Ear Nerve Stimulation Eases PTSD Anxiety by Rewiring Brain Glutamate Circuits

Post-traumatic stress disorder (PTSD) affects up to 6.8% of people globally over their lifetime, with anxiety comorbidity rates as high as 97%. Up to 40% of patients fail to respond to existing pharmacological or exposure-based therapies, making novel neuromodulatory approaches critically important. Transcutaneous auricular vagus nerve stimulation (taVNS) — a non-invasive technique targeting the auricular branch of the vagus nerve — has shown promise in epilepsy, depression, and migraine, but its mechanisms in PTSD-related anxiety were unknown.

In this study, researchers induced a PTSD-like state in adult male C57BL/6J mice using a modified single prolonged stress (mSPS) protocol combining restraint stress, forced swimming, deep anesthesia, and unconditioned foot shock. Following a one-week consolidation period, mice received 6 consecutive days of taVNS (1 mA, 2/15 Hz, 30 min/day) or sham stimulation. Anxiety-like behaviors were assessed through five validated behavioral tests: open field, marble burying, light-dark box, elevated plus maze, and three-chamber social interaction tests.

The key mechanistic work used Fos-TRAP2 transgenic mice to permanently label taVNS-activated neurons (TANs) in the anterior cingulate cortex (ACC) with tdTomato. Electrophysiological recordings revealed that glutamatergic TANs in the ACC exhibited markedly enhanced presynaptic excitatory transmission compared to non-activated glutamatergic neurons in the same region. This heightened baseline presynaptic release prevented further induction of presynaptic long-term potentiation (pre-LTP), a phenomenon termed presynaptic depotentiation — suggesting that taVNS stabilizes these circuits against pathological over-excitation patterns linked to PTSD anxiety.

Using chemogenetic tools (DREADDs), the team confirmed causal roles: inhibiting glutamatergic TANs-ACC with hM4Di diminished taVNS's anxiety-reducing effects, while activating them with hM3Dq did not further amplify taVNS benefits. This bidirectional chemogenetic evidence establishes that taVNS works specifically through this glutamatergic ACC neuronal ensemble rather than through diffuse cortical activation. taVNS did not alter body weight, temperature, or food intake, supporting its physiological safety in this model.

These findings provide mechanistic clarity for a growing clinical interest in taVNS as a non-invasive psychiatric intervention, identifying the glutamatergic ACC circuit as a key node mediating its anxiolytic effects. They also open the door to developing more targeted neuromodulation strategies that precisely engage these circuits in PTSD patients.