Stimulant-like action of nicotine on striatal dopamine transporter in the brain of adults with attention deficit hyperactivity disorder

Association between cigarette smoking and Parkinson’s disease: a neuroimaging study

Background:

Mounting evidence has revealed an inverse association between cigarette smoking and the risk of Parkinson’s disease (PD). Meanwhile, cigarette smoking has been found to be associated with cognitive impairment in PD patients. However, the neural mechanisms of the association between cigarette smoking and PD are not fully understood.

Objective:

The aim of this study is to explore the neural mechanisms of the association between cigarette smoking and PD.

Methods:

A total of 129 PD patients and 69 controls were recruited from the Parkinson’s Progression Markers Initiative (PPMI) cohort, including 39 PD patients with regular smoking history (PD-S), 90 PD patients without regular smoking history (PD-NS), 26 healthy controls with regular smoking history (HC-S), and 43 healthy controls without regular smoking history (HC-NS). Striatal dopamine transporter (DAT) binding and gray matter (GM) volume of the whole brain were compared among the four groups.

Results:

PD patients showed significantly reduced striatal DAT binding compared with healthy controls, and HC-S showed significantly reduced striatal DAT binding compared with HC-NS. Moreover, smoking and PD showed a significant interaction effect in the left medial prefrontal cortex (mPFC). PD-S showed reduced GM volume in the left mPFC compared with PD-NS.

Conclusion:

The degeneration of dopaminergic neurons in PD results in a substantial reduction of the DAT and dopamine levels. Nicotine may act as a stimulant to inhibit the action of striatal DAT, increasing dopamine levels in the synaptic gap. The inverse alteration of dopamine levels between PD and nicotine addiction may be the reason for the inverse association between smoking and the risk of PD. In addition, the mPFC atrophy in PD-S may be associated with cognitive impairment.

The cognitive and behavioral effects of D-amphetamine and nicotine sensitization in adult zebrafish

BACKGROUND

Zebrafish are growing in use as a model for understanding drug dependence and addiction. Sensitization paradigms have been a useful tool in identifying mechanisms involved in drug-induced behavioral and neurological changes, but in zebrafish have tended to focus on locomotor, rather than cognitive, endpoints.

METHODS

Here, we used a novel method, the FMP Y-maze, which measures continuous performance through a series of repeated binary choices (L vs R), to establish a model for assessing parameters associated with psychostimulant-induced behavioral and cognitive sensitization in adult zebrafish.

RESULTS

Repeat, intermittent exposure to d-amphetamine (AMPH) for 14 days increased alternations (LRLR) in the maze, suggesting improved working memory, which was enhanced further following drug challenge after a short withdrawal period, suggesting behavioral sensitization. However, this cognitive enhancement coincided with a reduction in the use of other exploration strategies, hypolocomotion, and inhibition of cognitive flexibility. Like AMPH, exposure to nicotine (NIC) increased alternations following drug challenge after chronic treatment. Repeat NIC exposure appeared to induce both cognitive and psychomotor sensitization, as evidenced by increased working memory performance (alternations) and locomotor activity, without negatively impacting other search strategies or cognitive flexibility.

CONCLUSION

Chronic treatment with AMPH or NIC boosts cognitive performance in adult zebrafish. Cognitive sensitization occurred with both drugs, resulting in enhanced working memory; however, repeat AMPH exposure, following a withdrawal period, resulted in inhibited cognitive flexibility, an effect not evident with repeat NIC exposure. Cognitive and behavioral sensitization paradigms in zebrafish could serve as a useful tool for assessing cognitive states which result in cognitive enhancing or impairing effects of drugs.

Electronic cigarettes – an important progress or just another risk for health?

Liquids for electronic cigarettes and the vapor generated from them were examined by chemical and biological methods in order to reveal potential risk factors and their acceptability for consumers. Although the majority of the liquids on the market appear to be safe, some aroma compositions have been identified as possibly toxic for human vein epithelial cells, similar to tobacco smoke, thus indicating potential health risks and suggesting suitable test procedures before marketing the liquids.

Molecular Imaging of Opioid and Dopamine Systems: Insights Into the Pharmacogenetics of Opioid Use Disorders

Opioid use in the United States has steadily risen since the 1990s, along with staggering increases in addiction and overdose fatalities. With this surge in prescription and illicit opioid abuse, it is paramount to understand the genetic risk factors and neuropsychological effects of opioid use disorder (OUD). Polymorphisms disrupting the opioid and dopamine systems have been associated with increased risk for developing substance use disorders. Molecular imaging studies have revealed how these polymorphisms impact the brain and contribute to cognitive and behavioral differences across individuals. Here, we review the current molecular imaging literature to assess how genetic variations in the opioid and dopamine systems affect function in the brain's reward, cognition, and stress pathways, potentially resulting in vulnerabilities to OUD. Continued research of the functional consequences of genetic variants and corresponding alterations in neural mechanisms will inform prevention and treatment of OUD.

Investigating possible causal effects of externalizing behaviors on tobacco initiation: A Mendelian randomization analysis

Observational studies suggest childhood externalizing disorders are associated with increased smoking and earlier initiation. However, causality cannot be inferred from observational data alone. The current study uses two-sample MR to examine the causal relationship between externalizing behaviors and tobacco use. Single nucleotide polymorphisms (SNPs) associated with aggression were obtained from the Early Life Epidemiology Consortium (mean age 8), ADHD from the Integrative Psychiatric Research and Psychiatric Genomics Consortiums (age range 6-18), and tobacco initiation and age of onset from the Tobacco and Genetics Consortium. SNPs were combined using the inverse variance weighted approach, weighted median approach, and MR-Egger regression. There was no clear evidence of an effect of aggression on tobacco initiation or age of onset for childhood aggression (initiation: β -0.002, 95% CI -0.005, 0.001, P = 0.286; age: β -0.001 95% CI -0.002, 0.000, P = 0.310) or adolescent aggression (initiation: β -0.001, 95% CI -0.006, 0.003, P = 0.610; age: β 0.000, 95% CI 0.000, 0.001, P = 0.183)]. However, there was some evidence of an association of ADHD on tobacco initiation (OR 1.23, 95% CI 1.10, 1.35, P = 0.016), although no clear evidence of an effect of ADHD on age of onset (OR = 1.022, 95% CI 0.992, 1.052, P = 0.215). Our results provide some evidence that genetic risk of childhood ADHD is causally related to increased risk of tobacco initiation; however, the causal estimate is relatively small. We found no clear evidence that genetic risk of childhood aggression is causally related to the risk of tobacco initiation or age of onset.

Effects of Smoking Cessation on Presynaptic Dopamine Function of Addicted Male Smokers

BACKGROUND

There is evidence of abnormal cerebral dopamine transmission in nicotine-dependent smokers, but it is unclear whether dopaminergic abnormalities are due to acute nicotine abuse or whether they persist with abstinence. We addressed this question by conducting longitudinal positron emission tomography (PET) examination of smokers before and after 3 months of abstinence.

METHODS

We obtained baseline 6-[(18)F]fluoro-L-DOPA (FDOPA)-PET scans in 15 nonsmokers and 30 nicotine-dependent smokers, who either smoked as per their usual habit or were in acute withdrawal. All smokers then underwent cessation treatment, and successful abstainers were re-examined by FDOPA-PET after 3 months of abstinence (n = 15). Uptake of FDOPA was analyzed using a steady-state model yielding estimates of the dopamine synthesis capacity (K); the turnover of tracer dopamine formed in living brain (kloss); and the tracer distribution volume (Vd), which is an index of dopamine storage capacity.

RESULTS

Compared with nonsmokers, K was 15% to 20% lower in the caudate nuclei of consuming smokers. Intraindividual comparisons of consumption and long-term abstinence revealed significant increases in K in the right dorsal and left ventral caudate nuclei. Relative to acute withdrawal, Vd significantly decreased in the right ventral and dorsal caudate after prolonged abstinence. Severity of nicotine dependence significantly correlated with dopamine synthesis capacity and dopamine turnover in the bilateral ventral putamen of consuming smokers.

CONCLUSIONS

The results suggest a lower dopamine synthesis capacity in nicotine-dependent smokers that appears to normalize with abstinence. Further investigations are needed to clarify the role of dopamine in nicotine addiction to help develop smoking prevention and cessation treatments.

Insomnia symptoms as a risk factor for cessation failure following smoking treatment

Insomnia symptoms are associated with smoking, and may interfere with smoking cessation. Specifically, studies have shown that smoking-related sleep problems are associated with long-term smoking relapse, and longer sleep duration is associated with successful smoking cessation. However, it is currently unclear whether pre- or post-quit insomnia symptoms are associated with smoking cessation outcomes. As such, the current study aimed to extend previous findings by using a measure of insomnia symptoms as a predictor of smoking cessation failure by month 3 following smoking cessation treatment. Additionally, we examined whether post-quit insomnia symptoms predicted cessation outcomes. Results indicated that pre-, but not post-quit insomnia, predicted smoking cessation failure by 3 months post-cessation, after covarying for depressive symptoms, anxiety sensitivity, alcohol use disorder severity, treatment condition, and number of cigarettes per day. These findings add to the literature on insomnia symptoms as a risk factor for difficulties with smoking cessation, and suggest it may be a worthy clinical target for smoking populations who are interested in quitting smoking.

Sleep Disturbances in the Elderly

Sleep disturbances are a common presenting symptom of older-age adults to their physicians. This article explores normal changes in sleep pattern with aging and primary sleep disorders in the elderly. Behavioral factors and primary psychiatric disorders affecting sleep in this population are reviewed. Further discussion examines sleep changes associated with 2 common forms of neurocognitive disorder: Alzheimer disease and Lewy Body Dementia. Common medical illnesses in the elderly are discussed in relation to sleep symptoms. Nonpharmacological and pharmacologic treatment strategies are summarized, with emphasis placed on risk of side effects in older adults. Future targets are considered.

Functional effects of dopamine transporter gene genotypes on in vivo dopamine transporter functioning: a meta-analysis

Much psychiatric genetic research has focused on a 40-base pair variable number of tandem repeats (VNTR) polymorphism located in the 3'-untranslated region (3'UTR) of the dopamine active transporter (DAT) gene (SLC6A3). This variant produces two common alleles with 9- and 10-repeats (9R and 10R). Studies associating this variant with in vivo DAT activity in humans have had mixed results. We searched for studies using positron emission tomography (PET) or single-photon emission computed tomography (SPECT) to evaluate this association. Random effects meta-analyses assessed the association of the 3'UTR variant with DAT activity. We also evaluated heterogeneity among studies and evidence for publication bias. We found twelve studies comprising 511 subjects, 125 from PET studies and 386 from SPECT studies. The PET studies provided highly significant evidence that the 9R allele was associated with increased DAT activity in human adults. The SPECT studies were highly heterogeneous. As a group, they suggested no association between the 3'UTR polymorphism and DAT activity. When the analysis was limited to the most commonly used ligand, [123I]β-CIT, stratification by affection status dramatically reduced heterogeneity and revealed a significant association of the 9R allele with increased DAT activity for healthy subjects. In humans, the 9R allele of the 3'UTR polymorphism of SLC6A3 regulates dopamine activity in the striatal brain regions independent of the presence of neuropsychiatric illness. Differences in study methodology account for the heterogeneous results across individual studies.

Recent advances in imaging of dopaminergic neurons for evaluation of neuropsychiatric disorders

Dopamine is the most intensely studied monoaminergic neurotransmitter. Dopaminergic neurotransmission plays an important role in regulating several aspects of basic brain function, including motor, behavior, motivation, and working memory. To date, there are numerous positron emission tomography (PET) and single photon emission computed tomography (SPECT) radiotracers available for targeting different steps in the process of dopaminergic neurotransmission, which permits us to quantify dopaminergic activity in the living human brain. Degeneration of the nigrostriatal dopamine system causes Parkinson's disease (PD) and related Parkinsonism. Dopamine is the neurotransmitter that has been classically associated with the reinforcing effects of drug abuse. Abnormalities within the dopamine system in the brain are involved in the pathophysiology of attention deficit hyperactivity disorder (ADHD). Dopamine receptors play an important role in schizophrenia and the effect of neuroleptics is through blockage of dopamine D₂ receptors. This review will concentrate on the radiotracers that have been developed for imaging dopaminergic neurons, describe the clinical aspects in the assessment of neuropsychiatric disorders, and suggest future directions in the diagnosis and management of such disorders.

Smoking, dopamine transporter, and hand tremor

AIM

The purpose of the study was to evaluate the relationship between the number of packs smoked per day and specific uptake ratio (SUR) in the striatum on Tc-99m TRODAT, and frequency of hand tremor.

METHODS

It was a prospective, cross-sectional study. In all, 23 healthy nonsmokers and 37 current smokers were recruited in the study. All subjects underwent Tc-99m TRODAT SPECT, brain CT scan, thyroid function test, tremor measurement system, and neurologic examinations.

RESULTS

There were significant differences in the SUR in the striatum on Tc-99m TRODAT and in the frequency of hand tremor in rest state and in arm extended state among nonsmokers (grade I), current smokers with less than 1 pack smoked per day (grade II), and current smokers with equal or more than 1 pack smoked per day (grade III) by ANOVA (all P < 0.001). After adjusting for age and gender, there was a significantly negative correlation between smoke grade and SUR in the striatum on Tc-99m TRODAT by multiple linear regression (β = -0.45, P < 0.001). Smoke grade was the significant predictor for the frequency of hand tremor in rest state and in arm extended state, after adjusting for age and gender by multiple linear regression (β = 14.70, P < 0.001; β = 15.37, P < 0.001).

CONCLUSIONS

There is a dose-response relationship between the number of packs smoked per day and SUR in the striatum, and the frequency of hand tremor. Decreased dopamine transporter binding in the striatum and increased frequency of hand tremor in smokers may have important implications for evaluating the impact of smoking on the central and peripheral nerve systems.

Chronic ethanol exposure changes dopamine D2 receptor splicing during retinoic acid-induced differentiation of human SH-SY5Y cells

There is evidence for ethanol-induced impairment of the dopaminergic system in the brain during development. The dopamine D2 receptor (DRD2) and the dopamine transporter (DAT) are decisively involved in dopaminergic signaling. Two splice variants of DRD2 are known, with the short one (DRD2s) representing the autoreceptor and the long one (DRD2l) the postsynaptic receptor. We searched for a model to investigate the impact of chronic ethanol exposure and withdrawal on the expression of these proteins during neuronal differentiation. RA-induced differentiation of human neuroblastoma SH-SY5Y cells seems to represent such a model. Our real-time RT-PCR, Western blot, and immunocytochemistry analyses of undifferentiated and RA-differentiated cells have demonstrated the enhanced expression of both splice variants of DRD2, with the short one being stronger enhanced than the long one under RA-treatment, and the DRD2 distribution on cell bodies and neurites under both conditions. In contrast, DAT was down-regulated by RA. The DAT is functional both in undifferentiated and RA-differentiated cells as demonstrated by [(3)H]dopamine uptake. Chronic ethanol exposure during differentiation for up to 4 weeks resulted in a delayed up-regulation of DRD2s. Ethanol withdrawal caused an increased expression of DRD2l and a normalization of DRD2s. Thus the DRD2s/DRD2l ratio was still disturbed. The dopamine level was increased by RA-differentiation compared to controls and was diminished under RA/ethanol treatment and ethanol withdrawal compared to RA-only treated cells. In conclusion, chronic ethanol exposure impairs differentiation-dependent adaptation of dopaminergic proteins, specifically of DRD2s. RA-differentiating SH-SY5Y cells are suited to study the impact of chronic ethanol exposure and withdrawal on expression of dopaminergic proteins during neuronal differentiation.

European consensus statement on diagnosis and treatment of adult ADHD: The European Network Adult ADHD

BACKGROUND

Attention deficit hyperactivity disorder (ADHD) is among the most common psychiatric disorders of childhood that persists into adulthood in the majority of cases. The evidence on persistence poses several difficulties for adult psychiatry considering the lack of expertise for diagnostic assessment, limited treatment options and patient facilities across Europe.

METHODS

The European Network Adult ADHD, founded in 2003, aims to increase awareness of this disorder and improve knowledge and patient care for adults with ADHD across Europe. This Consensus Statement is one of the actions taken by the European Network Adult ADHD in order to support the clinician with research evidence and clinical experience from 18 European countries in which ADHD in adults is recognised and treated.

RESULTS

Besides information on the genetics and neurobiology of ADHD, three major questions are addressed in this statement: (1) What is the clinical picture of ADHD in adults? (2) How can ADHD in adults be properly diagnosed? (3) How should ADHD in adults be effectively treated?

CONCLUSIONS

ADHD often presents as an impairing lifelong condition in adults, yet it is currently underdiagnosed and treated in many European countries, leading to ineffective treatment and higher costs of illness. Expertise in diagnostic assessment and treatment of ADHD in adults must increase in psychiatry. Instruments for screening and diagnosis of ADHD in adults are available and appropriate treatments exist, although more research is needed in this age group.

Environmental enrichment improves cognitive deficits in Spontaneously Hypertensive Rats (SHR): relevance for Attention Deficit/Hyperactivity Disorder (ADHD)

The interaction between genes and environment seems to be relevant for the development of Attention Deficit/Hyperactivity Disorder (ADHD), one of the most prevalent childhood psychiatric diseases. The occurrence of ADHD is typically associated with poor academic performance, probably reflecting learning difficulties and/or cognitive impulsiveness. The inbred Spontaneously Hypertensive Rats (SHR) strain has often been considered as an animal model of ADHD, since they 'naturally' display the main ADHD symptomatology. Although pharmacological agents improve SHR's cognitive deficits, little is known about the involvement of environmental factors in SHR disabilities and to what extent 'protective' non-pharmacological factors may be considered as strategy for ADHD prevention. Here we investigated whether the rearing environment during neurodevelopment may counteract later cognitive deficits presented by adult SHR. Wistar (WIS) rats were also used to investigate whether the putative effects of environmental enrichment depend on a specific genetic background. The animals were reared in enriched environment (EE) or standard environment (SE) from the post-natal day 21 until 3 months of age (adulthood) and tested for cognitive and non-cognitive phenotypes. EE improved SHR's performance in open field habituation, water maze spatial reference, social and object recognition tasks, while non-cognitive traits, such as nociception and hypertension, were not affected by EE. Response of WIS rats was generally not affected by the present EE. These results show that the general low cognitive performance presented by SHR rats strongly depends on the rearing environment and they may suggest modifications of the familial environment as a putative preventive strategy to cope with ADHD.

Reinforcing and subjective effects of methylphenidate in adults with and without attention deficit hyperactivity disorder (ADHD)

RATIONALE

There has been controversy over the abuse potential of methylphenidate (MPH) in the context of treatment for attention deficit hyperactivity disorder (ADHD).

OBJECTIVE

The objective of this study was to compare the reinforcing and subjective effects of oral MPH in adults with and without ADHD.

MATERIALS AND METHODS

Following screening, 33 adults (n = 16 with ADHD; n = 17 free from psychiatric diagnoses) completed four pairs of experimental sessions, each of which included a sampling session and a self-administration session. During sampling sessions, subjects received in randomized order 0 (placebo), 20, 40, and 60 mg MPH. During self-administration sessions, subjects completed a progressive ratio (PR) task to earn portions of the dose received on the corresponding sampling session. Subjective effects were recorded throughout all sessions. The main outcome measure for the study was the number of ratios completed on the PR task. Secondary measures included peak subjective effects and area-under-the-curve values for subjective effects.

RESULTS

Compared to the control group, the ADHD group completed more ratios on the PR task. Both groups showed robust effects of methylphenidate on subjective endpoints. Main effects of group were noted on subjective effects involving concentration and arousal.

CONCLUSIONS

Compared to placebo, MPH produced reinforcing effects only for the ADHD group and not for the control group. Increases in stimulant-related subjective effects in non-ADHD subjects were not associated with drug reinforcement.

The effect of methylphenidate on Internet video game play in children with attention-deficit/hyperactivity disorder

OBJECTIVE

A number of studies about attention-deficit/hyperactivity disorder (ADHD) and Internet video game play have examined the prefrontal cortex and dopaminergic system. Stimulants such as methylphenidate (MPH), given to treat ADHD, and video game play have been found to increase synaptic dopamine. We hypothesized that MPH treatment would reduce Internet use in subjects with co-occurring ADHD and Internet video game addictions.

METHODS

Sixty-two children (52 males and 10 females), drug-naive, diagnosed with ADHD, and Internet video game players, participated in this study. At the beginning of the study and after 8 weeks of treatment with Concerta (OROS methylphenidate HCl, Seoul, Korea), participants were assessed with Young's Internet Addiction Scale, Korean version (YIAS-K), Korean DuPaul's ADHD Rating Scale, and the Visual Continuous Performance Test. Their Internet usage time was also recorded.

RESULTS

After 8 weeks of treatment, the YIAS-K scores and Internet usage times were significantly reduced. The changes in the YIAS-K scores between the baseline and 8-week assessments were positively correlated with the changes in total and inattention scores from the Korean DuPaul's ADHD Rating Scale, as well as omission errors from the Visual Continuous Performance Test. There was also a significant difference in the number of omission errors among non-Internet-addicted, mildly Internet addicted, and severely Internet addicted participants.

DISCUSSION

We suggest that Internet video game playing might be a means of self-medication for children with ADHD. In addition, we cautiously suggest that MPH might be evaluated as a potential treatment of Internet addiction.

Neuroimaging of Nicotine Dependence: Key Findings and Application to the Study of Smoking-Mental Illness Comorbidity

Modern neuroimaging techniques offer the opportunity to non-invasively study neuroanatomical and neurofunctional correlates of nicotine dependence and its treatment. In the present review, the most widely used neuroimaging techniques-magnetic resonance imaging (MRI), positron emission tomography (PET) and functional MRI (fMRI)-are briefly described and their strengths and limitations discussed. The use of these techniques has resulted in new insights into the neuropharmacology of tobacco addiction. Studies comparing smokers and nonsmokers have shown that smokers have less grey matter density in frontal brain regions and greater concentrations of nicotinic receptors. Research on the effects of smoking a cigarette confirms that smoking leads to the release of dopamine in brain reward areas and to nicotinic receptor binding. Studies of smoking abstinence have identified functional brain correlates of increased reactivity to smoking-related cues, and worsening of concentration. To date, neuroimaging studies of nicotine dependence among individuals with mental illness have focused almost exclusively on schizophrenia. A conceptual/methodological framework for studying dual diagnosis using neuroimaging measures is provided with the aim of spurring additional research in this area.

Dopamine transporter imaging in adult patients with attention-deficit/hyperactivity disorder

The aim of this study was to provide in vivo evidence for the hypothesis that dopaminergic neurotransmission is altered in adult patients with attention-deficit/hyperactivity disorder (ADHD). We used high-resolution brain-dedicated single-photon emission computed tomography and the dopamine transporter (DAT) marker [(123)I]FP-CIT in 17 adult treatment-naïve ADHD patients and 14 age-matched controls. Magnetic resonance imaging-based region of interest analysis was performed to quantify the DAT availability (expressed as a ratio of specific to non-displaceable binding, V(3)'') in the striatum. Additionally, the specific radiotracer binding was assessed in the thalamus and the midbrain/brainstem regions (reflecting also the availability of the serotonin transporter to which [(123)I]FP-CIT binds with moderate affinity). In the striatal areas of the ADHD patients, a significantly reduced specific tracer binding was found (V(3)'': 5.18+/-0.98; controls 6.36+/-1.34). In contrast, the specific [(123)I]FP-CIT binding did not differ from controls in the thalamus and midbrain/brainstem areas. These data indicate a reduced dopaminergic but not serotonergic transmitter reuptake function in adult ADHD. Further studies will have to deal with the question of whether these findings have the potential to influence treatment decisions in this complex disorder.

In vivo brain imaging of human exposure to nicotine and tobacco

While most cigarette smokers endorse a desire to quit smoking, only 14-49% will achieve abstinence after 6 months or more of treatment. A greater understanding of the effects of smoking on brain function may result in improved pharmacological and behavioral interventions for this condition. Research groups have examined the effects of acute and chronic nicotine/cigarette exposure on brain activity using functional imaging; the purpose of this chapter is to synthesize findings from such studies and present a coherent model of brain function in smokers. Responses to acute administration of nicotine/smoking include reduced global brain activity; activation of the prefrontal cortex, thalamus, and visual system; activation of the thalamus and visual cortex during visual cognitive tasks; and increased dopamine (DA) concentration in the ventral striatum/nucleus accumbens. Responses to chronic nicotine/cigarette exposure include decreased monoamine oxidase (MAO) A and B activity in the basal ganglia and a reduction in alpha4beta2 nicotinic acetylcholine receptor (nAChR) availability in the thalamus and putamen (accompanied by an overall upregulation of these receptors). These findings indicate that smoking enhances neurotransmission through cortico-basal ganglia-thalamic circuits by direct stimulation of nAChRs, indirect stimulation via DA release or MAO inhibition, or a combination of these and possibly other factors. Activation of this circuitry may be responsible for the effects of smoking seen in tobacco-dependent smokers, such as improvements in attentional performance, mood, anxiety, and irritability.

Nicotine self-medication of cognitive-attentional processing

This article selectively reviews research concerning nicotine's effects on cognition, including the neurobiological mechanism for these effects, task and experimental features that may be important for elucidating these effects, and why these effects may have amplified motivational significance among smokers with cognitive deficit. Nicotine has effects on various cognitive processes, though most studies in humans have focused on the amelioration of cognitive deficits experienced during drug withdrawal. The direct cognitive-enhancing effect of nicotine remains a controversial topic. The relationship between attentional and non-attentional cognitive effects of nicotine is discussed in the context of cognitive self-medication. Further research should include theory-driven examination of cognitive effects of nicotine, and develop targeted smoking cessation programs based on an improved understanding of the role of cognitive self-medication in high-risk individuals.

ADHD and smoking: from genes to brain to behavior

Attention-deficit/hyperactivity disorder (ADHD) and tobacco smoking are among the most common and costly psychiatric and behavioral problems. The rates of co-occurrence of these two common problems are larger than expected by chance. Despite progress in identifying the neural and genetic substrates of each, the mechanisms underlying the high rates of comorbidity between ADHD and smoking remain largely unknown. We propose that ADHD and smoking involve dysregulation of dopaminergic and nicotinic-acetylcholinergic circuits and that these aberrations are likely to arise, at least in part, from genetic variations. This review describes an integrative model of the ADHD-smoking comorbidity, with an emphasis on shared neuropharmacological mechanisms. We first describe the prevalence of smoking among ADHD patients. We then describe how ADHD influences stages of smoking behavior (e.g., initiation, maintenance, and relapse). We review common potential genetic substrates of ADHD and smoking, focusing on genes that regulate monoaminergic neurotransmission. We review the behavioral and neuropharmacological bases of smoking and ADHD, focusing on the modulatory roles of nicotine on attention and behavioral control. Finally, we discuss the implications of this model for prevention and clinical outcomes.

Dopamine transporter levels in cocaine dependent subjects

Cocaine use is a significant problem in the US and it is well established that cocaine binds to the dopamine transporter (DAT) in the brain. This study was designed to determine if the DAT levels measured by 99mTc TRODAT SPECT (single photon emission computed tomography) brain scans are altered in cocaine dependent subjects and to explore clinical correlates of such alterations. SPECT brain scans were acquired on 21 cocaine dependent subjects and 21 healthy matched controls. There were significantly higher DAT levels in cocaine dependent subjects compared to controls for the anterior putamen (p=0.003; Cohen's d effect size=0.98), posterior putamen (p<0.001; effect size=1.32), and caudate (p=0.003; effect size=0.97). DAT levels in these regions were 10%, 17%, and 8% higher in the cocaine dependent subjects compared to controls. DAT levels were unrelated to craving, severity of cocaine use, or duration of cocaine use, but DAT levels in the caudate and anterior putamen were significantly (p<0.05) negatively correlated with days since last use of cocaine.

SPECT and PET of the dopamine transporter in attention-deficit/hyperactivity disorder

Abnormalities of frontostriatal circuits, which are modulated by dopamine, have been found by brain imaging studies in patients with attention-deficit/hyperactivity disorder (ADHD). With special radiolabeled ligands selective imaging of the dopamine transporter (DAT), which has a key function in dopamine metabolism, can be performed by SPECT and PET. Most of the studies showed a higher DAT availability in untreated patients with ADHD compared with controls. The relationship between DAT availability and a polymorphism of DAT1 gene in patients with ADHD is not clear and the results are controversial. It has been shown that methylphenidate lowers DAT availability very effectively in normal people and in patients with ADHD. First results seem to indicate that nonresponders to methylphenidate among ADHD patients have a low primary DAT availability, whereas patients with a good response to the drug have high DAT. Nicotine seems to lower DAT availability such as stimulant medication; this may explain the high percentage of smokers among patients with ADHD. Zinc is a DAT inhibitor and seems to have a positive therapeutic effect on ADHD symptoms. This article reviews the function and structure of the DAT, the results of DAT imaging with SPECT and PET, the relations between DAT availability and the DAT1 gene polymorphism, the influence of stimulants on DAT and the significance of DAT for therapeutic response, nicotine, zinc and psychotic symptoms in patients with ADHD.

Decreased dopamine transporter availability in male smokers -- a dual isotope SPECT study

INTRODUCTION

Although the mesolimbic dopaminergic system has been shown to play a role in reinforcing tobacco smoking, results of imaging studies that examine the relationship between tobacco smoking and the central dopamine system remain discrepant. To delineate the role of tobacco addiction in central pre- and post-synaptic dopaminergic activities, we analyzed the central D2-family receptors, the dopamine transporters (DAT), and degrees of dependence in male smokers.

METHODS

Eleven male smokers and 11 healthy non-smokers were recruited. The striatal dopamine D2/D3 receptor availability was approximated using SPECT and [123 I] IBZM while the DAT availability was approximated using SPECT and [99m Tc] TRODAT-1. All of the smokers completed the Fagerström Test for Nicotine Dependence (FTND) and other related questionnaires.

RESULTS

A decrease in DAT availability in the striatum of male smokers is noted (p<05). However, the striatal D2/D3 receptor availability in male smokers does not differ from that of non-smokers.

CONCLUSIONS

These findings suggest that cigarette smoking may alter central dopamine functions in males, particularly at the pre-synaptic sites.

Consequences of variations in genes that affect dopamine in prefrontal cortex

Patricia Goldman-Rakic played a groundbreaking role in investigating the cognitive functions subserved by dorsolateral prefrontal cortex and the key role of dopamine in that. The work discussed here builds on that including: 1) Studies of children predicted to have lower levels of prefrontal dopamine but otherwise basically normal brains (children treated for phenylketonuria [PKU]). Those studies changed medical guidelines, improving the children's lives. 2) Studies of visual impairments (in contrast sensitivity and motion perception) in PKU children due to reduced retinal dopamine and due to excessive phenylalanine during the first postnatal weeks. Those studies, too, changed medical guidelines. 3) Studies of working memory and inhibitory control differences in typically developing children due to differences in catechol-O-methyltransferase (COMT) genotype, which selectively affect prefrontal dopamine levels. 4) Studies of gender differences in the effect of COMT genotype on cognitive performance in older adults. 5) A hypothesis about fundamental differences between attention deficit hyperactivity disorder (ADHD) that includes hyperactivity and ADHD of the inattentive type. Those disorders are hypothesized to differ in the affected neural system, underlying genetics, responsiveness to medication, comorbidities, and cognitive and behavioral profiles. These sound quite disparate but they all grew systematically out the base laid down by Patricia Goldman-Rakic.

Relationship between VNTR polymorphisms of the human dopamine transporter gene and expression in post-mortem midbrain tissue

Attention deficit hyperactivity disorder (ADHD) is currently one of the most prevalent childhood behavioral disorders. The disorder is found to be highly heritable, suggesting a large genetic component. Association studies have repeatedly implicated the dopamine transporter (DAT1) gene, and in particular the 10-repeat allele of a variable number tandem repeat (VNTR) polymorphism located in the 3'UTR of the gene. Inconclusive data has been generated from several earlier studies on the functional effects of this polymorphism. Therefore, there is call for further investigation and thus the focus on data described here from TaqMan RT-PCR assays. The expression levels of the DAT1 gene from post-mortem midbrain tissue was measured in relation to the polymorphism present at the 3'UTR VNTR, together with a further VNTR marker located within intron 8 of the gene (Int8 VNTR). The findings suggest that the presence of the 10-repeat allele of the 3'UTR VNTR, the 3-repeat of the intron 8 VNTR and both VNTR markers are correlated with increased levels of the DAT1 transcript in midbrain post-mortem tissue. Further work using linear regression (LR) shows agreement with the correlation analysis, and either nominal significance or a trend in that direction. Given the small sample size, bootstrapping-derived confidence intervals were calculated for the LR. These empirical analyses suggest that the 3'UTR VNTR to show a significant main effect on relative DAT1 expression. Furthermore, a significant effect was found for the combined model (3'UTR and Int8 VNTR markers) on expression. These data provide further evidence on the plausible molecular mechanism underlying the aetiology of the disorder.

Neuronal nicotinic receptor agonists for the treatment of attention-deficit/hyperactivity disorder: focus on cognition

Attention deficit/hyperactivity disorder (ADHD) is the most commonly diagnosed neurobehavioral disorder in children and adolescents, and in about half of these patients, significant symptomology continues into adulthood. Although impulsivity and hyperactivity are the most salient features of ADHD, cognitive deficits, particularly impairments in attention and executive function, are an important component, particularly in adolescents and adults, with over 90% of adults seeking treatment for ADHD manifesting cognitive dysfunction. Currently available medications treat the core ADHD symptoms but typically do not adequately address cognitive aspects of ADHD, underscoring the need for new therapeutics. Dopamine and norepinephrine are hypothesized to be particularly important in ADHD, but there is emerging evidence that cholinergic neurotransmission, particularly involving neuronal nicotinic acetylcholine receptors (nAChRs), may play a role in the pathophysiology of ADHD. Nicotine has demonstrated procognitive effects in both humans and experimental animals and has produced signals of efficacy in small proof-of-concept adult ADHD trials. Although adverse effects associated with nicotine preclude its development as a therapeutic, a number of novel nAChR agonists with improved safety/tolerability profiles have been discovered. Of these, ABT-418 and ABT-089 have both demonstrated signals of efficacy in adults with ADHD. Notably, tolerability issues that might be expected of a nAChR agonist, such as nausea and emesis, were not observed at efficacious doses of ABT-089. Further understanding of the effects of novel neuronal nAChR agonists on specific aspects of cognitive functioning in ADHD is required to assess the full potential of this approach.

Características psicológicas associadas ao comportamento de fumar tabaco

Este artigo apresenta uma revisão da literatura sobre a psicologia do tabagismo, destacando características de personalidade do fumante como um dos obstáculos à cessação do tabagismo. Descreve-se a relação entre tabagismo e personalidade e, a seguir, a relação do tabagismo com os principais transtornos psiquiátricos. Estudos revelam que os fumantes tendem a ser mais extrovertidos, ansiosos, tensos, impulsivos e com mais traços de neuroticismo e psicoticismo, em comparação a ex-fumantes e não fumantes. A literatura revela, ainda, forte associação entre tabagismo e transtornos mentais, como esquizofrenia e depressão, entre outros. A compreensão dos fatores de natureza psicológica associados ao consumo e à dependência pode contribuir para a elaboração e aperfeiçoamento de estratégias terapêuticas para o tratamento da dependência e/ou programas de cunho educativo/preventivo.

Nicotine and alcohol dependence in patients with comorbid attention-deficit/hyperactivity disorder (ADHD)

AIMS

Several studies have shown that attention-deficit/hyperactivity disorder (ADHD) represents a significant risk factor for the onset and development of an addiction. Thirty-five per cent of adult ADHD patients are known to be addicted to alcohol. Many ADHD patients also have an increased nicotine consumption, which typically, leads to an improvement of attention, ability to concentrate and control of impulses. There may be pathophysiological connections here. On the other hand, it can also be assumed that there is a high prevalence of addicted patients with undiagnosed ADHD.

METHODS

Ninety-one adult alcohol-dependent patients were examined for ADHD in this study, using the Wender Utah Rating Scale (WURS-k), Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) symptom check-list for ADHD and the Conners' Adult ADHD Rating Scales (CAARS, Long Version). The patients were divided into diagnostic sub-groups according to DSM-IV (inattentive type, impulsive type, combined type). Nicotine consumption was investigated using the Fagerström Test of Nicotine Dependence (FTND) and then graded as 'minimal', 'average' or 'high' nicotine dependence.

RESULTS

There were 20.9% (WURS-k) or 23.1% (DSM-IV diagnostic criteria) of the patients addicted to alcohol, who showed evidence of ADHD in childhood. With the help of CAARS, it could be demonstrated that 33.3% of the patients who fulfilled the diagnostic criteria of ADHD, according to DSM-IV, had persisting ADHD in adulthood. The FTND showed a statistically significant difference in nicotine dependence between alcohol-dependent patients with and without ADHD in childhood. Patients numbering 76.2% with ADHD, demonstrated an 'average to high' level of nicotine dependence compared to 45.7% of those patients without ADHD. Furthermore, the number of patients not addicted to nicotine (19%) was significantly lower than among those without ADHD (36.6%) (P = 0.029).

CONCLUSIONS

The results of this investigation reveal that a large number of ADHD patients suffer from alcohol dependence, and an even greater number from excessive nicotine dependence. The outcome indicates that there are most likely pathophysiological connections with alcohol and nicotine dependence, and that this substance abuse is probably a form of 'self-medication'. The results clearly underline the great importance of early and adequate diagnosis and therapy of ADHD, in order to prevent exacerbation of addictive illness.

Dopamine Transporter Binding in Smokers and Nonsmokers

PURPOSE

Regional brain concentrations of dopamine transporters have been examined to elucidate the neurochemical substrates of neurologic and psychiatric conditions. Many of these conditions are associated with increased (or decreased) cigarette smoking prevalence; therefore, current smoking may confound the results of these investigations. This study determined whether healthy current smokers and nonsmokers exhibit differences in dopamine transporter (DAT) binding measured by Tc-99m TRODAT SPECT.

MATERIALS AND METHODS

Tc-99m TRODAT SPECT brain scans were retrospectively evaluated in 46 nonsmokers and 8 current smokers, all of whom had been recruited and screened as healthy controls for previous imaging studies. The scans were acquired approximately 3 hours after the intravenous administration of 740 MBq (20 mCi) of Tc-99m TRODAT and were reconstructed with a simple bandpass filter. Regions of interest (ROIs) were placed manually on subregions of the right and left basal ganglia and distribution volume ratios (DVRs) were compared for the smoker and nonsmoker groups.

RESULTS

There were significant decreases in DAT binding in current smokers compared with nonsmokers in the caudate nuclei bilaterally, the right anterior putamen and the left posterior putamen.

CONCLUSION

Reduced DAT binding in ROIs relevant to movement disorders as well as other neuropsychiatric conditions may have important implications for evaluating scans in these patient populations.

Brain dopamine transporter levels in treatment and drug naïve adults with ADHD

Attention deficit hyperactivity disorder (ADHD) is the most frequent psychiatric disorder in children, yet data are sparse on its pathophysiology. Particularly relevant are the dopamine transporters since these are the main targets of stimulant medications used for ADHD treatment. Though some imaging studies have shown increases in dopamine transporters in ADHD others have not and their role in the neurobiology of ADHD remains unclear. Here we investigate dopamine transporters in ADHD subjects with control of potentially confounding factors (previous medication and/or drug histories, comorbidity) and their association with clinical symptoms. Positron emission tomography and [11C]cocaine were used to measure dopamine transporters in 20 never medicated adults with ADHD and 25 controls. Dopamine transporters were lower in left caudate (13%, p < 0.05) and in left nucleus accumbens (p < 0.005) in ADHD subjects than in controls. In putamen dopamine transporters did not differ between groups but were associated with scores of inattention (Conners Adult Attention Rating Scale) both in ADHD subjects (p < 0.005) and in controls (p < 0.005). Thus, for a given transporter level the scores for inattention were on average five times greater in ADHD subjects than in controls. These results do not corroborate increases in dopamine transporters in ADHD subjects and show that in some they are reduced. It also provides evidence that dopamine transporter levels modulate attention but suggest that additional pathology (e.g., prefrontal or cingulostriatal pathways, noradrenergic neurotransmission) is necessary to account for the large differences in inattention observed between controls and ADHD subjects.

Striatal dopamine transporter availability and DAT-1 gene in adults with ADHD: no higher DAT availability in patients with homozygosity for the 10-repeat allele

In 29 adults with attention deficit hyperactivity disorder (ADHD) striatal dopamine transporter (DAT) availability was assessed by [(99m)Tc]TRODAT-1 SPECT and correlated with 3' VNTR polymorphism of the DAT gene on chromosome 5p15.3. Seventeen patients showed homozygosity for the 10-repeat allele, two homozygosity of the 9 allele and 10 were heterozygous (9-10). No statistically significant difference in DAT availability was found between patients with 10-10 carriers (DAT 1.28 +/- 0.34) and with at least one 9 allele (DAT 1.31 +/- 0.27); when smokers were excluded, DAT availability was 1.38 +/- 0.28 in the 10-10 carriers (n = 12) and 1.42 +/- 0.19 in the 9-10 and 9-9 carriers (n = 7). In conclusion, no higher striatal DAT was found in patients with homozygosity of the 10 allele of the DAT gene in this study. These results differ from a study in 11 Korean children with ADHD, in which 10-10 carriers showed higher DAT availability in [(123)I]IPT SPECT. Discrepancies may be explained by differences in patient's age, ethnical differences, different imaging techniques or the limited number of patients included in both studies.

Functional brain imaging of tobacco use and dependence

While most cigarette smokers endorse a desire to quit smoking, only about 14% to 49% will achieve abstinence after 6 months or more of treatment. A greater understanding of the effects of smoking on brain function may (in conjunction with other lines of research) result in improved pharmacological (and behavioral) interventions. Many research groups have examined the effects of acute and chronic nicotine/cigarette exposure on brain activity using functional imaging; the purpose of this paper is to synthesize findings from such studies and present a coherent model of brain function in smokers. Responses to acute administration of nicotine/smoking include: a reduction in global brain activity; activation of the prefrontal cortex, thalamus, and visual system; activation of the thalamus and visual cortex during visual cognitive tasks; and increased dopamine (DA) concentration in the ventral striatum/nucleus accumbens. Responses to chronic nicotine/cigarette exposure include decreased monoamine oxidase (MAO) A and B activity in the basal ganglia and a reduction in alpha4beta2 nicotinic acetylcholine receptor (nAChR) availability in the thalamus and putamen. Taken together, these findings indicate that smoking enhances neurotransmission through cortico-basal ganglia-thalamic circuits either by direct stimulation of nAChRs, indirect stimulation via DA release or MAO inhibition, or a combination of these factors. Activation of this circuitry may be responsible for the effects of smoking seen in tobacco dependent subjects, such as improvements in attentional performance, mood, anxiety, and irritability.

ADHD in adolescence and adulthood, with a special focus on the dopamine transporter and nicotine

The persistence of attention deficit hyperactivity disorder (ADHD) into adolescence and adulthood has now been accepted as a clinical entity. The rate of prevalence among adults is assumed to be from 2% to 4%. With increasing age, a symptom change has to be considered; disturbance of attention becomes more prominent, whereas hyperactivity often diminishes or changes to inactivity. Neuroimaging studies show a high striatal dopamine transporter (DAT) availability in most adults with ADHD; this can be reduced by stimulants. Nicotine seems to have a stimulant-like action on the DAT. In most adults with ADHD, therapy has to be multimodal, combining psychotherapy and medication. Methylphenidate is the first-line drug in adult ADHD; further options are amphetamine and noradrenaline reuptake inhibitors. Nonresponders to methylphenidate seem to have no elevated DAT availability prior to therapy. Combination with other psychiatric disorders occurs frequently in adults with ADHD; in these patients additional pharmacological treatment with special regard to the comorbid disease is recommended.

Attention-deficit disorder (attention-deficit/ hyperactivity disorder without hyperactivity): a neurobiologically and behaviorally distinct disorder from attention-deficit/hyperactivity disorder (with hyperactivity)

Most studies of attention-deficit/hyperactivity disorder (ADHD) have focused on the combined type and emphasized a core problem in response inhibition. It is proposed here that the core problem in the truly inattentive type of ADHD (not simply the subthreshold combined type) is in working memory. It is further proposed that laboratory measures, such as complex-span and dual-task dichotic listening tasks, can detect this. Children with the truly inattentive type of ADHD, rather than being distractible, may instead be easily bored, their problem being more in motivation (underarousal) than in inhibitory control. Much converging evidence points to a primary disturbance in the striatum (a frontal-striatal loop) in the combined type of ADHD. It is proposed here that the primary disturbance in truly inattentive-type ADHD (ADD) is in the cortex (a frontal-parietal loop). Finally, it is posited that these are not two different types of ADHD, but two different disorders with different cognitive and behavioral profiles, different patterns of comorbidities, different responses to medication, and different underlying neurobiologies.

Striatal dopamine transporter density in drug naive patients with attention-deficit/hyperactivity disorder

BACKGROUND AND AIM

Dopamine transporters are the target of psychostimulants used for treatment of attention-deficit/hyperactivity disorder (ADHD). Therefore, the present study aimed to evaluate striatal dopamine transporter density in adult patients with ADHD.

METHODS

Twenty patients (11 female, nine male; mean age 35+/-7 years) and 20 control subjects (11 female, nine male, mean age 32 +/- 8 years) were examined with SPECT using the specific radiotracer 123I-FP-CIT. The ratio of striatal to cortical radioactivity concentration was used for semiquantitative evaluation of dopamine transporter binding potential (V3''). There was a significant influence of age (P < 0.001) and a trend towards an influence of gender (P = 0.053) on V3''. An ANCOVA with these covariates showed a slightly higher V3'' in the patients than in the control subjects (4.24 +/- 0.48 vs. 4.03 +/- 0.56; P = 0.02).

CONCLUSION

This study provides further in-vivo evidence for an involvement of the dopamine transporter in ADHD. However, compared to previous studies, the increase of dopamine transporter density in the patient group is less pronounced here.

Nicotinic effects on cognitive function: behavioral characterization, pharmacological specification, and anatomic localization

RATIONALE

Nicotine has been shown in a variety of studies in humans and experimental animals to improve cognitive function. Nicotinic treatments are being developed as therapeutic treatments for cognitive dysfunction.

OBJECTIVES

Critical for the development of nicotinic therapeutics is an understanding of the neurobehavioral bases for nicotinic involvement in cognitive function.

METHODS

Specific and diverse cognitive functions affected by nicotinic treatments are reviewed, including attention, learning, and memory. The neural substrates for these behavioral actions involve the identification of the critical pharmacologic receptor targets, in particular brain locations, and how those incipient targets integrate with broader neural systems involved with cognitive function.

RESULTS

Nicotine and nicotinic agonists can improve working memory function, learning, and attention. Both alpha4beta2 and alpha7 nicotinic receptors appear to be critical for memory function. The hippocampus and the amygdala in particular have been found to be important for memory, with decreased nicotinic activity in these areas impairing memory. Nicotine and nicotinic analogs have shown promise for inducing cognitive improvement. Positive therapeutic effects have been seen in initial studies with a variety of cognitive dysfunctions, including Alzheimer's disease, age-associated memory impairment, schizophrenia, and attention deficit hyperactivity disorder.

CONCLUSIONS

Discovery of the behavioral, pharmacological, and anatomic specificity of nicotinic effects on learning, memory, and attention not only aids the understanding of nicotinic involvement in the basis of cognitive function, but also helps in the development of novel nicotinic treatments for cognitive dysfunction. Nicotinic treatments directed at specific receptor subtypes and nicotinic cotreatments with drugs affecting interacting transmitter systems may provide cognitive benefits most relevant to different syndromes of cognitive impairment such as Alzheimer's disease, schizophrenia, and attention deficit hyperactivity disorder. Further research is necessary in order to determine the efficacy and safety of nicotinic treatments of these cognitive disorders.

The reinforcing effects of nicotine and stimulant medication in the everyday lives of adult smokers with ADHD: A preliminary examination

Whereas the smoking prevalence rates in the general population are declining, rates among people diagnosed with attention-deficit/hyperactivity disorder (ADHD) continue to be elevated. Previous research has shown that nicotine may improve attention and mood, suggesting that nicotine may help ameliorate the attentional and emotional problems associated with ADHD. The present study examined the effects of nicotine with and without stimulant medication on ADHD symptoms, moods, and arousal in the everyday lives of smokers with ADHD. A total of 10 smokers with ADHD who were being treated with stimulant medication were asked to abstain from smoking while participating in the study. Participants underwent four conditions in randomized order: (a) Nicotine patch+stimulant medication, (b) nicotine patch only, (c) placebo patch+stimulant medication, and (d) placebo patch only. Each condition continued for 2 days, during which self-reports of ADHD symptoms and moods were obtained using electronic diaries. Lightweight ambulatory monitors recorded cardiovascular activity at each diary entry. Smoking abstinence was verified by expired carbon monoxide and salivary cotinine analysis. Results showed that nicotine patches and stimulant medication alone and in combination reduced difficulty concentrating and core ADHD symptoms compared with placebo patch only. Borderline improvement in impatience and self-control was seen with nicotine patch administration primarily on day 1. Nicotine patches also tended to elevate systolic and diastolic blood pressure compared with placebo patch during day 2. The findings suggest that smokers with ADHD experience nicotine-related reductions in ADHD symptoms during their everyday lives.

Striatal dopamine D2/D3 receptor availability in male smokers

It has been reported that the activation of the nicotine receptor evokes central endogenous dopamine release. However, whether smoking affects striatal dopamine D(2)/D(3) availability over the long run has not been well established in vivo. Fifteen male smokers and their matching controls were recruited. Striatal dopamine D(2)/D(3) receptor availability was assessed by single photon emission computed tomography with [(123)]IBZM Iodo-benzaimide. There was no significant difference in striatal D(2)/D(3) receptor availability between smokers and controls.

Influence of striatal dopamine transporter availability on the response to methylphenidate in adult patients with ADHD

In this study, we investigated whether availability of striatal dopamine transporter (DAT) may have an influence on the response of adult patients with attention deficit hyperactivity disorder (ADHD) on methylphenidate (MPH). In 18 non-smoking and non-medicated adult patients with ADHD, availability of DAT was measured with [(99m)Tc] TRODAT-1 SPECT. Then, the patients received methylphenidate (MPH), individually titrated up to 60 mg per day. Ten weeks later, clinical improvement was rated by Clinical Global Impressions scale. In all, 6 patients were classified as non-responders, and 12 responded to MPH. From the non-responders, 5 presented with a DAT availability below that of normal controls of the same age, whereas in the group of responders all patients had elevated DAT availability. There was a significant negative correlation between values for global clinical improvement and striatal DAT availability. In conclusion, ADHD patients with low DAT availability seem not to respond to therapy with MPH.

Attention-deficit disorder (attention-deficit/ hyperactivity disorder without hyperactivity): a neurobiologically and behaviorally distinct disorder from attention-deficit/hyperactivity disorder (with hyperactivity)

Most studies of attention-deficit/hyperactivity disorder (ADHD) have focused on the combined type and emphasized a core problem in response inhibition. It is proposed here that the core problem in the truly inattentive type of ADHD (not simply the subthreshold combined type) is in working memory. It is further proposed that laboratory measures, such as complex-span and dual-task dichotic listening tasks, can detect this. Children with the truly inattentive type of ADHD, rather than being distractible, may instead be easily bored, their problem being more in motivation (underarousal) than in inhibitory control. Much converging evidence points to a primary disturbance in the striatum (a frontal-striatal loop) in the combined type of ADHD. It is proposed here that the primary disturbance in truly inattentive-type ADHD (ADD) is in the cortex (a frontal-parietal loop). Finally, it is posited that these are not two different types of ADHD, but two different disorders with different cognitive and behavioral profiles, different patterns of comorbidities, different responses to medication, and different underlying neurobiologies.

Attention-deficit hyperactivity disorder

Attention-deficit hyperactivity disorder (ADHD) is a disorder of inattention, impulsivity, and hyperactivity that affects 8-12% of children worldwide. Although the rate of ADHD falls with age, at least half of children with the disorder will have impairing symptoms in adulthood. Twin, adoption, and molecular genetic studies show ADHD to be highly heritable, and other findings have recorded obstetric complications and psychosocial adversity as predisposing risk factors. Converging evidence from animal and human studies implicates the dysregulation of frontal-subcortical-cerebellar catecholaminergic circuits in the pathophysiology of ADHD, and molecular imaging studies suggest that abnormalities of the dopamine transporter lead to impaired neurotransmission. Studies during the past decade have shown the safety and effectiveness of new non-stimulant drugs and long-acting formulations of methylphenidate and amfetamine. Other investigations have also clarified the appropriate role of targeted psychosocial treatments in the context of ongoing pharmacotherapy.