@Marius T
From my limited understanding from psych studies and Google, there is a connection between stress and increased glucocorticoid secretion which in turn raises extracelluar glutamate levels, glutamate is considered to be a naturally occurring neurotoxin at concentrated levels, this is what AM-101 (Esketamine) is targeting in the ear, reducing glutamate based cell death and excitation. Drugs like Ketamine and its derivatives are noncompetitive NMDA antagonists, NMDA receptors has to remain open in order for electrical signals to process, and this process requires glutamate to bind with the NMDA receptors creating an activated ion channel. Ketamine inhibits these NMDA receptors through binding to its immediate areas. There are other drugs like Ketamine, but AM-101 (Esketamine) is the first of its kind to be injected locally into the ear, in hopes that it reduces the glutamate action more directly in the ear. Otonomy's OTO-311 uses a similar model, using a completely different drug called gacyclidine, if I understand correctly, it should be less toxic, more potent, and use only one injection since their solution is supposed to dissolve more slowly. I think we are living in a good time right now, many new treatments are coming out. It used to be "deal with it", soon enough our doctors will be offering a vast array of options for us.
Edit: In conclusion, acute and chronic stress might very well be toxic to our ears.