A parabrachial to hypothalamic pathway mediates defensive behavior.

Area of Science:

• Neuroscience
• Behavioral Biology
• Animal Survival Mechanisms

Background:

• Defensive behaviors are crucial for animal survival.
• The paraventricular nucleus (PVN) and parabrachial nucleus (PBN) are implicated in defensive behaviors.
• Direct neural connections between PBN and PVN in mediating these behaviors are not well understood.

Purpose of the Study:

• To investigate the direct neural pathway between the lateral PBN (LPB) and the PVN.
• To elucidate the role of cholecystokinin (CCK)-expressing neurons in the LPB (LPB^CCK) in defensive behaviors.
• To identify the specific contribution of the LPB^CCK-PVN pathway to threat responses.

Main Methods:

• Retrograde and anterograde tracing techniques to map neural connections.
• In vivo fiber photometry to record neuronal activity in response to stimuli.
• Optogenetic and chemogenetic manipulations to activate or inhibit specific neuronal populations and pathways.
• Pharmacological inhibition of PVN neurons.

Main Results:

• Identified a direct projection from LPB^CCK neurons to the PVN.
• LPB^CCK neurons show increased activity upon exposure to threat stimuli.
• Activation of LPB^CCK neurons or their terminals in the PVN promotes defensive behaviors and flight responses.
• Inhibition of LPB^CCK neurons or PVN neurons attenuates threat-induced defensive behaviors.

Conclusions:

• The LPB^CCK-PVN pathway is a critical neural circuit for initiating and executing defensive behaviors, particularly flight responses.
• LPB^CCK neurons modulate defensive behaviors by engaging downstream neurons within the PVN.
• This study reveals a novel pathway involved in the neurobiology of fear and defense.