Periodic Reporting for period 3 - BrainRedesign (Redesigning brain circuits in development)
Reporting period: 2023-10-01 to 2025-03-31
The focus of this research program is on the amygdala, a forebrain structure necessary for processing aversive and rewarding stimuli and orchestrating a wide array of behaviors associated with emotions and motivation. This brain structure which is characterized by a high degree of cellular heterogeneity and interconnectivity, is incompletely understood. Despite its importance, we do not have a circuit diagram that would depict the flow of information during the various emotional behaviors. The research program will provide new insights into the principles of assembly and function of this evolutionarily conserved brain structure. The successful completion of this project will considerably benefit society since the amygdala is implicated in a wide range of disease states, including anxiety disorders, addiction, eating disorders, and autism. Principles identified in rodents using this approach have the potential to be directly relevant to humans, because of the well-conserved anatomy of the amygdala.
The overall objective of this proposal is to genetically redesign specific amygdala circuits during mouse development in a predictable fashion, and to test the consequences for innate and learned behavior. We aim to demonstrate that targeted mis-expression of connectivity signals can alter specific neural circuits and communications between circuit components along measurable hypotheses. Activation of such an artificial circuit, by either natural stimuli or optogenetics, is likely to produce a set of behavioral outcomes that will reveal general connectivity rules, the capacity for behavioral plasticity, and possible functional redundancies between circuits. Anatomical and physiological dissection of the redesigned circuit will reveal to what extent the circuit is genetically hardwired or whether incoming information (afferents) instructs the target neurons to produce their correct output responses.
The overall objective of this proposal is to genetically redesign specific amygdala circuits during mouse development in a predictable fashion, and to test the consequences for innate and learned behavior. We aim to demonstrate that targeted mis-expression of connectivity signals can alter specific neural circuits and communications between circuit components along measurable hypotheses. Activation of such an artificial circuit, by either natural stimuli or optogenetics, is likely to produce a set of behavioral outcomes that will reveal general connectivity rules, the capacity for behavioral plasticity, and possible functional redundancies between circuits. Anatomical and physiological dissection of the redesigned circuit will reveal to what extent the circuit is genetically hardwired or whether incoming information (afferents) instructs the target neurons to produce their correct output responses.
Contributions from several laboratories indicate the existence of discrete amygdala circuits that respond to rewarding and aversive stimuli, and that these circuits produce valence-specific (attractive or defensive) behavioral outputs by virtue of their anatomical connectivity and genetic identity. In the first aim of this program, we have conducted extensive single-cell RNA sequencing (scRNAseq) analyses to characterize all the neuronal subpopulations in basolateral (BLA) and central amygdala (CeA) from embryonic stages to adulthood. We have identified connectivity cues during development that could serve as tools to redesign amygdala circuits. In proof-of-principle experiments, the first connectivity signals were shown to be required for synapse formation between incoming axons and attractive amygdala neurons. Novel transgenic lines were generated to specifically delete these connectivity signals from attractive neurons and eventually mis-express them in aversive neurons. Some of these transgenic lines are still being validated, before they can be used for brain redesign experiments. The ultimate goal is to show that the redesigned circuit mediates altered behavior. Therefore, we have spent considerable efforts in characterizing behaviors that are produced by specific neuron populations of the normal amygdala circuit. These include consummatory behaviors such as eating and drinking, non-consummatory attractive behaviors such as general rewarding and social interaction behavior, as well as defensive behavior such as anorexia, anxiety, and fear.
By the end of the project, we will have a much better understanding of the cellular landscape of BLA and CeA, of the physiological properties of selected cell populations, their anatomical features and inter-connectivity, and ultimately their functions in amygdala-mediated behaviours.
We will have generated a series of novel transgenic mouse lines expressing either Cre or FlpO recombinases for intersectional targeting of viral or genetic actuators (biological devices). Some of these lines may be of interest for other neurobiology laboratories.
We will have generated mice carrying a redesigned amygdala circuit. In the best-case scenario, some of these mice will be confused about attractive signals such as tasty food, and elicit defensive rather than the normal consummatory behaviour. Such results would be very informative, as they would give us confidence that we have understood some of the principles and building blocks of amygdala circuit assembly. They would further allow us to ask questions of synaptic plasticity and learning in amygdala circuits, as well as functional redundancies with other brain circuits.
We will have generated a series of novel transgenic mouse lines expressing either Cre or FlpO recombinases for intersectional targeting of viral or genetic actuators (biological devices). Some of these lines may be of interest for other neurobiology laboratories.
We will have generated mice carrying a redesigned amygdala circuit. In the best-case scenario, some of these mice will be confused about attractive signals such as tasty food, and elicit defensive rather than the normal consummatory behaviour. Such results would be very informative, as they would give us confidence that we have understood some of the principles and building blocks of amygdala circuit assembly. They would further allow us to ask questions of synaptic plasticity and learning in amygdala circuits, as well as functional redundancies with other brain circuits.