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.

Schizophrenia (SCZ) is a neurodevelopmental psychiatric disorder, in which cognitive function becomes disrupted at early stages of the disease. Although the mechanisms underlying cognitive impairments remain unclear, N-methyl-D-aspartate receptors (NMDAR) hypofunctioning in the prefrontal cortex (PFC) has been implicated. Moreover, cognitive symptoms in SCZ are usually unresponsive to treatment with current antipsychotics and by onset, disruption of the dopamine system, not NMDAR hypofunctioning, dominates the symptoms. Therefore, treating cognitive deficits at an early stage is a realistic approach. In this study, we tested whether an early treatment targeting mGluR2 would be effective in ameliorating cognitive impairments in the methylazoxymethanol acetate (MAM) model of SCZ. We investigated the effects of an mGluR2 agonist/mGluR3 antagonist, LY395756 (LY39), on the NMDAR expression and function in juveniles, as well as cognitive deficits in adult rats after juvenile treatment. We found that gestational MAM exposure induced a significant decrease in total protein levels of the NMDAR subunit, NR2B, and a significant increase of pNR2BTyr1472 in the juvenile rat PFC. Treatment with LY39 in juvenile MAM-exposed rats effectively recovered the disrupted NMDAR expression. Furthermore, a subchronic LY39 treatment in juvenile MAM-exposed rats also alleviated the learning deficits and cognitive flexibility impairments when tested with a cross-maze based set-shifting task in adults. Therefore, our study demonstrates that targeting dysfunctional NMDARs with an mGluR2 agonist during the early stage of SCZ could be an effective strategy in preventing the development and progression in addition to ameliorating cognitive impairments of SCZ.

Schizophrenia is a highly familial, neurodevelopmental disorder that is associated with several neuropsychiatric, psychological, and neuropathological features. Although pharmacological animal models of dopaminergic and glutamatergic dysfunction have helped advance our understanding of the disease biology, there is a clear need for translational models that capture the neuropathological and functional manifestations associated with the intermediate phenotype and the clinical illness. Neuroimaging of preclinical neurodevelopmental approaches such as methylazoxymethanol acetate (MAM) exposure may afford a powerful translational tool to establish endpoints with greater congruency across animals and humans. Using in vivo volumetric magnetic resonance imaging (MRI), manganese-enhanced MRI, and diffusion tensor imaging (DTI), we investigated morphological and cytoarchitectural changes of brain structures in MAM-exposed rats, a neurodevelopmental model of schizophrenia. Compared to saline-exposed controls, MAM-exposed rats showed significant enlargement of lateral and third ventricles as well as reduced hippocampal volumes, which is consistent with findings observed in schizophrenia. In addition, DTI revealed that diffusion fractional anisotropy retrieved from corpus callosum and cingulum were significantly decreased in MAM-exposed rats, suggesting that demyelination occurred in these white-matter fiber tracts. Imaging findings were confirmed by conducting histological analysis using hematoxylin and eosin and Luxol fast blue stainings. In summary, structural abnormalities resulting from a MAM environmental challenge parallel cerebral pathology observed in schizophrenia. The MAM model incorporating noninvasive imaging techniques may therefore serve as an improved translational research tool for assessing new treatments for schizophrenia.

Background and purpose:Several agonists of the alpha 7 nicotinic acetylcholine receptor (nAChR) have been developed for treatment of cognitive deficits. However, agonist efficacy in vivo is difficult to reconcile with rapid alpha 7 nAChR desensitization in vitro; and furthermore, the correlation between in vitro receptor efficacy and in vivo behavioural efficacy is not well delineated. The possibility that agonists of this receptor actually function in vivo as inhibitors via desensitization has not been finally resolved.Experimental approach:Two structurally related alpha 7 nAChR agonists were characterized and used to assess the degree of efficacy required in a behavioural paradigm.Key results:NS6784 activated human and rat alpha 7 nAChR with EC(50)s of 0.72 and 0.88 mu M, and apparent efficacies of 77 and 97% respectively. NS6740, in contrast, displayed little efficacy at alpha 7 nAChR (< 2% in oocytes, < 8% in GH4C1 cells), although its agonist-like properties were revealed by adding a positive allosteric modulator of alpha 7 nAChRs or using the slowly desensitizing alpha 7V274T receptor. In mouse inhibitory avoidance (IA) memory retention, NS6784 enhanced performance as did the 60% partial agonist A-582941. In contrast, NS6740 did not enhance performance, but blocked effects of A-582941.Conclusions and implications:Collectively, these findings suggest that a degree of alpha 7 nAChR agonist efficacy is required for behavioural effects in the IA paradigm, and that such behavioural efficacy is not due to alpha 7 nAChR desensitization. Also, a partial agonist of very low efficacy for this receptor could be used as an inhibitor, in the absence of alpha 7 nAChR antagonists with favourable CNS penetration.

Assessment of sensorimotor competence is an important part of the evaluation of animal behavior. Measurement of sensorimotor performance is of obvious importance in investigations of sensory or motor processes; however, the effects of experimental manipulations on sensorimotor performance have broader implications for behavioral neuroscience because behavioral experiments typically measure motor responses to sensory information. Thus, the results of behavioral experiments designed to assess other neurobiological processes often cannot be properly interpreted without considering concomitant effects on sensorimotor function. For example, if a lesion or genetic manipulation impairs performance on a spatial memory test, such as the radial arm maze, this impairment cannot be interpreted as evidence of cognitive dysfunction unless it is first established that it is not the result of sensorimotor deficits. Moreover, sensorimotor effects of manipulations can often be used in animal models as surrogates for effects that are more difficult to measure, and relatively simple variations of sensorimotor measures can be used as indices of performance in other behavioral domains, including cognition and emotion. A number of behavioral tasks have been designed to assess sensorimotor performance in rodents, and this chapter focuses on five general procedures—acoustic startle, sensory gating, open field exploration, rotarod, and beam walking.

Among the diverse sets of nicotinic acetylcholine receptors (nAChRs), the α7 subtype is highly expressed in the hippocampus and cortex and is thought to play important roles in a variety of cognitive processes. In this review, we describe the properties of a novel biaryl diamine α7 nAChR agonist, A‐582941. A‐582941 was found to exhibit high‐affinity binding and partial agonism at α7 nAChRs, with acceptable pharmacokinetic properties and excellent distribution to the central nervous system (CNS). In vitro and in vivo studies indicated that A‐582941 activates signaling pathways known to be involved in cognitive function such as ERK1/2 and CREB phosphorylation. A‐582941 enhanced cognitive performance in behavioral models that capture domains of working memory, short‐term recognition memory, memory consolidation, and sensory gating deficit. A‐582941 exhibited a benign secondary pharmacodynamic and tolerability profile as assessed in a battery of assays of cardiovascular, gastrointestinal, and CNS function. The studies summarized in this review collectively provide preclinical validation that α7 nAChR agonism offers a mechanism with potential to improve cognitive deficits associated with various neurodegenerative and psychiatric disorders.

Specific bilateral cholinergic lesions to the Nucleus Basalis Magnocelullaris (NBM) using 192- IgG Saporin (SAP) produce cortical cholinergic hypofunction similar to that present in Alzheimer's Disease (AD) (McGaughy et al, 2002). In rats, these lesions produce only minimal disruptive effects on learning and memory but can result in attentional deficits. Using this lesion model we investigated the importance of cortical cholinergic input in the cognition-enhancing effects of nicotine and two current AD treatments-the cholinesterase inhibitor donepezil and the NMDA antagonist memantine. Following bilateral SAP injections (21 nmol) to the NBM, Sprague-Dawley rats were allowed to recover for 12 – 14 days before being tested in the rat social recognition assay of short-term memory. An adult rat was placed in a clean cage with a juvenile, and the investigation time by the adult rat of the juvenile was measured in two-5 minute sessions separated by 2 hours. Drug was administered i.p. to the adult rat immediately following the first trial. The ratio of investigation times was used as a memory index. Histological examination of the brain revealed lesion-induced reductions of cholinergic fibers in the frontal cortex (35 -42 %) and the parietal cortex (45 – 50 %). Donepezil (0.25 mg/kg) enhanced memory in non-lesioned rats, but not in lesioned rats, whereas nicotine (0.3 mg/kg) and memantine (2.2 mg/kg) were each effective in both lesioned and non-lesioned animals. Thus, intact cortical cholinergic tone is more critical for the efficacy of donepezil than for the efficacy of nicotine and memantine in this model. This may have implications for the therapeutic potential of these different approaches in AD, which is characterized by cholinergic hypofuntion. Moreover, this model of cholinergic hypofunction may have relevance in identifying potential palliative therapies in AD.

The alpha-7 neuronal nicotinic acetylcholine receptor (nAChR) plays an important role in cognitive processes and represents a drug target for treating cognitive deficits in neurodegenerative diseases such as AD. In the present study, we used a novel alpha-7 nAChR-selective partial agonist A-582941 to interrogate cognitive efficacy, as well as to examine cellular mechanisms of cognition and neuroprotection. A range of in vitro and in vivo techniques were utilized to profile the novel biaryl diamine alpha-7 nAChR agonist. These include radioligand binding, in vitro functional assays, behavioral assays and immunohistochemistry approaches. A-582941 enhanced cognitive performance in behavioral assays including the monkey delayed matching-to-sample, rat social recognition, and mouse inhibitory avoidance models that capture domains of working memory, short-term recognition memory, and long-term memory consolidation, respectively. In addition, A-582941 normalized sensory gating deficits in DBA/2 mice. Examination of signaling pathways known to be involved in cognitive function revealed significant phosphorylation of ERK1/2 and CREB at behaviorally efficacious dose ranges. Studies were also conducted to assess the role of signaling pathways involving PI3K/Akt/GSK3beta. In in vivo studies, A-582941 evoked a dose-dependent increase in Ser-9 GSK-3β phosphorylation in mouse cingulate cortex and dentate gyrus. In APP overexpressing Tg2576 mice, decreased pCREB and pSer-9 GSK-3beta expression was reversed by treatment with A-582941. To determine whether inactivation of GSK-3beta activity could regulate tau hyperphosphorylation, the effects of A-582941 were assessed in a hypothermia-induced tau hyperphosphorylation mouse model and in a transgenic mouse line overexpressing APP/tau. Pentobarbital- increased tau phosphorylation was partially decreased by minipump infusion of A-582941. Likewise, A-582941 treatment led to a significant decline in AT8 labeling in the spinal cord in a transgenic mouse line that overexpressed APP/tau. These results demonstrate that alpha7 nAChR agonism (i) can elicit broad-spectrum symptomatic efficacy in animal models that capture diverse cognitive domains, at doses that enhance ERK1/2 and CREB phosphorylation and (ii) can alter disease progression by influencing GSK3beta-tau pathways. Thus, targeting alpha-7 nAChRs could represent an attractive mechanism that offers potential to improve cognitive deficits associated with Alzheimer's disease and other neurodegenerative diseases.

Introduction Schizophrenia is a complex disorder that can have a genetic and/or environmental etiology. Clinically, schizophrenia is characterized by three subsets of symptoms that are classed as positive (e.g. delusions, hallucinations; impulsive activity), negative (e.g. affective flattening, alogia, avolition, social withdrawal), and cognitive (e.g. disorganized thought, attentional, and speech processes) [1]. Although the etiology of schizophrenia remains elusive, structural and functional neuroimaging as well as the advance of new animal models have been providing great insights into its underlying pathophysiology [2, 3]. Herein, using T2-weighted and manganese-enhanced MRI (MEMRI) [4, 5] we aimed to investigate cytoarchitectural and morphological changes in methylazoxymethanol acetate (MAM)-treated rats – a neurodevelopmental model of schizophrenia [6, 7] – and to further evaluate the feasibility of translating these imaging data to schizophrenia patients. Materials and Methods Pregnant SD dams (Charles River, Portage, MI) were acquired on gestational day (GD) 10. On GD17, dams were administered saline or 25 mg/kg MAM i.p. Female offspring were weaned on postnatal day (PD) 21 and housed individually (n=11, saline-treated; n=8, MAM-treated) and later imaged on PD 45. Prior to imaging, rats were i.c.v. cannulated under isoflurane anesthesia. For MEMRI, MnCl2 (Sigma-Aldrich, St. Louis, MO) was dissolved in saline and injected via an i.c.v. cannula (0.08M, 5μL), 24-h before imaging. Rats were anesthetized and imaged using a 7T MRI scanner (Bruker Biospin, Karlsruhe, Germany) with a T1-weighted (TR/TE = 600/10 ms, NA=16), or T2weighted (TR/TE =3200/75ms, RARE factor = 8, NA=8) pulse sequence at a pixel size = 250 × 250 μm and slice thickness = 1.25 mm. Volumetric analysis was conducted using AFNI [8].

The alpha7 nicotinic acetylcholine receptor (nAChR) plays an important role in cognitive processes and may represent a drug target for treating cognitive deficits in neurodegenerative and psychiatric disorders. In the present study, we used a novel alpha7 nAChR-selective agonist, 2-methyl-5-(6-phenyl-pyridazin-3-yl)-octahydro-pyrrolo[3,4-c]pyrrole (A-582941) to interrogate cognitive efficacy, as well as examine potential cellular mechanisms of cognition. Exhibiting high affinity to native rat (Ki = 10.8 nM) and human (Ki = 16.7 nM) alpha7 nAChRs, A-582941 enhanced cognitive performance in behavioral assays including the monkey delayed matching-to-sample, rat social recognition, and mouse inhibitory avoidance models that capture domains of working memory, short-term recognition memory, and long-term memory consolidation, respectively. In addition, A-582941 normalized sensory gating deficits induced by the alpha7 nAChR antagonist methyllycaconitine in rats, and in DBA/2 mice that exhibit a natural sensory gating deficit. Examination of signaling pathways known to be involved in cognitive function revealed that alpha7 nAChR agonism increased extracellular-signal regulated kinase 1/2 (ERK1/2) phosphorylation in PC12 cells. Furthermore, increases in ERK1/2 and cAMP response element-binding protein (CREB) phosphorylation were observed in mouse cingulate cortex and/or hippocampus after acute A-582941 administration producing plasma concentrations in the range of alpha7 binding affinities and behavioral efficacious doses. The MEK inhibitor SL327 completely blocked alpha7 agonist-evoked ERK1/2 phosphorylation. Our results demonstrate that alpha7 nAChR agonism can lead to broad-spectrum efficacy in animal models at doses that enhance ERK1/2 and CREB phosphorylation/activation and may represent a mechanism that offers potential to improve cognitive deficits associated with neurodegenerative and psychiatric diseases, such as Alzheimer's disease and schizophrenia.

A series of exceptionally potent agonists at neuronal nicotinic acetylcholine receptors (nAChRs) has been investigated. Several N-(3-pyridinyl) derivatives of bridged bicyclic diamines exhibit double-digit-picomolar binding affinities for the alpha 4 beta 2 subtype, placing them with epibatidine among the most potent nAChR ligands described to date. Structure-activity studies have revealed that substitutions, particularly hydrophilic groups in the pyridine 5-position, differentially modulate the agonist activity at ganglionic vs central nAChR subtypes, so that improved subtype selectivity can be demonstrated in vitro. Analgesic efficacy has been achieved across a broad range of pain states, including rodent models of acute thermal nociception, persistent pain, and neuropathic allodynia. Unfortunately, the hydrophilic pyridine substituents that were shown to enhance agonist selectivity for central nAChRs in vitro tend to limit CNS penetration in vivo, so that analgesic efficacy with an improved therapeutic window was not realized with those compounds.

5-[(1R,5S)-3,6-Diazabicyclo[3.2.0]heptan-6-yl]nicotinonitrile (A-366833) is a novel nicotinic acetylcholine receptor (nAChR) ligand that binds to the agonist-binding site ([3H]-cytisine) with Ki value of 3.1 nM and exhibits agonist selectivity at alpha4beta2 nAChR relative to the alpha3beta4 nAChR subtype. The analgesic effects of A-366833 were examined across a variety of animal models including the mouse model of writhing pain (abdominal constriction), the rat models of acute thermal (hot box), persistent chemical (formalin) and neuropathic (spinal nerve ligation, SNL) pain. In the abdominal constriction model, A-366833 was effective at doses ranging from 0.062 to 0.62 micromol/kg (i.p.). In addition, A-366833 demonstrated significant effects in acute thermal pain (6.2-19.0 micromol/kg, i.p.), formalin (1.9-19 micromol/kg i.p.) and SNL (1.9-19 micromol/kg i.p.) models. The systemic effects of A-366833 were attenuated by pretreatment with mecamylamine (5 micromol/kg i.p.) in both the formalin and SNL models, suggesting that the analgesic effects of A-366833 in models of persistent nociceptive and neuropathic pain are mediated by activation of nAChRs. Pharmacokinetic investigations of A-366833 in rat revealed moderate brain:plasma distribution, half-life of 1.5h and excellent oral bioavailability of 73%. Comparison of peak plasma levels at the minimal effective doses across rat models of acute thermal pain, formalin and SNL with the maximal exposure that does not evoke emesis in ferret revealed therapeutic margins ranging from 6- to 22-fold. These studies indicate that compounds like A-366833 with improved agonist selectivity at alpha4beta2 vs. alpha3beta4 nAChR can elicit a broad spectrum of analgesic efficacy without concurrent adverse effects.

ABSTRACT A‐85380 [3‐(2(s)‐azetidinylmethoxy) pyridine] is a neuronal nicotinic acetylcholine receptor (nAChR) agonist that has been a useful tool in the investigation of the function of nAChRs in both preclinical and clinical studies. Amongst nAChR subtypes, A‐85380 shows selectivity for the α 4 β 2 vs. the α 7 or α 1 β 1 δγ nAChRs. In functional in vitro cation flux assays, A‐85380 is a potent and full agonist. A‐85380 has a broad‐spectrum analgesic profile with efficacy in acute, persistent, and neuropathic pain models. As demonstrated using selective nAChR antagonists or α 4 antisense, the α 4 β 2 nAChR mediates the analgesic effects of A‐85380. Interestingly, the site of action depends upon the type of pain as antinociception is mediated by descending inhibition into the spinal cord whereas anti‐allodynia in neuropathic pain is mediated at both central and peripheral sites. Radiolabelled forms of A‐85380 have been developed and shown to be safe for use in vivo in humans. In clinical studies using positron and photon emission tomography, marked decreases in α 4 β 2 nAChRs have been seen in patients with Parkinson's and Alzheimer's disease. Although not developed as a therapeutic agent, A‐85380 has proven to be an important component in the development of novel nAChR ligands for the treatment of pain and other disorders.

Selective and brain penetrating pharmacological antagonists for use in clarifying a role of α7 nicotinic acetylcholine receptors (nAChR) in behavioral paradigms are presently unavailable. Studies in α7 knock-out mice (KO) have not revealed convincing changes in behavioral phenotype, in particular measures of cognition that include contextual fear conditioning and spatial memory, which may be due to compensatory developmental changes. Therefore, an antisense oligonucleotide (aON) targeted toward the 3′- and 5′-UTR coding regions of the rat α7 nicotinic acetylcholine receptor was used. Following central injection of aON into the lateral ventricle of Long Evans rats for 6 days, treated rats exhibited a significant 42% and 25% decrease in α7 nAChR densities in hippocampus and cortex, respectively, as measured by [3H]-methyllycaconitine (MLA) binding. There was no change in α4β2 densities measured by [3H]-cytisine binding. Acquisition of Morris Water Maze (MWM) performance, a measure of spatial memory, was impaired in aON-treated rats. In addition, a reduction in target platform crossings during a subsequent probe-trial was observed. These data demonstrate the ability of this aON to reduce hippocampal and cortical α7 nicotinic receptor densities associated with impaired MWM performance and support the specific involvement of the α7 nAChR in spatial learning and memory, a phenotype not affected in α7 KO mice.