The increase in the threshold of a receptor when a series of stimuli of subthreshold intensity are applied in succession is called
Accommodation - Slow rising subthreshold stimulus failing to produce action potential even when the normal threshold levels are reached. 
This occurs because of inactivation of voltage-gated Na+ channels. 
Adaptation- Persistent application of suprathreshold stimulus fails to generate repetitive firing.
Adaptation
Accomodation
Initiation
Resistance