Dopamine modulates sodium currents in cochlear spiral ganglion neurons

Lateral olivocochlear (LOC) efferent neurons, putatively dopaminergic, synapse on afferent dendrites of type I spiral ganglion neurons (SGNs) in the cochlea and depress their activity. To investigate the underlying mechanisms, whole-cell patch clamp recordings were obtained from mouse SGNs. Dopamine (DA), and D1-like (D1, D5) and D2-like (D2, D3 and D4) receptor agonists, reduced AP amplitude and induced a slow transient depolarization. Under voltage clamp, D1-like and D2-like agonists induced a dose-dependent inward current that was reversibly blocked by their receptor antagonists. The inward current was blocked by tetrodotoxin (TTX), implicating Na⁺ channels. The reduction of AP amplitude and voltage-gated Na+ current by DA and DA agonists provides a mechanism for suppressing spike activity in type I afferent neurons.