Hippocampal Hyperexcitability Underlies Enhanced Fear Memories in TgNTRK3, a Panic Disorder Mouse Model

Panic attacks are a hallmark in panic disorder (PAND). During the panic attack, a strong association with the surrounding context is established suggesting that the hippocampus may be critically involved in the pathophysiology of PAND, given its role in contextual processing. We previously showed that variation in the expression of the neurotrophin tyrosine kinase receptor type 3 (NTRK3) in both PAND patients and a transgenic mouse model (TgNTRK3) may have a role in PAND pathophysiology. Our study examines hippocampal function and activation of the brain fear network in TgNTRK3 mice. TgNTRK3 mice showed increased fear memories accompanied by impaired extinction, congruent with an altered activation pattern of the amygdala-hippocampus-medial prefrontal cortex fear circuit. Moreover, TgNTRK3 mice also showed an unbalanced excitation-to-inhibition ratio in the hippocampal cornu ammonis 3 (CA3)-CA1 subcircuit toward hyperexcitability. The resulting hippocampal hyperexcitability underlies the enhanced fear memories, as supported by the efficacy of tiagabine, a GABA reuptake inhibitor, to rescue fear response. The fearful phenotype appears to be the result of hippocampal hyperexcitability and aberrant fear circuit activation. We conclude that NTRK3 plays a role in PAND by regulating hippocampus-dependent fear memories.