* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Why is parkinsonism not a feature of human methamphetamine users?
Neuroinformatics wikipedia , lookup
Human brain wikipedia , lookup
Blood–brain barrier wikipedia , lookup
Neurophilosophy wikipedia , lookup
Psychological effects of Internet use wikipedia , lookup
Selfish brain theory wikipedia , lookup
Holonomic brain theory wikipedia , lookup
Brain morphometry wikipedia , lookup
Neurolinguistics wikipedia , lookup
Neurotransmitter wikipedia , lookup
Neuroanatomy wikipedia , lookup
Haemodynamic response wikipedia , lookup
Brain Rules wikipedia , lookup
Neuroplasticity wikipedia , lookup
Cognitive neuroscience wikipedia , lookup
History of neuroimaging wikipedia , lookup
Biochemistry of Alzheimer's disease wikipedia , lookup
Metastability in the brain wikipedia , lookup
Neuropsychopharmacology wikipedia , lookup
Neuropsychology wikipedia , lookup
Vesicular monoamine transporter wikipedia , lookup
Impact of health on intelligence wikipedia , lookup
Biology of depression wikipedia , lookup
Neuroeconomics wikipedia , lookup
Aging brain wikipedia , lookup
Time perception wikipedia , lookup
DOI: 10.1093/brain/awh046 Brain (2004), 127, 363±370 Why is parkinsonism not a feature of human methamphetamine users? Anna Moszczynska,1 Paul Fitzmaurice,1 Lee Ang,2 Kathryn S. Kalasinsky,3 Gregory A. Schmunk,4 Frank J. Peretti,5 Sally S. Aiken,6 Dennis J. Wickham7 and Stephen J. Kish1 1Human Neurochemical Pathology Laboratory, Centre for Addiction and Mental Health, Toronto, 2Division of Neuropathology, London Health Science Centre, University of Western Ontario, London, Ontario, Canada, 3Division of Forensic Toxicology, Of®ce of the Armed Forces Medical Examiner, Division of Forensic Toxicology, Armed Forces Institute of Pathology, Rockville, MD, 4Santa Clara County Medical Examiner-Coroner, San Jose, CA, 5Arkansas State Crime Laboratory, 3 Natural Resources Drive, Little Rock, AR, 6Spokane County Medical Examiner's Of®ce, Spokane and 7Clark County Of®ce of the Medical Examiner, Vancouver, WA, USA Summary For more than 50 years, methamphetamine has been a widely used stimulant drug taken to maintain wakefulness and performance and, in high doses, to cause intense euphoria. Animal studies show that methamphetamine can cause short-term and even persistent depletion of brain levels of the neurotransmitter dopamine. However, the clinical features of Parkinson's disease, a dopamine de®ciency disorder of the brain, do not appear to be characteristic of human methamphetamine users. We compared dopamine levels in autopsied brain tissue of chronic methamphetamine users with those in patients with Parkinson's disease and in a control group. Mean dopamine levels in the methamphetamine users were reduced more in the caudate (±61%) than in the putamen (±50%), a pattern opposite to that of Correspondence to: Stephen J. Kish, PhD, Human Neurochemical Pathology Laboratory, Centre for Addiction and Mental Health, 250 College Street, Toronto, Ontario M5T 1R8, Canada E-mail: [email protected] Parkinson's disease. Some methamphetamine users had severely decreased dopamine levels, within the parkinsonian range, in the caudate (up to 97% dopamine loss) but not in the putamen. As the putamen and caudate subserve aspects of motor and cognitive function, respectively, our data suggest that methamphetamine users are not parkinsonian because dopamine levels are not suf®ciently decreased in the motor component of the striatum. However, the near-total reduction in the caudate could explain reports of cognitive disturbances, sometimes disabling, in some drug users, and suggests that treatment with dopamine substitution medication (e.g. levodopa) during drug rehabilitation might be helpful. Keywords: Parkinson's disease; caudate; putamen; methamphetamine; cognition Abbreviations: MA = methamphetamine Received July 8, 2003. Revised September 23, 2003. Accepted September 26, 2003. Advanced Access publication November 25, 2003 Introduction Methamphetamine (MA) is a widely used psychostimulant which stimulates neuronal release of the neurotransmitter dopamine in the human brain (Laruelle et al., 1995), an action related to the euphoric effects of the drug (Wise, 1996). In experimental animals, MA can deplete brain stores of dopamine and, if the dose is suf®cient, lead to long- term reductions in biochemical markers of dopamine neuronal integrity in the striatal nerve terminal (Fibiger and McGerr, 1971; Seiden et al., 1976; Frey et al., 1997; Harvey et al., 2000a, b) as well as those in the long axons which extend from the cell body to the nerve terminal (Harvey et al., 2000b). However, unlike the pathology of idiopathic Parkinson's disease, the brain Brain Vol. 127 No. 2 ã Guarantors of Brain 2003; all rights reserved 364 A. Moszczynska et al. morphological changes following MA exposure do not include obvious loss of dopamine cell bodies in the substantia nigra of either experimental animals (Woolverton et al., 1989; Linder et al., 1995; but see Sonsalla et al., 1996) or humans (Wilson et al., 1996a). The animal ®ndings of long-term reduction of brain dopaminergic markers, together with histological signs suggestive of nerve terminal injury following acute MA exposure (Linder et al., 1995), have led to the prevailing assumption that MA is toxic to brain dopamine neurons (Ricaurte and McCann, 1992). However, the actual structural extent of long-term MA toxicity to brain dopamine neurons in primates remains uncertain and even controversial because of the impossibility of establishing whether the persistent [but substantially reversible in the non-human primate (Harvey et al., 2000b)] reduction of dopamine nerve terminal/axonal markers is associated with actual physical loss of part of the dopamine neuron or only with loss of expression of dopaminergic markers therein (for discussion see below and Harvey et al., 2000b). Since the discovery that MA is harmful to brain dopamine nerve terminals in animals, by causing either short-term or persistent loss of dopamine, there has been a public health concern that illicit recreational use of the drug by humans will lead to the emergence of the symptoms of Parkinson's disease, a brain dopamine de®ciency disorder caused by degeneration of entire brain dopamine neurons (Hornykiewicz and Kish, 1986). Because parkinsonism develops only after substantial brain dopamine depletion (Hornykiewicz and Kish, 1986), we established whether dopamine levels in autopsied brain of a group of recreational MA users can be as low as those in patients with neuropathologically con®rmed idiopathic Parkinson's disease. Previously, we reported that mean striatal (caudate, putamen) dopamine levels were reduced, on average, by ~50% in the brain of 12 chronic MA users (Wilson et al., 1996a). In the present investigation we replicate this ®nding in a group of eight additional subjects but now show, unexpectedly, that dopamine loss in a major striatal subdivision of some of the MA users can actually be as severe as that observed in elderly patients with Parkinson's disease. Patients and methods Subjects and brain material Post-mortem brain material from MA users (n = 20) and control subjects (n = 14) was obtained from medical examiner of®ces in the USA and Canada. (Consent was obtained from next of kin to examine the brains and to obtain additional information on the subjects for research purposes.) Subject characteristics, including brain (occipital cortex) drug levels of 16 of the 20 MA users, have been reported previously (Wilson et al., 1996a; Kalasinsky et al., 2001; Tong et al., 2003). The control and MA groups were matched with respect to age (controls, 34.2 6 3.5 years; MA users, 31.4 6 1.9 years), post-mortem interval between death and autopsy (controls, 13.9 6 1.6 h; MA users, 14.6 6 1.5 h; P > 0.1, Student's two-tailed t-test) and sex (controls, 11 males, three females; MA users, 15 males, ®ve females; P > 0.1, Yates' corrected c2 test). All MA users had evidence, from the medical examiner investigation and/or structured interview with the next of kin, of the use of MA as the primary drug of abuse for at least 1 year; the presence of MA [assessed by GC-MS (gas chromatography±mass spectrometry, Kalasinsky et al., 2001)] in the blood, brain (occipital cortex) and, in the 14/ 20 MA users in which hair was available, in sequential scalp hair samples; and the absence, at autopsy, of brain pathology unrelated to MA use (Table 1). Sixteen MA users tested negative for other drugs of abuse, including alcohol, whereas heroin or cocaine and/or their metabolites were also detected in the blood and brain of three subjects (cases 559, 726 and 478) and in hair from four subjects (cases 559, 726, 478 and 678) (Table 1). Detailed information on the neurological status of the MA users was not available; however, anecdotal information from the next of kin and informants suggested that neurological status was not obviously abnormal. As shown in Table 2, the suspected or known causes of death of MA users were acute aortic dissection (n = 1), gunshot wounds to the chest (n = 2), severe coronary artery atherosclerosis with MA toxicity as a possible contributing factor (n = 2), multiple drug toxicity (n = 3) and MA intoxication (n = 12). Although it is likely that some of the MA users who had high blood MA levels had developed increased body temperature, examination of the body at autopsy (mean 15 h post-mortem) revealed no evidence of hyperthermia, with the exception of one subject who had an elevated temperature at autopsy (case 447). The results of biochemical analyses [dopamine and other dopamine nerve terminal markers (Wilson et al., 1996a); blood and brain MA levels (Wilson et al., 1996a; Kalasinsky et al., 2001)] on 12 of the 20 MA users have been reported previously. All control subjects were neurologically normal, had no history of drug use and tested negative for any drug of abuse in blood, autopsied brain and, in the 10 subjects for whom scalp hair was available, sequential scalp hair samples. The control subjects were selected so that most had died, like the MA users, a sudden death. The causes of death of control subjects were gunshot wound to the chest (n = 2), chest trauma (n = 2), drowning (n = 1), leukaemia (n = 1), myocardial infarction (n = 1) and cardiovascular disease (n = 7). At autopsy, one-half of the brain was ®xed in formalin ®xative and the other half was immediately frozen until dissection. Brain neuropathological analysis of the MA users (Table 1) and of the control subjects showed no signi®cant abnormalities in any brain area, including the substantia nigra, with the exception of prominent gliosis in the putamen in case 879 and mild gliosis in the substantia nigra in case Parkinsonism in methamphetamine users 365 Table 1 Toxicology and brain pathology summaries for human methamphetamine users Casea Toxicology Drug/metabolite Blood (mg/l) Brain nmol/g tissue Molar sum nmol/g tissue Hair Brain neuropathology 12.50 0.320 0.270 0.090 0.262 0.059 0.325 189 3.48 7.97 0.44 10.8 2.14 11.9 192 NA No abnormalities NA No abnormalities 12.9 NA No abnormalities 422 Methamphetamine Amphetamine Methamphetamine Amphetamine Methamphetamine Amphetamine Methamphetamine 12.9 NA 424 Amphetamine Methamphetamine 0.044 7.000 1.04 129 Slightly pale substantia nigra but no evidence of cell loss Positive Slightly pale substantia nigra but no evidence of cell loss 374 375 407 442 448 510 523 590 524 447 677 767 867 879 559 678 726 478 Amphetamine Methamphetamine Amphetamine Methamphetamine Amphetamine Methamphetamine Amphetamine Methamphetamine Amphetamine Methamphetamine Amphetamine Methamphetamine Amphetamine Methamphetamine Amphetamine Methamphetamine Amphetamine Methamphetamine Amphetamine Methamphetamine Amphetamine Methamphetamine Amphetamine Methamphetamine Amphetamine Morphine Methamphetamine Amphetamine Cocaine/BZE Methamphetamine Amphetamine Morphine Methamphetamine Amphetamine Cocaine/BZE 0.034 0.217 0.034 0.835 0.080 1.743 0.078 0.664 0.072 0.220 0.043 0.714 0.067 0.176 0.029 0.180 ND 3.000 ND 0.200 0.060 0.370 ND 0.260 ND 0.090 1.400 ND ND/ND ND 0.680 Positive 0.140 ND 4.28/5.83 1.26 2.41 0.37 13.3 0.52 47.5 1.85 8.71 0.52 5.90 0.22 19.0 0.81 31.3 2.22 10.9 4.73 296 23.5 4.77 2.37 9.12 1.70 13.4 1.41 0.36 67.3 4.13 ND/ND 9.80 53.5 0.31 7.63 ND 14.9/13.0 8.41 130 2.78 13.8 49.3 9.23 6.12 19.8 33.5 15.6 319 7.14 10.8 14.8 71.4 63.3 7.63 Positive Positive Positive Positive Positive Positive Positive Positive Positive Positive Positive Positive Positive Positive Positive NA Positive Positive Positive Positive Positive Positive Positive Positive Positive Positive Positive Positive/positive NA Positive Positive Positive/ND No abnormalities No abnormalities No abnormalities No abnormalities No abnormalities No abnormalities No abnormalities No abnormalities No abnormalities No abnormalities Prominent gliosis in putamen No abnormalities No abnormalities No abnormalities Mild gliosis in substantia nigra BZE = benzoylecgonine; NA = not available for analysis; ND = not detected. aAmong the 20 MA users, the ®rst 12 cases were originally described in Wilson et al. (1996a). 478. For the dopamine and homovanillic acid assays, samples (20±50 mg wet weight) were examined by HPLC (highpressure liquid chromatography) with electrochemical detection (Wilson et al., 1994). Statistical analyses Differences between the control and the total MA groups were analysed by the Student's two-tailed unpaired or, where appropriate, paired t-test. F M M M M M M M F M M F M M F M M M F M 374 375 407 422 424 442 448 510 523 590 524 447 677 767 867 879 559b 678b 726b 478b White White White White White White White White White White White White White Black White White White White White White Race 30 15 37 20 44 29 35 39 26 26 33 34 36 22 42 20 28 39 28 44 Age (years) 6 21 4.5 21 24 11 22 23 12 15 7 14 5 16 10 21 14 19 4 23 PI (h) >1 >1 8 3±4 15 >8 >1 15 >1 10 18 10 >10 8 >20 1 16 23 10 10 Duration of MA use (years) Chronic user, probably daily Line every 2 weeks Daily, 1/4 g per day Unknown Every few days Unknown Binges for 3±4 days, a few weeks apart; 2±3 days MA, 1 day heroin MA unknown, cocaine unknown MA unknown, heroin unknown MA unknown, cocaine 2±3 times per week Daily, limited only by funds $10 per day, daily ~ once per month 75 cc/hit daily, if money available 3±4 times per week Unknown Binges for 2±3 days, 7±10 days apart Daily, 4±5 hits per day Every 2 weeks 1±2 lines per day Amount/pattern of recent MA use I.v. I.v. Oral, nasal Smoking, oral, nasal Oral, nasal Nasal Nasal Unknown Oral, i.v. Unknown I.v. Nasal Nasal, i.v. i.v. Oral, nasal Oral I.v., smoking I.v. I.v. Nasal Route of administration Acute MA toxicity Acute multiple drug toxicity Acute multiple drug toxicity Acute MA toxicity Acute MA toxicity Acute MA toxicity Acute MA toxicity Acute MA toxicity Gunshot wound to chest Gunshot wound to chest Acute MA toxicity Coronary artery atherosclerosis Coronary artery atherosclerosis Acute MA toxicity Acute MA toxicity Acute aortic dissection Acute MA toxicity Acute MA toxicity Acute MA toxicity Acute multiple drug toxicity Suspected/known cause of death <72 <72 ~1 <72 <72 <72 <72 <12 <72 <72 ~6 ~16 12 3 ~6 ~1 ~3 <72 <12 8 Estimated interval since last administration (h) M = male; F = female; PI = post-mortem interval; MA = methamphetamine. For cases 523, 590 and 677, MA toxicity was considered to be a possible contributing factor to the cause of death. aAmong the 20 MA users, the ®rst 12 cases were originally described in Wilson et al. (1996a); bMA users who tested positive for other drugs in addition to MA in blood, brain and/or hair. Sex Casea Table 2 Subject information and drug histories of 20 chronic methamphetamine users 366 A. Moszczynska et al. Parkinsonism in methamphetamine users 367 Fig. 2 Individual caudate and putamen levels in control subjects, methamphetamine (MA) users and patients with Parkinson's disease (PD). Parkinson's disease values are from Wilson et al. (1996b). Note that some MA users have dopamine levels which fall within the range of levels in patients with Parkinson's disease in the caudate nucleus, but not in the putamen. Fig. 1 Individual caudate and putamen dopamine and homovanillic acid levels in 14 control subjects and in 20 methamphetamine (MA) users. Dopamine levels are reported separately for the 12 MA users from our earlier study (Wilson et al., 1996a) and for the eight new MA users of the present investigation. Note that the caudate dopamine but not homovanillic acid values for most of the MA users fall below the lower limit of the control range. The letters `a' and `b' denote two MA users with nearly total loss of striatal dopamine levels but who have above-normal (b) or normal (a) striatal levels of homovanillic acid, the major dopamine metabolite in human brain. Dopamine, but not homovanillic acid, levels in the 20 MA users were signi®cantly different from values in control subjects (P < 0.0001; Student's two-tailed t-test). Results Striatal dopamine levels can be profoundly decreased in some MA users Figure 1 shows the individual striatal dopamine levels of the 12 MA users reported in our earlier study (Wilson et al., 1996a) and of the eight new subjects of the present investigation. As shown in Fig. 1, mean striatal dopamine levels, compared with control values, were markedly and signi®cantly reduced in both groups of MA users (Wilson et al., 1996a: caudate ±55%, putamen ±51%; new MA users: caudate ±61%, putamen ±50%); the extent of the reduction in the caudate nucleus (±61%) exceeded that in the putamen (±50%) in the overall group of 20 MA users (Table 3; P < 0.05, Student's paired two-tailed t-test). Analysis of the individual subject data (Fig. 1) revealed that the majority of the striatal dopamine values of the MA users fell below the lower limit of the control range. Striatal dopamine loss in some MA users was quite severe, six subjects having caudate dopamine reduction of >70% and two subjects having nearly total loss of dopamine in the caudate (case 448, ±95%; case 678, ±97%) and, to a lesser extent, in the putamen (case 448, ±89%; case 678, ±90%). In the total group of MA users, mean striatal levels of the dopamine metabolites homovanillic acid, dihydroxyphenylacetic acid and 3-methoxytyramine, unlike those of dopamine, did not differ signi®cantly from the control values (Table 3 and Fig. 1). Thus, as shown in Fig. 1, the two MA users with severely depleted striatal dopamine had above-normal (448) or normal (678) striatal levels of homovanillic acid, the major dopamine metabolite in the human brain. Dopamine levels in some MA users can be parkinsonian in the caudate but not in the putamen To establish whether dopamine levels in any of the MA users might be as low as those in patients with Parkinson's disease, we compared the levels of dopamine in the striatum of each of the MA users with the levels we reported previously for the striatum of 12 patients (mean age, 77 years) with Parkinson's disease, who ranged in clinical severity from the early to the late stage (Wilson et al., 1996b). As shown in Fig. 2, the extent of dopamine loss was, as expected (Bernheimer et al., 1973; Kish et al., 1988), much more marked in the putamen than in the caudate of the patients with Parkinson's disease. None of the MA users had putamen dopamine values falling within the range of the Parkinson's disease patients, whereas a substantial overlap occurred between the ranges of the dopamine values in the caudate for the MA and Parkinson's disease groups. 368 A. Moszczynska et al. Table 3 Levels of dopamine and its metabolites in the striatum of control subjects (n = 14), methamphetamine (MA) users (n = 20) and patients with Parkinson's disease (n = 12) Caudate Controls MA users Parkinson's disease group Putamen Controls MA users Parkinson's disease group Dopamine DOPAC HVA 3-MT 7.03 6 0.50 2.76 6 0.31* (±61%) 1.24 6 0.27* (±82%) 0.41 6 0.05 0.36 6 0.04 (±12%) 0.16 6 0.03 (±61%) 6.78 6 0.66 7.33 6 0.65 (+8%) 3.19 6 0.53 (±53%) 1.99 6 0.16 1.96 6 0.16 (±2%) 1.06 6 0.22 (±47%) 7.61 6 0.61 3.78 6 0.47* (±50%) 0.21 6 0.05* (±97%) 0.52 6 0.07 0.44 6 0.05 (±15%) 0.07 6 0.01* (±87%) 10.3 6 0.9 10.5 6 0.9 (+2%) 3.09 6 0.43* (±70%) 2.51 6 0.19 2.40 6 0.15 (+4%) 0.35 6 0.08* (±86%) Data (ng/mg tissue) are mean 6 SEM. Dopamine and metabolite levels in 12 of the MA users (Wilson et al., 1996a) and in the patients with Parkinson's disease (Wilson et al., 1996b) have been published previously. (Reproduced with permission from Lippincott, Williams & Wilkins and Nature Publishing Group, respectively). *Signi®cantly different from the controls (P < 0.05; Student's two-tailed t-test). DOPAC = 3,4-dihydroxyphenylacetic acid; HVA = homovanillic acid; 3-MT = 3-methoxytyramine. We previously reported that levels of the sum of MA and its metabolite amphetamine are homogeneously distributed in the post-mortem brain of human MA users (Kalasinsky et al., 2001). No statistically signi®cant correlation was observed between the molar sum of MA and amphetamine (measured in the occipital cortex) and dopamine levels in the putamen (R = ±0.25, Spearman rank correlation test), whereas a trend for a negative correlation was found between brain MA and dopamine levels in the caudate nucleus (R = ±0.43, P = 0.059). No statistically signi®cant correlation was observed between brain dopamine or homovanillic acid levels and post-mortem time (range 4±24 h) in the caudate or putamen of either the control subjects or the MA users, consistent with previous ®ndings (Adolfsson et al., 1979; Spokes, 1979). Discussion Our major ®nding is that striatal dopamine levels in some MA users can be reduced to those observed in patients with Parkinson's disease in the caudate but not in the putamen subdivision of the striatum. Striatal dopamine is decreased in MA users Previously, we reported that mean striatal dopamine levels were reduced by ~50% in the brain of 12 chronic MA users (Wilson et al., 1996a). We now replicate this ®nding in a group of eight additional subjects and provide the individual values for all 20 subjects. As shown in Fig. 1, although the extent of striatal dopamine reduction in MA users is variable, dopamine levels in most of the MA users fall below the lower limit of the control range, and the decrease is near-total in some cases. The suspected cause of death in ®ve of the six MA users with marked (>70%) dopamine loss was drug intoxication, indicating that severe dopamine depletion might be a normal consequence of taking a dose of MA suf®cient to cause death by cardiovascular toxicity. However, the cause of death in one of the MA users having very low dopamine levels (±95% in the caudate) was trauma, suggesting that severe dopamine reduction probably occurs in users who take lower doses of the drug which are not life-threatening. Why is striatal dopamine decreased? As all of the MA users used the drug recently as well as chronically, any dopamine reduction could be explained by an actual physical loss of entire dopamine neurons or nerve endings, down-regulation of dopamine biosynthesis, and/or dopamine depletion due to excessive release and metabolism of the neurotransmitter. We found no evidence of loss of pigmented cell bodies in the substantia nigra of the MA users in either our ®rst (Wilson et al., 1996a) or our present investigation, indicating that there could not have been substantial loss of entire dopamine neurons in the MA users. However, our qualitative histopathological analysis, conducted by a neuropathologist experienced in examination of patients with degenerative parkinsonisms, would not have disclosed a slight loss of dopaminergic cell bodies. It is beyond the scope of the present investigation to establish whether the low brain dopamine level in the MA users could have been caused by an actual physical loss of dopamine nerve terminals. Because brain levels of dopamine nerve markers (e.g. dopamine, dopamine transporter) can change independently of differences in the number of dopamine neurons (for extensive discussion see Harvey et al., 2000b; Wilson et al., 1996a), we believe that it might never be possible to establish unequivocally whether there is loss of dopamine nerve terminals in human MA users using the presently available biochemical probes. However, striatal concentrations of one marker, the vesicular monoamine transporter (VMAT2), considered to be a somewhat more `stable' marker of striatal dopamine nerve terminal integrity (Vander Borght et al., 1995; Wilson and Kish 1996; but see Riddle et al., 2002 and de la FuenteFernaÂndez et al., 2003), are normal in postmortem brain of MA users (Wilson et al., 1996a) whereas in living brain of self-reported MA users (using PET) VMAT2 levels are, at Parkinsonism in methamphetamine users most, only slightly reduced (personal communication, C. Schuster and C.-E. Johanson, Wayne State University, Detroit MI; K. Frey, University of Michigan, Ann Arbor MI). These data suggest that striatal dopamine nerve terminal number might not be substantially decreased in human MA users. As all of the MA users had used the drug recently (MA was present in post-mortem blood and brain) it is more likely that much, if not all, of the decreased striatal dopamine in the MA users is explained by a recent massive drug-induced release of the neurotransmitter (Laruelle et al., 1995) which could not be compensated for by maximal dopamine biosynthesis. It is also not possible to exclude the possibility that some part of the reduction had occurred post-mortem. An acute effect of MA is suggested by our observation that striatal levels of the major dopamine metabolite homovanillic acid (Fig. 1) were not decreased in the MA users as a whole or even in the subgroup of six MA users with very low dopamine levels (caudate dopamine ±85% versus homovanillic acid +13%), as is the case in Parkinson's disease (Table 3), a disorder characterized by the physical loss of entire dopamine neurons. Striatal dopamine levels in MA users versus Parkinson's disease Irrespective of the cause of the dopamine reduction, we can now address the question of whether the magnitude of the striatal dopamine loss in the MA users is likely to be suf®cient to cause parkinsonism. Using the same high-pressure liquid chromatography procedure for post-mortem brain measurement in a group of much older (mean age 77 years) patients with mild to severe Parkinson's disease, we reported (Wilson et al., 1996b) levels of dopamine in the putamen, the `motor' nucleus of the striatum (Alexander et al., 1986), ranging from 0.08 to 0.54 ng/mg tissue (Fig. 2). Although the extent of putamen dopamine reduction required for the occurrence of very mild parkinsonism must be somewhat less than 0.54 ng/ mg tissue, none of the MA user values (range, 0.73±9.39 ng/ mg tissue) fell within the parkinsonian range (Fig. 2). Assuming that our biochemical data on 20 subjects are generally representative of MA users who regularly become intoxicated with the drug, the lack of a suf®ciently severe reduction in putamen dopamine to achieve the critical threshold probably explains the apparent absence of reports in the clinical literature of parkinsonism in MA users. In this regard, discussions with three centres extensively involved in the acute (acute MA intoxication) or chronic (rehabilitation during drug abstinence) treatment of MA users disclose no evidence of clinically obvious parkinsonism or even neuroleptic drug-induced parkinsonism during drug intoxication (personal communications, R. Rawson, Matrix, Los Angeles, CA, USA; R. Derlet, Emergency Department, University California at Davis, Sacramento, CA, USA; W. Haning, University of Hawaii, Honolulu, HI, USA). However, it is 369 possible that some MA users might be found to have subtle motor problems that are uncovered on formal testing. The available published literature on the question of movement disorders in MA/amphetamine users appears to be limited to anecdotal ®ndings of stereotyped behaviour or dyskinesias in a small minority of subjects (see Lundh and Tunving, 1981), and a report demonstrating normal motor function in MA users during abstinence on a motor task (pegboard) which patients with Parkinson's disease perform poorly (Chang et al., 2002). The extent of reduction of striatal dopamine in the MA users was slightly more marked in the caudate than in the putamen, with dopamine levels in the caudate decreased more than in the putamen in 15 of the 20 MA users. Interestingly, this subregional pattern of dopamine loss differs from that in Parkinson's disease, in which the putamen is much more severely affected (Fig. 2) (Bernheimer et al., 1973; Kish et al., 1988). As post-mortem levels of MA are similar in the caudate and putamen of MA users (Kalasinsky et al., 2001), it is unlikely that the intraregional difference is due to drug pharmacokinetic characteristics between the two striatal subdivisions, but it might be explained by differences in dopamine uptake, storage or release mechanisms. Since some of the MA subjects had caudate dopamine levels falling within the range observed in Parkinson's disease (Fig. 2), brain function subserved by the caudate dopamine system might be signi®cantly compromised, especially in the two MA users having very low caudate dopamine concentrations (0.22 and 0.38 ng/mg tissue). As the caudate nucleus is involved in aspects of cognitive behaviour (Alexander et al., 1986; Yeterian and Pandya, 1994), dopamine reduction in this striatal subdivision might explain the clinical ®nding of cognitive dif®culties in chronic MA users (Kramer et al., 1967; McKetin and Mattick, 1997; Rogers et al., 1999; Simon et al., 2000; Chang et al., 2002; Paulus et al., 2002). Cognitive problems in some MA users appear to be suf®ciently severe to decrease retention in a drug rehabilitation programme (personal communication, R. Rawson, Matrix, Los Angeles, CA, USA). Our post-mortem brain data further suggest the possibility that dopamine substitution medication (e.g. levodopa) might ameliorate cognitive impairment during MA abstinence and thereby increase retention in a treatment programme. However, consideration also has to be given to the possibility that exposure to dopamine-replenishing therapy following recent MA exposure might enhance the neurotoxic and rewarding effects of any residual MA. In conclusion, we ®nd that dopamine levels in the putamen of human MA users do not fall within the range observed in idiopathic Parkinson's disease, an observation which explains the absence of reports of overt parkinsonism as a feature of MA exposure in humans. However, the more marked reduction of the neurotransmitter in a striatal subdivision subserving aspects of cognition could explain in part the presence of cognitive problems in MA users. To date, most work on the harmful effects of MA on the human brain has 370 A. Moszczynska et al. been limited to the question whether MA causes an actual lesion of dopamine nerve terminals in humans, an issue which we believe will not be resolvable because of the lack of stability of the components of the dopamine nerve terminal markers which are used to assess neuronal integrity. However, given the severity of the striatal dopamine reduction in some MA users, from a public health perspective attention must also be devoted to the clinical consequences of brain dopamine depletion, irrespective of whether this abnormality is associated with physical loss of the nerve ending. Disclaimer The opinions and assertions contained herein are the private views of the authors and are not to be construed as of®cial or as re¯ecting views of the United States Department of Army or Department of Defense. Acknowledgement This study was supported by US NIH NIDA DA07182 to S.J.K. References Adolfsson R, Gottfries CG, Roos BE, Winblad B. Post-mortem distribution of dopamine and homovanillic acid in human brain, variations related to age, and a review of the literature. J Neural Transm 1979; 45: 81±105. Alexander GE, DeLong MR, Strick PL. Parallel organization of functionally segregated circuits linking basal ganglia and cortex. Annu Rev Neurosci 1986; 9: 357±81. Bernheimer H, Birkmayer W, Hornykiewicz O, Jellinger K, Seitelberger F. Brain dopamine and the syndromes of Parkinson and Huntington. Clinical, morphological and neurochemical correlations. J Neurol Sci 1973; 20: 415±55. Chang L, Ernst T, Speck O, Patel H, DeSilva M, Leonido-Yee M, et al. Perfusion MRI and computerized cognitive test abnormalities in abstinent methamphetamine users. Psychiatry Res 2002; 114: 65±79. De La Fuente-FernaÂndez R, Furtado S, Guttman M, Furukawa Y, Lee CS, et al. VMAT2 binding is elevated in dopa-responsive dystonia: visualizing empty vesicles by PET. Synapse 2003; 49: 20±28. Fibiger HC, MoGeer EG. Effect of acute and chronic methamphetamine treatment on tyrosine hydroxylase activity in brain and adrenal medulla. Eur J Pharmacol 1971; 16: 176±80. Frey K, Kilbourn M, Robinson T. Reduced striatal vesicular monoamine transporters after neurotoxic but not after behaviorally-sensitizing doses of methamphetamine. Eur J Pharmacol 1997; 334: 273±9. Harvey DC, Lacan G, Melegan WP. Regional heterogeneity of dopaminergic de®cits in vervet monkey striatum and substantia nigra after methamphetamine exposure. Exp Brain Res 2000a; 133: 349±58. Harvey DC, Lacan G, Tanious SP, Melega WP. Recovery from methamphetamine induced long-term nigrostriatal dopaminergic de®cits without substantia nigra cell loss. Brain Res 2000b; 871: 259±70. Hornykiewicz O, Kish SJ. Biochemical pathophysiology of Parkinson's disease. Adv Neurol 1986; 45: 19±34. Kalasinsky KS, Bosy TZ, Schmunk GA, Reiber G, Anthony RM, Furukawa Y, et al. Regional distribution of methamphetamine in autopsied brain of chronic human methamphetamine users. Forensic Sci Int 2001; 116: 163±9. Kish SJ, Shannak K, Hornykiewicz O. Uneven pattern of dopamine loss in the striatum of patients with idiopathic Parkinson's disease. Pathophysiologic and clinical implications. New Engl J Med 1988; 318: 876±80. Kramer JC, Fischman VS, Little®eld DC. Amphetamine abuse. Pattern and effects of high doses taken intravenously. JAMA 1967; 201: 305±9. Laruelle M, Abi-Dargham A, van Dyck CH, Rosenblatt W, Zea-Ponce Y, Zoghbi SS, et al. SPECT imaging of striatal dopamine release after amphetamine challenge. J Nucl Med 1995; 36: 1182±90. Linder JC, Young SJ, Groves PM. Electron microscopic evidence for neurotoxicity in the basal ganglia. Neurochem Int 1995; 26: 195±202. Lundh H, Tunving K. An extrapyramidal choreiform syndrome caused by amphetamine addiction. J Neurol Neurosurg Psychiatry 1981; 44: 728±30. McKetin R, Mattick RP. Attention and memory in illicit amphetamine users. Drug Alcohol Depend 1997; 48: 235±42. Paulus MP, Hozack NE, Zauscher BE, Frank L, Brown GG, Braff DL, et al. Behavioral and functional neuroimaging evidence for prefrontal dysfunction in methamphetamine-dependent subjects. Neuropsychopharmacology 2002; 26: 53±63. Ricaurte GA, McCann UD. Neurotoxic amphetamine analogues: effects in monkeys and implications for humans. Ann NY Acad Sci 1992; 648: 371± 82. Riddle EL, Topham MK, Haycock JW, Hanson GR, Fleckenstein AE. Differential traf®cking of the vesicular monoamine transporter-2 by methamphetamine and cocaine. Eur J Pharmacol 2002; 449: 71±4. Rogers RD, Everitt BJ, Baldacchino A, Blackshaw AJ, Swainson R, Wynne K, et al. Dissociable de®cits in the decision-making cognition of chronic amphetamine abusers, opiate abusers, patients with focal damage to prefrontal cortex, and tryptophan-depleted normal volunteers: evidence for monaminergic mechanisms. Neuropsychopharmacology 1999; 20: 322±39. Seiden LS, Fischman MW, Schuster CR. Long-term methamphetamine induced changes in brain catecholamines in tolerant rhesus monkeys. Drug Alcohol Depend 1976; 1: 215±9. Simon SL, Domier C, Carnell J, Brethen P, Rawson R, Ling W. Cognitive impairment in individuals currently using methamphetamine. Am J Addict 2000; 9: 222±31. Sonsalla PK, Jochnowitz ND, Zeevalk GD, Oostveen JA, Hall ED. Treatment of mice with methamphetamine produces cell loss in the substantia nigra. Brain Res 1996; 738: 172±5. Spokes EG. An analysis of factors in¯uencing measurements of dopamine, noradrenaline, glutamate decarboxylase and choline acetylase in human post-mortem brain tissue. Brain 1979; 102: 333±46. Tong J, Ross BM, Schmunk GA, Peretti FJ, Kalasinsky KS, Furukawa Y, et al. Decreased striatal dopamine D1 receptor-stimulated adenylyl cyclase activity in human methamphetamine users. Am J Psychiatry 2003; 160: 896±903. Vander Borght T, Kilbourn M, Desmond T, Kuhl DE, Frey KA. The vesicular monoamine transporter is not regulated by dopaminergic drug treatments. Eur J Pharmacol 1995; 294: 577±83. Wilson JM, Kish SJ. The vesicular monoamine transporter, in contrast to the dopamine transporter, is not altered by chronic cocaine self-administration in the rat. J Neurosci 1996; 16: 3507±10. Wilson JM, Nobrega JN, Carroll ME, Niznik HB, Shannak K, Lac ST, et al. Heterogeneous subregional binding patterns of 3H-WIN 35,428 and 3HGBR 12,935 are differentially regulated by chronic cocaine selfadministration. J Neurosci 1994; 14: 2966±79. Wilson JM, Kalasinsky KS, Levey AI, Bergeron C, Reiber G, Anthony RM, et al. Striatal dopamine nerve terminal markers in human, chronic methamphetamine users. Nat Med 1996a; 2: 699±703. Wilson JM, Levey AI, Rajput A, Ang L, Guttman M, Shannak K, et al. Differential changes in neurochemical markers of striatal dopamine nerve terminals in idiopathic Parkinson's disease. Neurology 1996b; 47: 718±26. Wise RA. Neurobiology of addiction. Curr Opin Neurobiol 1996; 6: 243±51. Woolverton WL, Ricaurte GA, Forno LS, Seiden LS. Long-term effects of chronic methamphetamine administration in rhesus monkeys. Brain Res 1989; 486: 73±8. Yeterian EH, Pandya DN. Laminar origin of striatal and thalamic projections of the prefrontal cortex in rhesus monkeys. Exp Brain Res 1994; 99: 383± 98.