Understanding how animals make behavioral decisions is one of the biggest problems in neuroscience. The
proposed study aims to understand molecular and neural mechanisms underlying innate defensive behaviors
elicited by chemical cues from predator species. Defensive responses to predatory threats are made through a
pre-programmed defensive brain circuit, which has an ability to instantly make an appropriate behavioral decision
upon sensing predator-derived sensory stimuli. It is widely appreciated that olfaction is one of the major sensory
modalities through which predator-derived chemical cues trigger behavioral responses in prey species. When
prey animals detect immediate danger in predator cues, they exhibit acute defense behaviors such as freezing
or flight. On the other hand, when prey animals detect only potential danger in predator cues, they exhibit
vigilance and risk assessment behaviors such as repetitive stretched sniffing. An important question in behavioral
neuroscience is whether these defensive decisions for predatory threats are made through distinct neural circuits
or by a shared neural population. Our preliminary data establish a framework of the proposed study to dissect
defensive behavioral circuitries activated by predator cues through the vomeronasal chemosensory organ (VNO),
which trigger either freezing or risk assessment behaviors in mice. In this proposal, we aim to identify the
freezing- and risk assessment-inducing predator cues and their sensory receptors in the VNO, and to assess
whether the sensory signals induce behavioral outputs through independent, parallel circuitries, or they are
integrated in the brain to induce an appropriate behavior. Our central hypothesis is that different predator cues
are detected by distinct sensory receptor circuitries and elicit distinct defensive behavioral outputs in parallel. To
test this hypothesis, we will investigate mechanisms of the predator cue sensation at molecular levels; more
specifically, we will first identify the sensory stimuli (Aim 1) and the sensory receptors (Aim 2). Moreover, using
freezing- and risk assessment-inducing sensory cues as tools, we will further examine whether the defensive
decision towards predator cues is made by independent neural circuitries or not (Aim 3). The results from these
experiments will provide new insights into the molecular mechanisms underlying the sensory processing in
predator cue sensation, and will reveal an operational principle of decision making circuitries for emotional
behaviors. This will critically contribute to our understanding of pre-programmed brain machinery that underlies
multiple levels of fear and stress processing in response to threat.