The Role of the Brain in the Regulation of Peripheral Organs-Noradrenaline Sources in Neonatal Rats: Noradrenaline Synthesis Enzyme Activity.

This work is aimed at studying the mechanisms of reciprocal humoral regulation of noradrenaline-producing organs in rats in the perinatal period of development. The activity of noradrenaline synthesis enzymes tyrosine hydroxylase and dopamine-beta-hydroxylase was measured in the brain and adrenal glands 48 and 72 h after the injection of immunotoxin (anti-dopamine-beta-hydroxylase-saporin) into the rat brain ventricles. It was shown that, 48 h after the immunotoxin injection into the brain, the activity of tyrosine hydroxylase in the brain decreased; however, 72 h after the injection it reached the control levels. This fact indicates that noradrenaline synthesis in the survived neurons increases. In the adrenal glands, 72 h after the immunotoxin injection into the brain, the activity of dopamine-beta-hydroxylase increased. This points to a compensatory increase in the rate of noradrenaline synthesis in the adrenal glands when the synthesis of noradrenaline in the brain is inhibited.

Catecholaminergic projections into an interconnected forebrain network control the sensitivity of male rats to diet-induced obesity.

Hindbrain catecholamine neurons convey gut-derived metabolic signals to an interconnected neuronal network in the hypothalamus and adjacent forebrain. These neurons are critical for short-term glycemic control, glucocorticoid and glucoprivic feeding responses, and glucagon-like peptide 1 (GLP-1) signaling. Here we investigate whether these pathways also contribute to long-term energy homeostasis by controlling obesogenic sensitivity to a high-fat/high-sucrose choice (HFSC) diet. We ablated hindbrain-originating catecholaminergic projections by injecting anti-dopamine-ß-hydroxylase-conjugated saporin (DSAP) into the paraventricular nucleus of the hypothalamus (PVH) of male rats fed a chow diet for up to 12 wk or a HFSC diet for 8 wk. We measured the effects of DSAP lesions on food choices; visceral adiposity; plasma glucose, insulin, and leptin; and indicators of long-term ACTH and corticosterone secretion. We also determined lesion effects on the number of carbohydrate or fat calories required to increase visceral fat. Finally, we examined corticotropin-releasing hormone levels in the PVH and arcuate nucleus expression of neuropeptide Y ( Npy), agouti-related peptide ( Agrp), and proopiomelanocortin ( Pomc). DSAP-injected chow-fed rats slowly increase visceral adiposity but quickly develop mild insulin resistance and elevated blood glucose. DSAP-injected HFSC-fed rats, however, dramatically increase food intake, body weight, and visceral adiposity beyond the level in control HFSC-fed rats. These changes are concomitant with 1) a reduction in the number of carbohydrate calories required to generate visceral fat, 2) abnormal Npy, Agrp, and Pomc expression, and 3) aberrant control of insulin secretion and glucocorticoid negative feedback. Long-term metabolic adaptations to high-carbohydrate diets, therefore, require intact forebrain catecholamine projections. Without them, animals cannot alter forebrain mechanisms to restrain increased visceral adiposity.

Future pharmacological therapy in hypertension.

PURPOSE OF REVIEW: Hypertension (HTN) is a widespread and growing disease, with medication intolerance and side-effect present among many. To address these obstacles novel pharmacotherapy is an active area of drug development. This review seeks to explore future drug therapy for HTN in the preclinical and clinical arenas. RECENT FINDINGS: The future of pharmacological therapy in HTN consists of revisiting old pathways to find new targets and exploring wholly new approaches to provide additional avenues of treatment. In this review, we discuss the current status of the most recent drug therapy in HTN. New developments in well trod areas include novel mineralocorticoid antagonists, aldosterone synthase inhibitors, aminopeptidase-A inhibitors, natriuretic peptide receptor agonists, or the counter-regulatory angiotensin converting enzyme 2/angiotensin (Ang) (1-7)/Mas receptor axis. Neprilysin inhibitors popularized for heart failure may also still hold HTN potential. Finally, we examine unique systems in development never before used in HTN such as Na/H exchange inhibitors, vasoactive intestinal peptide agonists, and dopamine beta hydroxylase inhibitors. SUMMARY: A concise review of future directions of HTN pharmacotherapy.

Elevated dopamine in the medial prefrontal cortex suppresses cocaine seeking via D1 receptor overstimulation.

Previous investigations indicate that the dopamine-ß-hydroxylase (DBH) inhibitors disulfiram and nepicastat suppress cocaine-primed reinstatement of cocaine self-administration behaviour. Moreover, both inhibitors increase dopamine release in the rat medial prefrontal cortex (mPFC) and markedly potentiate cocaine-induced dopamine release in this region. This study was aimed to clarify if the suppressant effect of DBH inhibitors on cocaine reinstatement was mediated by the high extracellular dopamine in the rat mPFC leading to a supra-maximal stimulation of D1 receptors in the dorsal division of mPFC, an area critical for reinstatement of cocaine-seeking behaviour. In line with previous microdialysis studies in drug-naïve animals, both DBH inhibitors potentiated cocaine-induced dopamine release in the mPFC, in the same animals in which they also suppressed reinstatement of cocaine seeking. Similar to the DBH inhibitors, L-DOPA potentiated cocaine-induced dopamine release in the mPFC and suppressed cocaine-induced reinstatement of cocaine-seeking behaviour. The bilateral microinfusion of the D1 receptor antagonist SCH 23390 into the dorsal mPFC not only prevented cocaine-induced reinstatement of cocaine seeking but also reverted both disulfiram- and L-DOPA-induced suppression of reinstatement. Moreover, the bilateral microinfusion of the D1 receptor agonist chloro-APB (SKF 82958) into the dorsal mPFC markedly attenuated cocaine-induced reinstatement of cocaine seeking. These results suggest that stimulation of D1 receptors in the dorsal mPFC plays a crucial role in cocaine-induced reinstatement of cocaine seeking, whereas the suppressant effect of DBH inhibitors and L-DOPA on drug-induced reinstatement is mediated by a supra-maximal stimulation of D1 receptors leading to their inactivation.

Chronic loss of noradrenergic tone produces ß-arrestin2-mediated cocaine hypersensitivity and alters cellular D2 responses in the nucleus accumbens.

Cocaine blocks plasma membrane monoamine transporters and increases extracellular levels of dopamine (DA), norepinephrine (NE) and serotonin (5-HT). The addictive properties of cocaine are mediated primarily by DA, while NE and 5-HT play modulatory roles. Chronic inhibition of dopamine ß-hydroxylase (DBH), which converts DA to NE, increases the aversive effects of cocaine and reduces cocaine use in humans, and produces behavioral hypersensitivity to cocaine and D2 agonism in rodents, but the underlying mechanism is unknown. We found a decrease in ß-arrestin2 (ßArr2) in the nucleus accumbens (NAc) following chronic genetic or pharmacological DBH inhibition, and overexpression of ßArr2 in the NAc normalized cocaine-induced locomotion in DBH knockout (Dbh -/-) mice. The D2/3 agonist quinpirole decreased excitability in NAc medium spiny neurons (MSNs) from control, but not Dbh -/- animals, where instead there was a trend for an excitatory effect. The Gαi inhibitor NF023 abolished the quinpirole-induced decrease in excitability in control MSNs, but had no effect in Dbh -/- MSNs, whereas the Gαs inhibitor NF449 restored the ability of quinpirole to decrease excitability in Dbh -/- MSNs, but had no effect in control MSNs. These results suggest that chronic loss of noradrenergic tone alters behavioral responses to cocaine via decreases in ßArr2 and cellular responses to D2/D3 activation, potentially via changes in D2-like receptor G-protein coupling in NAc MSNs.

Catecholaminergic neurons projecting to the paraventricular nucleus of the hypothalamus are essential for cardiorespiratory adjustments to hypoxia.

Brainstem catecholamine neurons modulate sensory information and participate in control of cardiorespiratory function. These neurons have multiple projections, including to the paraventricular nucleus (PVN), which contributes to cardiorespiratory and neuroendocrine responses to hypoxia. We have shown that PVN-projecting catecholaminergic neurons are activated by hypoxia, but the function of these neurons is not known. To test the hypothesis that PVN-projecting catecholamine neurons participate in responses to respiratory challenges, we injected IgG saporin (control; n = 6) or anti-dopamine ß-hydroxylase saporin (DSAP; n = 6) into the PVN to retrogradely lesion catecholamine neurons projecting to the PVN. After 2 wk, respiratory measurements (plethysmography) were made in awake rats during normoxia, increasing intensities of hypoxia (12, 10, and 8% O2) and hypercapnia (5% CO2-95% O2). DSAP decreased the number of tyrosine hydroxylase-immunoreactive terminals in PVN and cells counted in ventrolateral medulla (VLM; -37%) and nucleus tractus solitarii (nTS; -36%). DSAP produced a small but significant decrease in respiratory rate at baseline (during normoxia) and at all intensities of hypoxia. Tidal volume and minute ventilation (VE) index also were impaired at higher hypoxic intensities (10-8% O2; e.g., VE at 8% O2: IgG = 181 ± 22, DSAP = 91 ± 4 arbitrary units). Depressed ventilation in DSAP rats was associated with significantly lower arterial O2 saturation at all hypoxic intensities. PVN DSAP also reduced ventilatory responses to 5% CO2 (VE: IgG = 176 ± 21 and DSAP = 84 ± 5 arbitrary units). Data indicate that catecholamine neurons projecting to the PVN are important for peripheral and central chemoreflex respiratory responses and for maintenance of arterial oxygen levels during hypoxic stimuli.

Role of P-glycoprotein and permeability upon the brain distribution and pharmacodynamics of etamicastat: a comparison with nepicastat.

1. This study explores the impact of permeability and P-glycoprotein (P-gp) efflux, upon brain exposure to etamicastat, a new dopamine-ß-hydroxylase (DBH) inhibitor and consequently brain levels of catecholamines. 2. Brain exposure to etamicastat (10 mg/kg), following intravenous administration to mice, was residual and upon oral administration of the same dose no compound was detected, concurring with the absence of effects upon brain catecholamines. The intravenous co-administration of elacridar (1.0 mg/kg), a known P-gp/BCRP dual modulator, significantly increased brain etamicastat exposure, but the levels attained were very low when compared to those of nepicastat, a centrally active DBH inhibitor. 3. In vitro permeability studies from apical-to-basal direction conducted in Caco-2 cells and MDCK-II cells showed that etamicastat apparent permeability was 1.2 × 10(-5) and 1.1 × 10(-6 )cm/s, respectively, 5- and 50-fold lower as compared to nepicastat. The secretory efflux ratio in MDCK-II cells overexpressing human P-gp showed an efflux ratio greater than 2, for both compounds, which was significantly decreased by elacridar. Despite its lower bioavailability and higher clearance, as compared to nepicastat, etamicastat showed preferential distribution to peripheral tissues and high plasma free fraction (15.5%), which may explain its effects upon peripheral DBH and catecholamine levels. 4. Though P-gp-mediated efflux may contribute to the limited brain penetration of etamicastat, the low permeability along with the pharmacokinetic properties of etamicastat may be perceived as the main contributors for its peripheral selectivity, which is advantageous for a cardiovascular drug candidate.

Effects of pharmacologic dopamine ß-hydroxylase inhibition on cocaine-induced reinstatement and dopamine neurochemistry in squirrel monkeys.

Disulfiram has shown promise as a pharmacotherapy for cocaine dependence in clinical settings, although it has many targets, and the behavioral and molecular mechanisms underlying its efficacy are unclear. One of many biochemical actions of disulfiram is inhibition of dopamine ß-hydroxylase (DBH), the enzyme that converts dopamine (DA) to norepinephrine (NE) in noradrenergic neurons. Thus, disulfiram simultaneously reduces NE and elevates DA tissue levels in the brain. In rats, both disulfiram and the selective DBH inhibitor nepicastat block cocaine-primed reinstatement, a paradigm which is thought to model some aspects of drug relapse. This is consistent with some clinical results and supports the use of DBH inhibitors for the treatment of cocaine dependence. The present study was conducted to confirm and extend these results in nonhuman primates. Squirrel monkeys trained to self-administer cocaine were pretreated with disulfiram or nepicastat prior to cocaine-induced reinstatement sessions. Neither DBH inhibitor altered cocaine-induced reinstatement. Unexpectedly, nepicastat administered alone induced a modest reinstatement effect in squirrel monkeys, but not in rats. To investigate the neurochemical mechanisms underlying the behavioral results, the effects of DBH inhibition on extracellular DA were analyzed in the nucleus accumbens (NAc) using in vivo microdialysis in squirrel monkeys. Both DBH inhibitors attenuated cocaine-induced DA overflow in the NAc. Hence, the attenuation of cocaine-induced changes in accumbal DA neurochemistry was not associated with altered cocaine-seeking behavior. Overall, the reported behavioral effects of DBH inhibition in rodent models of relapse did not extend to nonhuman primates under the conditions used in the current studies.

The dopamine ß-hydroxylase inhibitor, nepicastat, reduces different alcohol-related behaviors in rats.

BACKGROUND: Recent experimental data indicate that treatment with the selective dopamine ß-hydroxylase inhibitor, nepicastat, suppressed different reward-related behaviors, including self-administration of chocolate and reinstatement of cocaine and chocolate seeking, in rats. This study was designed to extend to different alcohol-related behaviors the investigation on the "anti-addictive" properties of nepicastat. METHODS: Sardinian alcohol-preferring (sP) rats, selectively bred for excessive alcohol consumption, were exposed to different procedures of alcohol drinking and self-administration. RESULTS: Repeated treatment with nepicastat (0, 25, 50, and 100 mg/kg, intraperitoneally [i.p.], once daily for 10 consecutive days) produced a stable and dose-related reduction in daily alcohol intake in sP rats exposed to the homecage 2-bottle "alcohol (10% v/v) versus water" choice regimen with unlimited access. Acute treatment with nepicastat (0, 25, 50, and 100 mg/kg, i.p.) completely suppressed the "alcohol deprivation effect" (i.e., the temporary increase in alcohol intake occurring after a period of abstinence; model of alcohol relapse episodes) in sP rats exposed to the 2-bottle choice regimen. Acute treatment with nepicastat (0, 25, 50, and 100 mg/kg, i.p.) dose dependently and selectively reduced oral alcohol self-administration in sP rats trained to lever respond for alcohol (15% v/v) on a fixed ratio 4 schedule of reinforcement. Finally, combination of nepicastat (0, 50, and 100 mg/kg, i.p.) and alcohol (2 g/kg, intragastrically) did not alter spontaneous locomotor activity in sP rats. CONCLUSIONS: Together, these data extend to alcohol the capacity of nepicastat to suppress different behaviors motivated by natural stimuli and drugs of abuse.

Human disposition, metabolism and excretion of etamicastat, a reversible, peripherally selective dopamine ß-hydroxylase inhibitor.

AIMS: Etamicastat is a reversible dopamine-ß-hydroxylase inhibitor that decreases noradrenaline levels in sympathetically innervated tissues and slows down sympathetic nervous system drive. In this study, the disposition, metabolism and excretion of etamicastat were evaluated following [(14)C]-etamicastat dosing. METHODS: Healthy Caucasian males (n = 4) were enrolled in this single-dose, open-label study. Subjects were administered 600 mg of unlabelled etamicastat and 98 µCi weighing 0.623 mg [(14)C]-etamicastat. Blood samples, urine and faeces were collected to characterize the disposition, excretion and metabolites of etamicastat. RESULTS: Eleven days after administration, 94.0% of the administered radioactivity had been excreted; 33.3 and 58.5% of the administered dose was found in the faeces and urine, respectively. Renal excretion of unchanged etamicastat and its N-acetylated metabolite (BIA 5-961) accounted for 20.0 and 10.7% of the dose, respectively. Etamicastat and BIA 5-961 accounted for most of the circulating radioactivity, with a BIA 5-961/etamicastat ratio that was highly variable both for the maximal plasma concentration (19.68-226.28%) and for the area under the plasma concentration-time curve from time zero to the last sampling time at which the concentration was above the limit of quantification (15.82- 281.71%). Alongside N-acetylation, metabolism of etamicastat also occurs through oxidative deamination of the aminoethyl moiety, alkyl oxidation, desulfation and glucuronidation. CONCLUSIONS: Etamicastat is rapidly absorbed, primarily excreted via urine, and its biotransformation occurs mainly via N-acetylation (N-acetyltransferase type 2), although glucuronidation, oxidation, oxidative deamination and desulfation also take place.

Effects of acute inhibition of dopamine ß-hydroxylase on neural responses to pups in adult virgin male California mice (Peromyscus californicus).

The neural mechanisms underlying paternal care in biparental mammals are not well understood. The California mouse (Peromyscus californicus) is a biparental rodent in which virtually all fathers are attracted to pups, while virgin males vary widely in their behavior toward unrelated infants, ranging from attacking to avoiding to huddling and grooming pups. We previously showed that pharmacologically inhibiting the synthesis of the neurotransmitter norepinephrine (NE) with the dopamine ß-hydroxylase inhibitor nepicastat reduced the propensity of virgin male and female California mice to interact with pups. The current study tested the hypothesis that nepicastat would reduce pup-induced c-Fos immunoreactivity, a cellular marker of neural activity, in the medial preoptic area (MPOA), medial amygdala (MeA), basolateral amygdala (BLA), and bed nucleus of the stria terminalis (BNST), brain regions implicated in the control of parental behavior and/or anxiety. Virgin males were injected with nepicastat (75 mg/kg, i.p.) or vehicle 2 hours prior to exposure to either an unrelated pup or novel object for 60 minutes (n = 4-6 mice per group). Immediately following the 60-minute stimulus exposure, mice were euthanized and their brains were collected for c-Fos immunohistochemistry. Nepicastat reduced c-Fos expression in the MeA and MPOA of pup-exposed virgin males compared to vehicle-injected controls. In contrast, nepicastat did not alter c-Fos expression in any of the above brain regions following exposure to a novel object. Overall, these results suggest that the noradrenergic system might influence MeA and MPOA function to promote behavioral interactions with pups in virgin males.

Dopamine ß-hydroxylase inhibitors enhance the discriminative stimulus effects of cocaine in rats.

Inhibitors of dopamine ß-hydroxylase (DBH), the enzyme that converts dopamine (DA) to norepinephrine (NE) in noradrenergic cells, have shown promise for the treatment of cocaine abuse disorders. However, the mechanisms underlying the beneficial effects of these compounds have not been fully elucidated. We used the drug discrimination paradigm to determine the impact of DBH inhibitors on the interoceptive stimulus properties of cocaine. Sprague-Dawley rats were trained to discriminate cocaine (5.6 mg/kg) from saline using a multicomponent, food-reinforced discrimination procedure. On test days, subjects were pretreated with the nonselective DBH inhibitor disulfiram (0-100.0 mg/kg i.p.) or the selective DBH inhibitor nepicastat (0-56.0 mg/kg i.p.) 2 hours prior to a test session either alone or in combination with cumulatively administered cocaine (0-5.6 mg/kg i.p.). Neither disulfiram nor nepicastat substituted for the cocaine stimulus when tested up to doses that nonspecifically reduced responding. However, in combination studies, pretreatment with either disulfiram or nepicastat produced leftward shifts in the cocaine dose-response function and also conferred cocaine-like stimulus effects to the selective NE transporter inhibitor, reboxetine (0.3-5.6 mg/kg i.p.). These results indicate that pharmacological inhibition of DBH does not produce cocaine-like interoceptive stimulus effects alone, but functionally enhances the interoceptive stimulus effects of cocaine, possibly due to facilitated increases in DA released from noradrenergic terminals. These findings suggest that DBH inhibitors have low abuse liability and provide support to clinical reports that some subjective effects produced by cocaine, particularly aversive effects, are enhanced after DBH inhibition.

N-acetylation of etamicastat, a reversible dopamine-ß-hydroxylase inhibitor.

Etamicastat [(R)-5-(2-aminoethyl)-1-(6,8-difluorochroman-3-yl)-1H-imidazole-2(3H)-thione hydrochloride] is a reversible dopamine-ß-hydroxylase inhibitor that decreases norepinephrine levels in sympathetically innervated tissues. After in vivo administration, N-acetylation of etamicastat was found to be a main metabolic pathway. The purpose of the current study was to characterize the N-acetylation of etamicastat by N-acetyltransferases (NAT1 and NAT2) and evaluate potential species differences in etamicastat N-acetylation using a sensitive and specific liquid chromatography-mass spectrometry assay. Marked differences in etamicastat N-acetylation were observed among the laboratory species and humans. After oral administration, the rat, hamster, and human subjects presented the highest rates of etamicastat N-acetylation, whereas almost no acetylation was observed in the mouse, rabbit, minipig, and monkey and no acetylation was observed in the dog. In in vitro studies, rats and humans showed similar acetylation rates, whereas no acetylation was detected in the dog. Studies performed with human recombinant NAT1 4 and NAT2 4 enzymes revealed that both were able to conjugate etamicastat, although at different rates. NAT1 had lower affinity compared with NAT2 (Km, 124.8 ± 9.031 µM and 17.14 ± 3.577 µM, respectively). A significant correlation (r(2) = 0.65, P < 0.05) was observed in a comparison of etamicastat N-acetylation by human single-donor enzymes and sulfamethazine, a selective substrate to NAT2. No correlation was observed with p-aminosalicylic acid, a NAT1 selective substrate. In conclusion, these results suggest that NAT2 and, to a lesser extent, NAT1 contribute to etamicastat N-acetylation. Furthermore, the high interspecies and intraspecies differences in N-acetylation should be taken into consideration when evaluating the in vivo bioavailability of etamicastat.

The dopamine ß-hydroxylase inhibitor, nepicastat, suppresses chocolate self-administration and reinstatement of chocolate seeking in rats.

Craving for chocolate is a common phenomenon, which may evolve to an addictive-like behaviour and contribute to obesity. Nepicastat is a selective dopamine ß-hydroxylase (DBH) inhibitor that suppresses cocaine-primed reinstatement of cocaine seeking in rats. We verified whether nepicastat was able to modify the reinforcing and motivational properties of a chocolate solution and to prevent the reinstatement of chocolate seeking in rats. Nepicastat (25, 50 and 100 mg/kg, intraperitoneal) produced a dose-related inhibition of operant self-administration of the chocolate solution in rats under fixed-ratio 10 (FR10) and progressive-ratio schedules of reinforcement, measures of the reinforcing and motivational properties of the chocolate solution, respectively. The effect of nepicastat on the reinstatement of chocolate seeking was studied in rats in which lever-responding had been extinguished by removing the chocolate solution for approximately 8 d. Nepicastat dose-dependently suppressed the reinstatement of lever-responding triggered by a 'priming' of the chocolate solution together with cues previously associated with the availability of the reward. In a separate group of food-restricted rats trained to lever-respond for regular food pellets, nepicastat reduced FR10 lever-responding with the same potency as for the chocolate solution. Spontaneous locomotor activity was not modified by nepicastat doses that reduced self-administration of the chocolate solution and regular food pellets and suppressed the reinstatement of chocolate seeking. The results indicate that nepicastat reduces motivation to food consumption sustained by appetite or palatability. Moreover, the results suggest that DBH inhibitors may be a new class of pharmacological agents potentially useful in the prevention of relapse to food seeking in human dieters.

[Disulfiram as a treatment for cocaine dependency]. / Disulfiram als behandeling voor cocaïneafhankelijkheid.

BACKGROUND: Cocaine abuse and dependency have a considerable impact on society and health issues. Current treatment of cocaine dependency consists primarily of psychosocial and therapeutic interventions. There is a marked need for effective pharmacological treatments in addition to the currently available treatment options. Recently, there is some evidence that disulfiram (DSF) might reduce use of cocaine in patients presenting with cocaine dependency. AIM: To explore the efficacy of disulfiram as a treatment for cocaine dependency. METHOD: We performed a Medline search for randomised controlled trials (RCTs) relating to disulfiram as a treatment for cocaine dependency. RESULTS: We found six RCT's for this review. Disulfiram seemed to have a positive effect on the primary cocaine outcomes. In addition, a positive effect of disulfiram seemed to be independent of alcohol abuse. However, the quality of these studies was extremely variable both in terms of sample size and composition. A possible neurobiological explanation for this would be an inhibitory effect of disulfiram on dopamine beta-hydroxylase, thus generating lower levels of norepinefrine. CONCLUSION: Disulfiram seems to be a valuable drug for the treatment of cocaine dependency. Due to the limited number and quality of the published studies, further research is needed in order to support the early positive results.

Treatment with dopamine ß-hydroxylase (DBH) inhibitors prevents morphine use and relapse-like behavior in rats.

BACKGROUND: Opioid use disorders are serious contributors to the harms associated with the drug use. Unfortunately, therapeutic interventions for opioid addicts after detoxification have been limited and not sufficiently effective. Recently, several studies have led to promising results with disulfiram (DSF), a dopamine ß-hydroxylase (DBH) inhibitor, showing that it is a potent agent against not only alcohol but also addiction to various drugs. MATERIALS AND METHODS: This study was designed to examine whether DSF and nepicastat (NEP; another DBH inhibitor) modify morphine intake and reinstatement of seeking-behavior using the rat model of intravenous morphine self-administration. Additionally, we intended to estimate the effects of both inhibitors on the locomotor activity as well as on extracellular dopamine and its metabolite levels in the nucleus accumbens using microdialysis in naive rats. RESULTS: We demonstrated that both DBH inhibitors reduced responding to morphine self-administration. Moreover, DSF and NEP administered acutely before reinstatement test sessions consistently attenuated the reinforcing effects of morphine and a morphine-associated conditioned cue. The observed effects for lower doses (6.25-25 mg/kg; ip) of both DBH inhibitors seem to be independent of locomotor activity reduction and dopamine level in the nucleus accumbens. Neither DSF nor NEP administered daily during morphine abstinence with extinction training sessions had any effect on active lever-responding and changed the reinstatement induced by morphine priming doses. Reinstatement of drug-seeking behavior induced by a conditioned cue previously associated with morphine delivery was attenuated following repeated administration of DSF or NEP during the abstinence period. CONCLUSION: These results seem to point to the significance  of DBH inhibition as a potential pharmacotherapy against morphine use disorders.

RNAi-mediated knock-down of the dopamine beta-hydroxylase gene changes growth of razor clams.

Dopamine beta-hydroxylase (DßH) plays an essential role in the synthesis of catecholamines (CA) in neuroendocrine networks. In the razor clam, Sinonovacula constricta a novel gene for DßH (ScDßH-α) was identified that belongs to the copper type II ascorbate-dependent monooxygenase family. Expression analysis revealed ScDßH-α gene transcripts were abundant in the liver and expressed throughout development. Knock-down of ScDßH-α in adult clams using siRNA caused a reduction in the growth rate compared to control clams. Reduced growth was associated with strong down-regulation of gene transcripts for the growth-related factors, platelet derived growth factors A (PDGF-A) (P < 0.001) 24 h after ScDßH-α knock-down, vascular endothelial growth factor (VEGF1) (P < 0.001) and platelet derived growth factor B (PDGF-B-2) (P < 0.001) 24 h and 48 h after ScDßH-α knock-down and transforming growth factor beta (TGF-ß1) (P < 0.001) 48 h and 72 h after ScDßH-α knock-down. Taken together the results suggest that the novel ScDßH-α gene through its role in CA synthesis is involved in growth regulation in the razor clam and possibly other bivalves.

Dopamine ß hydroxylase as a potential drug target to combat hypertension.

INTRODUCTION: Despite a large number of commercially available drugs, hypertension and related cardiovascular diseases remain a global problem. It is thus imperative that novel drugs and therapeutic strategies are regularly identified, and alternative targets explored. Dopamine ß hydroxylase (DBH), a key player in the catecholamine biosynthetic pathway, may provide a therapeutic opportunity and should be extensively explored as a target for potent anti-hypertensives. Inhibitors of DBH have been successful in combating hypertension, as evidenced by the outcome of clinical trials for etamicastat and zamicastat. AREAS COVERED: We shed light on the strategies employed to identify inhibitors of the enzyme and outline the advantages that the target might offer. Structural and functional details of the enzyme are described along with specific methodologies for drug discovery that were never utilized for the therapeutic target. EXPERT OPINION: Effective inhibitors of the enzyme may be identified with computer-aided structure-based design. Adoption of new methodologies and the assessment of newly designed inhibitors in DBH-specific animal models will provide new, safe, and cost-effective therapeutic opportunities.

Accumulation of a tetrahydroisoquinoline in phenylketonuria.

3',4'-Deoxynorlaudanosolinecarboxylic acid (DNLCA), a tetrahydroisoquinoline derived from dopamine and phenylpyruvic acid, has been detected by computerized mass fragmentography in urine of phenylketonuric children and in urine and brain of rats with experimentally induced hyperphenylalaninemia. Levels of DNLCA in brain of treated animals were more than tenfold higher than controls, and the excess tetrahydroisoquinoline appeared to accumulate in the cerebellum and cortex. DNLCA is a noncompetitive inhibitor of dopamine beta-hydroxylase (inhibition constant, Ki, = 0.42 mM) and is taken up by the brain.

Dopamine nerve terminals in the rat limbic cortex: aspects of the dopamine hypothesis of schizophrenia.

The existence of cortical dopamine nerve terminals is demonstrated with a highly sensitive modification of the Falck-Hillarp fluorescence technique. This confirms previous biochemical reports of high dopamine levels in the cortex. The histochemistry reveals that the distribution is regional and confined to the limbic cortex.