Abstract
Evolution has selected a repertoire of defensive behaviors that are essential for survival across all animal species. These behaviors are often stereotyped actions elicited in response to innately aversive sensory stimuli, but their success requires enough flexibility for adapting to different spatial environments, which can change rapidly. Here, we describe a behavioral assay to evaluate the influence of learned spatial knowledge on defensive behaviors in mice. We have adapted the widely used Barnes maze spatial memory assay to investigate how mice navigate to a shelter during escape responses to innately aversive sensory stimuli in a novel environment, and how they adapt to acute changes in the environment. This new assay is an ethological paradigm that does not require training and exploits the natural exploration patterns and navigation strategies in mice. We propose that the set of protocols described here are a powerful means of studying goal-directed behaviors and stimulus-triggered navigation, which should be of interest to both the fields of instinctive behaviors and spatial memory.
Highlights
Instinctive defensive behaviors are largely considered to be hardwired stimulus-responses, such as the C-start movement in fish and amphibians, which moves the animal away from a threat source[1]
Escape responses were accurately directed to the shelter, and flight trajectories were close to a straight line
Observing a short latency from the stimulus is important to distinguish stimulus-evoked behavior from homing runs, and the high linearity of the flight trajectory demonstrates that the escape response has the goal of reaching the shelter, and not moving away from the stimulus
Summary
Instinctive defensive behaviors are largely considered to be hardwired stimulus-responses, such as the C-start movement in fish and amphibians, which moves the animal away from a threat source[1]. In the most commonly used assay[15,16], the animal has one habituation trial where it is guided to the shelter manually by the experimenter immediately after being positioned on the platform This is followed by a 4-day acquisition period, where each day the mouse is allowed to navigate freely in the maze for 3 min, after which it is again manually guided to the shelter if it does not reach it during the exploration period. We use innately aversive visual[22] and auditory[23] stimuli to elicit escape to shelter, which is distinguished from ongoing foraging behavior and allows the assessment and quantification of specific navigation strategies used during defense from imminent threats We propose that this assay will be useful for dissecting the role of spatial memory in the selection and implementation of defensive behaviors, and more generally to the broader study of goal-directed navigation and short-term spatial memory. All experiments were performed under the UK Animals (Scientific Procedures) Act of 1986 (PPL 70/7652) following local ethical approval
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