Increased spread and replication efficiency of Listeria monocytogenes in organotypic brain-slices is related to multilocus variable number of tandem repeat analysis (MLVA) complex.

BACKGROUND Listeria (L.) monocytogenes causes fatal infections in many species including ruminants and humans. In ruminants, rhombencephalitis is the most prevalent form of listeriosis. Using multilocus variable number tandem repeat analysis (MLVA) we recently showed that L. monocytogenes isolates from ruminant rhombencephalitis cases are distributed over three genetic complexes (designated A, B and C). However, the majority of rhombencephalitis strains and virtually all those isolated from cattle cluster in MLVA complex A, indicating that strains of this complex may have increased neurotropism and neurovirulence. The aim of this study was to investigate whether ruminant rhombencephalitis strains have an increased ability to propagate in the bovine hippocampal brain-slice model and can be discriminated from strains of other sources. For this study, forty-seven strains were selected and assayed on brain-slice cultures, a bovine macrophage cell line (BoMac) and a human colorectal adenocarcinoma cell line (Caco-2). They were isolated from ruminant rhombencephalitis cases (n = 21) and other sources including the environment, food, human neurolisteriosis cases and ruminant/human non-encephalitic infection cases (n = 26). RESULTS All but one L. monocytogenes strain replicated in brain slices, irrespectively of the source of the isolate or MLVA complex. The replication of strains from MLVA complex A was increased in hippocampal brain-slice cultures compared to complex C. Immunofluorescence revealed that microglia are the main target cells for L. monocytogenes and that strains from MLVA complex A caused larger infection foci than strains from MLVA complex C. Additionally, they caused larger plaques in BoMac cells, but not CaCo-2 cells. CONCLUSIONS Our brain slice model data shows that all L. monocytogenes strains should be considered potentially neurovirulent. Secondly, encephalitis strains cannot be conclusively discriminated from non-encephalitis strains with the bovine organotypic brain slice model. The data indicates that MLVA complex A strains are particularly adept at establishing encephalitis possibly by virtue of their higher resistance to antibacterial defense mechanisms in microglia cells, the main target of L. monocytogenes.

Modeling immune functions of the mouse blood-cerebrospinal fluid barrier in vitro: primary rather than immortalized mouse choroid plexus epithelial cells are suited to study immune cell migration across this brain barrier.

BACKGROUND The blood-cerebrospinal fluid barrier (BCSFB) established by the choroid plexus (CP) epithelium has been recognized as a potential entry site of immune cells into the central nervous system during immunosurveillance and neuroinflammation. The location of the choroid plexus impedes in vivo analysis of immune cell trafficking across the BCSFB. Thus, research on cellular and molecular mechanisms of immune cell migration across the BCSFB is largely limited to in vitro models. In addition to forming contact-inhibited epithelial monolayers that express adhesion molecules, the optimal in vitro model must establish a tight permeability barrier as this influences immune cell diapedesis. METHODS We compared cell line models of the mouse BCSFB derived from the Immortomouse(®) and the ECPC4 line to primary mouse choroid plexus epithelial cell (pmCPEC) cultures for their ability to establish differentiated and tight in vitro models of the BCSFB. RESULTS We found that inducible cell line models established from the Immortomouse(®) or the ECPC4 tumor cell line did not express characteristic epithelial proteins such as cytokeratin and E-cadherin and failed to reproducibly establish contact-inhibited epithelial monolayers that formed a tight permeability barrier. In contrast, cultures of highly-purified pmCPECs expressed cytokeratin and displayed mature BCSFB characteristic junctional complexes as visualized by the junctional localization of E-cadherin, β-catenin and claudins-1, -2, -3 and -11. pmCPECs formed a tight barrier with low permeability and high electrical resistance. When grown in inverted filter cultures, pmCPECs were suitable to study T cell migration from the basolateral to the apical side of the BCSFB, thus correctly modelling in vivo migration of immune cells from the blood to the CSF. CONCLUSIONS Our study excludes inducible and tumor cell line mouse models as suitable to study immune functions of the BCSFB in vitro. Rather, we introduce here an in vitro inverted filter model of the primary mouse BCSFB suited to study the cellular and molecular mechanisms mediating immune cell migration across the BCSFB during immunosurveillance and neuroinflammation.

Allogeneic haematopoietic stem cell transplantation for mitochondrial neurogastrointestinal encephalomyopathy.

Haematopoietic stem cell transplantation has been proposed as treatment for mitochondrial neurogastrointestinal encephalomyopathy, a rare fatal autosomal recessive disease due to TYMP mutations that result in thymidine phosphorylase deficiency. We conducted a retrospective analysis of all known patients suffering from mitochondrial neurogastrointestinal encephalomyopathy who underwent allogeneic haematopoietic stem cell transplantation between 2005 and 2011. Twenty-four patients, 11 males and 13 females, median age 25 years (range 10-41 years) treated with haematopoietic stem cell transplantation from related (n = 9) or unrelated donors (n = 15) in 15 institutions worldwide were analysed for outcome and its associated factors. Overall, 9 of 24 patients (37.5%) were alive at last follow-up with a median follow-up of these surviving patients of 1430 days. Deaths were attributed to transplant in nine (including two after a second transplant due to graft failure), and to mitochondrial neurogastrointestinal encephalomyopathy in six patients. Thymidine phosphorylase activity rose from undetectable to normal levels (median 697 nmol/h/mg protein, range 262-1285) in all survivors. Seven patients (29%) who were engrafted and living more than 2 years after transplantation, showed improvement of body mass index, gastrointestinal manifestations, and peripheral neuropathy. Univariate statistical analysis demonstrated that survival was associated with two defined pre-transplant characteristics: human leukocyte antigen match (10/10 versus <10/10) and disease characteristics (liver disease, history of gastrointestinal pseudo-obstruction or both). Allogeneic haematopoietic stem cell transplantation can restore thymidine phosphorylase enzyme function in patients with mitochondrial neurogastrointestinal encephalomyopathy and improve clinical manifestations of mitochondrial neurogastrointestinal encephalomyopathy in the long term. Allogeneic haematopoietic stem cell transplantation should be considered for selected patients with an optimal donor.

Changes in miRNA Expression in a Model of Microcephaly

miRNAs function to regulate gene expression through post-transcriptional mechanisms to potentially regulate multiple aspects of physiology and development. Whole transcriptome analysis has been conducted on the citron kinase mutant rat, a mutant that shows decreases in brain growth and development. The resulting differences in RNA between mutant and wild-type controls can be used to identify genetic pathways that may be regulated differentially in normal compared to abnormal neurogenesis. The goal of this thesis was to verify, with quantitative reverse transcriptase polymerase chain reaction (qRT-PCR), changes in miRNA expression in Cit-k mutants and wild types. In addition to confirming miRNA expression changes, bio-informatics software TargetScan 5.1 was used to identify potential mRNA targets of the differentially expressed miRNAs. The miRNAs that were confirmed to change include: rno-miR-466c, mmu-miR-493, mmu-miR-297a, hsa-miR-765, and hsa-miR-1270. The TargetScan analysis revealed 347 potential targets which have known roles in development. A subset of these potential targets include genes involved in the Wnt signaling pathway which is known to be an important regulator of stem cell development.

Cerebellar mechanisms for motor learning: Testing predictions from a large-scale computer simulation

The cerebellum is the major brain structure that contributes to our ability to improve movements through learning and experience. We have combined computer simulations with behavioral and lesion studies to investigate how modification of synaptic strength at two different sites within the cerebellum contributes to a simple form of motor learning—Pavlovian conditioning of the eyelid response. These studies are based on the wealth of knowledge about the intrinsic circuitry and physiology of the cerebellum and the straightforward manner in which this circuitry is engaged during eyelid conditioning. Thus, our simulations are constrained by the well-characterized synaptic organization of the cerebellum and further, the activity of cerebellar inputs during simulated eyelid conditioning is based on existing recording data. These simulations have allowed us to make two important predictions regarding the mechanisms underlying cerebellar function, which we have tested and confirmed with behavioral studies. The first prediction describes the mechanisms by which one of the sites of synaptic modification, the granule to Purkinje cell synapses (gr → Pkj) of the cerebellar cortex, could generate two time-dependent properties of eyelid conditioning—response timing and the ISI function. An empirical test of this prediction using small, electrolytic lesions of the cerebellar cortex revealed the pattern of results predicted by the simulations. The second prediction made by the simulations is that modification of synaptic strength at the other site of plasticity, the mossy fiber to deep nuclei synapses (mf → nuc), is under the control of Purkinje cell activity. The analysis predicts that this property should confer mf → nuc synapses with resistance to extinction. Thus, while extinction processes erase plasticity at the first site, residual plasticity at mf → nuc synapses remains. The residual plasticity at the mf → nuc site confers the cerebellum with the capability for rapid relearning long after the learned behavior has been extinguished. We confirmed this prediction using a lesion technique that reversibly disconnected the cerebellar cortex at various stages during extinction and reacquisition of eyelid responses. The results of these studies represent significant progress toward a complete understanding of how the cerebellum contributes to motor learning. ^

Mechanisms of Ad-p53 induced apoptosis in human malignant glioma

Malignant brain tumors are one of the most challenging cancers affecting society today. In a recent survey, an estimated 17,000 annual cases were recorded with a staggering total of 13,300 deaths. A unique degree of heterogeneity typifies glial tumors and presents a challenge for solitary anti-neoplastic treatments. Tumors subsist as heterogeneous masses that progress through dysplasia to astrocytomas, mixed glioma and glioblastoma multiforme. Although traditional therapeutic approaches have provided increments of success, the median survival time remains 12 months. The urgency to improve upon current clinical protocols has encouraged alternative experimental strategies such as p53 adenoviral gene therapy (Ad-p53). This study addresses the efficacy of Ad-p53 for the treatment of glioma. Our model presents a tumor response that is unique among human cancers. Ad-p53 effectively induces apoptosis in mutant p53 expressing cells yet fails to do so in those with wildtype p53. In order to adopt Adp53 as a standard anti-cancer modality, we characterized the role of the tumor suppressor gene p53 in mediating apoptosis. We demonstrate that altering cellular p53 status through the introduction of a dominant negative mutant p53 (175H, 248W, 273H) sensitized cells to Ad-p53. We discovered that wild-type p53 expressing glioma cells retain the apoptotic machinery necessary to accomplish cell death, but have developed mechanisms that interfere with p53 signaling. Earlier studies have not addressed the mechanisms of Ad-p53 apoptosis nor the resistance exhibited by wild-type p53 glioma. To explain the divergent phenotypes, we identified apoptotic pathways activated and effectors of the response. We illustrated that modulation of the death receptor Fas/APO-1 is a principal means of Ad-p53 signaling that is impaired in wild-type p53 glioma. Moreover, the apoptotic response was found to be a multi-faceted process that engaged several caspases, most notably caspases -1, -3 and -8. Lastly, we assessed the ability of anti-apoptotic molecules Bcl-2 and CrmA to inhibit Ad-p53 apoptosis. These studies revealed that Ad-p53 is a powerful tool for inducing apoptosis that can be delayed but not inhibited by anti-apoptotic means. This work is critical for understanding the development of glioma and the phenotypic and genotypic alterations that account for tumor resistance. ^

The Role of EphA4 in Glial Scar Formation Following Injury

Although many areas of the brain lose their regenerative capacity with age, stem cell niches have been identified in both the subventricular zone (SVZ) along the lateral walls of the lateral ventricles and the subgranular zone (SGZ) of the dentate gyrus (Gage, 2000; Alvarez-Buylla et al., 2001; Alvarez-Buylla and Lim, 2004). The SVZ niche utilizes many mechanisms to determine the migration patterns of neuroblasts along the RMS into the olfactory bulb, one being Eph/ephrin signaling (Conover et al., 2000; Holmberg et al., 2005). EphA4-mediated signaling is necessary for axon guidance during development, and its continued expression in the SVZ niche suggests a regulatory role throughout adulthood. Previous studies have suggested that EphA4 plays a role in the regulation of astrocytic gliosis and glial scar formation, which inhibits axonal regeneration in these areas following spinal cord injury (Goldshmit et al., 2004). Blood vessels may also play an important role in SVZ cell proliferation and neuroblast migration following injury (Tavazoie et al., 2008; Yamashita et al., 2006). The goal of this project is to examine glial scar formation as well as the relationship between SVZ vasculature, neuroblasts, and neural stem cells in EphA4 +/+, EphA4 +/-, and EphA4 -/- mice following a needle stick injury in the cortex or striatum. The outcome of these experiments will determine whether invasive procedures such as injections will affect neuroblast migration and/or the organization of the SVZ.

Current United States stem cell policy considerations and a recommendation for an alternative policy based on guidelines from existing international policies

Embryonic stem cell research is a widely debated topic in modern politics and religion. Differing views on the fetal rights conflict with the rights of an embryo. Those who believe an embryo has the same human qualities as a fetus accordingly believe embryonic stem cell research is unethical because it destroys a potential human life. However, scientists advocate the embryo does not have human qualities and should be used for valuable research in the stem cell field. Stem cell research may lead to vast developments in medical treatments, including cancer and brain conditions and injuries that are currently incurable. ^ The current stem cell policy introduced by President Bush in 2001 in an attempt to balance the moral issues with the need for scientific research has broad negative implications on the furthering of stem cell research. There is a limited diversity of available stem cell lines, there may be constitutional issues, there is an increasing disparity between the public and private research spheres, and the U.S. is struggling to maintain its scientific community. The U.S. must develop a new stem cell research policy that will balance the interest of science and public health with the moral issues that concern the public. ^ The United Kingdom allows researchers great liberty in conducting research, permitting the creation of embryos for the sole purpose of research, while Germany is equally conservative in their laws, as their policies support the philosophy that all embryos deserve the protection of full life. The United States should adopt a policy that takes the "middle ground" approach and permit research on excess embryos created for IVF purposes, rather than simply discarding those potentially valuable research tools. ^

Federal regulation of human embryonic stem cell research

President George W. Bush's 2001 statement, which laid out guidelines for research that uses human embryonic stem cells to qualify for federal funding, intends to prevent new embryonic stem cell lines from being developed, by prohibiting the federal funding of research that uses embryonic stem cell lines other than those that existed at the time of the policy's inception and were approved by the National Institutes of Health. This policy raises questions of medical and technological ethics and the governments' role in making decisions regarding the advancement of science based on moral and political opinions. Federal stem cell usage policy directly affects scientific research efforts that are currently on the path to understanding the mechanisms of cell differentiation and could potentially offer answers and therapies for disabilities and many chronic diseases. By reviewing the current literature on the background information on human embryonic stem cells, including what they are, where they come from, how they are used for research purposes, and the ethical controversy surrounding their use, I have researched and reported the impact of the 2001 policy on medical research. ^ Both those who support the current policy on human embryonic stem cell research and those who are advocates for policy change have relevant arguments and varying opinions on human embryonic stem cell usage itself. The ethical implication of how embryonic stem cells are obtained has led to fierce debate. This paper presents many arguments for and against hESC research in addition to the policy governing their use. This analysis concludes that the current policy on federal funding of human embryonic stem cell research should be revised to allow research using new stem lines to be eligible for federal funding under specific guidelines. Supporting evidence for this recommendation is provided.^

INDUCED-PLURIPOTENT STEM-DERIVED NEURONAL PROGENITOR CELLS AS A NOVEL TREATMENT FOR NEURODEGENERATIVE DISEASES

Cellular therapies, as neuronal progenitor (NP) cells grafting, are promising therapies for patients affected with neurodegenerative diseases like Creutzfeldt-Jakob Disease (CJD). At this time there is no effective treatment or cure for CJD. The disease is inevitably fatal and affected people usually die within months of the appearance of the first clinical symptoms. Compelling evidence indicate that the hallmark event in the disease is the conversion of the normal prion protein (termed PrPC) into the disease-associated, misfolded form (called PrPSc). Thus, a reasonable therapeutic target would be to prevent PrP misfolding and prion replication. This strategy has been applied with poor results since at the time of clinical intervention substantial brain damage has been done. It seems that a more effective treatment aimed at patients with established symptoms of CJD would need to stop further brain degeneration or even recover some of the previously lost brain tissue. The most promising possibility to recover brain tissue is the use of NPs that have the potential to replenish the nerve cells lost during the early stages of the disease. Advanced cellular therapies, beside their potential for cell replacement, might be used as biomaterials for drug delivery in order to stimulate cell survival or the resolution the disease. Also, implanted cells can be genetically manipulated to correct abnormalities causing disease or to make them more resistant to the toxic microenvironments present in damaged tissue. In recent years cell engineering has been within the scope of the scientific and general community after the development of technologies able to “de-differentiate” somatic cells into induced-pluripotent stem (IPS) cells. This new tool permits the use of easy-to-reach cells like skin or blood cells as a primary material to obtain embryonic stem-like cells for cellular therapies, evading all ethical issues regarding the use of human embryos as a source of embryonic stem cells. The complete work proposes to implant IPS-derived NP cells into the brain of prion-infected animals to evaluate their therapeutic potential. Since it is well known that the expression of prion protein in the cell membrane is necessary for PrPSc mediated toxicity, we also want to determine if NPs lacking the prion protein have better survival rates once implanted into sick animals. The main objective of this work is to develop implantable neural precursor from IPS coming from animals lacking the prion protein. Specific aim 1: To develop and characterize cellular cultures of IPS cells from prp-/- mice. Fibroblasts from prp-/- animals will be reprogrammed using the four Yamanaka factors. IPS colonies will be selected and characterized by immunohistochemistry for markers of pluripotency. Their developmental capabilities will be evaluated by teratoma and embryoid body formation assays. Specific aim 2: To differentiate IPS cells to a neuronal lineage. IPS cells will be differentiated to a NP stage by the use of defined media culture conditions. NP cells will be characterized by their immunohistochemical profile as well as by their ability to differentiate into neuronal cells. Specific aim 3: Cellular labeling of neuronal progenitors cells for in vitro traceability. In order to track the cells once implanted in the host brain, they will be tagged with different methods such as lipophilic fluorescent tracers and transduction with GFP protein expression.

MicroRNA Regulation of Prostate Cancer Stem/Progenitor Cells and Prostate Cancer Development

Most human tumors contain a population of cells with stem cell properties, called cancer stem cells (CSCs), which are believed to be responsible for tumor establishment, metastasis, and resistance to clinical therapy. It’s crucial to understand the regulatory mechanisms unique to CSCs, so that we may design CSC-specific therapeutics. Recent discoveries of microRNA (miRNA) have provided a new avenue in understanding the regulatory mechanisms of cancer. However, how miRNAs may regulate CSCs is still poorly understood. Here, we present miRNA expression profiling in six populations of prostate cancer (PCa) stem/progenitor cells that possess distinct tumorigenic properties. Six miRNAs were identified to be commonly and differentially expressed, namely, four miRNAs (miR-34a, let-7b, miR-106a and miR-141) were under-expressed, and two miRNAs (miR-301 and miR-452) were over-expressed in the tumorigenic subsets compared to the corresponding marker-negative subpopulations. Among them, the expression patterns of miR-34, let-7b, miR-141 and miR-301 were further confirmed in the CD44+ human primary prostate cancer (HPCa) samples. We then showed that miR-34a functioned as a critical negative regulator in prostate CSCs and PCa development and metastasis. Over-expression of miR-34a in either bulk or CD44+ PCa cells significantly suppressed clonal expansion, tumor development and metastasis. Systemic delivery of miR-34a in tumor-bearing mice demonstrated a potent therapeutic effect again tumor progression and metastasis, leading to extended animal survival. Of great interest, we identified CD44 itself as a direct and relevant downstream target of miR-34a in mediating its tumor-inhibitory effects. Like miR-34a, let-7 manifests similar tumor suppressive effects in PCa cells. In addition, we observed differential mechanisms between let-7 and miR-34a on cell cycle, with miR-34a mainly inducing G1 cell-cycle arrest followed by cell senescence and let-7 inducing G2/M arrest. MiR-301, on the other hand, exerted a cell type dependent effect in regulating prostate CSC properties and PCa development. In summary, our work reveals that the prostate CSC populations display unique miRNA expression signatures and different miRNAs distinctively and coordinately regulate various aspects of CSC properties. Altogether, our results lay a scientific foundation for developing miRNA-based anti-cancer therapy.

PROSTATE CANCER STEM CELLS: DRUG TOLERANCE, EXPERIMENTAL RECONSTITUTION AND CASTRATION RESISTANCE

Prostate cancer (PCa) is one of the leading malignancies affecting men in the Western world. Although tremendous effort has been made towards understanding PCa development and developing clinical treatments in the past decades, the exact mechanisms of PCa are still not clearly understood. Emerging evidence has postulated that a population of stem cell-like cells inside a tumor, termed ‘cancer stem cells (CSCs)’, may be the cells responsible for tumor initiation, progression, recurrence, metastasis and therapy resistance. Like CSC studies in other cancer types, it has been reported that PCa also contains CSCs. However, there remain several unresolved questions that need to be clarified. First, the relationship between prostate CSCs (PCSCs) and therapy resistance (chemo- and radio-) is not known. Herein, we have found that not all CSCs are drug-tolerant, and not all drug-tolerant cells are CSCs. Second, whether primary human PCa (HPCa) actually contain PCSCs remains unclear, due to the well-known fact that we have yet to establish a reliable assay system that can reproducibly and faithfully reconstitute tumor regeneration from single HPCa cells. Herein, after utilizing more than 114 HPCa samples we have provided evidence that immortalized bone marrow-derived stromal cells (Hs5) can help dissociated HPCa cells generate undifferentiated tumors in immunodeficient NOD/SCID-IL2Rγ-/- mice, and the undifferentiated PCa cells seem to have a survival advantage to generate tumors. Third, the evolution of PCa from androgen dependent to the lethally castration resistant (CRPC) stage remains enigmatic, and the cells responsible for CRPC development have not been identified. Herein, we have found a putative cell population, ALDH+CD44+α2β1+ PCa cells that may represent a cell-of-origin for CRPC. Taken together, our work has improved our understanding of PCSC properties, possibly highlighting a potential therapeutic target for CRPC.

Calcium-dependent mechanisms and long-term potentiation: Role of NMDA receptors, voltage -dependent calcium channels and persistent protein kinase activity

Long-term potentiation (LTP) is a rapidly induced and long lasting increase in synaptic strength and is the leading cellular model for learning and memory in the mammalian brain. LTP was first identified in the hippocampus, a structure implicated in memory formation. LTP induction is dependent on postsynaptic Ca2+ increases mediated by N-methyl-D-aspartate (NMDA) receptors. Activation of other postsynaptic routes of Ca2+ entry, such as voltage-dependent Ca2+ channels (VDCCs) have subsequently been shown to induce a long-lasting increase in synaptic strength. However, it is unknown if VDCC-induced LTP utilized similar cellular mechanisms as the classical NMDA receptor-dependent LTP and if these two forms of LTP display similar properties. This dissertation determines the similarities and differences in VDCC and NMDA receptor-dependent LTP in area CA1 of hippocampal slices and demonstrates that VDCCs and NMDA receptors activate similar cellular mechanisms, such as protein kinases, to induce LTP. However, VDCC and NMDA receptor activated LTP induction mechanisms are compartmentalized in the postsynaptic neuron, such that they do not interact. Consistent with activation properties of NMDA receptors and VDCCs, NMDA receptor and VDCC-dependent LTP have different induction properties. In contrast to NMDA-dependent LTP, VDCC-induced potentiation does not require evoked presynaptic stimulation or display input specificity. These results indicate that there are two different routes of postsynaptic Ca2+ which can induce LTP and the compartmentation of VDCCs and NMDA receptors and/or their resulting Ca2+ increases may account for the distinction between these LTP induction mechanisms.^ One of the molecular targets for postsynaptic Ca2+ that is required for the induction of LTP is protein kinases. Evidence for the role of protein kinase activity in LTP expression is either correlational or controversial. We have utilized a broad range and potent inhibitors of protein kinases to systematically examine the temporal requirement for protein kinases in the induction and expression of LTP. Our results indicate that there is a critical period of persistent protein kinase activity required for LTP induction activated by tetanic stimulation and extending until 20 min after HFS. In addition, our results suggest that protein kinase activity during and immediately after HFS is not sufficient for LTP induction. These results provide evidence for persistent and/or Ca2+ independent protein kinase activity involvement in LTP induction. ^

Brain rhythms alterations and their effect in functional networks: A simultaneous EEG/fMRI study in Fixation-off epilepsy

Fixation-off sensitivity (FOS) denotes the forms of EEG abnormalities, which are elicited by elimination of central vision or fixation. The phenomenon seems to depend on variables that modulate the alpha rhythm, however, the cerebral mechanisms underlying FOS remain unclear [1]. The scarce previous fMRI findings related to FOS have shown activation in extrastriate cortex [2] and also in frontal areas [3][4]. On the other hand, simultaneous EEG-fMRI technique has been used to assess the relationship between spontaneous power fluctuations of electrical rhythms and associated fMRI signal modulations. These studies have identified that lateral frontoparietal networks show a negative correlation with alpha band in healthy subjects. This neuroanatomical pattern is related to attentional processes and cognitive resources. Moreover, a sub-beta band (17-23 Hz) has been identified with posterior cingulate, temporoparietal junction and dorso-medial prefrontal cortex activations, which correspond to the DMN [5][6].

Advanced morphometric techniques applied to the study of human brain anatomy

El desarrollo de las técnicas de imágenes por resonancia magnética han permitido el estudio y cuantificación, in vivo, de los cambios que ocurren en la morfología cerebral ligados a procesos tales como el neurodesarrollo, el envejecimiento, el aprendizaje o la enfermedad. Un gran número de métodos de morfometría han sido desarrollados con el fin de extraer la información contenida en estas imágenes y traducirla en indicadores de forma o tamaño, tales como el volumen o el grosor cortical; marcadores que son posteriormente empleados para encontrar diferencias estadísticas entre poblaciones de sujetos o realizar correlaciones entre la morfología cerebral y, por ejemplo, la edad o la severidad de determinada enfermedad. A pesar de la amplia variedad de biomarcadores y metodologías de morfometría, muchos estudios sesgan sus hipótesis, y con ello los resultados experimentales, al empleo de un número reducido de biomarcadores o a al uso de una única metodología de procesamiento. Con el presente trabajo se pretende demostrar la importancia del empleo de diversos métodos de morfometría para lograr una mejor caracterización del proceso que se desea estudiar. En el mismo se emplea el análisis de forma para detectar diferencias, tanto globales como locales, en la morfología del tálamo entre pacientes adolescentes con episodios tempranos de psicosis y adolescentes sanos. Los resultados obtenidos demuestran que la diferencia de volumen talámico entre ambas poblaciones de sujetos, previamente descrita en la literatura, se debe a una reducción del volumen de la región anterior-mediodorsal y del núcleo pulvinar del tálamo de los pacientes respecto a los sujetos sanos. Además, se describe el desarrollo de un estudio longitudinal, en sujetos sanos, que emplea simultáneamente distintos biomarcadores para la caracterización y cuantificación de los cambios que ocurren en la morfología de la corteza cerebral durante la adolescencia. A través de este estudio se revela que el proceso de “alisado” que experimenta la corteza cerebral durante la adolescencia es consecuencia de una disminución de la profundidad, ligada a un incremento en el ancho, de los surcos corticales. Finalmente, esta metodología es aplicada, en un diseño transversal, para el estudio de las causas que provocan el decrecimiento tanto del grosor cortical como del índice de girificación en adolescentes con episodios tempranos de psicosis. ABSTRACT The ever evolving sophistication of magnetic resonance image techniques continue to provide new tools to characterize and quantify, in vivo, brain morphologic changes related to neurodevelopment, senescence, learning or disease. The majority of morphometric methods extract shape or size descriptors such as volume, surface area, and cortical thickness from the MRI image. These morphological measurements are commonly entered in statistical analytic approaches for testing between-group differences or for correlations between the morphological measurement and other variables such as age, sex, or disease severity. A wide variety of morphological biomarkers are reported in the literature. Despite this wide range of potentially useful biomarkers and available morphometric methods, the hypotheses and findings of the grand majority of morphological studies are biased because reports assess only one morphometric feature and usually use only one image processing method. Throughout this dissertation biomarkers and image processing strategies are combined to provide innovative and useful morphometric tools for examining brain changes during neurodevelopment. Specifically, a shape analysis technique allowing for a fine-grained assessment of regional thalamic volume in early-onset psychosis patients and healthy comparison subjects is implemented. Results show that disease-related reductions in global thalamic volume, as previously described by other authors, could be particularly driven by a deficit in the anterior-mediodorsal and pulvinar thalamic regions in patients relative to healthy subjects. Furthermore, in healthy adolescents different cortical features are extracted and combined and their interdependency is assessed over time. This study attempts to extend current knowledge of normal brain development, specifically the largely unexplored relationship between changes of distinct cortical morphological measurements during adolescence. This study demonstrates that cortical flattening, present during adolescence, is produced by a combination of age-related increase in sulcal width and decrease in sulcal depth. Finally, this methodology is applied to a cross-sectional study, investigating the mechanisms underlying the decrease in cortical thickness and gyrification observed in psychotic patients with a disease onset during adolescence.