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`Journal of psychopharmacology
`v.27, no. 6 (June 2013)
`General Collection
`W1 J0858JK
`2013-07-09 08:02:54
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`PROPERTY OF THE
`NATIONAL
`LIBRARY OF
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`KVK-TECH EXHIBIT 1011
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`KVK-TECH EXHIBIT 1011
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`Journal of Psychopharmacology
`
`Editors
`
`David J. Nutt DM MRCP FRCPsych
`Department of Neuropsychapharmacalogy and Molecular Imaging,
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`

`482532 JOP27610.1177/0269881113482532Journal of PsychopharmacologyHeal et al.
`
`2013
`
`Review
`
`Amphetamine, past and present – a
`pharmacological and clinical perspective
`
`David J Heal1, Sharon L Smith1, Jane Gosden1 and David J Nutt2
`
`Journal of Psychopharmacology
`27(6) 479 –496
`© The Author(s) 2013
`Reprints and permissions:
`sagepub.co.uk/journalsPermissions.nav
`DOI: 10.1177/0269881113482532
`jop.sagepub.com
`
`Abstract
`Amphetamine was discovered over 100 years ago. Since then, it has transformed from a drug that was freely available without prescription as a panacea
`for a broad range of disorders into a highly restricted Controlled Drug with therapeutic applications restricted to attention deficit hyperactivity disorder
`(ADHD) and narcolepsy. This review describes the relationship between chemical structure and pharmacology of amphetamine and its congeners.
`Amphetamine’s diverse pharmacological actions translate not only into therapeutic efficacy, but also into the production of adverse events and liability
`for recreational abuse. Accordingly, the balance of benefit/risk is the key challenge for its clinical use. The review charts advances in pharmaceutical
`development from the introduction of once-daily formulations of amphetamine through to lisdexamfetamine, which is the first d-amphetamine
`prodrug approved for the management of ADHD in children, adolescents and adults. The unusual metabolic route for lisdexamfetamine to deliver
`d-amphetamine makes an important contribution to its pharmacology. How lisdexamfetamine’s distinctive pharmacokinetic/pharmacodynamic profile
`translates into sustained efficacy as a treatment for ADHD and its reduced potential for recreational abuse is also discussed.
`
`Keywords
`Abuse liability, amphetamine, attention deficit hyperactivity disorder (ADHD), drug formulations, lisdexamfetamine, microdialysis
`
`A short history of amphetamine
`Although racemic α-methylphenethylamine (amphetamine) was
`discovered by Barger and Dale in 1910, it was not until 1927 that
`this molecule was first synthesised by the chemist, G. A. Alles,
`whilst he was searching for a less costly and more easily synthe-
`sised substitute for ephedrine. Experiments performed in animals
`and human subjects by Alles and others unequivocally revealed
`α-methylphenethylamine’s ability to reverse drug-induced anaes-
`thesia and produce arousal and insomnia (see reviews by Bett,
`1946; Guttmann and Sargent, 1937). The trade name ‘Benzedrine®’
`for racemic α-methylphenethylamine was registered by the phar-
`maceutical company, Smith, Kline and French. ‘Amphetamine’,
`which is the generic name for Benzedrine devised by the Council
`on Pharmacy and Chemistry of the American Medical Association,
`was not adopted until many years later. It is the reason why the
`name Benzedrine, not amphetamine, appears in all of the early
`publications (see Bett, 1946). Smith, Kline and French introduced
`Benzedrine onto the market in 1935 as a treatment for narcolepsy
`(for which it is still used today), mild depression, post-encepha-
`litic Parkinsonism and a raft of other disorders (see Bett, 1946;
`Guttmann and Sargent, 1937; Tidy, 1938).
`As a molecule with a single chiral centre, amphetamine exists
`in two optically active forms, i.e. the dextro- (or d-) and levo- (or
`l-) isomers or enantiomers (Figure 1). Smith, Kline and French
`synthesised both isomers, and in 1937 commenced marketing of
`d-amphetamine, which was the more potent of the two isomers,
`under the trade name of Dexedrine®. Sales of Benzedrine and
`Dexedrine in chemist stores were unrestricted until 1939, when
`these drugs could only be obtained either on prescription from a
`registered medical practitioner or by signing the Poison Register
`(Bett, 1946). The cognitive-enhancing properties of amphetamine
`were quickly recognised, with reports of Benzedrine producing
`improvements in intelligence tests leading to its widespread use to
`
`reduce stress and improve concentration and intellectual perfor-
`mance by academics, students and medical professionals (see
`Guttmann and Sargent, 1937; Tidy, 1938). In his 1946 review,
`Bett commented on the widespread use of ‘energy pills’ by the
`allied forces in World War II, estimating that 150 million
`Benzedrine tablets were supplied to British and American service
`personnel during the course of the global conflict. In spite of con-
`siderable coverage in the medical literature and the popular press
`describing the powerful central effects of these new drugs, the
`addictive potential of amphetamine was largely dismissed (see
`Bett, 1946; Guttmann and Sargent, 1937; Tidy, 1938).
`It was Bradley (1937) who first reported the beneficial effects
`of Benzedrine in treating children with severe behavioural prob-
`lems, who would now be diagnosed as suffering from attention
`deficit/hyperactivity disorder (ADHD) (American Psychiatric
`Association, 1994). Bradley treated 30 subjects for a week, and in
`approximately half of them he observed remarkable improve-
`ments in their school performance, behaviour and demeanour.
`These therapeutic benefits unequivocally derived from the drug
`because they were apparent from the first day of Benzedrine treat-
`ment and disappeared as soon as it was discontinued. Although
`
`1RenaSci Limited, Biocity, Nottingham, UK
`2 Department of Neuropsychopharmacology and Molecular Imaging,
`Division of Neuroscience & Mental Health, Imperial College London,
`London, UK
`
`Corresponding author:
`David J Heal, RenaSci Limited, Biocity, Pennyfoot Street, Nottingham
`NG1 1GF, UK.
`Email: david.heal@renasci.co.uk
`
`Page 3 of 20
`
`

`

`480
`
`Journal of Psychopharmacology 27(6)
`
`2-D structures:
`
`NH2
`
`2-phenethylamine (ß-phenylethylamine)
`
`HO
`
`HO
`
`OH
`*
`(R)
`
`NH2
`
`HO
`
`HO
`
`NH2
`
`OH
`
`CH3
`
`*
`
`HN
`
`CH3
`
`Noradrenaline
`
`Dopamine
`
`Ephedrine
`
`*
`
`NH2
`
`*
`
`NH2
`
`d-Amphetamine
`
`l-Amphetamine
`
`3-D structures:
`
`Figure 1. Chemical structures of various biologically active β-phenylethylamines.
`* Chiral centre. Red: Oxygen atom; White: Hydrogen atom; Black: Carbon atom; Blue: Nitrogen atom.
`
`l-amphetamine (Cydril®) achieved far less attention than either
`the racemate or d-isomer, clinical trials conducted in the 1970s
`demonstrated that both isomers of amphetamine were clinically
`effective in treating ADHD (Arnold et al., 1972, 1973, 1976). The
`use of Benzedrine to treat ADHD declined dramatically after
`Gross (1976) reported that the racemate was significantly less
`clinically effective than Dexedrine. Currently, the only use of
`l-amphetamine in ADHD medications is in mixed salts/mixed
`enantiomers amphetamine (MES-amphetamine), which consists
`of a 3:1 enantiomeric mixture d-amphetamine:l-amphetamine
`salts that is available in both immediate-release (Adderall®,
`generic) and extended-release (Adderall XR®, generic) formula-
`tions. A recent development in the amphetamine field is the intro-
`duction of an amphetamine prodrug, lisdexamfetamine dimesylate
`(Vyvanse®). Lisdexamfetamine comprises the naturally occurring
`amino acid, L-lysine, covalently bound to d-amphetamine via an
`amide linking group. It has been approved for the management of
`ADHD in children (age 6–12), adolescents and adults in the USA
`and Canada. It is currently being developed for clinical use in
`treating ADHD in a number of European countries. The metabolic
`
`route of lisdexamfetamine is unusual because after absorption into
`the bloodstream it is metabolised by red blood cells to yield
`d-amphetamine and the natural amino acid, L-lysine, by rate-
`limited, enzymatic hydrolysis (Pennick, 2010). An overview of
`amphetamine-based medications is provided in Table 1.
`
`A clinical perspective on the use of
`amphetamine in the treatment of ADHD
`ADHD is arguably the most under-diagnosed and treated of all
`psychiatric disorders, especially in adults (Kooij et al., 2010). The
`most recent European data suggest that about 5% of the population
`suffer from ADHD in any one year, with a total of about 3 million
`patients in Europe (Wittchen et al., 2011). Further estimates put the
`cost of each patient at about £5000 per year in the UK (Gustavsson
`et al., 2011). Of the total just over half are direct treatment costs
`and the rest indirect costs, for example lost productivity, social
`harm, negative impact on family life, increased incidence of acci-
`dents and costs associated with criminality and legal intervention.
`
`Page 4 of 20
`
`

`

`Heal et al.
`
`Table 1. Amphetamines – past and present.
`
`Product
`
`Racemic amphetamine
`
`Salt
`
`Base
`
`
`
`
`
`d-Amphetamine
`
`Sulphate
`
`Phosphate
`
`Sulphate
`
`
`
`
`l-Amphetamine
`Mixed enantiomers/
`mixed salts amphetamine
`(3:1 d:l isomers)
`
`
`Lisdexamfetamine
`
`Sulphate
`Sulphate
`Tannate
`Succinate
`Saccharate/
`aspartate/ sulphate
`
`Saccharate/
`aspartate/ sulphate
`Dimesylate
`
`Formulation
`
`Trade names
`
`Currently available
`
`481
`
`IR
`
`IR
`
`IR
`
`IR
`
`Liquid
`XR
`IR
`IR
`IR
`
`Benzedrine, Actedron, Allodene, Adipan,
`Sympatedrine, Psychedrine, Isomyn, Isoamyne,
`Mecodrine, Norephedrane, Novydrine,
`Elastonon, Ortédrine, Phenedrine, Profamina,
`Propisamine, Sympamine, Sympatedrin
`Benzedrine sulphate, Alentol, Psychoton,
`Simpamina
`Acetemin, Aktedron, Monophos, Profetamine
`phosphate, Racephen, Raphetamine phosphate
`Dexedrine sulphate, Afatin, d-Amfetasul,
`Domafate Obesedrin, Dexten, Maxiton,
`Sympamin, Simpamina-D, Albemap, Dadex,
`Ardex, Dexalone, Amsustain, Betafedrina,
`d-Betaphedrine, Diocurb, Dextrostat, generic
`Procentra
`Generic
`Synatan, Tanphetamine
`Cydril
`Adderall, generic
`
`XR
`
`Adderall XR, generic
`
`Prodrug
`
`Vyvanse
`
`No
`
`No
`
`No
`
`Some
`Yes
`
`Yes
`Yes
`No
`No
`Yes
`
`Yes
`
`Yes
`
`IR: immediate release; XR: extended release.
`Data taken from various sources including the Merck Index, Daily Med, electronic Medicines Compendium.
`
`The impact in terms of lost quality of life (days lived with disabil-
`ity) puts ADHD in the top 10 disorders of the brain in Europe.
`Treatment of ADHD is generally inadequate, with estimates sug-
`gesting that, at best, less than one-third of patients with the diagno-
`sis get appropriate treatment (Gustavsson et al., 2011).
`Although amphetamine has been established as an effective
`treatment for ADHD, as well as other central nervous system
`(CNS) disorders such as narcolepsy for decades, its use in the UK
`(and in the wider European context) has been rather limited in
`comparison with its widespread use in the USA. The reasons for
`this are complex and relate to social and medical attitudes to the
`condition of ADHD, pharmaceutical industry marketing policies,
`as well as to concerns regarding the use of drugs in paediatric
`indications which are perceived to have a high potential for rec-
`reational abuse and to cause addiction.
`ADHD has long suffered from being considered an
`‘American’ diagnosis, and for many decades there was a con-
`certed attempt by some experts in child psychiatry to deny, or
`at least minimise, its existence in the UK. On top of this, on the
`rare occasions when the disorder was identified, the preferred
`treatment option was psychotherapy because it fitted with the
`background of the child psychiatrists and psychologists who
`were responsible for managing these patients. It was left to
`certain paediatricians to develop the requisite expertise in the
`use of stimulants for treating children with ADHD, which
`many did quite successfully. In recent years, child psychiatrists
`have begun to assume a prescribing role as well, largely using
`methylphenidate preparations.
`
`Amphetamines, i.e. racemic amphetamine, d-amphetamine
`and methamphetamine, were widely used to promote wakefulness
`in World War II, which in turn led to a large increase in production
`that resulted in large surpluses of these drugs after the war. Much
`of these stocks got into the ‘black market’, and in the 1950s
`d-amphetamine abuse became recognised. In a classic study of
`that period, Connell from the Institute of Psychiatry reported a
`group of heavy d-amphetamine users who had become paranoid
`(Connell, 1966). This flagged up the potential psychiatric dangers
`of this drug and may have encouraged prescribers away from
`d-amphetamine and on to methylphenidate. Another factor was
`the use of d-amphetamine as an antidepressant in the 1950s before
`the discovery of the tricyclic monoamine reuptake inhibitors.
`There were cases of misuse by patients, and also a significant
`degree of diversion of the prescribed drug into youth misuse and/
`or abuse that may also have contributed to wariness by prescribers
`regarding its clinical use. In later years, local outbreaks of
`d-amphetamine abuse have occurred in various parts of the UK,
`often using locally synthesised d-amphetamine; again, this will
`have made doctors shy away from prescribing d-amphetamine lest
`it contributes to its misuse. In the USA, d-amphetamine-contain-
`ing medications, especially MES-amphetamine, have been very
`widely used as treatments for ADHD. Familiarity with prescribed
`amphetamines together with the increased availability of more
`and more tamper-deterrent drug formulations to reduce the poten-
`tial for abuse, for example Adderall XR®, have created a situation
`where in the USA the abuse risk of d-amphetamine is perceived as
`being similar to that of methylphenidate. This fact, along with the
`
`Page 5 of 20
`
`

`

`482
`
`Journal of Psychopharmacology 27(6)
`
`perception that d-amphetamine is much safer than the more potent
`and enduring stimulant methamphetamine, which is now widely
`abused, has resulted in a more relaxed attitude of physicians in the
`USA to the prescribing of d-amphetamine. Luckily, for reasons
`that are obscure, the recreational abuse methamphetamine has
`never really caught on in Europe, and almost all illegal use of the
`amphetamines is confined to d-amphetamine as the sulphate salt.
`
`The pharmacology of amphetamine
`The chemical structure, particularly the 3-dimensional (3-D)
`structure of amphetamine, is critical in determining the pharmaco-
`logical effects that underpin its considerable therapeutic benefits
`and also its liability for recreational abuse. Amphetamine belongs
`to the class of drugs called the ‘β-phenylethylamines’. Although it
`was synthesised many decades before the discovery that the mon-
`oamines, i.e. noradrenaline (norepinephrine), dopamine and
`5-hydroxytryptamine (5-HT; serotonin), were major neurotrans-
`mitters in the central and peripheral nervous systems, part of the
`rationale for synthesising racemic amphetamine was its structural
`similarity to the biologically active molecule, ephedrine.
`As shown in Figure 1, the similarity between the chemical
`structures of the catecholamine neurotransmitters, noradrenaline
`and dopamine, and the isomers of amphetamine is abundantly
`clear. The 3-D structures of the catecholamines and amphetamine
`molecules reveal the long planar conformation that is common to
`all of these compounds. For amphetamine’s isomers, it is their
`planar conformation, molecular size that is similar to the mono-
`amines, the presence of an aromatic ring and a nitrogen on the aryl
`side-chain which are the prerequisite physico-chemical properties
`of a competitive substrate for the monoamine reuptake transport-
`ers, i.e. NET (noradrenaline transporter), DAT (dopamine trans-
`porter) and SERT (5-HT transporter).
`Figure 2 illustrates the mechanism responsible for the uptake
`transport of monoamines and amphetamine into presynaptic nerve
`terminals. One molecule of monoamine neurotransmitter or
`amphetamine associates with two Na+ and one Cl- ion, and the
`resulting molecular complex is actively transported into the pre-
`synaptic terminal by the relevant monoamine reuptake transporter.
`The motive power for this active transport mechanism is a Na+ ion
`concentration gradient (high Na+ on the outside of the nerve termi-
`nal/low Na+ on the inside). The Na+ concentration gradient is
`maintained by Na+/K+ ATPase that pumps two Na+ ions out of the
`cell whilst simultaneously pumping in one K+ ion. There are two
`pools of monoamine neurotransmitter within each type of nerve
`terminal: the cytosolic pool that holds newly synthesised monoam-
`ines, and the vesicular pool that stores the monoamines and from
`which they are released when neurones fire action potentials.
`Although the concentration of a monoamine neurotransmitter
`in the cytosol of the presynaptic nerve terminal is regulated, con-
`trolled by its rates of synthesis, release, reuptake and catabolism,
`it is now recognised that transport of the monoamine into the
`vesicular storage granules has a critically important role to play in
`this process. Translocation of monoamines from the cytosolic
`pool into the storage pool is performed by a similar active trans-
`porter system, the vesicular monoamine transporter 2 (VMAT2)
`(Fei et al., 2008; Fleckenstein et al., 2009; Ramamoorthy et al.,
`2011). Since amphetamine competes with the endogenous mono-
`amines for transport into the nerve terminals via NET, DAT or
`
`SERT, the higher the concentration of amphetamine present in the
`synapse, the greater the number of amphetamine molecules trans-
`ported relative to every molecule of monoamine (see Figure 3).
`Once inside the presynaptic terminal, amphetamine displaces
`monoamines from the cytosolic pool. Furthermore, because
`amphetamine also has affinity for VMAT2 (Teng et al., 1998), it
`prevents the translocation of monoamines into the intraneuronal
`storage vesicles. The outcome of these actions is that the direction
`of the reuptake transporter reverses, so that instead of pumping
`neurotransmitter from the synapse into the nerve terminal, it
`pumps neurotransmitter out of neurones into the synapse. This
`process is called ‘reverse transport’ or ‘retro-transport’ (Robertson
`et al., 2009).
`Consistent with the mechanism described above, in vitro
`experiments have unequivocally demonstrated that ampheta-
`mine’s d- and l-isomers non-selectively release [3H]monoamines
`from preloaded slices or synaptosomes prepared from rat brain.
`There are experimental reports stating that d-amphetamine
`releases [3H] noradrenaline, dopamine and 5-HT from synapto-
`somes (Holmes and Rutledge, 1976; Rothman et al., 2001) and
`brain slices (Heal et al., 1998). l-Amphetamine releases noradren-
`aline, dopamine and 5-HT from synaptosomes (Heikkila et al.,
`1975; Holmes and Rutledge, 1976) and noradrenaline and dopa-
`mine from rat brain slices (Easton et al., 2007). Comparing the
`relative potencies of d- and l-amphetamine, Heikkila et al. (1975)
`and Easton et al. (2007) reported that the d-isomer was approxi-
`mately fourfold more potent than the l-isomer as a releaser of [3H]
`dopamine. In contrast, l-amphetamine was either as potent, or
`more so, than d-amphetamine as a releaser of [3H]noradrenaline
`(Easton et al., 2007; Heikkila et al., 1975). The monoamine trans-
`porters are not particularly selective in terms of which monoam-
`ines they transport, and this lack of selectivity is explained by the
`close structural similarity between them (Figure 1). Furthermore,
`this structural similarity between the monoamine neurotransmit-
`ters and amphetamine explains why the latter has promiscuous
`actions to release the important CNS monoamines (noradrenaline,
`dopamine and 5-HT). Amphetamine also releases adrenaline from
`the peripheral sympathetic nervous system, an action linked to its
`cardiovascular side effects. Although most of these experiments
`have looked at the effects of amphetamine isomers on basal [3H]
`monoamine release from synaptosomes or slices, amphetamine
`also augments electrically stimulated efflux (Easton et al., 2007).
`This action indicates that its retro-transport mechanism can act
`both co-operatively with, and independently of, neuronal firing.
`Although the pharmacological effect of amphetamine is pre-
`dominantly mediated by monoamine release, this mechanism is
`complemented by reuptake inhibition and probably also inhibition
`of monoamine oxidase (MAO) that combine additively or syner-
`gistically to augment synaptic monoamine concentrations. The
`description of amphetamine as a ‘monoamine reuptake inhibitor’
`often causes some confusion, and the difference between the
`mechanisms of amphetamine, which is a competitive reuptake
`transport substrate, and classical reuptake inhibitors is illustrated
`in Figure 3. The potency of amphetamine’s isomers as monoam-
`ine reuptake inhibitors is summarised in Table 2 and they are com-
`pared against some highly potent classical reuptake inhibitors.
`d-Amphetamine is generally accepted to be a weak dopamine
`reuptake inhibitor with a Ki value of ~100 nM, a moderately
`potent inhibitor of noradrenaline reuptake (Ki = 40–50 nM) and a
`
`Page 6 of 20
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`

`

`Heal et al.
`
`483
`
`Storage pool
`
`MAO
`
`X
`
`Na+
`
`Cl-
`
`Na+
`
`Releasing agent
`(amphetamine)
`
`Na+
`
`Na+
`
`Na+/K+ ATP’ase
`
`K+
`
`Cytosolic pool
`
`Neurotransmitter (noradrenaline, dopamine or serotonin)
`
`Monoamine reuptake transporter (NET, DAT or SERT)
`
`Vesicular monoamine transporter 2 (VMAT 2)
`
`Figure 2. Actions comprising the pharmacological mechanism of amphetamine.
`
`very weak inhibitor of 5-HT reuptake (Ki = 1.4-3.8 µM).
`Comparisons of the isomers of amphetamine reveal that l-amphet-
`amine is 3.2–7-fold less potent than d-amphetamine as a dopa-
`mine reuptake inhibitor (Easton et al., 2007; Kula and Baldessarini,
`1991; Richelson and Pfenning, 1984), but it is only 1.8-fold less
`potent against noradrenaline (Richelson and Pfenning, 1984). Its
`potency is so low that l-amphetamine would not be considered to
`be a 5-HT reuptake inhibitor.
`Finally, excess monoamines within the nerve terminal are
`catabolised by the mitochondrial-bound enzyme, MAO. Inhibition
`of MAO would further augment the quantity of neurotransmitter
`that is available for retro-transport into the synapse. Amphetamine’s
`isomers have long been known to be inhibitors of this important
`catabolising enzyme (Mantle et al., 1976; Miller et al., 1980;
`Robinson, 1985). Although this mechanism is often discounted
`because amphetamine is a relatively weak inhibitor of MAO, in
`the situation where amphetamine is concentrated in presynaptic
`nerve terminals, shown in Figure 3, it is probable that some inhibi-
`tion of this enzyme would occur.
`Although in vitro experiments provide a good insight into indi-
`vidual mechanisms, the efficacy of amphetamine relative to other
`
`indirect monoamine agonists, for example classical reuptake
`inhibitors, can only be estimated from in vivo experiments. We
`have used dual-probe intracerebral microdialysis to explore the in
`vivo effects of d- and l-amphetamine in the spontaneously hyper-
`tensive rat (SHR), which has been proposed as a rodent model of
`ADHD (Heal et al., 2008; Sagvolden, 2000; Sagvolden et al.,
`2005, 2009; see review by Wickens et al., 2011).
`Both isomers of amphetamine dose-dependently increased the
`extracellular concentrations of noradrenaline in the prefrontal cor-
`tex (PFC) and dopamine in the striatum. The pharmacodynamics
`of their effects are typical of those reported for monoamine releas-
`ing agents, i.e. a fast onset of action with peak increases of
`noradrenaline and dopamine efflux occurring at 30–45 min, large
`effects (400–450% of baseline for noradrenaline and 700–1500%
`of baseline for dopamine), with a relatively rapid decline after the
`maximum (Figure 4). Although no comparative results have been
`included in this review, the magnitude of the increases produced
`by amphetamine’s isomers are greater than those reported for clas-
`sical reuptake inhibitors such as atomoxetine or bupropion, and
`there is no dose-effect ceiling to amphetamine’s actions (Bymaster
`et al., 2002; Nomikos et al., 1989, 1990; Swanson et al., 2006; see
`
`Page 7 of 20
`
`

`

`484
`
`Journal of Psychopharmacology 27(6)
`
`Unmodified monoamine reuptake
`
`Monoamine reuptake inhibitor
`
`Monoamine releasing agent
`
`
`50% 50%
`
`reductionreduction
`
`
`50% 50%
`
`reductionreduction
`
`monoamine
`reuptake
`
`Monoamine reuptake inhibitor
`Monoamine releasing agent
`
`Figure 3. Different mechanisms leading to a 50% reduction in monoamine reuptake produced by a classical reuptake inhibitor versus a competitive
`substrate (releasing agent).
`
`Table 2. Inhibition of [3H]monoamine uptake into rat brain synaptosomes by amphetamine’s enantiomers in vitro.
`
`Inhibition of [3H]monoamine uptake (Ki = nM)
`
`Reference
`
`
`
`
`
`1 2 3 4 5 6
`
`1 3 6
`
`
`
`6 7
`
`2
`7
`
`[3H]Noradrenaline
`
`[3H]Dopamine
`
`[3H]5-HT
`
`1840
`3830
`
`– 1
`
`– –
`
`441
`
`10,000
`
`– –
`
`– 4
`
`3
`289
`0.73
`
`82
`34
`225
`132
`78
`206
`380
`720
`1435
`
`2355
`1400
`4
`1700
`
`50
`39
`–
`45
`
`– 5
`
`5
`90
`
`– 2
`
`59
`
`21
`1
`277
`33
`
`Drug
`
`
`
`Amphetamine enantiomers
`d-Amphetamine
`
`l-Amphetamine
`
`Reference reuptake
`inhibitors
`Atomoxetine
`
`GBR 12935
`Paroxetine
`
`- = Not tested;
`1: Richelson and Pfenning (1984); 2: Rothman et al. (2001); 3: Kula and Baldessarini (1991); 4: Heal et al. (1998); 5: Rowley et al. (2000); 6: Easton et al. (2007); 7:
`Bolden-Watson and Richelson (1993).
`
`Page 8 of 20
`
`

`

`Heal et al.
`
`485
`
`d-Amphetamine
`
`l-Amphetamine
`
`***
`
`***
`
`***
`
`*** *** **
`
`**
`
`*
`
`*
`
`***
`
`*
`
`45
`
`90
`Time (min)
`
`***
`
`***
`
`***
`
`*
`
`***
`
`***
`
`**
`
`*
`
`*
`
`600
`
`500
`
`400
`
`300
`
`200
`
`100
`
`******
`
`***
`
`*** *** ***
`
`***
`
`***
`
`**
`
`**
`
`**
`
`*
`
`135
`
`180
`
`0
`-45
`
`0
`
`45
`90
`Time (min)
`
`135
`
`180
`
`1500
`
`1250
`
`1000
`
`750
`
`500
`
`250
`
`*** **
`
`**
`
`**
`
`600
`
`500
`
`400
`
`300
`
`200
`
`100
`
`0
`
`-45
`
`0
`
`1500
`
`1250
`
`1000
`
`750
`
`500
`
`250
`
`0
`
`A
`
`Noradrenaline (% of baseline)
`
`B
`
`Dopamine (% of baseline)
`
`-45
`
`0
`
`90
`45
`Time (min)
`
`135
`
`180
`
`0
`-45
`
`0
`
`d-Amphetamine (1 mg/kg ip)
`d-Amphetamine (0.3 mg/kg ip)
`Saline (ip)
`
`90
`45
`Time (min)
`
`135
`
`180
`
`l-Amphetamine (3 mg/kg ip)
`l-Amphetamine (1 mg/kg ip)
`Saline (ip)
`
`Figure 4. A comparison of the effects of the d- and l-isomers of amphetamine on noradrenaline and dopamine efflux in the brains of freely moving rats.
`The effects of amphetamine’s d- and l-isomers on the extracellular levels of (A) noradrenaline in the prefrontal cortex and (B) dopamine in the striatum of freely moving SHRs
`measured by intracerebral microdialysis. Each data point represents mean % of baseline ± SEM. (n = 6–11). The vertical arrow indicates the time of administration of drug or
`saline. *p < 0.05, **p < 0.01, ***p < 0.001 significantly different from appropriate control group according to ANCOVA with Williams’ test for multiple comparisons.
`Data taken from Cheetham et al. (2007). Note the different doses of the two drugs.
`
`also Heal et al., 2009, 2012). When comparing the effects of drugs
`on the efflux of catecholamines in the PFC it is important to take
`into account the highly unusual neuroanatomy of this brain region.
`The density of DAT sites on PFC dopaminergic neurones is very
`low (Hitri et al., 1991), and as a consequence, most dopamine that
`is released is sequestered via NET into noradrenergic neurones
`(Mazei et al., 2002; Morón et al., 2002; Stahl, 2003). In spite of
`the fact that there are few DAT sites on PFC dopaminergic neu-
`rones, their reuptake capacity is sufficient for amphetamine to
`evoke substantial dopamine release from them (Maisonneuve
`et al., 1990; Pum et al., 2007; Shoblock et al., 2003), though it has
`been suggested that much of the release of dopamine in the PFC
`comes from noradrenergic neurones (Shoblock et al., 2004).
`When the in vivo pharmacological profiles of amphetamine’s
`isomers are compared, d-amphetamine is three to fivefold more
`potent than l-amphetamine (Figure 4). Moreover, an analysis of
`t