Defense Behavior
Defensive behaviors are critical for animal survival. They are dynamic and adaptive, as environmental contexts, properties and intensity of threats, as well as expectations from past experiences can all modulate the form as well as the magnitude of defensive behaviors. Threat signals in the external environment are sensed by different sensory modalities through distinct sensory pathways to initiate appropriate defensive behaviors. Previous studies have mostly been focused on defensive behaviors initiated under stimulation of one individual sensory modality. However, a danger may be associated with cues of multiple sensory modalities arriving at the same time, and the integration of information of these different modalities may profoundly influence the behavioral output. Intuitively, the presence of multisensory signals is helpful for strengthening defensive responses. However, neural circuit bases for the potential cross-modality interactions in defensive behaviors are largely unknown. In this project, we discovered that GABAergic neurons in the rostral sector of Zona incerta (ZIr) is engaged in modulating defense behaviors and further found defensive flight can be enhanced in a somatosensory context-dependent manner via recruiting Parvalbumin (PV) neurons in ventral sector of zona incerta (ZIv), which may be important for increasing survival of prey animals
Techniques
Research highlights
Firstly, we discover that GABAergic neurons in the rostral sector of Zona incerta (ZIr) directly innervate excitatory but not inhibitory neurons in the dorsolateral and ventrolateral compartments of periaqueductal gray (PAG), which can drive flight and freezing behaviors respectively. Optogenetic activation of ZIr neurons or their projections to PAG reduces both sound-induced innate flight response and conditioned freezing response, while optogenetic suppression of these neurons enhances these defensive behaviors, likely through a mechanism of gain modulation. ZIr activity progressively increases during extinction of conditioned freezing response, and suppressing ZIr activity impairs the expression of fear extinction. Furthermore, ZIr is innervated by the medial prefrontal cortex (mPFC), and silencing mPFC prevents the increase of ZIr activity during extinction and the expression of fear extinction.
Next, we demonstrated that additional tactile stimulation enhances flight behavior triggered by threats such as loud noise. Both SSp and ZIv PV+neurons, which receive SSp input, are necessary for this modulation, and activation of the SSp-ZIv projection is sufficient for driving the enhancement of the behavior. We also demonstrate that activation of ZIv PV+ neurons alone can enhance the flight behavior and that inactivation of the PV+ neurons or their projections to POm blocks the tac- tile enhancement of the flight behavior. Together, our data suggest that tactile input through whisker deflections can modulate defensive flight via the SSp-ZIv-POm pathway.
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