474 research outputs found
Retrosplenial connectivity with the (para)hippocampal region
No full textThe hippocampal formation and parahippocampal region (HF-PHR) receives input from a variety of cortical and subcortical structures, and one of the cortical regions which are heavily interconnected with HF-PHR is the retrosplenial cortex (RSC; Wyss and Van Groen, 1992). RSC is known to be important for a number of cognitive functions, and in both rodents and humans the RSC contribution to visuospatial cognition and memory has recently been reviewed in detail (Vann et al., 2009; Ranganath and Ritchey, 2012). The similar functional attributes of RSC and HF-PHR and the dense connections between the regions suggest a relationship. However exactly which HF-PHR subdivisions are connected with which part of RSC, the topographies of the connections within these subregions and how information carried by these connections are integrated in the receiving subregion is unknown.
In this thesis I explored anatomical connections between HF-PHR and RSC at several levels. In the first part of the thesis all published anatomical tract-tracing experiments which comprise HF-PHR - RSC connections were reanalyzed. All reported projections within and between HF-PHR and RSC were presented in an interactive connectome.
In the second part I explored the synaptic organization and postsynaptic targets of one of these connections namely the projection originating in RSC and terminating in medial entorhinal cortex (MEC), a subregion within PHR. I showed that RSC projects densely to layer V of MEC, with very few fibers targeting layer III. An ultrastructural assessment of the synaptic complexes and optogenetic stimulation of these fibers in an in vitro slice preparation indicated that the majority of RSC synapses in MEC layer V are excitatory. I further identified the layer V neurons postsynaptic to these synapses. The electron microscopical data show a striking dominance of spines of putative principal neurons as targets for RSC inputs. Confocal data and optogenetic data indicate that among the postsynaptic targets are spiny principal cells which project to superficial layers of MEC.
In the third and fourth part I took a developmental approach to study how the interconnections between the two regions develop. To this end I used classical retro- and anterograde tracers injected in differently aged rats. The development of the anatomical connections and the development of the topographical distribution of these connections from postnatal day (P)1 to approximately P28 were characterized. I showed that developing RSC - HF-PHR interconnections are organized in a topographical manner, similar to the adult situation and that this topographical organization is present already when the first axons arrive their termination site.
I thus concluded that information from RSC may reach HF through pyramidal neurons in layer V of MEC which issue projections to the superficial layers of MEC. Neurons in the latter layers may relay information from RSC to HF since these layers harbor neurons projecting to HF. Alternative multisynaptic pathways connecting RSC via PHR to HF likely include RSC projections to postrhinal cortex and presubiculum. Both structures receive RSC inputs among others in superficial layers, which harbor neurons projecting to superficial layers of MEC. The early development of the reciprocal connections between RSC and HF-PHR, already at an early postnatal stage, before neurons are functionally differentiated, suggests that RSC-PHR interconnections are organized by experience independent mechanisms. This experience independent topographic organization suggests that RSC and HF-PHR are parts of one tightly coupled functional system and that RSC - HF-PHR interaction is necessary for proper functioning of the two regions
Dissecting the complexities of Alzheimer's disease: Engineering selectively vulnerable neural networks in vitro
No full textKavli Institute for Systems Neuroscience and
Department for Neuromedicine and Movement ScienceAlzheimer’s disease (AD) is a progressive, neurodegenerative disease where accumulation of neuropathology can start up to two decades before symptom onset. With no cure for the disease, relevant models of AD are needed to better understand initial disease cascades. Transgenic AD animal models and cell culture models have been crucial in the study of AD, and have contributed to a better understanding of neuropathology, disease progression and altered network activity. Applying basic research strategies is crucial before testing new therapeutics to translate the efficacy of potential treatments to the clinic. In vitro modelling of AD introduces a reductionist approach for investigating the disease at the cellular and molecular level. Such models can be particularly useful for studying the early stages of AD, as they allow for the analysis of neural network dynamics. The harvest and in vitro culturing of adult primary neurons from AD animal models is an elegant way to model early phases of AD as the neurons retain their epigenetic profile and age-effects as in the living animal.
In this thesis, the overarching aim has been to develop new methods for modelling of AD by the use of cell cultures. In the first paper we present a method to dissect and longitudinally culture adult layer specific lateral entorhinal cortex layer II (LECLII) neurons from AD transgenic APP/PS1 model mice. Furthermore, in addition to LEC LII, we dissected hippocampal subregional DG, CA3 and CA1 neurons from adult AD transgenic mice and rats and cultured these on four-nodal microfluidic devices (Paper II). We show that adult neurons dissected from rodent AD models re-form structural connections and display sustained electrophysiological activity. By use of commercially available cortical-hippocampal neurons we show the utility of microfluidic devices ensuring feedforward connectivity with emergence of complex structure-function dynamics in our networks (Paper II). In the third paper we used twonodal microfluidic devices to study changes in structure-function neural network dynamics on networks perturbed with viral vector delivery of mutated tau protein (Paper III).
Altogether, work in this thesis presents an in vitro modelling system relevant for preclinical disease modelling. We provide novel results through the establishment of layer and subregion specific entorhinal and hippocampal neuron cultures dissected from adult transgenic AD model animals. As technology advances, these models will become increasingly sophisticated and realistic, allowing for more accurate and comprehensive investigations into the complex pathology of AD
A cytoarchitectonic study of the hippocampal formation of the tree shrew (Tupaia belangeri)
No full textCytoarchitectonic characterization of the parahippocampal region of the guinea pig
No full textThe cytoarchitectonic features of the parahippocampal region (PHR) in the guinea pig are described, based on coronal, horizontal, and sagittal 50-?m sections stained for Nissl substance, zinc, parvalbumin, or calbindin. We differentiate between perirhinal (PRC), postrhinal (POR), and entorhinal (ERC) cortices. PRC is divided into areas 35 and 36 occupying the fundus and the dorsal bank of the rhinal fissure, respectively. POR is located caudal to the PRC. POR and area 36 show a dense, clustered cellular layer II and a thinner layer III in comparison to the adjacent neocortex, and they differ from each other with respect to the orientation of the somata of layer VI neurons. Area 35 is characterized by a thin layer II that is not very different from layer III. Layer IV is (dys)granular in area 36 and POR, and is absent in area 35 and ERC. ERC, located ventromedial to the PRC and POR, is subdivided in six fields, of which field 5 is adjacent to area 35. In both area 35 and field 5, no clear differentiation between layers II and III is present. Field 5 shows a darker cellular stain and exhibits a cell-free zone or lamina dissecans between layers III and V. Medial to field 5, an area characterized by large cell clusters in layer II is designated field 4. The latter field is replaced by field 3 rostromedially, which also typically shows clustering of layer II neurons. These cell clusters in field 3, however, are much more constant in size in spacing compared to those in field 4. The caudomedial portion of ERC is subdivided into fields 1, 1′, and 2. The latter, characterized by a homogeneous distribution of neurons in all layers with large darkly stained neurons in layer V is positioned rostral to field 1 and caudomedial to fields 4 and 5. In field 1, layers V and VI are thinner, and layer II neurons are smaller then in field 1′ and field 2. We conclude that the architectonic features of the guinea pig PHR are comparable to those described in other mammals, particularly the rat. © 2004 Wiley-Liss, In
The inside-out of Alzheimer’s disease
No full textEvery three seconds someone is diagnosed with dementia, and Alzheimer’s disease (AD) constitutes most of these cases. In the absence of a cure for AD, testing hypotheses regarding disease onset and spread, and developing methods for early diagnosis and treatment of the disease remain an urgent priority. Researchers have made tremendous strides in research to understand the origin of AD, and we now know that the neurons in lateral entorhinal cortex (LEC) layer II (a small brain region in the temporal lobes) are at selective risk for neurodegeneration in patients going through transition stages to AD (referred to as mild cognitive impairment [MCI]), and during this transition stage as much as half of the cell population is lost. The disease progression in human AD has been well-characterized by biomarker studies to assess pathological hallmarks at various stages of the disease. Biomarkers in AD can be elucidated by cerebrospinal fluid (CSF) analysis (commonly used biomarkers include decreased amyloid-β (Aβ)42, increased total tau, and increased phosphorylated tau) or neuroimaging markers of disease, such as positron emission tomography (PET) revealing amyloid plaques and tau pathology. Despite these research efforts, we still do not know how to hinder cognitive decline in patients with AD, and one reason may be the poor translatability between preclinical models and patients.
Before any new hypotheses and treatments can reach the clinic, they first need to be tested in preclinical models using basic research strategies. We therefore need robust preclinical models that can help us achieve improved comparability with the human condition, and thereby improved translatability into the clinic. Here we used a highly clinically comparable rodent model of AD, the 3xTg AD mouse, which contains human genetic mutations recapitulating neuropathology observed in patients. First, we developed and applied our modified microdialysis method for repeated, longitudinal in vivo CSF collection and characterized biomarker protein changes in mice along the entire AD disease progression (Paper II). We subsequently applied our optimized microdialysis method to administer repurposed drugs aimed at attenuating AD-related Aβ and tau neuropathology (Paper III). In another set of experiments, we overexpressed human tau pathology in LEC layer II in mice using a viral vector delivery system, and then monitored tau spread from LEC layer II to its projection targets in the hippocampus (Paper IV). Lastly, we chemogenetically silenced neurons in LEC layer II and monitored the effect on intraneuronal Aβ levels in LEC and in downstream hippocampus (paper V).
Using our modified microdialysis protocol, we found that the concentrations of CSF Aβ and tau proteins in mouse models of AD are comparable to changes observed along the disease cascade in patients (Paper II). Repurposed drugs not only attenuated neuropathology at the molecular, but also at the functional level when administered in combination using our microdialysis protocol at various therapeutic time windows (Paper III). Moreover, we found that the presence and spread of tau from LEC layer II to the hippocampus increased with age and was affected by the presence of endogenous tau load (Paper IV). We also show a correlation between intraneuronal Aβ levels and neuronal activity, and that chemogenetic silencing of LEC layer II neurons led to reduced early intraneuronal Aβ in LEC and in the downstream hippocampus (Paper V).
In summary, I have (i) characterized CSF biomarkers along the entire disease cascade in a mouse model of AD and have validated the translational value of this model to patients. (ii) My findings lend support to the application of repurposed drugs to attenuate AD neuropathology at various therapeutic time windows. (iii) I have shown that tau spread from its site of anatomical origin depends upon aging and the pre-existence of tau. (iv) Lastly, I have demonstrated that the activity of LEC layer II neurons affects early intraneuronal Aβ build-up. In line with previous research, I have shown the vulnerability of EC layer II for developing ADrelated neuropathology, obtained insights into the origins and mechanisms of neuropathological spread, and shown that experimental animal models and molecular techniques are invaluable tools for answering fundamental questions within the field. Ultimately, I have aimed to develop a springboard for future integration of basic research findings to the clinic and AD patients
Parieto-frontal architecture, connectivity and behavioral representations in rodents
No full textThe posterior parietal cortex (PPC) and frontal motor cortices are important for a variety of cognitive processes including sensorimotor integration, decision-making, planning and execution goal-directed actions. Across mammals, PPC and frontal motor cortices are strongly connected and form the parietofrontal network, where ‘mirror’ neurons, perhaps the most famous example of sensorimotor integration, were first discovered in primates. Since rodents are serving an ever-greater role in studying the cellular mechanisms of cognitive processes in PPC and frontal cortical areas, the work in this thesis aims to describe the anatomical and functional properties of this network in both mice and rats. The first study in the thesis provides an anatomical description of the mouse PPC relative to the neighboring extrastriate areas, since PPC in mice is poorly defined, which confounds the interpretation of functional studies. I show that, like in rats, the mouse PPC is divided into anatomically distinguishable medial, lateral and posterior subdivisions (mPPC, lPPC and PtP, respectively), and that each of these areas partly overlaps with anterior aspects of multiple extrastriate areas. Second, I investigate whether the connections of rat PPC with frontal midline cortices are topographically organized as reported in primates. The results reveal that PPC is strongly connected with secondary motor cortex (M2) in a topographical manner, such that mPPC is preferentially connected with the most posterior portion of M2, whereas lPPC and PtP connect with the intermediate anterior-posterior portion. Connections with orbitofrontal cortex showed a medial-to-lateral trend, where mPPC preferentially connects with the medial half, including the medial and ventrolateral subregions. lPPC and PtP are preferentially connected with the medial and central portion of the ventrolateral orbitofrontal cortex. The topographical organization of connections with M2 indicates heterogeneity in both PPC and M2 in rodents, which prompts the final study in the thesis probing whether neurons in mouse M2 and PPC encode performed as well as observed actions like in primates. Using in vivo calcium imaging, we show that both M2 and PPC stably encode a variety of naturalistic behaviors when performed, but that such responses do not occur when the same animals observed the same behaviors being performed by another animal. In summary, I have (i) defined PPC anatomically in the mouse and (ii) shown that the rat PPC subregions are reciprocally connected with frontal midline cortices in a topographical manner, like in primates. (iii) In mice, neurons in M2 and PPC reliably encode performed but not observed behaviors, suggesting that that there are limits to the functional similarity of PPC and frontal cortices in rodents and primates
Immunohistochemical and morphological characterization of GABAergic cells in LEC
No full textThe two subdivisions of the entorhinal cortex, the medial and the lateral entorhinal cortex have been implicated a crucial role in spatial cognition but appear to be functionally distinct. To understand the functional contribution of the lateral entorhinal cortex basic knowledge about the neurons constituting the system is needed.
In this study, the GABAergic cell population in LEC was immunohistochemically and morphologically characterized. For this purpose, the transgenic mouse line GAD 67 – GFP was used for immunohistochemical investigation of co-localization of GABA with Ca2+ binding proteins and neuropeptides. A morphological study of GAD positive cells in L II / III of LEC was additionally performed by intracellular injections of Alexa Fluor Hydrazide 568 in fixed brain slices. The results indicate that the GABAergic cell population in LEC is neurochemically and morphologically diverse. The pattern of distribution across LEC for all immunoreactive cell groups, suggests that a diverse cell population is present across all areas of LEC but display a speficic pattern of distribution across LEC laminae
Projections of the posterior parietal cortex to the orbitofrontal cortex in the rat
No full textThe posterior parietal cortex (PPC) in the rat is a multimodal association area, implicated in spatial processing, decision-making, working memory and directed attention. PPC is commonly divided into a medial (mPPC), a lateral (lPPC) and a posterior (PtP) region, all reciprocally connected to specific parts of the thalamus. The orbitofrontal cortex (OFC) is part of the ventral prefrontal cortex and is commonly divided into the medial orbital (MO), ventral orbital (VO), ventrolateral orbital (VLO), lateral orbital (LO) and dorsolateral orbital (DLO) cortices. The subregions of OFC have distinct connectivity patterns and are functionally different regarding spatial information processing, value-based decision-making and behavioural flexibility.
Reciprocal connections between PPC and OFC have previously been described, but variations in delineation of both cortical regions and difficulties in distinguishing PPC from the secondary visual cortex (V2) hampered a clear understanding of the connections. Moreover, no study has addressed PPC-OFC projections, differentiating the origins in the three posterior parietal subdivisions.
The aim of this study was therefore to describe the projections of PPC to the subregions of OFC, with a special focus on the differences in projection patterns arising from the three subregions of PPC. To this end, we injected the anterograde tracers 10 KD biotinylated dextran amine (BDA) and phaseolus vulgaris-leucoagglutinin (PHA-L) into the subregions of PPC. The retrograde tracers Fast Blue (FB) and Fluorogold (FG) were injected into VO and VLO to study the layers of origin of these projections. The brains were cut in the coronal plane and cortical areas were delineated based on Nissl stains with Cresyl Violet. Anterograde tracers were visualised using either 3.3’-diaminobenzidin tetrahydrochloride (DAB) or AlexaFluor® dyes, and their distribution, as well as that of the retrograde fluorescent tracers was analysed with conventional microscopical techniques.
Anterograde tracing showed that the projections from PPC to OFC are not strong, which is supported by the retrograde tracer cases that showed an overall low number of labelled neurons in layers V and VI of PPC. mPPC projects mainly to lateral VO and medial VLO, with some sparse projections to MO. Projections from lPPC terminate in medial VLO, while the most lateral part of PPC, PtP, projects to central to lateral VLO. The results indicate that projections from PPC target OFC, showing a subtle topographical pattern within MO, VO and VLO, with a clear preference for VO and VLO and excluding LO and DLO.Oppgaven tilgjengelig fra 2018-06-01
Immunohistochemical and morphological characterization of GABAergic cells in LEC
No full textThe two subdivisions of the entorhinal cortex, the medial and the lateral entorhinal cortex have been implicated a crucial role in spatial cognition but appear to be functionally distinct. To understand the functional contribution of the lateral entorhinal cortex basic knowledge about the neurons constituting the system is needed.
In this study, the GABAergic cell population in LEC was immunohistochemically and morphologically characterized. For this purpose, the transgenic mouse line GAD 67 – GFP was used for immunohistochemical investigation of co-localization of GABA with Ca2+ binding proteins and neuropeptides. A morphological study of GAD positive cells in L II / III of LEC was additionally performed by intracellular injections of Alexa Fluor Hydrazide 568 in fixed brain slices. The results indicate that the GABAergic cell population in LEC is neurochemically and morphologically diverse. The pattern of distribution across LEC for all immunoreactive cell groups, suggests that a diverse cell population is present across all areas of LEC but display a speficic pattern of distribution across LEC laminae
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