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  • Björklund, Mikael (Helsingin yliopisto, 2004)
  • Greco, Dario (Helsingin yliopisto, 2009)
    The time of the large sequencing projects has enabled unprecedented possibilities of investigating more complex aspects of living organisms. Among the high-throughput technologies based on the genomic sequences, the DNA microarrays are widely used for many purposes, including the measurement of the relative quantity of the messenger RNAs. However, the reliability of microarrays has been strongly doubted as robust analysis of the complex microarray output data has been developed only after the technology had already been spread in the community. An objective of this study consisted of increasing the performance of microarrays, and was measured by the successful validation of the results by independent techniques. To this end, emphasis has been given to the possibility of selecting candidate genes with remarkable biological significance within specific experimental design. Along with literature evidence, the re-annotation of the probes and model-based normalization algorithms were found to be beneficial when analyzing Affymetrix GeneChip data. Typically, the analysis of microarrays aims at selecting genes whose expression is significantly different in different conditions followed by grouping them in functional categories, enabling a biological interpretation of the results. Another approach investigates the global differences in the expression of functionally related groups of genes. Here, this technique has been effective in discovering patterns related to temporal changes during infection of human cells. Another aspect explored in this thesis is related to the possibility of combining independent gene expression data for creating a catalog of genes that are selectively expressed in healthy human tissues. Not all the genes present in human cells are active; some involved in basic activities (named housekeeping genes) are expressed ubiquitously. Other genes (named tissue-selective genes) provide more specific functions and they are expressed preferably in certain cell types or tissues. Defining the tissue-selective genes is also important as these genes can cause disease with phenotype in the tissues where they are expressed. The hypothesis that gene expression could be used as a measure of the relatedness of the tissues has been also proved. Microarray experiments provide long lists of candidate genes that are often difficult to interpret and prioritize. Extending the power of microarray results is possible by inferring the relationships of genes under certain conditions. Gene transcription is constantly regulated by the coordinated binding of proteins, named transcription factors, to specific portions of the its promoter sequence. In this study, the analysis of promoters from groups of candidate genes has been utilized for predicting gene networks and highlighting modules of transcription factors playing a central role in the regulation of their transcription. Specific modules have been found regulating the expression of genes selectively expressed in the hippocampus, an area of the brain having a central role in the Major Depression Disorder. Similarly, gene networks derived from microarray results have elucidated aspects of the development of the mesencephalon, another region of the brain involved in Parkinson Disease.
  • Tornberg, Janne (Helsingin yliopisto, 2006)
    The cation-Cl- cotransporter (CCC) family comprises of Na+-Cl- cotransporter (NCC), Na+-K+-2Cl- cotransporters (NKCC1-2), and four K+-Cl- cotransporters (KCC1-4). These proteins are involved in several physiological activities, such as cell volume regulation. In neuronal tissues, NKCC1 and KCC2 are important in determining the intracellular Cl- levels and hence the neuronal responses to inhibitory neurotransmitters GABA and glycine. One aim of the work was to elucidate the roles for CCC isoforms in the control of nervous system development. KCC2 mRNA was shown to be developmentally up-regulated and follow neuronal maturation, whereas NKCC1 and KCC4 transcripts were highly expressed in the proliferative zones of subcortical regions. KCC1 and KCC3 mRNA displayed low expression throughout the embryogenesis. These expression profiles suggest a role for CCC isoforms in maturation of synaptic responses and in the regulation of neuronal proliferation during embryogenesis. The major aim of this work was to study the biological consequences of KCC2-deficiency in the adult CNS, by generating transgenic mice retaining 15-20% of normal KCC2 levels. In addition, by using these mice as a tool for in vivo pharmacological analysis, we investigated the requirements for KCC2 in tonic versus phasic GABAA receptor-mediated inhibition. KCC2-deficient mice displayed normal reproduction and life span, but showed several behavioral abnormalities, including increased anxiety-like behavior, impaired performance in water maze, alterations in nociceptive processing, and increased seizure susceptibility. In contrast, the mice displayed apparently normal spontaneous locomotor activity and motor coordination. Pharmacological analysis of KCC2-deficient mice revealed reduced sensititivity to diazepam, but normal gaboxadol-induced sedation, neurosteroid hypnosis and alcohol-induced motor impairment. Electrophysiological recordings from CA1-CA3 subregions of the hippocampus showed that KCC2 deficiency affected the reversal potentials of both the phasic and tonic GABA currents, and that the tonic conductance was not affected. The results suggest that requirement for KCC2 in GABAergic neurotransmission may differ among several functional systems in the CNS, which is possibly due to the more critical role of KCC2 activity in phasic compared to tonic GABAergic inhibition.
  • Pykäläinen, Anette (Helsingin yliopisto, 2011)
    Biological membranes are tightly linked to the evolution of life, because they provide a way to concentrate molecules into partially closed compartments. The dynamic shaping of cellular membranes is essential for many physiological processes, including cell morphogenesis, motility, cytokinesis, endocytosis, and secretion. It is therefore essential to understand the structure of the membrane and recognize the players that directly sculpt the membrane and enable it to adopt different shapes. The actin cytoskeleton provides the force to push eukaryotic plasma membrane in order to form different protrusions or/and invaginations. It has now became evident that actin directly co-operates with many membrane sculptors, including BAR domain proteins, in these important events. However, the molecular mechanisms behind BAR domain function and the differences between the members of this large protein family remain largely unresolved. In this thesis, the structure and functions of the I-BAR domain family members IRSp53 and MIM were thoroughly analyzed. By using several methods such as electron microscopy and systematic mutagenesis, we showed that these I-BAR domain proteins bind to PI(4,5)P2-rich membranes, generate negative membrane curvature and are involved in the formation of plasma membrane protrusions in cells e.g. filopodia. Importantly, we characterized a novel member of the BAR-domain superfamily which we named Pinkbar. We revealed that Pinkbar is specifically expressed in kidney and epithelial cells, and it localizes to Rab13-positive vesicles in intestinal epithelial cells. Remarkably, we learned that the I-BAR domain of Pinkbar does not generate membrane curvature but instead stabilizes planar membranes. Based on structural, mutagenesis and biochemical work we present a model for the mechanism of the novel membrane deforming activity of Pinkbar. Collectively, this work describes the mechanism by which I-BAR domain proteins deform membranes and provides new information about the biological roles of these proteins. Intriguingly, this work also gives evidence that significant functional plasticity exists within the I-BAR domain family. I-BAR proteins can either generate negative membrane curvature or stabilize planar membrane sheets, depending on the specific structural properties of their I-BAR domains. The results presented in this thesis expand our knowledge on membrane sculpting mechanisms and shows for the first time how flat membranes can be generated in cells.
  • Alakulppi, Noora (Helsingin yliopisto, 2008)
    Kidney transplantation (Tx) is the treatment of choice for end stage renal disease. Immunosuppressive medications are given to prevent an immunological rejection of the transplant. However, immunosuppressive drugs increase e.g. the risk of infection, cancer or nephrotoxicity. A major genetic contributors to immunological acceptance of the graft are human leukocyte antigen (HLA) genes. Also other non-HLA gene polymorphisms may predict the future risk of complications before Tx, possibly enabling individualised immunotherapy. Graft function after Tx is monitored using non-specific clinical symptoms and laboratory markers. The definitive diagnosis of graft rejection however relies on a biopsy of the graft. In the acute rejection (AR) diagnostics there is a need for an alternative to biopsy that would be an easily repeatable and simple method for regular use. Frequent surveillance of acute or subclinical rejection (SCR) may improve long-term function. In this thesis, associations between cytokine and thrombosis associated candidate genes and the outcome of kidney Tx were studied. Cytotoxic and co-stimulatory T lymphocyte molecule gene expression biomarkers for the diagnosis of the AR and the SCR were also investigated. We found that polymorphisms in the cytokine genes tumor necrosis factor and interleukin 10 (IL10) of the recipients were associated with AR. In addition, certain IL10 gene polymorphisms of the donors were associated with the incidence of cytomegalovirus infection and occurrence of later infection in a subpopulation of recipients. Further, polymorphisms in genes related to the risk of thrombosis and those of certain cytokines were not associated with the occurrence of thrombosis, infarction, AR or graft survival. In the study of biomarkers for AR, whole blood samples were prospectively collected from adult kidney Tx patients. With real-time quantitative PCR (RT-QPCR) gene expression quantities of CD154 and ICOS differentiated the patients with AR from those without, but not from the patients with other causes of graft dysfunction. Biomarkers for SCR were studied in paediatric kidney Tx patients. We used RT-QPCR to quantify the gene expression of immunological candidate genes in a low-density array format. In addition, we used RT-QPCR to validate the results of the microarray analysis. No gene marker differentiated patients with SCR from those without SCR. This research demonstrates the lack of robust markers among polymorphisms or biomarkers in investigated genes that could be included in routine analysis in a clinical laboratory. In genetic studies, kidney Tx can be regarded as a complex trait, i.e. several environmental and genetic factors may determine its outcome. A number of currently unknown genetic factors probably influence the results of Tx.
  • Palo, Jukka (Helsingin yliopisto, 2003)
  • Manninen, Outi (Helsingin yliopisto, 2000)
  • Broberg, Martin (Helsingin yliopisto, 2015)
    The interactions between phytopathogenic bacteria and their host plants can be characterized as an intricate web of signals and appropriate responses. Phytopathogenic soft rot bacteria occur globally, causing disease in Solanum tuberosum (potato) and other tubular staple foods in both the field and storage. One widely studied soft rot bacterium is Pectobacterium wasabiae, which has been identified in Eutrema wasabi (wasabi) plants in Japan and in potatoes in Finland. Generally, the interactions between this type of bacterium and host plants are characterized by maceration of plant tissue, due to the actions of secreted plant cell wall degrading enzymes (PCWDE), and the induction of phytohormone dependent defenses in the plants. The maceration of plant tissue involves the release of pectic oligogalacturonides (OGs) from plant cell walls. OGs have been identified as important signaling compounds, inducing the expression of a variety of defense-related genes. As the bacterial infection advances, the bacteria coordinate the production of virulence factors by utilizing regulatory proteins that modulate the transcriptome. Transcriptomic analyses have been used extensively in past studies to identify regulatory networks and signaling pathways, and these studies have provided insights into the processes underlying plant-pathogen interactions. The novel scientific results of this dissertation are derived from a combination of transcriptomic, genomic, genetic, and phenotypic analyses. This study analyzed various aspects of plant-pathogen interactions. The central bacterial model used was P. wasabiae, and the model plant of interest was Arabidopsis thaliana. This study characterized the genome of P. wasabiae via sequencing and bioinformatics analysis. Various virulence associated genes and operons, such as two distinct type 6 secretion systems, were identified and annotated. The bacterium was found to in fact be more related to P. wasabiae than Pectobacterium carotovorum, which the strain originally had been named after. Furthermore, a combination of functional genetics and transcriptomic methods, such as reverse transcription quantitative PCR (RT-qPCR) and microarrays, were used to determine the regulons controlled by the proteins ExpA and RsmA in P. wasabiae. These two proteins have been identified as important for the virulence of several γ-proteobacterial pathogens. This study analyzed the regulons via the use of three mutants: expA, rsmA, and an expA rsmA double mutant (DM). Overlapping and independently regulated targets were identified between ExpA and RsmA. Phenotypic assays for motility, growth, PCWDE activity, and virulence confirmed the transcriptomic data for the mutant strains. Novel findings included reduction of swimming motility in agar medium for P. wasabiae expA and rsmA mutants. In addition, the DM exhibited enhanced virulence and fitness in planta compared to either single mutant. Via analysis of transcriptomic data, a subset of genes was identified as affected in expression by an expA mutation independently of the presence of rsmA. The relatively unexplored role of short OGs (with a degree of polymerization (DP) less than 10) in damage-associated molecular pattern (DAMP) signaling in A. thaliana was characterized in this study. Comparative gene expression profiling based on RNA sequencing and RT-qPCR was performed on RNA harvested from plants treated with short OGs or with a mock suspension. Phenotypic assays confirmed the gene expression data. In a meta-data analysis, the resulting RNA sequencing and RT-qPCR data were compared with gene expression data from previous studies, in which long OGs (DP more than 10) were used to treat plants. This work demonstrated that short and long OGs induce genes and genesets associated with pathogen defense and phytohormone signaling, whereas reducing plant growth and development. The transcriptomic data of this study suggests that plant treatment with a mixture of short or long OGs yields a more pronounced and varied modulation of global gene expression, compared to treatment with only trimeric OGs. The regulation of the virulence of P. wasabiae, and the DAMP signaling triggered by plant cell wall damage in A. thaliana, are elements of the interactions between the plant and pathogen. The studies presented in this dissertation provide novel information about these two biological processes and highlights their connection.
  • DeFaveri, Jacquelin (Helsingin yliopisto, 2013)
    Spatial differentiation in phenotypic traits is commonly observed in the wild, but both the proximate (cf. environmental vs. genetic) and ultimate (cf. adaptive vs. stochastic) causes underlying this differentiation often remain obscure. Studies focussed on the genetic basis of this differentiation can inform us about these issues, especially if the genetic variants under investigation can be linked with information about their functional role(s) and/or gauged against expectations derived from evolutionary null models. However, due to the difficulties in deciphering and studying the genetic basis of phenotypic variability and differentiation in quantitative traits especially in marine vertebrates the occurrence and scale of local adaptation in them is still poorly understood. Yet, identifying patterns of adaptive divergence and the ecological factors that have contributed to them is essential for understanding how natural selection can maintain local adaptation in the face of gene flow. In this thesis I used a genome-wide set of candidate gene-based microsatellite markers, in combination with quantitative genetic approaches, to explore the patterns of adaptive diversity and divergence among stickleback populations from a variety of habitats ranging from global to local geographic scales. Through comparisons of several independent, isolated pairs of marine and freshwater populations, I found that selection is acting on many genomic regions harbouring genes whose putative functions are related to a wide variety of physiological processes. I also found indications that adaptation to freshwater environments may have been achieved through different genetic pathways in different populations. Importantly, the design of my study was such that alternative demographic explanations for observed patterns could be excluded. Focussing on populations within the physically continuous, yet environmentally heterogeneous marine habitat, I further investigated whether selection is acting strongly enough to promote adaptive population structuring despite high gene flow. Signatures of selection were detected in several candidate genes, along with clear evidence for adaptive differentiation in a phenotypic trait (lateral plate number). Analysis of population structure with only these outlier loci uncovered a higher degree of differentiation than was evident in neutral loci, and in some cases, patterns of adaptive differentiation were correlated with environmental variables likely to act as selective agents in the marine environment (viz. salinity and temperature). Evidence for local adaptation among Baltic Sea sticklebacks was confirmed in a common garden experiment, which demonstrated a loss of fitness in populations native to low salinity regions when exposed to high salinity treatments. Overall, the results from this thesis point to the conclusion that adaptive genetic and phenotypic differentiation is common, even in continuous marine habitats lacking obvious physical barriers to dispersal and gene flow. These results are particularly noteworthy, firstly from the perspective that earlier studies conducted using neutral marker genes have largely overlooked the patterns and magnitude of divergence, and secondly due to the comprehensive geographic coverage of the investigations.
  • Haimila, Katri (Helsingin yliopisto, 2009)
    Co-stimulatory signals are essential for the activation of naïve T cells and productive immune response. Naïve T cells receive first, antigen-specific signal through T cell receptor. Co-stimulatory receptors provide the second signal which can be either activating or inhibitory. The balance between signals determines the outcome of an immune response. CD28 is crucial for T cell activation; whereas cytotoxic T lymphocyte associated antigen 4 (CTLA4) mediates critical inhibitory signal. Inducible co-stimulator (ICOS) augments cytokine expression and plays role in immunoglobulin class switching. Programmed cell death 1 (PDCD1) acts as negative regulator of T cell proliferation and cytokine responses. The co-stimulatory receptor pathways are potentially involved in self-tolerance and thus, they provide a promising therapeutic strategy for autoimmune diseases and transplantation. The genes encoding CD28, CTLA4 and ICOS are located adjacently in the chromosome region 2q33. The PDCD1 gene maps further, to the region 2q37. CTLA4 and PDCD1 are associated with the risk of a few autoimmune diseases. There is strong linkage disequilibrium (LD) on the 2q33 region; the whole gene of CD28 exists in its own LD block but CTLA4 and the 5' part of ICOS are within a same LD block. The 3' part of ICOS and PDCD1 are in their own separate LD blocks. Extended haplotypes covering the 2q33 region can be identified. This study focuses on immune related conditions like coeliac disease (CD) which is a chronic inflammatory disease with autoimmune features. Immunoglobulin A deficiency (IgAD) belongs to the group of primary antibody deficiencies characterised by reduced levels of immunoglobulins. IgAD co-occurs often with coeliac disease. Renal transplantation is needed in the end stage kidney diseases. Transplantation causes strong immune response which is tried to suppress with drugs. All these conditions are multifactorial with complex genetic background and multiple environmental factors affecting the outcome. We have screened ICOS for polymorphisms by sequencing the exon regions. We detected 11 new variants and determined their frequencies in Finnish population. We have measured linkage disequilibrium on the 2q33 region in Finnish as well as other European populations and observed conserved haplotypes. We analysed genetic association and linkage of the co-stimulatory receptor gene region aiming to study if it is a common risk locus for immune diseases. The 2q33 region was replicated to be linked to coeliac disease in Finnish population and CTLA4-ICOS haplotypes were found to be associated with CD and IgAD being the first non-HLA risk locus common for CD and immunodeficiencies. We also showed association between ICOS and the outcome of kidney transplantation. Our results suggest new evidence for CTLA4-ICOS gene region to be involved in susceptibility of coeliac disease. The earlier published contradictory association results can be explained by involvement of both CTLA4 and ICOS in disease susceptibility. The pattern of variants acting together rather than a single polymorphism may confer the disease risk. These genes may predispose also to immunodeficiencies as well as decreased graft survival and delayed graft function. Consequently, the present study indicates that like the well established HLA locus, the co-stimulatory receptor genes predispose to variety of immune disorders.
  • Jaatinen, Taina (Helsingin yliopisto, 2002)
  • Kukkonen, Mari (Helsingin yliopisto, 2013)
    Both tobacco smoke and asbestos fibers enter the body mainly by inhalation. In the lungs, they may evoke oxidative stress, alter the protease-antiprotease balance, induce innate and adaptive immune responses, and create persistent inflammation leading eventually to lung injury. The type and severity of lung injury induced by foreign compounds varies greatly between individuals, even with similar exposure history. These differences are believed to originate from the complex interplay between genetic, epigenetic, environmental, and life course factors. In this thesis, the roles of several genes encoding proteins involved in xenobiotic metabolism (EPHX1, GSTM1, GSTM3, GSTP1, GSTT1, and NAT2), protease-antiprotease balance (MMP1, MMP9, MMP12, SERPINE2, and TIMP2), innate immunity (NLRP3 and CARD8), and inflammation (TNF, TGFB1, and GC) were studied in the development of asbestos and tobacco smoke exposure related nonmalignant pleural and pulmonary changes, peripheral obstruction, and impairment of pulmonary diffusing capacity in two clinically and radiologically examined cohorts of Finnish construction workers. The results indicate that polymorphisms of xenobiotic metabolizing genes are potential modifiers of the risk of developing pleural and pulmonary changes related to asbestos and tobacco smoke exposures. The most convincing evidence came from GSTT1; the deletion of this gene was significantly associated with several types of changes in the whole study population and in both of the study cohorts separately. In addition, certain genotype in GSTM3 gene was associated with lowered pulmonary function. Furthermore, gene polymorphisms in metalloproteinase MMP9, metalloproteinase inhibitor TIMP2, and inflammatory cytokines TNF and TGFB1 were associated with different emphysema subtypes and/or lung function. Together with the finding that certain genotypes of the serine protease inhibitor gene SERPINE2 predispose to panlobular emphysema, they imply that polymorphisms of genes involved in protease-antiprotease balance likely contribute to the development of pulmonary emphysema and bronchial obstruction, and different molecular mechanisms may explain the development of different emphysema subtypes. The present results also indicate that genetic variation in innate immunity related genes might have an important role in coping with asbestos exposure. One finding supporting this view was the association between interstitial lung fibrosis and polymorphism of NLRP3, an essential component of the NLRP3 inflammasome complex. Polymorphism in another member of the complex, CARD8, was associated with the greatest thickness of pleural plaques. In conclusion, the results of this thesis work show that genetic variation is an important modifier of the risks for developing non-malignant lung diseases related to external exposures. The present findings may also help to clarify the molecular mechanisms behind these diseases, expediting their prevention and the development of more efficient therapies.
  • Holopainen, Päivi (Helsingin yliopisto, 2002)
  • Kostia, Silja (Helsingin yliopisto, 2000)
  • Junnila, Siina (Helsingin yliopisto, 2009)
    Gastric cancer is the fourth most common cancer and the second most common cause of cancer-related death worldwide. Due to lack of early symptoms, gastric cancer is characterized by late stage diagnosis and unsatisfactory options for curative treatment. Several genomic alterations have been identified in gastric cancer, but the major factors contributing to initiation and progression of gastric cancer remain poorly known. Gene copy number alterations play a key role in the development of gastric cancer, and a change in gene copy number is one of the fundamental mechanisms for a cancer cell to control the expression of potential oncogenes and tumor suppressor genes. This thesis aims at clarifying the complex genomic alterations of gastric cancer to identify novel molecular biomarkers for diagnostic purposes as well as for targeted treatment. To highlight genes of potential biological and clinical relevance, we carried out a systematic microarray-based survey of gene expression and copy number levels in primary gastric tumors and gastric cancer cell lines. Results were validated using immunohistochemistry, real-time qRT-PCR, and affinity capture-based transcript (TRAC) assay. Altogether 192 clinical gastric tissue samples and 7 gastric cancer cell lines were included in this study. Multiple chromosomal regions with recurrent copy number alterations were detected. The most frequent chromosomal alterations included gains at 7q, 8q, 17q, 19q, and 20q and losses at 9p, 18q, and 21q. Distinctive patterns of copy number alterations were detected for different histological subtypes (intestinal and diffuse) and for cancers located in different parts of the stomach. The impact of copy number alterations on gene expression was significant, as 6-10% of genes located in the regions of gains and losses also showed concomitant alterations in their expression. By combining the information from the DNA- and RNA-level analyses many novel gastric cancer-related genes, such as ALPK2, ENAH, HHIPL2, and OSMR, were identified. Independent genome-wide gene expression analysis of Finnish and Japanese gastric tumors revealed an additional set of genes that was differentially expressed in cancerous gastric tissues compared with normal tissue. Overexpression of one of these genes, CXCL1, was associated with an improved survival of gastric cancer. Thus, using an integrative microarray analysis, several novel genes were identified that may be critically important for gastric carcinogenesis. Further studies of these genes may lead to novel biomarkers for gastric cancer diagnosis and targeted therapy.
  • Sencilo, Ana (Helsingin yliopisto, 2014)
    Viruses are ubiquitous, abundant and diverse members of the biosphere. Numerous sequencing projects focusing on isolated viruses and uncultured viral communities (metaviromes) have demonstrated that viruses harbor unprecedented genotypic richness. The genomics of some viruses, for example, tailed bacteriophages infecting several widely known hosts from moderate environments, has been studied relatively well. However, viruses are known to reside in various environments, including the extreme ones, and our knowledge on the genetic make-up of these viral populations is very superficial. In this PhD thesis, the genomics of the archaeal and bacterial viruses isolated from previously sparsely sampled extreme aquatic environments was studied. The genomes of altogether twenty haloarchaeal pleomorphic and tailed viruses from hypersaline environments as well as tailed bacteriophages from the sea ice were sequenced and analyzed. The largest portion of the genomic sequences was shown to encode proteins with no homologues in current databases emphasizing genetic distinctiveness of the studied viruses from the ones described previously. However, all tailed viruses from both hypersaline environment and sea ice were predicted to have a cluster of genes coding for functional analogues of virion assembly and structure components of other tailed phages. Overall arrangement of this gene cluster was conserved. Haloarchaeal pleomorphic viruses were also shown to share a conserved group of genes coding for the structural and hypothetical proteins. Based on the genome organization, haloarchaeal pleomorphic viruses were classified into three subgroups. The members of one of the subgroups were demonstrated to have an unusual genome type, consisting of single-stranded and double-stranded DNA regions. In one of the viruses switches between the regions were found to be associated with a conserved DNA motif. This genome type has not been reported previously for other viruses infecting prokaryotes. To conclude, annotation and analyses of the viral genome contents performed in this PhD thesis offered a glimpse into the diversity of putative functions of the studied viruses. Conducted comparative genomics analyses revealed different levels of relatedness among the viruses within the studied groups and similarities shared with other earlier described viruses. Overall, this work provided new insights into the genomics of understudied viruses residing in hypersaline and cold aquatic environments.
  • Bäckström, Pia (Helsingin yliopisto, 2006)
    The characteristics of drug addiction include compulsive drug use despite negative consequences and re-occurring relapses, returns to drug use after a period of abstinence. Therefore, relapse prevention is one of the major challenges for the treatment of drug addiction. There are three main factors capable of inducing craving for drugs and triggering relapse long after cessation of drug use and dissipation of physical withdrawal signs: stress, re-exposure to the drug, and environmental stimuli (cues) that have been previously associated with drug use. The neurotransmitters dopamine and glutamate have been implicated in the modulation of drug-seeking behavior. The aim of this project was to examine the role of glutamatergic neurotransmission in relapse triggered by conditioned drug-associated stimuli. The focus was on clarifying whether relapse to drug seeking can be attenuated by blockade of glutamate receptors. In addition, as the nucleus accumbens has been proposed to participate in the modulation of drug-seeking behavior, the effects of glutamate receptor blockade in this brain structure on cue-induced relapse were investigated. The studies employed animals models in which rats were trained to press a lever in a test cage to obtain alcohol or intravenous cocaine. Drug availability was paired with distinct olfactory, auditory, or visual stimuli. This phase was followed by extinction training, during which lever presses did not result in the presentation of the drug or the drug-associated stimuli. Extinction training led to a gradual decrease in the number of lever presses during test sessions. Relapse was triggered by presenting the rats with the drug-associated stimuli in the absence of alcohol or cocaine. The drug-associated stimuli were alone capable of inducing resumption of lever pressing and maintaining this behavior during repeated testing. The number of lever presses during a session represented the intensity of drug-seeking and relapse behavior. The results suggest that glutamatergic neurotransmission is involved in the modulation of drug-seeking behavior. Both alcohol and cocaine relapse were attenuated by systemic pretreatment with glutamate receptor antagonists. However, differences were found in the ability of ionotropic AMPA/kainate and NMDA receptor antagonists to regulate drug-seeking behavior. The AMPA/kainate antagonists CNQX and NBQX, and L-701,324, an antagonist with affinity for the glycine site of the NMDA receptor, attenuated cue-induced drug seeking, whereas the competitive NMDA antagonist CGP39551 and the NMDA channel blocker MK-801 were without effect. MPEP, an antagonist at metabotropic mGlu5 glutamate receptors, also decreased drug seeking, but its administration was found to lead to conditioned suppression of behavior during subsequent treatment sessions, suggesting that MPEP may have undesirable side effects. The mGluR2/3 agonist LY379268 and the mGluR8 agonist (S)-3,4-DCPG decreased both cue-induced relapse to alcohol drinking and alcohol consumption. Control experiments showed however that administration of the agonists was accompanied by motor suppression limiting their usefulness. Administration of the AMPA/kainate antagonist CNQX, the NMDA antagonist D-AP5, and the mGluR5 antagonist MPEP into the nucleus accumbens resulted also in a decrease in drug-seeking behavior, suggesting that the nucleus accumbens is at least one of the anatomical sites regulating drug seeking and mediating the effects of glutamate receptor antagonists on this behavior.