| 要旨 |
Animals must rapidly select defensive strategies, such as freezing or flight, in response to threatening stimuli, but the underlying neural mechanisms remain unclear. In this study, by comparing laboratory and wild-derived mouse strains, we demonstrate that a midbrain cholinergic circuit dictates the selection of defensive strategies. In response to looming stimuli, the Brazil-derived strain exhibited sustained freezing, whereas the USA-derived strain displayed a high frequency of escape. The superior colliculus (SC) governed this decision via a dual-threshold mechanism: weak activity induced freezing, while strong activity triggered escape. Excitatory cholinergic input from the parabigeminal nucleus (PBG) amplified SC activity via nicotinic receptors, driving the escape tendency observed in the USA-derived strain. Furthermore, local inhibition of nicotinic receptors within the SC selectively abolished escape behavior. These results demonstrate that this midbrain cholinergic circuit acts as a core mechanism shaping the selection of innate defensive behaviors.
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