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Serra M, Simola N, Pollack AE, Costa G. Brain dysfunctions and neurotoxicity induced by psychostimulants in experimental models and humans: an overview of recent findings. Neural Regen Res 2024; 19:1908-1918. [PMID: 38227515 DOI: 10.4103/1673-5374.390971] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2023] [Accepted: 11/10/2023] [Indexed: 01/17/2024] Open
Abstract
Preclinical and clinical studies indicate that psychostimulants, in addition to having abuse potential, may elicit brain dysfunctions and/or neurotoxic effects. Central toxicity induced by psychostimulants may pose serious health risks since the recreational use of these substances is on the rise among young people and adults. The present review provides an overview of recent research, conducted between 2018 and 2023, focusing on brain dysfunctions and neurotoxic effects elicited in experimental models and humans by amphetamine, cocaine, methamphetamine, 3,4-methylenedioxymethamphetamine, methylphenidate, caffeine, and nicotine. Detailed elucidation of factors and mechanisms that underlie psychostimulant-induced brain dysfunction and neurotoxicity is crucial for understanding the acute and enduring noxious brain effects that may occur in individuals who use psychostimulants for recreational and/or therapeutic purposes.
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Affiliation(s)
- Marcello Serra
- Department of Biomedical Sciences, Section of Neuroscience, University of Cagliari, Cagliari, Italy
| | - Nicola Simola
- Department of Biomedical Sciences, Section of Neuroscience, University of Cagliari, Cagliari, Italy
| | - Alexia E Pollack
- Department of Biology, University of Massachusetts-Boston, Boston, MA, USA
| | - Giulia Costa
- Department of Biomedical Sciences, Section of Neuroscience, University of Cagliari, Cagliari, Italy
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Abstract
Recent epidemiological evidence indicates that diagnosis of attention-deficit/hyperactivity disorder (ADHD) is associated with increased risk for diseases of the basal ganglia and cerebellum, including Parkinson's disease (PD). The evidence reviewed here indicates that deficits in striatal dopamine are a shared component of the causal chains that produce these disorders. Neuropsychological studies of adult ADHD, prodromal PD, and early-stage PD reveal similar deficits in executive functions, memory, attention, and inhibition that are mediated by similar neural substrates. These and other findings are consistent with the possibility that ADHD may be part of the PD prodrome. The mechanisms that may mediate the association between PD and ADHD include neurotoxic effects of stimulants, other environmental exposures, and Lewy pathology. Understanding the nature of the association between PD and ADHD may provide insight into the etiology and pathogenesis of both disorders. The possible contribution of stimulants to this association may have important clinical and public health implications.
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Li GHY, Ge GM, Cheung CL, Ip P, Coghill D, Wong ICK. Evaluation of causality between ADHD and Parkinson's disease: Mendelian randomization study. Eur Neuropsychopharmacol 2020; 37:49-63. [PMID: 32565043 DOI: 10.1016/j.euroneuro.2020.06.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/02/2020] [Revised: 05/25/2020] [Accepted: 06/02/2020] [Indexed: 12/11/2022]
Abstract
In a retrospective cohort study, patients with attention-deficit hyperactivity disorder (ADHD) and psychostimulant prescription were associated with increased risk of Parkinson's disease (PD). It is unclear whether ADHD per se or psychostimulant prescription is associated with PD. We aim to determine if genetic correlation or/and causal association exists between ADHD and PD using summary statistics obtained from the largest meta-analysis of genome-wide association studies of ADHD (20,183 cases; 35,191 controls) and PD (26,421 cases; 442,271 controls). Genetic correlation was tested between ADHD and PD by linkage disequilibrium score regression. Causal estimate was assessed by inverse-variance weighted (IVW) method as the main mendelian randomization analysis, with sensitivity analyses to detect horizontal pleiotropy. Weak and inverse genetic correlation existed between ADHD and PD (r=-0.100;SE=0.045;P = 0.026). Univariable IVW analysis with 10 and 77 genetic instruments respectively revealed null association for ADHD with PD (OR=0.930 per doubling in odds of ADHD; 95% CI:0.792-1.092) and PD with ADHD (OR=0.986 per doubling in odds of PD; 95% CI:0.956-1.015). Multivariable IVW analyses adjusted for BMI/smoking also revealed null association of ADHD with PD. Using 58 PD-associated genetic instruments, multivariable IVW analysis with/without adjustment for BMI/smoking suggested a weak and inverse causal association for PD on ADHD, but cautious interpretation is required. This well-powered study did not support causality between ADHD and PD. The observed positive association between ADHD and PD is more likely to be caused by unmeasured confounders. As psychostimulant use is associated with high risk of early-onset PD, future research should focus on this area.
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Affiliation(s)
- Gloria Hoi-Yee Li
- Department of Pharmacology and Pharmacy, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong
| | - Grace Mengqin Ge
- Department of Pharmacology and Pharmacy, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong
| | - Ching-Lung Cheung
- Department of Pharmacology and Pharmacy, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong.
| | - Patrick Ip
- Department of Paediatrics and Adolescents Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong
| | - David Coghill
- Departments of Paediatrics and Psychiatry, University of Melbourne, Melbourne, 3052, Australia; Murdoch Children's Research Institute, Melbourne, 3052, Australia
| | - Ian Chi-Kei Wong
- Department of Pharmacology and Pharmacy, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong; Research Department of Practice and Policy, School of Pharmacy, University College London, London, UK.
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Curtin K, Fleckenstein AE, Keeshin BR, Yurgelun-Todd DA, Renshaw PF, Smith KR, Hanson GR. Increased risk of diseases of the basal ganglia and cerebellum in patients with a history of attention-deficit/hyperactivity disorder. Neuropsychopharmacology 2018; 43:2548-2555. [PMID: 30209407 PMCID: PMC6224615 DOI: 10.1038/s41386-018-0207-5] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/16/2018] [Revised: 08/10/2018] [Accepted: 08/28/2018] [Indexed: 12/13/2022]
Abstract
Attention-deficit/hyperactivity disorder (ADHD) is marked by an ongoing pattern of inattention and/or hyperactivity and involves dysregulated dopaminergic pathways. Dopaminergic agents (i.e., amphetamine and methylphenidate) are thus prescribed to treat ADHD. As little is known regarding long-term consequences of either ADHD or its treatment, the objective of this study was to determine if either alters the risk of diseases of the basal ganglia and cerebellum, including Parkinson's disease. Statewide medical records from 1996 to 2016 were retrieved from the Utah Population Database to conduct a retrospective cohort study. Participants included ADHD patients (International Classification of Diseases, 9th revision (ICD-9) diagnosis codes 314.0-314.2, 314.8, 314.9) and 5:1 random sex-matched and age-matched subjects with no ADHD diagnosis history. Both patients and non-ADHD subjects met the following eligibility criteria: (1) no prior diagnosis of Parkinson's disease, secondary parkinsonism, basal ganglia disease, or essential tremor (ICD-9 codes 332.0, 332.1, 333.0, 333.1), (2) born in 1950 or later and age ≥20 years at last follow-up, and (3) no history of substance abuse (illicit drugs or alcohol). Outcomes were measured as time to diagnosis of diseases of the basal ganglia and cerebellum, death, or study-end. A Cox model incorporating a competing risk of death was used to provide hazard ratio estimates. Patients with ADHD (N = 31,769) had a 2.4-fold increased risk of basal ganglia and cerebellum diseases (95% confidence interval (CI): 2.0-3.0; P < 0.0001) compared with 158,790 non-ADHD persons, after controlling for sex and age and adjusting for tobacco use and psychotic conditions. In 4960 ADHD patients prescribed psychostimulants, risk of basal ganglia and cerebellum diseases between ages 21 and 49 years was especially pronounced, at 8.6-fold (95% CI: 4.8-15.6; P < 0001). The association of ADHD patients prescribed psychostimulants with higher risk of diseases of the basal ganglia and cerebellum may reflect a more severe ADHD phenotype rather than a direct association between prescribed stimulant use and basal ganglia or cerebellum disorders. Future studies to assess and stratify patient risk so as to inform treatment are warranted.
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Affiliation(s)
- Karen Curtin
- 0000 0001 2193 0096grid.223827.eDepartment of Internal Medicine, University of Utah School of Medicine, Salt Lake City, UT USA
| | - Annette E. Fleckenstein
- 0000 0001 2193 0096grid.223827.eUniversity of Utah School of Dentistry, Salt Lake City, UT USA
| | - Brooks R. Keeshin
- 0000 0001 2193 0096grid.223827.eDepartment of Pediatrics, University of Utah School of Medicine, Salt Lake City, UT USA ,0000 0004 0442 6404grid.415178.eDepartment of Pediatric Psychiatry, Intermountain Healthcare Primary Children’s Hospital, Salt Lake City, UT USA
| | - Deborah A. Yurgelun-Todd
- 0000 0001 2193 0096grid.223827.eDepartment of Psychiatry, University of Utah School of Medicine, Salt Lake City, UT USA
| | - Perry F. Renshaw
- 0000 0001 2193 0096grid.223827.eDepartment of Psychiatry, University of Utah School of Medicine, Salt Lake City, UT USA
| | - Ken R. Smith
- 0000 0001 2193 0096grid.223827.eHuman Development and Family Studies, University of Utah, Salt Lake City, UT USA
| | - Glen R. Hanson
- 0000 0001 2193 0096grid.223827.eUniversity of Utah School of Dentistry, Salt Lake City, UT USA
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van Elst LT, Maier S, Klöppel S, Graf E, Killius C, Rump M, Sobanski E, Ebert D, Berger M, Warnke A, Matthies S, Perlov E, Philipsen A. The effect of methylphenidate intake on brain structure in adults with ADHD in a placebo-controlled randomized trial. J Psychiatry Neurosci 2016; 41:422-430. [PMID: 27575717 PMCID: PMC5082513 DOI: 10.1503/jpn.150320] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
BACKGROUND Based on animal research several authors have warned that the application of methylphenidate, the first-line drug for the treatment of attention-deficit/hyperactivity disorder (ADHD), might have neurotoxic effects potentially harming the brain. We investigated whether methylphenidate application, over a 1-year period, results in cerebral volume decrease. METHODS We acquired structural MRIs in a double-blind study comparing methylphenidate to placebo. Global and regional brain volumes were analyzed at baseline, after 3 months and after 12 months using diffeomorphic anatomic registration through exponentiated lie algebra. RESULTS We included 131 adult patients with ADHD into the baseline sample, 98 into the 3-month sample (54 in the methylphenidate cohort and 44 in the placebo cohort) and 76 into the 1-year sample (37 in the methylphenidate cohort and 29 in the placebo cohort). Methylphenidate intake compared with placebo did not lead to any detectable cerebral volume loss; there was a trend toward bilateral cerebellar grey matter increase. LIMITATIONS Detecting possible neurotoxic effects of methylphenidate might require a longer observation period. CONCLUSION There is no evidence of grey matter volume loss after 1 year of methylphenidate treatment in adult patients with ADHD.
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Affiliation(s)
- Ludger Tebartz van Elst
- Correspondence to: L. Tebartz van Elst, Section for Experimental Neuropsychiatry, Hauptstr. 5, 79104, Freiburg, Germany;
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Korpi ER, den Hollander B, Farooq U, Vashchinkina E, Rajkumar R, Nutt DJ, Hyytiä P, Dawe GS. Mechanisms of Action and Persistent Neuroplasticity by Drugs of Abuse. Pharmacol Rev 2015; 67:872-1004. [DOI: 10.1124/pr.115.010967] [Citation(s) in RCA: 101] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
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Sahin S, Yuce M, Alacam H, Karabekiroglu K, Say GN, Salıs O. Effect of methylphenidate treatment on appetite and levels of leptin, ghrelin, adiponectin, and brain-derived neurotrophic factor in children and adolescents with attention deficit and hyperactivity disorder. Int J Psychiatry Clin Pract 2014; 18:280-7. [PMID: 24994482 DOI: 10.3109/13651501.2014.940054] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
OBJECTIVES We aimed to explore whether the use of methylphenidate relates leptin, ghrelin, adiponectin, and brain-derived neurotrophic factor (BDNF). In addition, the relationship between methylphenidate-related weight loss in attention deficit hyperactivity disorder (ADHD) patients and these biomolecules were evaluated. METHODS Thirty ADHD patients receiving methylphenidate and 20 healthy controls were included. Leptin, ghrelin, adiponectin, and BDNF levels were measured at baseline and after two-month treatment in both groups. RESULTS At baseline, leptin, ghrelin, adiponectin, and BDNF levels were similar in the ADHD and control groups. The most common adverse events occurring in the ADHD group after a 2-month treatment period included loss of appetite (70%) and weight loss (66.7%). A significant difference was found in body weight, BMI, and CGI scores of the ADHD patients after the treatment. While post-treatment ghrelin and adiponectin levels were significantly higher in the ADHD group, BDNF level was significantly lower. Post-treatment decrease in leptin levels was not significant. CONCLUSIONS Leptin and BDNF were not associated with poor appetite and/or weight loss due to methylphenidate treatment. However, ghrelin and adiponectin might be biomolecules that play a role in underlying neurobiological mechanisms of methylphenidate-related appetite or weight loss.
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Affiliation(s)
- Serkan Sahin
- Child and Adolescent Psychiatry Clinic, Balıkesir Atatürk State Hospital , Balikesir , Turkey
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Is the treatment with psychostimulants in children and adolescents with attention deficit hyperactivity disorder harmful for the dopaminergic system? ACTA ACUST UNITED AC 2013; 5:71-81. [PMID: 23605387 DOI: 10.1007/s12402-013-0105-y] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2013] [Accepted: 03/09/2013] [Indexed: 12/13/2022]
Abstract
A major concern regarding psychostimulant medication (amphetamine and methylphenidate) in the treatment of children and adolescents with attention deficit/hyperactivity disorder (ADHD) are the potential adverse effects to the developing brain, particularly in regard to dopaminergic brain function. The present review focuses on the pharmacology of these psychostimulants, their mode of action in the human brain and their potential neurotoxic effects to the developing brain in animals, particularly concerning DA brain function. The potential clinical significance of these findings for the treatment of ADHD in children and adolescents is discussed. Studies on sensitization to psychostimulants' rewarding effects, which is a process expected to increase the risk of substance abuse in humans, are not included. The available findings in non-human primates support the notion that the administration of amphetamine and methylphenidate with procedures simulating clinical treatment conditions does not lead to long-term adverse effects in regard to development, neurobiology or behaviour as related to the central dopaminergic system.
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Frölich J, Banaschewski T, Spanagel R, Döpfner M, Lehmkuhl G. [The medical treatment of attention deficit hyperactivity disorder (ADHD) with amphetamines in children and adolescents]. ZEITSCHRIFT FUR KINDER-UND JUGENDPSYCHIATRIE UND PSYCHOTHERAPIE 2012; 40:287-99; quiz 299-300. [PMID: 22869222 DOI: 10.1024/1422-4917/a000185] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
INTRODUCTION Psychostimulants (methylphenidate and amphetamines) are the drugs of first choice in the pharmacological treatment of children and adolescents with attention deficit hyperactivity disorder (ADHD). OBJECTIVE We summarize the pharmacological characteristics of amphetamines and compare them with methylphenidate, special emphasis being given to a comparison of effects and side effects of the two substances. Finally, we analyze the abuse and addiction risks. METHODS Publications were chosen based on a Medline analysis for controlled studies and meta-analyses published between 1980 and 2011; keywords were amphetamine, amphetamine salts, lisdexamphetamine, controlled studies, and metaanalyses. RESULTS AND DISCUSSION Amphetamines generally exhibit some pharmacologic similarities with methylphenidate. However, besides inhibiting dopamine reuptake amphetamines also cause the release of monoamines. Moreover, plasma half-life is significantly prolonged. The clinical efficacy and tolerability of amphetamines is comparable to methylphenidate. Amphetamines can therefore be used if the individual response to methylphenidate or tolerability is insufficient before switching to a nonstimulant substance, thus improving the total response rate to psychostimulant treatment. Because of the high abuse potential of amphetamines, especially in adults, the prodrug lisdexamphetamine (Vyvanse) could become an effective treatment alternative. Available study data suggest a combination of high clinical effect size with a beneficial pharmacokinetic profile and a reduced abuse risk. CONCLUSIONS In addition to methylphenidate, amphetamines serve as important complements in the psychostimulant treatment of ADHD. Future studies should focus on a differential comparison of the two substances with regard to their effects on different core symptom constellations and the presence of various comorbidities.
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Affiliation(s)
- Jan Frölich
- Zentralinstitut für Seelische Gesundheit, Klinik und Poliklinik für Psychiatrie und Psychotherapie des Kindes- und Jugendalters, Mannheim.
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Schmidt AJ, Krieg JC, Clement HW, Gebhardt S, Schulz E, Heiser P. Impact of drugs approved for treating ADHD on the cell survival and energy metabolism: an in-vitro study in human neuronal and immune cells. J Psychopharmacol 2010; 24:1829-33. [PMID: 19605603 DOI: 10.1177/0269881109105563] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The oxidative and antioxidative properties of psychostimulants such as methylphenidate and amphetamine are discussed controversially. The aim of the present study was to evaluate the impact of psychostimulants and atomoxetine in different concentrations between 31.25 and 5000 ng/ml on the survival of human neuronal (neuroblastoma SH-SY5Y) and immune (monocytic U-937) cells and the impact of psychostimulants and atomoxetine in different concentrations between 500 and 5000 ng/ml on energy metabolism (adenosine triphosphate [ATP] content) in SH-SY5Y cells. Statistical analysis revealed that incubation for 24 h with amphetamine led to a significantly enhanced cell survival in both cell lines after treatment with various (32.5, 125, 250 and 1250 ng/ml) concentrations. Methylphenidate and atomoxetine induced a significantly enhanced cell survival at lower concentrations in the SH-SY5Y cell line, whereas in the U-937 cell line higher concentrations increased the cell survival. Incubation with the highest concentration of methylphenidate (5000 ng/ml) caused a significant reduction of cell survival in both cell types. Measurement of ATP contents in the neuronal cell line revealed no significant effects of the investigated compounds. Our results show that the examined substances exert concentration-dependent effects on cell survival in both applied cell lines.
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Affiliation(s)
- A J Schmidt
- Department of Psychiatry and Psychotherapy, Philipps-University, Marburg, Germany
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Berman SM, Kuczenski R, McCracken JT, London ED. Potential adverse effects of amphetamine treatment on brain and behavior: a review. Mol Psychiatry 2009; 14:123-42. [PMID: 18698321 PMCID: PMC2670101 DOI: 10.1038/mp.2008.90] [Citation(s) in RCA: 157] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/31/2008] [Revised: 07/03/2008] [Accepted: 07/18/2008] [Indexed: 01/09/2023]
Abstract
Amphetamine stimulants have been used medically since early in the twentieth century, but they have a high abuse potential and can be neurotoxic. Although they have long been used effectively to treat attention deficit hyperactivity disorder (ADHD) in children and adolescents, amphetamines are now being prescribed increasingly as maintenance therapy for ADHD and narcolepsy in adults, considerably extending the period of potential exposure. Effects of prolonged stimulant treatment have not been fully explored, and understanding such effects is a research priority. Because the pharmacokinetics of amphetamines differ between children and adults, reevaluation of the potential for adverse effects of chronic treatment of adults is essential. Despite information on the effects of stimulants in laboratory animals, profound species differences in susceptibility to stimulant-induced neurotoxicity underscore the need for systematic studies of prolonged human exposure. Early amphetamine treatment has been linked to slowing in height and weight growth in some children. Because the number of prescriptions for amphetamines has increased several fold over the past decade, an amphetamine-containing formulation is the most commonly prescribed stimulant in North America, and it is noteworthy that amphetamines are also the most abused prescription medications. Although early treatment does not increase risk for substance abuse, few studies have tracked the compliance and usage profiles of individuals who began amphetamine treatment as adults. Overall, there is concern about risk for slowed growth in young patients who are dosed continuously, and for substance abuse in patients first medicated in late adolescence or adulthood. Although most adult patients also use amphetamines effectively and safely, occasional case reports indicate that prescription use can produce marked psychological adverse events, including stimulant-induced psychosis. Assessments of central toxicity and adverse psychological effects during late adulthood and senescence of adults who receive prolonged courses of amphetamine treatment are warranted. Finally, identification of the biological factors that confer risk and those that offer protection is also needed to better specify the parameters of safe, long-term, therapeutic administration of amphetamines to adults.
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Affiliation(s)
- S M Berman
- Department of Psychiatry and Biobehavioral Sciences, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, CA 90024-1759, USA
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Berman S, O'Neill J, Fears S, Bartzokis G, London ED. Abuse of amphetamines and structural abnormalities in the brain. Ann N Y Acad Sci 2008; 1141:195-220. [PMID: 18991959 DOI: 10.1196/annals.1441.031] [Citation(s) in RCA: 169] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
We review evidence that structural brain abnormalities are associated with abuse of amphetamines. A brief history of amphetamine use/abuse and evidence for toxicity is followed by a summary of findings from structural magnetic resonance imaging (MRI) studies of human subjects who had abused amphetamines and children who were exposed to amphetamines in utero. Evidence comes from studies that used a variety of techniques including manual tracing, pattern matching, voxel-based, tensor-based, or cortical thickness mapping, quantification of white matter signal hyperintensities, and diffusion tensor imaging. Ten studies compared controls to individuals who were exposed to methamphetamine. Three studies assessed individuals exposed to 3-4-methylenedioxymethamphetamine (MDMA). Brain structural abnormalities were consistently reported in amphetamine abusers, as compared to control subjects. These included lower cortical gray matter volume and higher striatal volume than control subjects. These differences might reflect brain features that could predispose to substance dependence. High striatal volumes might also reflect compensation for toxicity in the dopamine-rich basal ganglia. Prenatal exposure was associated with striatal volume that was below control values, suggesting that such compensation might not occur in utero. Several forms of white matter abnormality are also common and may involve gliosis. Many of the limitations and inconsistencies in the literature relate to techniques and cross-sectional designs, which cannot infer causality. Potential confounding influences include effects of pre existing risk/protective factors, development, gender, severity of amphetamine abuse, abuse of other drugs, abstinence, and differences in lifestyle. Longitudinal designs in which multimodal datasets are acquired and are subjected to multivariate analyses would enhance our ability to provide general conclusions regarding the associations between amphetamine abuse and brain structure.
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Affiliation(s)
- Steven Berman
- Psychiatry and Biobehavioral Sciences, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, CA 90024-1759, USA
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13
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Fleckenstein AE, Volz TJ, Hanson GR. Psychostimulant-induced alterations in vesicular monoamine transporter-2 function: neurotoxic and therapeutic implications. Neuropharmacology 2008; 56 Suppl 1:133-8. [PMID: 18662707 PMCID: PMC2634813 DOI: 10.1016/j.neuropharm.2008.07.002] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2008] [Revised: 07/02/2008] [Accepted: 07/02/2008] [Indexed: 11/20/2022]
Abstract
The vesicular monoamine transporter-2 (VMAT-2) is an important regulator of intraneuronal monoamine concentrations and disposition as this protein sequesters critical cytoplasmic monoaminergic transmitters and contributes to their subsequent exocytotic release. This review primarily discusses the impact of psychoactive drugs (including those with abuse potential) on dopamine (DA)-related VMAT-2 and its function. In particular, the different responses by DA-related VMAT-2 and associated vesicles to plasmalemmal uptake blockers like methylphenidate and releasers like methamphetamine are presented. Recent preclinical findings suggest that vesicular transporter systems are highly regulatable, both by changes in localization as well as alterations in the kinetics of the VMAT-2 protein. The capacity for such shifts in VMAT-2 functions suggests the presence of physiological regulation that likely influences the activity of DA systems. In addition, these findings may contribute to our understanding of the pathogenesis of a variety of DA-related disorders such as substance abuse and Parkinson's disease and also suggest new therapeutic targets for treating such diseases.
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Affiliation(s)
- Annette E Fleckenstein
- Department of Pharmacology and Toxicology, University of Utah, Salt Lake City, UT 84112, USA
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Waugh JL, Miller VS, Chudnow RS, Dowling MM. Juvenile Huntington disease exacerbated by methylphenidate: case report. J Child Neurol 2008; 23:807-9. [PMID: 18658080 DOI: 10.1177/0883073808314152] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The authors describe the case of an 8-year-old boy, otherwise healthy, who presented with symptoms consistent with attention-deficit hyperactivity disorder (ADHD) and was started on a trial of methylphenidate. Within 4 weeks, he experienced a rapid decline in fine motor skills, with dysarthria, intention tremor, motor impersistence, and diffusely increased tone. Symptoms persisted despite cessation of methylphenidate. At that time, a paternal history of Huntington disease was disclosed. Molecular analysis revealed an expansion in CAG repeats to 75 copies, within the range characteristic of juvenile Huntington disease. This report raises the possibility that use of dopaminergic agonists in patients with a family history of Huntington disease may lead to clinical exacerbation of motor symptoms and/or unwitting diagnosis in an unprepared family.
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Affiliation(s)
- Jeff L Waugh
- Department of Pediatrics, Children's Medical Center of Dallas, Texas, USA.
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Abstract
OBJECTIVE A review of amphetamine treatment for attention-deficit/hyperactivity disorder (ADHD) was conducted, to obtain information on the long-term neurological consequences of this therapy. METHOD Several databases were accessed for research articles on the effects of amphetamine in the brain of laboratory animals and ADHD diagnosed individuals. RESULTS In early studies, high doses of amphetamine, comparable to amounts used by addicts, were shown to damage dopaminergic pathways. More recent studies, using therapeutic regimens, appear contradictory. One paradigm shows significant decreases in striatal dopamine and transporter density after oral administration of "therapeutic" doses in primates. Another shows morphological evidence of "trophic" dendritic growth in the brains of adult and juvenile rats given systemic injections mimicking "therapeutic" treatment. Imaging studies of ADHD-diagnosed individuals show an increase in striatal dopamine transporter availability that may be reduced by methylphenidate treatment. CONCLUSION Clarification of the neurological consequences of chronic AMPH treatment for ADHD is needed.
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Williard RL, Middaugh LD, Zhu HJB, Patrick KS. Methylphenidate and its ethanol transesterification metabolite ethylphenidate: brain disposition, monoamine transporters and motor activity. Behav Pharmacol 2007; 18:39-51. [PMID: 17218796 DOI: 10.1097/fbp.0b013e3280143226] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Ethylphenidate is formed by metabolic transesterification of methylphenidate and ethanol. Study objectives were to (a) establish that ethylphenidate is formed in C57BL/6 (B6) mice; (b) compare the stimulatory effects of ethylphenidate and methylphenidate enantiomers; (c) determine methylphenidate and ethylphenidate plasma and brain distribution and (d) establish in-vitro effects of methylphenidate and ethylphenidate on monoamine transporter systems. Experimental results were that: (a) coadministration of ethanol with the separate methylphenidate isomers enantioselectively produced l-ethylphenidate; (b) d and dl-forms of methylphenidate and ethylphenidate produced dose-responsive increases in motor activity with stimulation being less for ethylphenidate; (c) plasma and whole-brain concentrations were greater for ethylphenidate than methylphenidate and (d) d and DL-methylphenidate and ethylphenidate exhibited comparably potent low inhibition of the dopamine transporter, whereas ethylphenidate was a less potent norepinephrine transporter inhibitor. These experiments establish the feasibility of the B6 mouse model for examining the interactive effects of ethanol and methylphenidate. As reported for humans, concurrent exposure of B6 mice to methylphenidate and ethanol more readily formed l-ethylphenidate than d-ethylphenidate, and the l-isomers of both methylphenidate and ethylphenidate were biologically inactive. The observed reduced stimulatory effect of d-ethylphenidate relative to d-methylphenidate appears not to be the result of brain dispositional factors, but rather may be related to its reduced inhibition of the norepinephrine transporter, perhaps altering the interaction of dopaminergic and noradrenergic neural systems.
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Affiliation(s)
- Robin L Williard
- Department of Pharmaceutical Sciences, Medical University of South Carolina, Charleston, South Carolina 29482, USA
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17
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Ludolph AG, Schaz U, Storch A, Liebau S, Fegert JM, Boeckers TM. Methylphenidate exerts no neurotoxic, but neuroprotective effects in vitro. J Neural Transm (Vienna) 2006; 113:1927-34. [PMID: 16736241 DOI: 10.1007/s00702-006-0487-5] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2006] [Accepted: 03/13/2006] [Indexed: 11/24/2022]
Abstract
Methylphenidate (MPH) is the most common used drug in child and adolescent psychiatry. Despite of this fact, however, little is known about its exact pharmacological mechanisms. Here we investigated the toxic effects of MPH in vitro in human embryonic kidney (HEK-293) cells stably expressing the human dopamine transporter (HEK-hDAT cells) and in cultured rat embryonic (E14.5) mesencephalic cultures. MPH alone (up to 1 mM) affected neither the growth of HEK-hDAT cells nor the survival of dopaminergic (DA) neurons in primary cultures after treatment up to 72 h. No differences in neuronal arborisation or in the density of synapses were detected. 1-methyl-4-phenylpyridinium (MPP(+)) showed no toxic effect in HEK-293 cells, but had significant toxic effects in HEK-hDAT cells and DA neurons. MPH (1 microM - 1 mM) dose-dependently reduced this cytotoxicity in HEK-hDAT cells and primary mesencephalic DA neurons. The presented results show that application of MPH alone does not have any toxic effect on DA cells in vitro. The neurotoxic effects of MPP(+) could be significantly reduced by co-application of MPH, an effect that is most likely explained by MPH blocking the DAT.
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Affiliation(s)
- A G Ludolph
- Department of Child and Adolescent Psychiatry, University of Ulm, Ulm, Germany.
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18
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Grund T, Lehmann K, Bock N, Rothenberger A, Teuchert-Noodt G. Influence of methylphenidate on brain development--an update of recent animal experiments. Behav Brain Funct 2006; 2:2. [PMID: 16403217 PMCID: PMC1363724 DOI: 10.1186/1744-9081-2-2] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2005] [Accepted: 01/10/2006] [Indexed: 01/26/2023] Open
Abstract
Methylphenidate (MPH) is the most commonly used drug to treat attention deficit/hyperactivity disorder (ADHD) in children effectively and safely. In spite of its widespread application throughout one of the most plastic and sensitive phases of brain development, very little is known to date about its long-term effects on brain structure and function. Hence, this short review updates the influence of MPH on brain development, since recent human and animal studies suggest that MPH alters the dopaminergic system with long-term effects beyond the termination of treatment. Animal studies imply that the effects of MPH may depend on the neural responder system: Whereas structural and functional parameters are improved by MPH in animals with psychomotor impairments, they remain unaltered or get worse in healthy controls. While recent behavioural studies do not fully support such a differential effect of MPH in ADHD, the animal studies certainly prompt for further investigation of this issue. Furthermore, the abuse of MPH, when (rarely) intravenously applied, may even impair the maturation of dopaminergic fibres in subcortical brain areas. This argues for careful clinical assessment and diagnostics of ADHD symptomatology not only in conjunction with the prescription of MPH. Hence, one should be assured that MPH is only given to children with clear ADHD symptomatology leading to psychosocial impairment. The animal data suggest that under these conditions MPH is supportive for brain development and the related behaviour in children with ADHD.
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Affiliation(s)
- Thorsten Grund
- Department of Neuroanatomy, Faculty of Biology, University of Bielefeld, Universitätsstr. 25, D-33615 Bielefeld, Germany
| | - Konrad Lehmann
- Department of Neuroanatomy, Faculty of Biology, University of Bielefeld, Universitätsstr. 25, D-33615 Bielefeld, Germany
| | - Nathalie Bock
- Child and Adolescent Psychiatry, University of Göttingen, von-Siebold-Strasse 5, D-37075 Göttingen, Germany
| | - Aribert Rothenberger
- Child and Adolescent Psychiatry, University of Göttingen, von-Siebold-Strasse 5, D-37075 Göttingen, Germany
| | - Gertraud Teuchert-Noodt
- Department of Neuroanatomy, Faculty of Biology, University of Bielefeld, Universitätsstr. 25, D-33615 Bielefeld, Germany
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19
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Schwartz K, Weizman A, Rehavi M. The effect of psychostimulants on [3H]dopamine uptake and release in rat brain synaptic vesicles. J Neural Transm (Vienna) 2005; 113:1347-52. [PMID: 16362637 DOI: 10.1007/s00702-005-0383-4] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2005] [Accepted: 09/10/2005] [Indexed: 10/25/2022]
Abstract
Amphetamine and its derivatives are psychostimulants active at the plasma membrane monoamine transporters. In the present study we assessed the interaction of parachloroamphetamine, D-amphetamine, fenfluramine and methylendioxymethamphetamine with brain vesicular monoamine transporter using purified rat striatal synaptic vesicles. All four psychostimulants inhibited vesicular [(3)H]dopamine uptake in a competitive and dose-dependent manner and had no effect on [(3)H]dihydrotetrabenazine binding. At higher concentrations the drugs enhanced [(3)H]dopamine vesicular efflux. Parachloroamphetamine was the most potent agent while methylendioxymethamphetamine was the weakest one. The vesicular activities may be relevant to their neurotoxicity.
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Affiliation(s)
- K Schwartz
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
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Feron FJM, Hendriksen JGM, van Kroonenburgh MJPG, Blom-Coenjaerts C, Kessels AGH, Jolles J, Weber WEJ, Vles JSH. Dopamine transporter in attention-deficit hyperactivity disorder normalizes after cessation of methylphenidate. Pediatr Neurol 2005; 33:179-83. [PMID: 16139732 DOI: 10.1016/j.pediatrneurol.2005.04.008] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/30/2004] [Revised: 02/17/2005] [Accepted: 04/18/2005] [Indexed: 11/23/2022]
Abstract
Attention-deficit hyperactivity disorder (ADHD) is a common neurodevelopmental disorder of childhood, which is frequently treated with methylphenidate. The short-term response to treatment with methylphenidate is a substantial decrease in dopamine transporter density, with improvement in neuropsychological tests. In this study, single-photon emission computed tomography was used to investigate possible long-term alterations in the cerebral dopamine system after cessation of treatment with methylphenidate in five children with ADHD. Three months after initiation of treatment with methylphenidate, a reduction of the dopamine transporter in the striatal system was observed. Methylphenidate was administered for a period of 9 to 20 months. Follow-up with single-photon emission computed tomography after withdrawal of methylphenidate medication disclosed an increase of dopamine transporter activity comparable with pretreatment values. The observed upregulation of dopamine transporter activity might support the assumption that methylphenidate does not lead to permanent damage of the nigrostriatal dopaminergic pathways.
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Affiliation(s)
- Frans J M Feron
- Youth Health Care Division of the Regional Public Health Institute Maastricht, Maastricht, The Netherlands
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21
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McFadyen-Leussis MP, Lewis SP, Bond TLY, Carrey N, Brown RE. Prenatal exposure to methylphenidate hydrochloride decreases anxiety and increases exploration in mice. Pharmacol Biochem Behav 2004; 77:491-500. [PMID: 15006459 DOI: 10.1016/j.pbb.2003.12.011] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/08/2003] [Revised: 12/03/2003] [Accepted: 12/05/2003] [Indexed: 11/21/2022]
Abstract
The administration of methylphenidate (MPH) to girls and adults has increased in the last decade. Given the similarity of MPH to cocaine and the increasing possibility of embryonic exposure, the gestational effects of this stimulant on development must be considered. We administered MPH (5 mg/kg) or saline to female CD-1 mice at three different periods during pregnancy [embryonic (E) days 8-10, 12-14, and 16-18]. MPH-exposed pups were compared with the saline-treated pups for changes in physical, motor, and behavioral development at postnatal day (PND) 3-11. In adulthood (>60 days of age) these mice were tested in the open field, elevated plus maze, and water maze, and given an acute MPH challenge. We observed limited effects of MPH exposure on early developmental variables. In adulthood, mice exposed to MPH on E8-10 exhibited a general decrease in anxiety-related behaviors and a concomitant increase in exploratory behavior. Prenatal MPH exposure did not alter water maze performance or the response to an acute MPH challenge. Our data provide an initial overview of the possible effects occurring as a result of prenatal exposure to MPH, and strongly suggest that further studies of the in utero and developmental effects of psychostimulants are needed.
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McFadyen MP, Brown RE, Carrey N. Subchronic methylphenidate administration has no effect on locomotion, emotional behavior, or water maze learning in prepubertal mice. Dev Psychobiol 2002; 41:123-32. [PMID: 12209654 DOI: 10.1002/dev.10059] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Methylphenidate hydrochloride (Ritalin, MPH) is frequently prescribed as a treatment for children with attention deficit hyperactivity disorder (ADHD), yet little research has been conducted to determine its potential long-term neurobehavioral effects. We assessed the effects of subchronic MPH administration (2.5, 5, 10, 20, 40, or 80 mg/kg) on male CD-1 mice treated from 26 to 32 days of age. When tested at 33 days of age in the open field and elevated plus maze, there were no significant differences in spontaneous locomotion, exploration, or fear- and anxiety-related behaviors. Testing from 34 to 37 days of age in a water maze task revealed no significant effects of any dose of MPH on learning in this simple paradigm. While it is difficult to extrapolate directly from these results to clinical effects in humans, our results indicate that preexposure of mice to MPH late in the postnatal developmental period does not appear to alter later behavior. We are currently conducting additional studies to further probe the potential effects of MPH administration during development and to examine various contributing factors including stage of development, duration of MPH administration, complexity of the task used to assess behavioral changes, and type of cognitive process being analyzed (attention, nonspatial working memory, etc.).
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Affiliation(s)
- Melanie P McFadyen
- Department of Psychology, Dalhousie University, Halifax, NS, B3H 4J1, Canada
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Penner MR, McFadyen MP, Pinaud R, Carrey N, Robertson HA, Brown RE. Age-related distribution of c-fos expression in the striatum of CD-1 mice after acute methylphenidate administration. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 2002; 135:71-7. [PMID: 11978395 DOI: 10.1016/s0165-3806(02)00308-5] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Ritalin (methylphenidate hydrochloride, MPH) is the drug of choice for the treatment of attention deficit hyperactivity disorder. Previous research has shown that MPH administration affects the adult brain in a manner different from the young brain. In the current study, we set out to determine the target brain regions of acutely administered MPH at different stages of development. On postnatal days 3, 7, 11, 24, and 45, mice were treated with a single injection (s.c.) of saline, 5 or 20 mg/kg of MPH, and sacrificed 1 h later. Localization of c-fos expression was determined by immunocytochemistry. Compared to saline treated controls, mice treated with the high dose of MPH (20 mg/kg) showed dense Fos-immunoreactivity (Fos-IR) in the striatum. In most cases the low dose of MPH (5 mg/kg) produced only weak c-fos expression that was nearly indistinguishable from saline-treated controls. At PND 3 and 7, Fos-IR was localized in patches in the striatum. This patchy distribution of c-fos positive cells began to decline by PND 11 and was absent in PND 45 mice, with Fos-IR showing a scattered distribution throughout the striatum. The results of this study indicate that MPH induces the expression of c-fos in the same brain regions as cocaine and amphetamine, and that this expression is distributed differentially according to the age of the mouse.
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Affiliation(s)
- Marsha R Penner
- Department of Pharmacology, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4J1
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24
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Carrey N. Developmental neurobiology: implications for pediatric psychopharmacology. CANADIAN JOURNAL OF PSYCHIATRY. REVUE CANADIENNE DE PSYCHIATRIE 2001; 46:810-8. [PMID: 11761632 DOI: 10.1177/070674370104600904] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Pediatric psychopharmacology can only be properly understood within the context of developmental neurobiology. Normal maturation of the brain is characterized by the complex anatomic, molecular, and organizational changes required for optimal adaptive functioning. In many areas of the developing nervous system, neurons, cell processes, neurotransmitters, and trophic nerve growth factors are produced in far greater numbers and in different areas than in the mature brain. Psychopathology and stressful environments can lead to enduring changes in brain structure and functioning. A few select psychopharmacological treatments are reviewed to assess their potential impact on CNS development. More clinical and basic science studies are needed to determine whether current treatments have neurotoxic or neuroprotective effects when administered over extended critical early periods of the lifespan.
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Affiliation(s)
- N Carrey
- Dept. of Psychiatry, Dalhousie University, Halifax, Nova Scotia.
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25
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Sproson EJ, Chantrey J, Hollis C, Marsden CA, Fonel KC. Effect of repeated methylphenidate administration on presynaptic dopamine and behaviour in young adult rats. J Psychopharmacol 2001; 15:67-75. [PMID: 11448090 DOI: 10.1177/026988110101500202] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Methylphenidate, a dopamine reuptake inhibitor, is the most common treatment for attention-deficit hyperactivity disorder and may be prescribed for years, despite little evidence of any long-term benefit, nor knowledge of potential chronic side-effects. Therefore, this study examined the acute and longer-term behavioural effects and assessed striatal dopamine function following subchronic methylphenidate administration to adolescent rats. Male hooded Lister rats received methylphenidate (4 mg/kg i.p. twice daily for 4 days) or saline (1 ml/kg) and the acute locomotor and stereotype behaviour was monitored on days 1 and 4, novel object exploration on day 2 and, following 12 days drug withdrawal, the long-term effect examined on social interaction on day 16. Ex-vivo K+ (20 mM)- and methylphenidate (0.1 mM)-induced [3H]dopamine release from striatal slices and striatal monoamine content were measured on day 18. Compared with saline, methylphenidate induced mild hyperactivity without stereotypy but did not alter novel object exploration and, following withdrawal, had no long-term effect on social interaction. In striatal slices from controls, both K+ and methylphenidate elevated [3H]dopamine release (p < 0.01) while only combined treatment elevated release in methylphenidate pretreated rats, although striatal monoamine content was unaltered compared with control rats. In summary, a repeated dose of methylphenidate that had acute behavioural effects produced no long-term alteration in social interaction but attenuated presynaptic striatal dopamine function.
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Affiliation(s)
- E J Sproson
- School of Biomedical Sciences, Queen's Medical Centre, Nottingham University, UK
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Reneman L, De Bruin K, Lavalaye J, Gunning WB, Booij J. Addition of a 5-HT receptor agonist to methylphenidate potentiates the reduction of [123I]FP-CIT binding to dopamine transporters in rat frontal cortex and hippocampus. Synapse 2001; 39:193-200. [PMID: 11169768 DOI: 10.1002/1098-2396(20010301)39:3<193::aid-syn1000>3.0.co;2-f] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
The neurotoxic potential of amphetamine and related drugs is well documented. However, methylphenidate, an amphetamine derivative used in the treatment of attention deficit hyperactivity disorder, and known to increase synaptic dopamine (DA) levels, seems to lack neurotoxic potential. It is hypothesized that both dopaminergic and serotonergic systems are involved in the neurotoxicity of amphetamine derivatives. The purpose of the present study was to evaluate the neurotoxic potential of methylphenidate and to test whether stimulation of the serotonergic system may confer neurotoxic properties to methylphenidate for DA or serotonin (5-HT) neurons. In addition, the present study was undertaken to evaluate the necessity to perform future SPECT studies in individuals using both methylphenidate and 5-HT-acting agents. We therefore measured monoaminergic transporters in rat brain using radioligands suitable for SPECT imaging ([123I]beta-CIT and [123I]FP-CIT). Groups of rats were treated with methylphenidate or saline for 4 days. Additional groups were treated with the selective 5-HT(2) receptor agonist quipazine or the selective 5-HT reuptake blocker fluoxetine, alone or in combination with methylphenidate. Binding studies were performed 5 days after the last treatment. In a second experiment, methylphenidate in combination with quipazine, along with a control group, was retested. In this experiment, monoaminergic terminal density was estimated 2 weeks (rather than 5 days) after drug treatment. Five days, but not 2 weeks, after treatment a significant reduction in specific [123I]FP-CIT binding was observed in the frontal cortex and hippocampus of rats treated with methylphenidate in combination with quipazine. These changes probably do not reflect neurotoxic changes of frontal cortex and hippocampal DA terminal markers, but a compensatory downregulation of DA transporters. These findings suggest potential harmful effects of concomitant use of drugs directly activating 5-HT2 receptors in patients using methylphenidate.
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Affiliation(s)
- L Reneman
- Graduate School of Neurosciences, Department of Nuclear Medicine, Academic Medical Center, 1105 AZ Amsterdam, The Netherlands.
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27
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Fleckenstein AE, Gibb JW, Hanson GR. Differential effects of stimulants on monoaminergic transporters: pharmacological consequences and implications for neurotoxicity. Eur J Pharmacol 2000; 406:1-13. [PMID: 11011026 DOI: 10.1016/s0014-2999(00)00639-7] [Citation(s) in RCA: 178] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Many psychostimulants alter plasmalemmal monoaminergic transporter function. Some, such as cocaine, prevent the reuptake of newly released dopamine, serotonin or norepinephrine into their associated neurons. Others, such as the amphetamines, facilitate release of these transmitters into the extraneuronal space by causing a reversal of function of these carrier proteins. An understanding of how psychostimulants regulate the function of not only plasmalemmal, but also vesicular monoamine transporter function is important to appreciate the pharmacological and sometimes neurotoxic consequences of administering these drugs, as well as the physiological regulation of these carrier proteins. Hence, this review will describe recent ex vivo studies investigating the rapid and differential affects of several stimulants on both plasmalemmal and vesicular monoamine transporter function.
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Affiliation(s)
- A E Fleckenstein
- Department of Pharmacology and Toxicology, University of Utah, 30 South 2000 East, Rm 201, Salt Lake City, UT 84112, USA.
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Sachdev PS, Trollor JN. How high a dose of stimulant medication in adult attention deficit hyperactivity disorder? Aust N Z J Psychiatry 2000; 34:645-50. [PMID: 10954396 DOI: 10.1080/j.1440-1614.2000.00732.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
OBJECTIVE This paper examines clinical and neuroscientific evidence to address the question whether high doses of stimulant drugs offer additional advantages in the treatment of adult attention deficit hyperactivity disorder (ADHD) and at what cost. It attempts to arrive at a reasonable upper limit of dosage for clinical purposes. METHOD The study involves a selective review of the treatment studies of ADHD in children and adults and an examination of the pharmacokinetic and pharmacodynamic data on psychostimulants in humans and animals. RESULTS AND CONCLUSIONS The clinical and experimental data justify the use of chronic low-dose stimulant treatment of ADHD in adults, with the recommended upper limit of dose being 1 mg/kg for methylphenidate and 0.5 mg/kg for dexamphetamine. There is no empirical evidence of greater improvement with higher doses and any beneficial effect is likely to be compromised by the adverse effects, some of which can be very serious. The recommended doses should be exceeded only after careful consideration and objective documentation of beneficial and adverse consequences. Monitoring of drug levels in blood may be of some value for compliance or pharmacokinetic considerations, as there is a direct relationship between blood and brain levels as well as dopamine transporter occupancy. These recommendations are tentative and further clinical research is warranted.
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Affiliation(s)
- P S Sachdev
- School of Psychiatry, University of New South Wales and Neuropsychiatric Institute, Prince of Wales Hospital, Randwick, Australia.
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