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Abstract
We developed a novel method to study dopaminergic neurotransmission using positron emission tomography (PET) with [1-(11)C]arachidonic acid ([1-(11)C]AA). Previous preclinical studies have shown the utility of [1-(11)C]AA as a marker of signal transduction coupled to cytosolic phospholipase A(2) (cPLA(2)). Using [1-(11)C]AA and [(15)O]water PET, we measured regional incorporation coefficients K(*) for AA and regional cerebral blood flow (rCBF), respectively, in healthy male volunteers given the D(1)/D(2) agonist (10 or 20 μg/kg subcutaneous) apomorphine. We confirmed a robust central dopaminergic response to apomorphine by observing significant increases in the serum concentration of growth hormone. We observed significant increases, as well as decreases in K(*) and increases in rCBF in response to apomorphine. These changes remained significant after covarying for handedness and apomorphine dosage. The magnitude of increases in K(*) was lower than those in our previous animal experiments, likely reflecting the smaller dose of apomorphine used in the current human study. Changes in K(*) may reflect neuronal signaling downstream of activated D(2)-like receptors coupled to cPLA(2). Changes in rCBF are consistent with previous studies showing net functional effects of D(1)/D(2) activation. [1-(11)C]AA PET may be useful for studying disturbances of dopaminergic neurotransmission in conditions such as Parkinson's disease and schizophrenia.
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Schellekens AFA, Grootens KP, Neef C, Movig KLL, Buitelaar JK, Ellenbroek B, Verkes RJ. Effect of apomorphine on cognitive performance and sensorimotor gating in humans. Psychopharmacology (Berl) 2010; 207:559-69. [PMID: 19834690 PMCID: PMC2784073 DOI: 10.1007/s00213-009-1686-1] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/19/2009] [Accepted: 09/23/2009] [Indexed: 01/04/2023]
Abstract
INTRODUCTION Dysfunction of brain dopamine systems is involved in various neuropsychiatric disorders. Challenge studies with dopamine receptor agonists have been performed to assess dopamine receptor functioning, classically using the release of growth hormone (GH) from the hindbrain as primary outcome measure. The objective of the current study was to assess dopamine receptor functioning at the forebrain level. METHODS Fifteen healthy male volunteers received apomorphine sublingually (2 mg), subcutaneously (0.005 mg/kg), and placebo in a balanced, double-blind, cross-over design. Outcome measures were plasma GH levels, performance on an AX continuous performance test, and prepulse inhibition of the acoustic startle. The relation between central outcome measures and apomorphine levels observed in plasma and calculated in the brain was modeled using a two-compartmental pharmacokinetic-pharmacodynamic analysis. RESULTS After administration of apomorphine, plasma GH increased and performance on the AX continuous performance test deteriorated, particularly in participants with low baseline performance. Apomorphine disrupted prepulse inhibition (PPI) on high-intensity (85 dB) prepulse trials and improved PPI on low intensity (75 dB) prepulse trials, particularly in participants with low baseline PPI. High cognitive performance at baseline was associated with reduced baseline sensorimotor gating. Neurophysiological measures correlated best with calculated brain apomorphine levels after subcutaneous administration. CONCLUSION The apomorphine challenge test appears a useful tool to assess dopamine receptor functioning at the forebrain level. Modulation of the effect of apomorphine by baseline performance levels may be explained by an inverted U-shape relation between prefrontal dopamine functioning and cognitive performance, and mesolimbic dopamine functioning and sensorimotor gating. Future apomorphine challenge tests preferentially use multiple outcome measures, after subcutaneous administration of apomorphine.
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Affiliation(s)
- Arnt F. A. Schellekens
- Department of Psychiatry, Radboud Medical Centre Nijmegen, Reinier Postlaan 10, 966 P.O. Box 9101, 6500 HB Nijmegen, The Netherlands ,Department of Psychiatry, University Medical Centre, Nijmegen, The Netherlands ,Donders Centre for Brain and Cognition, Nijmegen, The Netherlands
| | - K. P. Grootens
- Department of Psychiatry, Radboud Medical Centre Nijmegen, Reinier Postlaan 10, 966 P.O. Box 9101, 6500 HB Nijmegen, The Netherlands ,Department of Psychiatry, University Medical Centre, Nijmegen, The Netherlands ,Donders Centre for Brain and Cognition, Nijmegen, The Netherlands
| | - C. Neef
- Department of Pharmacy and Toxicology, Maastricht University Medical Centre, Maastricht, The Netherlands
| | - Kris L. L. Movig
- Department of Clinical Pharmacy, Medisch Spectrum Twente, Enschede, The Netherlands
| | - J. K. Buitelaar
- Department of Psychiatry, Radboud Medical Centre Nijmegen, Reinier Postlaan 10, 966 P.O. Box 9101, 6500 HB Nijmegen, The Netherlands ,Department of Psychiatry, University Medical Centre, Nijmegen, The Netherlands ,Donders Centre for Brain and Cognition, Nijmegen, The Netherlands
| | | | - R. J. Verkes
- Department of Psychiatry, Radboud Medical Centre Nijmegen, Reinier Postlaan 10, 966 P.O. Box 9101, 6500 HB Nijmegen, The Netherlands ,Department of Psychiatry, University Medical Centre, Nijmegen, The Netherlands ,Donders Centre for Brain and Cognition, Nijmegen, The Netherlands
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Serotonin transporter promoter polymorphism and dopaminergic sensitivity in alcoholics. J Neural Transm (Vienna) 2009; 117:133-8. [PMID: 19885717 DOI: 10.1007/s00702-009-0331-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2009] [Accepted: 10/07/2009] [Indexed: 10/20/2022]
Abstract
The central serotonin (5-HT) system plays an important role in the rewarding and addictive properties of alcohol by a direct activation of the mesolimbic dopamine (DA) system. An insertion/deletion (L/S) promoter polymorphism (5-HTTLPR) of the 5-HT transporter (5-HHT) gene (SLC6A4) has been shown to influence transcriptional activity. It is predicted that reduced transynaptic 5-HT neurotransmission in alcoholics with the L/L genotype of 5-HTTLPR would result in a change in DA function compared to the S/S genotype. Thus the present study has tested whether dopaminergic sensitivity is influenced by the 5-HTTLPR genotype. Dopaminergic sensitivity, 5-HTTLPR genotype and smoking status were assessed in 121 alcoholics. Dopaminergic sensitivity as an indicator of the functional state of the dopaminergic system was measured by the amount of growth hormone (GH) secretion after subcutaneous administration of apomorphine (APO, 0.01 mg/kg). 5-HTTLPR genotype was significantly associated with dopaminergic sensitivity (P = 0.004) explaining 9.2% of the variance of GH response. Subjects homozygous for the L allele (with high 5-HTT expression) showed the lowest GH response, whereas those homozygous for the S allele (with low 5-HTT expression) showed the highest GH response (this was intermediate in heterozygous participants). Furthermore smoking was associated with a significantly reduced GH response (P = 0.006). Our findings indicate that the postsynaptic dopaminergic sensitivity is influenced by the 5-HTTLPR genotype. It is hypothesized that the reduction of sensitivity of the central DA receptors in alcoholics with the L/L genotype might be due to their higher vulnerability to the neurotoxic effects of chronic alcohol consumption than the S carriers.
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Budde H, Zimmermann US, Steffin B, Rommelspacher H, Schmidt LG, Smolka MN. Apomorphine-Induced Growth Hormone Response Is Attenuated by Ethanol but Not Dextromethorphan. Alcohol Clin Exp Res 2007; 31:100-3. [PMID: 17207107 DOI: 10.1111/j.1530-0277.2006.00267.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
BACKGROUND Misuse of alcohol drinking is a major health problem. Alcohol decreases spontaneous growth hormone (GH) secretion, but the mechanism is unclear. The aim of this study was to test whether administration of alcohol (study 1) or a N-methyl d-aspartate (NMDA) receptor antagonist (study 2) attenuates the GH response to pharmacological dopaminergic stimulation. METHODS The 2-session repeated measures design was conducted at the endocrine laboratory at the Department of Psychiatry at the Free University Berlin. Twenty healthy Caucasian males aged 35+/-10 years without a history of alcohol use disorders were tested using the Apomorphine (APO) challenge test. In study 1, we injected APO (0.01 mg/kg s.c.) 1 hour after oral administration of 1 g/kg ethanol and placebo, respectively. In study 2, the APO challenge was conducted after 0.3 mg/kg dextromethorphan (DXM) and placebo. The main outcome measures were the peak serum GH concentration and area under the time/concentration curve up to 120 minutes after APO. The effects of ethanol and DXM were tested using the Wilcoxon signed-rank tests. RESULTS Compared with placebo, alcohol significantly decreased the APO-induced GH release (mean and SEM peak GH concentration 19.9+/-3.2 vs 6.2+/-1.9 ng/mL, p=0.002). Dextromethorphan did not change APO-induced GH response (22.5+/-5.4 vs 21.0+/-5.8 ng/mL, p=0.105). CONCLUSION A single intermediate alcohol dose markedly reduces GH response to dopaminergic stimulation. Although alcohol is thought to stimulate dopaminergic function in certain pathways, but not necessarily in the hypothalamus, our results are in line with the alcohol effect on baseline GH secretion. Growth hormone suppression appears not to be mediated by ethanol's NMDA-antagonistic properties.
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Affiliation(s)
- Henning Budde
- Institute of Sports Medicine, Charité Campus Benjamin Franklin, Berlin, Germany
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Smolka MN, Budde H, Karow AC, Schmidt LG. Neuroendocrinological and neuropsychological correlates of dopaminergic function in nicotine dependence. Psychopharmacology (Berl) 2004; 175:374-81. [PMID: 15114432 DOI: 10.1007/s00213-004-1824-8] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
RATIONALE There is multiple evidence that nicotine--as with ethanol and other drugs of abuse--stimulates dopamine release in the ventral striatum as a central part of the brain reward circuits. Chronic nicotine exposure leads to changes in these dopaminergic reward circuits. During nicotine withdrawal, an impaired dopaminergic function has been reported. On the behavioral level, this seems to result in motivational disturbances in abstaining smokers. OBJECTIVES To investigate the impact of smoking on dopaminergic function in humans both on a neuroendocrinological and on a neuropsychological level. METHODS Thirty-seven healthy smokers were assessed whilst smoking (test 1) and after abstaining overnight for 12 h (test 2). A control group of 18 non-smokers was also examined twice. Severity of nicotine dependence, incentive motivation, digit span and verbal fluency were assessed. The sensitivity of central dopamine (DA) D2 receptors was assessed with the apomorphine-induced growth hormone (GH) secretion. RESULTS ANOVA revealed that GH response was significantly lower in smokers than in non-smokers (P=0.04). The GH response was significantly inversely correlated with severity of nicotine dependence (r=-0.39). Neuropsychological performance was not influenced by smoking status. After overnight abstinence from nicotine GH response, digit span and verbal fluency were not affected, whereas incentive motivation was significantly impaired in smokers (P=0.04). CONCLUSIONS Smoking is significantly associated with a reduced sensitivity of central DA D2 receptors. This alteration of dopaminergic sensitivity is stable even after 12 h of abstinence from nicotine. Therefore, the hypothesis that the motivational impairment during withdrawal from nicotine is associated with an altered sensitivity of central DA D2 receptors cannot be supported.
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Affiliation(s)
- Michael N Smolka
- Department of Addictive Behaviour and Addiction Medicine, Central Institute of Mental Health, Universität Heidelberg, 68072 Mannheim, Germany.
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