Nicotinic α7 and α4β2 agonists enhance the formation and retrieval of recognition memory: Potential mechanisms for cognitive performance enhancement in neurological and psychiatric disorders

Role of medial prefrontal cortex voltage-dependent potassium 4.3 channels in nicotine-induced enhancement of object recognition memory in male mice

Nicotine has been shown to enhance object recognition memory in the novel object recognition (NOR) test by activating excitatory neurons in the medial prefrontal cortex (mPFC). However, the exact neuronal mechanisms underlying the nicotine-induced activation of mPFC neurons and the resultant memory enhancement remain poorly understood. To address this issue, we performed brain-slice electrophysiology and the NOR test in male C57BL/6J mice. Whole-cell patch-clamp recordings from layer V pyramidal neurons in the mPFC revealed that nicotine augments the summation of evoked excitatory postsynaptic potentials (eEPSPs) and that this effect was suppressed by N-[3,5-Bis(trifluoromethyl)phenyl]-N'-[2,4-dibromo-6-(2H-tetrazol-5-yl)phenyl]urea (NS5806), a voltage-dependent potassium (Kv) 4.3 channel activator. In line with these findings, intra-mPFC infusion of NS5806 suppressed systemically administered nicotine-induced memory enhancement in the NOR test. Additionally, miRNA-mediated knockdown of Kv4.3 channels in mPFC pyramidal neurons enhanced object recognition memory. Furthermore, inhibition of A-type Kv channels by intra-mPFC infusion of 4-aminopyridine was found to enhance object recognition memory, while this effect was abrogated by prior intra-mPFC NS5806 infusion. These results suggest that nicotine augments the summation of eEPSPs via the inhibition of Kv4.3 channels in mPFC layer V pyramidal neurons, resulting in the enhancement of object recognition memory.

Unlocking the role of dorsal hippocampal α4β2 nicotinic acetylcholine receptors in Ethanol-Induced conditioned place preference in mice

Alcohol Use Disorder (AUD) presents a significant and challenging public health concern, marked by a dearth of effective pharmacological treatments. Understanding the neurobiological underpinnings of AUD is of paramount importance for the development of efficacious interventions. The process of addiction entails the acquisition of associative behaviors, prominently engaging the dorsal region of the hippocampus for encoding these associative memories. Nicotinic receptor systems have been implicated in mediating the rewarding effects of ethanol, as well as memory and learning processes. In our current investigation, we delved into the role of α4β2 nicotinic acetylcholine receptors (nAChRs) within the dorsal hippocampus in the context of ethanol-induced conditioned place preference (CPP), a robust model for scrutinizing the rewarding properties and drug-associated behaviors. To establish CPP, ethanol (2 g/kg) was administered intraperitoneally during a 8-day conditioning phase. Fos immunohistochemistry was employed to assess the involvement of discrete subregions within the dorsal hippocampus in ethanol-induced CPP. Additionally, we probed the influence of α4β2 nAChRs on CPP via microinjections of a selective nAChR antagonist, dihydro-β-erythroidine (DHBE, at dosages of 6, 12, and 18 µg/0.5 µL per hemisphere) within the hippocampus. Our results unveiled that ethanol-induced CPP was associated with an increase Fos -positive cells in various subregions of the dorsal hippocampus, including CA1, CA2, CA3, and the dentate gyrus. Intrahippocampal administration of DHBE (at doses of 6 and 18 µg/0.50 µL per hemisphere) effectively blocked ethanol-induced CPP, while leaving locomotor activity unaffected. These findings underscore the critical involvement of the dorsal hippocampus and α4β2 nAChRs in the acquisition of ethanol-associated learning and reward.

Varenicline enhances recognition memory via α7 nicotinic acetylcholine receptors in the medial prefrontal cortex in male mice

Previous studies postulated that chronic administration of varenicline, a partial and full agonist at α4β2 and α7 nicotinic acetylcholine receptors (nAChRs), respectively, enhances recognition memory. However, whether its acute administration is effective, on which brain region(s) it acts, and in what signaling it is involved, remain unknown. To address these issues, we conducted a novel object recognition test using male C57BL/6J mice, focusing on the medial prefrontal cortex (mPFC), a brain region associated with nicotine-induced enhancement of recognition memory. Systemic administration of varenicline before the training dose-dependently enhanced recognition memory. Intra-mPFC varenicline infusion also enhanced recognition memory, and this enhancement was blocked by intra-mPFC co-infusion of a selective α7, but not α4β2, nAChR antagonist. Consistent with this, intra-mPFC infusion of a selective α7 nAChR agonist augmented object recognition memory. Furthermore, intra-mPFC co-infusion of U-73122, a phospholipase C (PLC) inhibitor, or 2-aminoethoxydiphenylborane (2-APB), an inositol trisphosphate (IP3) receptor inhibitor, suppressed the varenicline-induced memory enhancement, suggesting that α7 nAChRs may also act as Gq-coupled metabotropic receptors. Additionally, whole-cell recordings from mPFC layer V pyramidal neurons in vitro revealed that varenicline significantly increased the summation of evoked excitatory postsynaptic potentials, and this effect was suppressed by U-73122 or 2-APB. These findings suggest that varenicline might acutely enhance recognition memory via mPFC α7 nAChR stimulation, followed by mPFC neuronal excitation, which is mediated by the activation of PLC and IP3 receptor signaling. Our study provides evidence supporting the potential repositioning of varenicline as a treatment for cognitive impairment.

Activation of α7nAChR by PNU282987 improves cognitive impairment through inhibiting oxidative stress and neuroinflammation in D-galactose induced aging via regulating α7nAChR/Nrf2/HO-1 signaling pathway

Aging is an important risk factor for neurodegenerative diseases. The activation of α7 nicotinic acetylcholine receptor (α7nAChR) is involved in inflammation and cognition, but the specific role it plays in aging remains unknown. This study aimed to investigate the anti-aging effect of the activation of α7nAChR on aging rats and BV2 cells induced by D-galactose, as well as its potential mechanism. D-galactose induced an increase in the SA-β-Gal positive cells, expression of p16 and p21 in vivo and in vitro. α7nAChR selective agonist PNU282987 decreased levels of pro-inflammatory factors, MDA, and Aβ, enhanced SOD activity and levels of anti-inflammatory factor (IL10) in vivo. PNU282987 enhanced the expression of Arg1, decreased the expression of iNOS, IL1β and TNFα in vitro. PNU282987 upregulated the levels of α7nAChR, Nrf2 and HO-1 in vivo and in vitro. The results of Morris water maze and novel object recognition tests showed that PNU282987 improved cognitive impairment in aging rats. Furthermore, α7nAChR selective inhibitor methyllycaconitine (MLA) results were opposite with PNU282987. PNU282987 improves cognitive impairment through inhibiting oxidative stress and neuroinflammation in D-galactose induced aging via regulating the α7nAChR/Nrf2/HO-1 signaling pathway. Therefore, targeting the α7nAChR may be a viable therapeutic approach for anti-inflammaging and neurodegenerative diseases.

The effect of photoperiod and high fat diet on the cognitive response in photoperiod-sensitive F344 rats

In many species, seasonal changes in day length (photoperiod) have profound effects on physiology and behavior. In humans, these include cognitive function and mood. Here we investigated the effect of photoperiod and high fat diets on cognitive deficits, as measured by novel object recognition, in the photoperiod-sensitive F344 rat, which exhibits marked natural changes in growth, body weight and food intake in response to photoperiod. 32 male juvenile F344 rats were housed in either long or short photoperiod and fed either a high fat or nutrient-matched chow diet. Rats were tested in the novel object recognition test before photoperiod and diet intervention and re-tested 28 days after intervention. In both tests during the acquisition trials there was no significant difference in exploration levels of the left and right objects in the groups. Before intervention, all groups showed a significant increase in exploration of the novel object compared to the familiar object. However, following the photoperiod and diet interventions the retention trial revealed that only rats in the long photoperiod-chow group explored the novel object significantly more than the familiar object, whereas all other groups showed no significant preference. These results suggest that changing rats to short photoperiod impairs their memory regardless of diet. The cognitive performance of rats on long photoperiod-chow remained intact, whereas the high fat diet in the long photoperiod group induced a memory impairment. In conclusion, our study suggests that photoperiod and high fat diet have an impact on object recognition in photoperiod-sensitive F344 rats.

Nicotinic aspects of the discriminative stimulus effects of arecoline

Despite the evidence that the muscarinic agonist arecoline is a drug of abuse throughout Southeast Asia, its stimulus characteristics have not been well studied. The goal of this work was to understand more about the mediation of discriminative stimulus effects of arecoline. Arecoline (1.0 mg/kg s.c.) was trained as a discriminative stimulus in a group of eight rats. The ability of various cholinergic agonists and antagonists to mimic or antagonize the discriminative stimulus effects of arecoline and to modify its rate-suppressing effects was evaluated. A muscarinic antagonist, but neither of two nicotinic antagonists, was able to modify the discriminative stimulus effects of arecoline, suggesting a predominant muscarinic basis of arecoline's discriminative stimulus effects in this assay. However, both nicotine itself and two nicotine agonists with selective affinity for the α4β2* receptor (ispronicline and metanicotine) produced full arecoline-like discriminative stimulus effects in these rats. The discriminative stimulus effects of the selective nicotine agonists were blocked by both the general nicotine antagonist mecamylamine and by the selective α4β2* antagonist, dihydro-beta-erythroidine (DHβE). Surprisingly, only DHβE antagonized the rate-suppressing effects of the selective nicotine agonists. These data indicate a selective α4β2* nicotine receptor component to the behavioral effects of arecoline. Although the nicotinic aspects of arecoline's behavior effects could suggest that abuse of arecoline-containing material (e.g. betel nut chewing) is mediated through nicotinic rather than muscarinic actions, further research, specifically on the reinforcing effects of arecoline, is necessary before this conclusion can be supported.

Nicotine Enhances Object Recognition Memory via Stimulating α4β2 and α7 Nicotinic Acetylcholine Receptors in the Medial Prefrontal Cortex of Mice

Nicotine has been known to enhance recognition memory in various species. However, the brain region where nicotine acts and exerts its effect remains unclear. Since the medial prefrontal cortex (mPFC) is associated with memory, we examined the role of the mPFC in nicotine-induced enhancement of recognition memory using the novel object recognition test in male C57BL/6J mice. Systemic nicotine administration 10 min before training session significantly enhanced object recognition memory in test session that was performed 24 h after the training. Intra-mPFC infusion of mecamylamine, a non-selective nicotinic acetylcholine receptor (nAChR) antagonist, 5 min before nicotine administration blocked the effect of nicotine. Additionally, intra-mPFC infusion of dihydro-β-erythroidine, a selective α4β2 nAChR antagonist, or methyllycaconitine, a selective α7 nAChR antagonist, significantly suppressed the nicotine-induced object recognition memory enhancement. Finally, intra-mPFC infusion of nicotine 1 min before the training session augmented object recognition memory in a dose-dependent manner. These findings suggest that mPFC α4β2 and α7 nAChRs mediate the nicotine-induced object recognition memory enhancement.

Aerobic exercise improves memory and prevents cognitive deficits of relevance to schizophrenia in an animal model

INTRODUCTION AND OBJECTIVES

Cognitive impairment associated with schizophrenia (CIAS) greatly reduces patients' functionality, and remains an unmet clinical need. The sub-chronic phencyclidine (scPCP) rat model is commonly employed in studying CIAS. We have previously shown that voluntary exercise reverses impairments in novel object recognition (NOR) induced by scPCP. However, there has not been a longitudinal study investigating the potential protective effects of exercise in a model of CIAS. This study aimed to investigate the pro-cognitive and protective effects of exercise on CIAS using the translational NOR and attentional set-shifting tasks (ASST).

METHODS

Female Lister Hooded rats were either exercised (wheel running for one hour per day, five days per week, for six weeks; n=20) or not (n=20) and then tested in a natural-forgetting NOR test. Rats in each group were then administered either PCP (2 mg/kg intraperitoneally (i.p.)) or saline solution (1 mL/kg i.p.) for seven days, followed by seven days washout. Three NOR tests were conducted immediately and two and nine weeks after washout, and a natural-forgetting NOR test was carried out again eight weeks post washout. Rats were trained and tested in ASST from week 6 to week 10 post washout.

RESULTS

Non-exercised rats displayed a deficit in both of the natural-forgetting NOR tests, whereas exercised rats did not. The scPCP exercise group did not show the expected deficit in NOR at any time point, and had a significantly ameliorated deficit in the ASST compared to the scPCP control group.

CONCLUSION

Voluntary exercise has long-lasting pro-cognitive and protective effects in two cognitive domains. Exercise improves cognition and could provide protection against CIAS.

Neuroprotective effects of magnesium L-threonate in a hypoxic zebrafish model

BACKGROUND

Hypoxia inhibits the uptake of glutamate (a major neurotransmitter in the brain closely related to cognitive function) into brain cells, and the initial response of cells to cortical hypoxia depends on glutamate. Previous studies have suggested that magnesium may have protective effects against hypoxic injuries. In particular, magnesium L-threonate (MgT) may increase magnesium ion concentrations in the brain better than MgSO₄ and improve cognitive function.

METHODS

We evaluated cell viability under hypoxic conditions in the MgT- and MgSO₄-treated human SH-SY5Y neurons, in vivo behavior using the T-maze test following hypoxia in MgT-treated zebrafish, activity of brain mitochondrial dehydrogenase by 2,3,5-triphenyltetrazolium chloride (TTC) staining, and protein expression of the excitatory amino acid transporter (EAAT) 4 glutamate transporter by western blotting.

RESULTS

Among the groups treated with hypoxia, cell viability significantly increased when pre-treated with 1 or 10 mM MgT (p = 0.009 and 0.026, respectively). Despite hypoxic insult, MgT-treated zebrafish showed preferences for the red compartment (p = 0.025 for distance and p = 0.007 for frequency of entries), suggesting memory preservation. TTC staining showed reduced cerebral infarction and preserved absorbance in the MgT-treated zebrafish brain after hypoxia (p = 0.010 compared to the hypoxia group). In addition, western blot showed upregulation of EAAT4 protein in the MgT treated group.

CONCLUSIONS

Pre-treatment with MgT attenuated cell death and cerebral infarction due to hypoxia and protected cognitive function in zebrafish. In addition, MgT appeared to modulate expression of the glutamate transporter, EAAT4.

Desformylflustrabromine, a positive allosteric modulator of α4β2-containing nicotinic acetylcholine receptors, enhances cognition in rats

Rationale

The α4β2 nicotinic acetylcholine receptors (α4β2-nAChRs) may represent useful targets for cognitive improvement. It has been recently proposed that a strategy based on positive allosteric modulation of α4β2-nAChRs reveals several advantages over the direct agonist approach. Nevertheless, the procognitive effects of α4β2-nAChR positive allosteric modulators (PAMs) have not been extensively characterized.

Objectives

The aim of the present study was to evaluate the procognitive efficacy of desformylflustrabromine (dFBr), a selective α4β2-nAChR PAM.

Methods

Cognitive effects were investigated in the novel object recognition task (NORT) and the attentional set-shifting task (ASST) in rats.

Results

The results demonstrate that dFBr attenuated the delay-induced impairment in NORT performance and facilitated cognitive flexibility in the ASST. The beneficial effects of dFBr were inhibited by dihydro-β-erythroidine, a relatively selective α4β2-nAChR antagonist, indicating the involvement of α4β2-nAChRs in cognitive processes. The tested α4β2-PAM was also effective against ketamine- and scopolamine-induced deficits of object recognition memory. Moreover, procognitive effects were also observed after combined treatment with inactive doses of dFBr and TC-2403, a selective α4β2-nAChR agonist.

Conclusions

These findings indicate that dFBr presents procognitive activity, supporting the strategy based on α4β2-nAChR potentiation as a plausible therapy for cognitive impairment.

Electronic supplementary material

The online version of this article (10.1007/s43440-020-00092-4) contains supplementary material, which is available to authorized users.

α7 nicotinic acetylcholine receptors as therapeutic targets in schizophrenia: Update on animal and clinical studies and strategies for the future

Schizophrenia is a devastating mental illness and its effective treatment is among the most challenging issues in psychiatry. The symptoms of schizophrenia are heterogeneous ranging from positive symptoms (e.g., delusions, hallucinations) to negative symptoms (e.g., anhedonia, social withdrawal) to cognitive dysfunction. Antipsychotics are effective at ameliorating positive symptoms in some patients; however, they are not reliably effective at improving the negative symptoms or cognitive impairments. The inability to address the cognitive impairments is a particular concern since they have the greatest long-term impact on functional outcomes. While decades of research have been devoted to the development of pro-cognitive agents for schizophrenia, to date, no drug has been approved for clinical use. Converging behavioral, neurobiological, and genetic evidence led to the identification of the α7-nicotinic acetylcholine receptor (α7-nAChR) as a therapeutic target several years ago and there is now extensive preclinical evidence that α7-nAChR ligands have pro-cognitive effects and other properties that should be beneficial to schizophrenia patients. However, like the other pro-cognitive strategies, no α7-nAChR ligand has been approved for clinical use in schizophrenia thus far. In this review, several topics are discussed that may impact the success of α7-nAChR ligands as pro-cognitive agents for schizophrenia including the translational value of the animal models used, clinical trial design limitations, confounding effects of polypharmacy, dose-effect relationships, and chronic versus intermittent dosing considerations. Determining the most optimal pharmacologic strategy at α7-nAChRs: agonist, positive allosteric modulator, or potentially even receptor antagonist is also discussed. article is part of the special issue on 'Contemporary Advances in Nicotine Neuropharmacology'.

Cognitive dysfunction in diabetic rats is prevented by pyridoxamine treatment. A multidisciplinary investigation

OBJECTIVE

The impact of diabetes mellitus on the central nervous system is less widely studied than in the peripheral nervous system, but there is increasing evidence that it elevates the risk of developing cognitive deficits. The aim of this study was to characterize the impact of experimental diabetes on the proteome and metabolome of the hippocampus. We tested the hypothesis that the vitamin B6 isoform pyridoxamine is protective against functional and molecular changes in diabetes.

METHODS

We tested recognition memory using the novel object recognition (NOR) test in streptozotocin (STZ)-induced diabetic, age-matched control, and pyridoxamine- or insulin-treated diabetic male Wistar rats. Comprehensive untargeted metabolomic and proteomic analyses, using gas chromatography-mass spectrometry and iTRAQ-enabled protein quantitation respectively, were utilized to characterize the molecular changes in the hippocampus in diabetes.

RESULTS

We demonstrated diabetes-specific, long-term (but not short-term) recognition memory impairment and that this deficit was prevented by insulin or pyridoxamine treatment. Metabolomic analysis showed diabetes-associated changes in 13/82 identified metabolites including polyol pathway intermediates glucose (9.2-fold), fructose (4.9-fold) and sorbitol (5.2-fold). We identified and quantified 4807 hippocampal proteins; 806 were significantly altered in diabetes. Pathway analysis revealed significant alterations in cytoskeletal components associated with synaptic plasticity, glutamatergic signaling, oxidative stress, DNA damage and FXR/RXR activation pathways in the diabetic rat hippocampus.

CONCLUSIONS

Our data indicate a protective effect of pyridoxamine against diabetes-induced cognitive deficits, and our comprehensive 'omics datasets provide insight into the pathogenesis of cognitive dysfunction enabling development of further mechanistic and therapeutic studies.

Stabilized Low-n Amyloid-β Oligomers Induce Robust Novel Object Recognition Deficits Associated with Inflammatory, Synaptic, and GABAergic Dysfunction in the Rat

BACKGROUND

With current treatments for Alzheimer's disease (AD) only providing temporary symptomatic benefits, disease modifying drugs are urgently required. This approach relies on improved understanding of the early pathophysiology of AD. A new hypothesis has emerged, in which early memory loss is considered a synapse failure caused by soluble amyloid-β oligomers (Aβo). These small soluble Aβo, which precede the formation of larger fibrillar assemblies, may be the main cause of early AD pathologies.

OBJECTIVE

The aim of the current study was to investigate the effect of acute administration of stabilized low-n amyloid-β1-42 oligomers (Aβo1-42) on cognitive, inflammatory, synaptic, and neuronal markers in the rat.

METHODS

Female and male Lister Hooded rats received acute intracerebroventricular (ICV) administration of either vehicle or 5 nmol of Aβo1-42 (10μL). Cognition was assessed in the novel object recognition (NOR) paradigm at different time points. Levels of inflammatory (IL-1β, IL-6, TNF-α), synaptic (PSD-95, SNAP-25), and neuronal (n-acetylaspartate, parvalbumin-positive cells) markers were investigated in different brain regions (prefrontal and frontal cortex, striatum, dorsal and ventral hippocampus).

RESULTS

Acute ICV administration of Aβo1-42 induced robust and enduring NOR deficits. These deficits were reversed by acute administration of donepezil and rolipram but not risperidone. Postmortem analysis revealed an increase in inflammatory markers, a decrease in synaptic markers and parvalbumin containing interneurons in the frontal cortex, with no evidence of widespread neuronal loss.

CONCLUSION

Taken together the results suggest that acute administration of soluble low-n Aβo may be a useful model to study the early mechanisms involved in AD and provide us with a platform for testing novel therapeutic approaches that target the early underlying synaptic pathology.

Procognitive effects of varenicline in the animal model of schizophrenia depend on α4β2- and α 7-nicotinic acetylcholine receptors

BACKGROUND

Varenicline, a partial agonist of the α4β2 nicotinic acetylcholine receptor (α4β2-nAChR), is currently used to facilitate smoking cessation. Preclinical and clinical studies have suggested that this compound may also be effective in treating cognitive impairments in schizophrenia. However, it is unclear which nicotinic acetylcholine receptor subtypes may be involved because varenicline is not only a partial agonist for α4β2-nAChRs but also a full agonist for α7 nicotinic acetylcholine receptors (α7-nAChRs).

AIM

We investigated the effects of varenicline, compared to the α4β2-nAChR partial agonist TC-2403 and the α7-nAChR full agonist PNU-282987, in a ketamine-based model of schizophrenia-like cognitive deficits on the attentional set-shifting task in rats. The second goal was to elucidate whether the procognitive efficacy of varenicline was due to the compound's action on α4β2-nAChRs or α7-nAChRs.

METHODS

Ketamine was administered to rats for 10 consecutive days and the test was performed 14 days following the last injection. The tested compounds were administered 30 min prior to the attentional set-shifting task.

RESULTS

Varenicline, TC-2403 and PNU-282987 ameliorated ketamine-evoked set-shifting deficits. While the α4β2-nAChR antagonist dihydro-β-erythroidine and the α7-nAChR antagonist methyllycaconitine completely prevented the procognitive actions of TC-2403 and PNU-282987, respectively, varenicline's effect was only partially blocked by any given antagonist. Moreover, the combined treatment with TC-2403 and PNU-282987 more effectively facilitated rats' set-shifting ability than activation of either type of nicotinic acetylcholine receptor alone.

CONCLUSION

The present findings demonstrated that varenicline's actions on both α7-nAChRs and α4β2-nAChRs may be necessary to produce its full procognitive effect in the present experimental setting.

Serum levels of TNF-alpha in patients with chronic schizophrenia during treatment augmentation with sarcosine (results of the PULSAR study)

Sarcosine, glycine transporter inhibitor, increases glycine levels around NMDA receptor, improving primary negative symptoms of schizophrenia. The aim of our study was to find a potential relationship between initial TNF-alpha level, its changes and schizophrenia symptoms severity, resulting from adding sarcosine to a stable antipsychotic treatment. Sixty subjects with stable schizophrenia were randomized to receive either 2 g of sarcosine or placebo and completed a 6-month, double blind, placebo-controlled study. Three patients on sarcosine and one taking placebo did not complete TNF-alpha tests, planned at the beginning, after 6 weeks and after 6 months. For clinical assessments we used PANSS and CDSS scales. No changes in TNF-alpha serum concentrations in both groups at any time-points was noted. The sarcosine group achieved significant improvement in negative symptoms, general psychopathology and total PANSS score group, however without any significant correlations between TNF-alpha levels and PANSS scores in all assessments. Positive correlations between TNF-alpha levels and CDSS score were found in the placebo group and total study group. Initial TNF-alpha concentrations cannot be used as a predictor of the improvement resulting from adding sarcosine. Sarcosine does not significantly affect TNF-alpha levels. TNF-alpha may be involved in mechanisms related to depressive symptomatology in schizophrenia.

Revisiting Antipsychotic Drug Actions Through Gene Networks Associated With Schizophrenia

OBJECTIVE

Antipsychotic drugs were incidentally discovered in the 1950s, but their mechanisms of action are still not understood. Better understanding of schizophrenia pathogenesis could shed light on actions of current drugs and reveal novel "druggable" pathways for unmet therapeutic needs. Recent genome-wide association studies offer unprecedented opportunities to characterize disease gene networks and uncover drug-disease relationships. Polygenic overlap between schizophrenia risk genes and antipsychotic drug targets has been demonstrated, but specific genes and pathways constituting this overlap are undetermined. Risk genes of polygenic disorders do not operate in isolation but in combination with other genes through protein-protein interactions among gene product.

METHOD

The protein interactome was used to map antipsychotic drug targets (N=88) to networks of schizophrenia risk genes (N=328).

RESULTS

Schizophrenia risk genes were significantly localized in the interactome, forming a distinct disease module. Core genes of the module were enriched for genes involved in developmental biology and cognition, which may have a central role in schizophrenia etiology. Antipsychotic drug targets overlapped with the core disease module and comprised multiple pathways beyond dopamine. Some important risk genes like CHRN, PCDH, and HCN families were not connected to existing antipsychotics but may be suitable targets for novel drugs or drug repurposing opportunities to treat other aspects of schizophrenia, such as cognitive or negative symptoms.

CONCLUSIONS

The network medicine approach provides a platform to collate information of disease genetics and drug-gene interactions to shift focus from development of antipsychotics to multitarget antischizophrenia drugs. This approach is transferable to other diseases.

α7 Nicotinic Acetylcholine Receptor: A Potential Target in Treating Cognitive Decline in Schizophrenia

PURPOSE

The aim of this article is to review the recent trials of α7 nicotinic acetylcholine receptor (α7 nAChR) agonists and positive allosteric modulators (PAMs) on the treatment of cognitive decline in schizophrenia. α7 Nicotinic acetylcholine receptor abnormalities in schizophrenia and clinical implications of α7 nAChR agonists and PAMs are also discussed.

PROCEDURES

Studies were searched on PubMed with keywords "nicotinic," "alpha7," and "schizophrenia" over a 2-year period: January 1, 2016, to December 1, 2017. Cognition was not included in key terms in order to broaden the results. Inclusion criteria included (1) article categorization as a clinical study, review, or journal article; (2) schizophrenia diagnosis based on Diagnostic and Statistical Manual of Mental Disorders criteria; (3) article in English; (4) objective measure of cognition from effects of α7 nAChR agonists/PAMs; and (5) article currently published.

FINDINGS

A total of 76 studies were found over the past 2 years. Fifteen of these studies were included in this review. Human studies were limited. Cognitive-related improvements in rodent models were found across the 6 cognitive constructs: perception, executive functioning, social and affective processes, working memory, and long-term memory.

IMPLICATIONS

These results support the potential of nAChR agonists and PAMs to improve cognitive decline in patients with schizophrenia as an adjunct treatment to antipsychotics. However, these results were found primarily in rodent models of schizophrenia, and further primate/human studies are necessary to support this conclusion in humans.

Palmitoylation as a Functional Regulator of Neurotransmitter Receptors

The majority of neuronal proteins involved in cellular signaling undergo different posttranslational modifications significantly affecting their functions. One of these modifications is a covalent attachment of a 16-C palmitic acid to one or more cysteine residues (S-palmitoylation) within the target protein. Palmitoylation is a reversible modification, and repeated cycles of palmitoylation/depalmitoylation might be critically involved in the regulation of multiple signaling processes. Palmitoylation also represents a common posttranslational modification of the neurotransmitter receptors, including G protein-coupled receptors (GPCRs) and ligand-gated ion channels (LICs). From the functional point of view, palmitoylation affects a wide span of neurotransmitter receptors activities including their trafficking, sorting, stability, residence lifetime at the cell surface, endocytosis, recycling, and synaptic clustering. This review summarizes the current knowledge on the palmitoylation of neurotransmitter receptors and its role in the regulation of receptors functions as well as in the control of different kinds of physiological and pathological behavior.

Amyloid β synaptotoxicity is Wnt-PCP dependent and blocked by fasudil

Introduction

Synapse loss is the structural correlate of the cognitive decline indicative of dementia. In the brains of Alzheimer's disease sufferers, amyloid β (Aβ) peptides aggregate to form senile plaques but as soluble peptides are toxic to synapses. We previously demonstrated that Aβ induces Dickkopf-1 (Dkk1), which in turn activates the Wnt–planar cell polarity (Wnt-PCP) pathway to drive tau pathology and neuronal death.

Methods

We compared the effects of Aβ and of Dkk1 on synapse morphology and memory impairment while inhibiting or silencing key elements of the Wnt-PCP pathway.

Results

We demonstrate that Aβ synaptotoxicity is also Dkk1 and Wnt-PCP dependent, mediated by the arm of Wnt-PCP regulating actin cytoskeletal dynamics via Daam1, RhoA and ROCK, and can be blocked by the drug fasudil.

Discussion

Our data add to the importance of aberrant Wnt signaling in Alzheimer's disease neuropathology and indicate that fasudil could be repurposed as a treatment for the disease.

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Aβ synaptotoxicity is Dickkopf-1 and Wnt-PCP dependent.

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The Wnt-PCP pathway drives Aβ-driven synapse loss via RhoA and ROCK.

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ROCK inhibitor fasudil blocks Aβ-driven synapse loss and cognitive impairment.

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Fasudil should be assessed for repurposing for Alzheimer's disease.

Dopamine dysregulation in the prefrontal cortex relates to cognitive deficits in the sub-chronic PCP-model for schizophrenia: A preliminary investigation

RATIONALE

Dopamine dysregulation in the prefrontal cortex (PFC) plays an important role in cognitive dysfunction in schizophrenia. Sub-chronic phencyclidine (scPCP) treatment produces cognitive impairments in rodents and is a thoroughly validated animal model for cognitive deficits in schizophrenia. The aim of our study was to investigate the role of PFC dopamine in scPCP-induced deficits in a cognitive task of relevance to the disorder, novel object recognition (NOR).

METHODS

Twelve adult female Lister Hooded rats received scPCP (2 mg/kg) or vehicle via the intraperitoneal route twice daily for 7 days, followed by 7 days washout. In vivo microdialysis was carried out prior to, during and following the NOR task.

RESULTS

Vehicle rats successfully discriminated between novel and familiar objects and this was accompanied by a significant increase in dopamine in the PFC during the retention trial ( p < 0.01). scPCP produced a significant deficit in NOR ( p < 0.05 vs. control) and no PFC dopamine increase was observed.

CONCLUSIONS

These data demonstrate an increase in dopamine during the retention trial in vehicle rats that was not observed in scPCP-treated rats accompanied by cognitive disruption in the scPCP group. This novel finding suggests a mechanism by which cognitive deficits are produced in this animal model and support its use for investigating disorders in which PFC dopamine is central to the pathophysiology.

Role of cholinergic receptors in memory retrieval depends on gender and age of memory

The phenomenon of utilizing information acquired in the past to make decision and performance in present depends on memory retrieval, which is affected in retrograde amnesia. Role of cholinergic receptors in memory retrieval is not much explored. In this study we evaluated the gender specific role of cholinergic receptors, i.e. muscarinic and nicotinic receptors, in memory retrieval in young Balb/c mice. Acute (only one injection, 30min before test) and sub-chronic (five days) muscarinic blockade (using scopolamine=1mg/kg) before test impaired retrieval of contextual fear memory in male (31.45±5.39% and 33.36±3.78% respectively) and female mice (22.88±5.73%; P<0.05), except sub-chronically treated female group (33.31±4.90%; P>0.05). Only sub-chronic nicotinic receptor antagonism (using methyllycaconitine MLA=87.5μg/kg and dihydro β erythroidine DHβE=1mg/kg) in female showed significantly higher freezing response than control during contextual fear memory retrieval (60.85±7.71% and 40.91±7.53% respectively; P<0.001). Acute and sub-chronic muscarinic antagonism (but not nicotinic antagonism) impaired spatial memory retrieval in male (P<0.05) but not in female mice (P>0.05). There was no effect of acute and sub-chronic cholinergic receptor antagonism on discriminating novel object from the familiar one in male and female mice, however, nicotinic receptor blockade affected the working memory of all male and female mice on test day compared to the training sessions. Our results suggested that cholinergic receptors involvement in retrieving spatial and fear memories depends on the age of the memory and gender.

Partial agonism at the α7 nicotinic acetylcholine receptor improves attention, impulsive action and vigilance in low attentive rats

Inattention is a disabling symptom in conditions such as schizophrenia and attention deficit/hyperactivity disorder. Nicotine can improve attention and vigilance, but is unsuitable for clinical use due to abuse liability. Genetic knockout of the α7 nicotinic acetylcholine receptor (nAChR) induces attention deficits therefore selective agonism may improve attention, without the abuse liability associated with nicotine. The α7 nAChR partial agonist encenicline (formerly EVP-6124) enhances memory in rodents and humans. Here we investigate, for the first time, efficacy of encenicline to improve attention and vigilance in animals behaviourally grouped for low attentive traits in the 5 choice-continuous performance task (5C-CPT). Female Lister Hooded rats were trained to perform the 5C-CPT with a variable stimulus duration (SD). Animals were then grouped based on performance into upper and lower quartiles of d' (vigilance) and accuracy (selective attention), producing high-attentive (HA) and low-attentive (LA) groups. LA animals showed an increase in selective attention and vigilance at 0.3mg/kg encenicline, a reduction in impulsive action (probability of false alarms) and increase in vigilance following 1mg/kg at 0.75sSD. At 1mg/kg, HA animals had reduced selective attention at 0.75sSD and reduced vigilance at 0.75 and 1.25sSD. Improvement of attention, vigilance and impulsive action in LA animals demonstrates that encenicline has pro-attentive properties dependent on baseline levels of performance. Our work suggests that α7 nAChR partial agonism may improve attention particularly in conditions with low attention.

Tropisetron sensitizes α7 containing nicotinic receptors to low levels of acetylcholine in vitro and improves memory-related task performance in young and aged animals

Tropisetron, a 5-HT₃ receptor antagonist commonly prescribed for chemotherapy-induced nausea and vomiting also exhibits high affinity, partial agonist activity at α7 nicotinic acetylcholine receptors (α7 nAChRs). α7 nAChRs are considered viable therapeutic targets for neuropsychiatric disorders such as Alzheimer's disease (AD). Here we further explored the nAChR pharmacology of tropisetron to include the homomeric α7 nAChR and recently characterized heteromeric α7β2 nAChR (1:10 ratio) and we evaluated its cognitive effects in young and aged animals. Electrophysiological studies on human nAChRs expressed in Xenopus oocytes confirmed the partial agonist activity of tropisetron at α7 nAChRs (EC₅₀ ∼2.4 μM) with a similar effect at α7β2 nAChRs (EC₅₀ ∼1.5 μM). Moreover, currents evoked by irregular pulses of acetylcholine (40 μM) at α7 and α7β2 nAChRs were enhanced during sustained exposure to low concentrations of tropisetron (10 and 30 nM) indicative of a "priming" or co-agonist effect. Tropisetron (0.1-10 mg/kg) improved novel object recognition performance in young Sprague-Dawley rats and in aged Fischer rats. In aged male and female rhesus monkeys, tropisetron (0.03-1 mg/kg) produced a 17% increase from baseline levels in delayed match to sample long delay accuracy while combination of non-effective doses of donepezil (0.1 mg/kg) and tropisetron (0.03 and 0.1 mg/kg) produced a 24% change in accuracy. Collectively, these animal experiments indicate that tropisetron enhances cognition and has the ability to improve the effective dose range of currently prescribed AD therapy (donepezil). Moreover, these effects may be explained by tropisetron's ability to sensitize α7 containing nAChRs to low levels of acetylcholine.

Cholinergic agonist reverses H1-induced memory deficit in mice

This study investigated the effects of bilateral intraamygdalar microinjections of PNU-282987, a nicotinic cholinergic agonist, on anxiety and the reversal of amnesia induced by chlorpheniramine (CPA), an H1 histaminergic antagonist, in mice subjected to the elevated plusmaze (EPM). Two experiments were performed with seventy-nine adult male Swiss mice. The isolated microinjections of PNU-282987 did not produce effects on emotional memory; however, the combined microinjections of PNU-282987 and CPA were able to reverse the deficit in memory induced by CPA (ANOVA, p<0.05). Taken together, these results suggest that intraamygdalar injections of PNU-282987 did not induce effects on anxiety and emotional memory per se; however, concurrent microinjections of PNU-282987 and CPA-reverse amnesia induced-CPA which is suggestive of an interaction between the histaminergic and cholinergic systems in the modulation of emotion memory acquisition in mice.