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Willis GL, Freelance CB. Neurochemical Systems of the Retina Involved in the Control of Movement. Front Neurol 2017; 8:324. [PMID: 28725212 PMCID: PMC5497141 DOI: 10.3389/fneur.2017.00324] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2017] [Accepted: 06/21/2017] [Indexed: 12/30/2022] Open
Abstract
Recent studies have revealed that the retina may exert control over deep brain function and may be importantly involved in the etiology, progression, and treatment of disorders such as Parkinson's disease (PD). While such a concept is uncharted territory and even less is known about the mechanism by which this might be achieved, this study was undertaken to determine how retinal dopamine (DA), serotonin (5-HT), and melatonin (MEL) neurotransmitter systems might be involved in the control of movement in their own right. To explore these further, intravitreal (IVIT) injections of DA, 5-HT, and MEL were made 0.5 or 3 h prior to testing horizontal and vertical movement in the open field as well as assessment on three motor tests used routinely to evaluate movement as a preclinical model of PD. The doses of DA (2 µl of 25 and 75 µg/µl), 5-HT (2 µl of 5 and 15 µg/µl), and MEL (2 µl of 5 µg/µl) were chosen because of previous work demonstrating an anatomically precise effect of these transmitters after they were injected directly into the brain. The postinjection times of testing were also chosen on the basis of previous intracerebral and IVIT work intimating the importance of the circadian cycle in determining the efficacy of such effects. 0.5 h after IVIT injection of DA at the 25 and 75 µg/µl doses, significant inhibition of motor function was observed. While IVIT injection of 10 or 30 µg of 5-HT also inhibited motor performance, this was significantly less than that seen with DA. In fact, IVIT injection increases motor performance compared to vehicle injection on some parameters. The IVIT injection of 10 µg of MEL facilitated motor function on many parameters compared to DA, 5-HT, and vehicle injection. When rats were tested 3 h after IVIT injection, the inhibition of vertical movement was also observed compared to controls. The present results illustrate that specific retinal neurotransmitter systems participate in the normal control of bodily motor function. The possible involvement of these systems in movement disorders such as PD is the subject of ongoing research.
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Affiliation(s)
- Gregory L Willis
- Coliban Medical Centre, The Bronowski Institute of Behavioural Neuroscience, Kyneton, VIC, Australia
| | - Christopher B Freelance
- Coliban Medical Centre, The Bronowski Institute of Behavioural Neuroscience, Kyneton, VIC, Australia
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Crockett MJ, Siegel JZ, Kurth-Nelson Z, Ousdal OT, Story G, Frieband C, Grosse-Rueskamp JM, Dayan P, Dolan RJ. Dissociable Effects of Serotonin and Dopamine on the Valuation of Harm in Moral Decision Making. Curr Biol 2015; 25:1852-9. [PMID: 26144968 PMCID: PMC4518463 DOI: 10.1016/j.cub.2015.05.021] [Citation(s) in RCA: 79] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2015] [Revised: 05/09/2015] [Accepted: 05/12/2015] [Indexed: 01/10/2023]
Abstract
An aversion to harming others is a core component of human morality and is disturbed in antisocial behavior. Deficient harm aversion may underlie instrumental and reactive aggression, which both feature in psychopathy. Past work has highlighted monoaminergic influences on aggression, but a mechanistic account of how monoamines regulate antisocial motives remains elusive. We previously observed that most people show a greater aversion to inflicting pain on others than themselves. Here, we investigated whether this hyperaltruistic disposition is susceptible to monoaminergic control. We observed dissociable effects of the serotonin reuptake inhibitor citalopram and the dopamine precursor levodopa on decisions to inflict pain on oneself and others for financial gain. Computational models of choice behavior showed that citalopram increased harm aversion for both self and others, while levodopa reduced hyperaltruism. The effects of citalopram were stronger than those of levodopa. Crucially, neither drug influenced the physical perception of pain or other components of choice such as motor impulsivity or loss aversion, suggesting a direct and specific influence of serotonin and dopamine on the valuation of harm. We also found evidence for dose dependency of these effects. Finally, the drugs had dissociable effects on response times, with citalopram enhancing behavioral inhibition and levodopa reducing slowing related to being responsible for another's fate. These distinct roles of serotonin and dopamine in modulating moral behavior have implications for potential treatments of social dysfunction that is a common feature as well as a risk factor for many psychiatric disorders.
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Affiliation(s)
- Molly J Crockett
- Department of Experimental Psychology, University of Oxford, 9 South Parks Road, Oxford OX1 3UD, UK; Wellcome Trust Centre for Neuroimaging, University College London, 12 Queen Square, London WC1N 3BG, UK.
| | - Jenifer Z Siegel
- Department of Experimental Psychology, University of Oxford, 9 South Parks Road, Oxford OX1 3UD, UK
| | - Zeb Kurth-Nelson
- Wellcome Trust Centre for Neuroimaging, University College London, 12 Queen Square, London WC1N 3BG, UK; Max Planck-UCL Centre for Computational Psychiatry and Ageing, University College London, 12 Queen Square, London WC1N 3BG, UK
| | - Olga T Ousdal
- Wellcome Trust Centre for Neuroimaging, University College London, 12 Queen Square, London WC1N 3BG, UK; Department of Radiology, Haukeland University Hospital, Jonas Lies vei 65, 5021 Bergen, Norway
| | - Giles Story
- Wellcome Trust Centre for Neuroimaging, University College London, 12 Queen Square, London WC1N 3BG, UK
| | - Carolyn Frieband
- Wellcome Trust Centre for Neuroimaging, University College London, 12 Queen Square, London WC1N 3BG, UK
| | - Johanna M Grosse-Rueskamp
- Wellcome Trust Centre for Neuroimaging, University College London, 12 Queen Square, London WC1N 3BG, UK
| | - Peter Dayan
- Gatsby Computational Neuroscience Unit, University College London, Alexandra House, 17 Queen Square, London WC1N 3AR, UK
| | - Raymond J Dolan
- Wellcome Trust Centre for Neuroimaging, University College London, 12 Queen Square, London WC1N 3BG, UK; Max Planck-UCL Centre for Computational Psychiatry and Ageing, University College London, 12 Queen Square, London WC1N 3BG, UK
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Mao Z, Hsu A, Gupta S, Modi NB. Population pharmacodynamics of IPX066: an oral extended-release capsule formulation of carbidopa-levodopa, and immediate-release carbidopa-levodopa in patients with advanced Parkinson's disease. J Clin Pharmacol 2013; 53:523-31. [PMID: 23426902 PMCID: PMC3798100 DOI: 10.1002/jcph.63] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2012] [Accepted: 11/28/2012] [Indexed: 12/25/2022]
Abstract
A pharmacodynamic model is presented to describe the motor effects (tapping rate, Unified Parkinson's Disease Rating Scale [UPDRS] Part III, and investigator-rating of ON/OFF, including dyskinesia) of levodopa (LD) in patients with advanced idiopathic Parkinson's disease (PD) treated with immediate-release (IR) carbidopa-levodopa (CD-LD) or an extended-release (ER) formulation of CD-LD (IPX066). Twenty-seven patients participated in this open-label, randomized, single- and multiple-dose, crossover study. The pharmacodynamic models included a biophase effect site with a sigmoid E(max) transduction for tapping and UPDRS and an ordered categorical model for dyskinesia. The pharmacodynamics of LD was characterized by a conduction function with a half-life of 0.59 hours for tapping rate, and 0.4 hours for UPDRS Part III and dyskinesia. The LD concentration for half-maximal effect was 1530 ng/mL, 810 ng/mL, and 600 ng/mL for tapping rate, UPDRS Part III, and dyskinesia, respectively. The sigmoidicity of the transduction was 1.53, 2.5, and 2.1 for tapping rate, UPDRS Part III, and dyskinesia, respectively. External validation of the pharmacodynamic model using tapping rate indicated good performance of the model.
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Abstract
This paper reviews the clinically relevant determinants of levodopa peripheral pharmacokinetics and main observed changes in the levodopa concentration-effect relationship with Parkinson's disease (PD) progression. Available clinically practical strategies to optimise levodopa pharmacokinetics and pharmacodynamics are briefly discussed. Levodopa shows particular pharmacokinetics including an extensive presystemic metabolism, overcome by the combined use of extracerebral inhibitors of the enzyme L: -amino acid decarboxylase and rapid absorption in the proximal small bowel by a saturable facilitated transport system shared with other large neutral amino acids. Drug transport from plasma to the brain is mediated by the same carriers operating in the intestinal mucosa. The main strategies to assure reproducibility of both intestinal absorption and delivery to the brain, and the clinical effect include standardization of levodopa dosing with respect to meal times and a controlled dietary protein intake. Levodopa plasma half-life is very short, resulting in marked plasma drug concentration fluctuations which are matched, as the disease progresses, to swings in the therapeutic response ("wearing-off" phenomena). "Wearing-off" phenomena can also be associated, at the more advanced disease stages, with a "negative", both parkinsonism-exacerbating and dyskinetic effect of levodopa at low, subtherapeutic plasma concentrations. Dyskinesias may also be related to high-levodopa, excessive plasma concentrations. Recognition of the different levodopa toxic response patterns can be difficult on a clinical basis alone and simultaneous monitoring of the levodopa concentration-effect relationship may prove useful to disclose the underlying mechanism and in planning the correct management. Clinically practical strategies to optimise levodopa pharmacokinetics, and possibly its therapeutic response, include liquid drug solutions, controlled release formulations and the use of inhibitors of levodopa metabolism. Unfortunately, these attempts have proved so far only partly successful, due to the complex alterations in cerebral levodopa kinetics which accompany the progressive degeneration of the nigrostriatal dopaminergic system in PD patients.
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Gunzler SA, Koudelka C, Carlson NE, Pavel M, Nutt JG. Effect of low concentrations of apomorphine on parkinsonism in a randomized, placebo-controlled, crossover study. ACTA ACUST UNITED AC 2008; 65:193-8. [PMID: 18268187 DOI: 10.1001/archneurol.2007.58] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
OBJECTIVE To determine whether low concentrations of a dopamine agonist worsen parkinsonism, which would suggest that activation of presynaptic dopamine autoreceptors causes a super-off state. DESIGN Randomized, double-blind, placebo-controlled, crossover clinical trial. SETTING Academic movement disorders center. PATIENTS Patients with Parkinson disease and motor fluctuations. INTERVENTION Fourteen patients with Parkinson disease and motor fluctuations were randomized to receive 1 of 6 possible sequences of placebo, low-dose (subthreshold) apomorphine hydrochloride, and high-dose (threshold to suprathreshold) apomorphine hydrochloride infusions. Subthreshold doses of apomorphine hydrochloride (12.5 microg/kg/h every 2 hours and 25 microg/kg/h every 2 hours), threshold to suprathreshold doses of apomorphine hydrochloride (50 microg/kg/h every 2 hours and 100 microg/kg/h every 2 hours), and placebo were infused for 4 hours daily for 3 consecutive days. MAIN OUTCOME MEASURES Finger and foot tapping rates. RESULTS There was no decline in finger or foot tapping rates during the low-dose apomorphine hydrochloride infusions relative to placebo. The high-dose infusions increased foot tapping (P < .001) and trended toward increasing finger tapping compared with placebo infusions. CONCLUSIONS Subthreshold concentrations of apomorphine did not worsen parkinsonism, suggesting that presynaptic dopamine autoreceptors are not important to the motor response in moderate to advanced Parkinson disease. Trial Registration clinicaltrials.gov Identifier: NCT00472355.
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Affiliation(s)
- Steven A Gunzler
- Movement Disorders Center, Neurological Institute, University Hospitals Case Medical Center and Case Western Reserve University School of Medicine, 11100 Euclid Ave, Cleveland, OH 44106, USA.
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Holford N, Nutt JG. Disease progression, drug action and Parkinson's disease: why time cannot be ignored. Eur J Clin Pharmacol 2007; 64:207-16. [PMID: 18092155 DOI: 10.1007/s00228-007-0427-9] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2007] [Accepted: 11/22/2007] [Indexed: 12/21/2022]
Affiliation(s)
- Nick Holford
- Department of Pharmacology and Clinical Pharmacology, University of Auckland, Auckland, New Zealand.
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Gunzler SA, Shakil S, Carlson NE, Nutt JG, Meshul CK. Low doses of apomorphine transiently reduce locomotor activity in MPTP-treated mice. Neurosci Lett 2007; 428:64-7. [DOI: 10.1016/j.neulet.2007.09.049] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2007] [Revised: 09/20/2007] [Accepted: 09/25/2007] [Indexed: 10/25/2022]
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Chan PLS, Nutt JG, Holford NHG. Modeling the short- and long-duration responses to exogenous levodopa and to endogenous levodopa production in Parkinson's disease. J Pharmacokinet Pharmacodyn 2005; 31:243-68. [PMID: 15518246 DOI: 10.1023/b:jopa.0000039566.75368.59] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Clinicians recognize levodopa has a short-duration response (measured in hr) and a long-duration response (measured in days) in Parkinson's disease. In addition there is a diurnal pattern of motor function with better function in the morning. Previous pharmacokinetic-pharmacodynamic modeling has quantified only the short-duration response. We have developed a pharmacokinetic-pharmacodynamic model for the short- and long-duration responses to exogenous levodopa and the effects of residual endogenous levodopa synthesis in patients with Parkinson's disease. Thirteen previously untreated (de novo) patients with Parkinson's disease and twelve patients who had received levodopa orally for 9.7+/-4.0 years (chronic) were investigated. A 2 hr IV infusion of levodopa with concomitant oral carbidopa was given on two occasions separated by 3 days with no levodopa in between. A two compartment pharmacokinetic model was used to fit plasma levodopa concentrations. A sigmoid Emax model was used to relate concentrations from endogenous and exogenous sources to tapping rate (a measure of motor response). A model incorporating three effect compartments (fast equilibration (half life, Teqf). slow equilibration (Teqs) and dopa synthesis (Teqd)), yielded the most descriptive model for levodopa pharmacokinetics and pharmacodynamics. Baseline tapping rate reflected endogenous levodopa synthesis and the long-duration response. Partial loss of the long-duration response during the 3 days without levodopa in the chronic group lowered baseline tapping (36+/-7%, mean+/-SEM) and increased maximum levodopa induced response above baseline (112+/-31%). The maximum levodopa induced response after the drug holiday is a result of lowered baseline tapping due to the loss of long-duration response and not due to a change in levodopa pharmacokinetics or pharmacodynamics.
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Affiliation(s)
- Phylinda L S Chan
- Department of Pharmacology and Clinical Pharmacology, University of Auckland, Auckland, New Zealand.
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Nutt JG. Long-term l-DOPA therapy: challenges to our understanding and for the care of people with Parkinson's disease. Exp Neurol 2003; 184:9-13. [PMID: 14637071 DOI: 10.1016/s0014-4886(03)00304-2] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Affiliation(s)
- John G Nutt
- Department of Neurology, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, OP32, Portland, OR 97201-3098, USA.
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10
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Savola JM, Hill M, Engstrom M, Merivuori H, Wurster S, McGuire SG, Fox SH, Crossman AR, Brotchie JM. Fipamezole (JP-1730) is a potent alpha2 adrenergic receptor antagonist that reduces levodopa-induced dyskinesia in the MPTP-lesioned primate model of Parkinson's disease. Mov Disord 2003; 18:872-83. [PMID: 12889076 DOI: 10.1002/mds.10464] [Citation(s) in RCA: 118] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Previous studies in the MPTP-lesioned primate model of Parkinson's disease have demonstrated that alpha(2) adrenergic receptor antagonists such as idazoxan, rauwolscine, and yohimbine can alleviate L-dopa-induced dyskinesia and, in the case of idazoxan, enhance the duration of anti-parkinsonian action of L-dopa. Here we describe a novel alpha(2) antagonist, fipamezole (JP-1730), which has high affinity at human alpha(2A) (K(i), 9.2 nM), alpha(2B) (17 nM), and alpha(2C) (55 nM) receptors. In functional assays, the potent antagonist properties of JP-1730 were demonstrated by its ability to reduce adrenaline-induced (35)S-GTPgammaS binding with K(B) values of 8.4 nM, 16 nM, 4.7 nM at human alpha(2A), alpha(2B), and alpha(2C) receptors, respectively. Assessment of the ability of JP-1730 to bind to a range of 30 other binding sites showed that JP-1730 also had moderate affinity at histamine H1 and H3 receptors and the serotonin (5-HT) transporter (IC(50) 100 nM to 1 microM). In the MPTP-lesioned marmoset, JP-1730 (10 mg/kg) significantly reduced L-dopa-induced dyskinesia without compromising the anti-parkinsonian action of L-dopa. The duration of action of the combination of L-dopa and JP-1730 (10 mg/kg) was 66% greater than that of L-dopa alone. These data suggest that JP-1730 is a potent alpha(2) adrenergic receptor antagonist with potential as an anti-dyskinetic agent in the treatment of Parkinson's disease.
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MESH Headings
- Adrenergic alpha-2 Receptor Antagonists
- Adrenergic alpha-Antagonists/pharmacology
- Adrenergic alpha-Antagonists/therapeutic use
- Animals
- Antiparkinson Agents/adverse effects
- Antiparkinson Agents/therapeutic use
- Binding, Competitive/drug effects
- Callithrix
- Dyskinesia, Drug-Induced/drug therapy
- Dyskinesia, Drug-Induced/etiology
- Female
- Imidazoles/pharmacology
- Imidazoles/therapeutic use
- Indans/pharmacology
- Indans/therapeutic use
- Levodopa/adverse effects
- Levodopa/therapeutic use
- Male
- Parkinsonian Disorders/drug therapy
- Radioligand Assay
- Rats
- Receptors, AMPA/drug effects
- Receptors, Adrenergic/drug effects
- Receptors, Dopamine/drug effects
- Receptors, GABA/drug effects
- Receptors, Histamine/drug effects
- Receptors, N-Methyl-D-Aspartate/drug effects
- Receptors, Serotonin/drug effects
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Nutt JG, Carter JH, Lea ES, Woodward WR. Motor fluctuations during continuous levodopa infusions in patients with Parkinson's disease. Mov Disord 1997; 12:285-92. [PMID: 9159720 DOI: 10.1002/mds.870120304] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The cause of motor fluctuations occurring during constant-rate levodopa infusions is unknown. We examined whether known pharmacokinetic factors could explain the fluctuations and looked for clues to pharmacodynamic causes. Eleven subjects with stage III-V Parkinson's disease (PD) and a fluctuating response to levodopa underwent constant-rate infusions for 36-110 h. Levodopa, 3-O-methyldopa (3-OMD), and plasma large neutral amino acids (LNAAs) were measured at 2- to 6-h intervals and PD was monitored hourly from 07:00 to 22:00 h with tapping speed. Ten subjects had motor fluctuations during the infusions. Zero to 68% of the variability of tapping speed could be explained by variation in plasma LNAA concentrations in individual subjects. Fluctuations occurred more commonly later in the day, which may be related to the tendency for LNAAs to increase during the day. Motor fluctuations were not associated with minor variations in levodopa or 3-OMD concentrations. Fluctuations during constant infusions were more marked in patients using larger daily doses of oral levodopa; severity of PD did not predict fluctuations during the infusions. There was no trend for fluctuations or dyskinesia to decrease or increase during several days of constant-rate levodopa infusion. A portion of motor fluctuations occurring during constant levodopa infusions can be explained by peripheral pharmacokinetic mechanisms. Fluctuations are more prominent in subjects who have taken larger daily doses of levodopa, implicating pharmacodynamic factors as well.
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Affiliation(s)
- J G Nutt
- Department of Neurology, School of Medicine, Oregon Health Sciences University, Portland, USA
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Contin M, Riva R, Albani F, Baruzzi A. Pharmacokinetic optimisation in the treatment of Parkinson's disease. Clin Pharmacokinet 1996; 30:463-81. [PMID: 8792058 DOI: 10.2165/00003088-199630060-00004] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The current symptomatic treatment of Parkinson's disease mainly relies on agents which are able to restore dopaminergic transmission in the nigrostriatal pathway, such as the dopamine precursor levodopa or direct agonists of dopamine receptors. Ancillary strategies include the use of anticholinergic and antiglutamatergic agents or inhibitors of cerebral dopamine catabolism, such as monoamine oxidase type B inhibitors. Levodopa is the most widely used and effective drug. Its peculiar pharmacokinetics are characterised by an extensive presystemic metabolism, overcome by the combined use of extracerebral inhibitors of the enzyme aromatic-amino acid decarboxylase and rapid adsorption in the proximal small bowel by a saturable facilitated transport system shared with other large neutral amino acids. Drug transport from plasma to the brain is mediated by the same carriers operating in the intestinal mucosa. The main strategies to assure reproducibility of both drug intestinal absorption and delivery to the brain and clinical effect include standardisation of levodopa administration with respect to meal times and a controlled dietary protein intake. The levodopa plasma half-life is very short, resulting in marked plasma drug concentration fluctuations which are matched, as the disease progresses, with swings in the therapeutic response ('wearing-off' phenomena). 'Wearing-off' phenomena can be also associated, at the more advanced disease stages with a 'negative', both parkinsonism-exacerbating and dyskinetic effect of levodopa at subtherapeutic plasma concentrations. Dyskinesias may be also related to high-levodopa, excessive plasma concentrations. Recognition of the different levodopa toxic response patterns can be difficult on a clinical basis alone, and simultaneous monitoring of levodopa concentration-effect relationships may prove useful to disclose the underlying mechanism and in planning the correct pharmacokinetic management. Controlled-release levodopa formulations have been developed in an attempt to smooth out fluctuations in plasma profiles and matched therapeutic responses. The delayed levodopa absorption and lower plasma concentrations which characterise controlled-release formulations compared with standard forms must be taken into account when prescribing dosage regimens and can be complicating factors in the management of the advanced disease stages. The pharmacokinetic and pharmacodynamic characterisation of the other antiparkinsonian agents is hampered by the lack of sensitive and specific analytical methods to measure their very low plasma drug concentrations and by the difficulty in quantitatively assessing overall moderate drug clinical effects. In clinical practice an optimal dosage schedule is still generally found for each patient on an empirical basis. Future strategies should focus on the search for pharmacological agents with a better kinetic profile, particularly a higher and reproducible bioavailability and a predictable relationship between plasma drug concentration and clinical response. Treatments aimed not only at controlling the symptoms, but also at slowing the neurodegenerative process, are currently under intensive investigation.
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Affiliation(s)
- M Contin
- Laboratory of Neuropharmacology, University of Bologna, Italy
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Nutt JG, Holford NH. The response to levodopa in Parkinson's disease: imposing pharmacological law and order. Ann Neurol 1996; 39:561-73. [PMID: 8619540 DOI: 10.1002/ana.410390504] [Citation(s) in RCA: 201] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The seemingly unpredictable response to levodopa in patients with Parkinson's disease can be understood as an interaction between several distinct pharmacological effects of levodopa. The most important are a short-duration response with a half-life of minutes to hours and a long-duration response with a half-life of days, superimposed on diurnal motor variation. A negative response characterized by brief worsening before and after the short-duration response and dyskinesia accentuate the short-duration response. These various responses are modified by disease progression and long-term levodopa therapy. Pharmacodynamic modeling of the short-duration response indicates that with time, the response becomes less graded and small changes in levodopa concentrations can produce big changes in response. In this setting, unpredictability arises from the variation in absorption and distribution of levodopa.
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Affiliation(s)
- J G Nutt
- Department of Neurology, Oregon Health Sciences University, Portland 97201-3098, USA
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Abstract
1. Levodopa markedly reduces parkinsonism during the first years of treatment. However, with continued therapy the response to levodopa becomes erratic and is complicated by involuntary movements. To improve the therapy of parkinsonism, the challenge is to understand why fluctuations in response develop and, once developed, what controls the moment to moment motor status. 2. In patients with a fluctuating response to levodopa, three distinct responses can be recognized: a short-duration response, a long-duration response and a negative response. 3. The short-duration response, measured in minutes to hours, has a steep concentration-response relationship such that the response appears 'all or nothing.' The duration of effect is dose-responsive. The short-duration response becomes shorter during chronic therapy, possibly because of tolerance. The onset to effect becomes briefer and the magnitude of the response becomes larger during chronic therapy, possibly because of sensitization. 4. The long-duration response, measured in days to weeks, develops and decays slowly. The rate of decay is proportional to the severity of the parkinsonism and therefore this response may relate to dopamine storage capacity of remaining nerve terminals. 5. The negative response, measured in minutes, is a worsening of motor function as the short-duration improvement wears off. It may reflect a biphasic concentration-response relationship. 6. The response to levodopa in parkinsonian patients is a complex interplay between responses with different time courses and variably affected by sensitization, tolerance and disease progression.
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Affiliation(s)
- J G Nutt
- Department of Neurology, Oregon Health Sciences University, Portland 97201-3098, USA
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