Alpha7 nAChR Agonist Research Articles

Quantification of Proliferating and Mitotically Active Retinal Cells in Mice by Flow Cytometry.

Adult mammals lack the ability to regenerate retinal neurons after injury. However, in previous studies from this lab, topical application of the selective alpha7 nicotinic acetylcholine receptor (nAChR) agonist, PNU-282987, has been associated with an increase in the number of retinal neurons in adult murine models both in the presence and absence of injury to the retina. Additionally, studies assaying mitotic markers have shown a substantial increase in the amount of mitotically active and proliferating cells with the topical application of the alpha7 nAChR agonist. However, these previous studies were performed using fluorescent immunolabeling and subsequent confocal microscopy, thus limiting the number of antibodies that can be multiplexed. As a result, we have developed a flow cytometry method that allows for the multiplexing and analysis of multiple external and internal markers in dissociated retinal cells. In this paper, a step-by-step protocol is described for the labeling of multiple retinal cell types such as retinal ganglion cells, rod photoreceptors, and Müller glia, concurrently with Müller glia-derived progenitor cells that arise after treatment with PNU-282987. Key features • Neurogenesis in the adult mammalian retina. • Flow cytometry of retinal cells. • PNU-282987-induced mitotic activity in the retina. • Dissociation of the retina for flow cytometry analysis. Graphical overview Schematic demonstrating the protocol for preparation of retinal cells for flow cytometry analysis. (A) Adult mice (3-6 months) are subjected to topical PBS eyedrop treatment containing DMSO (control groups) or PNU-282987 (experimental groups). Both eyedrop treatments contain 1 mg/mL of BrdU to label proliferating cells. After treatment, mice are euthanized, and retinae are harvested for dissociation using papain. (B) Dissociated retina cells are fixed and permeabilized before aliquots are taken for cell counts on a hemocytometer. After determining the number of cells present, conjugated antibodies and unconjugated primary antibodies are added at the appropriate dilutions. Fluorescent secondary antibodies are added for markers that are unconjugated. Cells are then subjected to flow cytometric analysis using a BD LSRFortessa.

Functional Changes in the Adult Mouse Retina using an Alpha7 Nicotinic Acetylcholine Receptor Agonist after Blast Exposure

Currently, there is a lack of treatments for retinal neurotrauma. To address this issue, this study uses an alpha7 nAChR agonist, PNU-282987, to determine it effects on functional activity in the retina shortly after a traumatic blast exposure. The objectives of this research include: (1) examination of the cellular and functional damage associated with ocular blast exposure, and (2) evaluation of structural and functional changes that occur post PNU-282987 treatment. Significant ocular blast damage was induced in adult mice after exposure to a single blast of 35 psi to the left eye. Blast-exposed transgenic mice expressing tdTomato Müller glia were treated daily with eyedrops containing PNU-282987 for 4 weeks following the blast exposure. Antibody staining studies in these transgenic mice was conducted to examine lineage tracing and electroretinograms (ERGs) were obtained to examine functional changes. Blast exposure caused a significant loss of cells in all retinal layers after 4 weeks. Immunohistochemical analysis demonstrated tdTomato-positive labeled photoreceptors and retinal ganglion cells in blast-exposed mice treated with PNU-282987. ERG recordings were taken from control animals, from blast-damaged animals and from animals exposed to blast followed by 4 weeks of PNU-282987 treatment. Scotopic ERG recordings from blast-exposed mice had significantly decreased amplitudes of a-wave, b-wave, oscillatory potentials and flicker frequencies, which were prevented after PNU-282987 treatment. In photopic experiments, the PhNR response was reduced significantly after blast exposure but the decrease was prevented after treatment with PNU-282987. These are the first experiments that demonstrate preservation of retinal function after blast exposure using an alpha7 nAChR agonist.

Effect of Varenicline on Detrusor Overactivity in Rat Model of Parkinson’s Disease Induced by Intranigral 6-Hydroxydopamine

Background: Parkinson disease (PD) is a progressive neurodegenerative disorder characterized by both motor and non-motor symptoms. Bladder dysfunction is the common non-motor symptom of PD, most often presenting with detrusor overactivity (DO). Treatment of DO is currently limited, poorly tolerated and sometimes ineffective. Bladder responses are not only mediated by muscarinic cholinergic receptors (mAChR) but also by nicotinic cholinergic receptors (nAChR). However, nicotinic receptor subtypes and functions in the bladder are not clearly identified. Purpose: This study aimed at investigating the effect of varenicline, an alpha7 full agonist and alpha4beta2/alpha3 partial agonist, on detrusor strips in rat PD model induced by substantia nigra injection of 6-hydroxydopamine. Method: The detrusor activity was studied in an isolated organ bath system. Results: In PD group, the detrusor activity was increased, whereas varenicline decreased the DO. Conclusion: Alpha7 nAChR agonists may have therapeutic potential in treatment of bladder overactivity in PD.

Dissociation of nicotinic α7 and α4/β2 sub-receptor agonists for enhancing learning and attentional filtering in nonhuman primates.

Nicotinic acetylcholine receptors (nAChRs) modulate attention, memory, and higher executive functioning, but it is unclear how nACh sub-receptors mediate different mechanisms supporting these functions. We investigated whether selective agonists for the alpha-7 nAChR versus the alpha-4/beta-2 nAChR have unique functional contributions for value learning and attentional filtering of distractors in the nonhuman primate. Two adult rhesus macaque monkeys performed reversal learning following systemic administration of either the alpha-7 nAChR agonist PHA-543613 or the alpha-4/beta-2 nAChR agonist ABT-089 or a vehicle control. Behavioral analysis quantified performance accuracy, speed of processing, reversal learning speed, the control of distractor interference, perseveration tendencies, and motivation. We found that the alpha-7 nAChR agonist PHA-543613 enhanced the learning speed of feature values but did not modulate how salient distracting information was filtered from ongoing choice processes. In contrast, the selective alpha-4/beta-2 nAChR agonist ABT-089 did not affect learning speed but reduced distractibility. This dissociation was dose-dependent and evident in the absence of systematic changes in overall performance, reward intake, motivation to perform the task, perseveration tendencies, or reaction times. These results suggest nicotinic sub-receptor specific mechanisms consistent with (1) alpha-4/beta-2 nAChR specific amplification of cholinergic transients in prefrontal cortex linked to enhanced cue detection in light of interferences, and (2) alpha-7 nAChR specific activation prolonging cholinergic transients, which could facilitate subjects to follow-through with newly established attentional strategies when outcome contingencies change. These insights will be critical for developing function-specific drugs alleviating attention and learning deficits in neuro-psychiatric diseases.

628 Activation of the alpha7 nicotinic acetylcholine receptor improves skin fibrosis

Previously we showed an inhibitory effect of tropisetron on transforming growth factor (TGF)-beta1-induced collagen synthesis in human dermal fibroblasts (HDFs) which was alpha7 nicotinic acetylcholine receptors (alpha7nAchR) dependent. In vivo data disclose that tropisetron not only reduced but also prevented experimentally-induced skin fibrosis in the bleomycin (BLM) mouse model of scleroderma. To elucidate the role of the alpha7nAchR in fibrosis, we tested PHA-543613, a full agonist of the alpha7nAchR in the BLM mouse model of scleroderma. A preventive model with simultaneous treatment with BLM and PHA-543613 and a therapeutic model with application of the agonist after induction of fibrosis were used. PHA-543613 treatment resulted in a significant suppression of BLM-induced mRNA expression of murine collagen type I and extracellular matrix genes in mouse skin. Moreover, the α7nAchR agonist dramatically improved fibrosis when added in a therapeutic approach. These results were confirmed at protein level where skin samples injected with PHA-543613 in a preventive as well as therapeutic fashion had significantly lower collagen type I deposition compared to BLM-treated skin. Accordingly, histological analyses disclosed a reduction of dermal thickness after treatment with the alpha7nAchR agonist PHA-543613 in both the preventive and therapeutic approach. These anti-collagen effects could be imitated in vitro where HDFs were treated with the profibrotic factor TGF-beta1 alone and in comparison with PHA-543613 and another full alpha7nAchR agonist AR-R17779. Mechanistically, PHA-543613 and AR-R17779 elicit their anti-TGF-beta1 effect on collagen synthesis via modulation of specific microRNA (miRNAs), such as the profibrotic miR-21 and the antifibrotic miR-29a. In summary the alpha7nAchR agonist PHA-543613 is a novel potent antifibrotic agent, which further underlines the role of the alpha7nAchR in skin fibrosis. Experiments with alpha7nAchR deficient animals lacking this gene are in preparation in our laboratory to further clarify the role of this receptor in fibrosclerotic diseases.

Facilitation and inhibition of firing activity and N-methyl-D-aspartate-evoked responses of CA1 hippocampal pyramidal cells by alpha7 nicotinic acetylcholine receptor selective compounds in vivo

Alpha7 nicotinic acetylcholine receptors (nAChRs) are promising novel targets for the treatment of neurocognitive disorders. Although the cognitive enhancer potential of alpha7 nAChR agonists and positive allosteric modulators (PAMs) has been confirmed in several preclinical animal models, there are only sparse in vivo electrophysiological data on their effects on the firing activity and excitability of neurons. The present study investigated and compared local effects of alpha7 nAChR agonist PHA-543613 and PAMs PNU-120596 and NS-1738 on the spontaneous and N-methyl-D-aspartate-evoked (NMDA-evoked) firing rate of rat CA1 hippocampal pyramidal cells, in vivo. Furthermore, effects of alpha7 nAChR antagonist methyllycaconitine (MLA) and GABA were also tested. Results showed substantially different effects of the alpha7 nAChR agonist and PAMs. While PNU-120596 and NS-1738 predominantly and significantly increased both spontaneous and NMDA-evoked firing rate of the neurons, application of PHA-543613 resulted in almost equal distribution of facilitatory and inhibitory effects. The increase of the NMDA-evoked firing rate exerted by NS-1738 was superadditive over the sum of the single effects of NMDA and NS-1738. The simultaneous application of alpha7 nAChR agonist PHA-543613 and PAM NS-1738 resulted in additive increase of both spontaneous and NMDA-evoked firing rate. However, NS-1738 counteracted inhibitory effects of PHA-543613 in 5 out of 6 neurons, resulting in a synergistic potentiation of their firing responses to NMDA. Our results suggest that alpha7 nAChR PAMs increase neuronal excitability more potently than agonists, while the remarkable occurrence of inhibitory effects of PHA-543613 (possibly originating from receptor desensitization) implies that agonists may exert neuroprotective effects.

Cognitive Enhancer Effects of Low Memantine Doses Are Facilitated by an Alpha7 Nicotinic Acetylcholine Receptor Agonist in Scopolamine-Induced Amnesia in Rats.

Alpha7 nicotinic acetylcholine receptors (nAChRs) play an important role in learning and memory and are promising targets for pharmacological cognitive enhancement. Memantine, an approved substance for Alzheimer’s disease treatment, is an antagonist of the N-Methyl-D-aspartate receptor (NMDAR) and also acts as an alpha7 nAChR antagonist. Here, we tested the interaction between an alpha7 nAChR agonist (PHA-543613) and memantine. Efficacy of memantine, PHA-543613, and their co-administration were investigated on the spatial working memory of rats using the spontaneous alternation paradigm in T-maze. Scopolamine-induced transient amnesia was used to model cognitive impairment. First, the dose-response relationship was assessed for memantine, and its lowest effective dose was found to be 0.1 mg/kg. Then, co-administration treatments with subeffective doses of the alpha7 nAChR agonist PHA-543613 and different doses of memantine were tested. The co-administration of subeffective drug doses significantly improved memory performance of the rats and reversed scopolamine-induced deficits. Interestingly, a higher than effective (0.3 mg/kg) dose of memantine did not increase performance in monotreatment, only in co-administration with PHA-543613. However, the co-administration of PHA-543613 did not further increase the efficacy of the previously effective monotreatment doses of memantine. Thus, the efficacy of memantine monotreatment and its co-administration with PHA-543613 converged to create a common ceiling effect, with an additive interaction found in the behavioral effects. These results suggest that memantine and PHA-543613 may exert their cognitive enhancer effects on the same target, possibly on the alpha7 nAChRs. Results also suggest possible benefits of a combination therapy with memantine and alpha7 nAChR agonists.

Nicotine improves probabilistic reward learning in wildtype but not alpha7 nAChR null mutants, yet alpha7 nAChR agonists do not improve probabilistic learning

Cognitive impairments, e.g., reward learning, are present in various psychiatric disorders and warrant treatment. Improving reward-related learning could synergistically enhance psychosocial treatments and cognition generally. A critical first step is to understand the mechanisms underlying reward learning. The dopamine system has been implicated in such learning, but less known is how indirect activation of this system may affect reward learning. We determined the role of alpha7 nicotinic acetylcholine receptors (nAChR) on a probabilistic reversal learning task (PRLT) in mice that includes reward and punishment. Male alpha7 knockout (KO), heterozygous (HT), and wildtype (WT) littermate mice (n = 84) were treated with vehicle, 0.03, or 0.3 mg/kg nicotine. Two cohorts of C57BL/6NJ male mice were treated with various alpha7 nAChR ligands, including the full agonists PNU282877 and AR-R-17779, the positive allosteric modulator CCMI, the partial agonist SSR180711, and the antagonist methyllycaconitine. All mice were then tested in the PRLT. Nicotine (0.3 mg/kg) significantly improved initial reward learning in alpha7 WT and HT mice but did not improve learning in KO mice, suggesting an involvement of the alpha7 nAChR in the pro-learning effects of nicotine. Neither alpha7 nAChR treatments (PNU282987, AR-R-17779, CCMI, SSR180711, nor methyllycaconitine) affected mouse PRLT performance however. Nicotine improved reward learning via a mechanism that may include alpha7 nAChRs. This improvement unlikely relied solely on alpha7 nAChRs however, since no alpha7 nAChR ligand improved reward learning in normal mice. Future assessments of the effects of other nAChR subtypes on reward learning are needed.

S232. ALPHA7 NICOTINIC RECEPTOR AGONISTS REVERSE THE HYPERDOPAMINERGIC STATE IN THE MAM MODEL OF SCHIZOPHRENIA

BackgroundMost investigations into the pharmacology of schizophrenia have revolved around dopaminergic and glutamatergic neurotransmission; however, one neurotransmitter that has not received adequate attention is the cholinergic system. Indeed, several post-mortem, genetic and epidemiologic studies link specifically the alpha7 nicotinic receptor (nAChR) to schizophrenia, and the potential use of alpha7 modulators as a treatment strategy is an active field of research. Nevertheless, studies to date have been limited to normal animals rather than on a validated neurodevelopmental model of schizophrenia. Moreover, knowledge about the differential impact of orthosteric and allosteric modulators in vivo is lacking. Thus, we investigated the effects of alpha7 nAChR modulation on dopamine (DA) neuron activity in the ventral tegmental area (VTA) in the methylazoxymethanol acetate (MAM) animal model of schizophrenia.MethodsAll experimental procedures were conducted according to NIH guidelines and were approved by University of Pittsburgh Institutional Animal Care and Use Committee. Sprague-Dawley pregnant dams were treated with MAM or saline on gestational day 17. Recordings of VTA dopamine neuron activity was performed on the male offspring at adulthood. The effects of four different drugs were evaluated: PNU282987 (full agonist), SSR180711 (partial agonist) NS1738 (type I positive allosteric modulator - PAM) and PNU120596 (PAM type II).ResultsIntravenous administration of alpha7 selective ligands did not induce a major change in the firing profile of spontaneously active DA neurons when dosed during dopamine neuron recording. PNU120596 increased in the number of active DA neurons found in the VTA of normal rats, their mean firing rate and percentage of spikes in bursts. In contrast, the full agonist PNU282987 and the partial agonist SSR180711 reduced the hyperdopaminergic tone in MAM rats, with a more prominent decrease in the number of DA neurons recorded in the lateral VTA. In order to investigate the drug site of action, both PNU282987 and SSR1800711 were infused into the ventral hippocampus (vHipp) and basolateral amygdala (BLA). After vHipp infusion, the alpha7 nAChR agonists significantly decreased the number of active DA neurons in MAM rats, with no significant impact in control rats. Once more, the effects were more robust in the lateral VTA. In contrast, the same drugs when infused directly into the BLA increased the number of spontaneously active DA neurons in the VTA of normal rats, but not in the MAM model.DiscussionIn summary, our results show that alpha7 nAChR positive modulators can affect midbrain dopaminergic neuronal activity in vivo in a state-dependent manner. Interestingly, alpha7 nAChR agonists counterbalanced the hyperdopaminergic state of MAM rats and this effect is partially mediated by their action in the vHipp. This effect is consistent with the potential use of alpha7 nAChR agonists for schizophrenia treatment and fits the current search for drugs able to control dopaminergic function acting in structures upstream from the dopamine receptor. The predominant inhibition of the lateral VTA points to a lower propensity to produce unwanted side effects in comparison to current employed antipsychotic agents. Our data show that drug effects can vary according to the basal level of activity of specific brain circuits and highlights the importance of using appropriated animal models to make inferences about potential therapeutic use of new neuropsychiatric drug candidates.

Alpha7 nAChR Agonists for Cognitive Deficit and Negative Symptoms in Schizophrenia: A Meta-analysis of Randomized Double-blind Controlled Trials.

BackgroundPrevious clinical trials of α7-nicotinic acetylcholine receptor agonists (α7-nAChR agonists) showed mixed results in treating the cognitive and negative symptoms of schizophrenia.AimsTo assess the efficacy and safety of α7-nAChR agonists in treating the cognitive and negative symptoms in schizophrenia.MethodsA literature search was conducted to identify randomized double-blind placebo-controlled trials for schizophrenia published before May 26, 2017, by searching PubMed, Embase, ClinicalTrials.gov, the Cochrane Library and the Chinese language databases CNKI, Wanfang, and VIP Data. The effects of α7-nAChR agonists were evaluated for overall cognitive function and negative symptoms by calculating standard mean difference (SMDs) between active drugs and placebo added to antipsychotics.Results8 studies with low bias were included. We found no statistically significant effects of α7 nAChR agonists on the overall cognitive function (SMD=-0.10[-0.46, 0.25], I2 =88%) and negative symptoms (SMD=0.13 [-0.04, 0.30], I2 =64%) in patients with schizophrenia. Sensitivity analysis showed these results to be firm. And this drug is generally safe and well tolerated with no significant difference from placebo based on adverse events (RR=1.02, [0.85, 1.23]) and dropouts (RR=1.04, [0.61, 1.78]) data. Evidence based on outcomes from the meta-analysis was rated as ‘moderate’ as per the GRADE guidelines.Conclusionα7-nAChR agonists may not be effective in reversing overall cognitive impairments and negative symptoms in patients with schizophrenia as adjunctive therapies.

Alpha7 Nicotine Acetylcholine Receptor Agonist PNU-282987 Attenuates Acute Lung Injury in a Cardiopulmonary Bypass Model in Rats

Cardiopulmonary bypass (CPB) carries a risk of lung ischemia-reperfusion, leading to acute lung injury (ALI). Alpha7 nicotinic acetylcholine receptor (alpha7nAChR) has been implicated in the release of high mobility group box1 (HMGB1), which promotes systemic inflammation in response to ischemia-reperfusion injury. However, the specific role of alpha7nAChR in CPB is poorly understood. This study employed the alpha7nAChR agonist PNU-282987 and a rat model of CPB to determine whether alpha7nAChR was associated with CPB-induced lung damage. Thirty Sprague-Dawley rats were randomly divided into five groups as follows: normal group, sham group, CPB group, PNU-282987 plus CPB group, and PNU-282987 plus sham group. Rats were subjected to CPB under anesthesia for 60 min. PNU-282987 (4.8 mg/kg) was administered via arterial inflow. Two hours post-CPB, samples of blood, bronchoalveolar lavage fluid (BALF), and lung tissues were processed for investigations. In CPB rats, structural damage in the lung was marked. Density of alpha7nAChR of the lung in the CPB group was significantly less than all other groups, while lung edema, inflammatory markers in serum and lung, protein concentrations in BALF were significantly higher. In the PNU-282987 plus CPB group, by all the above measures the CPB-associated effects were significantly ameliorated but were not identical to the control groups. Our results suggest that PNU-282987 affords protective effect against CPB-induced ALI, and inhibits HMGB1 release.

Synthesis and biological activities of indolizine derivatives as alpha-7 nAChR agonists

Human α7 nicotinic acetylcholine receptor (nAChR) is a promising therapeutic target for the treatment of schizophrenia accompanied with cognitive impairment. Herein, we report the synthesis and agonistic activities of a series of indolizine derivatives targeting to α7 nAChR. The results show that all synthesized compounds have affinity to α7 nAChR and some give strong agonistic activity, particularly most active agonists show higher potency than control EVP-6124. The docking and structure–activity relationship studies provide insights to develop more potent novel α7 nAChR agonists.

Nicotine inhibits the production of proinflammatory cytokines of mice infected with coxsackievirus B3

AimsAlthough excessive sympathetic activation in viral myocarditis and the protective effects of sympathetic inhibition with β-blockers are clear, the effects of enhancing vagal tone on viral myocarditis remain unclear. In several models, vagus nerve activation with the α7 nicotinic acetylcholine receptor (α7-nAChR) agonists has been demonstrated to ameliorate inflammation. This study was therefore designed to examine the effects of cholinergic stimulation with α7-nAChR agonist nicotine in a murine model of acute viral myocarditis. Materials and methodsBALB/C mice were infected by an intraperitoneally injection with coxsackievirus B3. Nicotine and methyllycaconitine (an α7-nAChR antagonist) were administered at doses of 0.4mg/kg and 0.8mg/kg three times per day for 7 or 14 consecutive days, respectively. The effects of nicotine and methyllycaconitine on survival rate, myocardial histopathological changes, cardiac function, cytokine levels, viral RNA, malondialdehyde, and superoxide dismutase contents were investigated. Key findingsNicotine significantly increased survival rate of the infected mice, decreased myocardial inflammation, and improved the impairment of left ventricular function in murine coxsackievirus B3-induced myocarditis compared with methyllycaconitine. The proinflammatory cytokines TNF-α, IL-1β, IL-6 and IL-17A were significantly decreased in the infected mice treated with nicotine compared with methyllycaconitine. Nicotine had no significant anti-oxidative and antiviral effects in coxsackievirus B3-infected mice. SignificanceThe results indicate that cholinergic stimulation with nicotine significantly reduced the severity of viral myocarditis in mice. The findings suggest that alpha7 nAChR agonists may be a promising new strategy for patients with myocarditis.

Dose-dependent protective effect of nicotine in a murine model of viral myocarditis induced by coxsackievirus B3.

The alpha 7 nicotinic acetylcholine receptor (alpha7 nAChR) was recently described as an anti-inflammatory target in various inflammatory diseases. The aim of this study was to investigate the dose-related effects of nicotine, an alpha7 nAChR agonist, in murine model of viral myocarditis. BALB/C mice were infected by an intraperitoneally injection with coxsackievirus B3. Nicotine was administered at doses of 0.1, 0.2 or 0.4 mg/kg three times per day for 7 or 14 consecutive days. The effects of nicotine on survival, myocardial histopathological changes, cardiac function, and cytokine levels were studied. The survival rate on day 14 increased in a dose-dependent fashion and was markedly higher in the 0.2 and 0.4 mg/kg nicotine groups than in the infected untreated group. Treatment with high-dose nicotine reduced the myocardial inflammation and improved the impaired left ventricular function in infected mice. The mRNA expressions and protein levels of TNF-α, IL-1β, IL-6, and IL-17A were significantly downregulated in dose-dependent manners in the nicotine treatment groups compared to the infected untreated group. Nicotine dose-dependently reduced the severity of viral myocarditis through inhibiting the production of proinflammatory cytokines. The findings suggest that alpha7 nAChR agonists may be a promising new strategy for patients with viral myocarditis.

A new isoxazolic compound acts as alpha7 nicotinic receptor agonist in human umbilical vein endothelial cells.

Recent evidence suggests that the alpha7 nicotinic acetylcholine receptors (alpha7 nAChRs) participate in the development of angiogenesis and could be a new endothelial target for revascularization in therapeutic angiogenesis. It has been shown that in human umbilical vein endothelial cells (HUVECs) alpha7 nAChR agonists increase the intracellular calcium concentration ([Ca2+]i), thus inducing proliferation and vessel formation which are important stages of angiogenesis. In the present study we evaluated the effect of new isoxazole compounds on the cytosolic Ca2+ signal in HUVECs using the fluorescent Ca2+ indicator Fluo-3AM and probing the involvement of alpha7 nAChR by means of pharmacological tools. HUVECs expressed mainly alpha7 nAChR, since there was no significant difference in the increase in [Ca2+]i induced by nicotine, a non-selective nicotinic agonist, in relation to choline, a selective alpha7 nAChR agonist. The increase in [Ca2+]i induced by 1 mM choline was inhibited significantly (p = 0.014) in cells which had been pre-incubated for 15 min with methyllycaconitine (MLA), a selective alpha7 nAChR antagonist. The studied compounds 1, 2, and 3 induced an increase in [Ca2+]i in a dose-dependent manner. Compound 1 at 10 microM induced a greater increase in [Ca2+]i than compounds 2 and 3. The increase in [Ca2+]i induced by compound 1 was significantly inhibited by MLA (p = 0.013) and completely inhibited by mecamylamine, a non-selective nAChR antagonist, indicating that the isoxazolic compound 1 acts as an alpha7 nAChR agonist.

Effect of alpha7 nicotinic acetylcholine receptor agonists on attentional set-shifting impairment in rats

Attentional set shifting, a measure of executive function, is impaired in schizophrenia patients. Current standard of care has little therapeutic benefit for treating cognitive dysfunction in schizophrenia; therefore, novel drugs and animal models for testing novel therapies are needed. The NMDA receptor antagonist, MK-801, produces deficits in a rat maze-based set-shifting paradigm, an effect which parallels deficits observed on tests of executive function in schizophrenia patients. Alpha7 nicotinic acetylcholine receptor (nAChR) agonists, currently under clinical development by several companies, show promise in treating cognitive symptoms in schizophrenia patients and can improve cognition in various animal models. The objectives of the present study were to determine whether the MK-801 deficit in set shifting could be reproduced in a drug discovery setting and to determine whether cognitive improvement could be detected for the first time in this task with alpha7 nAChR agonists. The data presented here replicate findings that a systemic injection of the NMDA receptor antagonist MK-801 can induce a deficit in set shifting in rats. Furthermore, the deficit could be reversed by the atypical antipsychotic clozapine as well as by several alpha7 nAch receptor agonists (SSR-180711, PNU-282987, GTS-21) with varying in vitro properties. Results indicate that the MK-801 set-shift assay is a useful preclinical tool for measuring prefrontal cortical function in rodents and can be used to identify novel mechanisms for the potential treatment of cognitive deficits in schizophrenia.

The Anti-Inflammatory Potential of Selective Cholinergic Agonists

The Anti-Inflammatory Potential of Selective Cholinergic Agonists

Affinity purification of a chimeric nicotinic acetylcholine receptor in the agonist and antagonist bound states

Nicotinic acetylcholine receptors (nAChRs) form ligand-gated ion channels that mediate fast signal transmission at synapses. These receptors are members of a large family of pentameric ion channels that are of active medical interest. An expression system utilizing a chimerical construct of the N-terminal extracellular ligand binding domain of alpha7 type nAChR and the C-terminal transmembrane portion of 5HT3 type receptor resulted high level of expressions. Two ligand affinity chromatography purification methods for this receptor have been developed. One method relies on the covalent immobilization of a high affinity small molecule alpha7 nAChR agonist, (R)-5-(4-aminophenyl)-N-(quinuclidin-3-yl) furan-2-carboxamide, and the other uses mono biotinylated alpha-bungarotoxin, an antagonist, that forms a quasi-irreversible complex with alpha7 nAChR. Detergent solubilized alpha7/5HT 3 chimeric receptors were selectively retained on the affinity resins and could be eluted with free ligand or biotin. The proteins purified by both methods were characterized by gel electrophoresis, mass spectra, amino acid composition analysis, and N-terminal sequence determination. These analyses confirmed the isolation of a mature alpha7/5HT 3 receptor with the signal peptide removed. These results suggest a scalable path forward to generate multi-milligram amounts of purified complexes for additional studies including protein crystallization.

Can vagus nerve stimulation halt or ameliorate rheumatoid arthritis and lupus?

Acetylcholine, the principal vagus neurotransmitter, inhibits inflammation by suppressing the production of pro-inflammatory cytokines through a mechanism dependent on the α7 nicotinic acetylcholine receptor subunit (alpha7nAChR) that explains why vagus nerve stimulation is anti-inflammatory in nature. Strong expression of alpha7nAChR in the synovium of rheumatoid arthritis and psoriatic arthritis patients was detected. Peripheral macrophages and synovial fibroblasts respond in vitro to specific alpha7nAChR cholinergic stimulation with potent inhibition of proinflammatory cytokines. Fibroblasts balance inflammatory mechanisms and arthritis development through feedback cholinergic stimulation by nearby immune cells. Collagen induced arthritis in alpha7nAChR(-/-) mice was significantly severe and showed increased synovial inflammation and joint destruction compared to the wild-type mice. Similar to vagal nerve stimulation and alpha7nAChR agonists, polyunsaturated fatty acids: eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) also suppress inflammation. In view of their similar anti-inflammatory actions, it is proposed that vagal nerve stimulation, alpha7nAChR agonists and EPA and DHA may augment the formation of anti-inflammatory lipid molecules: lipoxins, resolvins, protectins and maresins. This implies that therapies directed at regulation of the cholinergic and alpha7nAChR mediated mechanisms and enhancing the formation of lipoxins, resolvins, protectins and maresins may halt and/or ameliorate rheumatoid arthritis, lupus and other rheumatological conditions.

Acrosome Reaction Induced by Zona Pellucida Is Mediated by Alpha-7 Nicotinic Acetylcholine and Epidermal Growth Factor Receptors.

In order to penetrate into the egg, the capacitated spermatozoon should bind to the zona pellucida (ZP) and undergo the acrosomal reaction. The acrosome reaction is mediated by receptor activation that leads to calcium influx into the sperm. In the present study we showed that isolated ZP activates sperm alpha7-nicotinic-achetylcholine receptor (á7nAChR) leading to the trans-activation of epidermal-growth-factor-receptor (EGFR), calcium influx and the acrosome reaction. The data revealed that alpha7nAChR agonist initiates the acrosome reaction which was inhibited by EGFR-antagonist, suggesting that EGFR mediates this reaction. Moreover, the ZP induced acrosome reaction was significantly inhibited by alpha-bungarotoxin (alpha7 antagonist) and by tyrphostin (EGFR antagonist), suggesting that EGFR and the alpha7 subunit are activated by ZP. Furthermore, ZP or EGF did not induce the acrosome reaction in sperm from alpha7 null mice, suggesting that ZP-induced acrosome raction depends on the existance of sperm alpha7 and mediated by EGFR. Inhibition of alpha7 in wild type sperm revealed only partial inhibition of the acrosome reaction induced by EGF, supporting the idea that the alpha7nAChR is localized up-stream to the EGFR. Recent studies suggest that Src kinase can activate EGFR in sperm. It was also shown that Src co-localized with the alpha7 in human sperm. We showed here that Src inhibitor blocked the alpha7-dependent acrosome reaction and EGFR-phosphorylation suggesting that SRC-family mediate these processes. Moreover, EGFR phosphorylation on tyrosine-845 induced by ZP is also inhibited by SRC-family inhibitor suggesting that this kinase mediate the ZP-induced EGFR phosphorylation. It was recently shown in our lab that EGFR activation leads to calcium influx. Here we showed that agonist of the alpha7, EGFR or ZP induced calcium influx that leads to the acrosome reaction. However, in alpha7 null mice, these agonists did not induce calcium influx or acrosome reaction, and this blockade could be bypassed using calcium ionophore supporting the role of alpha7 in calcium influx induced by ZP. In conclusion we suggest that activation of alpha7 by ZP leads to SRC-family dependent-EGFR activation, Ca2+ influx and the occurrence of the acrosome reaction. (poster)