Indirect modulation by alpha7 nicotinic acetylcholine receptors of noradrenaline release in rat hippocampal slices: interaction with glutamate and GABA systems and effect of nicotine withdrawal

Dose-dependent effects of GAT107, a novel allosteric agonist-positive allosteric modulator (ago-PAM) for the α7 nicotinic cholinergic receptor: a BOLD phMRI and connectivity study on awake rats

Background

Alpha 7 nicotinic acetylcholine receptor (α7nAChR) agonists have been developed to treat schizophrenia but failed in clinical trials due to rapid desensitization. GAT107, a type 2 allosteric agonist-positive allosteric modulator (ago-PAM) to the α7 nAChR was designed to activate the α7 nAChR while reducing desensitization. We hypothesized GAT107 would alter the activity of thalamocortical neural circuitry associated with cognition, emotion, and sensory perception.

Methods

The present study used pharmacological magnetic resonance imaging (phMRI) to evaluate the dose-dependent effect of GAT107 on brain activity in awake male rats. Rats were given a vehicle or one of three different doses of GAT107 (1, 3, and 10 mg/kg) during a 35 min scanning session. Changes in BOLD signal and resting state functional connectivity were evaluated and analyzed using a rat 3D MRI atlas with 173 brain areas.

Results

GAT107 presented with an inverted-U dose response curve with the 3 mg/kg dose having the greatest effect on the positive BOLD volume of activation. The primary somatosensory cortex, prefrontal cortex, thalamus, and basal ganglia, particularly areas with efferent connections from the midbrain dopaminergic system were activated as compared to vehicle. The hippocampus, hypothalamus, amygdala, brainstem, and cerebellum showed little activation. Forty-five min post treatment with GAT107, data for resting state functional connectivity were acquired and showed a global decrease in connectivity as compared to vehicle.

Discussion

GAT107 activated specific brain regions involved in cognitive control, motivation, and sensory perception using a BOLD provocation imaging protocol. However, when analyzed for resting state functional connectivity there was an inexplicable, general decrease in connectivity across all brain areas.

α7 Nicotinic acetylcholine receptor: a key receptor in the cholinergic anti-inflammatory pathway exerting an antidepressant effect

Depression is a common mental illness, which is related to monoamine neurotransmitters and the dysfunction of the cholinergic, immune, glutamatergic, and neuroendocrine systems. The hypothesis of monoamine neurotransmitters is one of the commonly recognized pathogenic mechanisms of depression; however, the drugs designed based on this hypothesis have not achieved good clinical results. A recent study demonstrated that depression and inflammation were strongly correlated, and the activation of alpha7 nicotinic acetylcholine receptor (α7 nAChR)-mediated cholinergic anti-inflammatory pathway (CAP) in the cholinergic system exhibited good therapeutic effects against depression. Therefore, anti-inflammation might be a potential direction for the treatment of depression. Moreover, it is also necessary to further reveal the key role of inflammation and α7 nAChR in the pathogenesis of depression. This review focused on the correlations between inflammation and depression as well-discussed the crucial role of α7 nAChR in the CAP.

Chronic, episodic nicotine exposure alters GABAergic synaptic transmission to hypoglossal motor neurons and genioglossus muscle function at a critical developmental age

Regulation of GABAergic signaling through nicotinic acetylcholine receptor (nAChR) activation is critical for neuronal development. Here, we test the hypothesis that chronic episodic developmental nicotine exposure (eDNE) disrupts GABAergic signaling, leading to dysfunction of hypoglossal motor neurons (XIIMNs), which innervate the tongue muscles. We studied control and eDNE pups at two developmentally vulnerable age ranges: postnatal days (P)1-5 and P10-12. The amplitude and frequency of spontaneous and miniature inhibitory postsynaptic currents (sIPSCs, mIPSCs) at baseline were not altered by eDNE at either age. In contrast, eDNE increased GABAAR-α1 receptor expression on XIIMNs and, in the older group, the postsynaptic response to muscimol (GABAA receptor agonist). Activation of nAChRs with exogenous nicotine increased the frequency of GABAergic sIPSCs in control and eDNE neurons at P1-5. By P10-12, acute nicotine increased sIPSC frequency in eDNE but not control neurons. In vivo experiments showed that the breathing-related activation of tongue muscles, which are innervated by XIIMNs, is reduced at P10-12. This effect was partially mitigated by subcutaneous muscimol, but only in the eDNE pups. Taken together, these data indicate that eDNE alters GABAergic transmission to XIIMNs at a critical developmental age, and this is expressed as reduced breathing-related drive to XIIMNs in vivo.NEW & NOTEWORTHY Here, we provide a thorough assessment of the effects of nicotine exposure on GABAergic synaptic transmission, from the cellular to the systems level. This work makes significant advances in our understanding of the impact of nicotine exposure during development on GABAergic neurotransmission within the respiratory network and the potential role this plays in the excitatory/inhibitory imbalance that is thought to be an important mechanism underlying neonatal breathing disorders, including sudden infant death syndrome.

The Neuromodulatory Role of the Noradrenergic and Cholinergic Systems and Their Interplay in Cognitive Functions: A Focused Review

The noradrenergic and cholinergic modulation of functionally distinct regions of the brain has become one of the primary organizational principles behind understanding the contribution of each system to the diversity of neural computation in the central nervous system. Decades of work has shown that a diverse family of receptors, stratified across different brain regions, and circuit-specific afferent and efferent projections play a critical role in helping such widespread neuromodulatory systems obtain substantial heterogeneity in neural information processing. This review briefly discusses the anatomical layout of both the noradrenergic and cholinergic systems, as well as the types and distributions of relevant receptors for each system. Previous work characterizing the direct and indirect interaction between these two systems is discussed, especially in the context of higher order cognitive functions such as attention, learning, and the decision-making process. Though a substantial amount of work has been done to characterize the role of each neuromodulator, a cohesive understanding of the region-specific cooperation of these two systems is not yet fully realized. For the field to progress, new experiments will need to be conducted that capitalize on the modular subdivisions of the brain and systematically explore the role of norepinephrine and acetylcholine in each of these subunits and across the full range of receptors expressed in different cell types in these regions.

Differentiating the Neuropharmacological Properties of Nicotinic Acetylcholine Receptor-Activating Alkaloids

Alkaloids that target nicotinic acetylcholine receptors (nAChR) are of great interest because of the critical role they play in mood and anxiety. However, understanding of the neuropharmacological effects of nicotinic alkaloids, such as cotinine and anatabine, is very limited. In this study, we investigated the neuropharmacological effects of three naturally occurring alkaloids-nicotine, cotinine, and anatabine-in vitro and in vivo. A single injection of nicotine induced anxiolytic-like behavioral features in mice by using the SmartCube® behavioral profiling system, while cotinine and anatabine had no detectable effect. The results were corroborated by using the zebrafish novel tank test (NTT), which showed a profound anxiolytic-like effect induced by multiple doses of nicotine after a single 20-min treatment. When the regulation of dopamine and norepinephrine release-the neurotransmitter systems relevant for anxiety-were examined in vitro, we found that nicotine stimulated the release of both norepinephrine and dopamine, while cotinine and anatabine mainly stimulated the dopamine release. The molecular targets of nicotine were confirmed to be nAChRs with its most potent activities against α4β2 and α6/3β2β3 subtypes in vitro. Anatabine was a weaker agonist for these receptors than nicotine. Cotinine was the least potent nAChR compound, only being able to activate α4β2 and α6/3β2β3 subtypes at high doses and no detectable activities against α3β4 and α7 subtypes at the concentrations tested. The observed effects were unlikely due to the off-target effect, because these alkaloids did not bind or regulate >160 other molecular targets in vitro. Thus, the present results suggest that natural nicotinic alkaloids can induce an anxiolytic-like behavior in nonclinical animal models, potency of which may depend on the activation of various nAChRs and regulation of various neurotransmitter systems. Further investigations would help understand their effects on humans, because non-clinical studies should not be taken as a direct indication for human behavior and nicotine is not risk free.

Sex differences in P50 inhibition defects with psychopathology and cognition in patients with first-episode schizophrenia

BACKGROUND

A large number of studies have shown that the pathophysiology of schizophrenia may be involved in sensory gating that appears to be P50 inhibition. However, few studies have investigated the relationship between clinical symptoms, cognitive impairment and sensory gating disorders in patients with first-episode schizophrenia. The purpose of this study was to explore the sex differences in the relationship between clinical symptoms, cognitive impairment and P50 inhibition defects in patients with first-episode schizophrenia, which has not been reported.

METHODS

130 patients with first-episode schizophrenia (53 males and 77 females) and 189 healthy controls (87 males and 102 females) participated in the study. Positive and Negative Syndrome Scale (PANSS) was used to evaluate the patients' psychopathological symptoms, and the 64-channel electroencephalogram (EEG) system was used to record the P50 inhibition.

RESULTS

Male patients had higher PANSS negative symptom, general psychopathology, cognitive factor and total scores than female patients (all p < 0.01). The S1 amplitude was smaller in male than female patients (all p < 0.05). Multiple regression analysis showed that in male patients, S1 latency was contributor to negative symptoms, while S1 latency, S2 latency, age, and smoking status were contributors to cognitive factor (all p < 0.05). In female patients, no P50 component was found to be an independent contributor to PANSS scores (all p > 0.05).

CONCLUSIONS

Our results indicate that there is a sex difference in the relationship between clinical symptoms, cognitive impairment and P50 inhibition defects in Chinese Han patients with first-episode schizophrenia.

A systems omics-based approach to decode substance use disorders and neuroadaptations

Substance use disorders (SUDs) are a group of neuropsychiatric conditions manifesting due to excessive dependence on potential drugs of abuse such as psychostimulants, opioids including prescription opioids, alcohol, inhalants, etc. Experimental studies have generated enormous data in the area of SUDs, but outcomes from such data have remained largely fragmented. In this review, we attempt to coalesce these data points providing an important first step towards our understanding of the etiology of SUDs. We propose and describe a 'core addictome' pathway that behaves central to all SUDs. Besides, we also have made some notable observations paving way for several hypotheses; MECP2 behaves as a master switch during substance use; five distinct gene clusters were identified based on respective substance addiction; a central cluster of genes serves as a hub of the addiction pathway connecting all other substance addiction clusters. In addition to describing these findings, we have emphasized the importance of some candidate genes that are of substantial interest for further investigation and serve as high-value targets for translational efforts.

Relationships and Interactions between Ionotropic Glutamate Receptors and Nicotinic Receptors in the CNS

Although ionotropic glutamate receptors and nicotinic receptors for acetylcholine (ACh) have usually been studied separately, they are often co-localized and functionally inter-dependent. The objective of this review is to survey the evidence for interactions between the two receptor families and the mechanisms underlying them. These include the mutual regulation of subunit expression, which change the NMDA:AMPA response balance, and the existence of multi-functional receptor complexes which make it difficult to distinguish between individual receptor sites, especially in vivo. This is followed by analysis of the functional relationships between the receptors from work on transmitter release, cellular electrophysiology and aspects of behavior where these can contribute to understanding receptor interactions. It is clear that nicotinic receptors (nAChRs) on axonal terminals directly regulate the release of glutamate and other neurotransmitters, α7-nAChRs generally promoting release. Hence, α7-nAChR responses will be prevented not only by a nicotinic antagonist, but also by compounds blocking the indirectly activated glutamate receptors. This accounts for the apparent anticholinergic activity of some glutamate antagonists, including the endogenous antagonist kynurenic acid. The activation of presynaptic nAChRs is by the ambient levels of ACh released from pre-terminal synapses, varicosities and glial cells, acting as a 'volume neurotransmitter' on synaptic and extrasynaptic sites. In addition, ACh and glutamate are released as CNS co-transmitters, including 'cholinergic' synapses onto spinal Renshaw cells. It is concluded that ACh should be viewed primarily as a modulator of glutamatergic neurotransmission by regulating the release of glutamate presynaptically, and the location, subunit composition, subtype balance and sensitivity of glutamate receptors, and not primarily as a classical fast neurotransmitter. These conclusions and caveats should aid clarification of the sites of action of glutamate and nicotinic receptor ligands in the search for new centrally-acting drugs.

Involvement of α7nAChR in the Protective Effects of Genistein Against β-Amyloid-Induced Oxidative Stress in Neurons via a PI3K/Akt/Nrf2 Pathway-Related Mechanism

Abnormal excessive production and deposition of β-amyloid (Aβ) peptides in selectively susceptible brain regions are thought to be a key pathogenic mechanism underlying Alzheimer's disease (AD), resulting in memory deficits and cognitive impairment. Genistein is a phytoestrogen with great promise for counteracting diverse Aβ-induced insults, including oxidative stress and mitochondrial dysfunction. However, the exact molecular mechanism or mechanisms underlying the neuroprotective effects of genistein against Aβ-induced insults are largely uncharacterized. To further elucidate the possible mechanism(s) underlying these protective effects, we investigated the neuroprotective effects of genistein against Aβ-induced oxidative stress mediated by orchestrating α7 nicotinic acetylcholine receptor (α7nAChR) signaling in rat primary hippocampal neurons. Genistein significantly increased cell viability, reduced the number of apoptotic cells, decreased accumulation of reactive oxygen species (ROS), decreased contents of malondialdehyde (MDA) and lactate dehydrogenase (LDH), upregulated BCL-2 expression, and suppressed Caspase-3 activity occurring after treatment with 25 μM Aβ25-35. Simultaneously, genistein markedly inhibited the decreases in α7nAChR mRNA and protein expression in cells treated with Aβ25-35. In addition, α7nAChR signaling was intimately involved in the genistein-mediated activation of phosphatidylinositol 3-kinase (PI3K)/Akt and Nrf2/keap1 signaling. Thus, α7nAChR activity together with the PI3K/Akt/Nrf2 signaling cascade likely orchestrates the molecular mechanism underlying the neuroprotective effects of genistein against Aβ-induced oxidative injury.

Low-Dose Nicotine Activates EGFR Signaling via α5-nAChR and Promotes Lung Adenocarcinoma Progression

Nicotine in tobacco smoke is considered carcinogenic in several malignancies including lung cancer. The high incidence of lung adenocarcinoma (LAC) in non-smokers, however, remains unexplained. Although LAC has long been less associated with smoking behavior based on previous epidemiological correlation studies, the effect of environmental smoke contributing to low-dose nicotine exposure in non-smoking population could be underestimated. Here we provide experimental evidence of how low-dose nicotine promotes LAC growth in vitro and in vivo. Screening of nicotinic acetylcholine receptor subunits in lung cancer cell lines demonstrated a particularly high expression level of nicotinic acetylcholine receptor subunit α5 (α 5-nAChR) in LAC cell lines. Clinical specimen analysis revealed up-regulation of α 5-nAChR in LAC tumor tissues compared to non-tumor counterparts. In LAC cell lines α 5-nAChR interacts with epidermal growth factor receptor (EGFR), positively regulates EGFR pathway, enhances the expression of epithelial-mesenchymal transition markers, and is essential for low-dose nicotine-induced EGFR phosphorylation. Functionally, low-dose nicotine requires α 5-nAChR to enhance cell migration, invasion, and proliferation. Knockdown of α 5-nAChR inhibits the xenograft tumor growth of LAC. Clinical analysis indicated that high level of tumor α 5-nAChR is correlated with poor survival rates of LAC patients, particularly in those expressing wild-type EGFR. Our data identified α 5-nAChR as an essential mediator for low-dose nicotine-dependent LAC progression possibly through signaling crosstalk with EGFR, supporting the involvement of environmental smoke in tumor progression in LAC patients.

Nicotine patch for cannabis withdrawal symptom relief: a randomized controlled trial

RATIONALE

Given that tetrahydrocannabinol (THC) and nicotine have similar effects on negative affect (NA), we hypothesized that a 7-mg nicotine patch (NP) would reduce NA-related cannabis (CAN) withdrawal symptoms in cannabis-dependent (CD) individuals who were not nicotine dependent.

OBJECTIVE

We sought to determine whether NP reduces NA across 15 days of CAN abstinence in two groups: non-tobacco smokers (NTS) and light tobacco smokers (LTS).

METHODS

CD participants (N = 127; aged 18-35) who used CAN at least 5 times/week for the past 12 + months were randomized to (1) NP or (2) a placebo patch (PP) and received $300 for sustained biochemically verified CAN abstinence. Of those randomly assigned, 52 of 63 NP, and 56 of 64 PP maintained biochemically verified CAN abstinence and 51 NP and 50 PP participants complied with all aspects of the study. Affect and other withdrawal symptoms were measured every 48 h across 15 days of CAN abstinence.

RESULTS

After controlling for age, tobacco use, baseline THC concentration, and baseline measurements of the dependent variable, NP reduced NA symptoms across the 15-day treatment relative to PP. Differences in NA and CAN withdrawal symptoms were not moderated by tobacco user status.

CONCLUSIONS

The findings provide the first evidence that NP may be able to attenuate NA-related withdrawal symptoms in individuals with cannabis use disorder who are not heavy users of tobacco or nicotine.

CLINICAL TRIALS REGISTRY

NCT01400243 http://www.clinicaltrials.gov.

Additive interaction between scopolamine and nitric oxide agents on immobility in the forced swim test but not exploratory activity in the hole-board

RATIONALE

The muscarinic cholinergic antagonist scopolamine has received an attention due to its unique antidepressant effects. However, the considerable adverse effects on nervous system limit the use of scopolamine as a psychiatric drug.

OBJECTIVE

In order to overcome the limitations and increase the therapeutic effects of scopolamine, we decided to examine the effects of joint administration of sub-effective dose of scopolamine and the sub-effective dose of a nitric oxide (NO) precursor L-Arginine or a non-selective nitric oxide synthase (NOS) inhibitor L-NAME on depression- and anxiety-related behaviors in male NMRI mice.

METHODS

To this aim, animal behavior was assessed in the forced swim test (FST) and hole-board apparatus.

RESULTS

Scopolamine (0.05 mg/kg) significantly decreased immobility time in the FST, suggesting an antidepressant-like effect. Moreover, L-Arginine (50 mg/kg) produced an antidepressant-like response in the FST and decreased head-dip counts in the hole-board apparatus, indicating an anxiety-like effect. The same doses of scopolamine and L-Arginine decreased the locomotor activity in mice. Joint administration of sub-effective dose of scopolamine (0.01 mg/kg) with a low dose of L-Arginine (25 mg/kg) or L-NAME (1 mg/kg) induced a profound antidepressant-like effect in the FST. These drug combinations did not influence on anxiety-related behaviors. Meanwhile, L-NAME alone did not alter the performance of mice in the FST and hole-board. Isobolographic analysis revealed an additive effect for scopolamine and L-Arginine or L-NAME.

CONCLUSION

Data suggests that NO agents could positively impact the therapeutic profile of scopolamine, because they might be useful for inducing antidepressant-like effect associated to scopolamine.

Cholinergic regulation of mood: from basic and clinical studies to emerging therapeutics

Mood disorders are highly prevalent and are the leading cause of disability worldwide. The neurobiological mechanisms underlying depression remain poorly understood, although theories regarding dysfunction within various neurotransmitter systems have been postulated. Over 50 years ago, clinical studies suggested that increases in central acetylcholine could lead to depressed mood. Evidence has continued to accumulate suggesting that the cholinergic system has a important role in mood regulation. In particular, the finding that the antimuscarinic agent, scopolamine, exerts fast-onset and sustained antidepressant effects in depressed humans has led to a renewal of interest in the cholinergic system as an important player in the neurochemistry of major depression and bipolar disorder. Here, we synthesize current knowledge regarding the modulation of mood by the central cholinergic system, drawing upon studies from human postmortem brain, neuroimaging, and drug challenge investigations, as well as animal model studies. First, we describe an illustrative series of early discoveries which suggest a role for acetylcholine in the pathophysiology of mood disorders. Then, we discuss more recent studies conducted in humans and/or animals which have identified roles for both acetylcholinergic muscarinic and nicotinic receptors in different mood states, and as targets for novel therapies.

Nicotine inhibits rapamycin-induced pain through activating mTORC1/S6K/IRS-1-related feedback inhibition loop

Mammalian target of rapamycin complex 1 (mTORC1) inhibitors increase the incidence of pain in patients, and this finding has been replicated in animal models. However, reports on possible analgesics for this condition are scant. Accumulating evidence finds that nicotinic acetylcholine receptors (nAChRs) are involved in mediating pain. However, whether nicotine, a full agonist of nAChRs, alleviates mTORC1 inhibition-induced pain and its underlying mechanisms remain unknown. In this study, pain was induced in naïve male C57BL/6J mice by intraperitoneally injecting rapamycin acutely or repeatedly. Subsequently, pain thresholds, including mechanical and thermal pain, were measured. The involving signaling pathway was tested using western blot analysis and immunofluorescent assay. Changes in neuronal excitability caused by different treatments were also analyzed using whole-cell recording. Microinjection into the anterior cingulate cortex (ACC) was used to test the role of nAChRs containing the α4β2 or α7 subtype in this brain region in pain modulation. Our results showed that nicotine significantly reduced hyperalgesia in mice that received acute or repeated rapamycin injections, and reversed the effects of rapamycin on the phosphorylation of S6K, 4E-BP1, insulin receptor substrate-1 (IRS-1) at Ser636/639, AKT at Ser473, and ERK at Thr202/Tyr204. Whole-cell recording results showed that nicotine reduced the firing rates of pyramidal neurons in the ACC, and a pharmacological blockade of nAChRs containing the α4β2 or α7 subtype in ACC inhibited the antinociceptive effects of nicotine in mice with rapamycin-induced pain. Our findings indicate that analgesics targeting nAChRs can be developed to help patients with rapamycin-induced pain.

Effects of alpha-7 nicotinic allosteric modulator PNU 120596 on depressive-like behavior after lipopolysaccharide administration in mice

Evidence suggests that α7 nicotinic acetylcholine receptor (α7 nAChR) in the central nervous system has a critical role in the regulation of microglial function and neuroinflammation associated with the pathophysiology of major depressive disorder. The objectives of the present study were to determine the effects of PNU 120596, an α7 nAChR positive allosteric modulator (PAM), on depressive-like behavior and expression of ionized calcium binding adaptor molecule 1 (Iba-1), a microglial marker, in male C57BL/6J mice following lipopolysaccharide (LPS) administration, an animal model for depressive-like behavior. Forced swim test (FST), tail suspension test (TST), and sucrose preference test were used to determine the effects of PNU 120596 on depressive-like behavior, measured by increased immobility time or decreased sucrose preference. We also examined the effects of PNU 120596 on Iba-1 expression by using Western blot analysis and immunofluorescence staining in the hippocampus and prefrontal cortex, the brain regions implicated in major depressive disorder. Administration of LPS (1 mg/kg, i.p.) significantly increased immobility time during FST and TST and decreased sucrose preference. The PNU 120596 (1 or 4 mg/kg, i.p.) dose-dependently prevented LPS-induced depressive-like behavior during FST, TST, and sucrose preference test. The PNU 120596 (1 or 4 mg/kg) alone did not show any significant alteration on immobility time and sucrose preference. Pretreatment of methyllycaconitine (3 mg/kg, i.p.), an α7 nAChR antagonist, significantly prevented the antidepressant-like effects of PNU (4 mg/kg). Similarly, the PNU 120596 (4 mg/kg, i.p.) significantly reduced LPS-induced increased expression of Iba-1 in the hippocampus or prefrontal cortex. Overall, these results suggest that PNU 120596 reduces LPS-induced depressive-like behavior and microglial activation in the hippocampus and prefrontal cortex in mice. Therefore, α7 nAChR PAMs could be developed as potential therapeutic utility for the treatment of major depressive disorder in humans.

Nicotinic Acetylcholine Receptor Subtype Alpha-9 Mediates Triple-Negative Breast Cancers Based on a Spontaneous Pulmonary Metastasis Mouse Model

Triple-negative breast cancer (TNBC) subtype is associated with poor prognosis and a high risk of recurrence-related death in women. Despite the aggressiveness of TNBCs, targeted TNBC therapy is not yet available in the clinic. To overcome this challenge, we generated highly metastatic TNBC cells (LM) derived from metastasized lung cells via a serial spontaneous pulmonary metastasis animal model to identify targetable molecules for attenuating the progression of TNBC metastasis. Gene analysis of primary tumor (P), first-round (1LM) and second-round (2LM) metastasized lung cells revealed that mesenchymal-related genes were significantly expressed in LM cells, especially in 2LM cells. Interestingly, α9-nAChR gene expression was also dramatically induced in LM cells, confirming our previous finding that α9-nAChR plays important roles in receptor-mediated carcinogenic signals in human breast cancer development. Using α9-nAChR as a biomarker, we transfected 2LM cells with CRISPR/Cas9 lentivirus targeting the α9-nAChR genomic region (2LM-α9-nAChR-null), showing that mesenchymal markers and the migration and invasion abilities of 2LM cells were significantly attenuated in 2LM-α9-nAChR-null cells both in vitro and in vivo. In addition, the high efficiency of editing the α9-nAChR gene using a CRISPR/Cas9 lentivirus was demonstrated by gene sequencing, genomic indel frequency and protein expression analyses. Collectively, these results confirmed those of our previous study that advanced-stage breast tumors are associated with substantially higher levels of α9-nAChR gene expression, indicating that α9-nAChR expression is essential for mediating TNBC metastasis during cancer development and may potentially act as a biomarker for targeted therapy in clinical investigations.

The current agonists and positive allosteric modulators of α7 nAChR for CNS indications in clinical trials

The alpha-7 nicotinic acetylcholine receptor (α7 nAChR), consisting of homomeric α7 subunits, is a ligand-gated Ca²⁺-permeable ion channel implicated in cognition and neuropsychiatric disorders. Enhancement of α7 nAChR function is considered to be a potential therapeutic strategy aiming at ameliorating cognitive deficits of neuropsychiatric disorders such as Alzheimer's disease (AD) and schizophrenia. Currently, a number of α7 nAChR modulators have been reported and several of them have advanced into clinical trials. In this brief review, we outline recent progress made in understanding the role of the α7 nAChR in multiple neuropsychiatric disorders and the pharmacological effects of α7 nAChR modulators used in clinical trials.

Alpha7 Nicotinic Acetylcholine Receptors Play a Predominant Role in the Cholinergic Potentiation of N-Methyl-D-Aspartate Evoked Firing Responses of Hippocampal CA1 Pyramidal Cells

The aim of the present study was to identify in vivo electrophysiological correlates of the interaction between cholinergic and glutamatergic neurotransmission underlying memory. Extracellular spike recordings were performed in the hippocampal CA1 region of anesthetized rats in combination with local microiontophoretic administration of N-methyl-D-aspartate (NMDA) and acetylcholine (ACh). Both NMDA and ACh increased the firing rate of the neurons. Furthermore, the simultaneous delivery of NMDA and ACh resulted in a more pronounced excitatory effect that was superadditive over the sum of the two mono-treatment effects and that was explained by cholinergic potentiation of glutamatergic neurotransmission. Next, animals were systemically treated with scopolamine or methyllycaconitine (MLA) to assess the contribution of muscarinic ACh receptor (mAChR) or α7 nicotinic ACh receptor (nAChR) receptor-mediated mechanisms to the observed effects. Scopolamine totally inhibited ACh-evoked firing, and attenuated the firing rate increase evoked by simultaneous application of NMDA and ACh. However, the superadditive nature of the combined effect was preserved. The α7 nAChR antagonist MLA robustly decreased the firing response to simultaneous application of NMDA and ACh, suspending their superadditive effect, without modifying the tonic firing rate increasing effect of ACh. These results provide the first in vivo electrophysiological evidence that, in the hippocampal CA1 region, α7 nAChRs contribute to pyramidal cell activity mainly through potentiation of glutamatergic signaling, while the direct cholinergic modulation of tonic firing is notably mediated by mAChRs. Furthermore, the present findings also reveal cellular physiological correlates of the interplay between cholinergic and glutamatergic agents in behavioral pharmacological models of cognitive decline.

Mechanisms and Effects Posed by Neurotoxic Products of Cyanobacteria/Microbial Eukaryotes/Dinoflagellates in Algae Blooms: a Review

Environmental toxins produced by cyanobacteria and dinoflagellates have increasingly become a public health concern due to their ability to damage several tissues in humans. In particular, emerging evidence has called attention to the neurodegenerative effects of the cyanobacterial toxin β-N-methylamino-L-alanine (BMAA). Furthermore, other toxins such as anatoxin, saxitoxin, microcystin, nodularin and ciguatoxin also have a different range of effects on human tissues, including hepatotoxicity, neurotoxicity and gastrointestinal irritation. However, the vast majority of known environmental toxins have not yet been examined in the context of neurodegenerative disease. This review aims to investigate whether neurotoxic mechanisms can be demonstrated in all aforementioned toxins, and whether there exists a link to neurodegeneration. Management of toxin exposure and potential neuroprotective compounds is also discussed. Collectively, all aforementioned microbial toxins are likely to exert some form of neuronal damage, with many of their modes of action consistent with neurodegeneration. This is important in advancing our current understanding of the cytotoxic potential of environmental toxins upon human brain function, particularly in the context of age-related neurodegenerative disease.

Nicotinic modulation of hippocampal cell signaling and associated effects on learning and memory

The hippocampus is a key brain structure involved in synaptic plasticity associated with long-term declarative memory formation. Importantly, nicotine and activation of nicotinic acetylcholine receptors (nAChRs) can alter hippocampal plasticity and these changes may occur through modulation of hippocampal kinases and transcription factors. Hippocampal kinases such as cAMP-dependent protein kinase (PKA), calcium/calmodulin-dependent protein kinases (CAMKs), extracellular signal-regulated kinases 1 and 2 (ERK1/2), and c-jun N-terminal kinase 1 (JNK1), and the transcription factor cAMP-response element-binding protein (CREB) that are activated either directly or indirectly by nicotine may modulate hippocampal plasticity and in parallel hippocampus-dependent learning and memory. Evidence suggests that nicotine may alter hippocampus-dependent learning by changing the time and magnitude of activation of kinases and transcription factors normally involved in learning and by recruiting additional cell signaling molecules. Understanding how nicotine alters learning and memory will advance basic understanding of the neural substrates of learning and aid in understanding mental disorders that involve cognitive and learning deficits.

Neuronal α7 Nicotinic Receptors as a Target for the Treatment of Schizophrenia

Schizophrenia is a lifelong disease, the burden of which is often underestimated. Characterized by positive (e.g., hallucinations) and negative (e.g., avolition, amotivation) symptoms, schizophrenia is also accompanied with profound impairments in cognitive function that progress throughout the development of the disease. Although treatment with antipsychotic medications can effectively dampen some of the positive symptoms, these medications largely fail to reverse cognitive deficits or to mitigate negative symptoms. With a worldwide prevalence of approximately 1%, schizophrenia remains a large unmet medical need that stands to benefit greatly from (1) continued research to better understand the biological underpinnings of the disease and (2) the targeted development of novel therapeutics to improve the lives of those affected individuals. Improvements in our understanding of the neuronal networks associated with schizophrenia as well as progress in identifying genetic risk factors and environmental conditions that may predispose individuals to developing the disease are advancing new strategies to study and treat it. Herein, we review the evidence that supports the role of α7 nicotinic acetylcholine receptors in the central nervous system and why these receptors constitute a promising target to treat some of the prominent symptoms of schizophrenia.

A Systematic Analysis of Candidate Genes Associated with Nicotine Addiction

Nicotine, as the major psychoactive component of tobacco, has broad physiological effects within the central nervous system, but our understanding of the molecular mechanism underlying its neuronal effects remains incomplete. In this study, we performed a systematic analysis on a set of nicotine addiction-related genes to explore their characteristics at network levels. We found that NAGenes tended to have a more moderate degree and weaker clustering coefficient and to be less central in the network compared to alcohol addiction-related genes or cancer genes. Further, clustering of these genes resulted in six clusters with themes in synaptic transmission, signal transduction, metabolic process, and apoptosis, which provided an intuitional view on the major molecular functions of the genes. Moreover, functional enrichment analysis revealed that neurodevelopment, neurotransmission activity, and metabolism related biological processes were involved in nicotine addiction. In summary, by analyzing the overall characteristics of the nicotine addiction related genes, this study provided valuable information for understanding the molecular mechanisms underlying nicotine addiction.

Pathways and networks-based analysis of candidate genes associated with nicotine addiction

Nicotine is the addictive substance in tobacco and it has a broad impact on both the central and peripheral nervous systems. Over the past decades, an increasing number of genes potentially involved in nicotine addiction have been identified by different technical approaches. However, the molecular mechanisms underlying nicotine addiction remain largely unclear. Under such situation, a comprehensive analysis focusing on the overall functional characteristics of these genes, as well as how they interact with each other will provide us valuable information to understand nicotine addiction. In this study, we presented a systematic analysis on nicotine addiction-related genes to identify the major underlying biological themes. Functional analysis revealed that biological processes and biochemical pathways related to neurodevelopment, immune system and metabolism were significantly enriched in the nicotine addiction-related genes. By extracting the nicotine addiction-specific subnetwork, a number of novel genes associated with addiction were identified. Moreover, we constructed a schematic molecular network for nicotine addiction via integrating the pathways and network, providing an intuitional view to understand the development of nicotine addiction. Pathway and network analysis indicated that the biological processes related to nicotine addiction were complex. Results from our work may have important implications for understanding the molecular mechanism underlying nicotine addiction.

Positive allosteric modulation of alpha-7 nicotinic receptors promotes cell death by inducing Ca(2+) release from the endoplasmic reticulum

Positive allosteric modulation of α7 isoform of nicotinic acetylcholine receptors (α7-nAChRs) is emerging as a promising therapeutic approach for central nervous system disorders such as schizophrenia or Alzheimer's disease. However, its effect on Ca(2+) signaling and cell viability remains controversial. This study focuses on how the type II positive allosteric modulator (PAM II) PNU120596 affects intracellular Ca(2+) signaling and cell viability. We used human SH-SY5Y neuroblastoma cells overexpressing α7-nAChRs (α7-SH) and their control (C-SH). We monitored cytoplasmic and endoplasmic reticulum (ER) Ca(2+) with Fura-2 and the genetically encoded cameleon targeting the ER, respectively. Nicotinic inward currents were measured using patch-clamp techniques. Viability was assessed using methylthiazolyl blue tetrazolium bromide or propidium iodide staining. We observed that in the presence of a nicotinic agonist, PNU120596 (i) reduced viability of α7-SH but not of C-SH cells; (ii) significantly increased inward nicotinic currents and cytosolic Ca(2+) concentration; (iii) released Ca(2+) from the ER by a Ca(2+) -induced Ca(2+) release mechanism only in α7-SH cells; (iv) was cytotoxic in rat organotypic hippocampal slice cultures; and, lastly, all these effects were prevented by selective blockade of α7-nAChRs, ryanodine receptors, or IP3 receptors. In conclusion, positive allosteric modulation of α7-nAChRs with the PAM II PNU120596 can lead to dysregulation of ER Ca(2+) , overloading of intracellular Ca(2+) , and neuronal cell death. This study focuses on how the type II positive allosteric modulator PNU120596 (PAM II PNU12) affects intracellular Ca(2+) signaling and cell viability. Using SH-SY5Y neuroblastoma cells overexpressing α7-nAChRs (α7-SH) and their control (C-SH), we find that PAM of α7-nAChRs with PNU120596: (i) increases inward calcium current (ICa ) and cytosolic Ca(2+) concentration ([Ca(2+) ]cyt ); (ii) releases Ca(2+) from the ER ([Ca(2+) ]ER ) by a Ca(2+) -induced Ca(2+) release mechanism; and (iv) reduces cell viability. These findings were corroborated in rat hippocampal organotypic cultures. [Ca(2+) ]cyt , cytosolic Ca(2+) concentration; [Ca(2+) ]ER , endoplasmic reticulum Ca(2+) concentration; α7 nAChR, α7 isoform of nicotinic acetylcholine receptors; α7-SH, SH-SY5Y stably overexpressing α7 nAChRs cells; C-SH, control SH-SY5Y cells; Nic, nicotine; PNU12, PNU120596.

Nicotinic, glutamatergic and dopaminergic synaptic transmission and plasticity in the mesocorticolimbic system: focus on nicotine effects

Cigarette smoking is currently the leading cause of preventable deaths and disability throughout the world, being responsible for about five million premature deaths/year. Unfortunately, fewer than 10% of tobacco users who try to stop smoking actually manage to do so. The main addictive agent delivered by cigarette smoke is nicotine, which induces psychostimulation and reward, and reduces stress and anxiety. The use of new technologies (including optogenetics) and the development of mouse models characterised by cell-specific deletions of receptor subtype genes or the expression of gain-of-function nAChR subunits has greatly increased our understanding of the molecular mechanisms and neural substrates of nicotine addiction first revealed by classic electrophysiological, neurochemical and behavioural approaches. It is now becoming clear that various aspects of nicotine dependence are mediated by close interactions of the glutamatergic, dopaminergic and γ-aminobutyric acidergic systems in the mesocorticolimbic system. This review is divided into two parts. The first provides an updated overview of the circuitry of the ventral tegmental area, ventral striatum and prefrontal cortex, the neurotransmitter receptor subtypes expressed in these areas, and their physiological role in the mesocorticolimbic system. The second will focus on the molecular, functional and behavioural mechanisms involved in the acute and chronic effects of nicotine on the mesocorticolimbic system.

Prioritizing Genes Related to Nicotine Addiction Via a Multi-source-Based Approach

Nicotine has a broad impact on both the central and peripheral nervous systems. Over the past decades, an increasing number of genes potentially involved in nicotine addiction have been identified by different technical approaches. However, the molecular mechanisms underlying nicotine addiction remain largely unknown. Under such situation, prioritizing the candidate genes for further investigation is becoming increasingly important. In this study, we presented a multi-source-based gene prioritization approach for nicotine addiction by utilizing the vast amounts of information generated from for nicotine addiction study during the past years. In this approach, we first collected and curated genes from studies in four categories, i.e., genetic association analysis, genetic linkage analysis, high-throughput gene/protein expression analysis, and literature search of single gene/protein-based studies. Based on these resources, the genes were scored and a weight value was determined for each category. Finally, the genes were ranked by their combined scores, and 220 genes were selected as the prioritized nicotine addiction-related genes. Evaluation suggested the prioritized genes were promising targets for further analysis and replication study.

Altered neurochemical levels in the rat brain following chronic nicotine treatment

Converging evidence shows that neurochemical systems are crucial mediators of nicotine dependence. Our present study evaluates the effect of 3-month chronic nicotine treatment on the levels of multiple quaternary ammonium compounds as well as glutamate and gamma aminobutyric acid in the rat prefrontal cortex, dorsal striatum and hypothalamus. We observed a marked decrease of acetylcholine levels in the dorsal striatum (22.88%, p<0.01), reflecting the impact of chronic nicotine in local interneuron circuits. We found decreases of carnitine in the dorsal striatum and prefrontal cortex (19.44%, p<0.01; 13.58%, p<0.01, respectively), but robust enhancements of carnitine in the hypothalamus (26.59%, p<0.01), which may reflect the alterations in food and water intake during chronic nicotine treatment. Finally, we identified an increase of prefrontal cortex glutamate levels (8.05%, p<0.05), supporting previous studies suggesting enhanced prefrontal activity during chronic drug use. Our study shows that quaternary ammonium compounds are regulated in a highly brain region specific manner during chronic nicotine treatment, and provides novel insights into neurochemical regulation during nicotine use.

Functional characterization of a novel family of acetylcholine-gated chloride channels in Schistosoma mansoni

Acetylcholine is the canonical excitatory neurotransmitter of the mammalian neuromuscular system. However, in the trematode parasite Schistosoma mansoni, cholinergic stimulation leads to muscle relaxation and a flaccid paralysis, suggesting an inhibitory mode of action. Information about the pharmacological mechanism of this inhibition is lacking. Here, we used a combination of techniques to assess the role of cholinergic receptors in schistosome motor function. The neuromuscular effects of acetylcholine are typically mediated by gated cation channels of the nicotinic receptor (nAChR) family. Bioinformatics analyses identified numerous nAChR subunits in the S. mansoni genome but, interestingly, nearly half of these subunits carried a motif normally associated with chloride-selectivity. These putative schistosome acetylcholine-gated chloride channels (SmACCs) are evolutionarily divergent from those of nematodes and form a unique clade within the larger family of nAChRs. Pharmacological and RNA interference (RNAi) behavioral screens were used to assess the role of the SmACCs in larval motor function. Treatment with antagonists produced the same effect as RNAi suppression of SmACCs; both led to a hypermotile phenotype consistent with abrogation of an inhibitory neuromuscular mediator. Antibodies were then generated against two of the SmACCs for use in immunolocalization studies. SmACC-1 and SmACC-2 localize to regions of the peripheral nervous system that innervate the body wall muscles, yet neither appears to be expressed directly on the musculature. One gene, SmACC-1, was expressed in HEK-293 cells and characterized using an iodide flux assay. The results indicate that SmACC-1 formed a functional homomeric chloride channel and was activated selectively by a panel of cholinergic agonists. The results described in this study identify a novel clade of nicotinic chloride channels that act as inhibitory modulators of schistosome neuromuscular function. Additionally, the iodide flux assay used to characterize SmACC-1 represents a new high-throughput tool for drug screening against these unique parasite ion channels.

Impact of neuro-psychological factors on smoking-associated lung cancer

Smoking has been extensively documented as a risk factor for all histological types of lung cancer and tobacco-specific nitrosamines and polycyclic aromatic hydrocarbons reproducibly cause lung cancer in laboratory rodents. However, the most common lung cancer, non-small cell lung cancer (NSCLC), frequently develops in never smokers and is particularly common in women and African Americans, suggesting that factors unrelated to smoking significantly impact this cancer. Recent experimental investigations in vitro and in animal models have shown that chronic psychological stress and the associated hyperactive signaling of stress neurotransmitters via β-adrenergic receptors significantly promote the growth and metastatic potential of NSCLC. These responses were caused by modulation in the expression and sensitization state of nicotinic acetylcholine receptors (nAChRs) that regulate the production of stress neurotransmitters and the inhibitory neurotransmitter γ-aminobutyric acid (GABA). Similar changes in nAChR-mediated neurotransmitter production were identified as the cause of NSCLC stimulation in vitro and in xenograft models by chronic nicotine. Collectively, these data suggest that hyperactivity of the sympathetic branch of the autonomic nervous system caused by chronic psychological stress or chronic exposure to nicotinic agonists in cigarette smoke significantly contribute to the development and progression of NSCLC. A recent clinical study that reported improved survival outcomes with the incidental use of β-blockers among patients with NSCLC supports this interpretation.

Elevated Norepinephrine may be a Unifying Etiological Factor in the Abuse of a Broad Range of Substances: Alcohol, Nicotine, Marijuana, Heroin, Cocaine, and Caffeine

A wide range of commonly abused drugs have effects on the noradrenergic neurotransmitter system, including alterations during acute intoxication and chronic use of these drugs. It is not established, however, that individual differences in noradrenergic signaling, which may be present prior to use of drugs, predispose certain persons to substance abuse. This paper puts forth the novel hypothesis that elevated noradrenergic signaling, which may be raised largely due to genetics but also due to environmental factors, is an etiological factor in the abuse of a wide range of substances, including alcohol, nicotine, marijuana, heroin, cocaine, and caffeine. Data are reviewed for each of these drugs comprising their interaction with norepinephrine during acute intoxication, long-term use, subsequent withdrawal, and stress-induced relapse. In general, the data suggest that these drugs acutely boost noradrenergic signaling, whereas long-term use also affects this neurotransmitter system, possibly suppressing it. During acute withdrawal after chronic drug use, noradrenergic signaling tends to be elevated, consistent with the observation that norepinephrine lowering drugs such as clonidine reduce withdrawal symptoms. Since psychological stress can promote relapse of drug seeking in susceptible individuals and stress produces elevated norepinephrine release, this suggests that these drugs may be suppressing noradrenergic signaling during chronic use or instead elevating it only in reward circuits of the brain. If elevated noradrenergic signaling is an etiological factor in the abuse of a broad range of substances, then chronic use of pharmacological agents that reduce noradrenergic signaling, such as clonidine, guanfacine, lofexidine, propranolol, or prazosin, may help prevent or treat drug abuse in general.

α7-Containing nicotinic acetylcholine receptors on interneurons of the basolateral amygdala and their role in the regulation of the network excitability

The basolateral amygdala (BLA) plays a key role in fear-related learning and memory, in the modulation of cognitive functions, and in the overall regulation of emotional behavior. Pathophysiological alterations involving hyperexcitability in this brain region underlie anxiety and other emotional disorders as well as some forms of epilepsy. GABAergic interneurons exert a tight inhibitory control over the BLA network; understanding the mechanisms that regulate their activity is necessary for understanding physiological and disordered BLA functions. The BLA receives dense cholinergic input from the basal forebrain, affecting both normal functions and dysfunctions of the amygdala, but the mechanisms involved in the cholinergic regulation of inhibitory activity in the BLA are unclear. Using whole cell recordings in rat amygdala slices, here we demonstrate that the α(7)-containing nicotinic acetylcholine receptors (α(7)-nAChRs) are present on somatic or somatodendritic regions of BLA interneurons. These receptors are active in the basal state enhancing GABAergic inhibition, and their further, exogenous activation produces a transient but dramatic increase of spontaneous inhibitory postsynaptic currents in principal BLA neurons. In the absence of AMPA/kainate receptor antagonists, activation of α(7)-nAChRs in the BLA network increases both GABAergic and glutamatergic spontaneous currents in BLA principal cells, but the inhibitory currents are enhanced significantly more than the excitatory currents, reducing overall excitability. The anxiolytic effects of nicotine as well as the role of the α(7)-nAChRs in seizure activity involving the amygdala and in mental illnesses, such as schizophrenia and Alzheimer's disease, may be better understood in light of the present findings.

Cellular, molecular, and genetic substrates underlying the impact of nicotine on learning

Addiction is a chronic disorder marked by long-lasting maladaptive changes in behavior and in reward system function. However, the factors that contribute to the behavioral and biological changes that occur with addiction are complex and go beyond reward. Addiction involves changes in cognitive control and the development of disruptive drug-stimuli associations that can drive behavior. A reason for the strong influence drugs of abuse can exert on cognition may be the striking overlap between the neurobiological substrates of addiction and of learning and memory, especially areas involved in declarative memory. Declarative memories are critically involved in the formation of autobiographical memories, and the ability of drugs of abuse to alter these memories could be particularly detrimental. A key structure in this memory system is the hippocampus, which is critically involved in binding multimodal stimuli together to form complex long-term memories. While all drugs of abuse can alter hippocampal function, this review focuses on nicotine. Addiction to tobacco products is insidious, with the majority of smokers wanting to quit; yet the majority of those that attempt to quit fail. Nicotine addiction is associated with the presence of drug-context and drug-cue associations that trigger drug seeking behavior and altered cognition during periods of abstinence, which contributes to relapse. This suggests that understanding the effects of nicotine on learning and memory will advance understanding and potentially facilitate treating nicotine addiction. The following sections examine: (1) how the effects of nicotine on hippocampus-dependent learning change as nicotine administration transitions from acute to chronic and then to withdrawal from chronic treatment and the potential impact of these changes on addiction, (2) how nicotine usurps the cellular mechanisms of synaptic plasticity, (3) the physiological changes in the hippocampus that may contribute to nicotine withdrawal deficits in learning, and (4) the role of genetics and developmental stage (i.e., adolescence) in these effects.

Involvement of α7 nAChR signaling cascade in epigallocatechin gallate suppression of β-amyloid-induced apoptotic cortical neuronal insults

Excessive generation and accumulation of the β-amyloid (Aβ) peptide in selectively vulnerable brain regions is a key pathogenic event in the Alzheimer's disease (AD), while epigallocatechin gallate (EGCG) is a very promising chemical to suppress a variety of Aβ-induced neurodegenerative disorders. However, the precise molecular mechanism of EGCG responsible for protection against neurotoxicity still remains elusive. To validate and further investigate the possible mechanism involved, we explored whether EGCG neuroprotection against neurotoxicity of Aβ is mediated through the α7 nicotinic acetylcholine receptor (α7 nAChR) signaling cascade. It was shown in rat primary cortical neurons that short-term treatment with EGCG significantly attenuated the neurotoxicity of Aβ1-42, as demonstrated by increased cell viability, reduced number of apoptotic cells, decreased reactive oxygen species (ROS) generation, and downregulated caspase-3 levels after treatment with 25-μM Aβ1-42. In addition, EGCG markedly strengthened activation of α7nAChR as well as its downstream pathway signaling molecules phosphatidylinositol 3-kinase (PI3K) and Akt, subsequently leading to suppression of Bcl-2 downregulation in Aβ-treated neurons. Conversely, administration of α7nAChR antagonist methyllycaconitine (MLA; 20 μM) to neuronal cultures significantly attenuated the neuroprotection of EGCG against Aβ-induced neurototoxicity, thus presenting new evidence that the α7nAChR activity together with PI3K/Akt transduction signaling may contribute to the molecular mechanism underlying the neuroprotective effects of EGCG against Aβ-induced cell death.

Maternal separation increases GABA(A) receptor-mediated modulation of norepinephrine release in the hippocampus of a rat model of ADHD, the spontaneously hypertensive rat

Experiencing early life stress increases the risk of developing a psychiatric disorder later in life, possibly by altering neural networks, such as the locus-coeruleus norepinephrine (LC-NE) system. Whether early life stress affects the LC-NE system directly, or whether the effects are via changes in glutamate and GABA modulation of the LC-NE system, is unclear. Early life stress has been shown to alter glutamate and GABA transmission, and in particular, to alter GABA(A) receptor expression. The LC-NE system has been implicated in attention-deficit/hyperactivity disorder (ADHD), amongst other disorders, and is over-responsive to glutamate stimulation in a validated rat model of ADHD, the spontaneously hypertensive rat (SHR). It is plausible that the LC-NE system, or glutamate and GABA modulation thereof, in an individual already genetically predisposed to develop ADHD, or in SHR, may respond in a unique way to early life stress. To investigate this we applied a mild developmental stressor, maternal separation, onto SHR, and onto their control strain, Wistar-Kyoto rats (WKY), from post-natal day (P)2-14. On P50-52, in early adulthood, we assayed glutamate and potassium stimulated release of radio-actively labelled NE ((3)[H]NE) from hippocampal slices using an in vitro superfusion technique, in the presence or absence of a GABA(A) receptor antagonist, bicuculline. Our results show that maternal separation altered GABA(A) receptor-mediated modulation of NE release in the hippocampus of the two strains in opposite directions, increasing it in SHR and decreasing it in WKY. Our findings indicate that effects of early life stress are highly dependent on genetic predisposition, since opposite changes in GABA(A) receptor-mediated modulation of NE release were observed in the rat model of ADHD, SHR, and their control strain, WKY.

Pharmacological differences between rat frontal cortex and hippocampus in the nicotinic modulation of noradrenaline release implicate distinct receptor subtypes

INTRODUCTION

Noradrenergic mechanisms in frontal cortex and hippocampus are relevant to attentional and stress-related aspects of addiction, respectively. Nicotinic receptors (nAChRs) modulate the release of noradrenaline (NA) in these tissues. This study determined if similar subtypes of nAChR regulate NA release in rat frontal cortex and hippocampus.

METHODS

The release of [(3)H]-NA from rat tissue prisms was characterized in a 96-well plate assay. In vivo microdialysis was used to monitor NA overflow from rat frontal cortex and hippocampus in conscious freely moving rats.

RESULTS

[(3)H]-NA release from frontal cortex prisms was more sensitive to nicotinic agonists than release from hippocampal prisms. The β2-selective agonist 5-iodo-A-85380 was 1000-fold more potent in frontal cortex compared with hippocampus. Agonist-evoked [(3)H]-NA release was inhibited by the β2-selective antagonist dihydro-beta-erythroidine (DHβE) in frontal cortex, whereas in hippocampal tissue, DHβE had no effect. In vivo, 5-iodo-A-85380 (1, 100 μM) applied locally via the dialysis probe, significantly increased NA overflow, compared with basal release, in frontal cortex but not in hippocampus.

CONCLUSIONS

These data support the modulation of NA release by different nAChR subtypes in frontal cortex and hippocampus. The pharmacological profile for rat hippocampus is consistent with previous studies, implicating α3β4* nAChRs in the modulation of NA release in this tissue. nAChRs having this function in frontal cortex are pharmacologically distinct and correspond to β2-containing nAChRs.

Prefrontal neuromodulation by nicotinic receptors for cognitive processes

RATIONALE

The prefrontal cortex (PFC) mediates executive functions, a set of control processes that optimize performance on cognitive tasks. It enables appropriate decision-making and mediates adapted behaviors, all processes impaired in psychiatric or degenerative disorders. Key players of normal functioning of the PFC are neurotransmitter (NT) systems arising from subcortical nuclei and targeting PFC subareas and, also, neuronal nicotinic acetylcholine receptors (nAChRs). These ion channels, located on multiple cell compartments in all brain areas, mediate direct cholinergic transmission and modulate the release of NTs that cross onto PFC neurons or interneurons.

OBJECTIVE

We compiled current knowledge concerning the role of nAChRs in NT release, focusing on the PFC. We point out plausible mechanisms of interaction among PFC circuits implicated in executive functions and emphasized the role of β2-containing nAChRs, the high-affinity receptors for acetylcholine (ACh). These receptors are more directly implicated in behavioral flexibility either when located on PFC neurons or in the monoaminergic or cholinergic systems targeting the PFC.

RESULTS

We shed light on potentially crucial roles played by nAChRs in complex interactions between local and afferent NTs. We show how they could act on cognition via PFC networks.

CONCLUSIONS

nAChRs are crucial for decision-making, during integration of emotional and motivational features, both mediated by different NT pathways in the PFC. We review the knowledge recently gained on cognitive functions in mice and our current understanding of PFC NT modulation. The combination of these data is expected to provide new hypotheses concerning the role of AChRs in cognitive processes.

Schizophrenia risk polymorphisms in the TCF4 gene interact with smoking in the modulation of auditory sensory gating

Several polymorphisms of the transcription factor 4 (TCF4) have been shown to increase the risk for schizophrenia, particularly TCF4 rs9960767. This polymorphism is associated with impaired sensorimotor gating measured by prepulse inhibition--an established endophenotype of schizophrenia. We therefore investigated whether TCF4 polymorphisms also affect another proposed endophenotype of schizophrenia, namely sensory gating assessed by P50 suppression of the auditory evoked potential. Although sensorimotor gating and sensory gating are not identical, recent data suggest that they share genetic fundamentals. In a multicenter study at six academic institutions throughout Germany, we applied an auditory P50 suppression paradigm to 1,821 subjects (1,023 never-smokers, 798 smokers) randomly selected from the general population. Samples were genotyped for 21 TCF4 polymorphisms. Given that smoking is highly prevalent in schizophrenia and affects sensory gating, we also assessed smoking behavior, cotinine plasma concentrations, exhaled carbon monoxide, and the Fagerström Test (FTND). P50 suppression was significantly decreased in carriers of schizophrenia risk alleles of the TCF4 polymorphisms rs9960767, rs10401120rs, rs17597926, and 17512836 (P < 0.0002-0.00005). These gene effects were modulated by smoking behavior as indicated by significant interactions of TCF4 genotype and smoking status; heavy smokers (FTND score ≥ 4) showed stronger gene effects on P50 suppression than light smokers and never-smokers. Our finding suggests that sensory gating is modulated by an interaction of TCF4 genotype with smoking, and both factors may play a role in early information processing deficits also in schizophrenia. Consequently, considering smoking behavior may facilitate the search for genetic risk factors for schizophrenia.

Cooperative regulation of non-small cell lung carcinoma by nicotinic and beta-adrenergic receptors: a novel target for intervention

Lung cancer is the leading cause of cancer death; 80-85% of lung cancer cases are non-small cell lung cancer (NSCLC). Smoking is a documented risk factor for the development of this cancer. Although nicotine does not have the ability to initiate carcinogenic events, recent studies have implicated nicotine in growth stimulation of NSCLC. Using three NSCLC cell lines (NCI-H322, NCI-H441 and NCI-H1299), we identified the cooperation of nicotinic acetylcholine receptors (nAChRs) and β-adrenergic receptors (β-ARs) as principal regulators of these effects. Proliferation was measured by thymidine incorporation and MTT assays, and Western blots were used to monitor the upregulation of the nAChRs and activation of signaling molecules. Noradrenaline and GABA were measured by immunoassays. Nicotine-treated NSCLC cells showed significant induction of the α7nAChR and α4nAChR, along with significant inductions of p-CREB and p-ERK1/2 accompanied by increases in the stress neurotransmitter noradrenaline, which in turn led to the observed increase in DNA synthesis and cell proliferation. Effects on cell proliferation and signaling proteins were reversed by the α7nAChR antagonist α-BTX or the β-blocker propranolol. Nicotine treatment also down-regulated expression of the GABA synthesizing enzyme GAD 65 and the level of endogenous GABA, while treatment of NSCLC cells with GABA inhibited cell proliferation. Interestingly, GABA acts by reducing β-adrenergic activated cAMP signaling. Our findings suggest that nicotine-induced activation of this autocrine noradrenaline-initiated signaling cascade and concomitant deficiency in inhibitory GABA, similar to modulation of these neurotransmitters in the nicotine-addicted brain, may contribute to the development of NSCLC in smokers. Our data suggest that exposure to nicotine either by tobacco smoke or nicotine supplements facilitates growth and progression of NSCLC and that pharmacological intervention by β blocker may lower the risk for NSCLC development among smokers and could be used to enhance the clinical outcome of standard cancer therapy.

Ability of baclofen to prevent somatic manifestations and neurochemical changes during nicotine withdrawal

BACKGROUND

Nicotine (NIC), the major active component of tobacco, is critical in the maintenance of the smoking habit. The aims of the present study were to analyze the behavioural and neurochemical variations during NIC withdrawal syndrome in mice, and whether they are prevented with baclofen (BAC, GABA(B) receptor agonist).

METHODS

Swiss-Webster albino mice received NIC (2.5 mg/kg, s.c.) 4 times daily, for 7 consecutive days. On day 8 (the day of the experiment), NIC-treated mice received the nicotine antagonist mecamylamine (MEC, 2 mg/kg, i.p.) 1h after the last dose of NIC. A second group of dependent mice received BAC (2mg/kg, i.p.) before MEC-precipitated abstinence. The somatic signs were measured for 30 min. Dopamine (DA), serotonin (5-hydroxytryptamine; 5-HT) and its metabolites concentrations were determined by HPLC in the striatum, cortex and hippocampus.

RESULTS

The global score was greater in the abstinent group compared to the control group. Moreover, the global score time course showed a higher increase at 10 min compared to the global score at 5 min or 30 min after MEC-precipitated NIC withdrawal. In addition, the global score was attenuated by BAC. The DA and dihydroxyphenyl acetic acid (DOPAC) cortical levels decreased in the abstinent group, while BAC reestablished these levels 10 min after NIC withdrawal. Furthermore, DA and 5-HT striatal levels decreased during NIC withdrawal, and BAC reverted this decrease.

CONCLUSION

In conclusion, the prevention of NIC withdrawal signs by BAC could be related to changes in dopaminergic and serotonergic activity.

Role of α7- and β4-containing nicotinic acetylcholine receptors in the affective and somatic aspects of nicotine withdrawal: studies in knockout mice

To assess which nicotinic acetylcholine receptors (nAChRs) are involved in the aversive aspects of nicotine withdrawal, brain reward function and the somatic signs of nicotine withdrawal were assessed in mice that lack α7 and β4 nAChR subunits. Brain reward function was assessed with the intracranial self-stimulation (ICSS) procedure, in which elevations in ICSS thresholds reflect an anhedonic mood state. At 3-6 h of spontaneous nicotine/saline withdrawal, thresholds were elevated in nicotine-withdrawing α7(+/+) and β4(+/+), but not α7(-/-) or β4(-/-), mice compared with saline-withdrawing mice, indicating a delay in the onset of withdrawal in the knockout mice. From 8 to 100 h of withdrawal, thresholds in α7(+/+) and α7(-/-) mice were equally elevated, whereas thresholds in β4(+/+) and β4(-/-) mice returned to baseline levels. Somatic signs were attenuated in nicotine-withdrawing β4(-/-), but not α7(-/-), mice. Administration of a low dose of the nAChR antagonist mecamylamine induced threshold elevations in α7(-/-), but not α7(+/+), mice, whereas the highest dose tested only elevated thresholds in α7(+/+) mice. Mecamylamine-induced threshold elevations were similar in β4(-/-) and β4(+/+) mice. In conclusion, null mutation of the α7 and β4 nAChR subunits resulted in a delayed onset of the anhedonic aspects of the spontaneous nicotine withdrawal syndrome. Previous findings of attenuated somatic signs of nicotine withdrawal in β4(-/-), but not α7(-/-), mice were confirmed in the present study, indicating an important role for β4-containing nAChRs in the somatic signs of nicotine withdrawal. The mecamylamine-precipitated withdrawal data suggest that compensatory adaptations may occur in constitutive α7(-/-) mice or that mecamylamine may interact with other receptors besides nAChRs in these mice. In summary, the present results indicate an important role for α7 and β4-containing nAChRs in the anhedonic or somatic signs of nicotine withdrawal.

Unichiral 2-(2'-pyrrolidinyl)-1,4-benzodioxanes: the 2R,2'S diastereomer of the N-methyl-7-hydroxy analogue is a potent α4β2- and α6β2-nicotinic acetylcholine receptor partial agonist

A series of unichiral 7-substituted 2-(1'-methyl-2'-pyrrolidinyl)-1,4-benzodioxanes were synthesized and tested for the affinity for the α4β2 and α7 central nicotinic receptors; the 2R,2'S diastereomer of the 7-OH analogue [(R,S)-7], unique in the series, has a high α4β2 affinity (12nM K(i)). N-Demethylation and configuration inversion of the stereocenters greatly weaken its α4β2 affinity, confirming that such a rigid molecule can be considered a new template for α4β2 ligands. Docking analysis showed how (R,S)-7 is capable of strongly and specifically interacting with the amino acidic counterpart of the α4β2 receptor binding site. Further pharmacological characterization demonstrated that (R,S)-7 also has a high affinity for the α6β2 receptor, and in vitro functional tests indicated that it is a potent α4β2 and α6β2 partial agonist, with modest affinity and potency for the α3β4 receptor. Comparison with varenicline, a well-known nicotinic partial agonist used as a smoking cessation aid, interestingly reveals similar nicotinoid profiles.

Fluctuations in endogenous kynurenic acid control hippocampal glutamate and memory

Kynurenic acid (KYNA), an astrocyte-derived metabolite, antagonizes the α7 nicotinic acetylcholine receptor (α7nAChR) and, possibly, the glycine co-agonist site of the NMDA receptor at endogenous brain concentrations. As both receptors are involved in cognitive processes, KYNA elevations may aggravate, whereas reductions may improve, cognitive functions. We tested this hypothesis in rats by examining the effects of acute up- or downregulation of endogenous KYNA on extracellular glutamate in the hippocampus and on performance in the Morris water maze (MWM). Applied directly by reverse dialysis, KYNA (30-300 nM) reduced, whereas the specific kynurenine aminotransferase-II inhibitor (S)-4-(ethylsulfonyl)benzoylalanine (ESBA; 0.3-3 mM) raised, extracellular glutamate levels in the hippocampus. Co-application of KYNA (100 nM) with ESBA (1 mM) prevented the ESBA-induced glutamate increase. Comparable effects on hippocampal glutamate levels were seen after intra-cerebroventricular (i.c.v.) application of the KYNA precursor kynurenine (1 mM, 10 μl) or ESBA (10 mM, 10 μl), respectively. In separate animals, i.c.v. treatment with kynurenine impaired, whereas i.c.v. ESBA improved, performance in the MWM. I.c.v. co-application of KYNA (10 μM) eliminated the pro-cognitive effects of ESBA. Collectively, these studies show that KYNA serves as an endogenous modulator of extracellular glutamate in the hippocampus and regulates hippocampus-related cognitive function. Our results suggest that pharmacological interventions leading to acute reductions in hippocampal KYNA constitute an effective strategy for cognitive improvement. This approach might be especially useful in the treatment of cognitive deficits in neurological and psychiatric diseases that are associated with increased brain KYNA levels.

Engineering of α-conotoxin MII-derived peptides with increased selectivity for native α6β2* nicotinic acetylcholine receptors

α6β2* Nicotinic acetylcholine receptors are expressed in selected central nervous system areas, where they are involved in striatal dopamine (DA) release and its behavioral consequences, and other still uncharacterized brain activities. α6β2* receptors are selectively blocked by the α-conotoxins MII and PIA, which bear a characteristic N-terminal amino acid tail [arginine (R), aspartic acid (D), and proline (P)]. We synthesized a group of PIA-related peptides in which R1 was mutated or the RDP motif gradually removed. Binding and striatal DA release assays of native rat α6β2* receptors showed that the RDP sequence, and particularly residue R1, is essential for the activity of PIA. On the basis of molecular modeling analyses, we synthesized a hybrid peptide (RDP-MII) that had increased potency (7-fold) and affinity (13-fold) for α6β2* receptors but not for the very similar α3β2* subtype. As docking studies also suggested that E11 of MII might be a key residue engendering α6β2* vs. α3β2* selectivity, we prepared MII[E11R] and RDP-MII[E11R] peptides. Their affinity and potency for native α6β2* receptors were similar to those of their parent analogues, whereas, for the oocyte expressed rat α3β2* subtype, they showed a 31- and 14-fold lower affinity and 21- and 3.5-fold lower potency. Thus, MII[E11R] and RDP-MII[E11R] are potent antagonists showing a degree of α6β2* vs. α3β2* selectivity in vivo.

Role of ionotropic glutamate receptors in the regulation of hippocampal norepinephrine output in vivo

In vitro evidence indicates that norepinephrine release in the mammalian hippocampus is modulated by glutamate receptors. With the use of microdialysis, we have now evaluated the role of ionotropic glutamate receptors in the regulation of hippocampal norepinephrine output in vivo. Stimulation of N-methyl-D-aspartate (NMDA)-sensitive glutamate receptors by local administration of NMDA (1-100μM) resulted in a concentration-dependent decrease in the extracellular concentration of norepinephrine in the hippocampus of freely moving rats, whereas the blockade of these receptors with MK801 (1-100μM) induced a concentration-dependent increase in norepinephrine output. Activation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)-sensitive glutamate receptors with AMPA (1-100μM) resulted in a biphasic effect on the extracellular norepinephrine concentration, with a decrease in this parameter apparent at 10μM and an increase at 100μM. The AMPA receptor antagonist 6,7-dinitroquinoxaline-2,3-dione had no effect on norepinephrine output. The GABA(A) receptor antagonist bicuculline (10μM) prevented the decrease in hippocampal norepinephrine output induced by either NMDA or 10μM AMPA. Our results thus implicate ionotropic glutamate receptors as key regulators of norepinephrine release in the hippocampus and may therefore provide a basis for the development of new drugs for stress-related disorders.

Genome-wide expression analysis reveals diverse effects of acute nicotine exposure on neuronal function-related genes and pathways

Previous human and animal studies demonstrate that acute nicotine exposure has complicated influences on the function of the nervous system, which may lead to long-lasting effects on the behavior and physiology of the subject. To determine the genes and pathways that might account for long-term changes after acute nicotine exposure, a pathway-focused oligoarray specifically designed for drug addiction research was used to assess acute nicotine effect on gene expression in the neuron-like SH-SY5Y cells. Our results showed that 295 genes involved in various biological functions were differentially regulated by 1 h of nicotine treatment. Among these genes, the expression changes of 221 were blocked by mecamylamine, indicating that the majority of nicotine-modulated genes were altered through the nicotinic acetylcholine receptors (nAChRs)-mediated signaling process. We further identified 14 biochemical pathways enriched among the nicotine-modulated genes, among which were those involved in neural development/synaptic plasticity, neuronal survival/death, immune response, or cellular metabolism. In the genes significantly regulated by nicotine but blocked by mecamylamine, 13 enriched pathways were detected. Nine of these pathways were shared with those enriched in the genes regulated by nicotine, including neuronal function-related pathways such as glucocorticoid receptor signaling, p38 MAPK signaling, PI3K/AKT signaling, and PTEN signaling, implying that nAChRs play important roles in the regulation of these biological processes. Together, our results not only provide insights into the mechanism underlying the acute response of neuronal cells to nicotine but also provide clues to how acute nicotine exposure exerts long-term effects on the nervous system.

The subtype-selective nicotinic acetylcholine receptor positive allosteric potentiator 2087101 differentially facilitates neurotransmission in the brain

Positive allosteric modulators of centrally expressed nicotinic acetylcholine receptors have therapeutic potentials in areas of cognition, motor function and reward. Several chemical classes of allosteric modulators that are selective for alpha7 nicotinic receptors have been characterised, but potentiators for the most widely expressed alpha4beta2 nicotinic receptor subtype are few and less defined, owing probably to the difficulty to achieve selectivity over other heteromeric receptor subtypes. 2087101 (2-amino-5-keto)thiazole) is a potent potentiator of both alpha7 and alpha4beta2 receptors and it has selectivity against the alpha3beta4 subtype, which may be responsible for the undesirable peripheral side effects. To further characterise its ability to differentiate between native nicotinic receptors, we examined the effects of 2087101 on alpha7, alpha4beta2* and alpha3beta4* receptor-mediated responses in the rat brain in electrophysiological and neurochemical experiments. 2087101 significantly potentiated agonist-induced, alpha7 and non-alpha7 receptor-mediated, GABAergic postsynaptic currents in cultured hippocampal neurones, but not the nicotine-stimulated [(3)H]noradrenaline release from hippocampal slices, which was primarily mediated by alpha3beta4* receptors, confirming its selectivity for alpha7 and alpha4beta2* receptors in native systems. 2087101 also significantly enhanced nicotine-stimulated firing increase in dopamine neurones of the ventral tegmental area, an effect that was dihydro-beta-erythroidine-sensitive and thereby mediated by alpha4beta2* nicotinic receptors. 2087101 can therefore enhance native nicotinic activities mediated by alpha7 and alpha4beta2*, but not alpha3beta4* receptors, showing its unique ability to discriminate between native heteromeric nicotinic receptor subtypes and its therapeutic potential for treating brain disorders by concurrent modulation of both alpha7 and alpha4beta2* nicotinic receptors.

Repeated administration of alpha7 nicotinic acetylcholine receptor (nAChR) agonists, but not positive allosteric modulators, increases alpha7 nAChR levels in the brain

The alpha7 nicotinic acetylcholine receptor (nAChR) is an important target for treatment of cognitive deficits in schizophrenia and Alzheimer's disease. However, the receptor desensitizes rapidly in vitro, which has led to concern regarding its applicability as a clinically relevant drug target. Here we investigate the effects of repeated agonism on alpha7 nAChR receptor levels and responsiveness in vivo in rats. Using [(125)I]-alpha-bungarotoxin (BTX) autoradiography we show that acute or repeated administration with the selective alpha7 nAChR agonist A-582941 increases the number of alpha7 nAChR binding sites in several brain regions, particularly in the prefrontal cortex. The alpha7 nAChR agonists SSR180711 and PNU-282987 also increase [(125)I]-BTX binding, suggesting that this is a general consequence of alpha7 nAChR agonism. Interestingly, the alpha7 nAChR positive allosteric modulators PNU-120596 and NS1738 do not increase [(125)I]-BTX binding. Furthermore, A-582941-induced increase in Arc and c-fos mRNA expression in the prefrontal cortex is enhanced and unaltered, respectively, after repeated administration, demonstrating that the alpha7 nAChRs remain responsive. Contrarily, A-582941-induced phosphorylation of Erk2 in the prefrontal cortex occurs following acute, but not repeated administration. Our results demonstrate that repeated agonist administration increases the number of alpha7 nAChRs in the brain, and leads to coupling versus uncoupling of specific intracellular signaling pathways. Additionally, our data suggest a fundamental difference between the sequelae of repeated administration with agonists and allosteric modulators of the alpha7 nAChR.