Differential recovery of background and evoked afferent activity in the frog semicircular canal following ototoxic insult

The present study was aimed to define the damage and recovery of pre- and postsynaptic activity in the frog crista ampullaris after ototoxic insult with gentamicin (GM). We found that the endoampullar potential (receptor potential) recorded from the isolated canal was abolished 6 days after GM administration and that it recovered close to the control 20 days after treatment. Consistently with the presynaptic damage, the afferent activity from the ampullar nerve was abolished 6 days after GM treatment, while the recovery of background and evoked afferent activity showed a different sequence. Background activity reappeared 7-8 days after GM treatment and in this period it was not driven by canal mechanical stimulation. In addition, background activity reached control values around 15 days after the ototoxic insult, while the evoked activity was detected 9-10 days after GM treatment and appeared normal close to 20 days. Intracellular recordings from single canal afferents confirmed the above mentioned results. The present study show that the frog semicircular canal rapidly and completely recovers its pre -and postsynaptic function following severe ototoxic insult and that during the recovery afferent transmission at rest becomes functional before the mechano-transduction function.