THE ROLE OF ESR1+ COLLATERAL VENTROMEDIAL HYPOTHALAMIC NEURONS IN DEFENSIVE BEHAVIOR PLASTICITY

Defensive fight-or-flight behaviors are fundamental survival strategies that enable animals to evade predation and other life-threatening situations. The ventromedial hypothalamus (VMH) is a key node in innate defense circuitry and engages distinct downstream pathways, including the periaqueductal gray (PAG) and anterior hypothalamic nucleus (AHN), which promote freezing and escape, respectively. Here, we investigated VMH collateral (VMH-coll) neurons that innervate both PAG and AHN to elucidate how this pathway shapes postsynaptic processing and defensive behavior plasticity. Using all-optical voltage imaging with the genetically encoded voltage indicator Voltron, we recorded activity from 22,151 postsynaptic neurons ex vivo and found that VMH-coll neurons recruit inhibitory mechanisms at both synaptic ends and can induce synaptic circuit plasticity. In vivo optogenetic activation of VMH-coll somas induced escape behaviors. We identified an Esr1-expressing VMH-coll subpopulation with a postsynaptic connectome resembling that of wild-type collaterals on the PAG side. Activation of Esr1+ VMH-coll neurons evoked freezing and an unexpected flattening behavior, previously not linked to VMH output. In parallel, all-optical voltage imaging revealed plasticity within local VMH circuitry. Neuropeptides, including PACAP and dynorphin, modulated Esr1+ VMH-coll connectome features, and in vivo κ-opioid receptor antagonism impaired Esr1+ VMH-coll–mediated defensive behaviors. Together, these findings identify VMH collateral pathways and neuropeptidergic control as key mechanisms shaping innate defensive behavior plasticity.