Hypothalamic Control of Learned Flight Induced by Threat Imminence

Area of Science:

• Neuroscience
• Behavioral Biology
• Learning and Memory

Background:

• Flexible, learned escape behaviors are vital for survival.
• Previous research primarily focused on innate threats, leaving conditioned escape less understood.
• The dorsal premammillary nucleus (PMd) and its cholecystokinin (cck)-expressing cells are known to be involved in innate escape and learned defense.

Purpose of the Study:

• To investigate the role of PMd-cck neurons in the acquisition and maintenance of conditioned escape behavior.
• To determine if PMd-cck neurons are specifically involved in learned escape from a moving threat.
• To explore how PMd-cck neurons encode information related to the threat and escape response.

Main Methods:

• Developed a novel "flight upon grid approach" (FUGA) paradigm where mice learn to escape a moving, shock-delivering grid.
• Utilized optogenetic inhibition to target PMd-cck neurons during the FUGA learning phase.
• Assessed learned escape behavior during a subsequent fear retrieval test without shock.
• Compared effects of PMd-cck inhibition in the FUGA paradigm versus traditional contextual and auditory-cued fear conditioning.
• Recorded neuronal activity of PMd-cck cells during the FUGA task.

Main Results:

• Inhibiting PMd-cck neurons during FUGA acquisition significantly impaired learned escape behavior during fear retrieval.
• This impairment was specific to the moving threat paradigm; PMd-cck inhibition did not affect fear conditioning in contextual or auditory-cued tasks.
• PMd-cck cells showed activity correlating with the distance to the moving grid and escape speed.
• These cells were not activated by fear-conditioned tones or conditioned freezing, indicating specificity.

Conclusions:

• PMd-cck neurons are critical for the maintenance of learned escape memories associated with a moving threat.
• The hypothalamus, particularly PMd-cck circuits, plays a key role in flexible, experience-dependent survival behaviors.
• This study highlights the importance of the PMd in learning and remembering threat-related information for adaptive escape responses.