Chronic nicotine improves short-term memory selectively in a G72 mouse model of schizophrenia

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.

Chronic but not acute nicotine treatment ameliorates acute inflammation-induced working memory impairment by increasing CRTC1 and HCN2 in adult male mice

BACKGROUND

Systemic inflammation in which lipopolysaccharide (LPS) is released into circulation can cause cognitive dysfunction and we have previously shown that LPS impaired working memory (WM) which refers to the ability to guide incoming behavior by retrieving recently acquired information. However, the mechanism is not very clear, and currently, there is no approved strategy to improve inflammation-induced WM deficit. Notably, epidemiological studies have demonstrated a lower occurrence rate of inflammatory-related diseases in smoking patients, suggesting that inflammation-induced WM impairment may be improved by nicotine treatment. Here, our object is to investigate the effect and potential mechanisms of acute and chronic nicotine treatment on LPS-produced WM deficiency.

METHODS

Delayed alternation T-maze task (DAT) was applied for evaluating WM which includes both the short-term information storage and the ability to correct errors in adult male mice. Immunofluorescence staining and immunoblotting were used for assessing the levels and distribution of CREB-regulated transcription coactivator 1 (CRTC1) and hyperpolarization-activated cation channels 2 (HCN2) in the medial prefrontal cortex (mPFC) and hippocampus. Quantitative PCR and ELISA were employed for analyzing the mRNA and protein levels of TNF-α and IL-1β.

RESULTS

Our results revealed that administration of LPS (i.p.) at a dose of 0.5 mg/kg significantly produced WM impairment in the DAT task accompanied by an increase in IL-1β and TNF-α expression in the mPFC. Moreover, intra-mPFC infusion of IL-1Ra, an IL-1 antagonist, markedly alleviated LPS-induced WM deficiency. More important, chronic (2 weeks) but not acute nicotine (0.2 mg/kg, subcutaneous) treatment significantly alleviated LPS-induced WM deficiency by upregulating CRTC1 and HCN2. Of note, intra-mPFC infusion of HCN blocker ZD7288 produced significant WM deficiency.

CONCLUSIONS

In summary, in this study, we show that chronic nicotine treatment ameliorates acute inflammation-induced working memory deficiency by increasing CRTC1 and HCN2 in adult male mice.

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.

Effects of Nicotine Administration in an Enriched Environment on the Behavior of Male MK-801-Exposed Rats

Background

Smoking is more common in patients with schizophrenia than in healthy populations. Some controversial hypotheses connect the disease with the high prevalence of smoking. Moreover, environmental factors affect the severity of the positive and negative symptoms of schizophrenia. The current study aimed to assess the effect of enriched environment (EE) and nicotine on the MK-801 animal model of schizophrenia.

Methods

Male Wistar rat pups randomly received saline or MK-801 (dose:1 mg/kg) for five days from the sixth postnatal day (P) until the tenth. The pups were placed in EE or standard cages (SCs) after weaning (P21). Morris water maze (MWM) was used to assess spatial learning and memory. The rats received 0.6 mg/kg nicotine twice for three days at the end of the second month and were examined in an open-field box and three-chamber social interaction test.

Findings

MK-801 rats' behaviors were the same as those of the saline rats when they were exposed to nicotine. No positive effects of EE were observed when the animals were exposed to nicotine.

Conclusion

The results suggested that nicotine decreased schizophrenia-like symptoms and covered the positive effects of EE.

Nicotine Exposure in a Phencyclidine-Induced Mice Model of Schizophrenia: Sex-Selective Medial Prefrontal Cortex Protein Markers of the Combined Insults in Adolescent Mice

Tobacco misuse as a comorbidity of schizophrenia is frequently established during adolescence. However, comorbidity markers are still missing. Here, the method of label-free proteomics was used to identify deregulated proteins in the medial prefrontal cortex (prelimbic and infralimbic) of male and female mice modelled to schizophrenia with a history of nicotine exposure during adolescence. Phencyclidine (PCP), used to model schizophrenia (SCHZ), was combined with an established model of nicotine minipump infusions (NIC). The combined insults led to worse outcomes than each insult separately when considering the absolute number of deregulated proteins and that of exclusively deregulated ones. Partially shared Reactome pathways between sexes and between PCP, NIC and PCPNIC groups indicate functional overlaps. Distinctively, proteins differentially expressed exclusively in PCPNIC mice reveal unique effects associated with the comorbidity model. Interactome maps of these proteins identified sex-selective subnetworks, within which some proteins stood out: for females, peptidyl-prolyl cis-trans isomerase (Fkbp1a) and heat shock 70 kDa protein 1B (Hspa1b), both components of the oxidative stress subnetwork, and gamma-enolase (Eno2), a component of the energy metabolism subnetwork; and for males, amphiphysin (Amph), a component of the synaptic transmission subnetwork. These are proposed to be further investigated and validated as markers of the combined insult during adolescence.

The application of cognitive behavioral therapy in patients with schizophrenia: A review

The aim of this review is to explore the clinical nursing application of cognitive behavioral therapy (CBT) in patients with schizophrenia. A literature search was conducted using the CINAHL and MEDLINE databases. The database search occurred during the month of December 2022. This article comprehensively summarizes the theoretical basis of CBT in improving schizophrenia in clinical nursing, its application in managing symptoms and improving social function, as well as research progress in this field. There are still inconsistencies in the research results on CBT, but overall, psychological intervention combined with drug treatment is more effective than conventional treatment alone. If social function training can be added at the same time, it is believed that it will have better effects on clinical treatment and can maintain long-lasting effectiveness. Only in this way can patients truly understand and recognize the disease, improve treatment compliance, and ultimately achieve the goal of improving prognosis and quality of life.

Nicotine's effect on cognition, a friend or foe?

Tobacco smoking is a preventable cause of morbidity and mortality throughout the world. Smoking comes in form of absorption of many compounds, among which nicotine is the main psychoactive component of tobacco and its positive and negative reinforcement effects are proposed to be the key mechanism for the initiation and maintenance of smoking. Growing evidence suggests that the cognitive enhancement effects of nicotine may also contribute to the difficulty of quitting smoking, especially in individuals with psychiatric disorders. In this review, we first introduce the beneficial effect of nicotine on cognition including attention, short-term memory and long-term memory. We next summarize the beneficial effect of nicotine on cognition under pathological conditions, including Alzheimer's disease, Parkinson's disease, Schizophrenia, Stress-induced Anxiety, Depression, and drug-induced memory impairment. The possible mechanism underlying nicotine's effect is also explored. Finally, nicotine's detrimental effect on cognition is discussed, including in the prenatal and adolescent periods, and high-dose nicotine- and withdrawal-induced memory impairment is emphasized. Therefore, nicotine serves as both a friend and foe. Nicotine-derived compounds could be a promising strategy to alleviate neurological disease-associated cognitive deficit, however, due to nicotine's detrimental effect, continued educational programs and public awareness campaigns are needed to reduce tobacco use among pregnant women and smoking should be quitted even if it is e-cigarette, especially for the adolescents.

Nicotine pretreatment alleviates MK-801-induced behavioral and cognitive deficits in mice by regulating Pdlim5/CRTC1 in the PFC

Increasing evidence shows that smoking-obtained nicotine is indicated to improve cognition and mitigate certain symptoms of schizophrenia. In this study, we investigated whether chronic nicotine treatment alleviated MK-801-induced schizophrenia-like symptoms and cognitive impairment in mice. Mice were injected with MK-801 (0.2 mg/kg, i.p.), and the behavioral deficits were assessed using prepulse inhibition (PPI) and T-maze tests. We showed that MK-801 caused cognitive impairment accompanied by increased expression of PDZ and LIM domain 5 (Pdlim5), an adaptor protein that is critically associated with schizophrenia, in the prefrontal cortex (PFC). Pretreatment with nicotine (0.2 mg · kg-1 · d-1, s.c., for 2 weeks) significantly ameliorated MK-801-induced schizophrenia-like symptoms and cognitive impairment by reversing the increased Pdlim5 expression levels in the PFC. In addition, pretreatment with nicotine prevented the MK-801-induced decrease in CREB-regulated transcription coactivator 1 (CRTC1), a coactivator of CREB that plays an important role in cognition. Furthermore, MK-801 neither induced schizophrenia-like behaviors nor decreased CRTC1 levels in the PFC of Pdlim5-/- mice. Overexpression of Pdlim5 in the PFC through intra-PFC infusion of an adreno-associated virus AAV-Pdlim5 induced significant schizophrenia-like symptoms and cognitive impairment. In conclusion, chronic nicotine treatment alleviates schizophrenia-induced memory deficits in mice by regulating Pdlim5 and CRTC1 expression in the PFC.

Does nicotine exposure during adolescence modify the course of schizophrenia-like symptoms? Behavioral analysis in a phencyclidine-induced mice model

The first symptoms of schizophrenia (SCHZ) are usually observed during adolescence, a developmental period during which first exposure to psychoactive drugs also occurs. These epidemiological findings point to adolescence as critical for nicotine addiction and SCHZ comorbidity, however it is not clear whether exposure to nicotine during this period has a detrimental impact on the development of SCHZ symptoms since there is a lack of studies that investigate the interactions between these conditions during this period of development. To elucidate the impact of a short course of nicotine exposure across the spectrum of SCHZ-like symptoms, we used a phencyclidine-induced adolescent mice model of SCHZ (2.5mg/Kg, s.c., daily, postnatal day (PN) 38-PN52; 10mg/Kg on PN53), combined with an established model of nicotine minipump infusions (24mg/Kg/day, PN37-44). Behavioral assessment began 4 days after the end of nicotine exposure (PN48) using the following tests: open field to assess the hyperlocomotion phenotype; novel object recognition, a declarative memory task; three-chamber sociability, to verify social interaction and prepulse inhibition, a measure of sensorimotor gating. Phencyclidine exposure evoked deficits in all analyzed behaviors. Nicotine history reduced the magnitude of phencyclidine-evoked hyperlocomotion and impeded the development of locomotor sensitization. It also mitigated the deficient sociability elicited by phencyclidine. In contrast, memory and sensorimotor gating deficits evoked by phencyclidine were neither improved nor worsened by nicotine history. In conclusion, our results show for the first time that nicotine history, restricted to a short period during adolescence, does not worsen SCHZ-like symptoms evoked by a phencyclidine-induced mice model.

Not Just a Bystander: The Emerging Role of Astrocytes and Research Tools in Studying Cognitive Dysfunctions in Schizophrenia

Cognitive dysfunction is one of the core symptoms in schizophrenia, and it is predictive of functional outcomes and therefore useful for treatment targets. Rather than improving cognitive deficits, currently available antipsychotics mainly focus on positive symptoms, targeting dopaminergic/serotoninergic neurons and receptors in the brain. Apart from investigating the neural mechanisms underlying schizophrenia, emerging evidence indicates the importance of glial cells in brain structure development and their involvement in cognitive functions. Although the etiopathology of astrocytes in schizophrenia remains unclear, accumulated evidence reveals that alterations in gene expression and astrocyte products have been reported in schizophrenic patients. To further investigate the role of astrocytes in schizophrenia, we highlighted recent progress in the investigation of the effect of astrocytes on abnormalities in glutamate transmission and impairments in the blood–brain barrier. Recent advances in animal models and behavioral methods were introduced to examine schizophrenia-related cognitive deficits and negative symptoms. We also highlighted several experimental tools that further elucidate the role of astrocytes. Instead of focusing on schizophrenia as a neuron-specific disorder, an additional astrocytic perspective provides novel and promising insight into its causal mechanisms and treatment. The involvement of astrocytes in the pathogenesis of schizophrenia and other brain disorders is worth further investigation.

Multiple nicotinic acetylcholine receptor subtypes regulate social or cognitive behaviors in mice repeatedly administered phencyclidine

Habitual smoking in patients with schizophrenia (SCZ) is considered to improve their own psychoses or to develop a vulnerability to psychological dependence on (-)-nicotine ([-]-NIC) by stimulating nicotinic acetylcholine receptors (nAChRs) in the central nervous system. In the present study, we investigated whether habitual smoking is due to get therapeutic effect or to psychological dependence and which nAChR subunits are associated with them using mice that were repeatedly administered phencyclidine (PCP: 10 mg/kg/day, s.c. for 14 days) as SCZ-like model mice. Mice that were repeatedly administered PCP showed impairments in social or cognitive behaviors; decreased expression of α7 and/or α4 nAChR subunits in the prefrontal cortex (PFC); and increased expression of α7, α4, and β2 nAChR subunits in the nucleus accumbens (NAc). These changes were attenuated by repeated administration of (-)-NIC. The attenuating effects on behavioral impairments were prevented by a selective α7 nAChR antagonist and a selective α4β2 nAChR antagonist. At non- or weak effective dose by themselves, co-administration of (-)-NIC (0.03 mg/kg) and risperidone (0.03 mg/kg) showed synergistic effects on behavioral impairments in PCP-administered mice. Repeated (-)-NIC administration did not affect the performance of conditioned place preference, while it showed behavioral sensitization to (-)-NIC in the PCP-administered mice. Repeated (-)-NIC administration did not affect the performance of conditioned place preference, while it showed behavioral sensitization to (-)-NIC and attenuating effect on haloperidol-induced catalepsy in the PCP-administered mice. Our findings suggest that habitual smoking in SCZ might be attributed to get therapeutic and reduce side effects mediated by α7 and α4β2 nAChR activation by (-)-NIC.

Involvement of nicotinic acetylcholine receptors in behavioral abnormalities and psychological dependence in schizophrenia-like model mice

The smoking incentive in patients with schizophrenia (SCZ) depends on stimulation of nicotinic acetylcholine receptors (nAChRs) in the central nervous system. To detect potential predictor genes for nicotine responses in SCZ, we explored common factor using research data in human and animal samples. In lymphoblastoid cell lines from SCZ, the mRNA expression level of α7 nAChR subunit was decreased. In SCZ-like model mice of phencyclidine (PCP; 10 mg/kg/day, subcutaneously for 14 days)-administered mice, the mRNA expression level of α7 nAChR subunit and protein expression level of α7 or α4 nAChR subunit were significantly decreased in the prefrontal cortex during PCP withdrawal. Protein, but not mRNA, expression levels of α7, α4, and β2 nAChR subunits were significantly increased in the nucleus accumbens. Acute (-)-nicotine [(-)-NIC: 0.3 mg/kg, s.c.] treatment attenuated impairments of social behaviors and visual recognition memory. These effects of (-)-NIC were completely blocked by both methyllycaconitine, a selective α7 nAChR antagonist, and dihydro-β-erythroidine (DHβE), a selective α4β2 nAChR antagonist. (-)-NIC did not induce conditioned place preference, but enhanced sensitivity to methamphetamine-induced hyperactivity. These findings suggest that α7 nAChR is associated with development of disease and is implicated in the therapeutic effect of nicotine in SCZ. The smoking incentive in SCZ might be attributed to treat their own symptoms, rather than a result of (-)-NIC dependence, by stimulating α7 and/or α4β2 nAChRs.

Impact of Nicotine Transport across the Blood-Brain Barrier: Carrier-Mediated Transport of Nicotine and Interaction with Central Nervous System Drugs

Nicotine, an addictive substance, is absorbed from the lungs following inhalation of tobacco smoke, and distributed to various tissues such as liver, brain, and retina. Recent in vivo and in vitro studies suggest the involvement of a carrier-mediated transport process in nicotine transport in the lung, liver, and inner blood-retinal barrier. In addition, in vivo studies of influx and efflux transport of nicotine across the blood-brain barrier (BBB) revealed that blood-to-brain influx transport of nicotine is more dominant than brain-to-blood efflux transport of nicotine. Uptake studies in TR-BBB13 cells, which are an in vitro model cell line of the BBB, suggest the involvement of H⁺/organic cation antiporter, which is distinct from typical organic cation transporters, in nicotine transport at the BBB. Moreover, inhibition studies in TR-BBB13 cells showed that nicotine uptake was significantly reduced by central nervous system (CNS) drugs, such as antidepressants, anti-Alzheimer's disease drugs, and anti-Parkinson's disease drugs, suggesting that the nicotine transport system can recognize these molecules. The cumulative evidence would be helpful to improve our understanding of smoking-CNS drug interaction for providing appropriate medication.

Chronic nicotine improves cognitive and social impairment in mice overexpressing wild type α-synuclein

In addition to dopaminergic and motor deficits, patients with Parkinson's disease (PD) suffer from non-motor symptoms, including early cognitive and social impairment, that do not respond well to dopaminergic therapy. Cholinergic deficits may contribute to these problems, but cholinesterase inhibitors have limited efficacy. Mice over-expressing α-synuclein, a protein critically associated with PD, show deficits in cognitive and social interaction tests, as well as a decrease in cortical acetylcholine. We have evaluated the effects of chronic administration of nicotine in mice over-expressing wild type human α-synuclein under the Thy1-promoter (Thy1-aSyn mice). Nicotine was administered subcutaneously by osmotic minipump for 6 months from 2 to 8 months of age at 0.4 mg/kg/h and 2.0 mg/kg/h. The higher dose was toxic in the Thy1-aSyn mice, but the low dose was well tolerated and both doses ameliorated cognitive impairment in Y-maze performance after 5 months of treatment. In a separate cohort of Thy1-aSyn mice, nicotine was administered at the lower dose for one month beginning at 5 months of age. This treatment partially eliminated the cognitive deficit in novel object recognition and social impairment. In contrast, chronic nicotine did not improve motor deficits after 2, 4 or 6 months of treatment, nor modified α-synuclein aggregation, tyrosine hydroxylase immunostaining, synaptic and dendritic markers, or microglial activation in Thy1-aSyn mice. These results suggest that cognitive and social impairment in synucleinopathies like PD may result from deficits in cholinergic neurotransmission and may benefit from chronic administration of nicotinic agonists.

Wheel running during chronic nicotine exposure is protective against mecamylamine-precipitated withdrawal and up-regulates hippocampal α7 nACh receptors in mice

BACKGROUND AND PURPOSE

Evidence suggests that exercise decreases nicotine withdrawal symptoms in humans; however, the mechanisms mediating this effect are unclear. We investigated, in a mouse model, the effect of exercise intensity during chronic nicotine exposure on nicotine withdrawal severity, binding of α4β2*, α7 nicotinic acetylcholine (nAChR), μ-opioid (μ receptors) and D2 dopamine receptors and on brain-derived neurotrophic factor (BDNF) and plasma corticosterone levels.

EXPERIMENTAL APPROACH

Male C57Bl/6J mice treated with nicotine (minipump, 24 mg·kg-1 ·day-1 ) or saline for 14 days underwent one of three concurrent exercise regimes: 24, 2 or 0 h·day-1 voluntary wheel running. Mecamylamine-precipitated withdrawal symptoms were assessed on day 14. Quantitative autoradiography of α4β2*, α7 nAChRs, μ receptors and D2 receptor binding was performed in brain sections of these mice. Plasma corticosterone and brain BDNF levels were also measured.

KEY RESULTS

Nicotine-treated mice undertaking 2 or 24 h·day-1 wheel running displayed a significant reduction in withdrawal symptom severity compared with the sedentary group. Wheel running induced a significant up-regulation of α7 nAChR binding in the CA2/3 area of the hippocampus of nicotine-treated mice. Neither exercise nor nicotine treatment affected μ or D2 receptor binding or BDNF levels. Nicotine withdrawal increased plasma corticosterone levels and α4β2* nAChR binding, irrespective of exercise regimen.

CONCLUSIONS AND IMPLICATIONS

We demonstrated for the first time a profound effect of exercise on α7 nAChRs in nicotine-dependent animals, irrespective of exercise intensity. These findings shed light onto the mechanism underlining the protective effect of exercise on the development of nicotine dependence.

LINKED ARTICLES

This article is part of a themed section on Nicotinic Acetylcholine Receptors. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.11/issuetoc.

Short-term nicotine exposure induces long-lasting modulation of gustatory plasticity in Caenorhabditis elegans

Nicotine administration induces many effects on animal behavior. In wild-type Caenorhabditis elegans, gustatory plasticity results in reduced chemotaxis toward NaCl of otherwise attractive concentrations after pre-exposure to 100 mM NaCl in the absence of food. However, acute nicotine administration during a 15 min pre-exposure period inhibits gustatory plasticity, whereas chronic nicotine administration during worm development facilitates the plasticity. To investigate the relationship between the duration of nicotine administration and its effects, we exposed worms to nicotine for various periods during development. The modulatory effect of nicotine on gustatory plasticity was gradually switched from inhibition to facilitation with increased duration of nicotine administration. Moreover, inhibition of plasticity was sustained after relatively short-term chronic administration, with effects lasting for 45 h after the removal of nicotine. Similar to the acute inhibitory effect after 15 min nicotine pre-exposure, the inhibitory effect after short-term chronic administration was dependent on the nicotinic acetylcholine receptor subunit genes lev-1 and unc-29, and genes involved in serotonin biosynthesis bas-1 and tph-1. The impaired inhibition in bas-1 and tph-1mutants was recovered by exogenous serotonin, demonstrating that serotonin plays an important role in the long-lasting inhibitory effects of short-term chronic nicotine exposure.

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We analyzed gustatory plasticity of C. elegans after nicotine administration.

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Nicotine modulates gustatory plasticity in various ways.

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Nicotine inhibits gustatory plasticity after short-term chronic administration.

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The inhibitory effect was long-lasting even after removal of nicotine.

Nicotine reverses hypofrontality in animal models of addiction and schizophrenia

The prefrontal cortex (PFC) underlies higher cognitive processes that are modulated by nicotinic acetylcholine receptor (nAChR) activation by cholinergic inputs. PFC spontaneous default activity is altered in neuropsychiatric disorders, including schizophrenia-a disorder that can be accompanied by heavy smoking. Recently, genome-wide association studies (GWAS) identified single-nucleotide polymorphisms (SNPs) in the human CHRNA5 gene, encoding the α5 nAChR subunit, that increase the risks for both smoking and schizophrenia. Mice with altered nAChR gene function exhibit PFC-dependent behavioral deficits, but it is unknown how the corresponding human polymorphisms alter the cellular and circuit mechanisms underlying behavior. Here we show that mice expressing a human α5 SNP exhibit neurocognitive behavioral deficits in social interaction and sensorimotor gating tasks. Two-photon calcium imaging in awake mouse models showed that nicotine can differentially influence PFC pyramidal cell activity by nAChR modulation of layer II/III hierarchical inhibitory circuits. In α5-SNP-expressing and α5-knockout mice, lower activity of vasoactive intestinal polypeptide (VIP) interneurons resulted in an increased somatostatin (SOM) interneuron inhibitory drive over layer II/III pyramidal neurons. The decreased activity observed in α5-SNP-expressing mice resembles the hypofrontality observed in patients with psychiatric disorders, including schizophrenia and addiction. Chronic nicotine administration reversed this hypofrontality, suggesting that administration of nicotine may represent a therapeutic strategy for the treatment of schizophrenia, and a physiological basis for the tendency of patients with schizophrenia to self-medicate by smoking.

Cognitive dysfunction correlates with elevated serum S100B concentration in drug-free acutely relapsed patients with schizophrenia

S100B, a biomarker of glial dysfunction and blood-brain barrier (BBB) disruption, has been proposed to be involved in the pathophysiology of schizophrenia. In the present study, we aimed at exploring the association of serum S100B levels with cognitive deficits using MATRICS Consensus Cognitive Battery (MCCB) in schizophrenia, by excluding the impact of antipsychotics. Sixty-two unmedicated patients with schizophrenia during their acute phases were divided into a drug-naïve group (n=34) and a drug-free group (n=28). S100B serum concentrations were measured and MCCB was administered to all of the patients. Forty healthy controls donated their blood samples for S100B assessment. The results indicated that serum S100B was significantly elevated in the drug-naive/free acute-stage schizophrenic patients when compared to the healthy controls. In the drug-free group, the serum S100B level was an independent contributor to the global cognitive dysfunctions, particularly for the speed of processing, attention/vigilance, visual learning and reasoning/problem solving subscores. Nevertheless, no significant associations between S100B and MCCB composite score or any cognitive domain subscore were observed in the drug-naïve group. These findings support the hypothesis that glial dysfunction and associated marker protein S100B may contribute to the pathophysiologic development of neurocognitive deficits in the relapsed individuals with schizophrenia.

G72 primate-specific gene: a still enigmatic element in psychiatric disorders

Numerous studies have demonstrated a link between genetic markers on chromosome 13 and schizophrenia, bipolar affective disorder, and other psychiatric phenotypes. The G72/G30 genes (transcribed in opposite directions) are located on chromosome 13q33, a region demonstrating strong evidence for linkage with various neuropsychiatric disorders. G72/G30 was identified in 2002 as a schizophrenia susceptibility locus; however, subsequent association studies did not reach consensus on single SNPs within the locus. Simultaneously, a new vision for the genetic architecture of psychiatric disorders suggested that schizophrenia was a quantitative trait, therefore ascribable to potentially hundreds of genes and subjected to the vagaries of the environment. The main protein product of G72 gene is named pLG72 or D-amino acid oxidase activator DAOA (153 amino acids) and its function is still debated. Functional analyses, also showing controversial results, indicate that pLG72 contributes to N-methyl-D-aspartate receptor modulation by affecting activity of the flavoprotein D-amino acid oxidase, the enzyme responsible for degrading the neuromodulator D-serine. In this review we, for the first time, summarize findings from molecular genetic linkage and association studies concerning G72 gene, cellular and molecular studies on pLG72, and investigations performed on G72/G30 transgenic mice. This will help elucidate the role of psychosis susceptibility genes, which will have a major impact on our understanding of disease pathophysiology and thus change classification and treatment.

Preclinical Evidence for a Role of the Nicotinic Cholinergic System in Parkinson's Disease

One of the primary deficits in Parkinson's disease (PD) is the loss of dopaminergic neurons in the substantia nigra pars compacta which leads to striatal dopaminergic deficits that underlie the motor symptoms associated with the disease. A plethora of animal models have been developed over the years to uncover the molecular alterations that lead to PD development. These models have provided valuable information on neurotransmitter pathways and mechanisms involved. One such a system is the nicotinic cholinergic system. Numerous studies show that nigrostriatal damage affects nicotinic receptor-mediated dopaminergic signaling; therefore therapeutic modulation of the nicotinic cholinergic system may offer a novel approach to manage PD. In fact, there is evidence showing that nicotinic receptor drugs may be useful as neuroprotective agents to prevent Parkinson's disease progression. Additional preclinical studies also show that nicotinic receptor drugs may be beneficial for the treatment of L-dopa induced dyskinesias. Here, we review preclinical findings supporting the idea that nicotinic receptors are valuable therapeutic targets for PD.

Chronic nicotine treatment enhances vascular smooth muscle relaxation in rats

AIM

To investigate the effect of chronic nicotine treatment on vascular function and to identify the underlying mechanisms.

METHODS

Adult rats were treated with nicotine (3 mg·kg(-1)·d(-1), sc) for 6 weeks. After the rats were sacrificed, aortic rings were prepared for detecting vascular reactivity, and thoracic aorta and periaortic fat samples were collected for histological and molecular biology studies.

RESULTS

Chronic nicotine treatment significantly reduced periaortic fat, and specifically enhanced smooth muscle relaxation without altering the aortic adventitial fat and endothelium function. Pretreatment with the soluble guanylyl cyclase inhibitor ODQ (3 μmol/L) or PKG inhibitor Rp-8-Br-PET-cGMP (30 μmol/L) abolished the nicotine-induced enhancement of smooth muscle relaxation, whereas the cGMP analogue 8-Br-cGMP could mimic the nicotine-induced enhancement of smooth muscle relaxation. However, the chronic nicotine treatment did not alter PKG protein expression and activity in aortic media.

CONCLUSION

Chronic nicotine treatment enhances vascular smooth muscle relaxation of rats via activation of PKG pathway.

Chronic nicotine exposure augments gustatory plasticity in Caenorhabditis elegans: involvement of dopamine signaling

The chemotaxis of wild-type NaCl-conditioned nematodes exposed to 100 mM NaCl, maintained on a growth medium containing 0.3 mM nicotine from first larva to young adult (YA) hermaphrodite, was significantly weaker than the chemotaxis of those maintained on a medium without nicotine. The result indicates that chronic nicotine exposure augments gustatory plasticity. The gustatory plasticity was also augmented when tph-1 mutants, with a defect in serotonin biosynthesis, were maintained on a medium containing nicotine until the YA stage. Chronic nicotine exposure did not augment gustatory plasticity in bas-1 mutants, which had defects in both serotonin and dopamine biosynthesis, and in cat-2 mutants, which had a defect in dopamine biosynthesis. However, augmentation of gustatory plasticity was observed when bas-1 and cat-2 mutants were maintained on a growth medium containing nicotine along with dopamine, suggesting that dopamine signaling is involved in the augmentation of gustatory plasticity due to chronic nicotine exposure.