Partial FMRP expression is sufficient to normalize neuronal hyperactivity in Fragile X neurons.

Fragile X syndrome (FXS) is the most common genetic form of intellectual disability caused by a CGG repeat expansion in the 5'-UTR of the Fragile X mental retardation gene FMR1, triggering epigenetic silencing and the subsequent absence of the protein, FMRP. Reactivation of FMR1 represents an attractive therapeutic strategy targeting the genetic root cause of FXS. However, largely missing in the FXS field is an understanding of how much FMR1 reactivation is required to rescue FMRP-dependent mutant phenotypes. Here, we utilize FXS patient-derived excitatory neurons to model FXS in vitro and confirm that the absence of FMRP leads to neuronal hyperactivity. We further determined the levels of FMRP and the percentage of FMRP-positive cells necessary to correct this phenotype utilizing a mixed and mosaic neuronal culture system and a combination of CRISPR, antisense and expression technologies to titrate FMRP in FXS and WT neurons. Our data demonstrate that restoration of greater than 5% of overall FMRP expression levels or greater than 20% FMRP-expressing neurons in a mosaic pattern is sufficient to normalize a FMRP-dependent, hyperactive phenotype in FXS iPSC-derived neurons.

Preclinical Characterization of (R)-3-((3S,4S)-3-fluoro-4-(4-hydroxyphenyl)piperidin-1-yl)-1-(4-methylbenzyl)pyrrolidin-2-one (BMS-986169), a Novel, Intravenous, Glutamate N-Methyl-d-Aspartate 2B Receptor Negative Allosteric Modulator with Potential in Major Depressive Disorder.

(R)-3-((3S,4S)-3-fluoro-4-(4-hydroxyphenyl)piperidin-1-yl)-1-(4-methylbenzyl)pyrrolidin-2-one (BMS-986169) and the phosphate prodrug 4-((3S,4S)-3-fluoro-1-((R)-1-(4-methylbenzyl)-2-oxopyrrolidin-3-yl)piperidin-4-yl)phenyl dihydrogen phosphate (BMS-986163) were identified from a drug discovery effort focused on the development of novel, intravenous glutamate N-methyl-d-aspartate 2B receptor (GluN2B) negative allosteric modulators (NAMs) for treatment-resistant depression (TRD). BMS-986169 showed high binding affinity for the GluN2B subunit allosteric modulatory site (Ki = 4.03-6.3 nM) and selectively inhibited GluN2B receptor function in Xenopus oocytes expressing human N-methyl-d-aspartate receptor subtypes (IC50 = 24.1 nM). BMS-986169 weakly inhibited human ether-a-go-go-related gene channel activity (IC50 = 28.4 µM) and had negligible activity in an assay panel containing 40 additional pharmacological targets. Intravenous administration of BMS-986169 or BMS-986163 dose-dependently increased GluN2B receptor occupancy and inhibited in vivo [3H](+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine ([3H]MK-801) binding, confirming target engagement and effective cleavage of the prodrug. BMS-986169 reduced immobility in the mouse forced swim test, an effect similar to intravenous ketamine treatment. Decreased novelty suppressed feeding latency, and increased ex vivo hippocampal long-term potentiation was also seen 24 hours after acute BMS-986163 or BMS-986169 administration. BMS-986169 did not produce ketamine-like hyperlocomotion or abnormal behaviors in mice or cynomolgus monkeys but did produce a transient working memory impairment in monkeys that was closely related to plasma exposure. Finally, BMS-986163 produced robust changes in the quantitative electroencephalogram power band distribution, a translational measure that can be used to assess pharmacodynamic activity in healthy humans. Due to the poor aqueous solubility of BMS-986169, BMS-986163 was selected as the lead GluN2B NAM candidate for further evaluation as a novel intravenous agent for TRD.

B-973, a novel piperazine positive allosteric modulator of the α7 nicotinic acetylcholine receptor.

The alpha7 (α7) nicotinic acetylcholine receptor is a therapeutic target for cognitive disorders. Here we describe 3-(3,4-difluorophenyl)-N-(1-(6-(4-(pyridin-2-yl)piperazin-1-yl)pyrazin-2-yl)ethyl)propanamide (B-973), a novel piperazine-containing molecule that acts as a positive allosteric modulator of the α7 receptor. We characterize the action of B-973 on the α7 receptor using electrophysiology and radioligand binding. At 0.1mM acetylcholine, 1µM B-973 potentiated peak acetylcholine-induced currents 6-fold relative to maximal acetylcholine (3mM) and slowed channel desensitization, resulting in a 6900-fold increase in charge transfer. The EC50 of B-973 was approximately 0.3µM at acetylcholine concentrations ranging from 0.03 to 3mM. At a concentration of 1µM, B-973 shifted the acetylcholine EC50 of peak currents from 0.30mM in control to 0.007mM. B-973 slowed channel deactivation upon acetylcholine removal (τ=50s) and increased the affinity of the α7 agonist [3H]A-585539. In the absence of exogenously added acetylcholine, application of B-973 at concentrations >1µM induced large methyllycaconitine-sensitive currents, suggesting B-973 can function as an Ago-PAM at high concentrations. B-973 will be a useful probe for investigating the biological consequences of increasing α7 receptor activity through allosteric modulation.

Development of a spontaneously active dorsal root ganglia assay using multiwell multielectrode arrays.

In vitro phenotypic assays of sensory neuron activity are important tools for identifying potential analgesic compounds. These assays are typically characterized by hyperexcitable and/or abnormally, spontaneously active cells. Whereas manual electrophysiology experiments provide high-resolution biophysical data to characterize both in vitro models and potential therapeutic modalities (e.g., action potential characteristics, the role of specific ion channels, and receptors), these techniques are hampered by their low throughput. We have established a spontaneously active dorsal root ganglia (DRG) platform using multiwell multielectrode arrays (MEAs) that greatly increase the ability to evaluate the effects of multiple compounds and conditions on DRG excitability within the context of a cellular network. We show that spontaneous DRG firing can be attenuated with selective Na(+) and Ca(2+) channel blockers, as well as enhanced with K(+) channel blockers. In addition, spontaneous activity can be augmented with both the transient receptor potential cation channel subfamily V member 1 agonist capsaicin and the peptide bradykinin and completely blocked with neurokinin receptor antagonists. Finally, we validated the use of this assay by demonstrating that commonly used neuropathic pain therapeutics suppress DRG spontaneous activity. Overall, we have optimized primary rat DRG cells on a multiwell MEA platform to generate and characterize spontaneously active cultures that have the potential to be used as an in vitro phenotypic assay to evaluate potential therapeutics in rodent models of pain.

Effect of acute NR2B antagonist treatment on long-term potentiation in the rat hippocampus.

The long lasting antidepressant response seen following acute, i.v. ketamine administration in patients with treatment-resistant depression (TRD) is thought to result from enhanced synaptic plasticity in cortical and hippocampal circuits. Using extracellular field recordings in rat hippocampal slices, we show that a single dose of the non-selective NMDA receptor antagonist ketamine or CP-101,606, a selective antagonist of the NR2B subunit of the NMDA receptor, enhances hippocampal synaptic plasticity induced with high frequency stimulation (HFS) 24h after dosing - a time at which plasma concentrations of the drug are no longer detectable in the animal. These results indicate that acute inhibition of NMDA receptors containing the NR2B subunit can lead to long-lasting changes in hippocampal plasticity.

TC-8831, a nicotinic acetylcholine receptor agonist, reduces L-DOPA-induced dyskinesia in the MPTP macaque.

Long-term L-DOPA treatment for Parkinson's disease (PD) is limited by motor complications, particularly L-DOPA-induced dyskinesia (LID). A therapy with the ability to ameliorate LID without reducing anti-parkinsonian benefit would be of great value. We assessed the ability of TC-8831, an agonist at nicotinic acetylcholine receptors (nAChR) containing α6ß2/α4ß2 subunit combinations, to provide such benefits in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine- (MPTP) lesioned macaques with established LID. Animals were treated orally for consecutive 14-day periods with twice-daily vehicle (weeks 1-2) or TC-8831 (0.03, 0.1 or 0.3 mg/kg, weeks 3-8). L-DOPA was also administered, once-daily, (weeks 1-12, median-dose 30 mg/kg, p.o.). For the following two-weeks (weeks 9-10), TC-8831 was washed out, while once-daily L-DOPA treatment was maintained. The effects of once-daily amantadine (3 mg/kg, p.o.) were then assessed over weeks 11-12. LID, parkinsonism, duration and quality of ON-time were assessed weekly by a neurologist blinded to treatment. TC-8831 reduced the duration of 'bad' ON-time (ON-time with disabling dyskinesia) by up to 62% and decreased LID severity (median score 18 cf. 34 (vehicle), 0.1 mg/kg, 1-3 h period). TC-8831 also significantly reduced choreiform and dystonic dyskinesia (median scores 6 and 31 cf. 19 and 31 respectively (vehicle), both 0.03 mg/kg, 1-3 h). At no time did TC-8831 treatment result in a reduction in anti-parkinsonian benefit of L-DOPA. By comparison, amantadine also significantly reduced dyskinesia and decreased 'bad' ON-time (up to 61%) but at the expense of total ON-time (reduced by up to 23%). TC-8831 displayed robust anti-dyskinetic actions and improved the quality of ON-time evoked by L-DOPA without any reduction in anti-parkinsonian benefit.

Validation of a high-throughput, automated electrophysiology platform for the screening of nicotinic agonists and antagonists.

High-throughput compound screening using electrophysiology-based assays represents an important tool for biomedical research and drug discovery programs. The recent development and availability of devices capable of performing high-throughput electrophysiology-based screening have brought the need to validate these tools by producing data that are consistent with results obtained with conventional electrophysiological methods. In this study, we compared the response properties of hα3ß4 and hα4ß2 nicotinic receptors to their endogenous ligand acetylcholine (ACh) using three separate electrophysiology platforms: Dynaflow (low-throughput, manual system), PatchXpress 7000A (medium-throughput automated platform), and IonWorks Barracuda (high-throughput automated platform). We found that despite the differences in methodological approaches between these technologies, the EC(50) values from the ACh dose-response curves were consistent between all three platforms. In addition, we have validated the IonWorks Barracuda for both competitive and uncompetitive inhibition assays by using the competitive nicotinic antagonist dihydro-beta-erythroidin (DHßE) and uncompetitive nicotinic antagonist mecamylamine. Furthermore, we have demonstrated the utility of a custom-written algorithm for generating dose-response curves from multiple extrapolated current metrics that allows for discriminating between competitive and uncompetitive inhibition while maintaining high-throughput capacity. This study provides validation of the consistency of results using low-, medium-, and high-throughput electrophysiology platforms and supports their use for screening nicotinic compounds.

Slice XVIvo™: a novel electrophysiology system with the capability for 16 independent brain slice recordings.

Here we validate the design and use of a novel, customized electrophysiology system (Slice XVIvo™) that is capable of recording from 16 independent brain slices. The system consists of 16 independent recording chambers in which individual electrodes can be manually manipulated and fixed in order to stimulate and record extracellular responses from 16 brain slices simultaneously. Responses from each brain slice are elicited with individual stimulus isolator units and recorded through separate channels, thus allowing for independent control and analysis of the evoked extracellular activity from each slice. The system was designed to fit on a standard anti-vibration table, thus the Slice XVIvo™ system occupies considerably less space than other currently available multi-slice recording systems. We have demonstrated the utility of the system to obtain stable, extracellular responses from the CA1 region of the hippocampus, as well as induce long-term potentiation. Additionally, we show the utility of the Slice XVIvo™ system to significantly improved throughput for testing compounds in an oxygen and glucose deprivation assay. Overall, we have designed, created and validated a considerably cost- and space-efficient electrophysiology system that greatly improves throughput while minimizing the number of animals used in experiments.

Ethosuximide reduces ethanol withdrawal-mediated disruptions in sleep-related EEG patterns.

BACKGROUND: Chronic ethanol (EtOH) leads to disruptions in resting electroencephalogram (EEG) activity and in sleep patterns that can persist into the withdrawal period. These disruptions have been suggested to be predictors of relapse. The thalamus is a key structure involved in both normal brain oscillations, such as sleep-related oscillations, and abnormal rhythms found in disorders such as epilepsy and Parkinson's disease. Previously, we have shown progressive changes in mouse thalamic T-type Ca channels during chronic intermittent EtOH exposures that occurred in parallel with alterations in theta (4 to 8 Hz) EEG patterns. METHODS: Two groups of 8-week-old male C57BL/6 mice were implanted with wireless EEG/electromyogram (EMG) telemetry and subjected to 4 weeks of chronic, intermittent EtOH vapor exposure and withdrawal. During the week after the final withdrawal, mice were administered ethosuximide (ETX; 200 mg/kg) or saline. EEG data were analyzed via discrete Fourier transform, and sleep-scored for further analysis. RESULTS: Chronic intermittent EtOH exposure produced changes in the diurnal rhythms of the delta (0.5 to 4 Hz) and theta bands that persisted into a subsequent week of sustained withdrawal. These disruptions were restored with the T-channel blocker ETX. Repeated EtOH exposures preferentially increased the relative proportion of lower frequency power (delta and theta), whereas higher frequencies (8 to 24 Hz) were decreased. The EtOH-induced decreases in relative power for the higher frequencies continued into the sustained withdrawal week for both groups. Increases in absolute delta and theta power were observed in averaged nonrapid eye movement and rapid eye movement sleep spectral data during withdrawal in ETX-treated animals, suggesting increased sleep intensity. CONCLUSIONS: These results suggest that persistent alterations in delta and theta EEG rhythms during withdrawal from chronic intermittent EtOH exposure can be ameliorated with ETX and that this treatment might also increase sleep intensity during withdrawal.

A method for bidirectional solution exchange--"liquid bullet" applications of acetylcholine to α7 nicotinic receptors.

Fast solution exchange techniques have revolutionized the study of synaptic transmission and promise to remain an important neuroscience research tool. Here we provide evidence for the hypothesis that using continuous, rapid transitions through an agonist solution can significantly increase the exchange rate around a cell by reducing the diffusion boundary at the membrane. This novel approach of rapid solution exchange during whole-cell recordings--described as a "liquid bullet" (LB) application--takes advantage of a bidirectional solution flow around the cell, allowing for a full solution exchange within a range of several milliseconds. An exchange rate (10-90% rise time) of about 2 ms could be achieved during both agonist application and washout. We recorded whole-cell currents from cells expressing the rapidly desensitizing α7 neuronal nicotinic receptor (NNR) subtype that exhibited very fast rise times of around 4-5 ms. We further demonstrated the advantages of a LB application over conventional methods by the ability of this method to elicit concentration-dependent responses for rapidly desensitizing compounds that were not measurable with conventional agonist applications. In addition, we illustrate the utility of this approach for frequency-based assays through fast, repeated agonist applications at frequencies of 1 Hz and 30 Hz. This approach could therefore be useful for the study of rapid agonist-receptor interactions that closely mimic the physiological conditions in the synaptic cleft during bursts of neuronal activity.

Intrinsic plasticity in acquired epilepsy: too much of a good thing?

Mechanisms of plasticity are important to the astounding capacity of the brain to adapt and learn. Ion channels are significant contributors to neuronal plasticity, but their dysfunction has been implicated in several nervous system diseases from movement disorders to epilepsy. Although many inherited ion channel mutations have been associated with these disorders, it has been recently recognized that channelopathies can also include aberrant ion channel function that is acquired after an insult or injury to the brain. These acquired alterations are being investigated in animal models of temporal lobe epilepsy, where studies have shown functional changes in voltage-gated ion channels that lead to increases in excitability. Studies of these hyperexcitable neurons have included recordings in the hippocampus, entorhinal cortex, and thalamus and support the existence of an extended seizure network with several nodes of altered activity that are established during epileptogenesis. A better understanding of the key ion channels and brain regions that are responsible for the development of this hyperexcitability, along with the molecular mechanisms involved, may provide novel treatment strategies for epilepsy.

An acquired channelopathy involving thalamic T-type Ca2+ channels after status epilepticus.

Some epilepsies are linked to inherited traits, but many appear to arise through acquired alterations in neuronal excitability. Status epilepticus (SE) is associated with numerous changes that promote spontaneous recurrent seizures (SRS), and studies have suggested that hippocampal T-type Ca(2+) channels underlie increased bursts of activity integral to the generation of these seizures. The thalamus also contributes to epileptogenesis, but no studies have directly assessed channel alterations in the thalamus during SE or subsequent periods of SRS. We therefore investigated longitudinal changes in thalamic T-type channels in a mouse pilocarpine model of epilepsy. T-type channel gene expression was not affected during SE; however Ca(V)3.2 mRNA was significantly upregulated at both 10 d post-SE (seizure-free period) and 31 d post-SE (SRS-period). Overall T-type current density increased during the SRS period, and the steady-state inactivation shifted from a more hyperpolarized membrane potential during the latent stage, to a more depolarized membrane potential during the SRS period. Ca(V)3.2 functional involvement was verified with Ca(V)3.2 inhibitors that reduced the native T-type current in mice 31 d post-SE, but not in controls. Burst discharges of thalamic neurons reflected the changes in whole-cell currents, and we used a computational model to relate changes observed during epileptogenesis to a decreased tendency to burst in the seizure-free period, or an increased tendency to burst during the period of SRS. We conclude that SE produces an acquired channelopathy by inducing long-term alterations in thalamic T-type channels that contribute to characteristic changes in excitability observed during epileptogenesis and SRS.