Figure 2. Different forms of LTPs in cortical excitatory synapses
Two major forms of LTPs have been reported in the ACC excitatory synapses: presynaptic form of LTP (pre-LTP) and postsynaptic form of LTP (post-LTP). In pre-LTP, the induction requires activation of glutamate KA receptors at presynaptic side. Postsynaptic activation of NMDA receptor is not required. The expression of pre-LTP is due to more release of glutamate from presynaptic terminals. For post-LTP, activation of NMDA receptors is required. The expression is mainly mediated by the phosphorylation of AMPA receptors by cAMP PKA signalling pathways. In addition, some synapses may be silent before the LTP induction, the expression of functional AMPA receptors in these synapses may also contribute to post-LTP. For long-lasting form of LTP, gene regulation and protein synthesis are required.