Serotonin and the therapeutic effects of ritalin

Chronic Methylphenidate Effects on Brain Gene Expression: An Exploratory Review

Methylphenidate (MP) is a psychostimulant commonly prescribed for individuals with attention deficit hyperactivity disorder (ADHD) but it is also taken with and without a prescription for performance enhancement. Prior research has characterized the effects of MP on behavior, cognition, and neurochemistry. This exploratory review covers the uses of MP and examined the effects of MP on gene expression in the brain following exposure. Overall, MP causes a wide-spread potentiation of genes, in a region-specific manner; consequently, inducing neuronal alterations, such as synaptic plasticity and transmission, resulting in observed behaviors and affects. Monoamine neurotransmitters and post-synaptic density protein genes generally had a potentiating effect in gene expression after exposure to MP.

Methylphenidate induces a different response in the dorsal raphe as compared to ventral tegmental area and locus coeruleus: behavioral and concomitant neuronal recordings in adult rats

Methylphenidate (MPD) is a psychostimulant used to treat attention deficit hyperactivity disorder. MPD exerts its neurocognitive effects through increasing concentrations of dopamine (DA), norepinephrine (NE), and serotonin (5-HT) in the neuronal synapse. This study recorded from adult freely behaving rats a total of 1170 neurons, 403 from the ventral tegmental area (VTA), 409 from locus coeruleus (LC), and 356 from dorsal raphe (DR) nucleus, which are the main sources of DA, NE, and 5-HT to the mesocorticolimbic circuitry, respectively. Electrophysiological and behavioral activities were recorded simultaneously following acute and repetitive (chronic) saline or 0.6, 2.5, or 10.0 mg/kg MPD. The uniqueness of this study is the evaluation of neuronal activity based on the behavioral response to chronic MPD. Animals received daily saline or MPD administration on experimental days 1-6 (ED1-6), followed by a 3-day wash-out period, and then MPD rechallenge on ED10. Each chronic MPD dose elicits behavioral sensitization in some animals, while in others, behavioral tolerance. Neuronal excitation following chronic MPD was observed in brains areas of animals exhibiting behavioral sensitization, while neuronal attenuation following chronic MPD was observed in those animals expressing behavioral tolerance. DR neuronal activity was most affected in response to acute and chronic MPD administration and responded differently compared to the neurons recorded from VTA and LC neurons at all doses. This suggests that although not directly related, DR and 5-HT are involved in the acute and chronic effects of MPD in adult rats, but exhibit a different role in response to MPD.

Dopamine, Norepinephrine and Serotonin Participate Differently in Methylphenidate Action in Concomitant Behavioral and Ventral Tegmental Area, Locus Coeruleus and Dorsal Raphe Neuronal Study in Young Rats

Methylphenidate (MPD), known as Ritalin, is a psychostimulant used to treat children, adults, and the elderly. MPD exerts its effects through increasing concentrations of dopamine (DA), norepinephrine (NE), and serotonin (5-HT) in the synaptic cleft. Concomitant behavioral and neuronal recording from the ventral tegmental area (VTA), locus coeruleus (LC), and from the dorsal raphe (DR) nucleus, which are the sources of DA, NE, and 5-HT to the mesocorticolimbic circuit, were investigated following acute and repetitive (chronic) saline, 0.6, 2.5, or 10.0 mg/kg MPD. Animals received daily saline or MPD administration on experimental days 1 to 6 (ED1-6), followed by a 3-day washout period and MPD rechallenge on ED10. Each chronic MPD dose elicits behavioral sensitization in some animals while inducing behavioral tolerance in others. The uniqueness of this study is in the evaluation of neuronal activity based on the behavioral response to chronic MPD. Neuronal excitation was observed mainly in brain areas of animals exhibiting behavioral sensitization, while neuronal attenuation following chronic MPD was observed in animals expressing behavioral tolerance. Different ratios of excitatory/inhibitory neuronal responses were obtained from the VTA, LC, or DR following chronic MPD. Thus, each brain area responds differently to each MPD dose used, suggesting that DA, NE, and 5-HT in the VTA, LC, and DR exert different effects.

Effects of curcumin nanoparticle on the histological changes and apoptotic factors expression in testis tissue after methylphenidate administration in rats

The present article sought to evaluate the impact of curcumin-loaded superparamagnetic iron oxide (Fe3O4) nanoparticles (NPs) on the histological variables and apoptotic agents in adult male rats after 3-weeks of methylphenidate (MPH) oral administration (20 mg/kg) versus vehicle therapy on the testis. Twenty-four male rats have been categorized randomly into four groups, in which Group 1 has been chosen as the controls, and Group 2 has been a vehicle and taken the sesame oil as curcumin carrier. Moreover, Group 3 has been taken MPH (20 mg/kg by gavage for 21 consecutive days). Group 4 received MPH plus Curcumin nanoparticles (5.4 mg/100 g) for twenty-one consecutive days. Then, testis histology, apoptosis as well as stereology have been examined. According to the examinations, curcumin nanoparticles are significantly capable of improving the sperms and stereological variables; for example, round spermatid and Leydig cells by enhancing the level of the serum testosterone in comparison with the MPH and vehicle groups. Besides, it was found that the gene expression in inflammation pathways and apoptosis genes largely diminished in the treatment group by curcumin nanoparticles in comparison with the MPH and vehicle groups, also we observed considerable differences for the weight of testes between the examined groups. Therefore, Curcumin effectively inhibited the testis damages and MPH-induced apoptosis, indicating possible protecting features of the Curcumin nanoparticles in opposition to MPH.

Toxicology of long-term and high-dose administration of methylphenidate on the kidney tissue - a histopathology and molecular study

The present study aims to assess the influences of oral methylphenidate on kidney function and structure versus vehicle treatment in adult male rats. In this study, thirty adult male rats equally into two treatment groups divided randomly, and among them, MPH has been administered for 21 days, at doses of 20 mg/kg, and the control group has received salin. In renal, under the effect of MPH applying quantitative real-time PCR, we analyzed nephrotoxicity-related molecular pathways like autophagy, inflammation, and apoptosis. Moreover, the levels of GSH, CAT, and SOD were investigated as antioxidant enzymes. Afterward, stereological analysis in MPH-treated rats has been performed. Analysis of qPCR displayed inflammation, impaired autophagy, and enhanced apoptosis with histological changes in the kidney's tissue, also an important rise in the antioxidant enzymes' level. Besides, 20 mg/kg of MPH led to a decline in the mean of Bowman's space thickness and renal corpuscle's volume in comparison to the control rats. Collectively, our histological and molecular data implicit that in the kidney region, administrating of MPH evoked discriminative expression alterations in nephrotoxicity-associated signaling cascades, specifically autophagy, inflammation, and apoptosis paired with important damage to kidney tissue.

Dopamine compartmentalization, selective dopaminergic vulnerabilities in Parkinson's disease and therapeutic opportunities

Progressive depletion of selected dopamine neurons is central to much Parkinson's disease (PD) disability. Although symptomatic treatments can ameliorate the disabilities that this neuronal depletion causes, no current strategy is documented to slow these losses. There is substantial evidence that dopamine in intracytoplasmic/extravesicular neuronal compartments can be toxic. Here, I review evidence that supports roles for dopamine compartmentalization, mediated largely by serial actions of plasma membrane SLC6A3/DAT and vesicular SLC18A2/VMAT2 transporters, in the selective patterns of dopamine neuronal loss found in PD brains. This compartmentalization hypothesis for the dopamine cell type specificity of PD lesions nominates available drugs for amelioration of damage arising from miscompartmentalized dopamine and raises cautions in using other drugs.

Galactorrhea Probably Related with Switching from Osmotic-release Oral System Methylphenidate (MPH) to Modified-release MPH: An Adolescent Case

Galactorrhea, as an adverse effect of psychotropic medications, usually develops due to high dose of antipsychotics. Selective serotonin reuptake inhibitors (SSRIs) have also been reported to be related to galactorrhea. To the best of our knowledge, no previous study reported galactorrhea with methylphenidate (MPH) use. Hereby, we report a case of an adolescent girl who developed galactorrhea after increasing his modifed-release oral MPH to 50 mg/day while under treatment of sertraline and very low dose haloperidol.

Methylphenidate modulates dorsal raphe neuronal activity: Behavioral and neuronal recordings from adolescent rats

Methylphenidate (MPD) is a widely prescribed psychostimulants used for the treatment of attention deficit hyperactive disorder (ADHD). Unlike the psychostimulants cocaine and amphetamine, MPD does not exhibit direct actions on the serotonin transporter, however there is evidence suggesting that the therapeutic effects of MPD may be mediated in part by alterations in serotonin transmission. This study aimed to investigate the role of the dorsal raphe (DR) nucleus, one of the major sources of serotonergic innervation in the mammalian brain, in the response to MPD exposure. Freely behaving adolescent rats previously implanted bilaterally with permanent electrodes were used. An open field assay and a wireless neuronal recording system were used to concomitantly record behavioral and DR electrophysiological activity following acute and chronic MPD exposure. Four groups were used: one control (saline) and three experimental groups treated with 0.6, 2.5, and 10.0mg/kg MPD respectively. Animals received daily MPD or saline injections on experimental days 1-6, followed by 3 washout days and MPD rechallenge dose on experimental day (ED)10. The same chronic dose of MPD resulted in either behavioral sensitization or tolerance, and we found that neuronal activity recorded from the DR neuronal units of rats expressing behavioral sensitization to chronic MPD exposure responded significantly differently to MPD rechallenge on ED10 compared to the DR unit activity recorded from animals that expressed behavioral tolerance. This correlation between behavioral response and DR neuronal activity following chronic MPD exposure provides evidence that the DR is involved in the acute effects as well as the chronic effects of MPD in adolescent rats.

Serotonin/dopamine interactions in a hyperactive mouse: reduced serotonin receptor 1B activity reverses effects of dopamine transporter knockout

Knockout (KO) mice that lack the dopamine transporter (SL6A3; DAT) display increased locomotion that can be attenuated, under some circumstances, by administration of drugs that normally produce psychostimulant-like effects, such as amphetamine and methylphenidate. These results have led to suggestions that DAT KO mice may model features of attention deficit hyperactivity disorder (ADHD) and that these drugs may act upon serotonin (5-HT) systems to produce these unusual locomotor decreasing effects. Evidence from patterns of brain expression and initial pharmacologic studies led us to use genetic and pharmacologic approaches to examine the influence of altered 5-HT_1B receptor activity on hyperactivity in DAT KO mice. Heterozygous 5-HT_1B KO and pharmacologic 5-HT_1B antagonism both attenuated locomotor hyperactivity in DAT KO mice. Furthermore, DAT KO mice with reduced, but not eliminated, 5-HT_1B receptor expression regained cocaine-stimulated locomotion, which was absent in DAT KO mice with normal levels of 5-HT_1B receptor expression. Further experiments demonstrated that the degree of habituation to the testing apparatus determined whether cocaine had no effect on locomotion in DAT KO or reduced locomotion, helping to resolve differences among prior reports. These findings of complementation of the locomotor effects of DAT KO by reducing 5-HT_1B receptor activity underscore roles for interactions between specific 5-HT receptors and dopamine (DA) systems in basal and cocaine-stimulated locomotion and support evaluation of 5-HT_1B antagonists as potential, non-stimulant ADHD therapeutics.

The rare DAT coding variant Val559 perturbs DA neuron function, changes behavior, and alters in vivo responses to psychostimulants

Despite the critical role of the presynaptic dopamine (DA) transporter (DAT, SLC6A3) in DA clearance and psychostimulant responses, evidence that DAT dysfunction supports risk for mental illness is indirect. Recently, we identified a rare, nonsynonymous Slc6a3 variant that produces the DAT substitution Ala559Val in two male siblings who share a diagnosis of attention-deficit hyperactivity disorder (ADHD), with other studies identifying the variant in subjects with bipolar disorder (BPD) and autism spectrum disorder (ASD). Previously, using transfected cell studies, we observed that although DAT Val559 displays normal total and surface DAT protein levels, and normal DA recognition and uptake, the variant transporter exhibits anomalous DA efflux (ADE) and lacks capacity for amphetamine (AMPH)-stimulated DA release. To pursue the significance of these findings in vivo, we engineered DAT Val559 knock-in mice, and here we demonstrate in this model the presence of elevated extracellular DA levels, altered somatodendritic and presynaptic D2 DA receptor (D2R) function, a blunted ability of DA terminals to support depolarization and AMPH-evoked DA release, and disruptions in basal and psychostimulant-evoked locomotor behavior. Together, our studies demonstrate an in vivo functional impact of the DAT Val559 variant, providing support for the ability of DAT dysfunction to impact risk for mental illness.

Emotional and risk seeking behavior after prepuberal subchronic or adult acute stimulation of 5-HT7-Rs in Naples High Excitability rats

We report here the results of studies aimed to investigate the involvement of serotonin receptor 7 subtype (5-HT7-R) in the modulation of emotional response in Naples High-Excitability (NHE) rat, a validated model for hyperactivity and impaired attention. A range of dosages (0.0, 0.125, 0.250, or 0.500 mg/kg) of LP-211, a selective agonist of 5-HT7-Rs, has been evaluated in animals at different age (adolescence and adulthood). Male NHE and random bred (NRB) control rats were tested in an Elevated Zero-Maze (EZM) after LP-211 treatment in two different regimens: at the issue of adolescent, subchronic exposure (14 intraperitoneal [i.p.] injections, once/day, pnd 31-44, tested on pnd 45--Exp. 1) or as adult, acute effect (15 min after i.p. injection--Exp. 2). Adolescent, subchronic LP-211 at 0.500 mg/kg dosage increased the frequency of head-dips only in NHE rats. Drug effect on time spent and entries in open EZM quadrants were revealed with adult, acute administration of 0.125 mg/kg LP-211 (both strains), indicating a tendency toward anxiolytic effects. In conclusion, data demonstrate that subchronic stimulation of 5-HT7-Rs during prepuberal period increases novelty-seeking/risk-taking propensity in NHE adults. These sequels are revealing increased disinhibition and/or motivation to explore in the NHE rats, which are characterized by a hyperactive dopaminergic system. These data may open new perspectives in studying mechanism of risk-seeking behavior.

Behavioral and dorsal raphe neuronal activity following acute and chronic methylphenidate in freely behaving rats

Concomitant behavioral and dorsal raphe (DR) neuronal activity were recorded following acute and chronic dose response of methylphenidate (MPD) in freely moving rats previously implanted with permanent semi-microelectrodes using telemetric (wireless) technology. On experimental day (ED) 1, the neuronal and locomotor activity were recorded after saline (baseline) and MPD (0.6, 2.5 or 10.0mg/kg) injection (i.p.). Animals were injected daily with a single dose of MPD for five consecutive days (ED 2-6) to elicit behavioral sensitization or tolerance. After three washout days, the neuronal and locomotor activity recording was resumed on ED 10 followed by saline and MPD rechallenge injection. The main findings were: (1) the same dose of chronic MPD administration elicited behavioral sensitization in some animals and behavioral tolerance in others. (2) 46%, 56% and 73% of DR units responded to acute 0.6, 2.5 and 10.0mg/kg MPD respectively. (3) 89%, 70% and 86% of DR units changed their baseline activity on ED 10 compared to that on ED 1 in the 0.6, 2.5 and 10.0mg/kg MPD groups respectively. (4) A significant difference in ED 10 baseline activity was observed in the DR neuronal population recording from animals expressing behavioral sensitization compared to that of animals expressing behavioral tolerance. (5) 89%, 78% and 88% of DR units responded to chronic 0.6, 2.5 and 10.0mg/kg MPD respectively. (6) The DR neuronal population recording following acute MPD on ED 1 and rechallenge MPD on ED 10 from animals expressing behavioral sensitization was significantly different from the neuronal population recorded from animals exhibited behavioral tolerance. The correlation between the DR neuronal activity and animal's behavior following chronic MPD exposure suggested that the DR neuronal activity may play an important role in the expression of behavioral sensitization and tolerance induced by chronic MPD administration.

Chronic Ritalin administration during adulthood increases serotonin pool in rat medial frontal cortex

BACKGROUND

Ritalin has high tendency to be abused. It has been the main indication to control attention deficit hyperactivity disorder. The college students may seek for it to improve their memory, decrease the need for sleep (especially during exams), which at least partially, can be related to serotonergic system. Therefore, it seems worthy to evaluate the effect of Ritalin intake on mature brain. There are many studies on Ritalin effect on developing brain, but only few studies on adults are available. This study was undertaken to find Ritalin effect on serotonin transporter (SERT) density in medial frontal cortex (MFC) of mature rat.

METHODS

Thirty male Wistar rats were used in the study. Rats were assigned into five groups (n = 6 per group): one control, two Ritalin and two vehicle groups. Twelve rats received Ritalin (20 mg/kg/twice a day) orally for eleven continuous days. After one week of withdrawal and another two weeks of rest, in order to evaluate short-term effects of Ritalin, six rats were sacrificed. Another six rats were studied to detect the long-term effects of Ritalin; therefore, they were sacrificed 12 weeks after the previous group. The immunohistochemistry was performed to evaluate the results.

RESULTS

Immunohistochemistry studies showed a higher density of SERT in both 2 and 12 weeks after withdrawal from Ritalin intake in MFC of rat and there was no significant difference between these two groups.

CONCLUSIONS

Our findings demonstrated both short- and long-term effects of Ritalin on frontal serotonergic system after withdrawal period.

Dorsal raphe neuronal activities are modulated by methylphenidate

This study investigated the electrophysiological properties of the dorsal raphe nucleus (DR) neurons in response to the acute and repetitive administration of methylphenidate (MPH). Activities of DR neurons were recorded from non-anesthetized, freely behaving rats previously implanted bilaterally with permanent semi microelectrodes. The main findings were: (1) after initial (acute) administration of MPH (2.5 mg/kg i.p.) on experimental day one (ED1), 56 % of DR units significantly changed their firing rates. The majority of the responsive units (88 %) exhibited increased firing rate; (2) daily MPH injections were given on ED2 through ED6 followed by 3 washout days. On ED10, 83 % of the DR units significantly changed their baseline activity compared to the baseline activity on ED1; (3) after rechallenge MPH administration on ED10, 63 % of DR units exhibited significant change in their firing rate; the majority of the responsive units (76 %) exhibited a significant increase in their firing rate; (4) The effect of rechallenge MPH administration on ED10 was compared to the effect of initial MPH on ED1, 47 % DR units exhibited a further significant increase in their firing rate while 53 % DR units exhibited decrease or non-change in their firing rate which can be interpreted as electrophysiological sensitization or tolerance. In conclusion, this study demonstrated that acute MPH administration modulated the DR neuronal activities. Repetitive MPH administration modulated the baseline activities of DR units and elicited neurophysiological sensitization or tolerance. The results indicated that MPH affects DR neuronal activity.

The 5-HTTLPR polymorphism of the serotonin transporter gene and short term behavioral response to methylphenidate in children with ADHD

BACKGROUND

Animal models of ADHD suggest that the paradoxical calming effect of methylphenidate on motor activity could be mediated through its action on serotonin transmission. In this study, we have investigated the relationship between the 5-HTTLPR polymorphism in the serotonin transporter gene (SLC6A4) and the response of ADHD relevant behaviors with methylphenidate treatment.

METHODS

Patients between ages 6-12 (n = 157) were assessed with regard to their behavioral response to methylphenidate (0.5 mg/kg/day) using a 2-week prospective within-subject, placebo-controlled (crossover) trial. The children were then genotyped with regard to the triallelic 5-HTTLPR polymorphism in the SLC6A4 gene.

MAIN OUTCOME MEASURE

Conners' Global Index for parents (CGI-Parents) and teachers (CGI-Teachers) at baseline and at the end of each week of treatment with placebo and methylphenidate. For both outcome measurements, we used a mixed model analysis of variance to determine gene, treatment and gene x treatment interaction effects.

RESULTS

Mixed model analysis of variance revealed a gene x treatment interaction for CGI-Parents but not for CGI-Teachers. Children homozygous for the lower expressing alleles (s+lG = s') responded well to placebo and did not derive additional improvement with methylphenidate compared to children carrying a higher expressing allele (lA). No genotype main effects on either CGI-Parents or CGI-teachers were observed.

CONCLUSIONS

A double blind placebo-controlled design was used to assess the behavioral effects of methylphenidate in relation to the triallelic 5-HTTLPR polymorphism of the SLC6A4 gene in children with ADHD. This polymorphism appears to modulate the behavioral response to methylphenidate in children with ADHD as assessed in the home environment by parents. Further investigation is needed to assess the clinical implications of this finding.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00483106.

Prepuberal subchronic methylphenidate and atomoxetine induce different long-term effects on adult behaviour and forebrain dopamine, norepinephrine and serotonin in Naples high-excitability rats

The psychostimulant methylphenidate and the non-stimulant atomoxetine are two approved drugs for attention-deficit hyperactivity disorder (ADHD) therapy. The aim of this study was to investigate the long-term effects of prepuberal subchronic methylphenidate and atomoxetine on adult behaviour and the forebrain neurotransmitter and metabolite content of Naples High-Excitability (NHE) rats, a genetic model for the mesocortical variant of ADHD. Male NHE rats were given a daily intraperitoneal injection (1.0mg/kg) of methylphenidate, atomoxetine or vehicle from postnatal day 29 to 42. At postnatal day 70-75, rats were exposed to spatial novelty in the Làt and radial (Olton) mazes. Behavioural analysis for indices of horizontal, vertical, non-selective (NSA) and selective spatial attention (SSA) indicated that only methylphenidate significantly reduced horizontal activity to a different extent, i.e., 39 and 16% respectively. Moreover methylphenidate increased NSA as assessed by higher leaning duration. The high-performance liquid chromatography (HPLC) tissue content assessment of dopamine, norepinephrine, serotonin and relative metabolites in the prefrontal cortex (PFC), cortical motor area (MC), dorsal striatum (DS), ventral striatum (VS), hippocampus and mesencephalon indicated that methylphenidate decreased (i) dopamine, DOPAC, norepinephrine, MHPG, 5-HT and 5-HIAA in the PFC, (ii) dopamine, DOPAC, HVA, serotonin, 5-HIAA in the DS, (iii) dopamine, DOPAC, HVA and MHPG (but increased norepinephrine) in the VS and (iv) norepinephrine, MHPG, serotonin and 5-HIAA in the hippocampus. Atomoxetine increased dopamine and decreased MHPG in the PFC. Like methylphenidate, atomoxetine decreased dopamine, DOPAC, HVA, serotonin and 5-HIAA in the DS, but decreased MHPG in the VS. These results suggest that methylphenidate determined long-term effects on behavioural and neurochemical parameters, whereas atomoxetine affected only the latter.

Modulation of motorcortical excitability by methylphenidate in adult voluntary test persons performing a go/nogo task

This study investigated the interaction between motorcortical excitability (short interval cortical inhibition, intracortical facilitation and long interval cortical inhibition), different requirement conditions [choice reaction test (CRT), attention/go/nogo], and their pharmacological modulation by methylphenidate (MPH) in normal healthy adults (n = 31) using a transcranial magnetic stimulation paradigm. MPH was administered in a dosage of 1 mg/kg body weight, maximum 60 mg. Additionally, serum level and clearance of MPH were controlled. The statistical analysis of variance revealed a significant three-way interaction of 2 (MPH) x 3 (CRT) x 6 (ISI) predicting motor evoked potential amplitudes (P = 0.032, MPH none and full dose, n = 31). In order to compare effects of dosage an additional between-subjects factor (half vs. full MPH dose) was introduced. None of the interactions involving this between-subject factor reached statistical significance. Exploring interactions with MPH only, a 3 (MPH none, half and full dose) x 3 (CRT) x 6 (ISI) analysis of variance revealed significant two-way interactions for MPH x ISI (P = 0.040) and condition x ISI (P < 0.001, n = 18). Effects observed for MPH were strongest on facilitatory processes, weaker for intracortical inhibition. In sum, MPH seems to interact via striato-thalamo-cortical pathways with original motorcortical processes (ISI), to a lesser extent with task-dependent or behavioral parameters (CRT).

Restoration of disturbed intracortical motor inhibition and facilitation in attention deficit hyperactivity disorder children by methylphenidate

BACKGROUND

Previous investigations using transcranial magnetic stimulation (TMS) have shown that neural inhibitory motor circuits are disturbed in ADHD children. We sought to investigate the influence of methylphenidate (MPH) on inhibitory and facilitatory motor circuits of ADHD children with TMS paired pulse protocols using surplus long interval inter-stimulus intervals (ISI) not investigated so far.

METHODS

Motorcortical modulation was tested with TMS paired pulse protocols employing ISI of 3, 13, 50, 100, 200, and 300 msec in 18 ADHD children before and on treatment with MPH. Clinical improvement by MPH was measured by the Conners score.

RESULTS

Analysis of variance (ANOVA) revealed a significant three-way interaction "Group x Amplitude x ISI," p = .001. Subsequent two-factorial ANOVAs and t-tests showed group specific differences of motor evoked potential (MEP) amplitudes for inhibitory ISIs of 3 and 100 msec, and for facilitatory ISIs of 13 and 50 msec. Compared to controls, an adjustment of these parameters by MPH could be shown. On MPH, a significant bivariate correlation was found between the Conners score reduction and averaged MEP amplitude changes only for inhibitory ISIs (3 and 100 msec).

CONCLUSIONS

In ADHD children, MPH modulates disturbed facilitatory and inhibitory motor circuits, which for the latter is associated with clinical improvement.

Clinical improvement in a case of frontotemporal dementia under aripiprazole treatment corresponds to partial recovery of disturbed frontal glucose metabolism

Frontotemporal dementia (FTD) is increasingly recognized as an important type of degenerative dementia but satisfactory pharmacological treatment has not yet been established. We examined the clinical effects of aripiprazole, a new antipsychotic with partial agonistic properties at serotonin 5-HT(1A) and dopamine D(2) receptors, in parallel with cortical glucose metabolism changes. We conducted a follow-up investigation of clinical status and (18)F-fluoro-2-deoxy-d-glucose (FDG) positron emission tomography (PET) in a 73-year-old male patient with FTD over a 13-month period. Under conventional drug treatment during the first 12 months a marked increase in dementia symptoms was observed. Frontal lobe glucose metabolism clearly decreased during this time period. Under consecutive treatment with aripiprazole a significant and stable improvement of clinical symptoms could be registered, while disturbed frontal glucose metabolism increased significantly. According to this case experience, further investigations should be undertaken to ascertain whether aripiprazole or other atypical antipsychotics with properties to improve impaired dopaminergic transmission in frontal brain regions could qualify for therapy of FTD.

Preadolescent methylphenidate versus cocaine treatment differ in the expression of cocaine-induced locomotor sensitization during adolescence and adulthood

BACKGROUND

Methylphenidate (MPH), the most commonly prescribed medication for childhood attention-deficit/hyperactivity disorder (ADHD), shares chemical and mechanistic similarities to cocaine which has stimulated research to address the addiction liability following treatment.

METHODS

Utilizing locomotor sensitization we examined the consequences of recurrent MPH versus cocaine treatment during preadolescence in altering cocaine-induced locomotor behavior in adolescent and adult mice. Black Swiss Webster mice were treated with MPH, cocaine, or saline during preadolescence. To test whether MPH pretreatment during preadolescence contributed to an altered sensitivity to cocaine during adolescence, these mice were treated with recurrent cocaine or saline during adolescence. All mice were challenged with cocaine as adults.

RESULTS

Recurrent MPH treatment, unlike cocaine treatment in preadolescent mice, had no effect on locomotor sensitization to cocaine during adolescence or adulthood, as compared with saline controls. Furthermore, unlike cocaine, administration of MPH in adolescence did not augment the response to cocaine challenge.

CONCLUSIONS

MPH treatment during preadolescence does not increase subsequent sensitivity to cocaine, whereas cocaine treatment does. Thus, MPH treatment during preadolescence does not appear to persistently induce long-term adaptations, which may underlie an enhanced liability for subsequent drug abuse.

ADHD and the dopamine transporter: are there reasons to pay attention?

The catecholamine dopamine (DA) plays an important role as a neurotransmitter in the brain in circuits linked to motor function, reward, and cognition. The presynaptic DA transporter (DAT) inactivates DA following release and provides a route for non-exocytotic DA release (efflux) triggered by amphetamines. The synaptic role of DATs first established through antagonist studies and more recently validated through mouse gene-knockout experiments, raises questions as to whether altered DAT structure or regulation support clinical disorders linked to compromised DA signaling, including drug abuse, schizophrenia, and attention deficit hyperactivity disorder (ADHD). As ADHD appears to have highly heritable components and the most commonly prescribed therapeutics for ADHD target DAT, studies ranging from brain imaging to genomic and genetic analyses have begun to probe the DAT gene and its protein for possible contributions to the disorder and/or its treatment. In this review, after a brief overview of ADHD prevalence and diagnostic criteria, we examine the rationale and experimental findings surrounding a role for human DAT in ADHD. Based on the available evidence from our lab and labs of workers in the field, we suggest that although a common variant within the human DAT (hDAT) gene (SLC6A3) is unlikely to play a major role in the ADHD, contributions of hDAT to risk maybe most evident in phenotypic subgroups. The in vitro and in vivo validation of functional variants, pursued for contributions to endophenotypes in a within family approach, may help elucidate DAT and DA contributions to ADHD and its treatment.

The dopamine D4 receptor is essential for hyperactivity and impaired behavioral inhibition in a mouse model of attention deficit/hyperactivity disorder

The dopamine D4 receptor (D4R) is a candidate gene for attention deficit/hyperactivity disorder (ADHD) based on genetic studies reporting that particular polymorphisms are present at a higher frequency in affected children. However, the direct participation of the D4R in the onset or progression of ADHD has not been tested. Here, we generated a mouse model with high face value to screen candidate genes for the clinical disorder by neonatal disruption of central dopaminergic pathways with 6-hydroxydopamine (6-OHDA). The lesioned mice exhibited hyperactivity that waned after puberty, paradoxical hypolocomotor responses to amphetamine and methylphenidate, poor behavioral inhibition in approach/avoidance conflict tests and deficits in continuously performed motor coordination tasks. To determine whether the D4R plays a role in these behavioral phenotypes, we performed 6-OHDA lesions in neonatal mice lacking D4Rs (Drd4(-/-)). Although striatal dopamine contents and tyrosine hydroxylase-positive midbrain neurons were reduced to the same extent in both genotypes, Drd4(-/-) mice lesioned with 6-OHDA did not develop hyperactivity. Similarly, the D4R antagonist PNU-101387G prevented hyperactivity in wild-type 6-OHDA-lesioned mice. Furthermore, wild-type mice lesioned with 6-OHDA showed an absence of behavioral inhibition when tested in the open field or the elevated plus maze, while their Drd4(-/-) siblings exhibited normal avoidance for the unprotected areas of these mazes. Together, our results from a combination of genetic and pharmacological approaches demonstrate that D4R signaling is essential for the expression of juvenile hyperactivity and impaired behavioral inhibition, relevant features present in this ADHD-like mouse model.

Pharmacokinetic and pharmacodynamic properties of stimulants: implications for the design of new treatments for ADHD

In the USA, the stimulant drug methylphenidate (MPH) is used to treat a large number (2 million or more per year) of children with Attention Deficit Hyperactivity Disorder (ADHD). Although the US FDA approved MPH in the 1960s, the pharmacokinetic (PK) properties of serum concentrations of MPH in children with ADHD were not described until the 1980s, and then in only a few cases. Recently, information from drug development programs have increased our knowledge about the serum PK and some pharmacodynamic (PD) characteristics of MPH in ADHD children, and studies based on positron emission tomograpy (PET) in adult volunteers have provided new knowledge about the PK properties of MPH at the primary site of action in the brain. We will review these two topics and use this new information to evaluate the mechanisms of action of MPH.