Atomoxetine produces changes in cortico-basal thalamic loop circuits: assessed by phMRI BOLD contrast.

Atomoxetine is a selective noradrenaline reuptake inhibitor used in the treatment of attention deficit hyperactivity disorder (ADHD) which has not yet been assessed using pharmacological neuroimaging for its effects on rat brain activity. The pharmacological magnetic resonance imaging (phMRI) blood oxygenation level dependent (BOLD) response was determined in rat brain regions following administration of atomoxetine. Rats were individually placed into a 2.35T Bruker magnet for 60min to achieve basal recording of changes in signal intensity. Either saline (n=9) or atomoxetine hydrochloride (2mg/kg; i.p.; n=10) was then administered and recording continued for a further 90min. Data were analysed for BOLD random effects using statistical parametric maps and time course analysis. The main changes observed were widespread negative BOLD responses in the caudate putamen and changes in brain regions associated with the cortico-basal thalamic loop circuits. BOLD changes in the basal ganglia help explain its efficacy in reducing hyperactivity observed in ADHD patients. Although positive BOLD changes in the prefrontal cortex were limited to the ventral orbital cortex this is an area associated with behavioral control and may be of relevance to the use of the drug in ADHD.

Effects of amphetamine isomers, methylphenidate and atomoxetine on synaptosomal and synaptic vesicle accumulation and release of dopamine and noradrenaline in vitro in the rat brain.

D- and L-amphetamine sulphate isomers, methylphenidate and atomoxetine, are effective treatments for attention-deficit hyperactivity disorder (ADHD). This study provides a detailed comparison of their effects on the synaptosomal and vesicular accumulation of dopamine (DA) and noradrenaline (NA) and release in vitro in rat prefrontal cortex and striatum. D-amphetamine was more potent than L-amphetamine at inhibiting accumulation of DA or NA in synaptosomes and vesicles. All drugs were weaker at inhibiting the accumulation of vesicular DA and NA compared to synaptosomal accumulation and more potently inhibited NA accumulation than DA. Methylphenidate was weak at inhibiting vesicular accumulation of DA and NA compared to its potent synaptosomal effects. The D-isomer had greater potency than the L-isomer on basal and electrically stimulated striatal DA release; however the L-isomer was 2-fold more potent than the D-isomer on basal fronto-cortical NA release. The selective DA reuptake inhibitor, GBR-12909 and NA reuptake inhibitors, maprotiline and atomoxetine, had different release profiles both on the potency and magnitude of basal and stimulated DA and NA release compared to the amphetamine isomers. These results identify distinct pharmacological action by the amphetamine isomers on dopaminergic and noradrenergic neurotransmission, which may impact on their therapeutic effects in the treatment of ADHD.

Differential effects of the D- and L- isomers of amphetamine on pharmacological MRI BOLD contrast in the rat.

RATIONALE: The D - and L-amphetamine sulphate isomers are used in the formulation of Adderall XR(R), which is effective in the treatment of attention-deficit hyperactivity disorder (ADHD). The effects of these isomers on brain activity has not been examined using neuroimaging. OBJECTIVES: This study determines the pharmacological magnetic resonance imaging blood-oxygenation-level-dependent (BOLD) response in rat brain regions after administration of each isomer. MATERIALS AND METHODS: Rats were individually placed into a 2.35 T Bruker magnet for 60 min to achieve basal recording of variation in signal intensity. Either saline (n = 9), D-amphetamine sulphate (2 mg/kg, i.p.; n = 9) or L: -amphetamine sulphate (4 mg/kg, i.p.; n = 9) were administered, and recording continued for a further 90 min. Data were analysed for BOLD effects using statistical parametric maps. Blood pressure, blood gases and respiratory rate were monitored during scanning. RESULTS: The isomers show overlapping effects on the BOLD responses in areas including nucleus accumbens, medial entorhinal cortex, colliculi, field CA1 of hippocampus and thalamic nuclei. The L-isomer produced greater global changes in the positive BOLD response than the D-isomer, including the somatosensory and motor cortices and frontal brain regions such as the orbitofrontal cortices, prelimbic and infralimbic cortex which were not observed with the D-isomer. CONCLUSIONS: The amphetamine isomers produce different BOLD responses in brain areas related to cognition, pleasure, pain processing and motor control probably because of variations on brain amine systems such as dopamine and noradrenaline. The isomers may, therefore, have distinct actions on brain regions affected in ADHD patients.

Guanfacine produces differential effects in frontal cortex compared with striatum: assessed by phMRI BOLD contrast.

RATIONALE: Guanfacine (an alpha-(2A) adrenoreceptor agonist) is a drug of benefit in the treatment of attention deficit hyperactivity disorder (ADHD) (Taylor FB, Russo J, J Clin Psychopharmacol 21:223-228, 2001). Assessment of this drug using neuroimaging will provide information about the brain regions involved in its effects. OBJECTIVES: The pharmacological magnetic resonance imaging blood oxygenation level dependent (BOLD) response was determined in rat brain regions following administration of guanfacine. METHODS: Male rats were individually placed into a 2.35 T Bruker magnet for 60 min to achieve basal recording of changes in signal intensity. Either saline (n = 9) or guanfacine (0.3 mg/kg, i.p.; n = 9) was then administered and recording was continued for a further 90 min. Data were analysed for BOLD effects using statistical parametric maps. Respiration rate, blood pressure and blood gases were monitored and remained constant throughout scanning. RESULTS: The main changes observed were negative BOLD effects in the caudate putamen and nucleus accumbens with positive BOLD effects in frontal association, prelimbic and motor cortex areas. CONCLUSIONS: These data suggest that guanfacine can decrease neuronal activity in the caudate while increasing frontal cortex activity. This ability to change neuronal activity in specific areas of rat brain that are known to be impaired in ADHD (Solanto MV, Behav Brain Res 130:65-71, 2002) may contribute to guanfacine's beneficial effects.

Ecstasy: are animal data consistent between species and can they translate to humans?

The number of 3,4-methylenedioxymethamphetamine (ecstasy or MDMA) animal research articles is rapidly increasing and yet studies which place emphasis on the clinical significance are limited due to a lack of reliable human data. MDMA produces an acute, rapid release of brain serotonin and dopamine in experimental animals and in the rat this is associated with increased locomotor activity and the serotonin behavioural syndrome in rats. MDMA causes dose-dependent hyperthermia, which is potentially fatal, in humans, primates and rodents. Subsequent serotonergic neurotoxicity has been demonstrated by biochemical and histological studies and is reported to last for months in rats and years in non-human primates. Relating human data to findings in animals is complicated by reports that MDMA exposure in mice produces selective long-term dopaminergic impairment with no effect on serotonin. This review compares data obtained from animal and human studies and examines the acute physiological, behavioural and biochemical effects of MDMA as well as the long-term behavioural effects together with serotonergic and dopaminergic impairments. Consideration is also given to the role of neurotoxic metabolites and the influence of age, sex and user groups on the long-term actions of MDMA.

Synthesis, in vitro formation, and behavioural effects of glutathione regioisomers of alpha-methyldopamine with relevance to MDA and MDMA (ecstasy).

Administration of 3,4-methylenedioxymethamphetamine (MDMA) or 3,4-methylenedioxyamphetamine (MDA) to rats produces serotonergic nerve terminal degeneration. However, they are not neurotoxic when injected directly into the brain, suggesting the requirement for peripheral metabolism of MDMA to a neurotoxic metabolite. Alpha-methyldopamine (alpha-MeDA) is a major metabolite of MDA. There are indications that a glutathione metabolite of alpha-MeDA and/or 3,4-dihydroxymethamphetamine may be responsible for the neurotoxicity and some of the behavioural effects produced by MDMA and/or MDA. The present study details the synthesis, purification and separation of the 5-(glutathion-S-yl)-alpha-MeDA and 6-(glutathion-S-yl)-alpha-MeDA regioisomers of alpha-MeDA. Incubation of MDA with human liver microsomes demonstrated that production of both glutathione adducts are related to cytochrome P450 2D6 isoform activity. Following intracerebroventricular administration (180 nmol) of either GSH adduct into Dark Agouti or Sprague-Dawley rats only 5-(glutathion-S-yl)-alpha-MeDA produced behavioural effects characterised by hyperactivity, teeth chattering, tremor/trembling, head weaving, splayed posture, clonus and wet dog shakes. Pre-treatment with a dopamine receptor antagonist (haloperidol, 0.25 mg/kg; i.p.) attenuated hyperactivity, teeth chattering, low posture and clonus and potentiated splayed postural effects. These results indicate that MDA can be converted into two glutathione regioisomers by human liver microsomes, but only the 5-(glutathion-S-yl)-alpha-MeDA adduct is behaviourally active in the rat.

Mapping the central effects of methylphenidate in the rat using pharmacological MRI BOLD contrast.

Methylphenidate (Ritalin) is a selective dopamine reuptake inhibitor and an effective treatment for attention deficit hyperactivity disorder (ADHD) however the anatomical foci and neuronal circuits involved in these therapeutic benefits are unclear. This study determines the temporal pattern of brain regional activity change produced by systemic administration of a therapeutically relevant dose of methylphenidate in anaesthetised Sprague-Dawley rats using BOLD MRI and a 2.35T Bruker magnet. Following 60 min basal recording separate rats received saline (n = 9) or +/- methylphenidate hydrochloride (2 mg/kg, i.p., n = 9) and BOLD changes were recorded for 90 min using statistical parametric maps. Methylphenidate produced significant positive random BOLD effects in the nucleus accumbens, substantia nigra, entorhinal cortex and medial orbital cortex. Negative random BOLD effects were more widespread and intense, occurring in the motor and somatosensory cortices, caudate putamen, lateral globus pallidus and bed nucleus of the stria terminalis, without accompanying changes in blood pressure or respiratory rate. Methylphenidate-induced negative BOLD in the striatum, and other dopamine terminal areas, may reflect post-synaptic changes produced by blockade of the neuronal dopamine reuptake transporter. While increased positive BOLD in the medial orbital cortex may reflect altered dopamine and/or noradrenaline release indirectly altering striatal activity. The overall pattern of BOLD changes is comparable to that seen in previous studies using guanfacine, amphetamine and atomoxetine, and suggests that although these compounds operate through distinct pharmacological mechanisms the BOLD changes may represent a 'fingerprint pattern' predictive of therapeutic benefit in ADHD.