Community Research and Development Information Service - CORDIS



Project ID: 647012
Funded under: H2020-EU.1.1.

Periodic Reporting for period 1 - SENSORTHALAMUS (Thalamic control of Neuroplasticity)

Reporting period: 2015-07-01 to 2016-12-31

Summary of the context and overall objectives of the project

The cerebral cortex is organized into highly specialized sensory areas. Thus, it is fundamental to understand how these areas acquire and maintain their identity and functional organization. Challenging normal brain development and forcing the brain to the limits of plasticity, offers us the possibility to shed light on these issues. Accordingly, we shall use prenatal sensory deprivation as a model to understand the mechanisms underlying early neuroplasticity, events that could influence the natural organization of sensory cortical areas. Early sensory deprivation produces profound changes in the cortex, provoking the reorganization of both the deprived and the spared cortical territories. Classically, this adaptation is thought to require sensory experience from the intact sensory modalities. However, our recent data from embryonic deprived mice challenge this view, suggesting that a component independent of experience contributes to this reorganization and that the thalamus plays a pivotal role in these events. Hence, we now propose to adopt multidisciplinary and innovative approaches to characterize the structural, genetic and functional rearrangements in the thalamus following embryonic sensory deprivation, and to define the factors and mechanisms that drive cortical specificity. Experimental results from sensory deprived animals in which the thalamus and gene expression is manipulated in vivo, will be integrated to explain when and how neuroplastic cortical adaptations are triggered in the deprived brain. To further understand the rewiring capacity of thalamic neurons and their potential role in sensory restoration, we will adopt a high-risk, high-gain approach to reprogramme nuclei specific thalamic neurons. The novel information obtained will establish how sensory inputs and thalamocortical connections govern cortical activity and architecture, ultimately sculpting perceptual behaviour.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

During this first period of the project (18 months), we have successfully reached important goals for the consecution of the Project. Moreover, the results we got so far from the project were included in two publications (Gezelius et al., Cerebral Cortex 2016, Moreno-Juan et al., Nature Communication 2017). The main results and achievements reached during this period are listed below.

Aim 1 – To generate animal models in which neuroplasticity is boosted

In this aim we proposed to generate mice in which a peripheral input (visual) is removed embryonically to produce severe plasticity in the cortical areas. We have successfully achieved this goal and generated embryonically visually deprived mice by in utero bilateral enucleations in embryos. We have exploited this animal model to check for neuroplastic compensatory mechanisms and found that after embryonic enucleations (embBE), the barrel field area in S1 is significantly expanded a few days after birth, before sensory processing.

Estimated completion: 70%

Aim 2 – The thalamus as an inducer of cross-modal neuroplasticity

Our following hypothesis was that that the thalamus, and its connectivity to the cortex, plays a central role in promoting these early cortical neuroplastic changes following sensory deprivation. Thus, we propose to analyze the changes in thalamic gene expression and thalamocortical connectivity in the embBE mice. During this period of the project, we performed a Microarray screen in the embBE mice and found several candidate genes which expression changed significantly. We concentrated in studying the role in the development of the somatosensory system of one of the genes that changed the most, RORB. We found that thalamic Rorb plays a role in controlling the complexity of the axonal arbors of the thalamocortical axons, then influencing the extension of the barrel-field area in S1. We have also performed dye tracing studies to unravel a possible rewiring of thalamocortical axons in the absence of retinal input. We found that somatosensory or auditory thalamocortical axons are not rewire in the absence of retinal input.
One important discovery we made during these first months of the project is the existence of waves of calcium spontaneous activity in the embryonic/perinatal thalamus. We found that this activity is crucial to communicate distinct sensory systems embryonically. When one input from a specific sensory modality is missing, the pattern of these waves in the remaining thalamic sensory nuclei is changed producing modifications in gene expression /e.g RorB) and the re-organization of cortical areas size. All this data is included in a recent publication by our laboratory, Moreno-Juan et al., 2017.
At present, we are recording the thalamic calcium waves in vivo in developing embryos by using a genetic strategy in which the GCaMP6 calcium indicator is expressed by thalamic neurons. Moreover, by using whole-cell patch-clamp recordings we are recording the electrical properties of embryonic and early postnatal thalamic neurons from the distinct sensory nuclei in control and sensory-deprived mice. Moreover, by using patch-clamp recordings and stimulating electrodes, we are determining the possible existence of an intrathalamic circuit and the role of GABAergic neurons in development of thalamic sensory-systems, as proposed in the project.
Finally, within this first period of the project and as a key step for its accomplishment, we have successfully generated a transgenic mouse, the Kir2.1-mCherry flox mice, to successfully manipulate the spontaneous activity of thalamic, cortical or peripheral activity in vivo.

Estimated completion: 40%

Aim 3 – Reprogramming thalamic neurons for neuroplasticity

The third Aim of the project proposes to define the molecular mechanisms that govern the programming of thalamic neurons involved in specific sensory modalities. We plan to use these cell-fate determinants to promote neuroplasticity by reprogramming thalamic cell identity in early post-mitotic neurons and endogenous astrocytes.
During this first period of the project, we have identified genes that might control cell type specification and differentiation of modality-dependent thalamocortical neurons. We have compared the gene expression profile of dLGN (visual), VPM (somatosensory) and MGv (auditory) cells by Microarray analysis using the CreER-loxP system to selectively activate reporter expression in a subset of thalamic neurons (included in Gezelius et al., 2016). Within the list of genes, we have found novel transcription factors specifically expressed in the distinct sensory-modality thalamic nuclei. Al present, we have selected promising candidate genes to perform functional studies. We are directly testing whether ectopic expression of nuclei-specific transcription factors is sufficient to specify neural progenitors to the lineage of one or another thalamocortical sensory modality. For that, we have cloned the candidate transcription factor in lentiviral vectors for their specific expression in postmitotic neurons. We are infecting thalamic cells at late embryonic, early-postnatal stages, and checking the capacity of the gene to change fate.
As a second part of this Aim, we are testing the potential conversion of thalamic astrocytes into specific thalamocortical sensory-modality neurons by the forced expression of Neurogenin 2. Neurogenin2 has been shown to reprogramme cortical astrocytes. During this first period of the project, we have successfully reprogram thalamic astrocytes in thalamocortical neurons in vitro. We are now testing the capacity of reprogramming in vivo in control and sensory-deprived mice.

Estimated completion: 30%

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The results obtained by this Project will provide important insight into the extent to which sensory inputs and thalamocortical connections control the functional modulation of cortical areas, and ultimately sculpt perceptual behaviour. Furthermore, this cutting edge research will provide a detailed understanding of the role of the thalamus as an inducer of neuroplastic changes during development, which will be essential to generate predictions regarding its response to sensory deprivation in the adult. Understanding the nature of these neuroplastic changes is not only important to establish the brain’s true adaptive potential but also, to elucidate the intervening developmental constraints and to guide future rehabilitation strategies.
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