carbohydrate on DA metabolism: hypercaloric ethanol diet and lowered carbohydrate intake per se enhance DA metabolism in midbrain, whereas inhibit it in cortex and hypothalamus, ii) lowered carbohydrate intake also declines DA metabolism in pons and medulla and hippocampus, whereas enhances DA synthesis in striatum, iii) the combined effect of ethanol and carbohydrate intake on DA metabolism is inhibited each other in the rats of isocaloric ethanol diet feeding, and this diet decreased DA metabolism in striatum. 2) Change of 5HT neuron Hypercaloric ethanol diet did not affect the contents of 5HT and 5HIAA in any region of brain.(ABSTRACT TRUNCATED AT 250 WORDS)

A comparison of domperidone and haloperidol effects on different dopaminergic neurons in the rat brain

Domperidone, a dopamine (DA) receptor antagonist with reportedly preferential actions outside of the blood-brain barrier, and haloperidol, a centrally active DA antagonist, were compared with respect to their abilities to increase the activity of dopaminergic neurons in the rat brain. The activity of nigrostriatal, mesolimbic, tuberohypophyseal and tuberoinfundibular dopamine nerves was estimated by measuring the in vivo rate of DA synthesis (dihydroxyphenylalanine accumulation following administration of an inhibitor of aromatic L-amino acid decarboxylase) in the striatum, olfactory tubercle, posterior pituitary and median eminence, respectively. In an initial study, the rates of DA synthesis in striatum, olfactory tubercle, and posterior pituitary were determined at 2, 8, and 16 h after subcutaneous administration of 0.25, 2.5, or 25 mg/kg domperidone. At the lowest dose of domperidone, DA synthesis was increased only in the posterior pituitary at 8 and 16 h; at the intermediate dose, DA synthesis increased in the posterior pituitary at 8 and 16 h and in the olfactory tubercle at 8 h. Only at 8 h after the highest dose of domperidone was DA synthesis increased in the striatum. When 2.5 mg/kg of doperidone or haloperidol were administered, DA synthesis in posterior pituitary and median eminence was increased in a similar fashion (in the latter region only at 16 h). In contrast, domperidone promoted only modest and delayed increases in DA synthesis in the olfactory tubercle and had no effect in the striatum. These results indicate that systemically administered domperidone preferentially increases DA synthesis in neurons terminating outside the blood-brain barrier, but after a pronounced delay, high doses of the drug can also activate DA neurons which project to the forebrain.

D-amphetamine and γ-butyrolactone alteration of dopamine synthesis in the terminals of nigrostriatal and mesolimbic neurons : Possible role of various autoreceptor sensitivities

The rate of synthesis of dopamine (DA) was estimated in vivo in terminals of nigrostriatal and mesolimbic neurons by measuring the accumulation of dihydroxyphenylalanine (DOPA_ in the striatum and in the nucleus accumbens and olfactory tubercle of male rats following the administration of an inhibitor of aromatic L-amino acid decarboxylase. Low to moderate doses of d-amphetamine (0.5 to 1.0 mg/kg) increased DA synthesis in the striatum but were without effect in the nucleus accumbens and olfactory tubercle; a higher dose (5.0 mg/kg) did not alter DA synthesis in any of the brain regions. Despite the lack of effect of d-amphetamine per se in the nucleus accumbens and olfactory tubercle, in both of these regions, as well as in the striatum, this drug was effective in reversing the decreased DA synthesis induced by a monoamine oxidase inhibitor (nialamide) or a DA agonist (apomorphine). γ-Butyrolactone (GBL) increased DA synthesis in the striatum, nucleus accumbens and olfactory tubercle, but it was less potent, less effective, and had a shorter duration of action in the latter two regions. d-Amphetamine, like GBL, may exert part of its effect on DA synthesis by reducing impulse flow in ascending DA neurons, since a low dose of d-amphetamine (0.125 mg/kg) potentiated the GBL-induced increase in DA synthesis in striatum, nucleus accumbens and olfactory tubercle. Regional differences in the actions of GBL and d-amphetamine on DA synthesis may be related to differences in receptor-mediated mechanisms that regulate the synthesis of this amine in neurons terminating in the striatum versus those terminating in nucleus accumbens and olfactory tubercle. At least one difference appears to be in the sensitivity of DA autoreceptors in these regions. The dose of apomorphine needed to reverse the GLB-induced increase of DA synthesis in nucleus accumbens and olfactory tubercle was approximately 1/10 that necessary to cause the same effect in the striatum. Pretreatment with a DA antagonist (haloperidol) potentiated the GBL-induced stimulation of DA synthesis in nucleus accumbens and olfactory tubercle, but not in the striatum. These results suggest that the reduced abilities of GBL and amphetamine to increase DA synthesis in nucleus accumbens and olfactory tubercle may result from a greater sensitivity of autoreceptors on mesolimbic DA neurons permitting a tighter regulatory control over DA synthesis in these neurons.

Lack of effect of cerebellectomy on ascending dopaminergic neurons in the rat brain

The dopamine content in striatum and substantia nigra of the rat was not altered 3 weeks after total or hemicerebellectomy. Furthermore, 3 days after hemicerebellectomy basal and haloperidol-stimulated activity of ascending mesolimbic and nigrostriatal dopaminergic neurons, as estimated from the in vivo rate of dopamine synthesis in striatum and nucleus accumbeens, was not altered. Cupric silver degeneration staining following hemicerebellectomy failed to identify a direct anatomical pathway between cerebellum and substantia nigra in the rat.

Effects of d-amphetamine and disruption of 5-hydroxytryptaminergic neuronal systems on the synthesis of dopamine in selected regions of the rat brain.

The rate of accumulation of DOPA following the administration of a decarboxylase inhibitor was employed to estimate the in vivo rate of dopamine (DA) synthesis in rat brain regions containing the cell bodies (substantia nigra) and terminals (striatum) of nigrostriatal nerves, and the terminals of mesolimbic (nucleus accumbens, olfactory tubercle) and tuberoinfundibular (median eminence) nerves. d-Amphetamine (0.5–2 mg/kg, i.p.) caused a marked increase in DA synthesis in striatum, a modest increase in olfactory tubercle, and was without effect in nucleus accumbens and median eminence. At the largest dose, f-amphetamine slightly reduced DA synthesis in substantia nigra. The mechanism of these regional differences is currently unknown. Depletion of 5-hydroxytryptamine (5-HT) with an intracerebroventricular injection of 5,7-dihydroxytryptamine (5,7-DHT) or a systemic injection of p-chlorophenylalanine (pCPA) enhanced spontaneous and amphetamine-stimulated locomotor activity. Pretreatment with 5,7-DHT did not alter DOPA accumulation in any brain region of animals injected with d-amphetamine or its vehicle. Pretreatment with pCPA reduced DOPA accumulation only in regions containing terminals of mesolimbic DA nerves. Thus, the increased amphetamine-induced hyperactivity in 5-HT-depleted rats is not reflected in a consistent change in the rate of DA synthesis in the brains of these animals.