Prefrontal Cortex Circuit Dynamics underlying Working Memory and its Serotonin Modulation

Project Information

PIANISM

Grant agreement ID: 892772

DOI

10.3030/892772

Project closed

EC signature date 11 March 2020

Start date 1 August 2020

End date 8 December 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 - PIANISM (Prefrontal Cortex Circuit Dynamics underlying Working Memory and its Serotonin Modulation)

Reporting period: 2020-08-01 to 2022-07-31

Summary of the context and overall objectives of the project

Attention is the cognitive process of selectively focusing on a particular stimulus or task while filtering out distractions. It allows us to selectively process and respond to important or relevant information, while ignoring irrelevant stimuli. Attention is a limited resource, and we can only attend to a certain amount of information at a given time. Research has shown that serotonin (5-HT) receptors play a role in regulating sensory processing and attention. Dysfunction in the 5-HT system has been linked to the development of disorders with symptoms, such as abnormal processing of multiple senses and problems with spatial attention. 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. Our initial plan was to create a behavioural task that examines how different senses work together in spatial attention, focusing on how 5-HT may influence information integration from these senses. This would allow us to test the effects of 5-HT on cross-modal spatial attention. Next, we investigated how the dynamic activation of 5-HT receptors influences SC networks. Using a new genetically encoded fluorescence sensor for 5-HT, large-scale neuronal recordings, and optogenetic techniques during the task, our goal was to determine the causal role of 5-HT in the modulation of excitatory and inhibitory neurons. To link specific 5-HT receptors to the circuit mechanism, we created a 3D map of 5-HT receptor subtypes at a cellular level using a multiplexed in-situ hybridisation method. Next, we aimed to understand the physiological role of these receptors by combining patch-clamp recordings with optogenetic and pharmacological techniques that target specific receptor types. Our method aims to create a comprehensive understanding of how 5-HT affects attention and how disruptions in its regulation may contribute to the development of neuropsychiatric disorders. Such a mechanistic account, at cellular- and circuit levels is required to guide the development of next-generation pharmacotherapies. In summary, we demonstrate that mice can learn to locate a target using various types of sensory information. We found that the mice's ability to perform this task is affected by factors such as the type of information being used, its importance, consistency, and the state of a specific brain region called the superior colliculus. Additionally, we found that the SC receives dense serotonergic input and expresses various 5-HT receptors. Our research revealed that altering specific 5-HT receptors in the SC has a notable and distinct effect on task performance, confirming the importance of serotonergic modulation in the SC 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 created a behavioral task for mice where they have to integrate or disregard information from various sensory channels to pinpoint a target of interest. Our results indicate that the prominence of the stimulus influences the mouse's performance in this task, and combining information from multiple senses either improves or hinders performance depending on their consistency. Through drug microinjections into the superior colliculus (SC) during task performance, which inhibited the SC, we could show that the SC is a key requirement for this spatial attention task.
We conducted high-density neural recordings during the task, focusing on the SC, and categorising its sensory neurons. Our results indicate that the positioning of visual, auditory and multi-sensory neurons corresponds with the layered organisation of the SC and their responses are influenced by the type of stimulus and its prominence. We examined the serotonergic projections from the dorsal raphe nucelus to the SC. Our findings demonstrate that the density of projections carries in different regions of the SC and across different layers. Additionally, we validated the expression of multiple 5-HT receptors in glutamatergic and GABAergic cells. We identified likely critical receptors in the SC based on their expression pattern. Furthermore, we found that the selective microinjections of specific 5-HT antagonists in the layer-specific regions of the SC during the task significantly impacted performance, thus confirming the relevance of serotonergic modulation in the SC. We created specialised optogenetic tools, which can be controlled with light, to mimic specific 5-HTRs. These tools will allow us to modulate these receptors during our behavioural task precisely. Additionally, we have established an advanced in vivo imaging method that enables us to visualise cellular activity and 5-HT release during the task. Our novel findings have already been presented on multiple posters during institutional retreats and at a public symposium at the Francis Crick Institute, informing a broad audience beyond the neuroscience community. Furthermore, our preliminary data was of such high impact that we could secure funding for an MRC Neuroscience and Mental Health grant, where I will continue my investigation of the role of serotonin in spatial attention 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 aimed to understand how different cell types in the superior colliculus (SC) modulated by serotonin (5-HT) interact with one another and to reveal their role in attention. However, due to an unexpected change of the host institution and the disruptions caused by the pandemic, the project faced delays and had to be significantly altered. As a result, it was impossible to complete the project within the duration of the fellowship. Despite the challenges, the support of the Francis Crick Institute, my supervisor Dr Iacaruso, my colleague Dr Eickelbeck, and all other lab members allowed us to gather valuable preliminary results. Using advanced technologies, we aim to create a mechanistic model of how 5-HT affects cross-model spatial attention in the SC. The project aims not only to gain insights at different levels, from the subcellular to the behavioural but also to enable the development of new treatments for neuropsychiatric disorders. This project is wide-ranging and employs an interdisciplinary approach, and the expected outcomes will benefit researchers from various fields. Our results will be of great significance to the broader neuroscience community, particularly for neuroscientists working on topics such as sensory processing, 5-HT signalling, and pharmacology related to autism and schizophrenia. The tools and approaches developed during this project will be valuable to other research fields. The optogenetic tools are a bridging link to understand signalling cascades and neural circuits. We will ensure that the research outcomes are widely disseminated to scientific and non-scientific audiences in a highly visible and easily accessible manner. Any analysis codes generated from this proposal will be publicly distributed via repositories such as GitHub upon publication. In summary, this project not only aims for scientific excellence and competitiveness but also has the potential to enhance the European Research Area and global science and mental health research. The project is intended to foster productive international collaborations, which will contribute to inclusive and sustainable scientific progress through the free exchange of knowledge and methods throughout the world.

Serotonergic modulation of the Superior Colliculus