Atomoxetine affects transcription/translation of the NMDA receptor and the norepinephrine transporter in the rat brain--an in vivo study.

Attention-deficit/hyperactivity disorder (ADHD) is the most frequently diagnosed neurodevelopmental disorder. The norepinephrine transporter (NET) inhibitor atomoxetine, the first nonstimulant drug licensed for ADHD treatment, also acts as an N-methyl-D-aspartate receptor (NMDAR) antagonist. The compound's effects on gene expression and protein levels of NET and NMDAR subunits (1, 2A, and 2B) are unknown. Therefore, adolescent Sprague Dawley rats were treated with atomoxetine (3 mg/kg, intraperitoneal injection [i.p.]) or saline (0.9%, i.p.) for 21 consecutive days on postnatal days (PND) 21-41. In humans, atomoxetine's earliest clinical therapeutic effects emerge after 2-3 weeks. Material from prefrontal cortex, striatum (STR), mesencephalon (MES), and hippocampus (HC) was analyzed either directly after treatment (PND 42) or 2 months after termination of treatment (PND 101) to assess the compound's long-term effects. In rat brains analyzed immediately after treatment, protein analysis exhibited decreased levels of the NET in HC, and NMDAR subunit 2B in both STR and HC; the transcript levels were unaltered. In rat brains probed 2 months after final atomoxetine exposure, messenger RNA analysis also revealed significantly reduced levels of genes coding for NMDAR subunits in MES and STR. NMDAR protein levels were reduced in STR and HC. Furthermore, the levels of two SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) proteins, synaptophysin and synaptosomal-associated protein 25, were also significantly altered in both treatment groups. This in vivo study detected atomoxetine's effects beyond NET inhibition. Taken together, these data reveal that atomoxetine seems to decrease glutamatergic transmission in a brain region-specific manner. Long-term data show that the compound's impact is not due to an acute pharmacological effect but lasts or even amplifies after a drug-free period of 2 months, leading to altered development of synaptic composition. These alterations might contribute to atomoxetine's clinical effects in the treatment of ADHD, a neurodevelopmental disorder in which synaptic processes and especially a dysregulated glutamatergic metabolism seem to be involved.

Nondopaminergic neurotransmission in the pathophysiology of Tourette syndrome.

A major pathophysiological role for the dopaminergic system in Tourette's syndrome (TS) has been presumed ever since the discovery that dopamine-receptor antagonists can alleviate tics. Especially recent molecular genetic studies, functional imaging studies, and some rare postmortem studies have given more and more hints that other neurotransmitter systems are involved as well. Dysfunction in the dopamine metabolism-in particular during early development-might lead to counter-regulations in the other systems or vice versa. This chapter will give an overview of the studies that prove the involvement of other neurotransmitter systems such as the major monoaminergic neurotransmitters norepinephrine, serotonin, and histamine; the most important excitatory neurotransmitter, the amino acid glutamate; the major inhibitory neurotransmitter y-aminobutyric acid, as well as acetylcholine, endocannabinoid, corticoid; and others. These studies will hopefully lead to fundamental advances in the psychopharmacological treatment of TS. While tic disorders have been previously treated mainly with dopamine antagonists, some authors already favor alpha-agonists. Clinical trials with glutamate agonists and antagonists and compounds influencing the histaminergic system are currently being conducted. Since the different neurotransmitter systems consist of several receptor subtypes which might mediate different effects on locomotor activity, patients with TS may respond differentially to selective agonists or antagonists. Effects of agonistic or antagonistic compounds on tic symptoms might also be dose dependent. Further studies will lead to a broader spectrum of psychopharmacological treatment options in TS.

Autistic-like behaviours and hyperactivity in mice lacking ProSAP1/Shank2.

Autism spectrum disorders comprise a range of neurodevelopmental disorders characterized by deficits in social interaction and communication, and by repetitive behaviour. Mutations in synaptic proteins such as neuroligins, neurexins, GKAPs/SAPAPs and ProSAPs/Shanks were identified in patients with autism spectrum disorder, but the causative mechanisms remain largely unknown. ProSAPs/Shanks build large homo- and heteromeric protein complexes at excitatory synapses and organize the complex protein machinery of the postsynaptic density in a laminar fashion. Here we demonstrate that genetic deletion of ProSAP1/Shank2 results in an early, brain-region-specific upregulation of ionotropic glutamate receptors at the synapse and increased levels of ProSAP2/Shank3. Moreover, ProSAP1/Shank2(-/-) mutants exhibit fewer dendritic spines and show reduced basal synaptic transmission, a reduced frequency of miniature excitatory postsynaptic currents and enhanced N-methyl-d-aspartate receptor-mediated excitatory currents at the physiological level. Mutants are extremely hyperactive and display profound autistic-like behavioural alterations including repetitive grooming as well as abnormalities in vocal and social behaviours. By comparing the data on ProSAP1/Shank2(-/-) mutants with ProSAP2/Shank3αß(-/-) mice, we show that different abnormalities in synaptic glutamate receptor expression can cause alterations in social interactions and communication. Accordingly, we propose that appropriate therapies for autism spectrum disorders are to be carefully matched to the underlying synaptopathic phenotype.

Amyloid beta protein-induced zinc sequestration leads to synaptic loss via dysregulation of the ProSAP2/Shank3 scaffold.

BACKGROUND: Memory deficits in Alzheimer's disease (AD) manifest together with the loss of synapses caused by the disruption of the postsynaptic density (PSD), a network of scaffold proteins located in dendritic spines. However, the underlying molecular mechanisms remain elusive. Since it was shown that ProSAP2/Shank3 scaffold assembly within the PSD is Zn2+-dependent and that the amyloid beta protein (Aß) is able to bind Zn2+, we hypothesize that sequestration of Zn2+ ions by Aß contributes to ProSAP/Shank platform malformation. RESULTS: To test this hypothesis, we designed multiple in vitro and in vivo assays demonstrating ProSAP/Shank dysregulation in rat hippocampal cultures following Aß oligomer accumulation. These changes were independent from alterations on ProSAP/Shank transcriptional level. However, application of soluble Aß prevented association of Zn2+ ions with ProSAP2/Shank3 in a cell-based assay and decreased the concentration of Zn2+ clusters within dendrites. Zn2+ supplementation or saturation of Aß with Zn2+ ions prior to cell treatment was able to counter the effects induced by Aß on synapse density and ProSAP2/Shank3 levels at the PSD. Interestingly, intracellular Zn2+ levels in APP-PS1 mice and human AD hippocampus are reduced along with a reduction in synapse density and synaptic ProSAP2/Shank3 and Shank1 protein levels. CONCLUSIONS: We conclude that sequestration of Zn2+ ions by Aß significantly contributes to changes in ProSAP2/Shank3 platforms. These changes in turn lead to less consolidated (mature) synapses reflected by a decrease in Shank1 protein levels at the PSD and decreased synapse density in hippocampal neurons.

Atomoxetine acts as an NMDA receptor blocker in clinically relevant concentrations.

BACKGROUND AND PURPOSE: There is increasing evidence that not only the monoaminergic but also the glutamatergic system is involved in the pathophysiology of attention-deficit hyperactivity disorder (ADHD). Hyperactivity of glutamate metabolism might be causally related to a hypoactive state in the dopaminergic system. Atomoxetine, a selective noradrenaline reuptake inhibitor, is the first non-stimulant approved for the treatment of this disorder. Here we have evaluated the effects of atomoxetine on glutamate receptors in vitro. EXPERIMENTAL APPROACH: The whole-cell configuration of the patch-clamp technique was used to analyse the effect of atomoxetine on N-methyl-d-aspartate (NMDA) receptors in cultured rodent cortical and hippocampal neurons as well as on NMDA receptors heterologously expressed in human TsA cells. KEY RESULTS: Atomoxetine blocked NMDA-induced membrane currents. Half-maximal inhibition emerged at about 3 microM which is in the range of clinically relevant concentrations found in plasma of patients treated with this drug. The inhibition was voltage-dependent, indicating an open-channel blocking mechanism. Furthermore, the inhibitory potency of atomoxetine did not vary when measured on NMDA receptors from different brain regions or with different subunit compositions. CONCLUSIONS AND IMPLICATIONS: The effective NMDA receptor antagonism by atomoxetine at low micromolar concentrations may be relevant to its clinical effects in the treatment of ADHD. Our data provide further evidence that altered glutamatergic transmission might play a role in ADHD pathophysiology.