Differential modulation of gene expression in the NMDA postsynaptic density of schizophrenic and control smokers

Chromosome 8p as a potential hub for developmental neuropsychiatric disorders: implications for schizophrenia, autism and cancer

Defects in genetic and developmental processes are thought to contribute susceptibility to autism and schizophrenia. Presumably, owing to etiological complexity identifying susceptibility genes and abnormalities in the development has been difficult. However, the importance of genes within chromosomal 8p region for neuropsychiatric disorders and cancer is well established. There are 484 annotated genes located on 8p; many are most likely oncogenes and tumor-suppressor genes. Molecular genetics and developmental studies have identified 21 genes in this region (ADRA1A, ARHGEF10, CHRNA2, CHRNA6, CHRNB3, DKK4, DPYSL2, EGR3, FGF17, FGF20, FGFR1, FZD3, LDL, NAT2, NEF3, NRG1, PCM1, PLAT, PPP3CC, SFRP1 and VMAT1/SLC18A1) that are most likely to contribute to neuropsychiatric disorders (schizophrenia, autism, bipolar disorder and depression), neurodegenerative disorders (Parkinson's and Alzheimer's disease) and cancer. Furthermore, at least seven nonprotein-coding RNAs (microRNAs) are located at 8p. Structural variants on 8p, such as copy number variants, microdeletions or microduplications, might also contribute to autism, schizophrenia and other human diseases including cancer. In this review, we consider the current state of evidence from cytogenetic, linkage, association, gene expression and endophenotyping studies for the role of these 8p genes in neuropsychiatric disease. We also describe how a mutation in an 8p gene (Fgf17) results in a mouse with deficits in specific components of social behavior and a reduction in its dorsomedial prefrontal cortex. We finish by discussing the biological connections of 8p with respect to neuropsychiatric disorders and cancer, despite the shortcomings of this evidence.

Association of the 5'-upstream regulatory region of the alpha7 nicotinic acetylcholine receptor subunit gene (CHRNA7) with schizophrenia

BACKGROUND

The alpha7 neuronal nicotinic acetylcholine receptor subunit gene (CHRNA7) is localized in a chromosomal region (15q14) linked to schizophrenia in multiple independent studies. CHRNA7 was selected as the best candidate gene in the region for a well-documented endophenotype of schizophrenia, the P50 sensory processing deficit, by genetic linkage and biochemical studies.

METHODS

Subjects included Caucasian-Non Hispanic and African-American case-control subjects collected in Denver, and schizophrenic subjects from families in the NIMH Genetics Initiative on Schizophrenia. Thirty-five single nucleotide polymorphisms (SNPs) in the 5'-upstream regulatory region of CHRNA7 were genotyped for association with schizophrenia, and for smoking in schizophrenia.

RESULTS

The rs3087454 SNP, located at position -1831 bp in the upstream regulatory region of CHRNA7, was significantly associated with schizophrenia in the case-control samples after multiple-testing correction (P=0.0009, African American; P=0.013, Caucasian-Non Hispanic); the association was supported in family members. There was nominal association of this SNP with smoking in schizophrenia.

CONCLUSIONS

The data support association of regulatory region polymorphisms in the CHRNA7 gene with schizophrenia.

Target identification for CNS diseases by transcriptional profiling

Gene expression changes in neuropsychiatric and neurodegenerative disorders, and gene responses to therapeutic drugs, provide new ways to identify central nervous system (CNS) targets for drug discovery. This review summarizes gene and pathway targets replicated in expression profiling of human postmortem brain, animal models, and cell culture studies. Analysis of isolated human neurons implicates targets for Alzheimer's disease and the cognitive decline associated with normal aging and mild cognitive impairment. In addition to tau, amyloid-beta precursor protein, and amyloid-beta peptides (Abeta), these targets include all three high-affinity neurotrophin receptors and the fibroblast growth factor (FGF) system, synapse markers, glutamate receptors (GluRs) and transporters, and dopamine (DA) receptors, particularly the D2 subtype. Gene-based candidates for Parkinson's disease (PD) include the ubiquitin-proteosome system, scavengers of reactive oxygen species, brain-derived neurotrophic factor (BDNF), its receptor, TrkB, and downstream target early growth response 1, Nurr-1, and signaling through protein kinase C and RAS pathways. Increasing variability and decreases in brain mRNA production from middle age to old age suggest that cognitive impairments during normal aging may be addressed by drugs that restore antioxidant, DNA repair, and synaptic functions including those of DA to levels of younger adults. Studies in schizophrenia identify robust decreases in genes for GABA function, including glutamic acid decarboxylase, HINT1, glutamate transport and GluRs, BDNF and TrkB, numerous 14-3-3 protein family members, and decreases in genes for CNS synaptic and metabolic functions, particularly glycolysis and ATP generation. Many of these metabolic genes are increased by insulin and muscarinic agonism, both of which are therapeutic in psychosis. Differential genomic signals are relatively sparse in bipolar disorder, but include deficiencies in the expression of 14-3-3 protein members, implicating these chaperone proteins and the neurotransmitter pathways they support as possible drug targets. Brains from persons with major depressive disorder reveal decreased expression for genes in glutamate transport and metabolism, neurotrophic signaling (eg, FGF, BDNF and VGF), and MAP kinase pathways. Increases in these pathways in the brains of animals exposed to electroconvulsive shock and antidepressant treatments identify neurotrophic and angiogenic growth factors and second messenger stimulation as therapeutic approaches for the treatment of depression.

Transcriptional correlates of human substance use

Drugs of abuse produce both acute and chronic changes in brain function, each of which is reflected in altered gene expression patterns. A number of large-scale gene expression studies have employed microarray analysis of human postmortem brain to identify transcriptional correlates of antemortem substance use. These studies have identified changes in transcripts encoding proteins functionally involved in neuronal function and synaptic plasticity, oligodendrocyte function and myelination, lipid and energy metabolism, mitochondrial function, oxidative phosphorylation, and cytoskeleton-related signal transduction. Overall, different types of substance use appear to share some of these effects, but there are more differences than similarities in gene expression for different types of substance use. Moreover, data suggest that transcriptional subtypes within a diagnostic classification of substance use may occur. These transcriptional subtypes, or "endophenotypes," may reflect complex patterns of substance use and co-morbid neuropsychiatric disorders or other diseases, which may interact with substance use to differentially affect gene expression. A broader understanding of the manner in which substance abuse causes long-term changes in brain function may be obtained from studies replicating and expanding the present gene expression data. In particular, cross-referencing comprehensive transcriptional data on regional and/or substance use-specific changes with genetic and proteomic data may further aid in identifying candidate biomarkers of altered brain function in substance-use disorders.

Regulation of a novel alphaN-catenin splice variant in schizophrenic smokers

The alphaN-catenin (CTNNA2) gene represents a promising candidate gene for schizophrenia based upon previous genetic linkage, expression, and mouse knockout studies. CTNNA2 is differentially regulated by smoking in schizophrenic patients. In this report, the genomic structure of a primate-specific alphaN-catenin splice variant (alphaN-catenin III) is described. A comparison of alphaN-catenin III mRNA expression across postmortem hippocampi from schizophrenic and non-mentally ill smokers and non-smokers revealed a significant decrease in expression among patient non-smokers compared to all other groups. The recent evolutionary divergence of this gene, as well as the differences in gene expression in postmortem brain of schizophrenic non-smokers, supports the role of alphaN-catenin III as a novel disease susceptibility gene.

Effects of transdermal nicotine on episodic memory in non-smokers with and without schizophrenia

RATIONALE

Nicotinic agonists may improve attention and memory in humans and may ameliorate some cognitive deficits associated with neuropsychiatric disorders such as schizophrenia.

MATERIALS AND METHODS

We investigated the effects of a single dose of nicotine on episodic memory performance in 10 adults with schizophrenia and 12 healthy controls. Participants were nonsmokers in order to avoid confounding effects of nicotine withdrawal and reinstatement on memory. At each of two study visits, participants performed a test of episodic memory before and 4 h after application of a 14-mg transdermal nicotine (or identical placebo) patch in counterbalanced order.

RESULTS

Compared with placebo, nicotine treatment was associated with more rapid and accurate recognition of novel items. There was a trend for a treatment by diagnosis interaction, such that the effect of nicotine to reduce false alarms was stronger in the schizophrenia than the control group. There was no effect of nicotine on accuracy or reaction time for identification of previously viewed items.

CONCLUSIONS

These data suggest that nicotine improves novelty detection in non-smokers, an effect that may be more pronounced in non-smokers with schizophrenia. Because memory deficits are associated with functional impairment in schizophrenia and because impaired novelty detection has been linked to the positive symptoms of schizophrenia, study of the effects of chronic nicotinic agonist treatment on novelty detection may be warranted.

Mice lacking the immediate early gene Egr3 respond to the anti-aggressive effects of clozapine yet are relatively resistant to its sedating effects

Immediate early genes (IEGs) of the early growth response gene (Egr) family are activated in the brain in response to stress, social stimuli, and administration of psycho-active medications. However, little is known about the role of these genes in the biological or behavioral response to these stimuli. Here we show that mice lacking the IEG transcription factor Egr3 (Egr3-/- mice) display increased aggression, and a decreased latency to attack, in response to the stressful social stimulus of a foreign intruder. Together with our findings of persistent and intrusive olfactory-mediated social investigation of conspecifics, these results suggest increased impulsivity in Egr3-/- mice. We also show that the aggression of Egr3-/- mice is significantly inhibited with chronic administration of the antipsychotic medication clozapine. Despite their sensitivity to this therapeutic effect of clozapine, Egr3-/- mice display a marked resistance to the sedating effects of acute clozapine compared with WT littermate controls. This indicates that the therapeutic, anti-aggressive action of clozapine is separable from its sedating activity, and that the biological abnormality resulting from loss of Egr3 distinguishes these different mechanisms. Thus Egr3-/- mice may provide an important tool for elucidating the mechanism of action of clozapine, as well as for understanding the biology underlying aggressive behavior. Notably, schizophrenia patients display a similar decreased susceptibility to the side effects of antipsychotic medications compared to non-psychiatric controls, despite the medications producing a therapeutic response. This suggests the possibility that Egr3-/- mice may provide insight into the neurobiological abnormalities underlying schizophrenia.

Nicotine effects on mismatch negativity in nonsmoking schizophrenic patients

BACKGROUND

The goal of the present study is to identify the effect of nicotine on auditory automatic processing, as reflected by mismatch negativity (MMN), in nonsmoking schizophrenic patients.

METHODS

Ten nonsmoking schizophrenic patients and 10 healthy volunteers underwent a reference session and 2 test sessions. The test sessions involved administration of a placebo patch and a nicotine skin patch, which were counterbalanced. Nicotine was administered transdermally under controlled dosage.

RESULTS

Nicotine administration shortened the MMN latencies (at Fz on nicotine/placebo: 134.8 +/- 5.7/157.6 +/- 6.4 ms) in healthy volunteers. In contrast, there were no significant differences in MMN latencies in schizophrenic patients (169.6 +/- 5.7/165.0 +/- 6.4 ms).

CONCLUSION

Nicotine activates and accelerates preattentive and automatic processing in healthy controls, whereas there were no such effects observed in nonsmoking patients. The impaired MMN response to nicotine administration in nonsmoking schizophrenic patients may be attributed to low nicotinic receptor function, implicated in dysregulation of the glutamatergic system.

Cerebrospinal fluid amino acids in pathological gamblers and healthy controls

Amino acids, such as valine, isoleucine and leucine compete with tyrosine and tryptophan for transport into the brain and might thus affect the central serotonin and catecholamine patterns. Furthermore, the excitatory amino acids glutamic acid, aspartic acid and glycine are known to act on the N-methyl-D-aspartate receptor, which is part of the reward system. Based on these facts, we have explored the role of cerebrospinal fluid (CSF) amino acids in pathological gambling. Concentrations of amino acids were determined in CSF obtained from one female and 11 pathological male gamblers and 11 healthy male controls. In an ANCOVA with best subset regression, pathological male gamblers had higher CSF levels of the excitatory glutamic and aspartic acids, as well as of phenylalanine, isoleucine, citrulline and glycine. A negative contribution of glycine in interaction with the neuraxis distance might mirror a reduced spinal supply or an altered elimination of glycine in pathological gamblers. A decreasing CSF gradient from the first (0-6 ml) to the third (13-18 ml) CSF fraction was found for glutamic acid, glycine, leucine, isoleucine, lysine, ornithine and glutamine in both pathological gamblers and healthy controls. A decreasing gradient was found, however, for aspartic acid and phenylalanine in pathological male gamblers. The altered pattern of CSF amino acids in pathological gamblers might exert an influence on central monoamines as well as on N-methyl-D-aspartate receptor function.

Nicotine and nicotinic system in hypoglutamatergic models of schizophrenia

Schizophrenia is a complex neuropsychiatric disorder with devastating consequences. It is characterized by thought fragmentation, hallucination and delusion, collectively referred to as positive symptoms. In addition, mood changes or affective disorders, referred to as negative symptoms, as well as cognitive impairments can be manifested in these patients. Arguably, modeling such a disorder in its entirety in animals might not be feasible. Despite this limitation, various models with significant construct, predictive and some face validity have been developed. One such model, based on hypoglutamatergic hypothesis of schizophrenia, makes use of administering NMDA receptor antagonists and evaluating behavioral paradigms such as sensorimotor gating. Because of very high incidence of smoking among schizophrenic patients, it has been postulated that some of these patients may actually be self medicating with tobacco's nicotine. Research on nicotinic-glutamatergic interactions using various animal models has yielded conflicting results. In this review, some of these models and possible confounding factors are discussed. Overall, a therapeutic potential for nicotinic agonists in schizophrenia can be suggested. Moreover, it is evident that various experimental paradigms or models of schizophrenia symptoms need to be combined to provide a wider spectrum of the behavioral phenotype, as each model has its inherent limitations.

Permutation-based adjustments for the significance of partial regression coefficients in microarray data analysis

The aim of this paper is to generalize permutation methods for multiple testing adjustment of significant partial regression coefficients in a linear regression model used for microarray data. Using a permutation method outlined by Anderson and Legendre [1999] and the permutation P-value adjustment from Simon et al. [2004], the significance of disease related gene expression will be determined and adjusted after accounting for the effects of covariates, which are not restricted to be categorical. We apply these methods to a microarray dataset containing confounders and illustrate the comparisons between the permutation-based adjustments and the normal theory adjustments. The application of a linear model is emphasized for data containing confounders and the permutation-based approaches are shown to be better suited for microarray data.

Postmortem diagnosis and toxicological validation of illicit substance use

The present study examines the diagnostic challenges of identifying ante-mortem illicit substance use in human postmortem cases. Substance use, assessed by clinical case history reviews, structured next-of-kin interviews, by general toxicology of blood, urine and/or brain, and by scalp hair testing, identified 33 cocaine, 29 cannabis, 10 phencyclidine and nine opioid cases. Case history identified 42% cocaine, 76% cannabis, 10% phencyclidine and 33% opioid cases. Next-of-kin interviews identified almost twice as many cocaine and cannabis cases as Medical Examiner (ME) case histories, and were crucial in establishing a detailed lifetime substance use history. Toxicology identified 91% cocaine, 68% cannabis, 80% phencyclidine and 100% opioid cases, with hair testing increasing detection for all drug classes. A cocaine or cannabis use history was corroborated by general toxicology with 50% and 32% sensitivity, respectively, and with 82% and 64% sensitivity by hair testing. Hair testing corroborated a positive general toxicology for cocaine and cannabis with 91% and 100% sensitivity, respectively. Case history corroborated hair toxicology with 38% sensitivity for cocaine and 79% sensitivity for cannabis, suggesting that both case history and general toxicology underestimated cocaine use. Identifying ante-mortem substance use in human postmortem cases are key considerations in case diagnosis and for characterization of disorder-specific changes in neurobiology. The sensitivity and specificity of substance use assessments increased when ME case history was supplemented with structured next-of-kin interviews to establish a detailed lifetime substance use history, while comprehensive toxicology, and hair testing in particular, increased detection of recent illicit substance use.

Mitochondrial involvement in psychiatric disorders

Recent findings of mitochondrial abnormalities in brains from subjects with neurological disorders have led to a renewed search for mitochondrial abnormalities in psychiatric disorders. A growing body of evidence suggests that there is mitochondrial dysfunction in schizophrenia, bipolar disorder, and major depressive disorder, including evidence from electron microscopy, imaging, gene expression, genotyping, and sequencing studies. Specific evidence of dysfunction such as increased common deletion and decreased gene expression in mitochondria in psychiatric illnesses suggests that direct examination of mitochondrial DNA from postmortem brain cells may provide further details of mitochondrial alterations in psychiatric disorders.

Glutamatergic substrates of drug addiction and alcoholism

The past two decades have witnessed a dramatic accumulation of evidence indicating that the excitatory amino acid glutamate plays an important role in drug addiction and alcoholism. The purpose of this review is to summarize findings on glutamatergic substrates of addiction, surveying data from both human and animal studies. The effects of various drugs of abuse on glutamatergic neurotransmission are discussed, as are the effects of pharmacological or genetic manipulation of various components of glutamate transmission on drug reinforcement, conditioned reward, extinction, and relapse-like behavior. In addition, glutamatergic agents that are currently in use or are undergoing testing in clinical trials for the treatment of addiction are discussed, including acamprosate, N-acetylcysteine, modafinil, topiramate, lamotrigine, gabapentin and memantine. All drugs of abuse appear to modulate glutamatergic transmission, albeit by different mechanisms, and this modulation of glutamate transmission is believed to result in long-lasting neuroplastic changes in the brain that may contribute to the perseveration of drug-seeking behavior and drug-associated memories. In general, attenuation of glutamatergic transmission reduces drug reward, reinforcement, and relapse-like behavior. On the other hand, potentiation of glutamatergic transmission appears to facilitate the extinction of drug-seeking behavior. However, attempts at identifying genetic polymorphisms in components of glutamate transmission in humans have yielded only a limited number of candidate genes that may serve as risk factors for the development of addiction. Nonetheless, manipulation of glutamatergic neurotransmission appears to be a promising avenue of research in developing improved therapeutic agents for the treatment of drug addiction and alcoholism.

Analysis of gene expression profiles in rat hippocampus following treatment with nicotine and an alpha7 nAChR selective agonist

The nicotinic acetylcholine receptors (nAChRs) play critical roles in neuronal transmission and modulation. Among the diverse nAChRs, the alpha7 subtype has been considered as a potential therapeutic target for treating cognitive deficits associated with neuropsychiatric and neurodegenerative diseases. Although a number of mechanisms including neurotransmitter and biochemical effects linking alpha7 nAChR activation and cognitive function are beginning to be described, the underlying molecular processes especially following repeated administration remain unclear. To address this, we have performed gene expression analysis in rats treated with nicotine and a selective alpha7 nAChR agonist, PNU-282987. Our results showed significant overlap in gene expression changes induced by PNU-282987 and nicotine, suggesting convergent pathways triggered by these compounds. Treatment with nicotine also resulted in regulation of a number of genes that were not regulated by PNU-282987, consistent with the interaction of nicotine with other nAChRs beyond the alpha7 subtype. Interestingly, these gene expression changes were observed 24 h post-dose, suggesting that both nicotine and PNU-282987 cause protracted changes in gene expression. Overall, our results identify gene expression changes that may contribute to further defining the roles of nAChR activation in cognitive function.

Smoking, Genetics and Schizophrenia: Evidence for Self Medication

Schizophrenia is a common mental illness with a high prevalence of smoking. More than 80% of schizophrenics smoke compared to 25% of the general population. Both schizophrenia and tobacco use have strong genetic components, which may overlap. It has been suggested that smoking in schizophrenia may be a form of self-medication in an attempt to treat an underlying biological pathology. Smoking normalizes auditory evoked potential and eye tracking deficits in schizophrenia, as well as improving cognitive function. Nicotine acts through a family of nicotinic receptors with either high or low affinity for nicotine. The loci for several of these receptors have been genetically linked to both smoking and to schizophrenia. Smoking changes gene expression for more than 200 genes in human hippocampus, and differentially normalizes aberrant gene expression in schizophrenia. The α7* nicotinic receptor, linked to schizophrenia and smoking, has been implicated in sensory processing deficits and is important for cognition and protection from neurotoxicity. Nicotine, however, has multiple health risks and desensitizes the receptor. A Phase I trial of DMXB-A, an α7* agonist, shows improvement in both P50 gating and in cognition, suggesting that further development of nicotinic cholinergic drugs is a promising direction in schizophrenia research.

Gene expression profiling in Brodmann's area 46 from subjects with schizophrenia

OBJECTIVE

To identify altered gene expression in the dorsolateral prefrontal cortex obtained after death from subjects with schizophrenia.

METHOD

Restriction fragment differential display (RFDD) was used to measure levels of mRNA in Brodmann area (BA) 46 from schizophrenia and control subjects. Findings on specific mRNA identified with RFDD were further investigated using real-time polymerase chain reaction (real-time PCR), PCR and western blotting.

RESULTS

Levels of mRNA for 63 of approximately 12,500 genes differed in BA 46 in schizophrenia. Subsequent real-time PCR has shown that mRNA for muscleblind protein 1 (MBNL1) and protocadherin 17 (PCDH17) are increased in BA 46 from subjects with schizophrenia of short, but not long, duration. Altered levels of mRNA for neither gene were present in BA 9 from subjects with schizophrenia or in either cortical area from subjects with bipolar 1 disorder. By contrast, both RFDD and real-time PCR failed to show altered expression of the schizophrenia candidate gene disrupted in schizophrenia 1 (DISC1) BA46 from any diagnostic cohort.

CONCLUSION

The present study has identified genes that are differentially expressed in BA 46 in schizophrenia. Initial studies have shown that there is a need for a careful validation of genes shown to be affected in schizophrenia using high-throughput technologies. In addition the present study has shown that gene expression may vary considerably depending on the duration of schizophrenia. This raises the hypothesis that changing gene expression may be underlying the change in symptom profile that occurs with disease progression in some subjects with schizophrenia.

The vulnerability to alcohol and substance abuse in individuals diagnosed with schizophrenia

Individuals with schizophrenia are at increased risk for developing substance abuse disorders. Here, we consider factors that might elevate their risk for substance abuse. The tendency among schizophrenic individuals to overvalue drug-like rewards and to devalue the potential negative consequences of substance abuse may be a contributing factor to their substance abuse risk. This bias, which may partly reflect the convergence of glutamatergic and dopaminergic input to the limbic striatum, also may contribute to disadvantageous decision-making and other impulsive behavior. This propensity to seek drug-like rewards is augmented by alterations in nicotinic cholinergic, GABAergic, glutamatergic, and cannabinnoid receptor function associated with schizophrenia that increase the abuse liability of low doses of nicotine, ethanol, and perhaps cannabis, and augment the dysphoric effects of higher doses of ethanol and cannabis. The distortions in reward processing and altered response to substances of abuse also increase the likelihood that individuals with schizophrenia will self-medicate their subjective distress with abused substances. The focus on distinctions between motivation and reward with respect to substance abuse risk by schizophrenic patients suggests a need for a reconsideration of the construct of "negative symptoms" for this dually-diagnosed patient group.

Comorbidity of substance abuse with other psychiatric disorders

Substance abuse is a frequent comorbid condition with other psychiatric disorders including schizophrenia and depression. These disorders may share a common substrate at the neurotransmitter or neurocircuit level. One candidate is hypofunction of the glutamate system. Several lines of evidence suggest that N-methyl-D-aspartate (NMDA) receptors may hypofunction in schizophrenia. Thus, NMDA receptor antagonists are schizophrenogenic; postmortem and imaging results point to reduced NMDA receptor function in schizophrenic brains; a number of genes that have been linked to schizophrenia code for proteins that influence NMDA function; and there is preliminary evidence that pro-NMDA drugs may be therapeutic in the treatment of schizophrenia. One of the most effective therapeutics for the treatment of substance abuse in schizophrenic people is clozapine, and clozapine may act at the glycine modulatory site to enhance NMDA receptor function. This preliminary line of evidence may link schizophrenia and drug abuse to a common neurochemical base, subnormal NMDA receptor function. People with schizophrenia and drug abusers similarly show deficits in tasks known to be sensitive to ventromedial prefrontal cortical damage, and both groups show decreased activation in the ventral striatum during reward anticipation in functional magnetic resonance imaging studies. These observations implicate common prefrontal cortical-striatal circuits and their modulation by hippocampal projections in schizophrenia and substance abuse. Withdrawal from substance abuse and depression both have been linked to changes in the function of several neurotransmitters including serotonin, dopamine and glutamate. These findings suggest possible common substrates and novel therapeutic approaches. Further studies are needed to fully characterize the neurocircuits and transmitters involved in various psychiatric disorders and their possible common elements in comorbid drug abuse.

Ventral Tegmental Transcriptome Response to Intermittent Nicotine Treatment and Withdrawal in BALB/cJ, C57BL/6ByJ, and Quasi-Congenic RQI Mice

The aim of this study was to identify neurochemical pathways and candidate genes involved in adaptation to nicotine treatment and withdrawal. Locomotor sensitization was assessed in a nicotine challenge test after exposure to intermittent nicotine treatment and withdrawal. About 24 h after the challenge test the ventral tegmentum of the mesencephaion was dissected and processed using oligonucleotide microarrays with 22,690 probe sets (Affymetrix 430A 2.0). Quasi-congenic RQI, and donor BALB/cJ mice developed significant locomotor sensitization, while sensitization was not significant in the background partner, C57BL/6By. Comparing saline treated controls of C57BL/6ByJ and BALB/cJ by a rigorous statistical microarray analysis method we identified 238 differentially expressed transcripts. Quasi-congenic strains B6.Cb4i5-alpha4/Vad and B6.Ib5i7-beta25A/Vad significantly differed from the background strain in 11 and 11 transcripts, respectively. Identification of several cis- and trans-regulated genes indicates that further work with quasi-congenic strains can quickly lead to mapping of Quantitative Trait Loci for nicotine susceptibility because donor chromosome regions have been mapped in quasi-congenic strains. Nicotine treatment significantly altered the abundance of 41, 29, 54, and 14 ventral tegmental transcripts in strains C57BL/6ByJ, BALB/cJ, B6.Cb4i5-alpha4/Vad, and B6.Ib5i7-beta25A/Vad, respectively. Although transcript sets overlapped to some extent, each strain showed a distinct profile of nicotine sensitive genes, indicating genetic effects on nicotine-induced gene expression. Nicotine-responsive genes were related to processes including regulation of signal transduction, intracellular protein transport, proteasomal ubiquitin-dependent protein catabolism, and neuropeptide signaling pathway. Our results suggest that while there are common regulatory mechanisms across inbred strains, even relatively small differences in genetic constitution can significantly affect transcriptome response to nicotine.

N-methyl-d-aspartate receptor 1 changes in the piglet braintem after nicotine and/or intermittent hypercapnic-hypoxia

Prone sleeping and cigarette smoke exposure are two major risk factors for the sudden infant death syndrome (SIDS). Utilizing piglet models of early postnatal nicotine and/or intermittent hypercapnic-hypoxia (IHH) exposure, we tested the hypothesis that these exposures, separately or combined, increase N-methyl-D-aspartate (NMDA) receptor 1 (NR1) expression in the brainstem medulla. We also tested for gender-specific effects. Three piglet exposure groups were compared against 14 controls; 1, nicotine [n = 14], 2, IHH [n = 10], and 3, nicotine+IHH [n = 14], with equal gender proportions in each group. Non-radioactive in situ hybridization and immunohistochemistry were performed for NR1 mRNA and protein expression, respectively, and were quantified in seven nuclei of the brainstem medulla. NR1 mRNA was significantly increased in the gracile and inferior olivary nucleus (ION) after nicotine exposure, in five of seven nuclei after IHH exposure, and in three of seven nuclei after nicotine+IHH. The increased mRNA changes were accompanied by increased protein only in the ION after IHH and nicotine+IHH (P = 0.019, and P = 0.008 respectively). By gender, control females had greater NR1 mRNA than males in the dorsal motor nucleus of vagus (P = 0.05) and for protein in the ION (P = 0.02). This gender difference was maintained after nicotine exposure in the ION with additional gender differences observed including greater mRNA in the cuneate nucleus (P = 0.04) and nucleus of the spinal trigeminal tract (P = 0.03) of males compared with females. Overall, more changes occurred at the mRNA level than protein, and IHH exposure induced more changes than nicotine or nicotine+IHH exposures. Together, these findings suggest that hypercapnic-hypoxic exposures (modeling prone sleeping or sleep apnea) are more likely to induce NMDA receptor changes in the developing brainstem than nicotine exposure alone.

Nicotinic modulation of gene expression in SH-SY5Y neuroblastoma cells

Exposure to nicotine has a broad range of physiological and psychological effects that can be long lasting and contribute to nicotine dependence. On a time course longer than that needed to activate nicotinic acetylcholine receptor (nAChR) function, nicotine exposure induces functional inactivation of nAChR, upregulation of nAChR radioligand binding sites, and other alterations of cellular functions. To identify possible mechanisms underlying nicotine-induced changes in nAChR numbers and function, we defined changes in gene expression in neuron-like, SH-SY5Y human neuroblastoma cells following 24 h of continuous exposure to 1 mM nicotine. This treatment condition produces both functional inactivation and upregulation of nAChR. Repeat and cross-controlled microarray ( approximately 5000 genes queried) analyses revealed 163 genes whose expression was consistently altered at the p<0.01 level following nicotine treatment. Quantitative, real-time, reverse transcription-polymerase chain reaction analyses confirmed altered expression of thirteen out of fourteen of these genes chosen for further study, including contactin 1, myozenin 2, and ubiquitin-conjugating enzymes E2C and E2S. Inhibition or reversal of these effects by the general nAChR antagonist, d-tubocurarine, indicated that gene expression changes are dependent on nAChR activation. Studies using other nAChR subtype-selective antagonists identified gene expression changes that required activation of both alpha7- and alpha3*-nAChR, alpha7-nAChR alone, or either alpha7- or alpha3beta4*-nAChR, suggesting some convergent and some divergent pathways of gene activation coupled to these nAChR subtypes. These results suggest that longer-term physiological and psychological effects of nicotine exposure and changes in nAChR expression may be due in part to effects on gene expression initiated by interactions with nAChR.

Nicotinic receptor agonists as neuroprotective/neurotrophic drugs. Progress in molecular mechanisms

In the present work we reviewed recent advances concerning neuroprotective/neurotrophic effects of acute or chronic nicotine exposure, and the signalling pathways mediating these effects, including mechanisms implicated in nicotine addiction and nAChR desensitization. Experimental and clinical data largely indicate long-lasting effects of nicotine and nicotinic agonists that imply a neuroprotective/neurotrophic role of nAChR activation, involving mainly alpha7 and alpha4beta2 nAChR subtypes, as evidenced using selective nAChR agonists. Compounds interacting with neuronal nAChRs have the potential to be neuroprotective and treatment with nAChR agonists elicits long-lasting neurotrophic effects, e.g. improvement of cognitive performance in a variety of behavioural tests in rats, monkeys and humans. Nicotine addiction, which is mediated by interaction with nACh receptors, is believed to involve the modification of signalling cascades that modulate synaptic plasticity and gene expression. Desensitization, in addition to protecting cells from uncontrolled excitation, is recently considered as a form of signal plasticity. nAChR can generate these longe-lasting effects by elaboration of complex intracellular signals that mediate medium to long-term events crucial for neuronal maintenance, survival and regeneration. Although a comprehensive survey of the gene-based molecular mechanisms that underlie nicotine effects has yet not been performed a growing amount of data is beginning to improve our understanding of signalling mechanisms that lead to neurotrophic/neuroprotective responses. Evidence for an involvement of the fibroblast growth factor-2 gene in nAChR mechanisms mediating neuronal survival, trophism and plasticity has been obtained. However, more work is needed to establish the mechanisms involved in the effects of nicotinic receptor subtype activation from cognition-enhancing and neurotrophic effects to smoking behaviour and to determine more precisely the therapeutic objectives in potential nicotinic drug treatments of neurodegenerative diseases.

Brain pH has a significant impact on human postmortem hippocampal gene expression profiles

Studies of neurobiological disorders in the brain, including schizophrenia, rely on the use of postmortem brain tissues, in which an understanding of the effects of various pre- and postmortem variables on gene expression is critical. In several different brain regions, pH has been shown to have a large effect on postmortem brain gene expression patterns. One region that has not yet been evaluated in such studies is the hippocampus, a region often implicated in schizophrenia research. In the present study, we show that postmortem brain pH is similar across different brain regions. Brain pH accounted for greater variation in hippocampal gene expression profiles than any other parameter evaluated, including gender and schizophrenia. The predictive value of brain pH in an independent sample set was also greater than the disease, demonstrating that pH represents one of the most important control parameters in human postmortem gene expression studies in schizophrenia.