ERC FUNDED PROJECTS

Pericytes, located at intervals along capillaries, have recently been revealed as major controllers of brain blood flow. Normally, they dilate capillaries in response to neuronal activity, increasing local blood flow and energy supply. But in pathology they have a more sinister role. After artery block causes a stroke, the brain suffers from the so-called “no-reflow” phenomenon - a failure to fully reperfuse capillaries, even after the upstream occluded artery has been reperfused successfully. The resulting long-lasting decrease of energy supply damages neurons. I have shown that a major cause of no-reflow lies in pericytes: during ischaemia they constrict and then die in rigor. This reduces capillary diameter and blood flow, and probably degrades blood-brain barrier function. However, despite their crucial role in regulating blood flow physiologically and in pathology, little is known about the mechanisms by which pericytes function. By using blood vessel imaging, patch-clamping, two-photon imaging, optogenetics, immunohistochemistry, mathematical modelling, and live human tissue obtained from neurosurgery, this programme of research will: (i) define the signalling mechanisms controlling capillary constriction and dilation in health and disease; (ii) identify the relative contributions of neurons, astrocytes and microglia to regulating pericyte tone; (iii) develop approaches to preventing brain pericyte constriction and death during ischaemia; (iv) define how pericyte constriction of capillaries and pericyte death contribute to Alzheimer’s disease; (v) extend these results from rodent brain to human brain pericytes as a prelude to developing therapies. The diseases to which pericytes contribute include stroke, spinal cord injury, diabetes and Alzheimer’s disease. These all have an enormous economic impact, as well as causing great suffering for patients and their carers. This work will provide novel therapeutic approaches for treating these diseases.

2 499 954 €

Start date: 2017-09-01, End date: 2022-08-31

Neuromodulators such as acetylcholine and dopamine are able to rapidly reprogram neuronal information processing and dynamically change brain states. Degeneration or dysfunction of cholinergic and dopaminergic neurons can lead to neuropsychiatric conditions like schizophrenia and addiction or cognitive diseases such as Alzheimer’s. Neuromodulatory systems control overlapping cognitive processes and often have similar modes of action; therefore it is important to reveal cooperation and competition between different systems to understand their unique contributions to cognitive functions like learning, memory and attention. This is only possible by direct comparison, which necessitates monitoring multiple neuromodulatory systems under identical experimental conditions. Moreover, simultaneous recording of different neuromodulatory cell types goes beyond phenomenological description of similarities and differences by revealing the underlying correlation structure at the level of action potential timing. However, such data allowing direct comparison of neuromodulatory actions are still sparse. As a first step to bridge this gap, I propose to elucidate the unique versus complementary roles of two “classical” neuromodulatory systems, the cholinergic and dopaminergic projection system implicated in various cognitive functions including associative learning and plasticity. First, we will record optogenetically identified cholinergic and dopaminergic neurons simultaneously using chronic extracellular recording in mice undergoing classical and operant conditioning. Second, we will determine the postsynaptic impact of cholinergic and dopaminergic neurons by manipulating them both separately and simultaneously while recording consequential changes in cortical neuronal activity and learning behaviour. These experiments will reveal how major neuromodulatory systems interact to mediate similar or different aspects of the same cognitive functions.

1 499 463 €

Start date: 2017-05-01, End date: 2022-04-30

Neurodegenerative diseases (NDs) are incurable, debilitating conditions, arise mid-late in life, represent an enormous health and socioeconomic burden and no therapies exist. An enigmatic finding in NDs is the early and selective alteration in intrinsic excitability of vulnerable neurons paralleling changes in its circuitry. However, a gap in understanding exists in ND field about the cause of these alterations and whether these modifications regulate degenerative pathomechanisms. Our recent study, examining mechanisms of Purkinje cell (PC) degeneration in Spinocerebellar ataxia type 1 (SCA1) revealed that the earliest cerebellar alterations occur in the major excitatory inputs onto PCs, the climbing fibers (CFs). Based on this, we propose a novel three-step model of neurodegeneration: First, suboptimal functioning of the presynaptic inputs initiates signaling deficits in target PCs. Second, those alterations trigger maladaptive responses such as altered intrinsic PC excitability, thus amplifying pathogenic cascades. Third, at network level progressive dysfunction triggers compensatory synaptic modifications within the cerebellar circuitry. In this proposal, we will test our new hypothesis for NDs on SCA1 and this will be the first study to test circuit-dependency in NDs by selectively silencing presynaptic inputs and examining molecular responses in the postsynaptic neuron. Specifically, we will 1) Identify the dysfunctional CF associated molecular signature in PCs. 2) Elucidate mechanisms involved in altering intrinsic PC excitability. 3) Map the connectome for a structural correlate of the pathology. Using conditional mouse models, pharmacogenetics, transcriptomics, proteomics and connectomics, we will delineate molecular alterations that govern disease from compensatory alterations. Our systematic approach will not only impact SCA related therapies but the entire spectrum of NDs and has the potential to change the conceptual approach of future studies on NDs.

2 000 000 €

Start date: 2017-06-01, End date: 2022-05-31

Microscopy enabled the birth of modern neuroscience, by allowing Ramón y Cajal to formulate the neuron doctrine. Since then, remarkable advances in optical resolution, speed and probe development allowed scientists to study the function of neuronal circuits with ever increasing detail – with one critical limitation: No conventional microscope can focus light deeper into intact tissue than a fraction of a mm. This leaves 90% of the intact rodent brain and over 99% of the intact primate brain inaccessible. As a result, the deepest layers of the neocortex and nearly all subcortical structures are currently outside the reach of non-invasive microscopy, representing a fundamental barrier towards further progress in understanding the brain. Existing fluorescence microscopy techniques, such as confocal and two-photon microscopy, attempt to image deeper by rejecting scattered light or by selecting non-scattered (ballistic) photons for focusing. However, beyond depths of several hundred µm this approach becomes futile because hardly any ballistic photons remain. We recently achieved two breakthroughs by turning this strategy upside down and focusing with scattered photons: First, we developed a new approach for fluorescence microscopy that uses a process called optical time reversal, with which we achieved an unprecedented imaging depth of 2.5 mm in ex vivo tissue. Second, we discovered a correlational structure of scattered light, which can be exploited for deep tissue imaging. Still, fundamental challenges remain for in vivo imaging. The goal of this proposal is to break the depth barrier of microscopy and investigate previously unreachable areas of the live brain, by harnessing optical time reversal and scattering correlations. We will demonstrate the power of this approach in layer 6b, the deepest and least understood layer of the mammalian neocortex. This project will thus enable functional imaging of neuronal circuitry at depths that have until now been inaccessible.

1 491 235 €

Start date: 2017-04-01, End date: 2022-03-31