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Importance: Although numerous children receive methylphenidate hydrochloride for the treatment of attention-deficit/hyperactivity disorder (ADHD), little is known about age-dependent and possibly lasting effects of methylphenidate on the human dopaminergic system., Objectives: To determine whether the effects of methylphenidate on the dopaminergic system are modified by age and to test the hypothesis that methylphenidate treatment of young but not adult patients with ADHD induces lasting effects on the cerebral blood flow response to dopamine challenge, a noninvasive probe for dopamine function., Design, Setting, and Participants: A randomized, double-blind, placebo-controlled trial (Effects of Psychotropic Drugs on Developing Brain-Methylphenidate) among ADHD referral centers in the greater Amsterdam area in the Netherlands between June 1, 2011, and June 15, 2015. Additional inclusion criteria were male sex, age 10 to 12 years or 23 to 40 years, and stimulant treatment-naive status., Interventions: Treatment with either methylphenidate or a matched placebo for 16 weeks., Main Outcomes and Measures: Change in the cerebral blood flow response to an acute challenge with methylphenidate, noninvasively assessed using pharmacological magnetic resonance imaging, between baseline and 1 week after treatment. Data were analyzed using intent-to-treat analyses., Results: Among 131 individuals screened for eligibility, 99 patients met DSM-IV criteria for ADHD, and 50 participants were randomized to receive methylphenidate and 49 to placebo. Sixteen weeks of methylphenidate treatment increased the cerebral blood flow response to methylphenidate within the thalamus (mean difference, 6.5; 95% CI, 0.4-12.6; P = .04) of children aged 10 to 12 years old but not in adults or in the placebo group. In the striatum, the methylphenidate condition differed significantly from placebo in children but not in adults (mean difference, 7.7; 95% CI, 0.7-14.8; P = .03)., Conclusions and Relevance: We confirm preclinical data and demonstrate age-dependent effects of methylphenidate treatment on human extracellular dopamine striatal-thalamic circuitry. Given its societal relevance, these data warrant replication in larger groups with longer follow-up., Trial Registration: identifier: NL34509.000.10 and trialregister.nl identifier: NTR3103., Competing Interests: Disclosures: Dr Niessen reported being cofounder, shareholder, and part-time scientific officer of Quantib BV. No other disclosures were reported.

Reduced cortical dopamine levels have been observed in individuals with attention deficit hyperactivity disorder (ADHD). Global dopamine depletions by 6-hydroxydopamine (6-OHDA; with noradrenergic protection) in neonatal rats produces locomotor hyperactivity, with less known about how cortical depletion modulates risky behaviors. Here, we determined the effect of a medial prefrontal cortex (PFC) 6-OHDA depletions (30-60%) or sham microinjection at postnatal day 11 on behavior in male and female juvenile rats. Separate groups were studied for delay discounting (impulsive choice), novelty-preference, and preferences for cues and environments associated with cocaine (10, 20, and 40 mg/kg), their extinction, and reinstatement with place conditioning. Because PFC D1 receptors play a role in these behaviors, confocal microscopy was used to measure D1-immunoreactive projections to the nucleus accumbens core. Both 6-OHDA males and females increased delay discounting relative to sham controls, although only 6-OHDA females increased novelty preferences. Preferences for cocaine-associated environments, their extinction, and reinstatement with a priming dose of cocaine were reduced in 6-OHDA subjects overall. However, impulsive choice at 5s positively correlated with preferences for cocaine-associated environments in 6-OHDA subjects, but not sham controls. As possible compensation for low dopamine levels, D1-immunoreactivity on traced neurons increased in 6-OHDA females; dopamine levels did not remain low in adolescent 6-OHDA males and D1 did not change. We believe that these modest depletions restricted to the PFC demonstrate the role of dopamine, and not norepinephrine, in understanding these behaviors in other animal models where cortical dopamine is reduced during development., Competing Interests: statement The authors declare no competing financial interests in relation to the work described., (Copyright © 2014. Published by Elsevier B.V.)

Parkinson's disease is caused by a progressive loss of the midbrain dopamine (DA) neurons in the substantia nigra pars compacta. Although the main cause of Parkinson's disease remains unknown, there is increasing evidence that it is a complex disorder caused by a combination of genetic and environmental factors, which affect key signalling pathways in substantia nigra DA neurons. Insights into pathogenesis of Parkinson's disease stem from in vitro and in vivo models and from postmortem analyses. Recent technological developments have added a new dimension to this research by determining gene expression profiles using high throughput microarray assays. However, many of the studies reported to date were based on whole midbrain dissections, which included cells other than DA neurons. Here, we have used laser microdissection to isolate single DA neurons from the substantia nigra pars compacta of controls and subjects with idiopathic Parkinson's disease matched for age and postmortem interval followed by microarrays to analyse gene expression profiling. Our data confirm a dysregulation of several functional groups of genes involved in the Parkinson's disease pathogenesis. In particular, we found prominent down-regulation of members of the PARK gene family and dysregulation of multiple genes associated with programmed cell death and survival. In addition, genes for neurotransmitter and ion channel receptors were also deregulated, supporting the view that alterations in electrical activity might influence DA neuron function. Our data provide a 'molecular fingerprint identity' of late-stage Parkinson's disease DA neurons that will advance our understanding of the molecular pathology of this disease.

Attention deficit hyperactivity disorder is associated with reduced cortical blood flow that is reversible with exposure to the psychostimulant methylphenidate (MPH). D3 dopamine receptors modulate stimulant-induced changes in blood flow and are associated with reward processing during young adulthood, but their role in the enduring effects of MPH during development is unknown. Rats were given vehicle (VEH) or MPH (2 mg/kg between postnatal days 20-35) and assessed in young adulthood for regional cerebral blood volume (rCBV) after MPH challenge and mRNA expression levels of dopamine receptors. To probe D3 receptor involvement, juvenile subjects were exposed to VEH, MPH, the D3-preferring agonist +/-7-OHDPAT (0.3 mg/kg), the D3 antagonist nafadotride (Naf; 0.05, 0.5 or 5.0 mg/kg) or a Naf (0.05 mg/kg)/MPH combination, and assessed biochemically and behaviorally. Juvenile MPH exposure increased MPH-induced rCBV in the cingulate and medial prefrontal cortex and thalamus in adulthood. Behaviorally, juvenile MPH- or +/-7-OHDPAT-exposed subjects demonstrated an aversion to cocaine-associated environments, which was prevented by juvenile co-treatment with MPH and Naf, or with adult cortical microinjections of +/-7-OHDPAT. Cortical D3 mRNA levels significantly decreased by 23.8 +/- 6.7% in MPH-treated subjects and normalized with combined Naf/MPH treatment, with no change in the other dopamine receptors. Enhanced cortical responsiveness to psychostimulants may occur through a reduction in D3 receptors, which in turn reduces drug-seeking behavior. These data provide evidence for a postnatal sensitive period when juvenile MPH exposure is able to alter cortical development.

The present study provides further evidence for transient D1 autoreceptor-like synthesis modulation in prefrontal cortex, but not striatum, of developing rats. DOPA accumulation was attenuated in a concentration-dependent manner in slices from the prefrontal cortex and striatum at 15 days of age by the partial D1 agonist SKF 38393 (0.01-10 microM) and the full D1 agonist SKF-81297 (0.01-10 microM) following NSD-1015; the response was no longer apparent by 40 days. Both agonists had greater potency in prefrontal cortex than striatum, and SKF-81297 exerted greater maximal inhibitory effects than SKF-38393. The inhibitory effects of both agonists were antagonized by pre-incubation with the D1 antagonist SCH-23390 in cortex, but not in striatum.

Background: Current animal models of obsessive-compulsive disorder (OCD) typically involve acute, drug-induced symptom provocation or a genetic association with stereotypies or anxiety. None of these current models demonstrate multiple OCD-like behaviors. Methods: Neonatal rats were treated with the tricyclic antidepressant clomipramine or vehicle between days 9 and 16 twice daily and behaviorally tested in adulthood. Results: Clomipramine exposure in immature rats produced significant behavioral and biochemical changes that include enhanced anxiety (elevated plus maze and marble burying), behavioral inflexibility (perseveration in the spontaneous alternation task and impaired reversal learning), working memory impairment (e.g., win-shift paradigm), hoarding, and corticostriatal dysfunction. Dopamine D2 receptors were elevated in the striatum, whereas serotonin 2C, but not serotonin 1A, receptors were elevated in the orbital frontal cortex. Conclusions: This is the first demonstration of multiple symptoms consistent with an OCD-like profile in animals. Moreover, these behaviors are accompanied by biochemical changes in brain regions previously identified as relevant to OCD. This novel model of OCD demonstrates that drug exposure during a sensitive period can program disease-like systems permanently, which could have implications for current and future therapeutic strategies for this and other psychiatric disorders. [ABSTRACT FROM AUTHOR]

Characterization of the ontogeny of the cerebral dopaminergic system is crucial for gaining a greater understanding of normal brain development and its alterations in response to drugs of abuse or conditions such as attention-deficit hyperactivity disorder. Pharmacological MRI (phMRI) was used to determine the response to dopamine transporter (DAT) blockers cocaine and methylphenidate (MPH), the dopamine releaser D-amphetamine (AMPH), the selective D1 agonist dihydrexidine, and the D2/D3 agonist quinpirole in young (<30 days old) and adult (>60 days old) rats. In adult rats, cocaine (0.5 mg/kg i.v.) or MPH (2 mg/kg) induced primarily positive cerebral blood volume (rCBV) changes in the dopaminergic circuitry, but negative rCBV changes in the young animals. Microdialysis measurements in the striatum showed that young rats have a smaller increase in extracellular dopamine in response to cocaine than adults. The young rats showed little rCBV response to the selective D1 agonist dihydrexidine in contrast to robust rCBV increases observed in the adults, whereas there was a similar negative rCBV response in the young and adult rats to the D2 agonist quinpirole. We also performed a meta-analysis of literature data on the development of D1 and D2 receptors and the DAT. These data suggest a predominance of D2-like over D1-like function between 20 and 30 days of age. These combined results suggested that the dopamine D1 receptor is functionally inhibited at young age. Copyright © 2010 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Working memory is regulated by neurotransmitters in prefrontal cortex (PFC), including dopamine and norepinephrine. Previous studies of dopamine function in working memory have focused on the D1 and D2 receptors, with most evidence suggesting a dominant role for the D1 receptor. Since the dopamine D4 receptor is highly expressed in PFC, we hypothesize that it may also contribute to working memory. To test this hypothesis, we examined behavioral effects of L-745,870, a highly selective, centrally active, D4 antagonist, using a delayed alternation task in rats. Task performance was dose-dependently affected by the D4 antagonist, depending on individual baseline functional status of working memory. In rats with good baseline performance, the D4 antagonist had no effects at low doses, whereas high doses disrupted working memory. In rats with poor baseline working memory, the D4 antagonist significantly improved working memory at low doses, and higher doses were not distinguishable from vehicle controls. Effects of the D4 antagonist among poor performers were most robust when task demand for working memory was high, with lesser effects at lower demand level, suggesting that such effects were selective for working memory. The present findings indicate a significant role of the D4 receptor in working memory, and suggest innovative, D4-based, treatment of cognitive deficits associated with neuropsychiatric disorders. [ABSTRACT FROM AUTHOR]

Males, but not females, overproduce dopamine receptors in the striatum of rats across the periadolescent period followed by their elimination during young adulthood. In order to investigate the role that gonadal hormones play in this pubertal process, rats were castrated or ovariectomized at postnatal day (P) 28 when estrogen and testosterone levels are beginning to surge. Dopamine D1 and D2 striatal receptor density was then determined with autoradiography at P40 (adolescence) and P80 (young adulthood) to determine if either testosterone stimulates the overproduction of receptors in males or if estrogen inhibits this process in females. Neither castration nor ovariectomy altered dopamine receptor density, although enhanced testosterone levels increased D1 receptor binding 4.2% and 19.5% in males and females, respectively. The results of this study suggest that the endogenous rise in gonadal steroid hormones during puberty is not responsible for the overproduction of receptors in males or the lack of overproduction in females. [Copyright &y& Elsevier]

The transitions that occur in the ascending dopamine systems between childhood and adulthood parallel the emergence, course, and severity of attention-deficit hyperactivity disorder (ADHD) symptoms. Behaviorally, rats are more active in open field during periadolescence, and activity levels decline by 50% in males by adulthood. This peak in behavior parallels a transient overproduction in D1 and D2 dopamine receptors that occurs at puberty in rat striatum (STR) and prefrontal cortex (PFC), followed by a decline in receptor density into adulthood. While tempting to speculate that receptor density plays a role in the waning of ADHD symptoms, receptor overproduction does not occur in the nucleus accumbens (NA), which demonstrates only a modest rise in receptor density (10–20%). Given the importance of the accumbens in locomotor activity, an alternative explanation for increased activity was sought. The second messenger system cyclic adenosine monophosphate (cAMP) has classically been associated with dopamine receptors. The results of these studies demonstrate that cAMP accumulation in the accumbens and the STR parallel the observed rise and fall in activity levels in rats. At puberty, basal cAMP levels are 35% higher relative to adulthood in male accumbens, while a modest 7% change was observed in STR. Forskolin-stimulated cAMP was 240–300% higher in STR and accumbens at puberty before declining with maturation. These findings suggest that, the adolescent dopamine system has a much higher ‘tone’ relative to adults. However, pharmacological responsiveness of cAMP to D1 or D2 stimulation demonstrates an overall blunted response during puberty relative to adulthood. This finding is consistent with a hyposensitivity to stress and pharmacological agents at puberty in animals that are in a hyperdopaminergic state. These findings of combined elevated cAMP accumulation and reduced cAMP sensitivity during adolescence have clinical implications for hypothesized mechanism and course of ADHD and its treatment. The maturational decline in cAMP activity may explain why this disorder recedes, while, simultaneously cAMP becomes more responsive to D1 and D2 receptor stimulation in adulthood. [Copyright &y& Elsevier]

Abstract: Adaptive motivated behaviors are at the core of a successful life. Conversely, perturbed motivated behaviors are the hallmark of psychiatric disorders. Based on the notion that most psychopathology is developmental in nature, understanding the neural mechanisms that control motivated behavior across development and in psychopathology is a critical step for preventing and treating psychiatric diseases. This review focuses on adolescence, which is the critical developmental period that determines the successful passage into adulthood. We first present a heuristic neural systems model of motivated behavior (triadic model) that integrates neuroscience theories and the emerging body of functional neuroimaging work on the neurodevelopment of motivated behavior. As a key feature of adolescence, social reorientation is particularly emphasized through the presentation of a parallel model of social integration processing network. Although not yet integrated in the triadic model, pubertal changes and their possible contribution to adolescent motivated behavior are reviewed. Similarly, given its central role in motivated actions, the dopamine system is discussed from the perspective of animal studies dedicated to changes of this system across adolescence. This review reveals vast gaps in knowledge about the neurobiology of motivated behavior in normally developing individuals, which makes the translation to psychopathology only tentative. However, it provides clear directions for future research. [Copyright &y& Elsevier]

Clinical and preclinical studies on attention deficit hyperactivity disorder (ADHD) show that juvenile males that are exposed to methylphenidate (MPH) show reduced risk for substance use later in life. In contrast, little is known about whether females have the same enduring treatment response to stimulants and how gonadal hormones influence their behavior later in life. Females received either a sham or 6-hydroxydopamine (6-OHDA) microinjection in the prefrontal cortex (PFC) at postnatal day (P)10. Subjects were then treated with Vehicle or MPH (2 mg/kg, p.o.) between P20-35 and tested during late adolescence/young adulthood (P60); half of these subjects underwent ovariectomy at P55 to determine hormonal influences. Females with 6-OHDA were depleted of PFC dopamine by 61% and demonstrated increased impulsive choice (delayed discounting) and preferences for cocaine-associated environments relative to control females. Both MPH and ovariectomy reduced impulsive choice and cocaine preferences in 6-OHDA females, but had no enduring effect in Sham females. Ovariectomy itself did not significantly affect impulsivity. Juvenile MPH interacted strongly with 6-OHDA to increase D4, D5, Alpha-1A, Alpha-2A, and 5-HT-1A mRNA receptor expression in the PFC. MPH alone effected D1 mRNA, while 6-OHDA increased BDNF; all markers were decreased by ovariectomy. Together, these data suggest that 6-OHDA changes in dopamine are not only relevant for ADHD-like behaviors, but their long-term modulation by treatment and the influence of cyclical differences in menstrual cycle. [ABSTRACT FROM AUTHOR]