Endbulb synaptic depression within the range of presynaptic spontaneous firing and its impact on the firing reliability of cochlear nucleus bushy neurons

► Endbulb synaptic depression at low rates (10-100 Hz) is rate-independent. ► This low rate depression is due to presynaptic P/Q type Ca channel inactivation. ► Spontaneous activity will chronically depress the endbulb synapse. ► Depressed synapses are more resistant to further synaptic depression at a higher rate. ► Slightly depressed endbulb synapses do not promote faithful synaptic transmission.