Understanding Serotonergic Regulation of Working Memory

Project Information

SERWOM

Grant agreement ID: 888270

DOI

10.3030/888270

Project closed

EC signature date 27 February 2020

Start date 1 July 2020

End date 7 November 2022

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 212 933,76

EU contribution

€ 212 933,76

Coordinated by

THE FRANCIS CRICK INSTITUTE LIMITED
United Kingdom

Periodic Reporting for period 1 - SERWOM (Understanding Serotonergic Regulation of Working Memory)

Reporting period: 2020-07-01 to 2022-06-30

Summary of the context and overall objectives of the project

Attention improves perceptual abilities by modulating sensory processing. Abnormalities in sensory processing and attention are profound problems in several neurological disorders. Serotonin receptors (5-HTRs) have been shown to modulate and maintain sensory processing and attention, and dysregulation of the 5-HT system has been implicated in the pathogenesis of these disorders sharing characteristic symptoms, such as aberrant multisensory processing and spatial attention (SA). Using the mouse as a model system, this project was aimed at elucidating 5-HT effects on the superior colliculus (SC), a brain area implicated in integrating endogenous with externally driven attention and recipient of dense 5-HT input. As a first step, we planned to develop a custom multisensory behavioural task that addresses cross-modal SA to test if and how 5-HT modulates the integration of inputs from different sensory modalities depending on behavioural context. We then wanted to investigate how the dynamic activation of distinct 5-HTRs influences SC networks. Using a novel genetically encoded 5-HT fluorescent sensor, large-scale neuronal recordings and next-generation optogenetic perturbations during our cross-modal behavioural task, we wanted to reveal the causal role of 5-HT on the modulation of excitatory and inhibitory neurons. Next, we planned to generate a three-dimensional map of 5-HTR subtypes at cellular resolution using a multiplexed in-situ hybridisation method and reveal the physiological role of the detected 5-HTRs by combining patch-clamp recordings in brain slices, receptor type-specific optogenetic and pharmacological perturbations. Our multiscale approach was envisaged to allow us to generate a detailed mechanistic model of 5-HT physiological effects on cross-modal SA and elucidate how its dysregulation can be the substrate for the pathogenesis of psychiatric and neurological disorders. Such a mechanistic account, at cellular- and circuit-level, is required to guide the development of next-generation pharmacotherapies. In conclusion, during the course of this project, we showed that mice can learn to utilise auditory, visual, multisensory and contextual information to localise a target of interest in our behavioural task and that their performance depends on stimulus modality, saliency, congruency of sensory information, context and SC functionality. We could show that the SC receives strong serotonergic innervation and that multiple 5-HTRs are distinctively expressed within the SC. We found out, that external modulation of specific 5-HTRs in the SC significantly and distinctively impacts task performance and thus, we confirmed that serotonergic modulation of the SC is relevant for spatial attention.

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

We successfully developed a behavioural task where mice need to combine (or ignore) information from different sensory modalities in order to localise a target of interest. We could show that performance in this task depends on the saliency of the stimulus and that multisensory information increases/decreases performance depending on congruency. Furthermore, the reaction time in this task is dependent on modality, saliency, congruency of sensory information and contextual information. Through drug microinjections into the SC during task performance, we could show that the SC is a key requirement for this spatial attention task. We performed high-density neuronal recordings during task performance in the SC and classified sensory neurons in the SC. We could show that the location of visual, auditory and multisensory neurons reflects the layered structure of the SC and that their responses are modality and saliency dependent, and we are currently in the process of analysing the responses in detail. We characterized the serotonergic projections of the dorsal raphe nucleus (DRN) to the SC through a variety of high-end techniques. We could show that projection density varies with depth and across SC subregions and that multiple 5-HTRs are expressed within the SC. Microinjections of 5-HT antagonists during behaviour had a significant impact on task-performance, revealing that 5-HT modulation of the SC is relevant for spatial attention. We developed light-controllable proteins that can be used to mimic 5-HTRs and will enable us to modulate these receptors during our task. Furthermore, we have established an in vivo imaging technique that allows us to image cellular activity and 5-HT release during our task. Our novel findings have already been presented during institutional retreats and on a public symposium at the Crick, informing a wide audience beyond the neuroscience community. We are currently finalizing a draft of our first publication. Furthermore, our preliminary data was of such high impact, that we could secure funding for an MRC grant, where I will continue my investigation as a researcher co-investigator.

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)

This project was envisaged to give insights into a truly circuit-centric mechanistic understanding of the interaction between distinct 5-HT modulated cell types within the SC and shed light on their relevance for attention and higher cognitive processes. Due to an unavoidable change of host-institution/supervisor, and being carried out during the COVID-pandemic, these major delays, including a replanning/reshaping of the project, made finalizing the project within the given time-frame impossible. Nonetheless, due to the support of the Crick, my supervisor Dr Iacaruso, my colleague Dr Karapinar and the rest of the lab, the preliminary results collected, enabled us to secure further funding through an MRC grant. Thus, our objectives still hold. Utilising cutting-edge technologies and state-of-the-art experimental designs, will allow us to generate a detailed mechanistic model of neuromodulatory effects on cross-modal SA in the SC, something that we still lack. The project is not only intended to generate knowledge and mechanistic insights ranging from sub-cellular over neuronal circuits to the behavioural level but will also inform translational work aiding in the development of novel neuropsychiatric treatments. Due to the broad spectrum of the project, the interdisciplinary methodology and the novelty of the expected results revolving around the characterisation of 5-HT mediated signalling in the SC for the first time, the results will benefit researchers and clinicians from a variety of disciplines. Notably, our results will be of great interest for the wider neuroscience community, especially for neuroscientists working on 1) neuronal circuits involved in sensory processing, 2) 5-HT signalling across the brain, and 3) autism- or schizophrenia-related psychopharmacology. Our findings are also likely to be of interest in the field of artificial intelligence and machine learning. Finally, we expect that the approaches and tools generated during the project will be of relevance to other disciplines, including structural biologists and biophysicists with an interest in subcellular signalling and receptor functionality. Altogether, in addition to displaying scientific excellence and competitiveness, potentially strengthening the European Research Area as well as worldwide science and health, the project and, most importantly, the creation of fruitful international collaborations beyond the scope of this project would promote inclusive and sustainable scientific growth with freely circulating knowledge and methodology around the globe.

Layers of the SC