Therapeutic Approaches for NOP Receptor Antagonists in Neurobehavioral Disorders: Clinical Studies in Major Depressive Disorder and Alcohol Use Disorder with BTRX-246040 (LY2940094).

Conventional antidepressants increase the efflux of biogenic amine neurotransmitters (the monoamine hypothesis of depression) in the central nervous system (CNS) and are the principle drugs used to treat major depressive disorder (MDD). However, the lack of efficacy in some patients, the slow onset of action, and the side effect profiles of existing antidepressants necessitate the exploration of additional treatment options. The discovery of the nociceptin/orphanin FQ peptide NOP receptor (N/OFQ-NOP receptor) system and its characterization in preclinical biological and pharmacological stress-related conditions supports the potential antidepressant and anti-stress properties of a NOP receptor antagonist for the treatment of neurobehavioral disorders. BTRX-246040 (formerly LY2940094) was designed to test this hypothesis in the clinic. A small clinical proof of concept study demonstrated efficacy of BTRX-246040 in MDD patients. In this study, BTRX-246040 (40 mg, p.o.) significantly reduced negative bias as assessed by the facial recognition test within 1 week of treatment and decreased depression symptoms after 8 weeks. BTRX-246040 also reduced depression symptoms in a second trial with heavy alcohol drinkers. Given the comorbidity of MDD and alcohol use disorder, a compound with such effects in patients could be a valuable addition to the medications available. A proof of concept study showed efficacy of BTRX-246040 in reducing heavy drinking and increasing the probability of abstinence in individuals diagnosed with alcohol dependence. In addition, plasma levels of gamma-glutamyl transferase were decreased by BTRX-246040 compared to placebo control implying improvement in liver function. Collectively, the clinical data reviewed within this chapter suggest that BTRX-264040 functions to normalize dysfunction in reward circuits. The overall efficacy and safety of this compound with a novel mechanism of action are encouraging of further clinical development. BTRX-246040 is currently under development for MDD by BlackThorn Therapeutics.

Peripheral complement interactions with amyloid ß peptide in Alzheimer's disease: 2. Relationship to amyloid ß immunotherapy.

INTRODUCTION: Our previous studies have shown that amyloid ß peptide (Aß) is subject to complement-mediated clearance from the peripheral circulation, and that this mechanism is deficient in Alzheimer's disease. The mechanism should be enhanced by Aß antibodies that form immune complexes (ICs) with Aß, and therefore may be relevant to current Aß immunotherapy approaches. METHODS: Multidisciplinary methods were employed to demonstrate enhanced complement-mediated capture of Aß antibody immune complexes compared with Aß alone in both erythrocytes and THP1-derived macrophages. RESULTS: Aß antibodies dramatically increased complement activation and opsonization of Aß, followed by commensurately enhanced Aß capture by human erythrocytes and macrophages. These in vitro findings were consistent with enhanced peripheral clearance of intravenously administered Aß antibody immune complexes in nonhuman primates. DISCUSSION: Together with our previous results, showing significant Alzheimer's disease deficits in peripheral Aß clearance, the present findings strongly suggest that peripheral mechanisms should not be ignored as contributors to the effects of Aß immunotherapy.

Peripheral complement interactions with amyloid ß peptide: Erythrocyte clearance mechanisms.

INTRODUCTION: Although amyloid ß peptide (Aß) is cleared from the brain to cerebrospinal fluid and the peripheral circulation, mechanisms for its removal from blood remain unresolved. Primates have uniquely evolved a highly effective peripheral clearance mechanism for pathogens, immune adherence, in which erythrocyte complement receptor 1 (CR1) plays a major role. METHODS: Multidisciplinary methods were used to demonstrate immune adherence capture of Aß by erythrocytes and its deficiency in Alzheimer's disease (AD). RESULTS: Aß was shown to be subject to immune adherence at every step in the pathway. Aß dose-dependently activated serum complement. Complement-opsonized Aß was captured by erythrocytes via CR1. Erythrocytes, Aß, and hepatic Kupffer cells were colocalized in the human liver. Significant deficits in erythrocyte Aß levels were found in AD and mild cognitive impairment patients. DISCUSSION: CR1 polymorphisms elevate AD risk, and >80% of human CR1 is vested in erythrocytes to subserve immune adherence. The present results suggest that this pathway is pathophysiologically relevant in AD.

Animal paradigms to assess cognition with translation to humans.

Cognition is a complex brain function that represents processes such as learning and memory, attention, working memory, and executive functions amongst others. Impairments in cognition are prevalent in many neuropsychiatric and neurological disorders with few viable treatment options. The development of new therapies is challenging, and poor efficacy in clinical development continues to be one of the most consistent reasons compounds fail to advance, suggesting that traditional animal models are not predictive of human conditions and behavior. An effort to improve the construct validity of neuropsychological testing across species with the intent of facilitating therapeutic development has been strengthening over recent years. With an emphasis on understanding the underlying biology, optimizing the use of appropriate systems (e.g., transgenic animals) to model targeted disease states, and incorporating non-rodent species (e.g., non-human primates) that may enable a closer comparison to humans, an improvement in the translatability of the results will be possible. This chapter focuses on some promising translational cognitive paradigms for use in rodents, non-human primates, and humans.

Characterization of RO5126946, a Novel α7 nicotinic acetylcholine receptor-positive allosteric modulator.

Both preclinical evidence and clinical evidence suggest that α7 nicotinic acetylcholine receptor activation (α7nAChR) improves cognitive function, the decline of which is associated with conditions such as Alzheimer's disease and schizophrenia. Moreover, allosteric modulation of α7nAChR is an emerging therapeutic strategy in an attempt to avoid the rapid desensitization properties associated with the α7nAChR after orthosteric activation. We used a calcium assay to screen for positive allosteric modulators (PAMs) of α7nAChR and report on the pharmacologic characterization of the novel compound RO5126946 (5-chloro-N-[(1S,3R)-2,2-dimethyl-3-(4-sulfamoyl-phenyl)-cyclopropyl]-2-methoxy-benzamide), which allosterically modulates α7nAChR activity. RO5126946 increased acetylcholine-evoked peak current and delayed current decay but did not affect the recovery of α7nAChRs from desensitization. In addition, RO5126946's effects were absent when nicotine-evoked currents were completely blocked by coapplication of the α7nAChR-selective antagonist methyl-lycaconitine. RO5126946 enhanced α7nAChR synaptic transmission and positively modulated GABAergic responses. The absence of RO5126946 effects at human α4ß2nAChR and 5-hydroxytryptamine 3 receptors, among others, indicated selectivity for α7nAChRs. In vivo, RO5126946 is orally bioavailable and brain-penetrant and improves associative learning in a scopolamine-induced deficit model of fear conditioning in rats. In addition, procognitive effects of RO5126946 were investigated in the presence of nicotine to address potential pharmacologic interactions on behavior. RO5126946 potentiated nicotine's effects on fear memory when both compounds were administered at subthreshold doses and did not interfere with procognitive effects observed when both compounds were administered at effective doses. Overall, RO5126946 is a novel α7nAChR PAM with cognitive-enhancing properties.

Discovery of a cyclopentylamine as an orally active dual NK1 receptor antagonist-serotonin reuptake transporter inhibitor.

Cyclopentylamine 4 was identified as a potent dual NK1R antagonist-SERT inhibitor. This compound demonstrated significant oral activity in the gerbil forced swimming test, suggesting that dual NK1R antagonists-SERT inhibitors may be useful in treating depression disorders.

Navacaprant, a novel and selective kappa opioid receptor antagonist, has no agonist properties implicated in opioid-related abuse.

Kappa opioid receptors (KORs) are implicated in the pathophysiology of various psychiatric and neurological disorders creating interest in targeting the KOR system for therapeutic purposes. Accordingly, navacaprant (NMRA-140) is a potent, selective KOR antagonist being evaluated as a treatment for major depressive disorder. In the present report, we have extended the pharmacological characterization of navacaprant by further demonstrating its selective KOR antagonist properties and confirming its lack of agonist activity at KORs and related targets involved in opioid-related abuse. Using CHO-K1 cells expressing human KOR, mu (MOR), or delta (DOR) opioid receptors, navacaprant demonstrated selective antagonist properties at KOR (IC50 = 0.029 µM) versus MOR (IC50 = 3.3 µM) and DOR (IC50 > 10 µM) in vitro. In vivo, navacaprant (10-30 mg/kg, i.p.) dose-dependently abolished KOR-agonist induced analgesia in the mouse tail-flick assay. Additionally, navacaprant (10, 30 mg/kg, p.o.) significantly reduced KOR agonist-stimulated prolactin release in mice and rats, confirming KOR antagonism in vivo. Navacaprant showed no agonist activity at any opioid receptor subtype (EC50 > 10 µM) in vitro and exhibited no analgesic effect in the tail-flick assays at doses ≤100 mg/kg, p.o. thereby confirming a lack of opioid receptor agonist activity in vivo. Importantly, navacaprant did not alter extracellular dopamine concentrations in the nucleus accumbens shell of freely-moving rats following doses ≤100 mg/kg, p.o., whereas morphine (10, 20 mg/kg, i.p.) significantly increased dopamine levels. These results demonstrate that navacaprant is a KOR-selective antagonist with no pharmacological properties implicated in opioid-related abuse.

Discovery of disubstituted piperidines and homopiperidines as potent dual NK1 receptor antagonists-serotonin reuptake transporter inhibitors for the treatment of depression.

This report describes the synthesis, structure-activity relationships and activity of piperidine, homopiperidine, and azocane derivatives combining NK1 receptor (NK1R) antagonism and serotonin reuptake transporter (SERT) inhibition. Our studies culminated in the discovery of piperidine 2 and homopiperidine 8 as potent dual NK1R antagonists-SERT inhibitors. Compound 2 demonstrated significant activity in the gerbil forced swimming test, suggesting that dual NK1R antagonists-SERT inhibitors may be useful in treating depression disorders.

Kappa opioid receptor antagonism protects working memory performance from mild stress exposure in Rhesus macaques.

Extensive preclinical and emerging clinical evidence point to an involvement of the kappa opioid receptor (KOR) in brain networks that promotes neurobehavioral stability. KOR expression in mesolimbic and mesocortical pathways has been the basis for characterizing the role of this receptor system in regulating motivation and emotion; however, the involvement of the KOR system in higher-order executive processes such as working memory (WM) is not well-understood. WM is readily impaired with uncontrollable stress exposure and is dysregulated in many neurobehavioral disorders. To empirically evaluate the role of the KOR system on WM performance, we administered a selective KOR antagonist, NMRA-140 (0, 0.1, 0.3, 1.0 mg/kg, intramuscular) to monkeys under both stress and non-stress conditions. In this study, NMRA-140 was co-administered with FG7142, a benzodiazepine inverse agonist, known to produce a mild stress response and to impair WM function in monkeys. NMRA-140 protected WM performance from the detrimental effects of FG7142-induced stress and exhibited no significant effect under non-stress conditions. Collectively, these data highlight the functional influence of the KOR system in mediating stress-induced dysfunction of executive processes and suggest that modulating KOR activity could offer therapeutic benefit in stress-related neurobehavioral disorders.

RG3487, a novel nicotinic α7 receptor partial agonist, improves cognition and sensorimotor gating in rodents.

Neuronal nicotinic α7 acetylcholine receptors (α7nAChRs) are expressed primarily in the brain and are implicated in modulating many cognitive functions (e.g., attention, working and episodic memory). Not surprisingly, much effort has been committed to the development of molecules acting at α7nAChRs as potential therapies for a variety of central nervous system diseases (e.g., Alzheimer's). N-[(3S)-1-azabicyclo[2.2.2]oct-3-yl]-1H-indazole-3-carboxamide hydrochloride (RG3487) binds potently to the human α7nAChR (K(i) = 6 nM), in which it acts as a partial agonist (63-69% of acetylcholine) as assessed by whole-cell patch-clamp recordings in both oocytes and QM7 cell lines. RG3487 activates human α7nAChRs with an EC(50) of 0.8 µM (oocytes) and 7.7 µM (QM7 cells). RG3487 also exhibits antagonist properties at the serotonin 3 receptor [IC(50) = 2.8 nM (oocytes), 32.7 nM (N1E-115 cells)]. In vivo, RG3487 improved object recognition memory in rats after acute [minimally effective dose (MED) 1.0 mg/kg p.o.] or repeated (10 day) administration at brain and plasma concentrations in the low-nanomolar range. Spatial learning deficits in age-impaired rats were reversed after RG3487 administration (MED: 0.03 mg/kg i.p.) as evaluated in the Morris water maze task. In the prepulse inhibition (PPI) of startle model of sensorimotor gating, RG3487 improved apomorphine-induced deficits in PPI performance (MED: 0.03 mg/kg i.p.) and reversed phencyclidine-induced impairments in an attentional set-shifting model of executive function (MED: ≤0.03 mg/kg i.p.). Cumulative evidence from these studies indicates RG3487 is a novel and potent α7nAChR partial agonist that improves cognitive performance and sensorimotor gating.

Basmisanil, a highly selective GABAA-α5 negative allosteric modulator: preclinical pharmacology and demonstration of functional target engagement in man.

GABAA-α5 subunit-containing receptors have been shown to play a key modulatory role in cognition and represent a promising drug target for cognitive dysfunction, as well as other disorders. Here we report on the preclinical and early clinical profile of a novel GABAA-α5 selective negative allosteric modulator (NAM), basmisanil, which progressed into Phase II trials for intellectual disability in Down syndrome and cognitive impairment associated with schizophrenia. Preclinical pharmacology studies showed that basmisanil is the most selective GABAA-α5 receptor NAM described so far. Basmisanil bound to recombinant human GABAA-α5 receptors with 5 nM affinity and more than 90-fold selectivity versus α1, α2, and α3 subunit-containing receptors. Moreover, basmisanil inhibited GABA-induced currents at GABAA-α5 yet had little or no effect at the other receptor subtypes. An in vivo occupancy study in rats showed dose-dependent target engagement and was utilized to establish the plasma exposure to receptor occupancy relationship. At estimated receptor occupancies between 30 and 65% basmisanil attenuated diazepam-induced spatial learning impairment in rats (Morris water maze), improved executive function in non-human primates (object retrieval), without showing anxiogenic or proconvulsant effects in rats. During the Phase I open-label studies, basmisanil showed good safety and tolerability in healthy volunteers at maximum GABAA-α5 receptor occupancy as confirmed by PET analysis with the tracer [11C]-Ro 15-4513. An exploratory EEG study provided evidence for functional activity of basmisanil in human brain. Therefore, these preclinical and early clinical studies show that basmisanil has an ideal profile to investigate potential clinical benefits of GABAA-α5 receptor negative modulation.

A Review of the Cholinergic System and Therapeutic Approaches to Treat Brain Disorders.

Since its identification over a hundred years ago, the neurotransmitter acetylcholine (ACh) has proven to play an essential role in supporting many diverse functions. Some well-characterized functions include: chemical transmission at the neuromuscular junction; autonomic function in the peripheral nervous system; and, sustained attention, sleep/wake regulation, and learning and memory within the central nervous system. Within the brain, major cholinergic projection pathways from the basal forebrain and the brainstem support these centrally mediated processes, and dysregulation of the cholinergic system is implicated in cognitive decline associated with aging and dementias including Alzheimer's disease. ACh exerts its effects by binding to two different membrane-bound receptor classes: (1) G­protein coupled muscarinic acetylcholine receptors (mAChRs), and (2) ligand-gated nicotinic acetylcholine receptors (nAChRs). These receptor systems are described in detail within this chapter along with discussion on the successes and failures of synthetic ligands designed to selectively target receptor subtypes for treating brain disorders. New molecular approaches and advances in our understanding of the target biology combined with opportunities to re-purpose existing cholinergic drugs for new indications continue to highlight the exciting opportunities for modulating this system for therapeutic purposes.

Differential effects of novel kappa opioid receptor antagonists on dopamine neurons using acute brain slice electrophysiology.

Activation of the kappa opioid receptor (KOR) contributes to the aversive properties of stress, and modulates key neuronal circuits underlying many neurobehavioral disorders. KOR agonists directly inhibit ventral tegmental area (VTA) dopaminergic neurons, contributing to aversive responses (Margolis et al. 2003, 2006); therefore, selective KOR antagonists represent a novel therapeutic approach to restore circuit function. We used whole cell electrophysiology in acute rat midbrain slices to evaluate pharmacological properties of four novel KOR antagonists: BTRX-335140, BTRX-395750, PF-04455242, and JNJ-67953964. Each compound concentration-dependently reduced the outward current induced by the KOR selective agonist U-69,593. BTRX-335140 and BTRX-395750 fully blocked U-69,593 currents (IC50 = 1.2 ± 0.9 and 1.2 ± 1.3 nM, respectively). JNJ-67953964 showed an IC50 of 3.0 ± 4.6 nM. PF-04455242 exhibited partial antagonist activity asymptoting at 55% blockade (IC50 = 6.7 ± 15.1 nM). In 3/8 of neurons, 1 µM PF-04455242 generated an outward current independent of KOR activation. BTRX-335140 (10 nM) did not affect responses to saturating concentrations of the mu opioid receptor (MOR) agonist DAMGO or the delta opioid receptor (DOR) agonist DPDPE, while JNJ-67953964 (10 nM) partially blocked DAMGO and DPDPE responses. Importantly, BTRX-335140 (10 nM) rapidly washed out with complete recovery of U-69,593 responses within 10 min. Collectively, we show electrophysiological evidence of key differences amongst KOR antagonists that could impact their therapeutic potential and have not been observed using recombinant systems. The results of this study demonstrate the value of characterizing compounds in native neuronal tissue and within circuits implicated in the neurobehavioral disorders of interest.

Differential Modulation of Ventral Tegmental Area Circuits by the Nociceptin/Orphanin FQ System.

The neuropeptide nociceptin/orphanin FQ (N/OFQ) can be released by stressors and is associated with disorders of emotion regulation and reward processing. N/OFQ and its receptor, NOP, are enriched in dopaminergic pathways, and intra-ventricular agonist delivery decreases dopamine levels in the dorsal striatum, nucleus accumbens (NAc), and ventral tegmental area (VTA). We used whole-cell electrophysiology in acute rat midbrain slices to investigate synaptic actions of N/OFQ. N/OFQ was primarily inhibitory, causing outward currents in both immunocytochemically identified dopaminergic (tyrosine hydroxylase positive (TH(+))) and non-dopaminergic (TH(-)) VTA neurons; effect at 1 µm: 20 ± 4 pA. Surprisingly, this effect was mediated by augmentation of postsynaptic GABAAR currents, unlike the substantia nigra pars compacta (SNc), where the N/OFQ-induced outward currents were K+ channel dependent. A smaller population, 17% of all VTA neurons, responded to low concentrations of N/OFQ with inward currents (10 nm: -11 ± 2 pA). Following 100 nm N/OFQ, the response to a second N/OFQ application was markedly diminished in VTA neurons (14 ± 10% of first response) but not in SNc neurons (90 ± 20% of first response). N/OFQ generated outward currents in medial prefrontal cortex (mPFC)-projecting VTA neurons, but inward currents in a subset of posterior anterior cingulate cortex (pACC)-projecting VTA neurons. While N/OFQ inhibited NAc-projecting VTA cell bodies, it had little effect on electrically or optogenetically evoked terminal dopamine release in the NAc measured ex vivo with fast scan cyclic voltammetry (FSCV). These results extend our understanding of the N/OFQ system in brainstem circuits implicated in many neurobehavioral disorders.

Spirometry use in Patients with Sickle Cell Disease with and without asthma and acute chest syndrome: A Multicenter Study.

A de-identified data repository of electronic medical record (EMR) data, i2b2 (Informatics for Integrating Biology and the Bedside), including 4 geographically diverse academic medical centers, was queried to determine the use of diagnostic spirometry testing in African American children and young adults 5-34 years old with sickle cell disease (SCD) with or without a documented history of asthma and/or acute chest syndrome (ACS). A total of 2,749 patients were identified with SCD, of these 577 had asthma and 409 had ACS. Cross-referencing the CPT code for diagnostic spirometry showed that for patients identified as having SCD, a history or ACS, and a diagnosis of asthma, only 31% across all 4 centers had spirometry. Having an asthma diagnosis was associated with ACS. Among SCD patients with asthma, the proportion with ACS for the four centers was 47%, 75%, 38%, and 36% respectively. The bivariate association between asthma and ACS for each Center was significant for each (p<.001). To summarize, only one third of patients with co-morbid SCD, ACS, and asthma received the spirometry procedure as recommended in evidence-based guidelines, suggesting limited testing for changes in pulmonary function. Future studies to determine barriers and facilitators to implementation of pulmonary testing in SCD are warranted.

Trace amine-associated receptor 1 agonism promotes wakefulness without impairment of cognition in Cynomolgus macaques.

Trace amine-associated receptor 1 (TAAR1) is a G-protein coupled receptor with affinity for the trace amines. TAAR1 agonists have pro-cognitive, antidepressant-, and antipsychotic-like properties in both rodents and non-human primates (NHPs). TAAR1 agonism also increases wakefulness and suppresses rapid-eye movement (REM) sleep in mice and rats and reduces cataplexy in two mouse models of narcolepsy. We investigated the effects of TAAR1 agonism in Cynomolgus macaques, a diurnal species that exhibits consolidated night-time sleep, and evaluated the effects of TAAR1 agonists on cognition using a working memory (WM) paradigm in this species. Adult male Cynomolgus macaques (n = 6) were surgically implanted to record the electroencephalogram (EEG), electromyogram, and locomotor activity (LMA) and the efficacy of the TAAR1 partial agonist RO5263397 (0.1,1,10 mg/kg, p.o.) on sleep/wake, EEG spectra, and LMA was determined. In a second experiment, the acute effects of RO5263397 (0.1,1,10 mg/kg, p.o.) were assessed on a delayed-match-to-sample test of WM in adult male macaques (n = 7). RO5263397 (10 mg/kg) administered at lights off, when sleep pressure was high, promoted wakefulness and reduced both REM and non-REM sleep without inducing hyperlocomotion. RO5263397 (10 mg/kg) also increased delta/theta activity during all vigilance states. RO5263397 had no effect on WM at either short (2 sec) or long (10 sec) delay intervals. The wake-enhancing and REM-suppressing effects of R05263397 shown here in a diurnal primate are consistent with previous results in nocturnal rodents. These effects and the associated alterations in EEG spectra occurred without inducing hyperlocomotion or affecting WM, encouraging further study of TAAR1 agonists as potential narcolepsy therapeutics.

Electrophysiological characterization of sleep/wake, activity and the response to caffeine in adult cynomolgus macaques.

Most preclinical sleep studies are conducted in nocturnal rodents that have fragmented sleep in comparison to humans who are primarily diurnal, typically with a consolidated sleep period. Consequently, we sought to define basal sleep characteristics, sleep/wake architecture and electroencephalographic (EEG) activity in a diurnal non-human primate (NHP) to evaluate the utility of this species for pharmacological manipulation of the sleep/wake cycle. Adult, 9-11 y.o. male cynomolgus macaques (n = 6) were implanted with telemetry transmitters to record EEG and electromyogram (EMG) activity and Acticals to assess locomotor activity under baseline conditions and following injections either with vehicle or the caffeine (CAF; 10 mg/kg, i.m.) prior to the 12 h dark phase. EEG/EMG recordings (12-36 h in duration) were analyzed for sleep/wake states and EEG spectral composition. Macaques exhibited a sleep state distribution and architecture similar to previous NHP and human sleep studies. Acute administration of CAF prior to light offset enhanced wakefulness nearly 4-fold during the dark phase with consequent reductions in both NREM and REM sleep, decreased slow wave activity during wakefulness, and increased higher EEG frequency activity during NREM sleep. Despite the large increase in wakefulness and profound reduction in sleep during the dark phase, no sleep rebound was observed during the 24 h light and dark phases following caffeine administration. Cynomolgus macaques show sleep characteristics, EEG spectral structure, and respond to CAF in a similar manner to humans. Consequently, monitoring EEG/EMG by telemetry in this species may be useful both for basic sleep/wake studies and for pre-clinical assessments of drug-induced effects on sleep/wake.

Enhanced long-term potentiation and impaired learning in phosphodiesterase 4D-knockout (PDE4D) mice.

Elevation of intracellular cyclic adenosine monophosphate (cAMP) concentrations and subsequent regulation of downstream target gene expression through phosphorylation of cAMP-responsive element binding protein (CREB) is hypothesized to underlie the mechanism(s) of long-term memory (LTM) formation. The phosphodiesterase 4 (PDE4) enzyme family is believed to play a key role in LTM by regulating cAMP levels. Thus far, four PDE4 isoforms have been identified (PDE4A, B, C and D); however, the requisite involvement of each of these isoforms in mediating LTM has yet to be elucidated. In the present study, genetic knockout mice were used to investigate the involvement of the PDE4D isoform in both in vitro and in vivo models of learning and memory. Hippocampal synaptic transmission measured electrophysiologically in CA1 slice preparations was similar between wild-type and PDE4D (-/-) mice yet, relative to wild-type controls, knockout mice displayed enhanced early long-term potentiation (LTP) following multiple induction protocols. Interestingly, the PDE4D (-/-) animals exhibited significant behavioral deficits in associative learning using a conditioned fear paradigm as compared with control littermates. The impairment in fear conditioning observed in the PDE4D (-/-) mice could not be attributed to differences in acquisition of the task, alterations in locomotor activity or effects on shock sensitivity. Overall, the in vitro and in vivo alterations in synaptic plasticity observed in the PDE4D (-/-) mice may be explained by adaptive responses occurring throughout development, and suggest that the PDE4D isoform may be an important mediator of LTM formation.

Alterations in High-Frequency Neuronal Oscillations in a Cynomolgus Macaque Test of Sustained Attention Following NMDA Receptor Antagonism.

A growing body of evidence indicates that neuronal oscillations in the gamma frequency range (30-80 Hz) are disturbed in schizophrenic patients during cognitive processes and may represent an endophenotype of the disease. N-methyl-D-aspartate (NMDA) receptor antagonists have been used experimentally to induce schizophrenia-like symptoms including cognitive deficits in animals and humans. Here we characterized neuronal oscillations and event-related potentials (ERPs) in Cynomolgus macaques fully trained to perform a continuous performance test (CPT) in the presence and absence of the NMDA antagonist phencyclidine (PCP). Macaques (n=8) were trained to touch 'target' stimuli and ignore 'distractor' stimuli presented randomly on a touchscreen. Subsequently, all subjects were implanted with epidural EEG electrodes over frontal (FC) and parietal cortices (PC) and later tested under vehicle (saline, i.m.) or acute PCP (0.1-0.3 mg/kg, i.m.) conditions. Compared with vehicle treatment, PCP produced a significant dose-dependent decrease in CPT performance accuracy and increased reaction times. Furthermore, PCP elevated the amplitudes of 'low' (30-50 Hz) and 'high' (51-80 Hz) gamma oscillations in FC and PC around target presentations for all correct responses. The CPT accuracy was inversely correlated with the gamma band amplitude in the presence of PCP. Additionally, PCP delayed the N100 peak latency in FC, and prolonged and suppressed the cognitively relevant P300 component of mean ERPs in FC and PC, respectively. The NMDA receptor antagonist-induced alteration in neuronal oscillations and ERPs may contribute to the observed cognitive deficits in macaques, and enhance our understanding of EEG recordings as a translatable biomarker.