What Electrophysiology Tells Us About Alzheimer’s Disease::A Window into the Synchronization and Connectivity of Brain Neurons

Electrophysiology provides a real-time readout of neural functions and network capability in different brain states, on temporal (fractions of milliseconds) and spatial (micro, meso, and macro) scales unmet by other methodologies. However, current international guidelines do not endorse the use of electroencephalographic (EEG)/magnetoencephalographic (MEG) biomarkers in clinical trials performed in patients with Alzheimer’s disease (AD), despite a surge in recent validated evidence. This Position Paper of the ISTAART Electrophysiology Professional Interest Area endorses consolidated and translational electrophysiological techniques applied to both experimental animal models of AD and patients, to probe the effects of AD neuropathology (i.e., brain amyloidosis, tauopathy, and neurodegeneration) on neurophysiological mechanisms underpinning neural excitation/inhibition and neurotransmission as well as brain network dynamics, synchronization, and functional connectivity reflecting thalamocortical and cortico-cortical residual capacity. Converging evidence shows relationships between abnormalities in EEG/MEG markers and cognitive deficits in groups of AD patients at different disease stages. The supporting evidence for the application of electrophysiology in AD clinical research as well as drug discovery pathways warrants an international initiative to include the use of EEG/MEG biomarkers in the main multicentric projects planned in AD patients, to produce conclusive findings challenging the present regulatory requirements and guidelines for AD studies

Acute atomoxetine effects on the EEG of children with Attention-Deficit/Hyperactivity Disorder

Although stimulant medications are the most commonly-used treatments for Attention-Deficit/Hyperactivity Disorder (AD/HD), as many as 20% of treated children do not respond clinically to stimulants. This study investigated the effects of an acute dose of atomoxetine, a selective noradrenaline reuptake inhibitor (SNRI), on the electroencephalogram (EEG) and performance of children with AD/HD. An initial pre-medication EEG was recorded during an eyes-closed resting condition. Within two weeks, a second EEG was recorded 1 h after ingestion of 20 mg of atomoxetine. Data were Fourier transformed to provide absolute and relative power estimates for the delta, theta, alpha, beta and gamma bands. Compared to controls, the unmedicated AD/HD children had significantly elevated global absolute and relative delta, with reduced global relative alpha, and absolute and relative gamma, and many topographic differences. Atomoxetine produced significant global increases in absolute and relative beta, with several topographic changes in other bands, and a significant reduction in omission errors on a Continuous Performance Task. These results indicate that SNRIs can produce substantial normalisation of the AD/HD EEG profile, together with behavioural performance improvements. Although EEG changes induced by acute administration of psychostimulants (methylphenidate/dexamphetamine) and atomoxetine are not identical, both classes of AD/HD drugs produce similar EEG band changes. Further analysis of EEG responses to SNRIs and psychostimulants could reveal common neurophysiological processes closely linked to clinical improvement of AD/HD symptoms in response to pharmacotherapy, providing translational markers for clinical efficacy studies and potential translational biomarkers for AD/HD drug discover

EEG coherence and symptom profiles of children with Attention-Deficit/Hyperactivity Disorder

Objective: We compared EEG coherence in children with and without AD/HD, and sought to relateobserved anomalies to AD/HD symptoms.Methods: Forty children with AD/HD and 40 age- and sex-matched controls had eyes-closed resting EEGcoherence calculated for eight interhemispheric electrode pairs and eight intrahemispheric pairs (fourwithin each hemisphere) in the delta, theta, alpha, beta and ``40 Hzÿÿ gamma bands.Results: At short-medium inter-electrode distances, the AD/HD group had increased intrahemisphericcoherence in delta and theta, and reduced (L \u3e R) laterality in delta, alpha, beta and gamma. Over longerinter-electrode distances, the AD/HD group had reduced intrahemispheric coherence in alpha. In interhemisphericcomparisons, the AD/HD group had reduced frontal coherence in delta, alpha and gamma,increased temporal theta and reduced temporal alpha coherences, and increased central/parietal/occipitalcoherence in theta. Smaller left-lateralized coherences in AD/HD correlated negatively with DSM Inattentiveand DSM Total scores, and smaller frontal interhemispheric coherence in alpha correlatednegatively with DSM Hyperactive/Impulsive score.Conclusions: The negative correlations between AD/HD coherence anomalies and symptoms suggest thatseveral anomalies reflect compensatory brain function.Significance: Coherence differences in AD/HD may reflect anomalous frontal right-hemisphere linkagesthat help compensate functional brain anomalies in the left frontal regions in this disorder. 2011 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd

Role of mitochondrial uncoupling protein-2 (UCP2) in higher brain functions, neuronal plasticity and network oscillation

Background/Purpose: Major psychiatric illnesses, affecting 36% of the world's population, are profound disorders of thought, mood and behavior associated with underlying impairments in synaptic plasticity and cellular resilience. Mitochondria support energy demanding processes like neural transmission and synaptogenesis and are thus points of broadening interest in the energetics underlying the neurobiology of mental illness. These experiments interrogated the importance of mitochondrial flexibility in behavior, synaptic and cortical activity in a mouse model. Methods: We studied mice with ablated uncoupling protein-2 expression (UCP2 KO) and analyzed cellular, circuit and behavioral attributes of higher brain regions. Results: We found that mitochondrial impairment induced by UCP2 ablation produces an anxiety prone, cognitively impaired behavioral phenotype. Further, NMDA receptor blockade in the UCP2 KO mouse model resulted in changes in synaptic plasticity, brain oscillatory and sensory gating activities. Conclusions: We conclude that disruptions in mitochondrial function may play a critical role in pathophysiology of mental illness. Specifically, we have shown that NMDA driven behavioral, synaptic, and brain oscillatory functions are impaired in UCP2 knockout mice. Keywords: Mental illness, Mitochondria, Uncoupling proteins, Auditory gating, NMDA receptor antagonism, Behavioral phenotyp

A novel positive allosteric modulator of the alpha7 neuronal nicotinic acetylcholine receptor: in vitro and in vivo characterization

Several lines of evidence suggest a link between the alpha7 neuronal nicotinic acetylcholine receptor (nAChR) and brain disorders including schizophrenia, Alzheimer's disease, and traumatic brain injury. The present work describes a novel molecule, 1-(5-chloro-2,4-dimethoxy-phenyl)-3-(5-methyl-isoxazol-3-yl)-urea (PNU-120596), which acts as a powerful positive allosteric modulator of the alpha7 nAChR. Discovered in a high-throughput screen, PNU-120596 increased agonist-evoked calcium flux mediated by an engineered variant of the human alpha7 nAChR. Electrophysiology studies confirmed that PNU-120596 increased peak agonist-evoked currents mediated by wild-type receptors and also demonstrated a pronounced prolongation of the evoked response in the continued presence of agonist. In contrast, PNU-120596 produced no detectable change in currents mediated by alpha4beta2, alpha3beta4, and alpha9alpha10 nAChRs. PNU-120596 increased the channel mean open time of alpha7 nAChRs but had no effect on ion selectivity and relatively little, if any, effect on unitary conductance. When applied to acute hippocampal slices, PNU-120596 increased the frequency of ACh-evoked GABAergic postsynaptic currents measured in pyramidal neurons; this effect was suppressed by TTX, suggesting that PNU-120596 modulated the function of alpha7 nAChRs located on the somatodendritic membrane of hippocampal interneurons. Accordingly, PNU-120596 greatly enhanced the ACh-evoked inward currents in these interneurons. Systemic administration of PNU-120596 to rats improved the auditory gating deficit caused by amphetamine, a model proposed to reflect a circuit level disturbance associated with schizophrenia. Together, these results suggest that PNU-120596 represents a new class of molecule that enhances alpha7 nAChR function and thus has the potential to treat psychiatric and neurological disorders

Application of Structure-Based Drug Design and Parallel Chemistry to Identify Selective, Brain Penetrant, In Vivo Active Phosphodiesterase 9A Inhibitors

Phosphodiesterase 9A inhibitors have shown activity in preclinical models of cognition with potential application as novel therapies for treating Alzheimer’s disease. Our clinical candidate, PF-04447943 (<b>2</b>), demonstrated acceptable CNS permeability in rats with modest asymmetry between central and peripheral compartments (free brain/free plasma = 0.32; CSF/free plasma = 0.19) yet had physicochemical properties outside the range associated with traditional CNS drugs. To address the potential risk of restricted CNS penetration with <b>2</b> in human clinical trials, we sought to identify a preclinical candidate with no asymmetry in rat brain penetration and that could advance into development. Merging the medicinal chemistry strategies of structure-based design with parallel chemistry, a novel series of PDE9A inhibitors was identified that showed improved selectivity over PDE1C. Optimization afforded preclinical candidate <b>19</b> that demonstrated free brain/free plasma ≥1 in rat and reduced microsomal clearance along with the ability to increase cyclic guanosine monophosphosphate levels in rat CSF

Application of Structure-Based Design and Parallel Chemistry to Identify a Potent, Selective, and Brain Penetrant Phosphodiesterase 2A Inhibitor

Phosphodiesterase 2A (PDE2A) inhibitors have been reported to demonstrate in vivo activity in preclinical models of cognition. To more fully explore the biology of PDE2A inhibition, we sought to identify potent PDE2A inhibitors with improved brain penetration as compared to current literature compounds. Applying estimated human dose calculations while simultaneously leveraging synthetically enabled chemistry and structure-based drug design has resulted in a highly potent, selective, brain penetrant compound <b>71</b> (PF-05085727) that effects in vivo biochemical changes commensurate with PDE2A inhibition along with behavioral and electrophysiological reversal of the effects of NMDA antagonists in rodents. This data supports the ability of PDE2A inhibitors to potentiate NMDA signaling and their further development for clinical cognition indications

Identification of a Potent, Highly Selective, and Brain Penetrant Phosphodiesterase 2A Inhibitor Clinical Candidate

Computational modeling was used to direct the synthesis of analogs of previously reported phosphodiesterase 2A (PDE2A) inhibitor <b>1</b> with an imidazotriazine core to yield compounds of significantly enhanced potency. The analog PF-05180999 (<b>30</b>) was subsequently identified as a preclinical candidate targeting cognitive impairment associated with schizophrenia. Compound <b>30</b> demonstrated potent binding to PDE2A in brain tissue, dose responsive mouse brain cGMP increases, and reversal of <i>N</i>-methyl-d-aspartate (NMDA) antagonist-induced (MK-801, ketamine) effects in electrophysiology and working memory models in rats. Preclinical pharmacokinetics revealed unbound brain/unbound plasma levels approaching unity and good oral bioavailability resulting in an average concentration at steady state (<i>C</i>_av,ss) predicted human dose of 30 mg once daily (q.d.). Modeling of a modified release formulation suggested that 25 mg twice daily (b.i.d.) could maintain plasma levels of <b>30</b> at or above targeted efficacious plasma levels for 24 h, which became part of the human clinical plan