PTD - Describes the reduction in sensitivity of a
synapse's response (excitatory or inhibitory) to incoming signals following a
tetanus.
This is generally caused by a reduction of the amount of neuro-transmitters on hand at the synaptic terminal.
[Ref 1]
Long Term Depression (LTD) - At some synapses
depression can last much longer; from minutes to hours, or even several days or months. In these cases, they are referred to as
LTD or
Long Term Depression. The mechanisms of LTD appear to be distinct from those of PTD. They also differ from synapse to synapse
[Ref 1]