A novel rodent continuous performance test (CPT) was developed as one of the goals of the NEWMEDS (Novel Methods leading to New Medications in Depression and Schizophrenia) consortium to improve its translatability to the CPT test used in human subjects.

The GABA(B) receptor has been indicated as a promising target for multiple CNS-related disorders. Baclofen, a prototypical orthosteric agonist, is used clinically for the treatment of spastic movement disorders, but is associated with unwanted side-effects, such as sedation and motor impairment. Positive allosteric modulators (PAM), which bind to a topographically-distinct site apart from the orthosteric binding pocket, may provide an improved side-effect profile while maintaining baclofen-like efficacy. GABA, the major inhibitory neurotransmitter in the CNS, plays an important role in the etiology and treatment of seizure disorders. Baclofen is known to produce anticonvulsant effects in the DBA/2J mouse audiogenic seizure test (AGS), suggesting it may be a suitable assay for assessing pharmacodynamic effects. Little is known about the effects of GABA(B) PAMs, however. The studies presented here sought to investigate the AGS test as a pharmacodynamic (PD) screening model for GABA(B) PAMs by comparing the profile of structurally diverse PAMs to baclofen. GS39783, rac-BHFF, CMPPE, A-1295120 (N-(3-(4-(4-chloro-3-fluorobenzyl)-6-methoxy-3,5-dioxo-4,5-dihydro-1,2,4-triazin-2(3H)-yl)phenyl)acetamide), and A-1474713 (N-(3-(4-(4-chlorobenzyl)-3,5-dioxo-4,5-dihydro-1,2,4-triazin-2(3H)-yl)phenyl)acetamide) all produced robust, dose-dependent anticonvulsant effects; a similar profile was observed with baclofen. Pre-treatment with the GABA(B) antagonist SCH50911 completely blocked the anticonvulsant effects of baclofen and CMPPE in the AGS test, indicating such effects are likely mediated by the GABA(B) receptor. In addition to the standard anticonvulsant endpoint of the AGS test, video tracking software was employed to assess potential drug-induced motor side-effects during the acclimation period of the test. This analysis was sensitive to detecting drug-induced changes in total distance traveled, which was used to establish a therapeutic index (TI = hypoactivity/anticonvulsant effects). Calculated TIs for A-1295120, CMPPE, rac-BHFF, GS39783, and A-1474713 were 5.31x, 5.00x, 4.74x, 3.41x, and 1.83x, respectively, whereas baclofen was <1. The results presented here suggest the DBA/2J mouse AGS test is a potentially useful screening model for detecting PD effects of GABA(B) PAMs and can provide an initial read-out on target-related motor side-effects. Furthermore, an improved TI was observed for PAMs compared to baclofen, indicating the PAM approach may be a viable therapeutic alternative to baclofen.

The low rate of success for identifying effective treatments for cognitive dysfunction has prompted recent efforts to improve pharmaceutical discovery and development. In particular, investigators have emphasized improving translation from pre-clinical to clinical research. A specific area of focus has been touchscreen technology; this computer-automated behavioral testing method provides an objective assessment of performance that can be used across species. As part of a larger multi-site study with partners from the Innovative Medicines Initiative (IMI), two US sites, AbbVie and Pfizer, conducted a cross-site experiment with a common protocol for the visual discrimination (VD) task using identical testing equipment, stimuli, and rats of the same strains, sex, and age from the same supplier. As most touchscreen-based rodent experiments have used Lister–Hooded rats that are not readily available outside of Europe, a strain comparison with male Long–Evans rats was conducted as part of the study. Rats were trained for asymptotic performance, and test sessions were performed once per week in a full crossover design with cognition-impairing drugs. Drugs tested were phencyclidine and S-ketamine (N-methyl-d-aspartate (NMDA) antagonists), d-amphetamine (indirect dopamine agonist), and scopolamine (muscarinic antagonist). Satellite brain and plasma samples were taken to confirm appropriate exposures. Results indicate that both rat strains show similar patterns of impairment, although Lister–Hooded rats were more sensitive than Long–Evans rats to three out of four drugs tested. This suggests that researchers should fully explore dose–response relationships in their strain of choice and use care in the interpretation of reversal of cognitive impairment.

Schizophrenia is a chronic disease that has been hypothesized to be linked to neurodevelopmental abnormalities. Schizophrenia patients exhibit impairments in basic sensory processing including sensory gating deficits in P50 and mismatch negativity (MMN). Neuronal nicotinic acetylcholine receptor (nAChR) agonists have been reported to attenuate these deficits. Gestational exposure of rats to methylazoxymethanol acetate (MAM) at embryonic day 17 leads to developmental disruption of the limbic-cortical system. MAM exposed offspring show neuropathological and behavioral changes that have similarities with those seen in schizophrenia. In this study, we aimed to assess whether N40 auditory sensory gating (the rodent form of P50 gating) and MMN deficits as measures of auditory evoked potential (AEP) electroencephalography (EEG) are present in MAM rats and whether nAChR agonists could attend the deficit. E17 male MAM and sham rats were implanted with cortical electrodes at 2 months of age. EEG recordings evaluating N40 gating and MMN paradigms were done comparing effects of vehicle (saline), nicotine and the α7 agonist ABT-107. Deficits were seen for MAM rats compared to sham animals in both N40 auditory sensory gating and MMN AEP recordings. There was a strong trend for N40 deficits to be attenuated by both nicotine (0.16 mg/kg i.p. base) and ABT-107 (1.0 mg/kg i.p. base). MMN deficits were significantly attenuated by ABT-107 but not by nicotine. These data support the MAM model as a useful tool for translating pharmacodynamic effects in clinical medicine studies of novel therapeutic treatments for schizophrenia.

Neuronal α4β2* nicotinic acetylcholine receptors mediate cognition, pain, and the discriminative and reinforcing effects of nicotine. In addition to traditional orthosteric agonists, α4β2* positive allosteric modulators (PAMs) have recently been identified. With increased subtype selectivity relative to agonists, PAMs administered alone or in combination with low-dose α4β2* agonists may be used as powerful tools for increasing our understanding of α4β2* pharmacology.

Cognitive impairment associated with schizophrenia (CIAS) is a major and disabling symptom domain of the disease that is generally unresponsive to current pharmacotherapies. Critically important to the discovery of novel therapeutics for CIAS is the utilization of preclinical models with robust predictive validity. We investigated the predictive validity of MK-801-induced memory impairments in mouse inhibitory avoidance (MK-IA) as a preclinical model for CIAS by investigating compounds that have been tested in humans, including antipsychotics, sodium channel blocker mood stabilizers, and putative cognitive enhancers. The atypical antipsychotic clozapine, as well as risperidone and olanzapine (see Brown et al., 2013), had no effect on MK-801-induced memory impairments. For sodium channel blockers, carbamazepine significantly attenuated memory impairments induced by MK-801, whereas lamotrigine had no effect. Nicotine, donepezil, modafinil, and xanomeline all significantly attenuated MK-801-induced memory impairments, but the magnitude of effects and the dose–responses observed varied across compounds. Clinically, only acute administration of nicotine has demonstrated consistent positive effects on CIAS, while inconsistent results have been reported for lamotrigine, donepezil, and modafinil; atypical antipsychotics produce only moderate improvements at best. A positive clinical signal has been observed with xanomeline, but only in a small pilot trial. The results presented here suggest that the MK-IA model lacks robust predictive validity for CIAS as the model is likely permissive and may indicate false positive signals for compounds and mechanisms that lack clear clinical efficacy for CIAS. Our findings also highlight the potential limitations and challenges of using NMDA receptor antagonists in rodents to model CIAS.

Cognitive deficits associated with schizophrenia (CDS) are implicated as a core symptom cluster of the disease and are associated with poor daily life functioning. Unfortunately, current antipsychotic agents provide little alleviation of CDS, representing a critical unmet therapeutic need. Here we investigated the effects of ABT-239 and A-431404, non-imidazole histamine H3 receptor (H3R) antagonists, in animal models with relevance to CDS. As N-methyl-d-aspartate receptor hypofunction is considered an important factor in the pathogenesis of schizophrenia, acute administration of ketamine or MK-801 was used to induce cognitive impairments. The assays employed in the current studies were spontaneous alternation in cross-maze, used as an indication of working memory, and inhibitory avoidance (IA), used to assess long-term memory retention. Risperidone and olanzapine were also tested to directly compare the effects of H3R antagonists to two widely used antipsychotics. ABT-239 and A-431404, but not risperidone and olanzapine, attenuated ketamine-induced deficits on spontaneous alternation in cross-maze, while none of these compounds affected alternation performance on their own. ABT-239 and A-431404 also attenuated MK-801-induced impairments in IA; no effects were observed when given alone. Risperidone and olanzapine, however, failed to attenuate MK-801-induced deficits in IA and produced dose-dependent impairments when given alone. ABT-239 was also investigated in methylazoxymethanol acetate (MAM) treated rats, a neurodevelopmental model for schizophrenia. Chronic, but not acute, treatment with ABT-239 significantly improved spontaneous alternation impairments in MAM rats tested in cross-maze. In summary, these results suggest H3R antagonists may have the potential to ameliorate CDS.

Background: Most animal models currently used to evaluate antinociceptive efficacy of analgesics rely on the assessment of evoked pain behaviours as primary endpoints.Mehtods: Here, we have developed and characterized the carrageenaninduced locomotor activity impairment (CLAIM) model to objectively assess non-evoked inflammatory pain behaviour in rats. In this model, 100 mu L of 1% carrageenan was subcutaneously injected into the plantar aspect of the right hind paw and exploratory behaviour in the novel testing chamber was recorded using an automated locomotor activity system.Results: Carrageenan-injected animals exhibited an exploratory behavioural deficit 2-7 h following injection compared to saline-injected animals. The severity of impairment was carrageenan dose related, and sensitive to the light intensity in the testing room. The effects of standard analgesics on CLAIM were examined 2 or 3 h following carrageenan injection. Diclofenac and ibuprofen, in a dose range exerting no effect on locomotor activity in naive rats, exhibited dose-related reversal of CLAIM (ED50 = 1.5 and 5.0 mg/kg, respectively), with comparable efficacy on carrageenan-induced thermal hyperalgesia (ED50 = 2.0 and 6.0 mg/kg, respectively). Gabapentin and duloxetine produced no reversal of CLAIM, or attenuation of thermal hyperalgesia. Efficacy discrepancy was noted for morphine on thermal hyperalgesia and CLAIM. Additionally, amphetamine dose dependently reversed CLAIM, and similarly increased locomotor activity in normal animals.Discussion and Conclusion: The results presented here demonstrate that CLAIM provides an objective assessment of non-evoked pain behaviours for acute inflammatory pain. The pharmacological profile of standard analgesics supports that CLAIM model can be used to identify agents to treat acute inflammatory pain in the clinic.

Rationale Drug development is a high-risk and high failure enterprise, and studies that provide an early read on the pharmacodynamic activity of novel compounds could save time and money, increasing the efficiency of the drug development process.Objective Preclinical and clinical experiments were designed to examine the utility of the scopolamine-induced cognitive impairment model in predicting pharmacodynamic signals of putatively procognitive compounds, utilizing the acetylcholinesterase inhibitor donepezil for illustration.Methods/Results In normal healthy rats, scopolamine (0.3 mg/kg) significantly impaired performance on the two-platform water maze and on the T-maze. The deficits in water maze performance were reversed by donepezil at 0.5 and 1.0 mg/kg. There was a trend towards reversal of scopolamine-induced deficits in performance on the T-maze with 1.0 mg/kg donepezil. In normal healthy humans, scopolamine (0.3 and 0.5 mg) reliably impaired performance on the Cognitive Drug Research test battery composite scores (power of attention, continuity of attention, quality of working memory, quality of episodic secondary memory, and speed of memory) in a dose-and time-dependent manner. Donepezil (10 mg) significantly attenuated the scopolamine-induced impairment in cognition on power of attention, continuity of attention, quality of working memory, and speed of memory.Conclusions These findings suggest that reversal of scopolamine-induced cognitive impairment is a viable model for predicting pharmacodynamic signals of procognitive compounds in both animals and humans. The utility of the scopolamine-induced cognitive impairment model is discussed and illustrated at various decision points in drug development, with a focus on Go/No Go decisions.

D-amino acid oxidase (DAO), an enzyme that degrades D-serine, has been suggested as a susceptibility factor for schizophrenia. Here we sought to understand more about the behavioral consequence of lacking DAO and the potential therapeutic implication of DAO inhibition by characterizing a mouse strain (ddY/DAO(-)) lacking DAO activity. We found that the mutant mice showed enhanced prepulse inhibition responses (PPI). Intriguingly, DAO-/- mice had increased sensitivity to the PPI-disruptive effect induced by the competitive NMDA antagonist, SDZ 220-581. In the 24-h inhibitory avoidance test, DAO-/- mice were not different from DAO+/+ mice during the recall. In Barnes Maze, we found that DAO-/- mice had a shortened latency to enter the escape tunnel. Interestingly, although these mice were hypoactive when tested in a protected open field, they showed a profound increase of activity on the edge of the unprotected open field of the Barnes Maze even with the escape tunnel removed. This increased edge activity does not appear to be related to a reduced level of anxiety given that there were no significant genotype effects on the measures of anxiety-like behaviors in two standard animal models of anxiety, elevated plus maze and novelty suppressed feeding. Our data suggest that DAO-/- mice might have altered functioning of NMDARs. However, these results provide only modest support for manipulations of DAO activity as a potential therapeutic approach to treat schizophrenia. (C) 2010 Elsevier B.V. All rights reserved.

Antipsychotics normalize responses in the DBA/2 mouse model of prepulse inhibition (PPI), a preclinical model of sensorimotor gating deficits. The α7 nicotinic acetylcholine receptor (nAChR) as a molecular target is considered an attractive approach for improvement of cognitive deficits in schizophrenia (CDS). Assessment of clinical efficacy of novel agents in CDS involves treating patients already on antipsychotic medications.

Anxiety disorders affect approximately 20% of the population, and women are twice as likely as men to develop anxiety disorders. Despite these findings, little is known about the effects of gender on tolerability and therapeutic efficacy of anxiolytic drugs. Sex differences are also observed in rodents, even though the majority of preclinical behavioral studies are conducted on males. The aim of this study was to investigate sex differences in anxiety-like behavior using the Vogel conflict test and the pharmacological responsiveness to a variety of psychoactive drugs in rats. Pharmacological treatments clinically used for the treatment of anxiety were tested in male and female rats. Overall, female rats accepted fewer punished responses, had lower levels of water intake even when matched for weight, and had a lower pain threshold for electrical footshock than males. Diazepam and chlordiazepoxide displayed anxiolytic-like effects in both genders. In contrast, buspirone, propranolol, fluoxetine and paroxetine showed activity only in male rats. Morphine had no anxiolytic-like activity in either gender. Analysis of the estrous cycle did not reveal any effect of cycle stage on behavioral or drug responses. This investigation highlights the importance of using female subjects in the preclinical research of anxiety and the screening of anxiolytic compounds in the drug development process.

Mounting evidence suggests excessive glucocorticoid activity may contribute to Alzheimer's disease (AD) and age-associated memory impairment. 11β-hydroxysteroid dehydrogenase type-1 (HSD1) regulates conversion of glucocorticoids from inactive to active forms. HSD1 knock-out mice have improved cognition, and the nonselective inhibitor carbenoxolone improved verbal memory in elderly men. Together, these data suggest that HSD1 inhibition may be a potential therapy for cognitive deficits, such as those associated with AD. To investigate this, we characterized two novel and selective HSD1 inhibitors, A-918446 and A-801195. Learning, memory consolidation, and recall were evaluated in mouse 24 h inhibitory avoidance. Inhibition of brain cortisol production and phosphorylation of cAMP response element-binding protein (CREB), a transcription factor involved in cognition, were also examined. Rats were tested in a short-term memory model, social recognition, and in a separate group cortical and hippocampal acetylcholine release was measured via in vivo microdialysis. Acute treatment with A-801195 (10-30 mg/kg) or A-918446 (3-30 mg/kg) inhibited cortisol production in the ex vivo assay by ∼ 35-90%. Acute treatment with A-918446 improved memory consolidation and recall in inhibitory avoidance and increased CREB phosphorylation in the cingulate cortex. Acute treatment with A-801195 significantly improved short-term memory in rat social recognition that was not likely due to alterations of the cholinergic system, as acetylcholine release was not increased in a separate set of rats. These studies suggest that selective HSD1 inhibitors work through a novel, noncholinergic mechanism to facilitate cognitive processing.

Mutant Tg2576 mice which possess the human "Swedish" APP mutation have been shown to demonstrate both Abeta plaque pathology and memory deficits in behavioral tasks. These mice are routinely maintained on a mixed C57BL/6xSJL genetic background which exhibits a high frequency of retinal degeneration allele and high variability in many behavioral assays. The same APP mutation is also available maintained on a 129 genetic background, providing more genetic homogeneity, but little data are published regarding the effects of the mutation on this background. We investigated whether transgenic mice expressing the Swedish mutation on the 129 background show similar behavioral deficits and Abeta pathology as those on the mixed background. Mice on the 129 background were tested at 6-7, 11-12, or 18-19 months of age in locomotor activity, Y-maze spontaneous alternation, and contextual fear conditioning. Differences were detected between WT and Tg mice in locomotor activity at 6-7 and 18-19 months, Y-maze at 6-7 and 11-12 months, and fear conditioning at 6-7, 11-12, and 18-19 months. In contrast, Tg mice on the mixed B6/SJL background tested at 6-7 months only demonstrated significant impairment in the contextual fear conditioning assay and in the Y-maze in one of 2 cohorts tested. Despite the behavioral differences observed, similar Abeta pathology was observed between Tg mice on the two genetic backgrounds. These results indicate that mice on the 129 genetic background may generate more consistent and robust behavioral differences, providing a useful model for testing therapeutic agents for Alzheimer's disease.

Blockade of the histamine H3 receptor (H3R) enhances central neurotransmitter release, making it an attractive target for the treatment of cognitive disorders. Here, we present in vitro and in vivo pharmacological profiles for the H3R antagonist 2-[4′-((3aR,6aR)-5-methyl-hexahydro-pyrrolo[3,4-b]pyrrol-1-yl)-biphenyl-4-yl]-2H-pyridazin-3-one (ABT-288). ABT-288 is a competitive antagonist with high affinity and selectivity for human and rat H3Rs (Ki = 1.9 and 8.2 nM, respectively) that enhances the release of acetylcholine and dopamine in rat prefrontal cortex. In rat behavioral tests, ABT-288 improved acquisition of a five-trial inhibitory avoidance test in rat pups (0.001–0.03 mg/kg), social recognition memory in adult rats (0.03–0.1 mg/kg), and spatial learning and reference memory in a rat water maze test (0.1–1.0 mg/kg). ABT-288 attenuated methamphetamine-induced hyperactivity in mice. In vivo rat brain H3R occupancy of ABT-288 was assessed in relation to rodent doses and exposure levels in behavioral tests. ABT-288 demonstrated a number of other favorable attributes, including good pharmacokinetics and oral bioavailability of 37 to 66%, with a wide central nervous system and cardiovascular safety margin. Thus, ABT-288 is a selective H3R antagonist with broad procognitive efficacy in rodents and excellent drug-like properties that support its advancement to the clinical area.

A growing body of evidence suggests excessive glucocorticoid activity may contribute to Alzheimer's disease (AD) and age-associated memory impairment. 11beta-hydroxysteroid dehydrogenase type 1 (11β-HSD1) regulates conversion of glucocorticoids from inactive to active forms. 11β-HSD1 knock-out mice have improved cognition and the non-selective inhibitor carbenoxolone improved verbal memory in elderly men. Taken together, these data suggest that 11β-HSD1 inhibition may be a potential new therapy for cognitive deficits associated with AD. We characterized two novel 11β-HSD1 inhibitors, A-918446 and A-801195. Mice were treated with A-918446 in diet for 18 days, tested in a 24-hour inhibitory avoidance (IA) test that measures memory consolidation/recall and then sacrificed to examine cAMP response element binding protein (CREB) phosphorylation in the cingulate cortex. To investigate the efficacy of acute administration, mice received A-918446 one hour before training in the IA test or before tissue collection. In rats, A-801195 was administered one hour before testing in a social recognition assay that measures short-term memory. Inhibition of brain cortisol production by A-801195 one hour post acute dosing was examined using an ex-vivo assay. Cortical and hippocampal acetylcholine release was measured via in vivo microdialysis in rats receiving acute A-801195. Dietary A-918446 (10 or 100 mg/kg/day for 18 days) improved memory consolidation and increased CREB phosphorylation in the cingulate cortex (100 mg/kg/day dose only) in mice. Furthermore, acute A-918446 (0.3-30 mg/kg) induced a dose-dependent improvement in memory consolidation/recall and increased cortical CREB phosphorylation. In rats, acute A-801195 (10 and 30 mg/kg, but not 3 mg/kg) significantly improved short-term memory. Efficacious doses of A-801195 (10 and 30 mg/kg) acutely inhibited brain cortisol production while a non-efficacious dose (3 mg/kg) did not. The cognitive improvement induced by 11β -HSD1 inhibitors is not likely a result of alterations to the cholinergic system, as no changes in cortical or hippocampal acetylcholine levels were observed in rats after treatment with A-801195 (30 mg/kg). These studies demonstrate that 11β-HSD1 inhibitors induce cognitive enhancement in two species and multiple cognitive domains through a novel, non-cholinergic mechanism, thereby suggesting that 11β-HSD1 inhibitors may be useful for the treatment of cognitive dysfunction associated with AD.