Periodic Reporting for period 4 - A-FRO (Actively Frozen - contextual modulation of freezing and its neuronal basis)
Período documentado: 2023-08-01 hasta 2024-07-31
When faced with a threat, an animal must decide whether to freeze, reducing its chances of being noticed, or to flee to the safety of a refuge. Animals from fish to primates choose between these two alternatives when confronted by an attacking predator, a choice that largely depends on the context in which the threat occurs. Recent work has made strides identifying the pre-motor circuits, and their inputs, which control freezing behavior in rodents, but how contextual information is integrated to guide this choice is still far from understood. We recently found that fruit flies in response to visual looming stimuli, simulating a large object on collision course, make rapid freeze/flee choices that depend on the social and spatial environment, and the fly’s internal state. Further, identification of looming detector neurons was recently reported and we identified the descending command neurons, DNp09, responsible for freezing in the fly. Knowing the sensory input and descending output for looming-evoked freezing, two environmental factors that modulate its expression, and using a genetically tractable system affording the use of large sample sizes, places us in an unique position to understand how a information about a threat is integrated with cues from the environment to guide the choice of whether to freeze (our goal). We focus on how social and spatial information impinges on survival circuits that gate defensive responses. Finally, we aim to understand how freezing, once selected, is instantiated, from its neuronal control to the somatic changes that accompany this behaviour. This project will provide a comprehensive understanding of the mechanism of freezing, a pervasive defensive response, and its modulation by the environment, from muscles, through neuronal circuits, to collective behaviour.
We have so far made great progress in our understanding of social regulation of freezing. Using a combination of tools, from quantitative analyses of behaviour, modelling, magnetic surrogates of flies, and genetics, we identified a social cue, the motion of others, as key regulators of the propensity of flies to both start freezing in response to a threat and resume normal activity after the threat. We have identified visual projection neurons involved in this process (Clara Ferreira and Marta Moita, 2020). We are also exploring how the spatial environment influences the animal’s defensive choices and found that learning about the environment through exploratory behaviour is key, for which a number of learning genes are required. Furthermore, we are investigating the instantiation of freezing, from its neuronal control to its somatic expression. We have found that a number of descending neurons are required for threat induced freezing and developed a system to image the muscle activity in the legs while flies are exposed to threat. Finally, we developed a method to imaged cardiac activity of flies exposed to threat and found that upon threat these animals regulate cardiac activity in a fast, flexible and behavior-dependent manner, suggesting a neuronal control that may share features with the vertebrate Autonomic Nervous System. Further, we demonstrate that threat-induced freezing corresponds to a costly internal state distinct from that found during spontaneous immobility (Barrios et al, 2021).
Although the pre-motor circuits, and their inputs, that control freezing behaviour in rodents, have been described to some detail, how contextual information is integrated to guide the choice to freeze or flee is still far from understood. We expect to bring new insights into this process by characterizing at the behavioural level how the social and spatial environment regulate threat-induced freezing, by identifying neurons and brain regions that process the relevant environmental cues and map how these impinge on the circuits that control freezing behaviour. Furthermore, virtually nothing was known regarding the instantiation of freezing in invertebrates. By studying cardiac and metabolic changes in flies exposed to threat has revealed that threat induced-freezing behaviour, characterized by complete immobility, is a costly behaviour that corresponds to a distinct internal state to that of spontaneous immobility. We hope to describe in detail the mechanisms and function of the coordinated changes, triggered by a sudden threat, in the brain and body of fruit flies, gaining insight into the workings of the brain-body axis.